JP7189488B2 - Diesel engine fuel injection controller - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device for a diesel engine in which a portion of a combustion chamber is defined by a crown surface of a piston having a cavity.

A combustion chamber of a diesel engine for vehicles such as automobiles is defined by the inner wall surface of the cylinder, the lower surface of the cylinder head (the ceiling surface of the combustion chamber), and the crown surface of the piston. Fuel is supplied to the combustion chamber from a fuel injection valve arranged near the radial center of the combustion chamber. A combustion chamber structure is known in which a cavity (recess) is arranged in the crown surface of the piston, and fuel is injected from the fuel injection valve toward this cavity. Patent Documents 1 and 2 disclose a combustion chamber structure in which the cavity has a two-stage structure of an upper cavity and a lower cavity, and fuel is injected into a branch portion of the two-stage structure cavity, and the upper cavity and the lower cavity are injected. A fuel injection control system is disclosed for distributing fuel to side cavities.

FR-A-2902462 Japanese Patent No. 4906055

When the two-stage structure cavity is adopted, the in-cylinder flow of the air-fuel mixture containing the fuel injected from the fuel injection valve is separated at the branch portion into a flow toward the upper cavity and a flow toward the lower cavity, A swirling flow is formed in each cavity. In the case of a single-stage cavity, since the separation does not occur, a relatively strong swirling flow is formed along the cavity. In comparison, the swirling flow in the two-stage cavity is relatively weak due to the separation. Therefore, there is a tendency that the air present in the radially central region of the combustion chamber is less likely to be drawn radially outward of the combustion chamber by the swirling flow. In this case, there arises a problem that the air utilization rate is lowered, that is, the oxygen remaining in the radially central region of the combustion chamber cannot be effectively utilized.

The present invention is a fuel injection control device for a diesel engine having a cavity on the crown surface of the piston, which effectively utilizes the air in the combustion chamber to form a homogeneous and lean air-fuel mixture, thereby minimizing the generation of soot and the like. It is an object of the present invention to provide a fuel injection control device capable of suppressing

A fuel injection control device for a diesel engine according to one aspect of the present invention includes a combustion chamber of an engine formed by a lower surface of a cylinder head, crown surfaces of a cylinder and a piston, a fuel injection valve that injects fuel into the combustion chamber, A diesel engine fuel injection control device comprising a supercharger for supercharging intake air and a fuel injection control unit for controlling the operation of the fuel injection valve, wherein the crown surface of the piston is provided with a cavity, The cavity includes a first cavity portion disposed in a radially central region of the crown surface and having a first bottom portion having a first depth in a cylinder axial direction, and an outer circumference of the first cavity portion on the crown surface. a second cavity portion disposed on the side of the cylinder and provided with a second bottom portion having a depth shallower than the first depth in the axial direction of the cylinder; and a connecting portion connecting the first cavity portion and the second cavity portion. , wherein the fuel injection valve injects fuel toward the cavity and is disposed at or near the radial center of the combustion chamber; Main injection for injecting fuel at timing near the top dead center, Pilot injection for injecting fuel at timing earlier than the main injection, Timing earlier than the pilot injection or timing later than the main injection a low-penetration injection that causes the fuel injection to be performed by the fuel injection valve, wherein at least one of the main injection and the pilot injection is performed at the timing of directing the fuel injection toward the connecting portion. a first injection control unit; and a second injection control unit that executes the low-penetration injection so that fuel is injected only in a radially central region of the combustion chamber, wherein the second injection control unit is When the injection pressure of the main injection is equal to or higher than a predetermined reference injection pressure, the injection timing of the low penetration injection is advanced when the supercharging pressure of the supercharger is low compared to when the supercharging pressure is high, and When the injection pressure of the injection is less than the reference injection pressure, the low penetration injection is executed at a later timing than the main injection, and the low penetration injection is performed more when the supercharging pressure is low than when the supercharging pressure is high. It is characterized by retarding the injection timing.

According to this fuel injection control device, a portion of the combustion chamber is formed by the crown surface including the first and second cavity portions, and fuel injection of the main injection or the pilot injection is performed toward the connecting portion. be done. Therefore, the in-cylinder flow of the air-fuel mixture is separated at the connecting portion, the in-cylinder swirling flow becomes relatively weak, and the air near the radial center region of the combustion chamber tends to be less likely to be drawn radially outward. However, according to the fuel injection control device, low-penetration injection is executed in addition to normal main injection and pilot injection. The low-penetration injection is performed such that fuel injection occurs only in a radially central region of the combustion chamber. Therefore, it is possible to form an air-fuel mixture with the air remaining in the radially central region of the combustion chamber and the fuel sprayed by the low-penetration injection. As a result, it is possible to effectively use the air in the combustion chamber to form a homogeneous and lean air-fuel mixture, thereby achieving high-quality diesel combustion that suppresses the generation of soot and the like.

Here, when the supercharging pressure is low, the ignitability of the air-fuel mixture is lowered. For example, if the supercharging pressure does not rise to a desired pressure due to a delay in driving the supercharger during acceleration, etc., the ignitability of the air-fuel mixture will be lower than the desired level. If the ignitability of the air-fuel mixture is low, there is a risk that even if low penetration injection is performed, the fuel associated with the injection will not burn properly, or will not burn properly due to an ignition delay. In contrast, in this device, when the supercharging pressure is low, the injection timing of the low-penetration injection is advanced more than when it is high. For example, when the shortage of the boost pressure with respect to the target value is large, the injection timing of the low-penetration injection is advanced more than when it is small. Therefore, when the supercharging pressure is low (when the amount of the supercharging pressure with respect to the target value is large), the mixing time of the fuel and air for low penetration injection is lengthened to promote the mixture and improve the ignitability. can be enhanced. Therefore, it is possible to appropriately burn the fuel for the low penetration injection and to reliably utilize the air remaining in the radially central region of the combustion chamber. When the supercharging pressure is high (when the amount of the supercharging pressure with respect to the target value is small), the injection timing of the low-penetration injection is set to the relatively retarded side so that the fuel and air for the low-penetration injection are mixed. Excessive acceleration and thus premature ignition can be prevented.

Further, when the injection pressure of the main injection is equal to or higher than a predetermined reference injection pressure, the second injection control unit advances the injection timing of the low penetration injection when the supercharging pressure is low compared to when the supercharging pressure is high. When the injection pressure of the main injection is less than the reference injection pressure, the low penetration injection is executed at a timing later than that of the main injection, and when the supercharging pressure is low, it is higher than when the supercharging pressure is high. The injection timing of the low penetration injection is retarded.

According to this configuration, the amount of soot discharged from the combustion chamber to the outside by the low penetration injection can be effectively reduced.

Specifically, when the injection pressure of the injector is low, soot is likely to be generated due to the increase in the particle size of the fuel spray. In contrast, in this device, when the injection pressure of the injector is less than the reference injection pressure, the low penetration injection is executed at a later timing than the main injection. Therefore, soot generated by combustion of fuel for pilot injection and/or main injection can be oxidized by combustion energy of fuel for low-penetration injection. Moreover, in this configuration, when the supercharging pressure is low, the injection timing of the low-penetration injection is retarded more than when it is high. Therefore, a relatively large amount of soot generated due to a low boost pressure and a small amount of oxygen introduced into the combustion chamber can be effectively oxidized by the thermal energy associated with the low penetration injection. In addition, when the injection pressure of the injector is high and the generation of soot is suppressed, by advancing the injection timing of the low penetration injection when the boost pressure is low compared to when it is high, the ignitability of the air-fuel mixture and the Fuel efficiency can be improved. Further, when the injection pressure of the injector is low and soot is unlikely to be generated, the injection timing of the low penetration injection is advanced when the supercharging pressure is low compared to when the supercharging pressure is high. and ignition delay can be prevented.

A fuel injection control device for a diesel engine according to another aspect of the present invention includes an engine combustion chamber formed by a lower surface of a cylinder head, crown surfaces of a cylinder and a piston, and a fuel injection valve that injects fuel into the combustion chamber. , a supercharger for supercharging intake air, and a fuel injection control unit for controlling the operation of the fuel injection valve, wherein the crown surface of the piston is provided with a cavity. , the cavity comprises a first cavity portion disposed in a radially central region of the crown surface and having a first bottom portion having a first depth in the axial direction of the cylinder; a second cavity portion disposed on the outer peripheral side and having a second bottom portion having a depth shallower than the first depth in the axial direction of the cylinder; and a connecting portion connecting the first cavity portion and the second cavity portion. and wherein the fuel injection valve injects fuel toward the cavity and is disposed at or near the radial center of the combustion chamber, and the fuel injection control unit controls at least the piston to A main injection that causes fuel injection at a timing positioned near compression top dead center, a pilot injection that causes fuel injection at a timing earlier than the main injection, and a timing earlier than the pilot injection or later than the main injection. a low-penetration injection that causes the fuel injection valve to perform fuel injection with timing, wherein at least one of the main injection and the pilot injection is performed at the timing of injecting fuel directed toward the connecting portion. and a second injection control unit that executes the low-penetration injection so that the fuel is injected only in a radially central region of the combustion chamber, wherein the second injection control unit advances the injection timing of the low penetration injection when the supercharging pressure of the supercharger is lower than when the supercharging pressure is high, and the outer edge of the radially central region of the combustion chamber becomes spray penetration. ( Claim 2 ).

According to this arrangement, the location of the outer edge of the radially central region of the combustion chamber is targeted for spray penetration. Therefore, the air existing in the radially central region can be fully utilized to form an air-fuel mixture, and as a result, the generation of soot and the like can be further suppressed.

In the above configuration, the second injection control unit controls the injection pressure, the injection amount, and the injection timing of the main injection or the pilot injection by the first injection control unit. It is desirable to estimate a survivable region and execute the low-penetration injection so that the outer edge of the survivable oxygen region becomes spray penetration (claim 3 ).

According to this configuration, the residual oxygen region in which the oxygen to be utilized remains is estimated from the injection control result by the first injection control unit, and low penetration injection is performed within the estimated residual oxygen region. be done. Therefore, it is possible to achieve combustion that makes effective use of the oxygen remaining in the combustion chamber.

According to the present invention, there is provided a fuel injection control device for a diesel engine that can effectively utilize the air in the combustion chamber to form a homogeneous and lean air-fuel mixture, thereby suppressing the generation of soot and the like as much as possible. can be done.

FIG. 1 is a system diagram of a diesel engine to which a fuel injection control device according to the present invention is applied. FIG. 2(A) is a perspective view of the crown portion of the piston of the diesel engine shown in FIG. 1, and FIG. 2(B) is a perspective view with a cross section of the piston. FIG. 3 is an enlarged view of the cross section of the piston shown in FIG. 2(B). FIG. 4 is a cross-sectional view of the piston for explaining the relationship between the crown surface of the piston and the injection axis of fuel by the injector. FIG. 5 is a block diagram showing the control system of the diesel engine. FIG. 6A is a diagram schematically showing the in-cylinder swirling flow when the cavity according to the comparative example is employed, and FIG. 6B is the in-cylinder swirling flow when the cavity according to the present embodiment is employed. It is a figure which shows typically. FIG. 7A shows how residual air is generated in the combustion chamber when the cavity according to the comparative example is used, and FIG. 7B shows the residual air in the combustion chamber when the cavity according to the present embodiment is used. 2 is a cross-sectional view of a combustion chamber showing the occurrence of . FIG. 8 is a cross-sectional view of the combustion chamber showing how low-penetration injection is executed in this embodiment. FIGS. 9A to 9C are diagrams for explaining a method of setting a target line for low-penetration injection. FIG. 10 is a time chart showing basic injection pattern aspects. FIG. 11 is a time chart showing modes of low-penetration injection according to the first embodiment. FIG. 12 is a flowchart showing low penetration injection control according to the first embodiment. FIG. 13 is a time chart showing changes over time of each parameter when the low penetration injection control according to the first embodiment is performed. FIG. 14 is a time chart showing modes of low-penetration injection according to the second embodiment. FIG. 15 is a diagram showing control divisions in the low penetration injection control according to the second embodiment. FIGS. 16A to 16D are time charts showing modes of low-penetration injection according to the second embodiment. FIGS. 17A to 17C are time charts showing modes of low-penetration injection according to the second embodiment. FIG. 18 is a flow chart showing part of the low-penetration injection control according to the second embodiment. FIG. 19 is a flowchart showing part of the low-penetration injection control according to the second embodiment.

