JP2010138712A - Combustion control device for diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a combustion control device for a diesel engine inhibiting emission of smoke even in transient operation, reducing emission of NOx, and improving exhaust gas performances by executing appropriate combustion control corresponding to an operation state of an engine. <P>SOLUTION: A second premixed combustion mode adjusting fuel injection timing by feedback control based on a fuel mixing period is selected when the fuel mixing period is not less than a first threshold and is less than a second threshold. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a combustion control device for a diesel engine, and more particularly to a technique for controlling combustion based on a fuel mixing period.

Normally, in a diesel engine, spontaneous ignition (compression ignition) due to compression occurs during fuel injection, and so-called diffusion combustion occurs. Such combustion is generally called diesel combustion, and operation in the diesel combustion is called normal combustion mode.
In recent years, in diesel engines, a large amount of EGR gas is introduced for the purpose of simultaneously reducing smoke and NOx, and fuel is injected on a relatively advanced angle side, and fuel and air are mixed in advance, and then compression ignition is performed. There is a so-called low temperature premixed combustion fuel mode (hereinafter referred to as a premixed combustion mode) for burning.

The normal combustion mode and the premixed combustion mode are selectively used according to the operating state of the engine. Generally, the premixed combustion mode is used in the low load and low speed region, and the normal combustion mode is used in the high load and high speed region. Selected.
When the operating state fluctuates due to acceleration or deceleration, the two combustion modes are switched. For example, as a method for switching between the two combustion modes, the target value of the control parameter in each combustion mode (control mode) is set. There is a diesel engine control device that is individually set in advance and gradually changes a target value of one combustion mode to a target value of the other combustion mode when switching from one combustion mode to the other combustion mode (Patent Document) 1).
JP 2006-105046 A

However, since the in-cylinder intake state, the fuel state, and the like change according to the driving operation state of the driver and the environmental conditions in which the vehicle is traveling, one combustion is performed as in the technique disclosed in Patent Document 1 above. In the control for simply shifting from one mode to the other combustion mode, there is a region where it is not possible to cope with changes in the intake state and the fuel state, and combustion may become unstable.
For example, in the premixed combustion mode, there is a problem that a period for mixing air and fuel is insufficient, the fuel does not burn out well, and smoke is generated. In addition, the engine output may decrease due to unstable combustion in this manner.

  The present invention has been made to solve such problems, and the object of the present invention is to perform appropriate combustion control according to the operating state of the engine and realize stable combustion even during transient operation. Thus, an object of the present invention is to provide a diesel engine combustion control device that can suppress smoke emission, reduce NOx emission, and improve exhaust gas performance and engine output.

  In order to achieve the above-described object, the combustion control apparatus for a diesel engine according to claim 1 is a combustion control apparatus for a diesel engine that compresses and ignites the fuel supplied into the cylinder, from the fuel injection end timing to the ignition timing. And a predetermined combustion mode for adjusting the fuel injection timing based on the fuel mixing period detected by the fuel mixing period detecting means and causing combustion after the end of the fuel injection. And a combustion control means for selecting the predetermined combustion mode when the fuel mixing period detected by the fuel mixing period detecting means is within a predetermined range.

According to a second aspect of the present invention, there is provided the diesel engine combustion control apparatus according to the first aspect, wherein in the predetermined combustion mode, the fuel injection timing is adjusted so that the fuel mixing period is not less than a predetermined period.
According to a third aspect of the present invention, there is provided a combustion control system for a diesel engine according to the first or second aspect, wherein the combustion control means adjusts the fuel injection timing based on the in-cylinder combustion state or the intake state as the combustion mode, A first combustion mode in which the fuel injection timing is adjusted based on the in-cylinder combustion state or the intake state and combustion is caused after the fuel injection is completed, and the second combustion mode is the predetermined combustion mode. A premixed combustion mode is selected, and the normal combustion mode, the first premixed combustion mode, or the second premixed combustion mode is selected according to the fuel mixing period detected by the fuel mixing period detecting means. It is characterized by that.

  According to a fourth aspect of the present invention, there is provided a combustion control apparatus for a diesel engine according to the third aspect, wherein the combustion control means includes a first threshold that is an upper limit of a fuel mixing period in which the normal combustion mode is established, and a value greater than the first threshold. And a second threshold value set from the relationship of smoke generation, and when the fuel mixing period detected by the fuel mixing period detecting means is less than the first threshold value, the normal combustion mode is set. The second premixed combustion mode is selected when it is greater than or equal to the first threshold and less than the second threshold, and the first premixed combustion mode is selected when it is greater than or equal to the second threshold. It is characterized by doing.

