JP2020101133A - Engine control device - Google Patents

Abstract

To provide an engine control device provided in a compression ignition engine which performs multiple injection of fuel into a combustion chamber, the engine control device allowing for maintaining of favorable combustion characteristics and thermal efficiency and furthermore allowing for suppression of combustion noise even when an environmental parameter changes.SOLUTION: The control device is provided that is provided in a compression ignition engine in which pre-ignition P1 and main ignition P2 of fuel are performed. The control device performs control in such a manner that: when the opening of an EGR valve 45 is decreased, an injection start timing for the pre-ignition P1 is advanced, the injection amount of the pre-ignition P1 is increased and the injection amount of the main injection P2 is decreased in an amount of the increase of the pre-ignition while an injection timing for the main injection P2 is fixed; and when the opening of the EGR valve 45 is increased on the other hand, the injection start timing for the pre-ignition P1 is delayed, the amount of the pre-ignition P1 is decreased, and the injection amount of the main injection P2 is increased in an amount of the decrease of the pre-ignition while the injection timing for the main injection P2 is fixed.SELECTED DRAWING: Figure 22

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine control device, and more particularly to a pressure ignition engine control device that performs multi-stage injection of fuel into a combustion chamber.

In an engine that employs premixed compression ignition combustion, a technique is known in which fuel is injected a plurality of times into a combustion chamber during one cycle. As a technique for suppressing combustion noise in a pressure ignition engine that performs such multi-stage injection of fuel, for example, in Patent Document 1 (JP-A-2016-166587), there is combustion by the first fuel injection (pre-stage injection). The time interval (peak interval) between the peak of the pressure rise of the fuel injection and the peak of the pressure rise of the combustion due to the second fuel injection (post-injection) is set to approximately 1/2 of the period of the combustion noise due to the injection, so that the phases are opposite to each other. There is disclosed a technique of suppressing the generation of combustion noise by canceling out the combustion noise of the first-stage injection and the combustion noise of the second-stage injection.

JP, 2016-166587, A

In an engine that performs such multi-stage injection of fuel, when the combustion by the pre-stage injection is premixed compression ignition combustion, there is a time lag called ignition delay from the injection of fuel to the ignition, and the ignition delay is long. The temperature changes due to changes in environmental parameters such as the temperature and oxygen concentration in the combustion chamber. Therefore, even if the peak interval between the first-stage injection and the second-stage injection is optimized to suppress the combustion noise, the peak interval varies from the optimum value (approximately 1/2 cycle of the combustion noise) due to the change in the environmental parameter. It may happen. In order to deal with such a situation, it is possible to adjust the injection timings of the first-stage injection and the second-stage injection so that the peak interval becomes the optimum value again, but if the injection timing is simply changed, The characteristics of the combustion (heat generation rate) of (1) will change, and the thermal efficiency will deteriorate.

The present invention has been made in consideration of the above circumstances, and an object thereof is to control an engine provided in a compression ignition engine that performs multi-stage injection of fuel into a combustion chamber, even when environmental parameters are changed. Another object of the present invention is to provide an engine control device capable of suppressing combustion noise while maintaining good combustion characteristics and thermal efficiency.

In order to achieve the above object, the following solution is adopted in the present invention. That is, as described in claim 1,
In an engine control device provided in a compression ignition engine in which multi-stage injection of fuel into a combustion chamber is executed,
A pre-injection executed on the advance side of the compression top dead center of the compression ignition engine, and a fuel injection executed on the retard side of the pre-injection while the fuel injected by the pre-injection is burning. A fuel injection unit for injecting injection into the combustion chamber,
An injection control unit that controls the injection timing and injection amount of each injection executed by the fuel injection unit,
An EGR valve control unit that controls an opening degree of an EGR valve of an EGR device included in the compression ignition engine,
The injection control unit,
The interval between the first peak of the heat release rate caused by the combustion of the fuel injected by the pre-injection and the second peak of the heat release rate caused by the combustion of the fuel injected by the main injection is the pre-injection and the main injection. A base setting determination means for determining the base setting of the injection timing and the injection amount of each injection so that the pressure waves generated by the combustion of the respective fuels have intervals that cancel each other out,
Injection timing variation calculation means for calculating a variation in the injection timing of the pre-injection due to a change in the oxygen concentration and gas temperature in the combustion chamber due to a change in the opening degree of the EGR valve,
When the opening degree of the EGR valve is reduced by the EGR valve control unit, the injection start timing of the pre-injection is calculated by the injection timing variation calculation means while maintaining the injection timing of the main injection at the base setting. Setting correction means for changing the base setting from the base setting to the advance side, increasing the injection amount of the pre-injection from the base setting, and decreasing the injection amount of the main injection by the increase amount of the injection amount of the pre-injection according to Equipped with.

According to the above solution method, when the opening degree of the EGR valve is reduced, the peak temperature of the heat generation rate due to the pre-injection is delayed due to the influence of the gas temperature decrease in the combustion chamber. Since the control for advancing the injection start timing of the pre-injection is executed, the peak generation timing of the heat generation rate by the pre-injection can be brought close to the timing (crank angle) before the EGR valve is reduced. Further, in this case, since the injection amount of the pre-injection is increased, it is possible to suppress the decrease in the height of the heat release rate peak due to the advance of the injection timing of the pre-injection, and to increase the injection amount of the pre-injection only. Since the injection amount of the main injection is reduced, the total fuel injection amount of the pre-injection and the main injection is kept constant. Therefore, even if the opening degree of the EGR valve is made small, the heat release rate characteristic in the combustion chamber can be made close to the characteristic before the change of the EGR valve opening degree, so that the pre-injection and the main injection make mutual combustion noise appropriate. And the combustion noise can be appropriately suppressed, and the deterioration of thermal efficiency can be prevented.

A preferred mode based on the above solution method is as described in claims 2 and below in the claims. That is, the base setting determination means determines the base setting based on the target fuel injection amount, and when the target fuel injection amount is changed, the EGR valve control unit performs the injection based on the changed target fuel injection amount. Prior to being started, the opening degree of the EGR valve is changed to an opening degree according to the changed target fuel injection amount, and the setting correction means, after the opening degree of the EGR valve is changed, During the period until the injection based on the changed target fuel injection amount is started, the control for correcting the injection start timing of the pre-injection and the injection amounts of the pre-injection and the main injection is executed. ). In this case, when the EGR valve opening degree is reduced prior to the start of fuel injection at the target fuel injection amount during acceleration, parameters such as the fuel injection amount and the engine speed remain constant and the internal combustion chamber In a situation where only the oxygen concentration and the in-cylinder gas temperature change gradually, the desired heat release rate characteristics can be maintained and combustion noise can be appropriately suppressed.

The advance amount of the injection start timing of the pre-injection by the setting correction means is the advance amount of the heat generation rate peak occurrence timing of the pre-injection caused by the advance angle of the injection timing of the pre-injection. It is set to be smaller than the retard amount of the timing of the peak of the heat generation rate due to the pre-injection due to the reduction of the valve opening (corresponding to claim 3). In this case, since the advance amount of the pre-injection is prevented from becoming excessively large, the generation timing of the peak of the heat release rate does not advance too much as before the change of the EGR valve opening degree, and the EGR valve opening degree is not increased. It is possible to approach the time (crank angle) before the change.

The increase amount of the injection amount of the pre-injection by the setting correction means is that the increase amount of the first peak of the heat generation rate due to the pre-injection caused by the increase amount is such that the opening degree of the EGR valve is reduced. Is set so as not to exceed the amount of decrease in the first peak of the heat generation rate due to the pre-injection (corresponding to claim 4). In this case, since the increase amount of the injection amount of the pre-injection is prevented from becoming excessively large, the peak of the heat release rate does not become too higher than before the change of the EGR valve opening degree, and the peak of the heat release rate does not change before the EGR valve opening degree change. Can be appropriately approached to the height of.

When the injection start timing of the pre-injection set by the setting correction means exceeds a predetermined advance angle limit, a plurality of pre-injections are executed between the advance angle limit and the injection timing of the main injection. The pre-injection is divided and executed (corresponding to claim 5). In this case, when the injection start timing of the pre-injection set by the setting correction means exceeds the advance limit, the pre-injection is divided into a plurality, so that the injection amount of each divided pre-injection can be reduced. it can. Therefore, due to the advance of the injection timing, injection may be performed in a state where the temperature in the combustion chamber (cylinder gas temperature) has not risen sufficiently, and the injected fuel may adhere to the engine wall surface. On the other hand, since the injection amount for each injection is reduced, the adhesion of fuel to the engine wall surface can be appropriately suppressed.

Further, as in the invention of claim 6,
In an engine control device provided in a compression ignition engine in which multi-stage injection of fuel into a combustion chamber is executed,
A pre-injection executed on the advance side of the compression top dead center of the compression ignition engine, and a fuel injection executed on the retard side of the pre-injection while the fuel injected by the pre-injection is burning. A fuel injection unit for injecting injection into the combustion chamber,
An injection control unit that controls the injection timing and injection amount of each injection executed by the fuel injection unit,
An EGR valve control unit that controls an opening degree of an EGR valve of an EGR device included in the compression ignition engine,
The injection control unit,
The interval between the first peak of the heat release rate caused by the combustion of the fuel injected by the pre-injection and the second peak of the heat release rate caused by the combustion of the fuel injected by the main injection is the pre-injection and the main injection. A base setting determination means for determining the base setting of the injection timing and the injection amount of each injection so that the pressure waves generated by the combustion of the respective fuels have intervals that cancel each other out,
Injection timing variation calculation means for calculating a variation in the injection timing of the pre-injection due to a change in the oxygen concentration and gas temperature in the combustion chamber due to a change in the opening degree of the EGR valve,
When the opening degree of the EGR valve is increased by the EGR valve control unit, the injection start timing of the pre-injection is calculated by the injection timing variation calculation means while maintaining the injection timing of the main injection at the base setting. Setting correction means for changing from the base setting to the retard angle side according to the above, decreasing the injection amount of the pre-injection from the base setting, and increasing the injection amount of the main injection by the decrease amount of the injection amount of the pre-injection. Equipped with.