[Overall structure of the engine]
BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a diesel engine fuel injection control device according to the present invention will be described in detail below with reference to the drawings. First, the overall configuration of a diesel engine system to which a fuel injection control device according to the present invention is applied will be described with reference to FIG. The diesel engine shown in FIG. 1 is a four-cycle diesel engine mounted on a vehicle as a power source for running. The diesel engine system includes an engine body 1 which has a plurality of cylinders 2 and is driven by being supplied with fuel containing light oil as a main component, an intake passage 30 through which intake air introduced into the engine body 1 flows, an engine body 1, an EGR device 44 for recirculating part of the exhaust gas flowing through the exhaust passage 40 to the intake passage 30, and the exhaust gas passing through the exhaust passage 40. A turbocharger (supercharger) 46 is provided.

The engine body 1 has a plurality of cylinders 2 (only one of which is shown in FIG. 1) arranged in a direction perpendicular to the paper surface of FIG. is the engine. The engine body 1 includes a cylinder block 3 , a cylinder head 4 and pistons 5 . Cylinder block 3 has a cylinder liner that forms cylinder 2 . The cylinder head 4 is attached to the upper surface of the cylinder block 3 and closes the upper opening of the cylinder 2 . A piston 5 is housed in the cylinder 2 so as to be reciprocally slidable, and is connected to the crankshaft 7 via a connecting rod 8 . As the piston 5 reciprocates, the crankshaft 7 rotates about its central axis. The structure of the piston 5 will be detailed later.

A combustion chamber 6 is formed above the piston 5 . The combustion chamber 6 is defined by the lower surface of the cylinder head 4 (combustion chamber ceiling surface 6U, see FIGS. 3 and 4), and crown surfaces 50 of the cylinder 2 and the piston 5. As shown in FIG. The fuel is supplied to the combustion chamber 6 by injection from an injector 15, which will be described later. Then, the mixture of the supplied fuel and air is combusted in the combustion chamber 6, and the piston 5, which is pushed down by the expansion force due to the combustion, reciprocates in the vertical direction.

A crank angle sensor SN1 and a water temperature sensor SN2 are attached to the cylinder block 3 . The crank angle sensor SN1 detects the rotation angle (crank angle) of the crankshaft 7 and the rotation speed of the crankshaft 7 (engine rotation speed). The water temperature sensor SN2 detects the temperature (atmospheric pressure) of cooling water that flows through the engine body 1, that is, the cylinder block 3 and the cylinder head 4 to cool them.

An intake port 9 and an exhaust port 10 communicating with the combustion chamber 6 are formed in the cylinder head 4 . An intake side opening, which is the downstream end of the intake port 9 , and an exhaust side opening, which is the upstream end of the exhaust port 10 , are formed on the lower surface of the cylinder head 4 . The cylinder head 4 is assembled with an intake valve 11 that opens and closes the intake side opening and an exhaust valve 12 that opens and closes the exhaust side opening. Although illustration is omitted, the valve format of the engine body 1 is a 4-valve format of 2 intake valves x 2 exhaust valves, and two intake ports 9 and two exhaust ports 10 are provided for each cylinder 2. In addition, two intake valves 11 and two exhaust valves 12 are also provided.

The cylinder head 4 is provided with an intake-side valve mechanism 13 and an exhaust-side valve mechanism 14 including camshafts. The intake valve 11 and the exhaust valve 12 are driven to open and close by these valve mechanisms 13 and 14 in conjunction with the rotation of the crankshaft 7 . The intake valve mechanism 13 incorporates an intake VVT capable of changing at least the opening timing of the intake valve 11, and the exhaust valve mechanism 14 incorporates an exhaust VVT capable of changing at least the closing timing of the exhaust valve 12. It is

One injector 15 (fuel injection valve) for injecting fuel into the combustion chamber 6 from the tip of the cylinder head 4 is attached to each cylinder 2 . The injector 15 injects fuel supplied through a fuel supply pipe (not shown) into the combustion chamber 6 . The injector 15 is assembled to the cylinder head 4 and formed on the crown surface 50 of the piston 5 so that the tip (nozzle 151; FIG. 4) for injecting fuel is positioned at or near the radial center of the combustion chamber 6. The fuel is injected toward a cavity 5C (FIGS. 2 to 4), which will be described later.

The injector 15 is connected to a pressure accumulation common rail (not shown) common to all the cylinders 2 via a fuel supply pipe. High-pressure fuel pressurized by a fuel pump (not shown) is stored in the common rail. The fuel pressure-accumulated in this common rail is supplied to the injector 15 of each cylinder 2, and fuel is injected into the combustion chamber 6 from each injector 15 at a high pressure (approximately 50 MPa to 250 MPa). A fuel pressure regulator 16 (not shown in FIG. 1, see FIG. 5) is provided between the fuel pump and the common rail to change the injection pressure, which is the pressure of the fuel injected from the injector 15.

The intake passage 30 is connected to one side surface of the cylinder head 4 so as to communicate with the intake port 9 . Air (fresh air) taken from the upstream end of the intake passage 30 is introduced into the combustion chamber 6 through the intake passage 30 and the intake port 9 . An air cleaner 31 , a turbocharger 46 , a throttle valve 32 , an intercooler 33 and a surge tank 34 are arranged in the intake passage 30 in this order from the upstream side.

The air cleaner 31 cleans the intake air by removing foreign substances in the intake air. The throttle valve 32 opens and closes the intake passage 30 in conjunction with depression of an accelerator (not shown) to adjust the flow rate of intake air in the intake passage 30 . The turbocharger 46 sends out the intake air to the downstream side of the intake passage 30 while compressing the intake air. The intercooler 33 cools the intake air compressed by the supercharger 46 . The surge tank 34 is a tank that is arranged immediately upstream of the intake manifold connected to the intake port 9 and provides a space for evenly distributing the intake air to the plurality of cylinders 2 .

An airflow sensor SN3, an intake air temperature sensor SN4, an intake pressure sensor SN5 and an intake _O2 sensor SN6 are arranged in the intake passage 30. As shown in FIG. The airflow sensor SN3 is arranged on the downstream side of the air cleaner 31 and detects the flow rate of intake air passing through this portion. The intake air temperature sensor SN4 is arranged downstream of the intercooler and detects the temperature of the intake air passing through that portion. An intake pressure sensor SN5 and an intake _O2 sensor SN6 are arranged in the vicinity of the surge tank 34, and detect the pressure of the intake air passing through these portions and the oxygen concentration of the intake air, respectively. Although not shown in FIG. 1, an injection pressure sensor SN7 for detecting the injection pressure of the injector 15 is provided.

The exhaust passage 40 is connected to the other side surface of the cylinder head 4 so as to communicate with the exhaust port 10 . Burned gas (exhaust gas) generated in the combustion chamber 6 is discharged outside the vehicle through the exhaust port 10 and the exhaust passage 40 . An exhaust purification device 41 is provided in the exhaust passage 40 . The exhaust purification device 41 includes a three-way catalyst 42 for purifying harmful components (HC, CO, NOx) contained in the exhaust gas flowing through the exhaust passage 40, and a particulate matter contained in the exhaust gas. A DPF (Diesel Particulate Filter) 43 for collecting is built in.

An exhaust _O2 sensor SN8 and a differential pressure sensor SN9 are arranged in the exhaust passage 40 . The exhaust _O2 sensor SN8 is arranged between the turbocharger 46 and the exhaust purification device 41, and detects the oxygen concentration of the exhaust passing through that portion. A differential pressure sensor SN9 detects a differential pressure between the upstream end and the downstream end of the DPF 43 .

The EGR device 44 includes an EGR passage 44A connecting the exhaust passage 40 and the intake passage 30, and an EGR valve 45 provided in the EGR passage 44A. The EGR passage 44A connects a portion of the exhaust passage 40 upstream of the turbocharger 46 and a portion of the intake passage 30 between the intercooler 33 and the surge tank 34 to each other. An EGR cooler (not shown) is arranged in the EGR passage 44A to cool the exhaust gas (EGR gas) recirculated from the exhaust passage 40 to the intake passage 30 by heat exchange. The EGR valve 45 adjusts the flow rate of exhaust gas flowing through the EGR passage 44A.

The turbocharger 46 includes a compressor 47 arranged on the intake passage 30 side and a turbine 48 arranged on the exhaust passage 40 . The compressor 47 and the turbine 48 are connected to each other by a turbine shaft so as to be rotatable together. The turbine 48 rotates with the energy of the exhaust gas flowing through the exhaust passage 40 . As the compressor 47 rotates in conjunction with this, the air flowing through the intake passage 30 is compressed (supercharged). The exhaust passage 40 is provided with a passage that bypasses the turbine 48 and a bypass valve that opens and closes the passage (not shown). By opening and closing the bypass valve, the amount of exhaust gas flowing into the turbine 48 is changed, and the boost pressure is adjusted.

[Detailed structure of the piston]
Next, the structure of the piston 5, especially the structure of the crown surface 50 will be described in detail. FIG. 2A is a perspective view mainly showing the upper portion of the piston 5. FIG. The piston 5 has an upper piston head and a lower skirt portion, and FIG. 2A shows the piston head portion having a crown surface 50 on its top surface. FIG. 2B is a perspective view of the piston 5 with a radial cross section. FIG. 3 is an enlarged view of the radial cross section shown in FIG. 2(B). In FIGS. 2A and 2B, the axial direction A of the cylinder and the radial direction B of the combustion chamber are indicated by arrows. In the following description, the plane perpendicular to the cylinder axis is assumed to be a horizontal plane (assuming that the piston 5 is arranged so that the plane perpendicular to the cylinder axis is a horizontal plane).

The piston 5 includes a cavity 5</b>C, a peripheral flat portion 55 and a side peripheral surface 56 . As described above, a part (bottom surface) of the combustion chamber wall surface defining the combustion chamber 6 is formed by the crown surface 50 of the piston 5, and the cavity 5C is provided in the crown surface 50. The cavity 5</b>C is a portion where the crown surface 50 is recessed downward in the axial direction A of the cylinder and receives fuel injection from the injector 15 . The peripheral flat portion 55 is an annular flat portion arranged in a region near the outer peripheral edge in the radial direction B of the crown surface 50 . The cavity 5</b>C is arranged in the central region in the radial direction B of the crown surface 50 excluding the peripheral flat portion 55 . The side peripheral surface 56 is a surface that comes into sliding contact with the inner wall surface of the cylinder 2, and is provided with a plurality of ring grooves into which piston rings (not shown) are fitted.

The cavity 5</b>C includes a first cavity portion 51 , a second cavity portion 52 , a connecting portion 53 and a peak portion 54 . The first cavity portion 51 is a concave portion arranged in the center region in the radial direction B of the crown surface 50 . The second cavity portion 52 is an annular concave portion arranged on the crown surface 50 on the outer peripheral side of the first cavity portion 51 . The connecting portion 53 is a portion that connects the first cavity portion 51 and the second cavity portion 52 in the radial direction B. As shown in FIG. The peak portion 54 is a peak-shaped convex portion arranged at the center position in the radial direction B of the crown surface 50 (the first cavity portion 51). The peak portion 54 is protruded at a position directly below the nozzle 151 of the injector 15 (FIG. 4).

The first cavity part 51 includes a first upper end 511 , a first bottom 512 and a first inner end 513 . The first upper end portion 511 is located at the highest position in the first cavity portion 51 and continues to the connecting portion 53 . The first bottom portion 512 is the most recessed area in the first cavity portion 51 and has an annular shape when viewed from above. The first bottom portion 512 is the deepest portion of the entire cavity 5C, and the first cavity portion 51 has a predetermined depth (first depth) in the cylinder axial direction A at the first bottom portion 512. there is When viewed from above, the first bottom portion 512 is positioned close to the inner side in the radial direction B with respect to the connecting portion 53 .