  According to a fifth aspect of the present invention, there is provided the combustion control system for a diesel engine according to the third or fourth aspect, wherein the in-cylinder pressure detecting means for detecting the in-cylinder pressure of the diesel engine and the in-cylinder pressure detected by the in-cylinder pressure detecting means. Combustion ratio calculating means for calculating the combustion ratio, and in the normal combustion mode and the first premixed combustion mode, the combustion control means has a predetermined combustion ratio calculated by the combustion ratio calculating means as a predetermined value. The fuel injection timing is adjusted so that the crank angle is obtained.

According to the diesel engine combustion control apparatus of the first aspect of the present invention using the above means, in the diesel engine, the fuel injection timing is adjusted based on the fuel mixing period from the fuel injection end timing to the ignition timing, and the combustion is performed after the fuel injection ends. When the fuel mixing period is within a predetermined range, the predetermined combustion mode is selected.
In so-called premixed combustion in which combustion occurs after the end of fuel injection, if the fuel mixing period is short, the mixing period of air and fuel is insufficient, and the premixed gas is diluted and not uniformized, which may cause smoke. If the fuel mixing period has a predetermined combustion mode that adjusts the fuel injection timing based on the fuel mixing period, and the fuel mixing period is within a predetermined range that generates smoke, the predetermined combustion mode is used to reduce the smoke. It can control appropriately in the fuel mixing period which does not generate | occur | produce.

Therefore, for example, even during a transient operation in which the fuel mixing period changes, it is possible to shift to stable premixed combustion that does not generate smoke.
Thereby, NOx reduction by stable premixed combustion and the operation range which can suppress smoke can be expanded, and the exhaust gas performance and engine output of a diesel engine can be improved.

According to the combustion control apparatus for a diesel engine according to claim 2, in the predetermined combustion mode, the fuel injection timing is adjusted so that the fuel mixing period is equal to or longer than the predetermined period.
As described above, in the predetermined combustion mode in which the premixed combustion is performed, by adjusting the fuel injection timing so that the fuel mixing period is longer than the predetermined period in which the smoke is not generated, the generation of smoke in the premixed combustion is more reliably performed. Can be suppressed.

According to the combustion control apparatus for a diesel engine according to claim 3, in the diesel engine, the normal combustion mode and the first premixed combustion mode for controlling the fuel injection timing based on the in-cylinder combustion state or the intake state, and the fuel mixing There is a second premixed combustion mode that controls the fuel injection timing based on the period, and these combustion modes are switched according to the fuel mixing period.
In addition to the second premixed combustion mode (predetermined combustion mode) controlled based on the fuel mixing period in this way, the normal combustion mode and the first premixed combustion mode for controlling the fuel injection timing based on the combustion state or the intake state Is selected based on the fuel mixing period, so that appropriate combustion according to the operation state can be caused.

Thereby, stable operation of the engine can be realized while suppressing the generation of smoke.
According to the combustion control apparatus for a diesel engine according to claim 4, the first threshold which is the upper limit of the fuel mixing period in which the normal combustion mode is established and the relationship which is larger than the first threshold and causes smoke generation are set. A normal combustion mode when the fuel mixing period is less than the first threshold, and second when the fuel mixing period is greater than or equal to the first threshold and less than the second threshold. If the premixed combustion mode is equal to or greater than the second threshold value, the first premixed combustion mode is selected.

That is, when shifting from the normal combustion mode to the premixed combustion, the mode is switched to the first premixed combustion mode through the second premixed combustion mode, whereby the premixed combustion is suppressed while suppressing smoke. And can be migrated.
According to the combustion control apparatus for a diesel engine according to claim 5, in the normal combustion mode and the first premixed combustion mode, the fuel injection timing is adjusted so that the predetermined combustion ratio becomes the predetermined crank angle.

  In other words, in the normal combustion mode and the first premixed combustion mode, by adjusting the fuel injection timing based on the combustion ratio, it is possible to cause appropriate combustion in accordance with the in-cylinder combustion state. Performance can be realized.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic configuration diagram of a combustion control device for a diesel engine according to the present invention, which will be described below with reference to FIG.
An engine 1 shown in FIG. 1 is a four-cylinder common rail diesel engine that directly injects high-pressure fuel accumulated in a common rail (not shown) into each cylinder 2. FIG. 1 shows a cross section of one of the four cylinders.

