JP2009185735A - Exhaust purification control device - Google Patents

Abstract

When performing fuel addition control for adding fuel to exhaust gas based on the state of an exhaust emission control device, even if the fuel has a high biofuel concentration, the generation of particulate matter and the exhaust fuel addition valve To provide an exhaust purification control device capable of suppressing nozzle hole clogging.
An exhaust gas purification device includes a fuel injection device that injects fuel into a cylinder of an internal combustion engine and an exhaust fuel addition valve that injects fuel upstream of an exhaust gas purification device in an exhaust passage. An exhaust purification control device for performing fuel addition control for adding fuel to exhaust gas based on the state of the above, a detection estimation means 128 for detecting or estimating the concentration of biofuel contained in the fuel, a fuel injection device, and And a control means 100 for controlling the exhaust fuel addition valve, and the control means performs fuel injection for fuel addition control when the biofuel concentration is equal to or higher than a predetermined concentration. This is divided into injection and fuel injection by the exhaust fuel addition valve.
[Selection] Figure 1

Description

  The present invention relates to an exhaust purification control device, and more particularly to an exhaust purification control device that executes fuel addition control for adding fuel to exhaust gas flowing toward the exhaust purification device based on the state of the exhaust purification device that purifies exhaust gas. About.

  2. Description of the Related Art A diesel internal combustion engine (hereinafter simply referred to as “diesel engine”) is generally provided with an exhaust purification catalyst that purifies harmful components in exhaust gas by catalytic reaction as an exhaust purification device. Examples of the exhaust purification catalyst include a NOx occlusion reduction type catalyst that stores nitrogen oxide (NOx) in exhaust gas and reduces it to nitrogen. By supplying hydrocarbon as a reducing agent to the NOx occlusion reduction catalyst, the occluded nitrogen oxide can be reacted with the hydrocarbon to be reduced to nitrogen.

  In this way, in a diesel engine equipped with an exhaust purification catalyst that requires supply of a reducing agent, in order to supply hydrocarbons as a reducing agent to the exhaust purification catalyst, fuel is contained in the exhaust gas flowing toward the exhaust purification catalyst. It is necessary to execute the fuel addition control to be added.

  In order to add fuel to the exhaust gas flowing to the exhaust purification catalyst, in a diesel engine, fuel is added upstream of the exhaust purification catalyst in the exhaust passage, separately from the fuel injection device that supplies fuel into the cylinder. A device provided with an “exhaust fuel addition valve” is known (for example, see Patent Document 1).

  In recent years, in diesel engines, bio-derived diesel fuel (hereinafter simply referred to as “biofuel”) synthesized from vegetable oils such as rapeseed oil, palm oil, and soybean oil may be used. Biofuels contain more high-boiling components than light oil, and have characteristics such as being hard to vaporize (low volatility).

  Such a biofuel may be mixed with light oil at a predetermined concentration and used in a diesel engine. For this reason, in the control technology of the diesel engine disclosed in Patent Document 1, the concentration of the biofuel contained in the mixed fuel is detected from the output of the air-fuel ratio sensor provided on the downstream side of the NOx storage reduction catalyst. As the concentration of biofuel increases, the amount of fuel added in the initial stage of fuel addition is increased and the amount of fuel added in the latter stage of fuel addition is decreased as compared with the case where a predetermined light oil (reference fuel) is used. Further, as the exhaust gas temperature becomes lower, control is performed so that the difference between the fuel addition amount at the initial stage of fuel addition and the fuel addition amount at the later stage of fuel addition becomes larger than when a predetermined light oil is used.

  As a result, even when a mixed fuel having a volatility (evaporation) different from that of the predetermined light oil (reference fuel) is used, the behavior (time variation) of the air-fuel ratio in the vicinity of the NOx storage reduction catalyst is determined. It is close to the behavior when no diesel oil is added.

JP 2006-177313 A

  However, in the control technique described in Patent Document 1, the amount of fuel added at the initial stage of fuel addition is increased as the concentration of biofuel (hereinafter referred to as biofuel concentration) increases. Is used, the atomization and vaporization of the fuel injected from the exhaust fuel addition valve deteriorates, making it difficult for the injected fuel to oxidize and increasing the amount of particulate matter such as soot. .

  The exhaust fuel addition valve is in contact with the hot exhaust gas. For this reason, depending on the mode of injection control of the exhaust fuel addition valve, the exhaust fuel addition valve becomes hot, the fuel remaining at the tip of the exhaust fuel addition valve becomes steamed, soot is generated, and the nozzle hole There is a possibility of clogging.

  The present invention has been made in view of the above, and when performing fuel addition control for adding fuel to the exhaust gas flowing toward the exhaust purification device based on the state of the exhaust purification device, the biofuel concentration The nozzle hole of the exhaust fuel addition valve that can suppress the generation of particulate matter such as soot and add fuel on the upstream side of the exhaust purification catalyst in the exhaust passage even when high fuel is used An exhaust purification control device capable of suppressing the occurrence of clogging is provided.

  An exhaust purification control apparatus according to the present invention includes a fuel injection device that injects fuel into a cylinder of an internal combustion engine, and an exhaust that injects the fuel upstream of an exhaust purification device that purifies exhaust gas in an exhaust passage of the internal combustion engine. An exhaust purification control device that performs fuel addition control for adding the fuel to the exhaust gas flowing toward the exhaust purification device based on a state of the exhaust purification device, the fuel purification control device comprising: Detection and estimation means for detecting or estimating the concentration of the biofuel contained in the fuel, and control means for controlling the fuel injection by the fuel injection device and the exhaust fuel addition valve, wherein the control means comprises the detection and estimation means When the concentration detected or estimated by the step is equal to or higher than a predetermined concentration, the fuel injection for the fuel addition control is performed by the fuel injection device. And performing divided into said fuel injection by injection and the exhaust fuel addition valve.

  In the exhaust purification control device of the present invention, the control means causes the fuel injection device to mainly inject the fuel for the fuel addition control when the concentration is equal to or higher than the predetermined concentration, and In the fuel addition control, when the state where the fuel injection by the exhaust fuel addition valve is stopped continues for a predetermined period, the fuel injection for the fuel addition control is performed on the exhaust fuel addition valve. It is characterized by making it.

  In the exhaust purification control apparatus of the present invention, the predetermined period is set shorter when the temperature of the exhaust gas is high than when the temperature of the exhaust gas is low.

  In the exhaust purification control apparatus of the present invention, the predetermined period is set longer when the concentration is high than when the concentration is low.

  In the exhaust purification control apparatus of the present invention, the exhaust purification apparatus is a NOx storage reduction catalyst that stores nitrogen oxides, and the fuel addition control is the storage of the nitrogen oxides of the NOx storage reduction catalyst. The control is characterized in that the fuel is added to the exhaust gas based on the state to form a reducing atmosphere in the NOx occlusion reduction type catalyst.

  According to the present invention, when fuel addition control for adding fuel to the exhaust gas flowing toward the exhaust purification device is executed based on the state of the exhaust purification device, a fuel with a high biofuel concentration is used. Even so, generation of particulate matter such as soot can be suppressed, and occurrence of clogging of the exhaust fuel addition valve that adds fuel on the upstream side of the exhaust purification catalyst in the exhaust passage can be suppressed. .

  Hereinafter, an embodiment of an exhaust purification control apparatus of the present invention will be described in detail with reference to the drawings.

(First embodiment)
The first embodiment will be described with reference to FIGS. 1 to 6. The present embodiment relates to an exhaust gas purification control device that executes fuel addition control for adding fuel to exhaust gas flowing toward the exhaust gas purification device based on the state of the exhaust gas purification device that purifies the exhaust gas.

  In this embodiment, based on the state of the exhaust purification catalyst (see reference numeral 55 in FIG. 1) that stores nitrogen oxides in exhaust gas discharged from the diesel engine (see reference numeral 10 in FIG. 1) and reduces it to nitrogen. Then, fuel addition control for adding fuel to the exhaust gas flowing toward the exhaust purification catalyst 55 is executed. When it is determined in the exhaust purification catalyst 55 that the stored nitrogen oxides need to be reduced, fuel addition control is executed in order to form a reducing atmosphere in the exhaust purification catalyst 55.

  As an apparatus for injecting fuel for fuel addition control, an exhaust fuel addition valve (in FIG. 5) that injects fuel upstream of the exhaust purification catalyst 55 in the exhaust passage 26 in the exhaust passage 26 of the diesel engine 10 of the present embodiment. 1 (see reference numeral 88). Here, when fuel addition control is executed by the exhaust fuel addition valve 88, there is a problem that the amount of soot generated in the exhaust gas increases if the concentration of biofuel in the fuel is high. This is presumably because biofuel contains more high-boiling components than light oil and is less likely to vaporize, and has a higher kinematic viscosity and less atomized than light oil.

  In the present embodiment, when the biofuel concentration is equal to or higher than a predetermined concentration, fuel injection by the exhaust fuel addition valve 88 is stopped, and fuel injection for fuel addition control is performed in the cylinder. This is performed by a fuel injection device (see reference numeral 80 in FIG. 1) for injecting fuel. Thereby, even when a fuel with a high biofuel concentration is used, the generation of particulate matter such as soot by fuel addition control can be suppressed.