The first upper end portion 511 and the first bottom portion 512 are connected by a radial recess portion 514 curved outward in the radial direction B. As shown in FIG. The radial recessed portion 514 has a portion recessed outward in the radial direction B from the connecting portion 53 . The first inner end portion 513 is located at the radially innermost position in the first cavity portion 51 and continues to the lower end of the peak portion 54 . The first inner end portion 513 and the first bottom portion 512 are connected by a curved surface gently curved in a foot shape.

The second cavity portion 52 includes a second inner end 521 , a second bottom 522 , a second top end 523 , a tapered region 524 and a standing wall region 525 . The second inner end portion 521 is located at the radially innermost position in the second cavity portion 52 and continues to the connecting portion 53 . The second bottom portion 522 is the most recessed area in the second cavity portion 52 . The second cavity portion 52 has a depth shallower than the first bottom portion 512 in the cylinder axial direction A at the second bottom portion 522 . That is, the second cavity portion 52 is a concave portion positioned above the first cavity portion 51 in the cylinder axial direction A. As shown in FIG. The second upper end portion 523 is located at the highest position and radially outermost in the second cavity portion 52 and continues to the peripheral flat portion 55 .

The tapered region 524 is a portion that extends from the second inner end portion 521 toward the second bottom portion 522 and has a surface shape that slopes downward in the radial direction outward. As shown in FIG. 3, the tapered region 524 extends along an inclined line C2 that intersects a horizontal line (a line along a plane orthogonal to the cylinder axis A) C1 extending in the radial direction B at an inclination angle α. has an inclination. The standing wall region 525 is a wall surface formed to rise relatively steeply on the radially outer side of the second bottom portion 522 . In the cross-sectional shape in the radial direction B, the wall surface of the second cavity portion 52 is curved upward from the horizontal direction from the second bottom portion 522 to the second upper end portion 523 . A standing wall region 525 is a wall surface portion near the vertical wall in the vicinity of 523 .

In the cross-sectional shape in the radial direction B, the connecting portion 53 has a shape that protrudes radially inward in the form of a hump between the first cavity portion 51 positioned on the lower side and the second cavity portion 52 positioned on the upper side. is doing. The connecting portion 53 has a lower end portion 531, a third upper end portion 532 (upper end portion in the axial direction of the cylinder), and a central portion 533 located in the center between them. The lower end portion 531 is a continuous portion to the first upper end portion 511 of the first cavity portion 51 . The third upper end portion 532 is a continuous portion with respect to the second inner end portion 521 of the second cavity portion 52 .

In the cylinder axial direction A, the lower end portion 531 is the lowermost portion of the connecting portion 53, and the third upper end portion 532 is the uppermost portion. The tapered region 524 described above is also the region extending from the third top end 532 toward the second bottom portion 522 . The second bottom portion 522 is located below the third upper end portion 532 . In other words, the second cavity portion 52 of the present embodiment does not have a bottom surface extending horizontally outward in the radial direction B from the third upper end portion 532 . It has a second bottom portion 522 that is recessed below the third upper end portion 532 instead of being connected to 55 on a horizontal plane.

The peak portion 54 protrudes upward, but its protruding height is the same as the height of the third upper end portion 532 of the connecting portion 53 and is recessed from the peripheral flat portion 55 . The peak portion 54 is positioned at the center of the circular first cavity portion 51 when viewed from above, so that the first cavity portion 51 is in the form of an annular groove formed around the peak portion 54 .

[In-cylinder flow after fuel injection]
Next, the state of fuel injection into the cavity 5C by the injector 15 and the flow of the air-fuel mixture after injection will be described with reference to FIG. FIG. 4 is a simplified cross-sectional view of the combustion chamber 6, showing the relationship between the crown surface 50 (cavity 5C) and the injection axis AX of the injected fuel 15E injected from the injector 15, and the flow of the air-fuel mixture after injection. arrows F11, F12, F13, F21, F22, and F23 schematically representing

The injector 15 has a nozzle 151 arranged to protrude downward into the combustion chamber 6 from the combustion chamber ceiling surface 6U (the lower surface of the cylinder head 4). The nozzle 151 has injection holes 152 for injecting fuel into the combustion chamber 6 . Although one injection hole 152 is shown in FIG. 4, a plurality of injection holes 152 are actually arranged in the circumferential direction of the nozzle 151 at equal pitches. The fuel injected from the injection hole 152 is injected along the injection axis AX in the figure. The injected fuel diffuses at a spray angle θ. FIG. 4 shows an upper diffusion axis AX1 indicating upward diffusion with respect to the injection axis AX, and a lower diffusion axis AX2 indicating downward diffusion. The spray angle θ is the angle between the upper diffusion axis AX1 and the lower diffusion axis AX2. The fuel injected from the injection hole 152 scatters through a region between the upper diffusion axis AX1 and the lower diffusion axis AX2 in side view. The injection axis AX is the central axis of the fuel spray injected from the injector 15 and substantially coincides with the extension of the central axis of the injection hole 152 .

The injection hole 152 can inject fuel toward the connecting portion 53 of the cavity 5C. That is, the injection axis AX can be oriented toward the connecting portion 53 by injecting fuel from the injection hole 152 at a predetermined crank angle of the piston 5 . FIG. 4 shows the positional relationship between the injection axis AX and the cavity 5C at the predetermined crank angle. The fuel injected from the injection hole 152 is mixed with the air in the combustion chamber 6 to form an air-fuel mixture, and blows against the connecting portion 53 .

As shown in FIG. 4, the fuel 15E injected along the injection axis AX toward the connecting portion 53 collides with the connecting portion 53 and then travels toward the first cavity portion 51 (downward) ( It is spatially separated into arrow F11) and one directed toward the second cavity portion 52 (upward) (arrow F21). That is, the fuel injected toward the central portion 533 of the connecting portion 53 is separated into upper and lower portions, and then mixed with the air present in the first and second cavity portions 51 and 52, respectively. , 52 along the surface shape.

Specifically, the air-fuel mixture flowing in the direction of arrow F11 (downward) enters from the lower end portion 531 of the connecting portion 53 into the radial recess portion 514 of the first cavity portion 51 and flows downward. After that, the air-fuel mixture changes its flow direction from the downward direction to the inner direction in the radial direction B due to the curved shape of the radial recess portion 514, and as indicated by the arrow F12, the bottom surface of the first cavity portion 51 having the first bottom portion 512. It follows the shape and flows. At this time, the air-fuel mixture is mixed with the air in the first cavity portion 51 to reduce its concentration. Due to the presence of the peak portion 54, the bottom surface of the first cavity portion 51 has a shape that rises toward the center in the radial direction. Therefore, the air-fuel mixture flowing in the direction of arrow F12 is lifted upward, and finally flows radially outward from the combustion chamber ceiling surface 6U as indicated by arrow F13. Even during such flow, the air-fuel mixture mixes with the air existing in the combustion chamber 6 and becomes a homogeneous and lean air-fuel mixture.

On the other hand, the air-fuel mixture traveling in the direction of arrow F21 (upward) enters the tapered region 524 of the second cavity portion 52 from the third upper end portion 532 of the connecting portion 53 and travels obliquely downward along the inclination of the tapered region 524. . Then, the air-fuel mixture reaches the second bottom portion 522 as indicated by an arrow F22. Here, the tapered region 524 is a surface having an inclination along the ejection axis AX. Therefore, the air-fuel mixture can smoothly flow radially outward. That is, the air-fuel mixture reaches a deep position radially outside of the combustion chamber 6 due to the presence of the tapered region 524 and the presence of the second bottom portion 522 below which the third upper end portion 532 of the connecting portion 53 is also located. can be done.

Thereafter, the air-fuel mixture is lifted upward by the rising curved surface between the second bottom portion 522 and the rising wall region 525, and flows radially inward along the combustion chamber ceiling surface 6U. During the flow indicated by the arrow F22, the air-fuel mixture mixes with the air in the second cavity portion 52 to become a homogeneous and thin air-fuel mixture. Here, since the standing wall region 525 extending generally vertically extends radially outward of the second bottom portion 522 , the injected fuel (air-fuel mixture) is injected into the inner peripheral wall of the cylinder 2 (generally, a liner (not shown)). exists). In other words, the formation of the second bottom portion 522 allows the air-fuel mixture to flow to the vicinity of the radially outer side of the combustion chamber 6 , but the presence of the standing wall region 525 prevents the air-fuel mixture from interfering with the inner peripheral wall of the cylinder 2 . Therefore, it is possible to suppress the occurrence of cold loss due to the interference.

As described above, the fuel injected toward the connection portion 53 along the injection axis AX collides with the connection portion 53 and is spatially separated, and exists in the spaces of the first and second cavity portions 51 and 52, respectively. It utilizes the air to generate the air-fuel mixture. As a result, the space of the combustion chamber 6 can be widely used to form a homogeneous and lean air-fuel mixture, and the generation of soot and the like during combustion can be suppressed.

[Control configuration]
FIG. 5 is a block diagram showing the control configuration of the diesel engine system. The engine system of this embodiment is centrally controlled by a processor 70 (a fuel injection control device for a diesel engine). The processor 70 is composed of a CPU, ROM, RAM, and the like. Detection signals from various sensors mounted on the vehicle are input to the processor 70 . In addition to the sensors SN1 to SN9 described above, the vehicle is equipped with an accelerator opening sensor SN10 that detects the accelerator opening, an atmospheric pressure sensor SN11 that measures the atmospheric pressure of the environment in which the vehicle is running, and an external temperature, that is, the vehicle running. and an outside air temperature sensor SN12 for measuring the temperature of the environment.

The processor 70 controls the aforementioned crank angle sensor SN1, water temperature sensor SN2, airflow sensor SN3, intake air temperature sensor SN4, intake pressure sensor SN5, intake _O2 sensor SN6, injection pressure sensor SN7, exhaust _O2 sensor SN8, differential pressure sensor SN9. , an accelerator position sensor SN10, an atmospheric pressure sensor SN11, and an outside air temperature sensor SN12. Information detected by these sensors SN1 to SN12, that is, crank angle, engine speed, atmospheric pressure, intake flow rate, intake air temperature, intake pressure, intake oxygen concentration, injection pressure of injector 15, exhaust oxygen concentration, before and after DPF 43 Information such as differential pressure, accelerator opening, outside air temperature, atmospheric pressure, etc. are sequentially input to the processor 70 . The intake pressure sensor SN5 is provided downstream of the compressor 47, and the intake pressure detected by the intake pressure sensor SN5 is the same as the supercharging pressure. In the following, the intake pressure is referred to as supercharging pressure.

The processor 70 controls each section of the engine while executing various judgments and calculations based on the input signals from the sensors SN1 to SN12. That is, the processor 70 is electrically connected to the injector 15 (fuel pressure regulator 16), the throttle valve 32, the EGR valve 45, and the like, and outputs control signals to these devices based on the results of the above calculations. do.

The processor 70 functionally controls a fuel injection control section 71 (first injection control section, second injection control section) that controls the operation of the injector 15, and controls boost pressure (controls the operation of the bypass valve). ) and a supercharging pressure control unit 80 .

The supercharging pressure control unit 80 sets a target value of the boost pressure according to the operating state of the engine (for example, engine speed and engine load), and opens the bypass valve so that this target value is achieved. change the degree.

In the present embodiment, the fuel injection control unit 71 performs at least main injection at a timing when the piston 5 is positioned near the compression top dead center, and pilot injection at a timing earlier than the main injection. and low-penetration injection in which fuel is injected at a timing earlier than the pilot injection or at a timing later than the main injection.

Here, the main injection and the pilot injection are fuel injections commonly used in conventional combustion control. There are many modes of these injections. After-injection may be performed at a timing later than the main injection to suppress soot. In addition to these injections, the present embodiment is characterized in that low-penetration injection, in which penetration is more limited than other injections, is performed. As will be described in detail later, the low-penetration injection is fuel injection for effectively utilizing the air (oxygen) remaining in the radially central region of the combustion chamber 6 . The fuel injection control unit 71 performs a first injection control that executes at least one of the main injection and the pilot injection at the timing of injecting fuel directed toward the connecting portion 53 of the cavity 5C, and the low penetration injection, in the combustion chamber. and a second injection control that causes fuel injection to be performed only within the radially central region of No. 6.

The fuel injection control unit 71 functionally includes an injection range setting unit 72 , an operating state determination unit 73 , a residual oxygen amount determination unit 74 , a mode determination unit 76 , an injection pattern setting unit 77 and an injection timing setting unit 78 .