The engine 1 is configured such that a cylinder head 6 is mounted on an upper portion of a cylinder block 4 in which a plurality of cylinders 2 are formed.
Each cylinder 2 is provided with a piston 8 that can slide up and down, and a combustion chamber 10 is formed surrounded by the top surface of the piston 8, the inner wall of the cylinder 2, and the lower surface of the cylinder head 6.
In the cylinder head 6, a fuel injection valve 12 that directly injects fuel into the combustion chamber 10, and an in-cylinder pressure sensor 14 (in-cylinder pressure detecting means) that detects the pressure in the combustion chamber 10, that is, the in-cylinder pressure, are burned. It is provided so as to face the room 10.

  The cylinder head 6 is formed with an intake port 16 that communicates with the combustion chamber 10 and extends on one side in the width direction of the engine 1 and an exhaust port 18 that communicates with the combustion chamber 10 and extends on the other side in the width direction of the engine 1. ing. Further, the cylinder head 6 is provided with an intake valve 20 and an exhaust valve 22 corresponding to the intake port 16 and the exhaust port 18, respectively, for communicating and blocking the ports 16 and 18 and the combustion chamber 10. Yes. Two intake ports 16 and two exhaust ports 18 are provided for each cylinder, and two intake valves 20 and two exhaust valves 22 are provided correspondingly.

An intake pipe 24 communicating with the intake port 16 is connected to one side in the width direction of the engine 1.
The intake pipe 24 is provided with an air cleaner (not shown) on the intake upstream side, and an air flow sensor 26 for detecting the intake air amount in the engine 1 is provided on the intake downstream side. The intake pipe 24 includes a compressor 28a of a turbocharger 28 that pressurizes the intake air, an intercooler 30 that cools the pressurized intake air, and a throttle valve 32 that adjusts the intake air amount, downstream of the air flow sensor 26. It is provided in order.

On the other hand, an exhaust pipe 34 communicating with the exhaust port 18 is connected to the other side in the width direction of the engine 1.
The exhaust pipe 34 is provided with a turbine 28b that is connected to the compressor 28a of the turbocharger 28 and a rotating shaft and rotates by an exhaust flow.
Further, the exhaust upstream side portion of the exhaust pipe 34 and the intake downstream side portion of the intake pipe 24 communicate with each other via an EGR passage 36 so that the exhaust gas can be recirculated to the intake system. The EGR passage 36 is provided with an EGR cooler 38 that cools the EGR gas and an EGR valve 40 that adjusts the amount of EGR gas returned to the intake system.

Further, a vehicle equipped with the engine 1 is provided with an ECU 42 (combustion control means) as a control device for performing comprehensive control including operation control of the engine 1 and the like. The ECU 42 is composed of a CPU, a memory, a timer counter, and the like, and calculates various control amounts and controls various devices based on the control amounts.
For example, on the input side of the ECU 42, the in-cylinder pressure sensor 14, the airflow sensor 26, the crank angle sensor 44 that detects the crank angle of the engine 1, and the accelerator that detects the accelerator opening according to the amount of depression of the accelerator pedal by the driver. Various sensors such as the opening sensor 46 are connected, and the load acting on the engine 1, the engine speed, the intake oxygen (O ₂ ) concentration, and the like can be calculated from the detected values. Various devices such as the fuel injection valve 12, the throttle valve 32, and the EGR valve 40 of each cylinder are connected to the output side of the ECU.

The ECU 42 performs combustion control in each cylinder of the engine 1 based on the information acquired from the various sensors.
Hereinafter, the configuration of the ECU 42 in the combustion control will be described in detail.
2 to 5, FIG. 2 is a control block diagram corresponding to the combustion control in the present embodiment, FIG. 3 is a diagram showing a fuel mixing period in the present embodiment, and FIG. 4 is a fuel in the present embodiment. FIG. 5 shows a combustion mode setting map at the time of steady operation, and a description will be given below based on these diagrams.