  In addition, when the period during which fuel injection by the exhaust fuel addition valve 88 is stopped exceeds a predetermined period, fuel for fuel addition control is performed by the exhaust fuel addition valve 88 instead of the fuel injection device 80. Is injected. This is because if the period during which the fuel injection by the exhaust fuel addition valve 88 is stopped becomes long, the exhaust fuel addition valve 88 becomes hot, and there is a possibility that the injection hole is clogged. Every time the predetermined period elapses, the exhaust fuel addition valve 88 injects fuel, and the exhaust fuel addition valve 88 is cooled by the heat of vaporization of the injected fuel. Thereby, the occurrence of nozzle hole clogging due to the temperature rise of the exhaust fuel addition valve 88 can be suppressed. Therefore, according to the present embodiment, when fuel addition control is executed, the generation of particulate matter such as soot can be suppressed even when a fuel with a high biofuel concentration is used, and the exhaust gas is controlled. Occurrence of the injection hole clogging of the fuel addition valve 88 can be suppressed.

  First, schematic configurations of the diesel engine and the vehicle system according to the present embodiment will be described with reference to FIG. FIG. 1 is a schematic diagram showing a schematic configuration of a vehicle system including a diesel engine. In FIG. 1, only the main parts related to the present invention are schematically shown for the diesel engine and the vehicle system.

  The diesel engine according to the present embodiment is a compression self-ignition internal combustion engine that spontaneously ignites the fuel by supplying the fuel to the atmosphere in the combustion chamber that has been compressed to a high temperature. A diesel engine is mounted on a vehicle as a prime mover, and the vehicle is provided with an electronic control unit (hereinafter referred to as ECU) as a control means for controlling a vehicle system including the diesel engine.

  As shown in FIG. 1, the diesel engine 10 is a so-called direct injection type diesel engine 10 in which a fuel injection device 80 provided for each cylinder directly injects fuel into the cylinder. The diesel engine 10 includes a turbocharger 60 that compresses intake air by the kinetic energy of exhaust gas discharged from the cylinder, and a part of the exhaust gas discharged from the cylinder is taken from the exhaust passage and flows into the intake passage. A so-called exhaust gas recirculation device 70 (hereinafter referred to as an EGR device) is provided. In order to control the diesel engine 10 configured as described above, the vehicle system 1 is provided with an ECU 100 for the diesel engine 10.

  The diesel engine 10 is provided with a cylinder block, a piston, a connecting rod, a crankshaft, and a cylinder head 20 (not shown) as parts of an engine body system in which a cylinder is formed. A cylinder bore is formed in the cylinder block, and a piston has a piston ring (not shown) in sliding contact with an inner wall surface (hereinafter referred to as a cylinder wall) of the cylinder bore, and reciprocates in the cylinder bore.

  A cylinder head 20 is coupled to the cylinder block so as to face the top surface of the piston and close the cylinder bore. A space surrounded by the cylinder bore, the piston, and the cylinder head 20 is a “cylinder”. Note that the cylinder arrangement of the diesel engine 10 according to the present embodiment is an in-line four cylinder.

  When the crankshaft rotates, the piston reciprocates and air is sucked into the cylinder. Further, fuel is supplied to the cylinder by a fuel injection device 80. The supplied fuel is exposed to a high temperature atmosphere in the cylinder and ignites. The reciprocating motion of the piston caused by fuel ignition / combustion is converted into rotational motion via the connecting rod and output from the crankshaft. A crank angle sensor that detects a rotation angle position of the crankshaft (hereinafter referred to as a crank angle) is provided in the vicinity of the crankshaft, and a signal related to the detected crank angle is sent to the ECU 100.

  The cylinder head 20 is formed with an intake port 24 that guides intake air from an intake passage, which will be described later, to the cylinder on one side of the cylinder bore 20 with the axis of the cylinder bore interposed therebetween. An exhaust port 26 for discharging the exhaust gas to an exhaust passage described later is formed.

  The cylinder head 20 is provided with intake and exhaust valves (not shown) corresponding to the cylinder side openings of the intake port 24 and the exhaust port 26. These intake valve and exhaust valve are driven by receiving mechanical power from a camshaft (not shown). The intake valve and the exhaust valve are configured to be openable and closable at a predetermined timing according to the crank angle.

  When the intake valve is opened, the intake port 24 communicates with the inside of the cylinder, and the diesel engine 10 can intake air in an intake passage, which will be described later, from the intake port 24 into the cylinder. When the exhaust valve is opened, the exhaust port 26 communicates with the inside of the cylinder, and the diesel engine 10 can exhaust the exhaust gas in the cylinder from the exhaust port 26 to an exhaust passage described later. .

  Further, the diesel engine 10 includes an external air duct 41 that introduces air from outside air as an intake system component that guides air from outside air to the cylinder, and an air cleaner 42 that removes dust from the intake air (hereinafter referred to as intake air). An air flow meter (not shown) for measuring the flow rate of the intake air, an intercooler 45 for cooling the air compressed by the turbocharger 60, a throttle valve 46 for adjusting the flow rate of the intake air, and the intake air An intake manifold 48, which is a distribution pipe that distributes the gas to each cylinder, is provided. In the following description, the upstream side in the flow direction of intake air is simply referred to as “upstream side”, and the downstream side in the flow direction is simply referred to as “downstream side”.

  The downstream side of the intake manifold 48 is connected to the cylinder head 20, and the branch passage 49 communicates with the intake port 24. A surge chamber 40 a communicating with the branch passage 49 is formed on the upstream side of the branch passage 49.

  On the other hand, a throttle valve 46 is provided on the upstream side of the surge chamber 40 a in the intake manifold 48. The throttle valve 46 adjusts the flow rate of intake air taken into the cylinder (hereinafter referred to as intake air amount). The opening degree of the throttle valve 46 is controlled by the ECU 100.

  An intake pipe 47 is connected to the upstream side of the throttle valve 46. A passage 40 c formed in the intake pipe 47 communicates with the surge chamber 40 a in the intake manifold 48. An intercooler 45 is connected to the upstream side of the intake pipe 47. The intercooler 45 is configured as a heat exchanger, and cools the intake air that has been compressed by a compressor 62 of the turbocharger 60 described later and has reached a high temperature.

  An intake pipe 44 is connected to the upstream side of the intercooler 45. The passage 40e formed in the intake pipe 44 communicates with the passage 40c in the intake pipe 47 via a passage (not shown) in the intercooler 45. A compressor 62 of the turbocharger 60 is connected to the upstream side of the intake pipe 44. The passage 40 e in the intake pipe 44 communicates with the compressor 62 of the turbocharger 60.

  An intake pipe 43 is connected to the upstream side of the compressor 62 of the turbocharger 60. A passage 40 g formed in the intake pipe 43 communicates with the compressor 62 of the turbocharger 60. An air cleaner 42 is connected to the upstream side of the intake pipe 43, and an outside air duct 41 is provided on the upstream side of the air cleaner 42. The passage 40 g in the intake pipe 43 communicates with the outside air duct 41 through the air cleaner 42.

  An air flow meter (not shown) is provided on the downstream side of the element of the air cleaner 42. The air flow meter detects the amount of intake air introduced from the outside air duct 41. The air flow meter sends a signal related to the detected intake air amount to the ECU 100.

  The fresh air introduced from the outside air duct 41 passes through the air cleaner 42, the flow rate is detected by the air flow meter, and is compressed by the compressor 62 of the turbocharger 60. The compressed intake air (fresh air) that has become hot is cooled by the intercooler 45 and flows to the throttle valve 46. The intake air whose flow rate is adjusted by the throttle valve 46 flows into the surge chamber 40a of the intake manifold 48, is distributed to each cylinder from the branch passage 49, and flows into the cylinder through the intake port 24.

  The “intake passage” means a passage formed by the above-described intake system components and the intake pipe and through which the intake air introduced from the outside air duct 41 flows into the cylinder. In the present embodiment, the intake passage includes not only the surge chamber 40 a in the intake manifold 48 but also the intake port 24 of the cylinder head 20.

  Further, the diesel engine 10 includes exhaust manifolds 52 that join exhaust gases from the cylinders and lead them to the turbocharger 60 as exhaust system parts that exhaust exhaust gases from the cylinders to the outside air. An exhaust purification catalyst (exhaust purification device) 55 for treating nitrogen oxides and particulate matter (hereinafter simply referred to as “PM”), and an oxidation catalyst 58 for purifying exhaust gas from the exhaust purification catalyst 55 by an oxidation reaction; An A / F sensor 98 that detects the oxygen concentration of the exhaust gas in the passage 50g between the oxidation catalyst 58 and the exhaust purification catalyst 55 is provided. In the following description, the upstream side in the flow direction of the exhaust gas is simply referred to as “upstream side”, and the downstream side in the flow direction is simply referred to as “downstream side”.

  A manifold passage 50a is formed in the exhaust manifold 52, and branch portions 51 are provided on the upstream side of the manifold passage 50a corresponding to the respective cylinders. A branch portion 51 formed in the exhaust manifold 52 communicates with the exhaust port 26 of each cylinder. Further, a merging portion 50c where exhaust gases from the cylinders merge is provided on the downstream side of the manifold passage 50a. A manifold passage 50a formed in the exhaust manifold 52 joins exhaust gas discharged from a plurality of cylinders of the diesel engine 10 through the intake port 26 at a joining portion 50c, and a turbine 64 of a turbocharger 60 described later. Lead to.