According to the above solution method, when the opening degree of the EGR valve is increased, the peak generation of the heat generation rate due to the pre-injection advances as it is due to the influence of the gas temperature rise in the combustion chamber. Since the control for retarding the injection start timing of the pre-injection is executed, the peak generation timing of the heat generation rate due to the pre-injection can be brought close to the timing (crank angle) before the EGR valve opening degree change. Further, in this case, since the injection amount of the pre-injection is reduced, it is possible to suppress an increase in the height of the heat release rate peak due to the retardation of the injection timing of the pre-injection, and to reduce the injection amount of the pre-injection. Since the injection amount of the main injection is increased, the total fuel injection amount of the pre-injection and the main injection is kept constant. Therefore, even if the opening degree of the EGR valve becomes large, the heat release rate characteristic in the combustion chamber can be brought close to the characteristic before the EGR valve opening degree is changed, so that the pre-injection and the main injection properly make mutual combustion noise. It is possible to cancel each other out, appropriately suppress combustion noise, and prevent deterioration of thermal efficiency.

A preferred mode based on the above solution method is as described in claims 7 and below in the claims. That is, the base setting determination means determines the base setting based on the target fuel injection amount, and when the target fuel injection amount is changed, the EGR valve control unit performs the injection based on the changed target fuel injection amount. Prior to being started, the opening degree of the EGR valve is changed to an opening degree according to the changed target fuel injection amount, and the setting correction means, after the opening degree of the EGR valve is changed, During the period until the injection based on the changed target fuel injection amount is started, the control for correcting the injection start timing of the pre-injection and the injection amounts of the pre-injection and the main injection is executed. ). In this case, in this case, when the EGR valve opening is increased prior to the start of fuel injection at the target fuel injection amount during deceleration, parameters such as the fuel injection amount and the engine speed remain constant, In a situation where only the oxygen concentration in the combustion chamber and the in-cylinder gas temperature gradually change, the desired heat release rate characteristics can be maintained and combustion noise can be appropriately suppressed.

The retard amount of the injection start timing of the pre-injection by the setting correction means is the retard amount of the generation timing of the first peak of the heat generation rate by the pre-injection caused by the retard angle of the injection timing of the pre-injection. , Is set to be smaller than the advance amount of the generation timing of the first peak of the heat generation rate due to the pre-injection due to the increased opening degree of the EGR valve (corresponding to claim 8). In this case, the pre-injection retardation amount is prevented from becoming excessively large, so that the heat generation rate peak generation timing will not be retarded more than before the EGR valve opening degree is changed, and the EGR valve opening degree will not be delayed. It is possible to approach the time (crank angle) before the change.

The decrease amount of the injection amount of the pre-injection by the setting correction unit is that the decrease amount of the first peak of the heat generation rate due to the pre-injection caused by the decrease amount is such that the opening degree of the EGR valve is increased. Is set so as not to exceed the amount of increase in the first peak of the heat generation rate due to the pre-injection (corresponding to claim 9). In this case, the amount of decrease in the injection amount of the pre-injection is prevented from becoming excessively large, so the peak of the heat release rate does not become too lower than before the change of the EGR valve opening degree, and before the EGR valve opening degree change. Can be appropriately approached to the height of.

According to the present invention, when the opening degree of the EGR valve is changed, the injection start timing of the pre-injection and the fuel injection amounts of the pre-injection and the main injection are appropriately changed. Can be brought close to the characteristic before the EGR valve opening is changed. Therefore, even when the opening degree of the EGR valve is changed, combustion noise can be appropriately suppressed, and deterioration of thermal efficiency can be prevented.

1 is a system diagram of a diesel engine to which an engine control device according to the present invention is applied. (A) is a perspective view of a crown portion of the piston of the diesel engine shown in FIG. 1, and (B) is a perspective view with a cross section of the piston. FIG. 3 is an enlarged view of a piston cross section shown in FIG. 2(B). It is a sectional view of a piston for explaining a relation between a crown surface of a piston and an injection axis of fuel by an injector. 6 is a time chart showing the timing of fuel injection and the heat generation rate. It is a figure which shows typically the generation condition of air-fuel mixture in a combustion chamber. It is a block diagram showing a control system of a diesel engine. (A) is a graph showing an example of a target heat release rate characteristic, and (B) is a schematic view showing peaks and ratios of heat release rates generated by each combustion of the front injection and the post injection, and an interval between these peaks. It is a figure. It is a schematic diagram for demonstrating the cancellation effect of combustion noise. It is a graph which shows a correction example for making a predicted heat release rate characteristic close to a target heat release rate characteristic. It is a schematic diagram for demonstrating the combustion environment factor which affects achievement of a target heat release rate characteristic. (A) is a diagram showing a peak delay of pre-stage combustion caused by pilot injection, (B) is a prediction model formula of the peak delay, and (C) is a table format diagram showing a calibration result of the prediction model formula. is there. (A) And (B) is a figure which shows the factor which affects the peak height of pre-stage combustion resulting from pilot injection, (C) is the prediction model formula of said peak height, (D) is the prediction model formula It is a table format diagram showing the calibration results of. It is a figure for explaining an outline of control when an opening of an EGR valve is made small. 6 is a graph showing the relationship between the oxygen concentration in the combustion chamber, the in-cylinder gas temperature, and the change rate of the ignition delay with respect to the change rate of the injection timing. It is a graph which shows the relationship of the rate of change of a heat release rate peak with respect to the rate of change of a pre-injection amount or a peak delay. 7 is a timing chart showing an example of control when the opening degree of the EGR valve is reduced. It is a figure for demonstrating control when the opening degree of an EGR valve is enlarged. 6 is a timing chart showing an example of control when the opening degree of the EGR valve is increased. FIG. 6 is a diagram for explaining control when the calculated pre-injection start timing exceeds the advance angle limit when the opening degree of the EGR valve is reduced. It is a flow chart which shows an example of fuel injection control. 7 is a flowchart showing an example of control in the case where the opening degree of the EGR valve is changed in the fuel injection control.

[Overall engine configuration]
Hereinafter, an embodiment of an engine control device according to the present invention will be described in detail with reference to the drawings. First, the overall configuration of a diesel engine system to which the control device according to the present invention is applied will be described based on FIG. The diesel engine shown in FIG. 1 is a 4-cycle diesel engine mounted on a vehicle as a power source for traveling. The diesel engine system includes an engine body 1 that has a plurality of cylinders 2 and that is driven by being supplied with fuel containing light oil as a main component, an intake passage 30 through which intake air introduced into the engine body 1 flows, and an engine body. 1 is driven by exhaust gas passing through the exhaust passage 40, the EGR device 44 that recirculates a part of the exhaust gas flowing through the exhaust passage 40 to the intake passage 30, and the exhaust gas passing through the exhaust passage 40. The turbocharger 46 is provided.

The engine body 1 has a plurality of cylinders 2 (only one of which is shown in FIG. 1) arranged in a direction perpendicular to the paper surface of FIG. 1, and is driven by the supply of fuel containing light oil as a main component. It is an engine. The engine body 1 includes a cylinder block 3, a cylinder head 4 and a piston 5. The cylinder block 3 has a cylinder liner forming the cylinder 2. The cylinder head 4 is attached to the upper surface of the cylinder block 3 and closes the upper opening of the cylinder 2. The piston 5 is housed in the cylinder 2 so as to be capable of reciprocating sliding movement, and is connected to the crankshaft 7 via a connecting rod 8. The crankshaft 7 rotates about its central axis in response to the reciprocating movement of the piston 5. The structure of the piston 5 will be described in detail later.

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

A crank angle sensor SN1 and a water temperature sensor SN2 are attached to the cylinder block 3. The crank angle sensor SN1 detects the rotation angle (crank angle) of the crank shaft 7 and the rotation speed (engine rotation speed) of the crank shaft 7. The water temperature sensor SN2 detects the temperature of the cooling water (engine water temperature) flowing inside the cylinder block 3 and the cylinder head 4.

An intake port 9 and an exhaust port 10 that communicate with the combustion chamber 6 are formed in the cylinder head 4. An intake side opening which is a downstream end of the intake port 9 and an exhaust side opening which is an upstream end of the exhaust port 10 are formed on the lower surface of the cylinder head 4. An intake valve 11 that opens and closes the intake side opening and an exhaust valve 12 that opens and closes the exhaust side opening are attached to the cylinder head 4. Although not shown, the valve type of the engine body 1 is a 4-valve type of intake 2 valves×exhaust 2 valves, and two intake ports 9 and two exhaust ports 10 are provided for each cylinder 2. At the same time, two intake valves 11 and two exhaust valves 12 are provided.