The injection range setting unit 72 sets a penetration target for each fuel injection described above. Especially in the low penetration injection, the injection range setting unit 72 predicts the aspect of the in-cylinder swirling flow formed by the cavity 5C and sets the penetration target (described in detail later with reference to FIG. 9).

The operating state determination unit 73 determines the operating state of the engine body 1 from the engine rotation speed based on the value detected by the crank angle sensor SN1 and the engine load based on the opening information of the accelerator opening sensor SN10. This determination result is used to determine whether or not the operation mode is for executing the low penetration injection.

A residual oxygen amount determination unit 74 determines the oxygen utilization state in the combustion chamber 6, that is, whether or not residual oxygen is generated in the combustion chamber 6, based on the detection value of the exhaust _O2 sensor SN8. determine the level of The residual oxygen may be derived by model calculation referring to the amount of intake air detected by the air flow sensor SN3, the amount of fuel injected from the injector 15, etc., without depending on the detected value of the exhaust _O2 sensor SN8.

The mode determination unit 76 determines the current operation mode based on the injection pressure of the injector 15 detected by the injection pressure sensor SN7 or by receiving set value data of the injection pressure calculated according to the engine load. .

The injection pattern setting unit 77 sets the pattern of fuel injection from the injector 15 . In the low-penetration injection, the injection pattern setting unit 77 sets the injection pattern of the low-penetration injection according to the operation mode determined by the mode determination unit 76 . Variable elements of this injection pattern are the rough execution timing of low-penetration injection (for example, whether it is earlier than pilot injection or later than main injection), the number of times of low-penetration injection (single injection or split injection). or), etc.

The injection timing setting unit 78 sets the injection timing of fuel injection from the injector 15 according to various conditions.

[Reason why low penetration injection is necessary]
As described above, by adopting the two-stage structure cavity having the first and second cavity portions 51 and 52, the air in the combustion chamber 6, especially the radially outer squish region (in this embodiment, the peripheral flat portion 55) can be effectively used to form a homogeneous and lean air-fuel mixture, and the advantage of suppressing the occurrence of cold loss through the inner peripheral wall of the cylinder 2 can be expected. On the other hand, the inventors have found that the utilization of air in the radially central region of the combustion chamber 6 tends to decrease when the two-stage cavity is employed. This point will be explained based on FIG.

FIG. 6A is a diagram schematically showing an in-cylinder swirling flow when employing a cavity according to a comparative example. The piston 500 of the comparative example has a single-stage cavity 500C. The cavity 500</b>C includes a cavity portion 501 , a cavity edge 502 serving as a radially outer opening edge of the cavity portion 501 , and a peak portion 503 protruding from the central region in the radial direction B. The cavity portion 501 has an egg-shaped curved cross-sectional shape.

Suppose that fuel is injected from an injector (not shown) toward the cavity edge 502 along the injection axis AX in the combustion chamber 6A defined by the cavity 500C. In this case, the in-cylinder flow of the air-fuel mixture containing the injected fuel becomes a swirling flow E1 indicated by an arrow in the drawing. The swirling flow E1 hits the cavity edge 502, travels downward in the axial direction A and inward in the radial direction B in sequence along the shape of the cavity portion 501, is guided upward by the peak portion 503, and flows outward in the radial direction B. Create a flow in the direction Such a swirling flow E1 is a relatively strong vortex, and the drawing force EP1 that draws the air AR present in the radially central region of the combustion chamber 6A (near the upper portion of the peak 503) outward in the radial direction B is also strong. . Therefore, the air-fuel mixture can be formed using the air AR in the radially central region.

On the other hand, FIG. 6B is a diagram schematically showing the in-cylinder swirling flow when the piston 5 having the two-stage structure cavity 5C according to the present embodiment is employed. In the combustion chamber 6, fuel is injected from an injector (not shown) toward the connecting portion 53 along the injection axis AX. In this case, the in-cylinder flow of the air-fuel mixture is branched at the connecting portion 53 and separated into a flow toward the first cavity 51 on the lower side in the axial direction A and a flow toward the second cavity portion 52 on the upper side. A lower swirling flow E2 and an upper swirling flow E3 are formed in the cavities 51 and 52, respectively. The lower swirl flow E2 is a flow similar to the swirl flow E1, and is sequentially directed downward in the axial direction A and inward in the radial direction B along the shape of the first cavity portion 51, and then upward by the peak portion 54. induced flow outward in radial direction B; The upper swirling flow E3 is a flow that flows from the outside in the radial direction B upward in the axial direction A and then inward in the radial direction B in sequence. It can be seen that the formation of the upper swirling flow E3 makes it possible to utilize the air in the squish area compared to the one-stage cavity 500C.

However, the utilization rate of the air AR in the radial central region of the combustion chamber 6 tends to be inferior to that of the single-stage cavity 500C. That is, in the case of the two-stage cavity 5C, the swirl flow is separated into the lower swirl flow E2 and the upper swirl flow E3, so the drawing force EP2 for drawing the air AR outward in the radial direction B is relatively weak. becomes. That is, the lower swirling flow E2 that contributes to the drawing of the air AR becomes weaker than the swirling flow E1 of the comparative example due to the separation of the swirling flow, and the drawing force EP2 based on the swirling flow is weakened.

FIG. 7A shows how residual air is generated in the combustion chamber 6A when the cavity 500C according to the comparative example is used, and FIG. 7B shows combustion when the cavity 5C according to the present embodiment is used. 4A and 4B are cross-sectional views each showing how residual air is generated in the chamber 6. FIG. As described with reference to FIG. 6A, in the comparative example, a relatively strong swirl flow E1 is formed. Therefore, as shown in FIG. 7A, the air existing in the central region in the radial direction B of the combustion chamber 6A is easily drawn into the swirling flow E1, and the oxygen remaining possible region where unused air (oxygen) can remain. G1 becomes a relatively narrow region.

On the other hand, in the cavity 5C according to the present embodiment, as described with reference to FIG. It becomes difficult for the air to be drawn into the lower swirling flow E2. That is, it becomes difficult for the air to move outward in the radial direction B. Therefore, as shown in FIG. 7(B), an oxygen remaining possible region G2 where unused air (oxygen) can remain occupies a large area in the radial central region. Therefore, there arises a problem that the oxygen remaining in the radially central region of the combustion chamber 6 cannot be effectively utilized.

[Utilization of residual air by low penetration injection]
In view of the above problem, in this embodiment, in addition to the main injection and pilot injection that are generally performed in combustion control in a diesel engine, low-penetration injection that injects fuel only in the radially central region of the combustion chamber 6 is performed. be done. FIG. 8 is a cross-sectional view of the combustion chamber 6 showing how the low penetration injection 15A from the injector 15 is executed.

The low penetration injection 15A is an injection for generating an air-fuel mixture by utilizing the air remaining in the central region in the radial direction B of the combustion chamber 6 . Therefore, the spray penetration of the low penetration injection 15A is set at the outer edge H of the area where air (oxygen) can exist in the radially central area of the combustion chamber 6 . That is, the arrival position of the tip of the fuel spray of the low penetration injection 15A is set to the outer edge H described above. The outer edge H corresponds to the outer edge of the residual oxygen possible region G2 previously shown in FIG. 7(B). The spray penetration of the low penetration jet 15A may be set inside the outer edge H in the radial direction B. However, from the viewpoint of making the best use of the oxygen in the oxygen residual region G2, it is desirable to set the outer edge H to spray penetration. If the spray penetration is set outside the outer edge H in the radial direction B, an excessively fuel-rich region may occur outside the outer edge H in the radial direction B, so it is desirable to avoid this.

For the above reasons, the injection range setting unit 72 (FIG. 5; second injection control unit) sets the outer edge H to be the target line of the spray penetration when performing the low penetration injection 15A. Although this outer edge H cannot be detected by a sensor or the like, it can be estimated from the arrival position in the radial direction B of the swirl flow (lower swirl flow E2 and upper swirl flow E3) generated in the combustion chamber 6. can be done.

FIGS. 9A to 9C are diagrams for explaining a method of setting the target line H1 of the low penetration injection 15A, which is the outer edge H of the oxygen remaining possible region G2. It can be said that the oxygen survivable region G2 where unused air stays is generated in a region where the swirling currents of the lower swirling flow E2 and the upper swirling flow E3 do not occur, or where the swirling flows do not reach. Therefore, the target line H1 can be derived by obtaining the inner boundary line in the radial direction B that the swirling flow reaches. That is, the position where the outermost peripheral portions of the swirling flows E2 and E3 are closest to the center of the combustion chamber 6 in the radial direction B is the boundary line described above, that is, the target line H1.

The size of the swirling flow of the lower swirling flow E2 and the upper swirling flow E3 generated in the combustion chamber 6 having the two-stage cavity 5C is determined by the injection with the maximum energy per cycle, that is, the spray penetration of the main injection. It is determined by factors such as the distribution of the spray penetration to the upper and lower cavity portions 51 and 52, the shape (turning curvature) and volume (turning distance) of the cavity portions 51 and 52, and the like.

As shown in FIG. 9A, the swirling flows E2 and E3 are vortex flows having a swirling radius in the radial direction B that varies according to the factors described above. Since the shape and volume of the cavity 5C are fixed, the fluctuation factors of the orbital diameter are the spray penetration and its distribution. The position where the outermost peripheral portions of the swirling flows E2 and E3 are closest to the center of the combustion chamber 6 in the radial direction B is the boundary line described above, that is, the target line H1. In the present embodiment, the target line H1 is determined by the swirling diameter of the lower swirling flow E2 generated exclusively in the first cavity portion 51 arranged radially inward of the second cavity portion 52 .

The spray penetration of the main injection is determined by the injection pressure and injection amount of fuel from the injector 15, as shown in FIG. 9(B). That is, the greater the integrated value of the injection pressure and the injection amount, the greater the spray penetration, which means that the swirl diameter (swirl energy) of the swirl flow also increases. On the other hand, the distribution of the spray penetration to the upper and lower cavity portions 51 and 52 depends on the positional relationship between the injection axis AX and the cavity portions 51 and 52, that is, the injection timing.

FIG. 9C is a graph showing the relationship between the injection timing and the spray penetration in the first cavity portion 51 on the lower side. Since the main injection is generally performed after the top dead center of the compression stroke, the more retarded the angle, the lower the piston 5 will be. Therefore, the more the injection timing is retarded, the more the injection axis AX is oriented above the connecting portion 53, that is, toward the second cavity portion 52 side. That is, the more the injection timing is retarded, the smaller the spray penetration distributed to the first cavity portion 51, and thus the smaller the swirl diameter (swirl energy) of the lower swirl flow E2.

As described above, the swirl diameter of the lower swirl flow E2 can be estimated from the injection pressure, injection amount, and injection timing of the main injection. Based on the estimated swirl diameter of the lower swirl flow E2, the injection range setting unit 72 (Fig. 5) determines the size of the residual oxygen possible region G2 (Fig. 7(B)) generated in the radial central region of the combustion chamber 6. to estimate Then, the injection range setting unit 72 sets the outer edge H (FIG. 8) of the oxygen remaining possible region G2 as the target line H1 in the low penetration injection. Then, the fuel injection control unit 71 executes the low penetration injection with the target line H1 as the penetration target at an appropriate timing, so that the air remaining in the oxygen remaining possible region G2 and the sprayed fuel by the low penetration injection, A mixture can be formed. As a result, it is possible to effectively use the air in the combustion chamber 6 to form a homogeneous and lean air-fuel mixture, thereby realizing good diesel combustion with suppressed generation of soot and the like.

[First embodiment]
Next, a first embodiment of low penetration injection control will be shown. In the first embodiment, the low-penetration injection described above is executed at "timing earlier than the pilot injection" (hereinafter referred to as "pilot region"), and the injection timing is adjusted to the amount of the boost pressure lacking the target value. Here is an example that changes accordingly.

10 and 11 are diagrams schematically showing the injection timing (crank angle CA) and the injection amount of fuel injection performed per cycle.