  The turbocharger 60 includes a compressor 62 provided between the intake pipe 43 and the intake pipe 44, and a turbine 64 provided between the exhaust manifold 52 and the exhaust pipe 54. is doing. A compressor wheel (not shown) that compresses air by rotating is accommodated in the housing of the compressor 62, and a turbine wheel that is driven to rotate by the flow of exhaust gas (shown in the figure). (Not shown) is housed. The compressor wheel and the turbine wheel are joined together.

  In the turbocharger 60, the turbine wheel and the compressor wheel are rotationally driven by the kinetic energy of the exhaust gas flow flowing into the turbine 64 from the merging portion 50c of the manifold passage 50a, and the intercooler is compressed by compressing the air in the compressor 62. 45. The exhaust gas in the turbine 64 flows downstream through the passage 50 e in the exhaust pipe 54 and flows into the exhaust purification catalyst 55.

  A front stage (upstream side) of the exhaust purification catalyst 55 is provided with a NOx occlusion reduction type catalyst 55a that is an exhaust purification catalyst that stores nitrogen oxide in exhaust gas and reduces it to nitrogen. On the other hand, a downstream side (downstream side) is provided with a DPNR catalyst system 55c that is an exhaust purification catalyst with a filter mechanism and simultaneously purifies PM and nitrogen oxides. The NOx storage reduction catalyst 55a and the DPNR catalyst system 55c are exhaust purification catalysts that require the supply of a reducing agent, and will be described in detail below.

  The NOx occlusion reduction type catalyst 55a occludes nitrogen oxides in the exhaust gas in the form of nitrate when the exhaust gas flowing through the NOx storage reduction catalyst 55a is in an oxygen-excess atmosphere (lean atmosphere) containing a large amount of oxygen. On the other hand, when the exhaust gas flowing through the NOx storage reduction catalyst 55a has a reducing atmosphere (rich atmosphere) containing a large amount of unburned hydrocarbons (hereinafter simply referred to as “HC”), The stored nitrogen oxides are reduced to nitrogen by HC as a reducing agent contained. In this way, the NOx storage reduction catalyst 55a can purify nitrogen oxides in the exhaust gas.

  On the other hand, the DPNR catalyst system 55c has a function of a diesel particulate filter (hereinafter referred to as DPF) that collects PM, burns the collected PM, and regenerates the filter by releasing it as carbon dioxide. This is a combination of the functions of the NOx storage reduction catalyst described above, and it is possible to simultaneously purify PM and nitrogen oxides.

  Specifically, the DPNR catalyst system 55c collects PM in the exhaust gas flowing through the filter in a filter, and when the exhaust gas is in an oxygen-excess atmosphere, the nitrogen oxide is changed to nitrate and stored. The collected PM is oxidized by the active oxygen generated at this time and oxygen in the exhaust gas. On the other hand, when the exhaust gas flowing through the DPNR catalyst system 55c is in a reducing atmosphere (rich atmosphere), the stored nitrogen oxides are reduced to nitrogen by HC as a reducing agent contained in the exhaust gas. In both cases, PM is oxidized by the active oxygen generated at this time. In this way, the DPNR catalyst system 55c can oxidize and burn PM continuously to regenerate the filter in which PM is collected.

  Thus, the exhaust purification catalyst 55, such as the NOx storage reduction catalyst 55a and the DPNR catalyst system 55c, requires supply of a reducing agent to purify harmful components in the exhaust gas, and is sufficient as a reducing agent. It is necessary to form a reducing atmosphere containing unburned hydrocarbons (HC) vaporized.

  An oxidation catalyst 58 is provided on the downstream side of the exhaust purification catalyst 55 described above via an exhaust pipe 56. The oxidation catalyst 58 oxidizes and purifies hydrocarbons and carbon monoxide contained in the exhaust gas that has passed through the exhaust purification catalyst 55. The exhaust gas purified by the oxidation catalyst is released to the outside air.

  The “exhaust passage” means a passage through which exhaust gas discharged from the cylinder passes before flowing into the exhaust purification catalyst 55. In the present embodiment, the exhaust passage includes, in addition to the manifold passage 50a (branch portion 51, merging portion 50c) formed in the exhaust manifold 52, the exhaust port 26 of the cylinder head 20, the flow passage in the turbine 64, and the exhaust. A passage 50e formed in the pipe 54 and a passage in the exhaust purification catalyst 55 are included.

  Further, the diesel engine 10 is provided with a so-called exhaust gas recirculation device 70 (hereinafter referred to as an EGR device) that takes a part of the exhaust gas discharged from the cylinder from the exhaust passage and flows it into the intake passage. . The EGR device 70 includes an EGR passage that connects the exhaust passage and the intake passage, an EGR valve 77 that adjusts the flow rate of exhaust gas that flows through the EGR passage (hereinafter referred to as EGR gas), an EGR cooler 74 that cools the EGR gas, The details will be described below.

  The exhaust manifold 52 described above is provided with an EGR gas intake 71, and an EGR pipe 72 is connected to the intake 71. An EGR cooler 74 is connected to the EGR pipe 72 on the downstream side in the flow direction of the EGR gas (hereinafter simply referred to as “downstream side”). The EGR cooler 74 is constituted by a heat exchanger, and can cool the inflow EGR gas. An EGR pipe 76 is connected to the downstream side of the EGR cooler 74.

  An EGR valve 77 is disposed at the downstream end of the EGR pipe 76. The EGR valve 77 is an electromagnetic valve. An EGR pipe 78 is connected to the downstream side of the EGR valve 77. The EGR pipe 78 connects an EGR gas outlet 79 provided in the intake manifold 48 and an EGR valve 77. The opening degree of the EGR valve 77, that is, the flow rate of the EGR gas flowing through the EGR passage is controlled by the ECU 100.

  The “EGR passage” is formed by the EGR pipes 72, 76, 78, the EGR cooler 74, and the EGR valve 77 until the exhaust gas introduced from the intake port 71, that is, the inert gas, reaches the outlet 79. It means the flow path that passes through. In the present embodiment, the EGR passage includes not only the passage in the EGR pipes 72, 76, and 78 but also the passage formed in the EGR cooler 74 and the EGR valve 77.

  Further, the diesel engine 10 is provided for each cylinder as a part of a fuel supply system that supplies fuel to the cylinder, and a fuel injection device 80 that directly injects fuel into the cylinder, and the fuel is distributed to each fuel injection device 80. And a high-pressure fuel pump 84 that pumps fuel to the fuel rail 82. The fuel pressure-fed from the high-pressure fuel pump 84 to the fuel rail 82 is distributed by the fuel rail 82 and supplied to each fuel injection device 80.

  The high-pressure fuel pump 84 operates by receiving mechanical power from a camshaft (not shown) of the diesel engine 10 and sucks fuel from the fuel tank 120 to increase the pressure. The high-pressure fuel pump 84 supplies the fuel that has been pressurized to a high pressure from the fuel pipe 83 to the fuel rail 82. The operation of the high pressure fuel pump 84 is controlled by the ECU 100.

  The fuel rail 82 is configured to be capable of accumulating fuel at a predetermined fuel pressure. The fuel rail 82 distributes and supplies fuel to each fuel injector 80. High pressure (for example, 180 MPa) fuel is supplied to the fuel rail 82 from the high pressure fuel pump 84.

  Each fuel injection device 80 is supplied with fuel at a predetermined fuel pressure from a common fuel rail 82. The fuel injection device 80 is constituted by a piezo drive type fuel injection valve, and can perform so-called multistage injection, in which fuel is injected a plurality of times in one cycle. The injection period of the fuel injection device 80 in each cycle, that is, the injection timing and the injection time length (valve opening time) are controlled by the ECU 100 via a driver unit (not shown).

  The fuel injected from the fuel injection device 80 is injected at a fuel pressure higher than that of an exhaust fuel addition valve 88, which will be described later, and is atomized compared to the fuel injected (added) from the exhaust fuel addition valve 88. In addition, most of the injected fuel from the fuel injection device 80 is injected into a high-temperature atmosphere formed in the cylinder and burns. Therefore, the HC contained in the exhaust gas discharged from the cylinder is sufficiently high. It is evaporating. That is, the fuel from the fuel injection device 80 can flow into the exhaust purification catalyst 55 in a sufficiently vaporized state.

  The diesel engine 10 is provided with an exhaust fuel addition valve 88 that adds fuel to the exhaust passage, in addition to the fuel injection device 80 that supplies fuel into the cylinder. The exhaust fuel addition valve 88 is constituted by an electromagnetically driven fuel injection valve, and is supplied with fuel at a predetermined fuel pressure (for example, 1 MPa) from a high-pressure fuel pump 84 through a fuel pipe 86.

  The exhaust fuel addition valve 88 is provided in the vicinity of the exhaust port 26 of the cylinder having the shortest exhaust path from the exhaust port 26 to the turbine 64 among a plurality of cylinders in the diesel engine 10. The exhaust fuel addition valve 88 can add fuel to the exhaust gas from the cylinder flowing through the exhaust passage by injecting fuel from the nozzle hole exposed in the exhaust port 26 toward the junction 50c. It has become.