The cylinder head 4 is provided with an intake valve operating mechanism 13 and an exhaust valve operating mechanism 14 including a camshaft. The intake valve 11 and the exhaust valve 12 are opened and closed by the valve operating mechanisms 13 and 14 in conjunction with the rotation of the crankshaft 7. The intake-side valve mechanism 13 has an intake VVT capable of changing at least the opening timing of the intake valve 11, and the exhaust-side valve mechanism 14 has an exhaust VVT capable of changing at least the closing timing of the exhaust valve 12. Has been done.

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

The injector 15 is connected to a common pressure accumulating common rail (not shown) common to all the cylinders 2 via a fuel supply pipe. High-pressure fuel pressurized by a fuel pump (not shown) is stored in the common rail. By supplying the fuel accumulated in the common rail to the injector 15 of each cylinder 2, the fuel is injected into the combustion chamber 6 at a high pressure (about 50 MPa to 250 MPa) from each injector 15. Between the fuel pump and the common rail, a fuel pressure regulator 16 (not shown in FIG. 1, see FIG. 7) for changing the injection pressure, which is the pressure of the fuel injected from the injector 15, is provided.

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

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

An air flow sensor SN3, an intake air temperature sensor SN4, an intake pressure sensor SN5, and an intake O ₂ sensor SN6 are arranged in the intake passage 30. The air flow sensor SN3 is arranged on the downstream side of the air cleaner 31 and detects the flow rate of intake air passing through the portion. The intake air temperature sensor SN4 is arranged on the downstream side of the intercooler and detects the temperature of the intake air passing through the portion. The intake pressure sensor SN5 and the intake O ₂ sensor SN6 are arranged in the vicinity of the surge tank 34, and detect the pressure of the intake air passing through the portion and the oxygen concentration of the intake air, respectively. Although not shown in FIG. 1, an injection pressure sensor SN7 (FIG. 7) that detects the injection pressure of the injector 15 is provided.

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

An exhaust O ₂ sensor SN8 and a differential pressure sensor SN9 are arranged in the exhaust passage 40. The exhaust gas O ₂ sensor SN8 is arranged between the turbocharger 46 and the exhaust gas purification device 41, and detects the oxygen concentration of the exhaust gas passing through the portion. The differential pressure sensor SN9 detects the differential pressure between the upstream end and the downstream end of the DPF 43.

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

The turbocharger 46 includes a compressor 47 arranged on the intake passage 30 side and a turbine 48 arranged on the exhaust passage 40. The compressor 47 and the turbine 48 are connected by a turbine shaft so as to be integrally rotatable. The turbine 48 receives the energy of the exhaust gas flowing through the exhaust passage 40 and rotates. As the compressor 47 rotates in conjunction with this, the air flowing through the intake passage 30 is compressed (supercharged).

[Detailed structure of piston]
Next, the structure of the piston 5, especially the structure of the crown surface 50 will be described in detail. FIG. 2A is a perspective view mainly showing the upper portion of the piston 5. The piston 5 includes an upper piston head and a skirt portion located on the lower side. In FIG. 2A, the piston head portion having the crown surface 50 on the top surface is shown. FIG. 2B is a perspective view of the piston 5 with a radial cross section. FIG. 3 is an enlarged view of the radial cross section shown in FIG. 2A and 2B, the cylinder axis direction A and the combustion chamber radial direction B are indicated by arrows.

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

The cavity 5C includes a first cavity portion 51, a second cavity portion 52, a connecting portion 53, and a mountain portion 54. The first cavity portion 51 is a concave portion arranged in the central region of the crown surface 50 in the radial direction B. The second cavity portion 52 is an annular concave portion that is arranged on the outer peripheral side of the first cavity portion 51 in the crown surface 50. The connecting portion 53 is a portion that connects the first cavity portion 51 and the second cavity portion 52 in the radial direction B. The mountain portion 54 is a mountain-shaped convex portion arranged at the center of the crown surface 50 (first cavity portion 51) in the radial direction B. The mountain portion 54 is provided so as to project at a position directly below the nozzle 151 of the injector 15 (FIG. 4).

The first cavity portion 51 includes a first upper end portion 511, a first bottom portion 512 and a first inner end portion 513. The first upper end portion 511 is at the highest position in the first cavity portion 51 and is continuous with the connecting portion 53. The first bottom portion 512 is the most recessed portion in the first cavity portion 51, which is an annular region in a top view. Even in the entire cavity 5C, the first bottom portion 512 is the deepest portion, and the first cavity portion 51 has a predetermined depth (first depth) in the cylinder axial direction A at the first bottom portion 512. There is. In a top view, the first bottom portion 512 is located closer to the inner side in the radial direction B with respect to the connecting portion 53.

The first upper end 511 and the first bottom 512 are connected by a radial recess 514 that is curved outward in the radial direction B. The radial recessed portion 514 has a portion recessed outward in the radial direction B with respect to the connecting portion 53. The first inner end portion 513 is located at the innermost position in the radial direction in the first cavity portion 51, and is connected to the lower end of the mountain portion 54. The first inner end portion 513 and the first bottom portion 512 are connected by a curved surface gently curved in a skirt shape.

The second cavity portion 52 includes a second inner end portion 521, a second bottom portion 522, a second upper end portion 523, a tapered region 524, and a standing wall region 525. The second inner end portion 521 is located at the innermost position in the radial direction of the second cavity portion 52 and is continuous with the connecting portion 53. The second bottom portion 522 is the most recessed region in the second cavity portion 52. The second cavity portion 52 has a depth in the second bottom portion 522 that is shallower than the first bottom portion 512 in the cylinder axis direction A. That is, the second cavity portion 52 is a concave portion that is located above the first cavity portion 51 in the cylinder axis direction A. The second upper end portion 523 is located at the highest position in the second cavity portion 52 and on the outermost side in the radial direction, and is continuous with the peripheral flat surface portion 55.

The tapered region 524 is a portion that extends from the second inner end portion 521 toward the second bottom portion 522 and has a surface shape that is inclined downward toward the outside in the radial direction. As shown in FIG. 3, the tapered region 524 has an inclination along an inclined line C2 that intersects the horizontal line C1 extending in the radial direction B at an inclination angle α.

The standing wall region 525 is a wall surface formed so as to rise relatively steeply on the outer side in the radial direction with respect to the second bottom portion 522. In the cross-sectional shape in the radial direction B, the wall surface of the second cavity portion 52 is a curved surface curved from the horizontal direction to the upper direction from the second bottom portion 522 to the second upper end portion 523, and the second upper end portion is formed. A portion of the wall near 523, which is close to the vertical wall, is a standing wall region 525. The lower portion of the standing wall region 525 is located inside the radial direction B with respect to the upper end position of the standing wall region 525. This prevents the air-fuel mixture from returning too much to the inside of the combustion chamber 6 in the radial direction B, and makes it possible to perform combustion by effectively utilizing the space (squish space) radially outside the standing wall region 525.

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

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

The ridge portion 54 projects upward, but the protrusion height thereof is the same as the height of the third upper end portion 532 of the connecting portion 53, and is at a position recessed from the peripheral flat surface portion 55. The crest portion 54 is located at the center of the circular first cavity portion 51 in a top view, and thus the first cavity portion 51 is in the form of an annular groove formed around the crest portion 54.

[Spatial separation of fuel injection]
Next, the state of fuel injection into the cavity 5C by the injector 15 and the flow of the air-fuel mixture after injection will be described based on FIG. FIG. 4 is a schematic cross-sectional view of the combustion chamber 6, showing the relationship between the crown surface 50 (cavity 5C) and the injection axis AX of the injected fuel 15E injected from the injector 15, and the flow of the air-fuel mixture after injection. Arrows F11, F12, F13, F21, F22, and F23 that schematically represent are shown.

The injector 15 includes a nozzle 151 arranged so as to project downward from the combustion chamber ceiling surface 6U (the lower surface of the cylinder head 4) into the combustion chamber 6. The nozzle 151 has an injection hole 152 for injecting fuel into the combustion chamber 6. Although FIG. 4 shows one injection hole 152, a plurality of injection holes 152 are actually arranged in the circumferential direction of the nozzle 151 at equal pitches. The fuel injected from the injection hole 152 is injected along the injection axis AX in the figure. The injected fuel diffuses with a spray angle θ. FIG. 4 shows an upper diffusion axis AX1 indicating upward diffusion with respect to the ejection axis AX and a lower diffusion axis AX2 indicating downward diffusion. The spray angle θ is an angle formed by the upper diffusion axis AX1 and the lower diffusion axis AX2.

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

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

Specifically, the air-fuel mixture directed in the direction of arrow F11 (downward) enters the radial recess 514 of the first cavity portion 51 from the lower end portion 531 of the connecting portion 53 and flows downward. Thereafter, the air-fuel mixture changes the flow direction from the downward direction to the inner side in the radial direction B by the curved shape of the radial recess 514, and as shown by the arrow F12, the bottom surface of the first cavity portion 51 having the first bottom portion 512. Flows following the shape. At this time, the air-fuel mixture is mixed with the air in the first cavity portion 51 to dilute the concentration. Due to the presence of the crests 54, the bottom surface of the first cavity portion 51 has a shape that rises toward the center in the radial direction. Therefore, the air-fuel mixture flowing in the direction of the arrow F12 is lifted upward, and finally flows from the combustion chamber ceiling surface 6U toward the radially outer side as shown by the arrow F13. Even during such a flow, the air-fuel mixture mixes with the air remaining in the combustion chamber 6 and becomes a homogeneous and thin air-fuel mixture.