First, as shown in FIG. 2, the ECU 42 mainly includes a combustion ratio calculation unit 50 (combustion ratio calculation unit), a combustion history storage unit 52, a fuel mixture period calculation unit 54 (fuel mixture period detection unit), a fuel injection timing. A calculation unit 56, a threshold setting unit 58, an operation region calculation unit 60, and a combustion mode switching unit 62 are formed.
The combustion rate calculation unit 50 has a function of calculating the combustion rate in each cylinder from information detected by the crank angle sensor 44 and the in-cylinder pressure sensor 14.

The combustion rate (hereinafter also referred to as MFB: Mass Fraction of Burnt Fuel) is calculated by calculating the heat generation rate from the in-cylinder pressure information detected by the in-cylinder pressure sensor 14 and integrating the heat generation rate according to the crank angle. Calculated from the amount generated.
More specifically, in the combustion cycle of the engine 1, the product of the in-cylinder pressure P and the value obtained by raising the in-cylinder volume V to the power of the polytropic index n is constant from the polytropic equation shown in the following equation (1). Further, when the combustion cycle of the engine 1 is regarded as an adiabatic change, the polytropic index n is replaced with the specific heat ratio κ in the cylinder.

PV ⁿ = PV ^κ = constant (1)
The heat generation rate dQ / dθ, which is the heat generation amount per unit crank angle of the heat generation amount Q generated in the combustion chamber 10, is expressed by the in-cylinder pressure P, the in-cylinder volume V, It is calculated from the specific heat ratio κ.

That is, the amount of heat generation is calculated by integrating (integrating) the heat generation rate dQ / dθ.
Then, assuming that the heat generation amount at the end of combustion, that is, the maximum value of the heat generation amount is 100%, the ratio of the heat generation amount according to the crank angle is obtained as the combustion ratio.
The specific heat ratio κ used in the above formulas (1) and (2) varies depending on the change in gas accompanying combustion, but for the sake of simplification of calculations, etc. It will be handled as a constant value.

The combustion ratio calculation unit 50 outputs the combustion ratio calculated as described above to the combustion history storage unit 52.
The combustion history storage unit 52 has a function of storing information such as the combustion rate from the combustion rate calculation unit 50 as a combustion history.
As shown in FIG. 3, the fuel mixing period calculation unit 54 detects the ignition timing from the combustion history stored in the combustion history storage unit 52, and detects the fuel injection end timing from the drive signal to the fuel injection valve 12. Thus, it has a function of calculating a fuel mixing period that is a period from the fuel injection end timing to the ignition timing. It should be noted that the ignition timing is detected from the combustion ratio increase start timing, and the fuel injection end timing is detected from the drive signal end timing to the fuel injection valve 12.

The fuel injection timing calculation unit 56 has a function of calculating the fuel injection timing corresponding to each combustion mode.
Specifically, the fuel injection timing calculation unit 56 includes three combustion mode units, a normal combustion mode unit 56a, a first premixed combustion mode unit 56b, and a second premixed combustion mode unit 56c. The fuel injection timing corresponding to each combustion mode is calculated in the section.

In the normal combustion mode 56a, the fuel injection timing for performing operation by general diesel combustion in which diffusion combustion occurs during fuel injection after the premixing period is calculated.
The calculation of the fuel injection timing in the normal combustion mode unit 56a is performed by feedback control based on the combustion ratio stored in the combustion history storage unit 52. That is, a crank angle (hereinafter referred to as an actual MFB angle) of a predetermined combustion ratio (for example, MFB 50%) in the previous combustion is calculated from the combustion history stored in the combustion history storage unit 52, and the predetermined combustion ratio is determined in the next combustion. The fuel injection timing is advanced or retarded so that the combustion rate (for example, MFB 50%) becomes a target predetermined crank angle (for example, ATDC 10 °) (hereinafter referred to as a target MFB angle). Hereinafter, the feedback control of the fuel injection timing based on the combustion ratio is also referred to as MFB feedback control.

The first premixed combustion mode unit 56b is set so that the fuel injection timing on the relatively advanced angle side is calculated in order to perform an operation by premixed combustion that causes combustion by compression ignition after mixing air and fuel in advance. Has been.
In the first premixed combustion mode portion 56b, the fuel injection timing is adjusted by MFB feedback control, similarly to the normal combustion mode portion 56a.

  The second premixed combustion mode unit 56c is set so as to calculate a relatively advanced fuel injection timing in order to perform an operation by premixed combustion, and the calculation of the fuel injection timing is performed by calculating the fuel mixing period. This is performed by feedback control based on the fuel mixing period calculated in the unit 54. Hereinafter, the feedback control of the fuel injection timing based on the fuel mixing period is referred to as mixing period feedback control.