FIG. 10 shows a basic injection pattern when low penetration injection is not executed. Here, an example is shown in which main injection P1, pilot injection P2, and after-injection P3 are executed as the basic injection pattern. The main injection P1 is an injection having the maximum energy (injection amount), and is an injection executed near the compression top dead center (for example, 2 to 6 deg_ATDC). The pilot injection P2 is an injection that is executed at a timing (for example, 1 to 10 deg_BTDC) earlier than the main injection P1, and is executed for the purpose of increasing ignitability by creating an air-fuel mixture in advance. FIG. 10 shows an example in which the pilot injection P2 is performed in two stages, a first pilot injection P21 and a second pilot injection P22. The after-injection P3 is an injection that is executed at a timing (for example, 8 to 15 deg_BTDC) later than the main injection P1, and is executed for the purpose of completely burning the fuel and not generating soot. These injections P1, P2, and P3 are injections in which the spray penetration is not limited to the central region within the target line H1, like the low-penetration injection described above.

FIG. 11 is a diagram showing a mode of low-penetration injection according to the first embodiment. As shown in FIG. 11 and as described above, in the first embodiment, the low-penetration injection P4 is executed in the pilot region on the advanced side of the pilot injection P2. Since the spray penetration of the low-penetration injection P4 is limited to the target line H1, the injection amount is generally smaller than those of the injections P1, P2, and P3 of the basic injection pattern.

The solid line in FIG. 11 indicates the low-penetration injection P4 when the boost pressure is approximately at the target value. At this time, the low-penetration injection P4 is performed at the preset basic injection timing CA1. The basic injection timing CA1 is set according to, for example, the engine speed and the engine load.

On the other hand, when the shortage of the boost pressure with respect to the target value, that is, the value obtained by subtracting the actual boost pressure from the target value of the boost pressure becomes large, the injection timing of the low penetration injection P4 is changed as shown by the dashed line. is changed from the basic injection timing CA1 to the advance side. In the present embodiment, the injection timing of the low-penetration injection P4 is set based on the shortage amount and the basic injection timing CA1 so that the advance amount from the basic injection timing CA1 is substantially proportional to the shortage amount. be done. Here, in this embodiment, when the shortage amount is less than 0, that is, when the boost pressure is higher than the target value, the injection timing of the low penetration injection P4 is maintained at the basic injection timing CA1, and the shortage amount is This injection timing is changed only when it is 0 or more.

FIG. 12 is a flowchart showing low penetration injection control according to the first embodiment.

First, the fuel injection control unit 71 (FIG. 5) of the processor 70 acquires information about the vehicle travel area (operating state of the engine body 1) from the sensors SN1 to SN12 shown in FIG. 5 and other sensors. The supercharging pressure control unit 80 (FIG. 5) acquires the current supercharging pressure (detection value of the intake pressure sensor SN5) (step S1). Subsequently, the supercharging pressure control unit 80 subtracts the current supercharging pressure from the separately set target value of the supercharging pressure to determine the amount of shortage of the supercharging pressure with respect to the target value (hereinafter, appropriately referred to as the amount of shortage of the boost pressure). is calculated (step S2).

Next, the operating state determination unit 73 determines that the engine rotation speed detected by the crank angle sensor SN1 and the engine load detected by the accelerator opening sensor SN10 fall within a predetermined travel region (operating state). It is determined whether or not to do so (step S3). The predetermined running region is a running region in which the oxygen remaining possible region G2 shown in FIG. 7B is formed. A region that is not included in the predetermined travel region is, for example, a case where the spray penetration of main injection P1 or pilot injection P2 is larger than a predetermined set amount. The predetermined set amount is a spray penetration that creates an injection amount that does not allow air to remain in the radially central region of the combustion chamber 6, and the region not included in the predetermined travel region generally has a high load and high rotation. This corresponds to the speed running area.

If the driving range does not fall within the predetermined driving range (NO in step S3), that is, if the oxygen remaining possible range G2 is not formed, the driving state determination unit 73 determines that the driving mode is not for executing low penetration injection. In this case, the fuel injection control unit 71 prohibits low penetration injection (step S4). This is because if the low-penetration injection is executed in such a driving range, the air-fuel mixture becomes richer, deteriorating the combustibility and fuel efficiency.

On the other hand, if the running region falls within the predetermined travel region (YES in step S3), an oxygen remaining-possible region G2 is formed in the radial central region of the combustion chamber 6 . In this case, the remaining oxygen amount determining section 74 determines whether or not the oxygen remaining amount G2, that is, the central area of the combustion chamber, contains a predetermined amount of oxygen or more (step S5). This determination is performed based on the detected value of the exhaust _O2 sensor SN8 or model calculation, as described above. If the amount of oxygen equal to or greater than the predetermined value does not remain in the remaining oxygen possible region G2 (NO in step S5), there is no oxygen to be utilized by executing the low penetration injection in the first place. Penetration injection is prohibited (step S4).

On the other hand, when the remaining oxygen amount determination unit 74 determines that the oxygen amount equal to or greater than the predetermined value remains in the oxygen remaining possible area G2, which is the radial center area (YES in step S5), the low penetration injection is performed. mode to be executed. In this case, the injection pattern setting unit 77 then determines whether or not the boost pressure shortage is greater than 0 (step S6).

In step S6, if it is determined that the amount of boost pressure shortage is 0 or less (NO in step S6), that is, if the actual boost pressure matches the target value or is higher than the target value, injection The pattern setting unit 77 sets the injection timing of the low penetration injection to the separately set basic injection timing (step S7). On the other hand, if it is determined that the boost pressure shortage amount is greater than 0, the injection pattern setting unit 77 calculates an advance amount of the injection timing of the low penetration injection with respect to the basic injection timing based on the boost pressure shortage amount (step S8). As described above, at this time, the advance amount is increased in proportion to the boost pressure shortage amount as the boost pressure shortage amount increases. Subsequently, the injection pattern setting unit 77 sets the timing advanced by the calculated advance amount from the basic injection timing as the injection timing of the low penetration injection (step S9). After that, the fuel injection control unit 71 drives the injector 11 so that the low penetration injection is performed at this injection timing.

FIG. 13 is a time chart showing changes over time in each parameter during acceleration when this control is carried out. Each graph in FIG. 13 shows, from top to bottom, accelerator opening, engine speed, supercharging pressure, and injection timing of low penetration injection. When the accelerator pedal is depressed at time t1 to increase the opening of the accelerator, the target value (broken line) of the supercharging pressure increases accordingly. Also, the engine speed increases. As the target value of the boost pressure increases, the actual boost pressure (solid line, hereinafter appropriately referred to as the actual boost pressure) is also increased (for example, the bypass valve is controlled to the closing side to increase the of the exhaust gas is introduced into the turbine 48).

However, due to the response delay of the turbocharger 46 and the delay in movement of air from the turbocharger 46 to the combustion chamber 6 (intake pressure sensor SN5), the actual boost pressure does not reach the target value immediately. However, the deficit of the supercharging pressure becomes larger than zero. Since the boost pressure deficit is greater than 0, the injection timing (solid line) of the low-penetration injection is advanced from the basic injection timing CA1 indicated by the dashed line, as described above. Until the actual boost pressure reaches the target value, the injection timing of the low-penetration injection is advanced from the basic injection timing CA1. When the actual boost pressure reaches the target value at time t2, The basic injection timing CA1 is set. Note that in the example shown in FIG. 13, the basic injection timing CA1 is changed to the advance side as the engine speed increases.

Thus, in the first embodiment, the injection timing of the low-penetration injection is advanced according to the boost pressure shortage.

[Second embodiment]
Next, a second embodiment of low penetration injection control will be shown. In the second embodiment, the operation mode is determined according to the injection pressure of the injector 15 determined according to the operation state, and the injection pattern of the low penetration injection is determined according to each operation mode and the boost pressure shortage amount. . In addition, hereinafter, "the timing later than the main injection" is referred to as "the AFTER region".

FIG. 14 shows an injection pattern in which the low-penetration injection P5 is executed in the AFTER region on the retard side of the after injection P3. The injection amount of the low penetration injection P5 performed in the AFTER region is also smaller than the injection amounts P1, P2, and P3 of the basic injection pattern.

<Description of basic control categories>
FIG. 15 is a diagram showing basic control divisions in the low penetration injection control according to the second embodiment. In FIG. 15, the horizontal axis represents the injection pressure of fuel from the injector 15, that is, the injection pressure of the injector 15, and indicates the set maximum injection pressure FPmax and the set minimum injection pressure FPmin. The vertical axis is the amount of fuel injected from the injector 15 by low penetration injection. The oblique line H2 in the figure is a line connecting the injection pressure and the injection amount when the spray penetration (tip position of the spray) of the low penetration injection becomes the target line H1 (FIG. 9), that is, the spray penetration of the low penetration injection. is a basic control target line for the injection pressure and the injection amount for making the target line H1. The vertical axis of FIG. 15 is the amount of fuel injected from the injector 15 by one low-penetration injection. Hereinafter, the amount of fuel injected from the injector 15 by one low-penetration injection will be referred to as a single-shot low-penetration injection amount.

As described above, the higher the injection pressure, the greater the spray penetration, and the greater the injection amount, the greater the spray penetration. Accordingly, the control target line H1 is a line in which the single-shot low-penetration injection amount decreases as the injection pressure increases.

In this embodiment, the injection pressure is set according to the operating state of the engine body 1 as described above. Accordingly, the injection amount is adjusted according to the set injection pressure in order to fly the low-penetration injection spray to the target line H1. That is, in the low-penetration injection control of the present embodiment, the injection pressure data is received as an existing value, and the injection amount is set according to the injection pressure, thereby achieving the spray penetration of the target line H1. A control target line H2 represents such an injection amount setting line.

In general, low-penetration injection is performed using the PILOT area in areas where the injection pressure is relatively high, and low-penetration injection is performed using the AFTER area in areas where the injection pressure is relatively low. The reason for this broad classification is as follows.

First, from the aspect of fuel consumption performance, it is more advantageous to utilize the PILOT region. Since the injection in the AFTER region is performed after the combustion of the main injection, heat is generated mainly during the descent of the piston, increasing fuel consumption loss. On the other hand, the fuel injected in the PILOT region is burned with high thermal efficiency near the compression top dead center, and most of the combustion energy can be extracted as effective torque. Therefore, it is desirable to utilize the PILOT region as much as possible in order to improve fuel efficiency.

However, as indicated by the control target line H2, when the injection pressure is low, it is necessary to increase the injection amount so that the tip of the spray reaches the target line H1. Supplying too much fuel to the combustion chamber 6 in the PILOT region creates the problem of pre-ignition. Specifically, when a large amount of fuel is supplied to the combustion chamber 6 by low penetration injection in the PILOT region, there is a risk that this fuel will start burning before the start of combustion of fuel related to pilot injection or main injection, and low penetration injection The reaction between the fuel and air accelerates the reaction of the fuel for the pilot injection and the main injection, and there is a risk that the fuel for these injections will start burning earlier than the desired timing. On the other hand, when the low penetration injection is performed in the AFTER region, the fuel for the low penetration injection is burned after the fuel for the pilot injection and the main injection is burned, so the problem of pre-ignition does not occur.

From this, in this embodiment, basically, when the injection pressure is low and the amount of fuel supplied to the combustion chamber 6 by low penetration injection is large, the AFTER region is utilized and the fuel is supplied to the combustion chamber 6 by low penetration injection. Use the PILOT region when the amount of fuel to be drawn is low.

Here, there is a characteristic of a diesel engine that the lower the injection pressure, the larger the particle size of sprayed particles and the more likely soot is generated. Therefore, if the fuel is injected in the AFTER region when the injection pressure is low as described above, it is possible to obtain the effect that the soot can be reburned.

As described above, in general, the PILOT region is utilized in the high injection pressure region, and the AFTER region is utilized in the low injection pressure region.

Further segmentation of the PILOT and AFTER regions described above will now be described. As shown in FIG. 15, the PILOT region includes a first region on the high injection pressure side in which the low penetration injection is dividedly performed in the PILOT region, and a first region on the low injection pressure side in which the low penetration injection is performed singly in the PILOT region. It is divided into two areas. The AFTER region is also divided into a third region on the high injection pressure side in which injection is divided and a fourth region on the low injection pressure side in which injection is performed singly.