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

Then, the air-fuel mixture is lifted upward by the rising curved surface between the second bottom portion 522 and the standing wall region 525, and flows from the combustion chamber ceiling surface 6U toward the radially inner side. During the flow indicated by the arrow F22, the air-fuel mixture mixes with the air in the second cavity portion 52 to become a homogeneous and thin air-fuel mixture. Here, since the standing wall region 525 that extends substantially in the vertical direction exists on the outer side in the radial direction of the second bottom portion 522, the injected fuel (fuel mixture) allows the injected fuel (fuel mixture) to form an inner peripheral wall of the cylinder 2 (generally, a liner (not shown)). Is present) is reached. That is, the air-fuel mixture can flow to the vicinity of the radially outer side of the combustion chamber 6 due to the formation of the second bottom portion 522, but the presence of the standing wall region 525 suppresses the interference with the inner peripheral wall of the cylinder 2. Therefore, it is possible to suppress the occurrence of cold loss due to the interference.

Here, the standing wall region 525 has a shape such that the lower portion thereof is located inside the radial direction B with respect to the upper end position. Therefore, the flow indicated by the arrow F22 does not become excessively strong, and the air-fuel mixture can be prevented from returning too far inward in the radial direction B. If the flow of the arrow F22 is too strong, the partially combusted air-fuel mixture collides with the fuel before the newly injected fuel is sufficiently diffused, hinders homogeneous combustion and causes soot and the like. However, the standing wall region 525 of the present embodiment does not have a shape that is hollowed outward in the radial direction, the flow of the arrow F22 is suppressed, and the flow outward in the radial direction B indicated by the arrow F23 is also generated. To do. In particular, in the latter stage of combustion, it may be pulled by the reverse squish flow, and the flow of arrow F23 is likely to occur. Therefore, the space radially outside the standing wall region 252 (squish space on the peripheral flat surface portion 55) can also be effectively used for combustion. Therefore, it is possible to suppress the generation of soot and the like, and to realize combustion that effectively utilizes the entire combustion chamber space.

As described above, the fuel injected toward the connecting portion 53 along the injection axis AX collides with the connecting portion 53, is spatially separated, and exists in the spaces of the first and second cavity portions 51 and 52, respectively. Generate air-fuel mixture by utilizing the air. This makes it possible to widely use the space of the combustion chamber 6 to form a homogeneous and thin air-fuel mixture, and suppress the generation of soot and the like during combustion.

[About temporal separation of fuel injection]
In the present embodiment, an example is shown in which, in addition to the above-described spatial separation of fuel injection, the fuel injection is also separated temporally to more effectively use the air in the combustion chamber 6. FIG. 5 is a time chart showing an example of fuel injection timing from the injector 15 to the cavity 5C and a heat release rate characteristic H at that time. The fuel injection operation by the injector 15 is controlled by a fuel injection control unit 71 (see FIG. 7) described later. The fuel injection control unit 71 (divided injection control unit) performs a pre-stage injection that injects fuel at a predetermined first timing and a post-stage injection that injects fuel at a second timing later than the pre-stage injection per cycle. Let it run.

In the present embodiment, an example in which the fuel injection control unit 71 causes the injector 15 to execute the pre-injection P1 as the front-stage injection and the main injection P2 as the rear-stage injection, respectively. The main injection P2 is fuel injection executed at the timing (second timing) when the piston 5 is located near the compression top dead center (TDC). FIG. 5 shows an example in which the main injection P2 is executed at a timing slightly retarded from TDC. The pre-injection P1 is a fuel injection that is executed at a timing (first timing) earlier than the main injection P2 and earlier than TDC. In the present embodiment, an example is shown in which the pre-injection P1 is divided into the advance-side first pre-injection P11 and the retard-side second pre-injection P12.

FIG. 5 shows an example in which the first pre-injection P11 is executed during the crank angle −CA16 to −CA12. The fuel injection rate peak value is the same in the first pre-injection P11 and the main injection P2, but the fuel injection period is set longer in the former. The second pre-injection P12 is a small amount of fuel injection executed between the first pre-injection P11 and the main injection P2. This second pre-injection P12 is executed for the purpose of reducing noise by reducing the valley portion between the peaks in the heat release rate characteristic H (valley portion near the crank angle CA2 to 3 deg) as much as possible. The 2nd pre-injection P12 may be omitted.

The fuel injection directed to the connecting portion 53 is executed during the first pre-injection P11. The main injection P2 is performed after the fuel (fuel mixture) injected in the first pre-injection P11 is spatially separated into the lower first cavity portion 51 and the upper second cavity portion 52 as described above. , The injection injected between the separated upper and lower air-fuel mixtures. This point will be described with reference to FIG. FIG. 6 is a diagram schematically showing the state of generation of the air-fuel mixture in the combustion chamber 6 at the timing when the main injection P2 ends.

The injected fuel of the first pre-injection P11 is mixed with the air in the combustion chamber 6 to form an air-fuel mixture, and is blown onto the connecting portion 53. As shown in FIG. 6, the air-fuel mixture is separated into a lower air-fuel mixture M11 heading for the first cavity portion 51 and an upper air-fuel mixture M12 heading for the second cavity portion 52 by blowing on the connecting portion 53. .. This is the above-mentioned spatial separation of the air-fuel mixture. The main injection P2 includes two separated air-fuel mixtures after the fuel (air-fuel mixture) injected in the pre-injection P1 enters the spaces of the first and second cavities 51 and 52 and is spatially separated. This is an injection executed to form a new air-fuel mixture by utilizing the air remaining in the space between them.

Further description will be added based on FIG. At the execution timing of the main injection P2, the piston 5 is at the position of approximately TDC, so the fuel of the main injection P2 is injected toward a position slightly below the connecting portion 53. The lower mixture M11 and the upper mixture M12 of the first pre-injection P11, which have been previously injected, enter the first cavity portion 51 and the second cavity portion 52, respectively, and are mixed with the air in the respective spaces to be diluted. Is in progress. Immediately before the main injection P2 is started, unused air (air that is not mixed with fuel) is present between the lower air-fuel mixture M11 and the upper air-fuel mixture M12. The egg shape of the first cavity portion 51 contributes to the formation of such an unused air layer. The injected fuel of the main injection P2 enters between the lower mixture M11 and the upper mixture M12, and is mixed with the unused air to become the second mixture M2. This is the temporal separation of fuel injection. As described above, in the present embodiment, the combustion in which the air existing in the combustion chamber 6 is effectively used can be realized by spatially and temporally separating the fuel injection.

[Control configuration]
FIG. 7 is a block diagram showing a control configuration of the diesel engine system. The engine system of the present embodiment is comprehensively controlled by the processor 70 (fuel injection control device for diesel engine). The processor 70 is composed of a CPU, ROM, RAM and the like. Detection signals from various sensors mounted on the vehicle are input to the processor 70. In addition to the sensors SN1 to SN9 described above, the vehicle has an accelerator opening sensor SN10 that detects an accelerator opening, an atmospheric pressure sensor SN11 that measures the atmospheric pressure of the traveling environment of the vehicle, and a temperature of the traveling environment of the vehicle. And an outside air temperature sensor SN12 for measuring

The processor 70 includes the crank angle sensor SN1, the water temperature sensor SN2, the air flow sensor SN3, the intake temperature sensor SN4, the intake pressure sensor SN5, the intake O ₂ sensor SN6, the injection pressure sensor SN7, the exhaust O ₂ sensor SN8, and the differential pressure sensor SN9. , The accelerator opening sensor SN10, the atmospheric pressure sensor SN11, and the outside air temperature sensor SN12 are electrically connected. Information detected by these sensors SN1 to SN12, namely, crank angle, engine speed, engine water temperature, intake flow rate, intake temperature, intake pressure, intake oxygen concentration, injection pressure of injector 15, exhaust oxygen concentration, accelerator opening. , Outside air temperature, atmospheric pressure, etc. are sequentially input to the processor 70.

The processor 70 controls each part of the engine while performing various determinations and calculations based on the input signals from the sensors SN1 to SN12 and others. That is, the processor 70 is electrically connected to the injector 15 (fuel pressure regulator 16), the throttle valve 32, the EGR valve 45, and the like, and outputs a control signal to each of these devices based on the result of the above calculation. To do.

The processor 70 functionally includes a fuel injection control unit 71 (divided injection control unit, setting unit, calculation unit) that controls the operation of the injector 15, and a storage unit 77. The fuel injection control unit 71 has a predetermined timing (first timing) before the compression top dead center in each cycle of an operation region (hereinafter referred to as a PCI region) in which at least premixed compression ignition (Premixed Compression Ignition) combustion is applied. ), a pre-injection (pre-stage injection) for injecting fuel, and a main injection (post-stage injection) for injecting fuel at the timing when the piston 5 is located near the compression top dead center (second timing later than the pre-stage injection). , And causes the injector 15 to execute.

The fuel injection control unit 71 executes a predetermined program, whereby the operating state determination unit 72, the injection pattern selection unit 73 (divided injection control unit), the injection setting unit 74 (setting unit), the prediction unit 75, and the correction unit. 76 is functionally provided.

The operating state determination unit 72 determines the operating state of the engine body 1 from the engine speed based on the detected value of the crank angle sensor SN1 and the engine load based on the opening information of the accelerator opening sensor SN10. This determination result is used to determine whether or not the current operating region is the PCI region in which the pre-injection P1 and the main injection P2 are executed.

The injection pattern selection unit 73 sets the pattern of fuel injection from the injector 15 according to various conditions. At least in the PCI region, the injection pattern selection unit 73 sets a fuel injection pattern including the pre-injection P1 (pre-stage injection) and the main injection P2 (post-stage injection).