  In the mixing period feedback control, a fuel mixing period (hereinafter referred to as an actual fuel mixing period) calculated by the fuel mixing period calculation unit 54 is a target fuel mixing period (predetermined period) in which smoke does not occur according to the operating state of the engine 1. ) To advance or retard the fuel injection timing. For example, when premixed combustion is performed on the advance side with respect to the top dead center (TDC), if the actual fuel mixing period is shorter than the target fuel mixing period, the fuel injection timing is moved to the advanced side, and the actual fuel mixing is performed. When the period is longer than the target fuel mixing period, the fuel injection timing is moved to the retard side.

In the first premixed combustion mode and the second premixed combustion mode, the recirculation amount of the EGR gas is increased with respect to the premixed combustion that is at a high temperature, thereby lowering the temperature and suppressing the generation of NOx. .
The threshold value setting unit 58 is based on the engine speed calculated by the engine speed calculation unit 44a based on the engine load corresponding to the accelerator opening sensor 46 and information detected by the crank angle sensor 44, during transient operation of the engine 1. Has a function of calculating the threshold value of the fuel mixing period used for selecting the combustion mode.

Referring now to FIG. 4, the oxygen concentration and the amount of smoke generated according to the fuel mixing period are shown under the condition that the fuel injection amount, MFB angle, and rail pressure of the common rail are constant.
Then, as shown in FIG. 4, the threshold setting unit 58 sets the upper limit of the fuel mixing period in which the normal combustion mode is established, that is, a value near the fuel mixing period 0 in which diesel combustion is established as the first threshold.

Further, as shown in FIG. 4, the amount of smoke generated increases within a predetermined range in which the fuel mixing period is greater than the first threshold value, and the threshold setting unit 58 has a predetermined range in which the amount of smoke generated increases. The upper limit value is set as the second threshold value.
The generation of the smoke is understood to be because if the fuel mixing period is short in the premixed combustion, the mixing time of air and fuel is insufficient, and the premixed gas is not sufficiently diluted and uniformized. In the MFB feedback control, the fuel mixing period is not taken into consideration, and even if the target MFB angle is satisfied, the fuel injection period is extended due to a low rail pressure or an increased injection amount, and the fuel mixing period is shortened. If it is in the range from the first threshold to the second threshold, smoke may be generated.

The threshold setting unit 58 stores a map of the relationship between the fuel mixing period and smoke generation according to the engine load and the engine speed, and sets the first threshold and the second threshold based on the map. .
As shown in FIG. 5, the operation region calculation unit 60 stores a map that can select a combustion mode during steady operation from the engine load and the engine speed. As shown in FIG. 5, the map is set such that the low load low rotation speed region is a region for selecting the first premixed combustion mode, and the high load high rotation speed region is a region for selecting the normal combustion mode.

The combustion mode switching unit 62 uses the threshold value based on the map stored in the operation region calculation unit 60 and the map stored in the threshold value setting unit 58, so that the three combustion modes of the fuel injection timing calculation unit 56 are included. It has a function of switching the output from the mode and outputting the command injection timing to each fuel injection valve 12.
Specifically, according to the map stored in the operation region calculation unit 60, the combustion mode switching unit 62 determines that the first premixed combustion mode unit 56b and the high load / high rotation number are in the low load / low rotation speed region. In the case of the region, switching is performed so that the output from the normal combustion mode unit 56a is selected as the command injection timing.

Further, when the fuel mixing period is less than the first threshold set by the map of the threshold setting unit 58, the normal combustion mode unit 56a, and when the fuel mixing period is not less than the first threshold and less than the second threshold, the second premixed combustion. When the mode portion 56c is equal to or greater than the second threshold, switching is performed so that the output from the first premixed combustion mode portion 56b is selected as the command injection timing.
Next, the flow of combustion control by the combustion control apparatus for a diesel engine according to the present invention will be described.

FIG. 6 is a flowchart showing a combustion control routine by the combustion control apparatus for a diesel engine according to the present invention. The ECU 42 performs control according to the flowchart at a predetermined control cycle. Hereinafter, description will be made along the flowchart of FIG. 2 with reference to FIG.
First, the ECU 42 reads the operation region in the previous control cycle from the operation region calculation unit 60 as step S1 of the combustion control.