The distinction between the single-shot injection and the split injection ensures the injection amount necessary to burn all the oxygen in the oxygen residual possible region G2 generated in the radial central region of the combustion chamber 6 in the injection along the control target line H2. or not. In the regions where the injection pressure is high (the first region and the third region), the injection amount per injection (single-shot low penetration injection amount) is small (if it is increased, the injection will exceed the target line H1. Therefore, two or more injections are performed to ensure the required injection amount. On the other hand, in the region where the injection pressure is low, the injection amount per injection (single-shot low-penetration injection amount) is relatively large, so the necessary injection amount can be secured for one injection.

The first area is a "pilot division" area in which low penetration injection is performed in multiple divisions in the pilot area, and the second area is a "pilot single shot" in which low penetration injection is performed in a single shot in the pilot area. area. In addition, the third area is an "after division" area in which low penetration injection is performed by dividing it multiple times in the after area, and the fourth area is an "after single shot" in which low penetration injection is performed in a single shot in the after area. ” area. FIG. 15 shows first, second, third, fourth, and fifth lines L1, L2, L3, L4, and L5 indicating the upper limit or lower limit injection amounts of these categories. The injection amount of fuel has a relationship of L1<L2<L3<L4<L5.

The third line L3 is the upper limit of the injection amount of the low-penetration injection when utilizing the PILOT area, and the first area and the second area are set to areas where at least the single-shot low-penetration injection amount is equal to or less than the third line L3. It is As described above, pre-ignition occurs when a large amount of fuel is supplied into the combustion chamber 6 by low-penetration injection in the PIROT region. The third line L3 is the upper limit line of the injection amount at which pre-ignition does not occur when low penetration injection is performed in the PILOT range.

Here, the third line L3 is the upper limit line of the total amount of fuel supplied into the combustion chamber 6 per one combustion cycle by low penetration injection. Therefore, when the low-penetration injection is performed in a plurality of times in the PILOT region, it is necessary to prevent the total amount of fuel for each injection from exceeding the third line L3.

Although the third line L3 eventually becomes the lower limit of the AFTER split injection in the third region, this is not the lower limit of the AFTER split injection in a functional sense. As described above, the use of the PILOT region is advantageous in terms of fuel consumption loss, so the PILOT region is applied preferentially, and the injection amount region that cannot be covered by the PILOT region due to the problem of premature ignition is supplemented with the AFTER region. is the lower limit in terms of

The second line L2 is a lower limit line that secures an injection amount that does not cause ignition delay in the residual oxygen possible region G2 in the single PILOT injection of the second region. When the injection amount per injection (single-shot low-penetration injection amount) becomes equal to or less than the second line L2, the injection cannot secure a sufficient amount of fuel for the air existing in the oxygen remaining possible region G2, and oxygen Combustion does not occur in the survivable region G2, or the combustion start timing is delayed. In other words, the second line L2 is a line set from the viewpoint of providing the minimum amount of heat by one low-penetration injection so as to cause proper combustion using the oxygen in the region G2.

Accordingly, the second region in which the PILOT single-shot injection is performed is the region between the second line L2 and the third line L3 on the control target line H2.

The first region in which the PILOT split injection is performed is the region below the second line L2 on the control target line H2. That is, as described above, when the injection amount per injection becomes equal to or less than the second line L2, the necessary injection amount cannot be secured by one low-penetration injection, and split injection becomes necessary. Below L2, the low-penetration injection is divided into multiple times.

In the present embodiment, the low penetration injection is performed twice in the first region. The level (injection amount) of the second line L2 is set to be half or less of the level (injection amount) of the third line L3. is suppressed to an amount equal to or less than that of the third line L3.

The first line L1 with the smallest injection amount is a lower limit line that secures an injection amount that does not cause ignition delay in the residual oxygen possible region G2 in the PILOT split injection of the first region. If the injection amount per injection decreases further, the necessary injection amount cannot be secured even by split injection, and as a result, combustion does not occur in the oxygen remaining possible region G2, or the combustion start timing is delayed. That is, the first line L1 is set from the viewpoint of providing the minimum amount of heat that can cause combustion using the oxygen in the region G2. The first line L1 is also the injection amount at which the control target line H2 and the set maximum injection pressure FPmax intersect, and is also the line where the injection amount cannot be reduced any further.

A fourth line L4 is a lower limit line that secures an injection amount that exhibits the function of oxidizing soot in the AFTER single-shot injection in the fourth region. If the injection amount per injection is less than that of the fourth line L4, the injection amount for sufficiently oxidizing soot cannot be secured by single injection, and split injection is required (third area). On the other hand, the fifth line L5 is an upper limit line that limits the injection amount so that the residual oxygen possible region G2 does not become excessively rich in the AFTER single-shot injection in the fourth region. If the injection amount per injection is larger than that of the fifth line L5, the amount of heat will be greater than the amount of oxygen existing in the oxygen remaining possible region G2, and soot may be newly generated.

As described above, the low-penetration injection uses different injection patterns depending on the division of the first to fourth regions. However, these divisions (first to fifth lines L1 to L5) and injection timing are not fixed, and are corrected (set) according to the operating conditions. The classification and the injection timing are mainly affected by the ignitability of the air-fuel mixture in the combustion chamber 6 and the development of soot. In this embodiment, the target value of the supercharging pressure is set so that the ignitability and soot generation are good, and the ignitability and soot generation change depending on the deviation from the target value of the boost pressure. . Thus, the injection pattern and the like are corrected according to the difference between the boost pressure and the target value. Further, the difference between the boost pressure and the target value becomes large when the boost pressure does not reach the target value during acceleration or the like as described above. Therefore, in the present embodiment, the correction is performed when the supercharging pressure is insufficient with respect to the target value, and the correction is performed according to the amount of the shortage.

Specifically, when the amount of boost pressure shortage, which is the amount of shortage of the boost pressure with respect to the target value, is large, the ignitability of the air-fuel mixture is low. Also, when the amount of boost pressure deficiency is large, the weight of oxygen introduced into the combustion chamber 6 is less than the desired amount, and soot is likely to be generated.

The ignitability that accompanies the change in the boost pressure shortage affects the setting of the second line L2 and the third line L3 shown in FIG.

When the amount of boost pressure deficiency is large and ignitability is low, it is desirable to set the second line L2 to a higher injection amount level in order to ensure ignitability. On the other hand, the third line L3 can be set to a higher injection amount level because pre-ignition tends not to occur when the boost pressure shortage is large and the ignitability is low. In other words, when the boost pressure shortage is large and the ignitability is low, the utilization range of the PILOT region (second region), which is advantageous in terms of fuel consumption loss, can be expanded.

Also, regarding the injection timing, when utilizing the PILOT region, if the amount of boost pressure shortage is large and ignitability is low, the degree of mixture of fuel and air by low penetration injection is increased to improve ignitability. In addition, it is desirable to set the injection timing of the low penetration injection to advance.

A change in the appearance of soot associated with a change in the amount of boost pressure deficiency affects the setting of the fourth line L4 shown in FIG.

When the amount of boost pressure shortage is large and soot is likely to be generated, the fourth line L4 is set to a higher injection amount level to promote the oxidation of soot. It is desirable that the penetration injection be performed multiple times.

In the case of utilizing the AFTER region, when the boost pressure shortage is large and soot is likely to be generated, low penetration injection is performed so that the energy generated by the low penetration injection is effectively used to oxidize the soot. It is desirable to set the injection timing of .

On the other hand, when the amount of boost pressure shortage is small and soot is relatively unlikely to be generated, the fourth line is used to prevent deterioration in fuel efficiency due to a large amount of fuel being injected after the main injection. It is desirable to set L4 to a lower injection level to reduce the total amount of fuel supplied to combustion chamber 6 by low penetration injection.

Also, when utilizing the AFTER region, if the amount of boost pressure shortage is small and soot is relatively unlikely to occur, the injection timing of the low penetration injection should be set to advance in order to prevent deterioration of fuel efficiency. is desirable.

<Setting of injection pattern based on boost pressure>
(Specific example of injection pattern)
FIGS. 16A to 16D and 17A to 17C are time charts schematically showing seven injection modes of low penetration injection employed in the second embodiment. Here, as in FIG. 11, an example in which main injection P1, pilot injection P2 (first and second pilot injections P21 and P22), and after injection P3 are executed as the basic injection pattern is shown. In addition to these injections P1-P3, low penetration injection is performed.

FIG. 16A shows an injection pattern called "PILOT division-A", which is adopted as the basic injection pattern for the first area in FIG. In PILOT split-A, low penetration injection P4 is performed in the PILOT region preceding injections P1-P3 of the basic injection pattern. The low penetration injection P4 consists of a first injection P41 performed at a predetermined crank angle CA11, and a second injection P42 performed at a retarded side with a predetermined interval t11 from the first injection P41. The injection amounts of the first injection P41 and the second injection P42 are set to an injection amount Fa along the control target line H2.

FIG. 16B shows an injection pattern called "PILOT split-B", in which the low penetration injection P4 is executed at a timing more advanced than the PILOT split-A. The low penetration injection P4 of PILOT split-B is the same split injection as PILOT split-A, but the first injection P41 is executed at crank angle CA12 advanced from crank angle CA11. Then, the second injection P42 is executed on the retarded side with an interval t12 shorter than the interval t11. By advancing the injection timing of the first injection P41, it is possible to gain time from injection to ignition, thereby improving ignitability. Further, by setting the interval t12 between the first and second injections P41 and P42 to be short, a rich zone is formed in which the injected fuel of the first injection P41 and the injected fuel of the second injection P42 are superimposed. Ignition can be improved.

FIG. 16C shows an injection pattern called "PILOT single shot-A", which is adopted as the basic injection pattern for the second region. In PILOT single shot-A, low penetration injection P4 consisting of single shot injection is executed at a predetermined crank angle CA2 in the PILOT region. The injection amount of the low penetration injection P4 is set to the injection amount Fb along the control target line H2. That is, the injection amount Fb is larger than the injection amount Fa for one split injection. In "PILOT single-shot-A", the injection timing (CA2) of the low penetration injection P4 is the injection timing of the low penetration injection P4 of PILOT split-A (Fig. 16A) (the injection timing of the first injection P41, This pattern is set on the retard side of CA11).

FIG. 16D shows an injection pattern called "Single PILOT-B", in which the single low penetration injection P4 is executed at a timing advanced by ΔCA2 from the single PILOT-A. By advancing ΔCA2, ignitability can be improved in the same manner as in PILOT division-B.

FIG. 17A shows an injection pattern called "AFTER division-A", which is adopted as the basic injection pattern of the third region. In the AFTER division-A, the low penetration injection P5 is performed in the AFTER region after the injections P1 to P3 of the basic injection pattern are performed. The low-penetration injection P5 consists of a first injection P51 executed at a predetermined crank angle CA31 and a second injection P52 executed at a retarded side with a predetermined interval t21 from the first injection P51. The injection amounts of the first injection P51 and the second injection P52 are set to an injection amount Fc along the control target line H2.

FIG. 17B shows an injection pattern called "AFTER split-B", in which the low penetration injection P5 is executed at a timing later than AFTER split-A. The low penetration injection P5 of the AFTER split-B is the same split injection as the AFTER split-A, but the first injection P51 is executed at a crank angle CA32 retarded from the crank angle CA31. Then, the second injection P52 is executed on the retarded side with an interval t22 longer than the interval t21. By retarding the injection timing of the first injection P51, it is advantageous for the oxidation and combustion of soot, and the generation of soot can be further suppressed. Setting a long interval t22 between the first and second injections P51 and P52 also contributes to the suppression of soot.

FIG. 17C shows an injection pattern called "AFTER single-shot-A", which is adopted as the basic injection pattern of the fourth area. In the AFTER single-shot-A, low penetration injection P5 consisting of a single injection is executed at a predetermined crank angle CA4 in the AFTER region. The injection amount of the low penetration injection P5 is set to the injection amount Fd along the control target line H2. That is, the injection amount Fd is larger than the injection amount Fc for one split injection. Further, in "AFTER single-shot -A", the injection timing of the low penetration injection P5 is the injection timing of the low penetration injection P5 in "AFTER split-B" (Fig. 17(B)) (the injection timing of the first injection P51, This pattern is set on the advance side of CA32).