The injection setting unit 74 sets the fuel injection amount or fuel injection timing from the injector 15 according to various conditions. In the above PCI region, the injection setting unit 74 causes the first peak, which is the rising peak of the heat generation rate in the combustion chamber 6 associated with the pre-injection P1 (pre-stage injection), and the combustion associated with the main injection P2 (post-stage injection). The pre-injection P1 (particularly, in the present embodiment, the first pre-injection is performed so that the target heat release rate characteristic in which the ratio with the second peak, which is the rising peak of the heat derivation rate in the chamber 6, is a predetermined target value is obtained. The fuel injection amount or fuel injection timing in injection P11) is set. FIG. 8A shows an example of the target heat release rate characteristic Hs. In the illustrated target heat release rate characteristic Hs, the first peak appears near the crank angle=4 degrees and the second peak appears near the crank angle=8 degrees. By setting the target heat release rate characteristic Hs to a characteristic that can suppress combustion noise such as diesel knock noise most, the combustion noise can be minimized.

Further, the injection setting unit 74 determines that the peak interval between the timing at which the first peak occurs and the timing at which the second peak occurs causes the pressure wave resulting from the combustion of the fuel in the pre-injection P1 (first pre-injection P11). The fuel injection amount from the injector 15 or the fuel injection timing is set so that the amplitude of the fuel injection and the amplitude of the pressure wave resulting from the combustion of the fuel of the main injection P2 cancel each other. As a result, the combustion noises generated by the first pre-injection P11 and the main injection P2 cancel each other out, and the combustion noise can be suppressed to an extremely low level. These will be described in detail later.

Here, in order to obtain the target heat release rate characteristic Hs, it is possible to adjust not only the first pre-injection P11 but also the fuel injection amount or fuel injection timing of the second pre-injection P12 and the main injection P2. However, in the present embodiment, the first pre-injection P11 is the control target, and the first peak (ignition timing) is the control target.

When the fuel injection is performed by dividing into the pre-stage injection and the post-stage injection as in the present embodiment, the ignition timing and the like are determined only by the execution state of the pre-stage injection. If the mode of the first-stage injection is determined, the combustion accompanying the second-stage injection will be a combustion with relatively high robustness. Therefore, by appropriately changing the fuel injection amount or the fuel injection timing of the first pre-injection P11 that injects a relatively large amount of fuel at the earliest timing, the ratio between the first peak and the second peak becomes the target value. It is possible to accurately perform the control of approaching and the control of setting the interval between the first and second peaks. If the mode of the main injection P2 (injection amount or injection timing) is changed initiatively, the combustion period may shift as a whole, which may affect fuel efficiency and torque.

The predicting unit 75 determines the fuel injection amount or fuel injection timing of the pre-injection P1 set by the injection setting unit 74 based on the target heat release rate characteristic Hs, and a predetermined combustion environment factor that affects combustion in the combustion chamber 6. Based on the above, processing for predicting at least one of the generation time of the first peak and the peak value of the first peak in the current condition is performed. For this prediction, the prediction unit 75 uses a predetermined prediction model formula (described later based on FIGS. 12 and 13). The generation timing and the peak value of the first peak can be adjusted by feedback control based on the detection results of the various sensors SN1 to SN12. However, in the feedback control, a diesel knock noise may actually occur, which may cause a driver discomfort. Therefore, the predicting unit 75 predicts the deviation of the generation time or peak value of the first peak from the target value in the target heat release rate characteristic Hs by the feedforward method using the prediction model formula.

The correction unit 76 corrects the fuel injection amount or the fuel injection timing of the first pre-injection P11 set by the injection setting unit 74 based on the occurrence timing or peak value of the first peak predicted by the prediction unit 75. That is, the correction unit 76 eliminates the deviation between the predicted value of the generation time and the peak value of the first peak obtained by the prediction unit 75 with reference to the combustion environment factor and the target value in the target heat release rate characteristic Hs. The fuel injection amount or the fuel injection timing is corrected so as to make it. That is, the correction for eliminating the deviation is performed before the diesel knock sound is generated.

The storage unit 77 stores a prediction model formula used when the prediction unit 75 performs a predetermined calculation process. The prediction model formula is a formula for predicting the variation of the generation timing of the first peak or the peak value of the first peak with respect to the target heat release rate characteristic Hs based on a predetermined combustion environment factor. The combustion environment factor is, for example, directly or indirectly derived from the measured values of the sensors SN1 to SN12, the wall surface temperature of the cylinder block 3, the cylinder pressure, the cylinder temperature, the cylinder oxygen concentration, the engine load. And so on.

[Two-stage heat generation rate and noise cancellation]
FIG. 8(B) is a diagram showing peaks and height ratios of the heat release rates generated by the combustions of the pre-injection P1 (first pre-injection P11) and the main injection P2, and the intervals between these peaks. The heat release rate characteristic H shown in FIG. 8B is a more schematic view of the heat release rate characteristic H shown in FIG.

The heat release rate characteristic H is a characteristic that is closely related to the rate of increase of the combustion pressure in the combustion chamber 6, and is determined by the pre-combustion portion HA that is a mountain portion generated by the combustion accompanying the pre-injection P1 and the combustion accompanying the main injection P2. It has a post-combustion portion HB that is a mountain portion that occurs. The first-stage combustion portion HA and the second-stage combustion portion HB have a first peak HAp and a second peak HBp that have the highest heat release rates in the respective mountain portions. Corresponding to these first and second peaks HAp and HBp, two peaks also occur in the rate of change (rate of increase) in combustion pressure.

FIG. 8 shows an example in which the value of the first peak HAp is smaller than the value of the second peak HBp. If the value of the first peak HAp or the second peak HBp is outstandingly high, combustion noise will increase due to this. Therefore, it is desirable to control the heat generation rates of the front-stage combustion portion HA and the rear-stage combustion portion HB so that the height ratios of the first peak HAp and the second peak HBp are made as uniform as possible.

The interval between the time when the first peak HAp occurs and the time when the second peak HBp occurs also has a great influence on the suppression of combustion noise. If the interval is set to an interval in which the amplitude of the pressure wave (sound wave) resulting from the combustion of the front-stage combustion portion HA and the amplitude of the pressure wave resulting from the combustion of the rear-stage combustion portion HB cancel each other out, it is expressed by the frequency effect. The generated pressure wave (combustion noise) can be suppressed. This point will be further described with reference to FIG.

FIGS. 9A to 9C are schematic diagrams for explaining the effect of canceling combustion noise. In FIG. 9(A), a first-stage combustion portion HA having a first peak HAp having a certain heat generation rate and a second-stage combustion portion HB having a second peak HBp having the same heat generation rate as the first peak HAp. And are schematically depicted by solid lines. The interval between the first peak HAp and the second peak HBp is set to the first interval In1 in which the pressure waves resulting from each combustion cancel each other out. Further, in FIG. 9(A), as a comparative example, a second-stage combustion portion HB1 having a peak HAp1 having the same height as the first peak HAp but occurring in a second interval In2 longer than the first interval In1 is provided as a comparative example. The front-stage combustion portion HA1 having a peak HAp1 higher than the first peak HAp is shown.

FIG. 9B shows a front pressure wave EAw generated due to the combustion of the front combustion portion HA and a rear pressure wave EBw generated due to the combustion of the rear combustion portion HB. Since the first peak HAp and the second peak HBp have the same peak height, the amplitude of the front pressure wave EAw and the amplitude of the rear pressure wave EBw are the same. In addition, the first interval In1 is set to 1/2 times the cycle of the front pressure wave EAw and the rear pressure wave EBw. In this case, the former-stage pressure wave EAw and the latter-stage pressure wave EBw have opposite phases and interfere with each other so as to cancel each other, and the amplitude of the combined wave EM becomes zero. That is, the combustion noise is canceled by the cancellation effect.

On the other hand, when the second interval In2 is placed with respect to the front-stage combustion portion HA and the rear-stage combustion portion HB1 of the comparative example is generated, the front-stage pressure wave EAw and the rear-stage pressure wave EBw are not in completely opposite phases. In this case, the canceling effect of both the pressure waves EAw and EBw shown in FIG. 9B is diminished, and the combined wave EM may be amplified in reverse. For example, when both the pressure waves EAw and EBw have the same phase, the combined wave EM has a large amplitude by adding the both pressure waves EAw and EBw. That is, combustion noise increases.

The canceling effect becomes maximum when the amplitudes of both pressure waves EAw and EBw are the same. FIG. 9C shows the front pressure wave EAw1 generated due to the combustion of the front combustion portion HA1 of the comparative example and the above-mentioned rear pressure wave EBw. Since the amplitude of the front stage pressure wave EAw1 is larger than the amplitude of the rear stage pressure wave EBw, even if the first interval In1 is adopted and the both are in opposite phases, the combined wave EM has an amplitude corresponding to the difference. Therefore, the effect of canceling combustion noise is reduced.

In view of the above points, in order to reduce the difference between the first peak HAp and the second peak HBp as much as possible, and to have an interval in which the front pressure wave EAw and the rear pressure wave EBw cancel each other, It is desirable that the injection setting unit 74 controls the fuel injection operation of the injector 15. That is, the target heat release rate characteristic Hs that can exert the effect of canceling the combustion noise is set, and the pre-injection P1 or the main injection P2 (particularly the first pre-injection P11 is performed so that the combustion that achieves the target heat release rate characteristic Hs is performed. It is desirable to set the fuel injection amount or the fuel injection timing in (1).