  Thus, the exhaust fuel addition valve 88 that injects fuel into the exhaust passage injects fuel at a lower fuel pressure than the fuel injection device 80 that injects fuel into the cylinder. That is, the fuel injected (added) from the exhaust fuel addition valve 88 into the exhaust passage is injected at a fuel pressure lower than that of the fuel injection device 80, so that it is much finer than the fuel injected from the fuel injection device 80. It has not been converted. In addition, since the fuel from the exhaust fuel addition valve 88 is added to the exhaust passage having a temperature lower than that in the cylinder, it is difficult to sufficiently vaporize the fuel from the fuel injection device 80. That is, depending on the temperature of the exhaust gas, the fuel from the exhaust fuel addition valve 88 may flow into the exhaust purification catalyst 55 without being sufficiently vaporized.

  In the vehicle system 1 including the diesel engine 10 described above, the low-pressure fuel pump 122 is provided in the fuel tank 120 for storing the refueled fuel, and the fuel is pumped toward the high-pressure fuel pump 84 described above. is doing. The fuel from the low pressure fuel pump 122 is filtered for impurities by the fuel filter 124 and supplied to the high pressure fuel pump 84.

  The vehicle system 1 is also provided with an accelerator pedal position sensor 102 that detects the amount of operation of the accelerator pedal by the driver. The accelerator pedal position sensor 102 sends a signal related to the detected accelerator pedal operation amount (hereinafter referred to as accelerator operation amount) to the ECU 100.

  In the vehicle system 1 configured as described above, the ECU 100 receives a signal related to the crank angle from the crank angle sensor, a signal related to the intake air amount (fresh air amount) from the air flow meter, and the accelerator pedal position sensor 102. A signal related to the accelerator operation amount and a signal related to the oxygen concentration in the exhaust gas after passing through the exhaust purification catalyst 55 (before inflow of the oxidation catalyst 58) are detected from the A / F sensor 98.

  Based on these signals, the ECU 100 calculates various control variables. The control variables include the rotational angle position of the crankshaft (hereinafter referred to as the crank angle), the rotational speed of the crankshaft (hereinafter referred to as the engine rotational speed), and the mechanical power output from the crankshaft by the diesel engine 10 ( (Hereinafter referred to as engine load), accelerator operation amount, intake air amount, and oxygen concentration contained in exhaust gas after passing through the exhaust purification catalyst 55 and before flowing into the oxidation catalyst 58.

  The ECU 100 determines and controls the fuel injection amount of the fuel injection device 80, the opening degree of the throttle valve 46, and the opening degree of the EGR valve 77 based on the operating state of the diesel engine 10 ascertained from these control variables. It is possible.

  In the diesel engine 10, the ECU 100 causes the fuel injection device 80 to perform fuel injection (hereinafter referred to as “main injection”) that is performed near the compression top dead center for the purpose of generating output and diffuses and burns fuel in the cylinder. It is possible.

  In addition, the ECU 100 is performed at a time (for example, 70 ° CA before compression top dead center) at which the lead angle is advanced with respect to the main injection mainly for the purpose of reducing PM such as smoke and soot and combustion noise. It is possible to cause the fuel injection device 80 to perform fuel injection (hereinafter referred to as pilot injection) for premixed combustion of the fuel.

  Further, the ECU 100 mainly aims at reducing the PM generated by the main injection, the timing retarded with respect to the main injection, specifically, the close timing after the main injection (for example, 0 after the main injection ends). The fuel injection device 80 can perform fuel injection (hereinafter referred to as after-injection) that activates diffusion combustion (later stage) generated by the main injection.

  In addition, the ECU 100 performs a major delay with respect to the main injection (for example, 40 ° CA after compression top dead center) mainly for the purpose of raising exhaust gas temperature and supplying a reducing atmosphere to the exhaust purification catalyst. In other words, it is possible to cause the fuel injection device 80 to perform fuel injection (hereinafter referred to as post-injection) that increases HC contained in the exhaust gas from the cylinder.

  Further, the ECU 100 controls the fuel injection device 80 to perform pilot injection and main injection, thereby supplying the fuel amount corresponding to the theoretical air-fuel ratio to the intake air amount into the cylinder for combustion. it can. Hereinafter, the combustion at the stoichiometric air-fuel ratio in the cylinder is referred to as “stoichiometric combustion”, and the control of the fuel injection device 80 executed by the ECU 100 to perform the stoichiometric combustion in the cylinder is referred to as “stoichiometric combustion control”. By performing stoichiometric combustion, almost all the oxygen in the air that flows into the cylinder is used for the oxidation reaction with the fuel, and it is possible to create a state in which almost no oxygen is contained in the burned gas in the cylinder It has become.

  Further, the ECU 100 causes the fuel injection device 80 to perform post-injection at a time (crank angle) delayed from the main injection after performing the stoichiometric combustion described above, and burned gas containing almost no oxygen. By supplying fuel to the exhaust gas, it is possible to supply unburned hydrocarbon (HC) as a reducing agent in the exhaust gas from the cylinder and supply it to the exhaust purification catalyst in a sufficiently vaporized state. It has become.

  In this way, the ECU 100 causes the fuel injection device 80 to perform main injection and fuel injection performed at a timing advanced with respect to the main injection, for example, pilot injection. To cause the diesel engine 10 to perform stoichiometric combustion to create a state in which almost no oxygen is contained in the cylinder.

  Further, the ECU 100 causes the fuel injection device 80 to perform fuel injection performed at a time retarded with respect to the main injection, for example, post injection, thereby supplying fuel to the combustion gas containing almost no oxygen in the cylinder. HC as a reducing agent can be supplied to the exhaust purification catalyst in a sufficiently vaporized state. In this way, in the diesel engine 10, the ECU 100 controls the fuel injection device 80, so that the exhaust purification catalyst 55 instantaneously creates a reducing atmosphere for a very short time (for example, a time length of about 200 msec). It is possible to form.

  Further, the ECU 100 controls the exhaust fuel addition valve 88 to add (inject) fuel to the exhaust passage, thereby supplying fuel into the exhaust gas from the cylinder and vaporizing HC as a reducing agent. In this state, it can be supplied to the exhaust purification catalyst. Thus, in the diesel engine 10, the ECU 100 controls the exhaust fuel addition valve 88, so that a reducing atmosphere can be instantaneously formed in the exhaust purification catalyst as in the fuel injection device 80. Yes.

  As described above, the ECU 100 controls the fuel injection device 80 and the exhaust fuel addition valve 88 so that the reducing agent needs to be supplied by the fuel from the fuel injection device 80 or the fuel from the exhaust fuel addition valve 88. In the exhaust purification catalyst 55 (NOx occlusion reduction catalyst 55a and DPNR catalyst system 55c), it is possible to instantaneously form a reducing atmosphere. By providing such a reducing atmosphere, the nitrogen oxides stored in the exhaust purification catalyst 55 can be reduced to nitrogen. In this way, the control of the fuel injection device 80 and the exhaust fuel addition valve 88 executed by the ECU 100 to form a reducing atmosphere in the exhaust purification catalyst 55 will be referred to as “rich spike control” in the following description.

  By the way, the fuel tank 120 is made using not only diesel fuel (hereinafter referred to as light oil) produced by fractionating crude oil, which is a mineral resource, but also biological organic resources (for example, vegetable oil). Diesel fuel (hereinafter referred to as biofuel) may be mixed and supplied at a predetermined concentration. The “biofuel” is composed of fatty acid methyl ester (FAME) or the like obtained by esterifying vegetable oil such as rapeseed oil or palm oil with methanol or the like.

  Biofuel has a feature that it contains more high-boiling components than light oil and is difficult to vaporize. In addition, since biofuel has a higher kinematic viscosity than light oil, the fuel injected from the exhaust fuel addition valve 88 is difficult to atomize. In addition, unlike light oil, biofuel contains oxygen (oxygen-containing compounds) in the molecules that make up the fuel. This oxygen promotes the combustion of fuel, and soot and other particulate matter (PM) It is characterized by a reduction in emissions.

  For this reason, in the diesel engine 10 provided with the exhaust fuel addition valve 88 capable of adding fuel from the upstream side of the exhaust purification catalyst 55 in the exhaust passage in addition to the fuel injection device 80 that can inject fuel directly into the cylinder. When fuel mixed with light oil and biofuel (mixed fuel) is used, the amount of “soot” contained in the exhaust gas discharged from the cylinder, or when fuel is added by the exhaust fuel addition valve 88 The amount of “soot” contained in the exhaust gas after passing through the exhaust purification catalyst 55 varies depending on the biofuel concentration (hereinafter referred to as biofuel concentration Cbio). This will be described below with reference to FIG.