In step S <b> 2, the operation region calculation unit 60 calculates the current operation region from the load and rotation speed of the engine 1.
In step S3, it is determined whether or not the previous and current operation regions are both normal combustion mode regions. If the determination result is true (Yes), that is, if the steady operation is performed at a relatively high load and high speed, the process proceeds to step S9.

On the other hand, when the determination result of step S3 is false (No), that is, when the previous and current operation regions are both in the first premixed combustion mode region, or in the normal combustion mode region and the first premixed combustion mode region. If it is in a transient operation state that spans between, the process proceeds to step S4.
In step S <b> 4, the fuel mixing period calculation unit 54 calculates the fuel mixing period from the combustion history stored in the combustion history storage unit 52 and the previous drive signal to the fuel injection valve 14.

In subsequent step S5, the combustion mode switching unit 62 determines whether or not the fuel mixing period calculated in step S4 is equal to or greater than the second threshold set by the threshold setting unit 58.
If the determination result is true (Yes), the process proceeds to step S6.
In step S6, the combustion mode switching unit 62 selects the output from the first premixed combustion mode unit 56b as the command injection timing. That is, the fuel injection timing is adjusted by MFB feedback control to cause premixed combustion.

On the other hand, if the determination result in step S5 is false (No), that is, if the fuel mixing period is less than the second threshold value, the process proceeds to step S7.
In step S <b> 7, the combustion mode switching unit 62 determines whether or not the fuel mixing period calculated in step S <b> 4 is greater than or equal to the first threshold set by the threshold setting unit 58.
If the determination result is true (Yes), that is, if the fuel mixing period is greater than or equal to the first threshold and less than the second threshold, the process proceeds to step S8.

In step S8, the combustion mode switching unit 62 selects the output from the second premixed combustion mode unit 56c as the command injection timing. That is, the fuel injection timing is adjusted by feedback control based on the fuel mixing period to cause premixed combustion.
On the other hand, if the determination result in step S7 is false (No), that is, if the fuel mixing period is less than the first threshold value, the process proceeds to step S9.

In step S9, the combustion mode switching unit 62 selects the output from the normal combustion mode unit 56a as the command injection timing. That is, the fuel injection timing is adjusted by MFB feedback control to cause diesel combustion.
After going through any of these steps S6, S8, S9, the routine is returned.
As described above, the combustion control has the second premixed combustion mode in which the fuel injection timing is adjusted based on the fuel mixing period as the combustion mode, and the fuel mixing period is the first during the transient operation of the engine 1. The second premixed combustion mode is selected when the predetermined range is greater than or equal to the threshold and less than the second threshold.

Thereby, when shifting from the normal combustion to the premixed combustion, the second premixed combustion mode is switched to the first premixed combustion mode.
In the second premixed combustion mode, the fuel injection timing is adjusted so as to ensure a target fuel mixing period in which smoke does not occur, so that the generation of smoke in the premixed combustion is reliably suppressed.

Therefore, by shifting to the first premixed combustion mode via the second premixed combustion mode, it is possible to shift to stable premixed combustion while suppressing smoke.
Thereby, NOx reduction by stable premixed combustion and the operation range in which smoke can be suppressed can be expanded, and the exhaust gas performance of the engine 1 can be improved.
In addition to the second premixed combustion mode, there are a normal combustion mode and a first premixed combustion mode in which the fuel injection timing is adjusted by MFB feedback control, which may cause smoke during steady operation. By selecting the normal combustion mode and the first premixed combustion mode when there is no transient operation, it is possible to generate appropriate combustion according to the in-cylinder combustion state, realizing good exhaust gas performance and engine output can do.

From the above, the diesel engine combustion control apparatus according to the present invention performs appropriate combustion control in accordance with the operating state of the engine 1 and realizes stable combustion even during transient operation, thereby reducing smoke emission. It is possible to suppress, reduce NOx emission, and improve exhaust gas performance and engine output.
Although the description about the embodiment of the combustion control device of the diesel engine according to the present invention is finished above, the embodiment is not limited to the above embodiment.