(Proper use of injection patterns)
Next, the proper use of the seven injection patterns described above will be described.

In the following, the injection pressure and the single-shot low-penetration injection amount are the injection pressure and the injection amount that use the PILOT division-A pattern in FIG. The second zone mode is the injection pressure and injection amount for which the PILOT single-shot-A pattern of FIG. 16C is used when the boost pressure matches the target value. 17(A) with the injection pressure and injection quantity using the pattern of AFTER division-A in FIG. 17(A); The injection pressure and injection amount for which the AFTER single-shot-A pattern is used is referred to as the fourth region mode.

The mode determination unit 76 sets a control target line H2 (relationship between target injection pressure and injection amount) based on the target line H1 set by the injection range setting unit 72 as described above. Also, the mode determination unit 76 calculates the injection pressure at the intersection of the control target line H2 and the second to fourth lines L2 to L4 when the boost pressure matches the target value. That is, on the control target line H2, the injection pressure is calculated so that the injection amount is at the level of the second line L2 to the fourth line L4 when the boost pressure matches the target value. The levels of these lines L2 to L4 when the supercharging pressure matches the target value are preset and stored in the mode determination unit . The mode determination unit 76 compares the separately set injection pressure with the injection pressure corresponding to the lines L2 to L4 when the boost pressure matches the target value. When the set injection pressure is equal to or higher than the second injection pressure FP2, which is the injection pressure at the intersection of the control target line H2 and the second line L2, the mode determination unit 76 determines that the mode is the first region mode. do. Further, when the set injection pressure is less than the second injection pressure FP2 and equal to or higher than the third injection pressure FP3, which is the injection pressure at the intersection of the control target line H2 and the third line L3, the mode determination unit 76 It is determined that the mode is the second area mode. Further, when the set injection pressure is less than the third injection pressure FP3 and is equal to or greater than the fourth injection pressure FP4, which is the injection pressure at the intersection of the control target line H2 and the fourth line L4, the mode determination unit 76 It is determined that the 3-region mode is selected. Also, the mode determination unit 76 determines that the fourth region mode is set when the set injection pressure is less than the fourth injection pressure FP4. Here, the fourth injection pressure FP4 corresponds to the "reference injection pressure" in the claims.

(1) First Area Mode In the first area mode, when the boost pressure shortage is equal to or less than a predetermined judgment value, the pattern of PILOT division-A in FIG. 16(A) is used. The determination value is a value greater than 0 and is stored in preset mode determination section 76 . A state in which the amount of boost pressure shortage is equal to or less than a preset determination value is a state in which the amount of shortage is equal to or less than the determination value with respect to the target value of boost pressure, and the actual boost pressure is close to the target value.

On the other hand, in the first region mode, when the amount of boost pressure shortage is larger than the judgment value and accordingly the ignitability is low, the pattern of PILOT division-B in FIG. 16B is used. That is, the injection timing of the first injection P41 is advanced more than when the boost pressure shortage amount is equal to or less than the judgment value. Also, the interval between the first and second injections P41 and P42 is shortened, and the injection timing of the second injection P41 is advanced more than when the boost pressure shortage amount is equal to or less than the judgment value. This is to improve the ignitability when the ignitability is low as described above.

(2) Second Region Mode In the second region mode, when the boost pressure shortage is equal to or less than the judgment value, the single PILOT-A pattern of FIG. 16(C) is used.

On the other hand, in the second region mode, when the boost pressure shortage is larger than the judgment value and accordingly the ignitability is low, the PILOT division-B pattern of FIG. 16B is used. This is because as the ignitability deteriorates, the injection amount that defines the second line L2 increases as described above. Here, as described above, the injection timing CA2 of the low-penetration injection P4 of the PILOT single-shot-A pattern is on the retard side of the injection timing CA11 of the low-penetration injection (first injection P41) of the PILOT split-A pattern. , the injection timing CA12 of the low penetration injection (first injection P41) of the PILOT division-B pattern is on the advanced side of the injection timing CA11, and in the PILOT division-B pattern, the injection timing CA12 of the PILOT single shot-A The injection timing of the low-penetration injection P4 is set to be more advanced than the pattern. As a result, when the boost pressure shortage amount is larger than the determination value, the injection timing of the low penetration injection is advanced more than when the boost pressure shortage amount is equal to or less than the determination value. By advancing the injection timing and performing the low-penetration injection in segments, the mixing of fuel and air is promoted and ignitability is improved.

(3) Third Region Mode In the third region mode, when the boost pressure shortage amount is equal to or less than the judgment value, the AFTER division-A pattern of FIG. 17(A) is used.

On the other hand, in the third region mode, when the amount of boost pressure shortage is larger than the judgment value and accordingly the ignitability is low, the PILOT single shot-B pattern of FIG. 16(D) is used. That is, the injection timing of the low-penetration injection is advanced from the timing retarded relative to the after injection P3 to the timing advanced relative to the pilot injection P2. This is because the low ignitability creates an environment in which pre-ignition is unlikely to occur, and the injection amount that defines the third line L3 can be increased, so the PILOT region with little fuel consumption loss can be utilized. Another reason for adopting PILOT single-shot-B is that ignitability can be improved by executing advanced low-penetration injection P4.

(4) Fourth Region Mode In the fourth region mode, when the boost pressure shortage is equal to or less than the judgment value, the single AFTER-A pattern of FIG. 17(C) is used.

On the other hand, in the fourth region mode, when the amount of boost pressure shortage is larger than the judgment value and soot is likely to be generated accordingly, the AFTER division-B pattern of FIG. 17(B) is used. This is because it is necessary to increase the injection amount that defines the fourth line L4 in order to oxidize the soot more reliably. Here, as described above, the injection timing (the injection timing of the first injection P51) of the low penetration injection P5 of the AFTER split-B pattern is earlier than the injection timing CA4 of the low penetration injection P5 of the AFTER single-shot-A pattern. It is on the retard side. As a result, when the boost pressure shortage amount is larger than the determination value, the injection timing of the low penetration injection is retarded more than when the boost pressure shortage amount is equal to or less than the determination value. The retardation of the injection timing and the division of the low-penetration injection to inject a large amount of fuel accelerate the oxidation and combustion of soot.

As described above, in the second embodiment, in the first region mode, the second region mode, and the third region mode, that is, when the injection pressure is equal to or higher than the fourth injection pressure FP4, the supercharging pressure is low. When the amount of pressure underpressure is large (when the amount of boost pressure shortage is greater than the judgment value), it is more important than when the boost pressure is high and the amount of boost pressure shortage is small (the amount of boost pressure shortage is the judgment value). or less), the injection timing of the low-penetration injection is advanced. On the other hand, in the fourth region mode, that is, when the injection pressure is less than the fourth injection pressure FP4, when the boost pressure is low and the boost pressure shortage is large (the boost pressure shortage is greater than the judgment value The injection timing of the low penetration injection is retarded more than when the boost pressure is high and the boost pressure shortage is small (more than when the boost pressure shortage is equal to or greater than the judgment value).

<Control Flow of Low Penetration Injection>
Next, the flow of low-penetration injection control according to the second embodiment will be described with reference to the flowcharts shown in FIGS. 18 and 19. FIG.

Referring to FIG. 18, first, processes similar to those shown in steps S1 to S4 of FIG. 12 are executed. That is, the fuel injection control unit 71 (FIG. 5) of the processor 70 acquires information regarding the travel region of the vehicle, and the boost pressure control unit 80 (FIG. 5) acquires the current boost pressure (step S11). . Subsequently, the supercharging pressure control unit 80 subtracts the current supercharging pressure from the separately set target value of the supercharging pressure to calculate a supercharging pressure shortage (step S12).

Next, the operating state determination unit 73 determines whether or not the engine rotation speed and the engine load fall within a predetermined running range (high load, high rotation speed operating state) ( step S13).

If the driving region does not fall within the predetermined driving range (NO in step S13), the driving state determination unit 73 determines that the driving mode is not one for executing the low penetration injection, and the fuel injection control unit 71 prohibits the low penetration injection (step S14). On the other hand, if the travel region falls within the predetermined travel region (YES in step S13), the remaining oxygen amount determining unit 74 determines whether or not the oxygen remaining amount equal to or greater than a predetermined value remains in the oxygen remaining possible region G2. (Step S15). If the amount of oxygen equal to or greater than the predetermined value does not remain in the oxygen remaining possible region G2 (NO in step S15), the fuel injection control unit 71 prohibits low penetration injection (step S14).

On the other hand, when the remaining oxygen amount determination unit 74 determines that the oxygen amount equal to or greater than the predetermined value remains in the oxygen remaining possible region G2 (YES in step S15), low penetration injection is performed. In this case, next, the mode determination unit 76 determines whether or not the operation mode is the first region mode (whether or not the injection pressure is equal to or higher than the second injection pressure FP2) (step S16). As the set value data of the injection pressure, the detected value of the injection pressure sensor SN7 or the calculated value calculated by the processor 70 according to the engine load can be used.

If the current operation mode is the first region mode (YES in step S16), the injection pattern setting unit 77 determines whether or not the boost pressure shortage amount is equal to or less than the determination value (step S17). If the boost pressure shortage amount is equal to or less than the determination value (YES in step S17), the injection pattern setting unit 77 sets the pattern of PILOT division-A in FIG. 16A as the injection pattern for low penetration injection (step S18). As a result, in this cycle, the injector 15 injects fuel in the PILOT division-A pattern.

On the other hand, if it is determined that the boost pressure shortage amount is larger than the determination value (NO in step S17), the injection pattern setting unit 77 sets the injection pattern of low penetration injection to PILOT division-B in FIG. 16B. pattern is set (step S19).

On the other hand, if it is determined in step S16 that the current operating mode is not the first region mode (NO in step S16), the mode determination unit 76 determines whether or not the current operating mode is the second region mode. (step S20). If the current operation mode is the second region mode (YES in step S20), the injection pattern setting unit 77 determines whether or not the boost pressure shortage amount is equal to or less than the determination value ( step S22). If the boost pressure shortage amount is equal to or less than the determination value (YES in step S22), the injection pattern setting unit 77 sets the single PILOT-A pattern of FIG. S22). On the other hand, if the boost pressure shortage amount is greater than the determination value (NO in step S21), the injection pattern setting unit 77 sets the pattern of PILOT division-B in FIG. 16B as the injection pattern (step S23).

In step S20, when the mode determination unit 76 determines that the current operating mode is not the second region mode (NO in step S20), the process proceeds to the flow of FIG. In this case, the mode determination unit 76 determines whether or not the current operating mode is the third region mode (step S24). If the current operation mode is the third region mode (YES in step S24), the injection pattern setting unit 77 determines whether or not the boost pressure shortage amount is equal to or less than the determination value, as in steps S17 and S21. (step S25). If the amount of boost pressure shortage is equal to or less than the determination value (YES in step S25), the injection pattern setting unit 77 sets the AFTER division-A pattern in FIG. 17A as the injection pattern for low penetration injection (step S26).

On the other hand, if the boost pressure shortage is greater than the determination value (NO in step S25), the injection pattern setting unit 77 sets the injection pattern to the single PILOT-B pattern of FIG. 16(D) (step S27).

If it is determined in step S24 that the current operating mode is not the third region mode (NO in step S24), the mode determination unit 76 determines whether the current operating mode is the fourth region mode ( step S28). If the current operation mode is the fourth region mode (YES in step S28), the injection pattern setting unit 77 determines whether the boost pressure shortage amount is equal to or less than the determination value, as in steps S17, S21, and 25. is determined (step S29). If the amount of boost pressure shortage is equal to or less than the determination value (YES in step S29), the injection pattern setting unit 77 sets the AFTER single shot-A pattern in FIG. 17C as the injection pattern for low penetration injection (step S30).

On the other hand, if the boost pressure shortage amount is greater than the determination value (NO in step S29), the injection pattern setting unit 77 sets the AFTER division-B pattern of FIG. 17B as the injection pattern (step S31).

If it is determined in step S28 that the operation mode is not in the fourth region (NO in step S28), the current operation mode is said to be in an irregular state that does not correspond to any of the first to fourth region modes. It will be. In this case, the fuel injection control unit 71 prohibits low penetration injection (step S14).