  FIG. 2 is a graph showing the increase / decrease rate of “soot” due to a change in the biofuel concentration Cbio based on the case where only light oil is used as the fuel (0%). In FIG. 2, “●” indicates the increase / decrease rate of “soot” contained in the exhaust gas discharged from the cylinder, that is, the exhaust gas before flowing into the exhaust purification catalyst, and “◇” indicates the exhaust fuel The increase / decrease rate of the soot contained in the exhaust gas after passing through the exhaust purification catalyst 55 when fuel is added by the addition valve 88 is shown. In FIG. 2, the biofuel is a mixed fuel of rapeseed oil methyl ester obtained by reacting rapeseed oil with methanol and light oil having a predetermined property, and the concentration of rapeseed oil methyl ester in the mixed fuel is determined. The figure indicates the biofuel concentration Cbio.

  In FIG. 2, the amount of soot in the case where the biofuel concentration Cbio is zero, that is, when only a predetermined light oil is used as the fuel, is shown as 0%. When the biofuel concentration Cbio increases from zero to 30%, the amount of soot in the exhaust gas both before flowing into the exhaust purification catalyst 55 and after passing through the exhaust purification catalyst 55 as the biofuel concentration Cbio increases. Decrease. This is because, as the biofuel concentration Cbio increases, the fuel becomes more difficult to atomize and vaporize, but the concentration of oxygenated compounds in the fuel increases, so that the combustion (oxidation) of the fuel is promoted and the exhaust gas This is thought to be due to a decrease in the amount of soot contained in. In particular, when the biofuel concentration Cbio is 30%, the amount of soot contained in the exhaust gas after passing through the exhaust purification catalyst 55 when fuel is added by the exhaust fuel addition valve 88 uses only light oil as fuel. Compared to the case of 0% (0%), it is greatly reduced to minus 40%.

  When the biofuel concentration Cbio increases from 30% to 100%, the amount of soot contained in the exhaust gas after passing through the exhaust purification catalyst 55 when fuel is added by the exhaust fuel addition valve 88 is as fuel. Compared with the case where only light oil is used (0%), the increase / decrease rate is 170%. This is because, as the biofuel concentration Cbio increases from 30%, the combustion promoting effect due to the increase in the concentration of oxygen-containing components in the fuel is affected by the deterioration of fuel atomization and vaporization from the exhaust fuel addition valve 88. This is considered to be because the amount of soot contained in the exhaust gas increases.

  On the other hand, the amount of “soot” discharged from the cylinder and contained in the exhaust gas before flowing into the exhaust purification catalyst, that is, the amount of soot in the exhaust gas not affected by the fuel addition by the exhaust fuel addition valve 88 Even if the biofuel concentration Cbio is increased from 30% to 100%, it further decreases. Even when the biofuel concentration Cbio is 100%, compared with the case where only light oil is used as the fuel (0%) Therefore, the rate of change is -60%. This is because the fuel from the fuel injection device 80 is injected into the high-temperature atmosphere formed in the cylinder and burned mostly even though it is difficult to atomize and vaporize the fuel due to the increase in the biofuel concentration Cbio. Since the HC contained in the exhaust gas from the cylinder is sufficiently vaporized and combustion is promoted by oxygen (oxygen-containing compound) in the fuel, the exhaust gas from the cylinder It is thought that the amount of soot contained in is reduced.

  As described above, when fuel is added by the exhaust fuel addition valve 88, when the biofuel concentration Cbio is higher than a predetermined value, the amount of soot contained in the exhaust gas after passing through the exhaust purification catalyst 55 increases. The problem arises. Further, the amount of soot contained in the exhaust gas before being discharged from the cylinder and flowing into the exhaust purification catalyst 55 (not affected by the added fuel from the exhaust fuel addition valve 88) increases as the biofuel concentration Cbio increases. Since there is a tendency to decrease, when the biofuel concentration Cbio is high, there is also a desire to control the amount of soot by controlling the fuel injection device 80 and the exhaust fuel addition valve 88 according to this tendency.

  Therefore, when the estimated biofuel concentration Cbio exceeds a predetermined concentration, fuel addition from the exhaust fuel addition valve 88 is stopped (stopped), and exhaust purification is performed with fuel from the fuel injection device 80. It has been studied to form a reducing atmosphere in the catalyst 55. Thereby, the amount of soot generated in the exhaust gas can be suppressed while forming a reducing atmosphere in the exhaust purification catalyst 55. In this case, the generation of soot is suppressed by stopping the fuel addition from the exhaust fuel addition valve 88. However, as will be described below, the nozzle hole of the exhaust fuel addition valve 88 may be used depending on the fuel addition stop period. It may cause clogging.

  Since the exhaust fuel addition valve 88 is exposed to high-temperature exhaust gas, if the fuel addition by the exhaust fuel addition valve 88 is stopped for a long period, the fuel remaining at the tip of the exhaust fuel addition valve 88 is steamed. There is a possibility of generating soot and clogging the nozzle hole. For this reason, in this embodiment, the fuel injection for fuel addition control is divided into the fuel injection by the fuel injection device 80 and the fuel injection by the exhaust fuel addition valve 88, thereby performing the temperature of the exhaust fuel addition valve 88. Suppresses the rise.

  More specifically, when the reducing atmosphere is formed in the exhaust purification catalyst 55, the fuel injection device 80 mainly performs fuel injection for fuel addition control, and the fuel addition of the exhaust fuel addition valve 88 is suspended. Is longer than a predetermined period, the fuel is added to the exhaust gas by the fuel from the exhaust fuel addition valve 88 instead of the fuel from the fuel injection device 80. By causing the fuel injection device 80 to mainly perform fuel injection for fuel addition control, soot generation can be sufficiently suppressed. In addition, the fuel injection by the exhaust fuel addition valve 88 is performed every time the predetermined period elapses, thereby cooling the exhaust fuel addition valve 88 and suppressing the temperature rise. Occurrence of clogging can be suppressed.

  The operation of this embodiment will be described below with reference to FIGS. FIG. 3 is a flowchart of fuel addition control (rich spike control) for forming a reducing atmosphere in the exhaust purification catalyst 55 executed by the ECU 100. FIG. 4 is a diagram for explaining a fuel injection pattern in the rich spike control. FIG. 5 is a diagram for explaining the fuel injection control of the fuel injection device and the exhaust fuel addition valve in the rich spike control when the biofuel concentration Cbio is high. FIG. 6 is a diagram showing a stoichiometric combustible region in the operation region of the diesel engine.

  As shown in FIG. 1, in the diesel engine 10 according to the present embodiment, the biofuel concentration of the fuel supplied to the diesel engine 10 is in the middle of the fuel pipe 126 that sends the fuel from the fuel tank 120 to the high-pressure fuel pump 84. A biofuel concentration sensor (detection estimation means) 128 for detecting or estimating Cbio is provided.

  The biofuel concentration sensor 128 is an optical sensor and measures the light absorption rate of a specific wavelength band in the fuel. It is known that there is a correlation between the absorption rate of light in a specific wavelength band close to infrared and the concentration of oxygen-containing hydrocarbons (fatty acids). It is possible to estimate the biofuel concentration Cbio from the absorption rate of light. The biofuel concentration sensor 128 sends a signal related to the detected biofuel concentration Cbio to the ECU 100. The biofuel concentration sensor 128 may be provided in the fuel tank 120.

  The ECU 100 detects a signal related to the biofuel concentration Cbio from the biofuel concentration sensor 128, estimates the biofuel concentration Cbio based on this signal, and acquires it as a control variable. That is, the ECU 100 has a function of estimating the biofuel concentration Cbio in the fuel supplied to the diesel engine 10.

  Note that, as described above, the method for estimating the biofuel concentration Cbio is such that the biofuel concentration sensor 128 directly detects the fuel property information related to the biofuel concentration Cbio from the fuel supplied to the diesel engine 10, The ECU 100 is not limited to the method for estimating the biofuel concentration Cbio. For example, in a predetermined operating state of the diesel engine 10, fuel supply system components such as the fuel injection device 80 are operated in the same manner as when only light oil is used as the fuel, and at this time, detected by the A / F sensor 98. The ECU 100 grasps the oxygen concentration in the exhaust gas in the exhaust passage, that is, the behavior (time change) of the air-fuel ratio in the exhaust passage, and is obtained in the case where only light oil is used as the fuel, which is obtained in advance by a conformance experiment or the like By comparing with the behavior of the air-fuel ratio, the biofuel concentration Cbio can be estimated.

  In the vehicle system 1 configured as described above, the ECU 100 executes the following “rich spike control” in order to form a reducing atmosphere instantaneously in the exhaust purification catalyst 55 that requires supply of a reducing agent. The rich spike control is repeatedly executed by the ECU 100 when the diesel engine 10 is in operation. Hereinafter, the rich spike control will be described with reference to FIG.

  First, in step S10, the ECU 100 acquires various parameters such as the engine speed (engine speed), the accelerator opening (engine load), the biofuel concentration Cbio, the crank angle, and the intake air amount as control variables. By acquiring these control variables, the ECU 100 grasps the operating state of the diesel engine 10.

  Note that the ECU 100 operates the diesel engine 10 by setting the air-fuel ratio in the cylinder to an oxygen-excess state (for example, an air-fuel ratio of 30 to 60) during normal times when stoichiometric combustion is not performed. The exhaust gas flowing through the exhaust passage contains a large amount of oxygen, and the exhaust purification catalyst 55 forms an oxygen-excess atmosphere (lean atmosphere).