For example, in the above embodiment, the engine 1 is a four-cylinder common rail type diesel engine, but is not limited to the engine having the configuration, and may be a diesel engine having another configuration.
In the above embodiment, in the normal combustion mode and the first premixed combustion mode, the fuel injection timing is adjusted by MFB feedback control. The adjustment of the fuel injection timing in these combustion modes is performed in such a combustion state. It is not restricted to the control based on. For example, an in-cylinder pressure sensor 14 that is expensive is not provided, but an intake state such as an oxygen concentration or an excess air ratio of the intake air sucked into the cylinder is detected, and the fuel injection timing is adjusted by feedback control based on the intake state. It doesn't matter.

  In the above embodiment, the fuel injection timing is adjusted by the mixing period feedback control in the second premixed combustion mode, but the adjustment of the fuel injection timing in the second premixed combustion mode is limited to this. Instead, for example, when switching to the second premixed combustion mode, the fuel injection timing may be controlled to be set to a predetermined fuel injection timing. By controlling in this way, the control can be simplified and the switching response to the second premixed combustion mode can be improved.

It is a schematic block diagram in one Embodiment of the combustion control apparatus of the diesel engine which concerns on this invention. It is a control block diagram in one Embodiment of the combustion control apparatus of the diesel engine which concerns on this invention. It is a figure which shows the fuel mixing period in one Embodiment of the combustion control apparatus of the diesel engine which concerns on this invention. It is a related figure of the fuel mixing period and smoke generation in one embodiment of the diesel engine combustion control device according to the present invention. It is a combustion mode setting map at the time of steady operation in one embodiment of a combustion control device of a diesel engine concerning the present invention. It is a flowchart which shows the combustion control routine in one Embodiment of the combustion control apparatus of the diesel engine which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 12 Fuel injection valve 14 Cylinder pressure sensor (cylinder pressure detection means)
42 ECU (combustion control means)
50 Combustion Ratio Calculation Unit 52 Combustion History Storage Unit 54 Fuel Mixing Period Calculation Unit (Fuel Mixing Period Detection Unit)
56 fuel injection timing calculation unit 56a normal combustion mode unit 56b first premixed combustion mode unit 56c second premixed combustion mode unit 58 threshold setting unit 60 operating region calculation unit 62 combustion mode switching unit

Claims (5)

A diesel engine combustion control device for compressing and igniting fuel supplied into a cylinder,
Fuel mixing period detection means for detecting a fuel mixing period from the fuel injection end timing to the ignition timing;
A fuel that has a predetermined combustion mode that adjusts the fuel injection timing based on the fuel mixing period detected by the fuel mixing period detecting means and causes combustion after the end of fuel injection, and is detected by the fuel mixing period detecting means Combustion control means for selecting the predetermined combustion mode when the mixing period is within a predetermined range;
A combustion control device for a diesel engine, comprising:   2. The diesel engine combustion control device according to claim 1, wherein in the predetermined combustion mode, fuel injection timing is adjusted such that the fuel mixing period is equal to or longer than a predetermined period. The combustion control means adjusts the fuel injection timing based on the in-cylinder combustion state or the intake state as a combustion mode, and causes the combustion to occur during fuel injection, or the fuel injection based on the in-cylinder combustion state or the intake state. A first premixed combustion mode that adjusts the timing and causes combustion after completion of fuel injection, and a second premixed combustion mode that is the predetermined combustion mode;
2. The normal combustion mode, the first premixed combustion mode, or the second premixed combustion mode is selected according to a fuel mixing period detected by the fuel mixing period detecting means. Or the combustion control apparatus of the diesel engine of 2. The combustion control means sets a first threshold value that is an upper limit of a fuel mixing period in which the normal combustion mode is established, and a second threshold value that is larger than the first threshold value and is set based on the relationship of smoke generation. And
When the fuel mixing period detected by the fuel mixing period detecting means is less than the first threshold, the normal combustion mode is set to be greater than or equal to the first threshold and less than the second threshold. 4. The diesel engine combustion control device according to claim 3, wherein the first premixed combustion mode is selected when the second premixed combustion mode is equal to or greater than the second threshold value. 5. In-cylinder pressure detecting means for detecting the in-cylinder pressure of the diesel engine,
Combustion rate calculation means for calculating a combustion rate based on the in-cylinder pressure detected by the in-cylinder pressure detection means,
In the normal combustion mode and the first premixed combustion mode, the combustion control means adjusts the fuel injection timing so that the predetermined combustion ratio calculated by the combustion ratio calculation means becomes a predetermined crank angle. The combustion control apparatus for a diesel engine according to claim 3 or 4,

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