[Effect]
According to the fuel injection control device for a diesel engine according to the present embodiment described above, the following effects are obtained. The bottom surface of the combustion chamber 6 of the diesel engine to be controlled is defined by a crown surface 50 including first and second cavity portions 51 and 52 and a connecting portion 53 connecting the two. Then, the fuel injection control unit 71 causes the injector 15 to perform the main injection P<b>1 or the pilot injection P<b>2 directed toward the connecting portion 53 . Therefore, the in-cylinder flow of the air-fuel mixture is separated at the connecting portion 53, the in-cylinder swirling flow becomes relatively weak, and the air in the vicinity of the central region in the radial direction B of the combustion chamber 6 is less likely to be drawn radially outward. tend to emerge.

However, according to the fuel injection control device, the fuel injection control unit 71 injects fuel only in the radially central region of the combustion chamber 6 in addition to the normal main injection P1 and pilot injection P2. The injector 15 is caused to perform low penetration injection with the penetration target being the outer edge H (FIG. 8) of the central region where oxygen may remain due to the weakening of the swirling flow. Therefore, the air remaining in the radially central region of the combustion chamber 6 and the fuel sprayed by the low-penetration injection can form an air-fuel mixture. In addition, since the outer edge H is targeted for penetration, the air-fuel mixture can be formed by making full use of the air present in the radially central region. As a result, it is possible to effectively use the air in the combustion chamber 6 to form a homogeneous and lean air-fuel mixture, thereby realizing good diesel combustion with suppressed generation of soot and the like.

Further, in the first embodiment, when the boost pressure is low and the shortage of the boost pressure with respect to the target value (supercharging pressure shortage) is large, the boost pressure is high and the target boost pressure is increased. The injection timing of the low-penetration injection is advanced more than when the shortage (supercharging pressure shortage) with respect to the value is small. Also in the second embodiment, in the first to third region modes in which the injection pressure is equal to or higher than the fourth injection pressure FP4, the fuel injection control unit 71 controls the amount of shortage of the boost pressure with respect to the target value (insufficient boost pressure). amount) is larger than the judgment value, the injection timing of the low penetration injection is set to be advanced compared to when the amount of shortage of the boost pressure with respect to the target value (supercharging pressure shortage amount) is equal to or less than the judgment value, and supercharging is performed. When the pressure is low, the injection timing of the low penetration injection is advanced compared to when the pressure is high (when the supercharging pressure is high, the injection timing of the low penetration injection is retarded compared to when the pressure is low).

Therefore, when there is a large shortage of the boost pressure with respect to the target value (the boost pressure is low) and the ignitability is lowered and ignition delay tends to occur, the fuel-air mixing time for low penetration injection is lengthened. Since the mixing of these can be promoted, ignition delay can be prevented. Also, when the shortfall of the boost pressure to the target value is small (boost pressure is high) and ignitability is high, pre-ignition tends to occur, the fuel and air mixing time for low penetration injection can be shortened. Since it is possible to suppress the excessive promotion of mixing of these components, it is possible to prevent premature ignition.

Further, in the second embodiment, the fuel injection control unit 71 executes the low penetration injection at a timing later than the main injection in the fourth region mode in which the injection pressure is less than the fourth injection pressure FP4. Therefore, when the injection pressure is low and the particle size of the fuel spray is large, soot is likely to be generated, the generated soot can be effectively oxidized by the combustion energy of the fuel associated with the low-penetration injection. Moreover, at this time, when the boost pressure is low and the shortage of the boost pressure with respect to the target value (supercharging pressure shortage) is greater than the judgment value, the boost pressure is high and the boost pressure is high. The low-penetration injection is retarded more than when the shortage (supercharging pressure shortage) with respect to the target value is equal to or less than the judgment value. That is, when the injection pressure is less than the fourth injection pressure FP4, the injection timing of the low penetration injection is retarded when the supercharging pressure is low than when it is high. Therefore, in addition to the low injection pressure, the amount of boost pressure shortage is low (the boost pressure is low) and the amount of soot generated increases due to the low charging efficiency. can be oxidized.

Further, the fuel injection control unit 71 prohibits the low penetration injection when the spray penetration of the main injection P1 or the pilot injection P2 is larger than a predetermined set amount (steps S3 and S4 in FIG. 12, step S13 in FIG. 18). , S14). The spray penetration of the main injection P1 or the pilot injection P2 becomes larger than the predetermined set amount, for example, when the engine load is large and the fuel injection amount in these injections is relatively large. In such a case, no air remains in the radially central region of the combustion chamber 6 (the oxygen remaining possible region G2 does not occur). can be prevented.

Furthermore, the fuel injection control unit 71 prohibits the low penetration injection under the condition that the amount of oxygen in the radial central region of the combustion chamber 6 is equal to or less than a predetermined value (steps S5 and S4 in FIG. 12, step S15 in FIG. 18). , S14). Under conditions where the amount of oxygen in the radially central region of the combustion chamber 6 is lean, there is no need to perform low-penetration injection in the first place, even under conditions where the residual oxygen possible region G2 occurs. Since the fuel injection control unit 71 prohibits low penetration injection under such conditions, unnecessary fuel consumption can be prevented.

[Modification]
Although the embodiment of the present invention has been described above, the present invention is not limited to this, and for example, the following modified embodiments can be adopted.

(1) In the above-described embodiment, an example in which the main injection P1, the pilot injection P2, and the after-injection P3 are executed as the basic injection pattern was shown (FIGS. 10, 11, 14, and 16). The basic injection pattern should include at least the main injection P1 and the pilot injection P2, and the after injection P3 may be omitted. Further, in the above-described embodiment, an example was shown in which the pilot injection P2 is performed in two stages, the first pilot injection P21 and the second pilot injection P22. Alternatively, the pilot injection P2 may be a single injection or three or more injections. Furthermore, in the above-described embodiment, the main injection P1 has the maximum energy (injection amount). It is good also as an aspect. In this case, the injection range setting unit 72 is configured to set the outer edge H of the oxygen remaining possible region G2, that is, the target line H1, based on the injection amount, injection pressure, and injection timing of the pilot injection P2.

(2) In the above-described embodiment, regarding the injection timing of the low-penetration injection, the timing earlier than the pilot injection P2 (PILOT region) or the timing later than the main injection P1 (AFTER region) is selectively used depending on the operating state and environment. I gave an example. Alternatively, low-penetration injection may be executed in both the PILOT area and the AFTER area in consideration of the functions in each area. Alternatively, the low penetration injection may be performed only in one of the PILOT region and the AFTER region.

(3) In the above embodiment, when the low-penetration injection is performed by split injection, an example is shown in which the injection is split into two times, but split injection may be performed three times or more. Further, in the PILOT split-B control of 16(B) and the AFTER split-B control of FIG. 17(B), an example is shown in which the split injection interval is reduced or expanded compared to the injection control in the center region. Alternatively, control may be performed without changing the interval.

(4) In the above embodiment, the case where the injection timing of the low penetration injection is changed according to the magnitude of the shortage of the boost pressure with respect to the target value (supercharging pressure shortage) has been described. Alternatively, the absolute value of boost pressure may be used.

(5) In the second embodiment, the injection patterns shown in FIGS. 16A to 16D and 17A to 17C are set, and these injection An example of changing the injection timing of the low-penetration injection according to the amount of boost pressure shortage by switching the pattern has been shown. Alternatively, only the injection timing of the low penetration injection may be changed according to the boost pressure shortage (or boost pressure) without changing the injection pattern. Specifically, PILOT-splitting is performed in the first area mode, PILOT-single shot is performed in the second area mode, AFTER-splitting is performed in the third area mode, and AFTER-single shot is performed in the fourth area mode. Configure to enforce. Then, the injection timing of the low-penetration injection may be changed according to the amount of supercharging pressure shortage (or supercharging pressure) while executing the injection pattern in each operation mode.

1 engine body 2 cylinder 4 cylinder head 44 EGR device 5 piston 50 crown surface 5C cavity 51 first cavity portion 512 first bottom portion 52 second cavity portion 522 second bottom portion 53 connecting portion 6 combustion chamber 6U combustion chamber ceiling surface (cylinder head underside)
15 injector (fuel injection valve)
70 processor (fuel injection control device for diesel engine)
71 fuel injection control unit (first injection control unit, second injection control unit)
P1 Pilot injection P2 Main injection P4, P5 Low penetration injection

Claims (3)

a combustion chamber of the engine formed by the lower surface of the cylinder head, the crown surface of the cylinder and the piston;
a fuel injection valve that injects fuel into the combustion chamber;
a supercharger for supercharging intake air;
A fuel injection control device for a diesel engine comprising a fuel injection control unit that controls the operation of the fuel injection valve,
A cavity is provided in the crown surface of the piston, and the cavity is
a first cavity portion disposed in a radially central region of the crown surface and having a first bottom portion having a first depth in the axial direction of the cylinder;
a second cavity portion disposed on the crown surface on the outer peripheral side of the first cavity portion and having a second bottom portion having a depth shallower than the first depth in the cylinder axial direction;
a connecting portion that connects the first cavity portion and the second cavity portion;
The fuel injection valve injects fuel toward the cavity and is arranged at or near the radial center of the combustion chamber,
The fuel injection control unit is
A main injection for injecting fuel at a timing at least when the piston is positioned near compression top dead center, a pilot injection for injecting fuel at a timing earlier than the main injection, and a timing earlier than the pilot injection or the main injection. a low-penetration injection that causes the fuel injection to be performed at a timing later than the injection, and
a first injection control unit that executes at least one of the main injection and the pilot injection at a timing of injecting fuel directed toward the connecting portion;
a second injection control unit that executes the low-penetration injection so that fuel is injected only in a radially central region of the combustion chamber;
The second injection control unit is
when the injection pressure of the main injection is equal to or higher than a predetermined reference injection pressure, advancing the injection timing of the low penetration injection when the supercharging pressure of the supercharger is lower than when the supercharging pressure is high;
When the injection pressure of the main injection is less than the reference injection pressure, the low penetration injection is executed at a later timing than the main injection, and the low penetration injection is performed when the supercharging pressure is low than when the supercharging pressure is high. A fuel injection control device for a diesel engine, characterized by retarding the injection timing of injection. a combustion chamber of the engine formed by the lower surface of the cylinder head, the crown surface of the cylinder and the piston;
a fuel injection valve that injects fuel into the combustion chamber;
a supercharger for supercharging intake air;
A fuel injection control device for a diesel engine comprising a fuel injection control unit that controls the operation of the fuel injection valve,
A cavity is provided in the crown surface of the piston, and the cavity is
a first cavity portion disposed in a radially central region of the crown surface and having a first bottom portion having a first depth in the axial direction of the cylinder;
a second cavity portion disposed on the crown surface on the outer peripheral side of the first cavity portion and having a second bottom portion having a depth shallower than the first depth in the cylinder axial direction;
a connecting portion that connects the first cavity portion and the second cavity portion;
The fuel injection valve injects fuel toward the cavity and is arranged at or near the radial center of the combustion chamber,
The fuel injection control unit is
A main injection for injecting fuel at a timing at least when the piston is positioned near compression top dead center, a pilot injection for injecting fuel at a timing earlier than the main injection, and a timing earlier than the pilot injection or the main injection. a low-penetration injection that causes the fuel injection to be performed at a timing later than the injection, and
a first injection control unit that executes at least one of the main injection and the pilot injection at a timing of injecting fuel directed toward the connecting portion;
a second injection control unit that executes the low-penetration injection so that fuel is injected only in a radially central region of the combustion chamber;
The second injection control unit is
When the supercharging pressure of the supercharger is low, the injection timing of the low penetration injection is advanced more than when the supercharging pressure is high,
A fuel injection control device for a diesel engine, characterized in that the low-penetration injection is executed so that an outer edge of the radially central region of the combustion chamber becomes spray penetration. In the diesel engine fuel injection control device according to claim 1 or 2,
The second injection control unit adjusts the oxygen remaining possible region generated in the radial center region of the combustion chamber based on the injection pressure, injection amount and injection timing of the main injection or the pilot injection by the first injection control unit. A fuel injection control device for a diesel engine, characterized by estimating and executing the low-penetration injection so that the outer edge of the oxygen remaining-possible region becomes spray penetration.

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