  Next, in step S20, the ECU 100 determines whether or not the exhaust purification catalyst 55 needs to reduce nitrogen oxides. Specifically, the ECU 100 estimates the amount of nitrogen oxides discharged from the cylinder per hour according to the operating state of the diesel engine 10, and the time integrated value of the estimated amount of nitrogen oxide discharged is When the threshold set according to the nitrogen oxide storage capacity of the exhaust purification catalyst 55, that is, the NOx storage reduction catalyst 55a and the DPNR catalyst system 55c is reached, the exhaust purification catalyst 55 needs to reduce the nitrogen oxide. Can be determined.

  In the map showing the relationship between the operating state (engine rotational speed and engine load) of the diesel engine 10 and the emission amount of nitrogen oxides, and the exhaust purification catalyst 55 (NOx storage reduction catalyst 55a and DPNR catalyst system 55c). The storage capacity of nitrogen oxides is obtained in advance by a fitting experiment or the like, and is stored in a ROM (not shown) of the ECU 100 as a control constant. As a result of the determination in step S20, if it is determined that the exhaust purification catalyst 55 needs to reduce nitrogen oxides (step S20-Y), the process proceeds to step S30, and if not (step S20-N). This control flow is terminated.

  In step S30, the ECU 100 determines whether or not the biofuel concentration Cbio acquired as a control variable exceeds a preset determination concentration (predetermined concentration) C0. The determination concentration C0 is “soot” included in the exhaust gas after passing through the exhaust purification catalyst 55 when fuel is added from the exhaust fuel addition valve 88 when a mixed fuel having a biofuel concentration Cbio exceeding this is used. Is set to a concentration that increases as compared with the case where only light oil is used as the fuel. The determination density C0 is set to 80%, for example. The determination concentration C0 is obtained in advance by a matching experiment or the like, and is stored in the ROM of the ECU 100 as a control constant. As a result of the determination in step S30, if it is determined that the biofuel concentration Cbio exceeds the determination concentration C0 (step S30-Y), the process proceeds to step S40. If not (step S40-N), the process proceeds to step S130. move on.

  In step S40, the ECU 100 determines whether or not stoichiometric combustion is possible in the cylinder according to the operating state of the diesel engine 10. Specifically, it is determined whether or not the engine rotation speed and the engine load of the diesel engine 10 are in an operation region where the stoichiometric combustion can be performed in the cylinder (hereinafter, referred to as a stoichiometric combustion possible region).

  The “stoichiometric combustion possible region” means that in the diesel engine 10, the fuel injection device 80 is a fuel whose biofuel concentration Cbio exceeds the above-described determination concentration C0, and fuel corresponding to the theoretical air-fuel ratio with respect to the intake air amount. This is an operating region of the diesel engine 10 in which combustion of the injected fuel is promoted by the combustion promoting effect of the oxygen-containing component in the biofuel even if it is injected into the cylinder, and soot is not generated. As shown in FIG. 6, the stoichiometric combustion possible region (region surrounded by a two-dot chain line T in the drawing) is the engine rotation speed side of the diesel engine 10 operating region (region surrounded by the solid line A in the drawing). And the engine load is set to a low load side region. The boundary T between the stoichiometric burnable region and the “stoichiometric non-burnable region”, which is the other region, is obtained in advance by a conformance experiment or the like, and is stored in the ROM of the ECU 100 as a control constant.

  As a result of the determination in step S40, if it is determined that stoichiometric combustion is possible (step S40-Y), the process proceeds to step S50, and if not (step S40-N), this control flow ends.

  In step S50, the ECU 100 executes stoichiometric combustion control. The ECU 100 controls the fuel injection amount by the fuel injection device 80 (injection amounts by pilot injection and main injection) so that stoichiometric combustion is performed in the diesel engine 10.

  Next, in step S60, the ECU 100 reads the rich spike injection map and reads the exhaust addition suspension upper limit number Ni described later. In step S60, the injection pattern for performing the rich spike control is set according to the operating state of the diesel engine 10, and the injection timings (respective injections) of the fuel injection device 80 and the exhaust fuel addition valve 88 in the rich spike control are set. The number of times, the order of injection, the injection pause period, etc.) are set.

  As will be described below, in the present embodiment, when the biofuel concentration Cbio exceeds the determination concentration C0 (step S30-Y), fuel injection for the rich spike is mainly executed by the fuel injection device 80. In this case, when the number of injections for the rich spike by the fuel injection device 80 reaches the exhaust addition stop upper limit number Ni, the fuel injection for the next rich spike is replaced with the fuel injection device 80 and the exhaust fuel. This is done by the addition valve 88. In other words, when the state where the fuel injection by the exhaust fuel addition valve 88 is stopped in the rich spike continues for a predetermined period, a part of the fuel injection amount in the rich spike is replaced with the fuel injection device 80. The exhaust fuel addition valve 88 is injected. When the exhaust fuel addition valve 88 injects fuel, the exhaust fuel addition valve 88 is cooled by the heat of vaporization of the fuel every time a predetermined period elapses. Thereby, it is possible to suppress the occurrence of clogging of the injection hole due to the temperature of the exhaust fuel addition valve 88 becoming too high.

  First, an injection pattern when performing rich spike will be described with reference to FIG. The ECU 100 sets, as target values, the air-fuel ratio of the reducing atmosphere that should reach the exhaust purification catalyst 55, the length of time during which the reducing atmosphere is formed (see symbol L in FIG. 4), and the time during which the adjacent reducing atmosphere is formed. An interval (see reference numeral I in FIG. 4) and the number of times the reducing atmosphere is formed are set. That is, a target pattern of a reducing atmosphere to be formed in the exhaust purification catalyst 55 is set. At the same time, the ECU 100 grasps the current air-fuel ratio (hereinafter referred to as a base air-fuel ratio) from the operating state of the diesel engine 10. In the present embodiment, as described above, the base air-fuel ratio in the rich spike is controlled to the stoichiometric air-fuel ratio. For this reason, compared with the case where the rich spike is performed in a state where the base air-fuel ratio is lean, the step of the output torque caused by the rich spike can be made smaller, and the drivability can be prevented from being lowered.

  The ECU 100 sets the fuel injection pattern in the rich spike control as shown in FIG. 4 based on the target pattern of the reducing atmosphere and the base air-fuel ratio. Based on the set fuel injection pattern, the fuel is injected into the exhaust gas from the cylinder by the exhaust fuel addition valve 88, or the burned gas after the stoichiometric combustion is performed in the cylinder by the fuel injection device 80. Rich spike is executed by fuel injection. As shown in FIG. 4, the information related to the injection pattern includes the injection time length L of each injection pulse P, the time interval I between adjacent injection pulses P, and the number of injection pulses P (target number). ing.

Next, the exhaust addition suspension upper limit number Ni will be described. In the present embodiment, as described above, when the biofuel concentration Cbio exceeds the determination concentration C0 (step S30-Y), fuel injection for the rich spike is mainly executed by the fuel injection device 80. In this case, if the number of times of injection for the rich spike by the fuel injection device 80 (rich spike counter n ₀ described later) reaches the exhaust addition suspension upper limit number Ni, fuel injection for the next rich spike ( (Ni + 1) fuel injection) is performed by the exhaust fuel addition valve 88 instead of the fuel injection device 80.

  The exhaust addition suspension upper limit number Ni is set from the viewpoint of suppressing occurrence of nozzle hole clogging in the exhaust fuel addition valve 88. The exhaust addition suspension upper limit number Ni is set based on the temperature of the exhaust gas, for example. This is because the temperature of the exhaust fuel addition valve 88 tends to be higher as the temperature of the exhaust gas is higher. When the temperature of the exhaust gas is high, the exhaust addition suspension upper limit number Ni is set as a small value (small number of times) compared to when the temperature of the exhaust gas is low. In other words, when the temperature of the exhaust gas is high, the period during which fuel injection by the exhaust fuel addition valve 88 is stopped is shortened, and the exhaust fuel addition valve 88 injects fuel at shorter intervals. Thus, when the temperature of the exhaust gas is high, the exhaust fuel addition valve 88 is cooled at short intervals by fuel injection. The exhaust addition suspension upper limit number Ni may be set based on the temperature of the exhaust fuel addition valve 88. In this case, for example, a temperature sensor that detects the temperature of the tip of the exhaust fuel addition valve 88 is provided. When the temperature detected by the temperature sensor is high, the exhaust addition suspension upper limit number Ni is set to a smaller value than when the temperature is low.

  By variably setting the period during which fuel injection by the exhaust fuel addition valve 88 is stopped in accordance with the temperature of the exhaust gas, both the reduction of soot generation and the suppression of injection hole clogging are achieved at the maximum. can do. For example, when the exhaust addition suspension upper limit number Ni is set to a constant value regardless of the temperature of the exhaust gas, the exhaust addition suspension upper limit is set so that the occurrence of nozzle clogging can be suppressed even when the exhaust gas is at a high temperature. It is necessary to set the number of times Ni to a small value (shorten the fuel injection interval by the exhaust fuel addition valve 88). However, in this case, when the exhaust gas is at a low temperature, fuel injection for rich spike is performed by the exhaust fuel addition valve 88 exceeding the frequency (amount) necessary to suppress clogging of the nozzle hole, soot. The amount of generation increases. According to the present embodiment, since the exhaust addition suspension upper limit number Ni is variably set according to the temperature of the exhaust gas, it is possible to achieve both the reduction of the amount of soot generation and the suppression of the occurrence of injection hole clogging.