[Basic form of correction of heat release rate characteristics]
Subsequently, a basic form of correction of the heat release rate characteristic by the correction unit 76 will be described. 10A and 10B are graphs showing a basic form of correction for making the predicted heat release rate characteristic Hp predicted by the predicting unit 75 closer to the target heat release rate characteristic Hs. First, FIG. 10A shows an example in which the peak values of the first peak HAp and the second peak HBp are corrected to target values. When correcting the peak value, the injection amount of the first pre-injection P11 is corrected in the mode that simplifies the control most.

The heat release rate characteristic H1 shown by the solid line in FIG. 10(A) has a first peak HAp1 having a certain peak value in the front combustion portion HA and a second peak HBp1 having a certain peak value in the second combustion portion HB. .. A case where such a heat release rate characteristic H1 is corrected to a heat release rate characteristic H2 shown by a dotted line will be exemplified. The first and second peaks HAp2 and HBp2 included in the heat release rate characteristic H2 have peak values larger than the first and second peaks HAp1 and HBp1 included in the heat release rate characteristic H1. It is assumed that the injection amounts of the pre-injection P1 and the main injection P2 indicated by the solid line are the injection amounts capable of executing the combustion along the heat release rate characteristic H1.

In this case, the correction unit 76 performs control to increase the injection amount of the first pre-injection P11 to the injection amount of the injection P11a shown by the dotted line in the drawing (the injection timing is constant). As a result, the peak value of the first peak of the pre-stage combustion portion HA can be increased from HAp1 to HAp2. Further, following this, the peak value of the second peak of the latter combustion portion HB can also be increased from HBp1 to HBp2. On the contrary, when lowering the first peak HAp1, it suffices to perform control to reduce the injection amount of the first pre-injection P11. In this way, by correcting the injection amount of the first pre-injection P11, it is possible to adjust the slopes of the first-stage and second-stage combustion portions HA and HB and the peak values of the first and second peaks HAp1 and HBp1, which in turn are caused by the combustion. The amplitude (sound pressure) of the pressure wave can be controlled.

The heat release rate characteristics H1 and H2 can be replaced with the target heat release rate characteristic Hs and the predicted heat release rate characteristic Hp. For example, the solid heat release rate characteristic H1 in FIG. 10A is the target heat release rate characteristic Hs and the heat release rate characteristic H2 stored in the storage unit 77 are predicted by the predicting unit 75. The rate characteristic is Hp. The injection amounts of the pre-injection P1 and the main injection P2 shown by the solid line are the injection amounts that can execute combustion along the predicted heat release rate characteristic Hp if the environmental condition (combustion environment factor) is a steady condition. Suppose However, under the current environmental conditions, it is assumed that the prediction unit 75 predicts that combustion such as the predicted heat release rate characteristic Hp will occur when the injection amount is adopted. That is, it is a case where the peak value of the first peak HAp2 predicted by the prediction unit 75 is deviated from the peak value of the first peak HAp1 based on the target heat release rate characteristic Hs. In this case, the correction unit 76 corrects the injection amount of the first pre-injection P11 so that the predicted first peak HAp2 approaches the target first peak HAp1, that is, the deviation is eliminated. In this case, the injection amount is reduced from P11a to P11.

Next, FIG. 10B shows an example in which the peak interval between the first peak HAp and the second peak HBp is corrected to the target interval. When correcting the peak interval, the injection timing of the first pre-injection P11 is corrected in the mode that simplifies the control most.

The heat release rate characteristic H1 shown in FIG. 10(B) has a certain peak interval a1 between the first peak HAp1 of the pre-combustion portion HA and the second peak HBp1 of the post-combustion portion HB. A case where such a heat release rate characteristic H1 is corrected to a heat release rate characteristic H2 will be exemplified. The peak interval a2 between the first and second peaks HAp2, HBp2 of the heat release rate characteristic H2 is shorter than the peak interval a1 of the heat release rate characteristic H1. It is assumed that the injection amounts of the pre-injection P1 and the main injection P2 indicated by the solid line are the injection amounts capable of executing the combustion along the heat release rate characteristic H1.

In this case, the correction unit 76 performs control to delay the injection timing of the first pre-injection P11 to the injection timing P11b shown by the dotted line in the figure (the injection amount is constant). This makes it possible to retard the timing of occurrence of the first peak of the front-stage combustion portion HA from HAp1 to HAp2. Along with this, the timing of occurrence of the second peak HBp2 in the latter-stage combustion portion HB also changes. Here, an example is shown in which the angle is advanced from HBp1 to HBp2, so that the peak interval a2 is shorter than the peak interval a1. On the contrary, when advancing the first peak HAp1, it is sufficient to perform control to advance the injection timing of the first pre-injection P11 to the injection timing P11c shown by the dotted line in the figure. In this way, by correcting the injection timing of the first pre-injection P11, it is possible to adjust the slopes of the first-stage and second-stage combustion portions HA and HB and the peak intervals of the first and second peaks HAp1 and HBp1 and, by extension, the combustion occurs. It is possible to control the frequency of the pressure wave so that the cancellation effect shown in FIG. 9 is produced.

It is assumed that the heat release rate characteristics H1 and H2 in FIG. 10B are the target heat release rate characteristic Hs and the predicted heat release rate characteristic Hp, respectively. Then, the injection amounts of the pre-injection P1 and the main injection P2 shown by the solid line are the injection amounts capable of executing the combustion along the predicted heat release rate characteristic Hp if the environmental conditions (combustion environmental factors) are normal conditions. Suppose However, under the current environmental conditions, it is assumed that the prediction unit 75 predicts that combustion such as the predicted heat release rate characteristic Hp will occur when the injection amount is adopted. That is, the generation time of the first peak HAp2 predicted by the prediction unit 75 is shifted from the generation time of the first peak HAp1 based on the target heat generation rate characteristic Hs. In this case, the correction unit 76 performs the injection of the first pre-injection P11 so that the predicted generation timing of the first peak HAp2 approaches the target generation timing of the first peak HAp1, that is, the deviation is eliminated. Correct the timing amount. In this case, the injection timing is advanced from P11 to P11c.

The patterns shown in FIGS. 10A and 10B are the basic forms of the correction of the heat release rate characteristic, and in practice, both patterns may be used in combination. For example, in order to set the peak values of the first peak HAp and the second peak HBp to target values, not only the injection amount of the pre-injection P1 but also the injection timing may be changed. Similarly, not only the injection timing of the pre-injection P1 but also the injection amount may be changed in order to set the peak generation timing as the target value. Such an injection control example is also shown in specific examples of FIGS. 14 and 15 described later.

[About prediction model formula]
Next, a specific example of the prediction model formula used by the prediction unit 75 will be described. FIG. 11 is a schematic diagram for explaining combustion environment factors that affect the achievement of the target heat release rate characteristic. It is assumed that the target heat release rate characteristic Hs as shown in the upper left of FIG. 11 is stored in the storage unit 77. If the combustion environment factor is within the assumed steady range, the target heat generation is performed by executing the pre-injection P1 (pre-stage injection) and the main injection P2 (post-stage injection) at a predetermined reference injection amount and reference injection timing. Combustion along the rate characteristic Hs can be realized in the combustion chamber 6.

However, when the combustion environment factor is out of the steady range, the in-cylinder state quantity of the combustion chamber 6 changes. As a result, the target heat release rate characteristic Hs may not be obtained even if the reference injection amount and the reference injection timing are adopted. For example, premature ignition or ignition delay occurs as shown in the lower left of FIG. Premature ignition is a case where the pre-combustion portion HA has a high heat release rate as a result of the ignition of the air-fuel mixture becoming earlier than the desired timing. The ignition delay is a case in which the ignition of the air-fuel mixture is delayed from the intended timing and, as a result, the pre-stage combustion portion HA almost disappears.

The main combustion environment factors that affect the in-cylinder state quantity are, as listed in the right column of FIG. 11, wall surface temperature of the cylinder block 3, cylinder pressure, cylinder temperature, cylinder oxygen concentration, engine rotation speed. Number (load), fuel injection amount, injection timing, injection pressure. For example, the wall surface temperature, the in-cylinder pressure, and the in-cylinder temperature vary depending on the outside air temperature, the outside air pressure, and the engine cooling water temperature. Further, the in-cylinder oxygen concentration changes depending on the amount of EGR gas taken into the combustion chamber 6 and the like. Further, the combustion environment factor may also change due to a transient factor (such as a transient shift in intake air temperature or supercharging pressure) when the operating state changes significantly.

FIG. 12 is a diagram for explaining a model formula for predicting the generation timing of the first peak HAp of the upstream combustion portion HA in the heat release rate characteristic H. As shown in FIG. 12A, the generation timing of the first peak HAp is the period from the injection start timing of the pre-injection P1 (the first pre-injection P11 in this embodiment) to the occurrence of the first peak HAp. It is predicted by "peak delay".

FIG. 12B shows the prediction model formula of the peak delay. Here, the characteristics of each factor are expressed by an Arrhenius type prediction formula. On the right side of the equation, in addition to the coefficient A, the fuel injection amount, injection timing, injection pressure, in-cylinder pressure, in-cylinder temperature, wall surface temperature, in-cylinder oxygen concentration, and engine The number of rotations is listed as an item. The coefficient A is an intercept that changes the value on the right side as a whole. The indexes B to I attached to each item on the right side show the sensitivity of the item, and a plus sign means proportional and a minus sign means inversely proportional. The engine oil temperature and the like may be added to the above items.