  The ECU 100 reads the exhaust addition suspension upper limit number Ni corresponding to the exhaust gas temperature with reference to a map stored in advance. The temperature of the exhaust gas can be calculated based on control variables such as the engine speed and the accelerator opening acquired in step S10, for example. Alternatively, the fuel injection amount in the main injection or pilot injection by the fuel injection device 80 may be used as a value corresponding to the temperature of the exhaust gas. Note that the exhaust addition suspension upper limit number Ni is obtained in advance by a matching experiment and stored in the ROM of the ECU 100. When the rich spike injection map and the exhaust addition suspension upper limit number Ni are read in step S60, the process proceeds to step S70.

  In step S70, the ECU 100 executes a rich spike by the fuel injection device 80. FIG. 5 is a diagram for explaining the fuel injection control of the fuel injection device 80 and the exhaust fuel addition valve 88 in the rich spike control when the biofuel concentration Cbio is high.

In FIG. 5, reference numeral 201 denotes a rich spike execution flag. The ECU 100 turns on the rich spike execution flag 201 when the condition for executing the rich spike control is satisfied. In the present embodiment, when the biofuel concentration Cbio exceeds the determination concentration C0 (step S30-Y), for example, it is determined that the exhaust purification catalyst 55 needs to reduce nitrogen oxides (step S20-Y). When it is determined that stoichiometric combustion is possible (step S40-Y), the rich spike execution flag 201 is turned ON. In FIG. 5, the rich spike execution flag 201 is turned ON at time t1, and rich spike is started. Symbol n ₀ indicates a rich spike counter. The rich spike counter n ₀ indicates the number of executions of fuel injection (injection pulse P) for the rich spike by the fuel injection device 80.

Reference numeral 202 denotes an exhaust fuel addition execution flag. When the rich spike counter n ₀ reaches the exhaust addition suspension upper limit number Ni, the exhaust fuel addition execution flag 202 is turned ON, and fuel for the rich spike is injected by the exhaust fuel addition valve 88 instead of the fuel injection device 80. The The symbol λ indicates the excess air ratio of the exhaust gas flowing into the exhaust purification catalyst 55. When the excess air ratio λ is 1, it indicates that the air-fuel ratio (oxygen concentration) of the exhaust gas flowing into the exhaust purification catalyst 55 is equal to the stoichiometric air-fuel ratio.

  When fuel injection for rich spike is performed by the fuel injection device 80 or the exhaust fuel addition valve 88, the excess air ratio λ becomes a value smaller than 1 (rich side). In FIG. 5, times t1 to t5 indicate timings at which fuel injection for rich spikes is performed, respectively, and the excess air ratio λ becomes rich at these timings, that is, the reducing atmosphere is present in the exhaust purification catalyst 55. It is formed. When fuel injection for rich spike is executed by the fuel injection device 80 in step S70, the process proceeds to step S80.

At step S80, ECU 100, the rich spike counter _{n 0} is counted up.

Next, in step S90, the ECU 100 determines whether or not rich spike control is completed. In addition to the rich spike counter n ₀ , the ECU 100 counts the total number of rich spikes (the number of executions of the injection pulse P) from the start point of the rich spike control. In this cumulative number, the total number of rich spikes by the fuel injection device 80 and the number of rich spikes by the exhaust fuel addition valve 88 are counted. The ECU 100 performs the determination in step S90 based on whether or not the cumulative number has reached the target value of the number of rich spikes to be executed in the rich spike control set in step S60. As a result of the determination, when it is determined that the rich spike control is completed (step S90-Y), the present control flow is ended, and when not (step S90-N), the process proceeds to step S100.

At step S100, ECU 100 by, whether the rich spike counter _{n 0} is greater than the exhaust addition halt upper limit number Ni is determined. In step S100, it is determined whether or not the state where the fuel injection by the exhaust fuel addition valve 88 is stopped continues for a predetermined period, that is, the temperature of the exhaust fuel addition valve 88 rises and requires cooling. It is determined whether or not. As a result of the determination, when it is determined that the rich spike counter n ₀ is larger than the exhaust addition suspension upper limit number Ni (step S100-Y), the process proceeds to step S110, and otherwise (step S100-N). Then, the process proceeds to step S70.

In step S110, the exhaust fuel addition valve 88 is operated by the ECU 100. The ECU 100 executes the rich spike by the fuel injection by the exhaust fuel addition valve 88 instead of the fuel injection by the fuel injection device 80. At the same, ECU 100 resets the rich spike counter _{n 0.} When the fuel is injected by the exhaust fuel addition valve 88, the exhaust fuel addition valve 88 is cooled by the heat of vaporization of the injected fuel. Thereby, the occurrence of nozzle hole clogging due to the temperature rise of the exhaust fuel addition valve 88 is suppressed.

  Next, in step S120, ECU 100 determines whether or not rich spike control is completed. The ECU 100 determines whether or not the cumulative number of rich spikes executed in the rich spike control has reached the target value for the number of rich spikes, as in step S90. As a result of the determination, when it is determined that the rich spike control has been completed (step S120-Y), the present control flow is terminated, and when not (step S120-N), the process proceeds to step S70.

  When a negative determination is made in step S30 and the process proceeds to step S130, the rich spike injection map is read by the ECU 100 in step S130. With reference to the rich spike injection map, the injection time length L of each injection pulse P set according to the operating state of the diesel engine 10, the time interval I between adjacent injection pulses P, the number of injection pulses P, and the like Can be the same as the value set in step S60.

Next, in step S140, the ECU 100 executes rich spike. When the biofuel concentration Cbio does not exceed the determination concentration C0 (step S30-N), fuel injection for the rich spike is all performed by the exhaust fuel addition valve 88. The ECU 100 drives the exhaust fuel addition valve 88 to execute a rich spike once. At the same, ECU 100 resets the rich spike counter _{n 0.} In the present embodiment, as described above, fuel injection for rich spike is performed by the exhaust fuel addition valve 88 in cases other than the case where the biofuel concentration Cbio exceeds the determination concentration C0. This suppresses dilution of the lubricating oil of the diesel engine 10 as described below.

  When post injection is performed by the fuel injection device 80, the injected fuel may be mixed with the lubricating oil in the cylinder, and the lubricating oil may be diluted. For this reason, it is desirable to reduce the number of post injections from the viewpoint of suppressing the dilution of the lubricating oil. In the present embodiment, when the biofuel concentration Cbio exceeds the determination concentration C0, priority is given to suppressing the generation of soot, and rich spike is performed mainly by fuel injection by the fuel injection device 80, while biofuel When the concentration Cbio does not exceed the determination concentration C0, dilution of the lubricating oil can be suppressed by performing a rich spike by fuel injection by the exhaust fuel addition valve 88.

  Next, in step S150, the ECU 100 determines whether or not rich spike control has been completed. ECU 100 determines whether the cumulative number of rich spikes executed in the rich spike control has reached the target value for the number of rich spikes, as in steps S90 and S120. As a result of the determination, when it is determined that the rich spike control has been completed (step S150-Y), the present control flow is terminated, and when not (step S150-N), the process proceeds to step S140.

  According to this embodiment, when the biofuel concentration Cbio exceeds the determination concentration C0 (step S30-Y), the fuel injection for the fuel addition control is performed by the fuel injection device 80 and the exhaust fuel addition valve 88. It is divided into the fuel injection by. Thereby, generation | occurrence | production of particulate matter, such as a soot, can be suppressed compared with the case where all the fuel injection for fuel addition control is performed by the injection by the exhaust fuel addition valve 88. FIG. Further, the exhaust fuel addition valve 88 is cooled by injecting a part of the fuel injection amount for fuel addition control by the exhaust fuel addition valve 88. Thereby, generation | occurrence | production of the nozzle hole clogging in the exhaust fuel addition valve 88 can be suppressed. In addition, the amount of post-injection by the fuel injection device 80 can be reduced and the dilution of the lubricating oil in the cylinder can be suppressed as compared with the case where all the fuel injection for fuel addition control is performed by the fuel injection device 80. can do.

  In the present embodiment, when the biofuel concentration Cbio exceeds the determination concentration C0 (step S30-Y), the fuel injection device 80 mainly performs fuel injection for fuel addition control (steps S70 and S80). In the addition control, when the state where the fuel injection by the exhaust fuel addition valve 88 is stopped continues for a predetermined period of time (step S100-Y), the fuel injection for fuel addition control to the exhaust fuel addition valve 88 is performed. (Step S110). Thereby, reduction of the amount of soot generation | occurrence | production and suppression of generation | occurrence | production of nozzle hole clogging can be achieved more reliably. In particular, in the present embodiment, the exhaust addition suspension upper limit number Ni is set variably according to the temperature of the exhaust gas. Thereby, reduction of the amount of soot generation and suppression of generation | occurrence | production of nozzle hole clogging can be made compatible to the maximum.

(First modification of the first embodiment)
A first modification of the first embodiment will be described.

  In the first embodiment, the fuel addition control for adding fuel to the exhaust gas flowing toward the exhaust purification device based on the state of the exhaust purification device forms a reducing atmosphere in the exhaust purification catalyst 55 and the exhaust purification catalyst 55. However, the fuel addition control is not limited to this. For example, the fuel injection control of the first embodiment can also be applied when the fuel addition control is to increase the temperature of the exhaust gas by adding the fuel to the exhaust gas. The control for raising the temperature of the exhaust gas can be for regenerating an exhaust purification device (for example, DPF).

  As in the first embodiment, when the biofuel concentration Cbio exceeds the determination concentration C0, the fuel injection in the fuel addition control for raising the temperature of the exhaust gas flowing toward the exhaust purification device is mainly fuel injection. This is done by the device 80. In the fuel addition control, when the state where the fuel injection by the exhaust fuel addition valve 88 is stopped continues for a predetermined period, fuel injection for fuel addition is performed by the exhaust fuel addition valve 88 instead of the fuel injection device 80. Done.

(Second modification of the first embodiment)
A second modification of the first embodiment will be described.

  In the first embodiment (FIG. 3), when fuel is added by the exhaust fuel addition valve 88 (step S110), the amount of fuel to be injected in one rich spike (injection pulse P, see FIG. 4) is supplied. All of the fuel was injected by an exhaust fuel addition valve 88 instead of the fuel injection device 80. Instead of this, the amount of fuel injected by the exhaust fuel addition valve 88 may be a part of the amount of fuel injected by one rich spike. That is, the fuel injected in one rich spike may be injected separately into the fuel injection device 80 and the exhaust fuel addition valve 88. For example, from the viewpoint of more effectively suppressing the temperature rise of the exhaust fuel addition valve 88 or from the viewpoint of reducing the amount of soot (PM) generation, the fuel injection amount by the exhaust fuel addition valve 88 in the rich spike is reduced. Can be set.

  The number of rich spikes by the exhaust fuel addition valve 88 when fuel is injected by the exhaust fuel addition valve 88 instead of the fuel injection device 80 is not limited to one. For example, the rich spike may be performed by the exhaust fuel addition valve 88 a plurality of times and then the rich spike by the fuel injection device 80 may be shifted.

(Second Embodiment)
A second embodiment will be described. In the second embodiment, only differences from the first embodiment will be described.

  In the first embodiment (FIG. 3), the exhaust addition suspension upper limit number Ni is set according to the temperature of the exhaust gas (step S60). In the present embodiment, in addition to this, the exhaust addition suspension upper limit number Ni is set according to the biofuel concentration Cbio. As will be described below, when the biofuel concentration Cbio is high, the exhaust addition suspension upper limit number Ni is set as a large value (a large number) compared to when the biofuel concentration Cbio is low. Is done. In other words, when the biofuel concentration Cbio is high, the frequency with which the exhaust fuel addition valve 88 injects fuel is reduced. As a result, the amount of fuel injected by the exhaust fuel addition valve 88 can be reduced within a range in which the occurrence of injection hole clogging in the exhaust fuel addition valve 88 can be suppressed, and soot generation can be suppressed.

  As described above, unlike light oil, biofuel contains oxygen (oxygen-containing compound) in the molecule constituting the fuel. For this reason, the higher the biofuel concentration Cbio, the smaller the stoichiometric air-fuel ratio, that is, the greater the amount of fuel to be supplied for a predetermined intake air amount for performing stoichiometric combustion. Therefore, the rich spike fuel injection amount required to form a reducing atmosphere in the exhaust purification catalyst 55 is set as a large value corresponding to the increase in the biofuel concentration Cbio.

  As a result, the amount of fuel injected when the fuel is injected by the exhaust fuel addition valve 88 in the rich spike control also increases, so that the tip of the exhaust fuel addition valve 88 is easily cooled. As a result, when the biofuel concentration Cbio is high, the period (predetermined period) during which the fuel injection of the exhaust fuel addition valve 88 is stopped is longer (exhaust addition stop) than when the biofuel concentration Cbio is low. The upper limit number Ni can be increased).

  By setting the exhaust addition suspension upper limit number Ni to an appropriate value according to the biofuel concentration Cbio, the fuel injection frequency (injection amount) of the exhaust fuel addition valve 88 is suppressed while the injection hole clogging of the exhaust fuel addition valve 88 is suppressed. ) As a necessary minimum, and it is possible to reduce the frequency of soot (PM) increase in the exhaust gas and the total amount of soot generated in the exhaust gas.

  Next, specific control contents will be described with reference to FIG.

  Steps S10 to S50 can be the same as those in the first embodiment. In step S60, the ECU 100 reads the rich spike injection map and the exhaust addition suspension upper limit number Ni. The exhaust addition suspension upper limit number Ni read here is set not only based on the temperature of the exhaust gas as in the first embodiment, but also based on the biofuel concentration Cbio. The exhaust addition suspension upper limit number Ni is set as a smaller value when the temperature of the exhaust gas is high than when it is low. On the other hand, the exhaust addition suspension upper limit number Ni is set as a larger value when the biofuel concentration Cbio is high than when it is low. Note that the exhaust addition suspension upper limit number Ni is obtained in advance by a matching experiment or the like, and is stored in the ROM of the ECU 100 as a control constant.

  Based on the rich spike injection map read in step S60 and the exhaust addition suspension upper limit number Ni, the ECU 100 executes rich spike control from step S70 to step S120. Other operations can be the same as those in the first embodiment.

It is a schematic block diagram of 1st Embodiment of the exhaust gas purification control apparatus of this invention. It is a figure which shows the increase / decrease rate of the soot by the change of biofuel concentration on the basis of the case where only light oil is used as a fuel (0%). It is a flowchart which shows operation | movement of 1st Embodiment of the exhaust gas purification control apparatus of this invention. It is a figure explaining the injection pattern of the fuel in the rich spike control of 1st Embodiment of the exhaust purification control apparatus of this invention. In the first embodiment of the exhaust purification control apparatus of the present invention, it is a diagram for explaining the fuel injection control of the fuel injection device and the exhaust fuel addition valve in the rich spike control when the biofuel concentration is high. In 1st Embodiment of the exhaust gas purification control apparatus of this invention, it is a figure which shows the stoichiometric combustion possible area | region in the driving | operation area | region of a diesel engine.

Explanation of symbols

1 Vehicle system 10 Diesel engine 24 Intake port (intake passage)
26 Exhaust port (exhaust passage)
42 Air cleaner 46 Throttle valve 48 Intake manifold 50a Manifold passage (exhaust passage)
50c Junction (exhaust passage)
50e passage (exhaust passage)
52 Exhaust Manifold 55 Exhaust Purification Catalyst 55a NOx Storage Reduction Catalyst (Exhaust Purification Catalyst)
55c DPNR catalyst system (exhaust gas purification catalyst)
60 Turbocharger 80 Fuel injector (fuel injection valve)
82 Fuel Rail 84 High Pressure Fuel Pump 88 Exhaust Fuel Addition Valve 98 A / F Sensor 100 Electronic Control Unit (ECU) for Diesel Engine
102 Accelerator Pedal Position Sensor 120 Fuel Tank 122 Low Pressure Fuel Pump 128 Biofuel Concentration Sensor Cbio Biofuel Concentration C0 Determination Concentration n ₀ Rich Spike Counter Ni Exhaust Addition Pause Upper Limit λ Excess Air Excess Ratio

Claims (5)

A fuel injection device for injecting fuel into a cylinder of the internal combustion engine;
An exhaust fuel addition valve that injects the fuel upstream of an exhaust purification device that purifies exhaust gas in the exhaust passage of the internal combustion engine;
An exhaust purification control device that executes fuel addition control for adding the fuel to the exhaust gas flowing toward the exhaust purification device based on a state of the exhaust purification device,
Detection estimation means for detecting or estimating the concentration of biofuel contained in the fuel;
Control means for controlling the fuel injection by the fuel injection device and the exhaust fuel addition valve,
When the concentration detected or estimated by the detection estimating unit is equal to or higher than a predetermined concentration, the control unit performs the fuel injection for the fuel addition control by the fuel injection device. And the fuel injection by the exhaust fuel addition valve. The exhaust purification control apparatus according to claim 1,
The control means causes the fuel injection device to mainly inject the fuel for the fuel addition control when the concentration is equal to or higher than the predetermined concentration, and the exhaust fuel addition valve in the fuel addition control. When the state in which the fuel injection by the engine is stopped continues for a predetermined period, the exhaust gas control valve causes the exhaust fuel addition valve to inject the fuel for the fuel addition control. apparatus. The exhaust purification control apparatus according to claim 2,
The predetermined period is set to be shorter when the temperature of the exhaust gas is high than when the temperature of the exhaust gas is low. The exhaust purification control device according to claim 2 or 3,
The predetermined period is set to be longer when the concentration is high than when the concentration is low. The exhaust purification control apparatus according to any one of claims 1 to 4,
The exhaust purification device is a NOx occlusion reduction type catalyst that occludes nitrogen oxides,
The fuel addition control is control for adding the fuel to the exhaust gas based on the storage state of the nitrogen oxides of the NOx storage reduction catalyst to form a reducing atmosphere in the NOx storage reduction catalyst. An exhaust purification control apparatus characterized by the above.

Images