FIG. 12C is a tabular diagram showing the calibration result of the prediction model formula, showing the value of the coefficient A and the values of the indexes BI. This result shows that the parameters related to the injection such as the fuel injection amount, the injection timing and the injection pressure are fixed to the reference values corresponding to the target heat release rate characteristic Hs, while the outside air temperature, the outside air pressure, the engine cooling water temperature and the EGR gas are fixed. A large amount of data is obtained by varying the state quantity such as the quantity, and the multiple regression analysis associates the variation of the combustion state (heat release rate) with the in-cylinder state variation. It has been confirmed that the predicted difference between the prediction result of the "peak delay" (the crank angle at which the first peak HAp occurs) by the prediction model formula and the actually measured "peak delay" is ±2 deg or less.

Next, the prediction model formula of the peak height (peak value) of the first peak HAp will be described with reference to FIG. The peak height of the first peak HAp can be expressed by a combination of the “peak delay” prediction model formula shown in FIG. 12 and a known combustion efficiency prediction model formula. 13A and 13B are diagrams showing factors that affect the peak height (the peak height of the pre-stage combustion) resulting from the injection (pre-injection in this embodiment).

As shown in FIG. 13A, even if the combustion efficiency in the combustion chamber 6 is constant, the peak height of the heat release rate characteristic fluctuates due to the fluctuation of the “peak delay”. For example, when the injection timing is retarded as P11→P12→P13 (variation of “peak delay”), even if the combustion efficiency is constant, the peak height fluctuates to be higher as h1→h2→h3. .. Further, as shown in FIG. 13B, even if the “peak delay” is fixed, the peak height of the heat release rate characteristic changes when the combustion efficiency changes. For example, even if the injection timings are set to the same P11, P12, and P13, if the combustion efficiency becomes good in the order of P11→P12→P13, the peak height fluctuates to become higher, h1→h2→h3.

FIG. 13C shows a prediction model formula for the peak height. Similar to FIG. 12B, the characteristics of each factor are expressed by an Arrhenius type prediction formula. On the right side of the equation, in addition to the coefficient A, the above-mentioned “peak delay” and combustion efficiency, and the engine speed and injection amount that affect the absolute value of the peak height are listed as items. FIG. 13D is a table format showing the calibration result of the prediction model formula of FIG. 13C. FIG. 13D shows the value of the coefficient A and the values of the indexes B to E obtained by multiple regression analysis of a large number of data obtained by waving the values of the respective items. It has been confirmed that the prediction difference between the “peak height” prediction result (heat generation rate at which the first peak HAp occurs) by the prediction model formula and the actually measured “peak height” is ±2 deg or less.

The prediction model formulas illustrated in FIGS. 12B and 13C are stored in the storage unit 77 in advance. The prediction unit 75 reads the prediction model formula from the storage unit 77 and performs a prediction calculation of the occurrence time and peak value of the first peak HAp under the current environmental conditions.

[Control when the opening of the EGR valve is changed]
Next, in the fuel injection control executed by the fuel injection control unit 71 of the processor 70, the control when the opening degree of the EGR valve 45 is changed will be described.

First, the control when the opening degree of the EGR valve 45 is reduced will be described with reference to FIGS. 14(A) to 14(C) to FIG. FIG. 14A shows the heat release rate characteristic H in the combustion chamber 6 in the setting (base setting) before the opening degree of the EGR valve 45 is changed.

In this base setting, the injection timings and injection amounts of the pre-injection P1 and the main injection P2 are set so that the combustion sound frequency of the pre-injection P1 and the combustion frequency of the main injection P2 cancel each other out and the combustion noise is suppressed. ing. That is, in the base setting, the time interval (peak interval) from the generation of the heat release rate peak HAp (first peak) by the pre-injection P1 to the generation of the heat release rate peak HBp (second peak) by the main injection P2 is: The combustion sound is set to be approximately 1/2 of the cycle (the combustion sound of the combustion by the pre-injection P1 and the combustion sound of the combustion by the main injection P2 have opposite phases), and the heat from each injection is set. The peak heights of the occurrence rates (heights of the peaks HAp and HBp) are set so as not to be greatly different values. As a result, the combustion noise of the pre-injection P1 and the combustion noise of the main injection P2 cancel each other out, and the combustion noise is reduced (see FIG. 9).

The fuel injected in the pre-injection P1 performs premixed compression ignition combustion, and is injected when the in-cylinder temperature (the temperature of the combustion chamber 6) has not risen sufficiently, and the fuel is injected in the combustion chamber after injection. Due to the temperature rise due to compression of No. 6, it ignites and burns. Therefore, in the combustion by the pre-injection P1, the timing (crank angle) at which the peak HAp of the heat generation rate appears has a delay (peak delay) from the timing (crank angle) of fuel injection. On the other hand, the main injection P2 is injected near the compression top dead center (TDC) of the engine, and is injected after the temperature in the combustion chamber 6 has risen sufficiently, and the injected fuel is diffused and burned. It will be.

From this state, when the accelerator is depressed to accelerate the vehicle, the target fuel injection amount increases due to the increase in the target torque, and the oxygen concentration required for combustion increases. Therefore, in order to increase the oxygen concentration in the combustion chamber 6, the opening degree of the EGR valve 45 of the EGR device 44 is reduced and the inflow amount of EGR gas into the combustion chamber 6 is limited. As a result, the oxygen concentration in the combustion chamber 6 increases, while the inflow of high-temperature EGR gas is restricted, so that the gas temperature in the combustion chamber 6 (cylinder gas temperature) decreases.

When the opening degree of the EGR valve 45 is reduced in this way, the oxygen concentration in the combustion chamber 6 does not suddenly increase to a concentration that matches the changed target fuel injection amount, but gradually increases. Therefore (the oxygen concentration change is delayed by the distance of the intake passage 30 between the EGR valve 45 and the combustion chamber 6), the fuel injection with the increased target fuel injection amount is performed before the oxygen concentration becomes sufficiently high. In order to prevent the generation of unburned gas due to the injection, it is started at a time interval after the opening degree of the EGR valve 45 is changed. As a result, during the period from when the opening degree of the EGR valve 45 is reduced to when the fuel injection control with the new target fuel injection amount is started, the parameters such as the fuel injection amount and the engine speed remain constant and the combustion is performed. A situation occurs in which only the oxygen concentration in the chamber 6 and the in-cylinder gas temperature gradually change.

In the period immediately after changing the opening degree of the EGR valve 45, the peak delay from the injection start of the pre-injection P1 to the appearance of the heat release rate peak HAp is as shown in FIG. 14(B). It becomes longer than before the EGR valve opening degree change shown in A).

More specifically, when the opening degree of the EGR valve 45 decreases, the oxygen concentration in the combustion chamber 6 rises, while the gas temperature (cylinder gas temperature) in the combustion chamber 6 falls, but the oxygen concentration rises at the peak. It acts to shorten the delay, and the decrease in in-cylinder gas temperature acts to lengthen the peak delay. This relationship is known from the above-mentioned Arrhenius type prediction formula (see FIGS. 12 and 13).

FIG. 15 is a graph showing the relationship of the change rate of the ignition delay (peak delay) with respect to the change rates of the oxygen concentration and the in-cylinder gas temperature, which are calculated using the Arrhenius type prediction formula. As shown in the graph b in FIG. 15, it can be seen that the ignition delay increases as the in-cylinder gas temperature decreases, and as shown in the graph c in FIG. 15, the ignition delay decreases as the oxygen concentration increases.

In this case, as can be seen by comparing the slopes of the graph b and the graph c, the influence of the decrease in the in-cylinder gas temperature on the ignition delay is larger than the influence of the increase in the oxygen concentration on the ignition delay, so the opening of the EGR valve 45 is small. When the inflow amount of the EGR gas is reduced, the peak delay becomes longer due to the influence of the lowering of the in-cylinder gas temperature, which has a greater influence.

As described above, when the opening degree of the EGR valve 45 is made small, the peak delay in the injection of the pre-injection P1 becomes large, whereas the timing of the peak generation of combustion by the main injection P2, which is diffusion combustion, fluctuates greatly. Therefore, the peak interval (time interval) of the heat release rate peaks of the combustion by the pre-injection P1 and the main injection P2 varies from before the EGR valve opening degree change. For this reason, the combustion noise of the combustion by the pre-injection P1 and the combustion noise of the combustion by the main injection P2 are no longer in a relationship of canceling each other (a relationship of being shifted by 1/2 cycle and having an opposite phase). It becomes impossible to control.

On the other hand, in the present control, the injection timing and the injection amount of the pre-injection P1 and the main injection P2 are corrected to cope with this. More specifically, as a correction of the injection timing, first, as shown in FIG. 14C, by advancing the injection timing of the pre-injection P1 from the base setting while maintaining the timing of the main injection P2 in the base setting, The timing at which the heat release rate peak HAp of combustion due to the pre-injection P1 appears is retarded so as to approach the timing before the change of the EGR valve opening. In this case, the advance amount of the injection start timing of the pre-injection P1 is set such that the advance amount of the peak of the heat release rate due to the advance angle of the injection timing of the pre-injection is set to the opening degree of the EGR valve 45. It is set so as to be smaller than the retard amount of the peak timing of the heat release rate due to the pre-injection, and the advance amount of the pre-injection is prevented from becoming excessive.

As a result, the peak interval (time interval) of the heat release rate peaks of the combustion by the pre-injection P1 and the main injection P2 is brought closer to before the EGR valve opening degree is changed, and the combustion sound frequency of the combustion by the pre-injection P1 and the combustion by the main injection P2 are made. The combustion sound frequencies of (1) and (2) are returned to the relationship of canceling each other (the relationship of being shifted by 1/2 cycle and having opposite phases). On the other hand, since the injection timing of the main injection P2 is not changed, the diffusion combustion by the main injection P2 has appropriate characteristics as scheduled in the base setting.

As described above, in the present control, the control for advancing the injection timing of the pre-injection P1 is performed, but with this alone, the state in which the peak delay is increased is maintained and the high heat release rate peak HAp due to the pre-injection P1 is maintained. This is lower than before the EGR valve opening was changed. Therefore, the height of the heat release rate peak HAp by the pre-injection P1 becomes lower than the height of the heat release rate peak HBp by the main injection P2, which is insufficient to cancel the combustion noise of the combustion by the main injection P2. It has a large size.

FIG. 16 shows the relationship (relationship calculated by the Arrhenius type prediction formula) of the change rate of the peak height of the heat generation rate with respect to the change rate of the peak delay. As shown in the graph e of FIG. 16, when the peak delay increases, the peak height of the heat release rate decreases.

Therefore, in the present control, in addition to the correction for advancing the injection timing of the pre-injection P1, as the correction for the injection amount, the injection amount of the pre-injection P1 is increased by a predetermined amount, and the injection amount of the main injection P2 is increased. Correction is performed to reduce the increase amount of P1. In this case, the increase amount of the injection amount of the pre-injection P1 does not exceed the decrease amount of the heat generation rate peak due to the advance of the injection timing of the pre-injection P1. Within the range, the increase amount of the heat release rate peak resulting from the increase amount is set to be substantially equal to the fall amount of the heat release rate peak resulting from the advance of the injection timing of the pre-injection P1.

By such correction of the injection amount, while maintaining the total injection amount of the pre-injection P1 and the main injection P2 constant, the height of the heat release rate peak HAp due to the pre-injection P1 is increased to the heat release rate peak HBp due to the main injection P2. You can get closer to that. That is, the amplitude of the combustion sound of the combustion by the pre-injection P1 and the amplitude of the combustion by the main injection P2 can be made close to each other. Further, since the increase in the injection amount of the pre-injection P1 is also prevented from becoming excessively large, the peak of the heat release rate does not become higher than that before the change of the EGR valve opening, and the peak of the heat release rate before the change of the EGR valve opening Can be appropriately approached to the height of.

Note that the graph d in FIG. 16 shows the relationship between the rate of change in the peak height of the heat release rate and the rate of change in the injection amount of pre-injection (the relationship calculated by the Arrhenius-type prediction equation). As shown in the figure, the peak height of the heat release rate increases as the pre-injection amount increases.

As described above, according to the present control, when the opening degree of the EGR valve 45 is reduced, the injection of the new target fuel injection amount is started (the control based on the new target fuel injection amount is started). During the period of, while maintaining the injection timing of the main injection P2, the injection timing of the pre-injection P1 is advanced, the injection amount of the pre-injection P1 is increased by a predetermined amount, and the injection amount of the main injection P2 is changed to that of the pre-injection P1. Since the amount of increase is decreased, even after the EGR valve opening is changed, the combustion noise of the combustion by the pre-injection P1 and the combustion noise of the combustion by the main injection P2 can be offset from each other, and the combustion noise can be appropriately adjusted. Suppressed. Further, the heat release rate characteristics that combine the pre-injection P1 and the main injection P2 can be made close to before the EGR valve opening is changed, and since the area change of the heat release rate waveform can be suppressed, deterioration of thermal efficiency can also be suppressed. it can.

FIG. 17 is a timing chart showing the control when the opening degree of the EGR valve 45 is reduced. As shown in the timing chart, this control is executed at the timing when the target fuel injection amount is increased and the opening degree of the EGR valve 45 is decreased as a result of the accelerator being depressed. When the EGR valve opening is reduced, the oxygen concentration in the combustion chamber 6 gradually increases and the in-cylinder gas temperature gradually decreases until the actual injection amount switches to the target fuel injection amount. I will do it. On the other hand, during the period from the change of the EGR valve opening degree to the start of injection at the target fuel injection amount, while advancing the injection timing of the pre-injection while maintaining the timing of the main injection, A control is executed to increase the injection amount by a predetermined amount D and decrease the injection amount of the main injection by the same amount as the predetermined amount D.

Next, control when the opening degree of the EGR valve 45 is increased will be described with reference to FIGS. 18 and 19. In the upper, middle, and lower stages of FIG. 18, the base setting, the EGR gas amount is decreased (when the EGR valve 45 opening is decreased), and the EGR gas amount is increased (the EGR valve 45 opening is set, respectively). The injection timings of the pre-injection P11, the middle-stage injection P12, and the main injection P2 (when increased) are shown.

In this embodiment, the pre-injection P11 and the middle-stage injection P12 are executed as the pre-stage injection. In the middle-stage injection P12, the injected fuel is burned by the combustion heat of the pre-injection P11, the injection amount is small, and the influence on the combustion noise is small. Therefore, in this control, the pre-injection P11 and the main injection P2 are the control targets, and the middle-stage injection P12 is not the control target (the setting is not changed from the base setting).

When the opening degree of the EGR valve 45 is increased, a phenomenon opposite to the case where the opening degree of the EGR valve 45 is decreased occurs. Therefore, the phenomenon is opposite to the case where the EGE valve opening degree is decreased. Control will be executed. More specifically, when the target fuel injection amount is reduced during deceleration, the opening degree of the EGR valve 45 is increased, the oxygen concentration in the combustion chamber 6 is reduced, and the in-cylinder gas temperature rises. The peak delay (ignition delay) from the start of the injection to the appearance of the heat release rate peak is shorter than that before the change of the EGR valve opening degree due to the influence of the rise in the in-cylinder gas temperature, which has a greater effect.

Therefore, in this control, as shown in the lower part of FIG. 18, the injection timing of the pre-injection P11 is retarded while maintaining the injection timing of the main injection P2 (and the middle-stage injection P12). The timing at which the heat release rate peak of combustion appears is close to that before the change of the EGR valve opening. Thereby, the peak interval (time interval) of the heat release rate peaks of the combustion by the pre-injection P11 and the main injection P2 is brought close to before the EGR valve opening degree is changed, and the combustion of the combustion by the pre-injection P1 and the combustion of the combustion by the main injection P2 are performed. The sounds are returned to the relationship of canceling each other (the relationship of being shifted by 1/2 cycle and having opposite phases). In this case, the retard amount of the injection start timing of the pre-injection P1 is the retard amount of the peak generation timing of the heat release rate due to the retard angle of the injection timing of the pre-injection, and the opening degree of the EGR valve 45 is It is set to be smaller than the advance amount of the generation timing of the peak of the heat release rate due to the pre-injection due to the increase in the pre-injection, and the pre-injection retard amount is prevented from becoming excessive.

Further, in this case, if the injection amount of the pre-injection P11 remains unchanged, the height of the heat generation rate peak due to the pre-injection P11 becomes high, so the injection amount of the pre-injection P11 is reduced by a predetermined amount, Correction is performed to increase the injection amount of the main injection P2 by this decrease amount. In this case, the amount of decrease in the injection amount of the pre-injection P1 does not exceed the amount of decrease in the heat generation rate peak resulting from this decrease amount than the amount of increase in the heat generation rate peak resulting from the retardation of the injection timing of the pre-injection P1. Within the range, the decrease amount of the heat release rate peak due to the decrease amount is set to substantially match the increase amount of the heat release rate peak due to the retard of the injection timing of the pre-injection P1.

As a result, while maintaining the total injection amount of the pre-injection P11 and the main injection P2 constant, the height of the heat release rate peak due to the pre-injection P11 is lowered (see the graph d in FIG. 16), and the heat release rate due to the pre-injection P11. The height of the peak can be brought close to the height of the heat release rate peak due to the main injection P2. Further, since the reduction amount of the injection amount of the pre-injection P1 is also prevented from becoming excessively large, the peak of the heat release rate does not become too lower than that before the change of the EGR valve opening degree, and before the change of the EGR valve opening degree. Can be appropriately approximated to the height of.

By the control as described above, even when the opening degree of the EGR valve 45 becomes large, the peak interval and the peak height of the heat release rate of combustion by the pre-injection P11 and the main injection P2 are optimally adjusted. The combustion noise of combustion by the pre-injection P11 and the combustion noise of combustion by the main injection P2 cancel each other out, and the combustion noise is appropriately suppressed. In addition, since the heat release rate characteristics of the pre-injection P11 and the main injection P2 can be brought close to before the EGR valve opening degree is changed, deterioration of thermal efficiency can be suppressed.

FIG. 19 is a timing chart showing the control when the opening degree of the EGR valve 45 becomes large. As shown in the timing chart, this control is executed at a timing when the accelerator depression amount is reduced, the target fuel injection amount is reduced, and the opening degree of the EGR valve 45 is increased. When the EGR valve opening becomes large, the oxygen concentration in the combustion chamber 6 gradually decreases and the in-cylinder gas temperature gradually increases until the actual injection amount is switched to the target fuel injection amount. Go On the other hand, during the period from the change of the EGR valve opening to the start of injection at the target fuel injection amount, the injection timing of the pre-injection is retarded while the injection timing of the pre-injection is retarded while maintaining the timing of the main injection. The control is executed to decrease the predetermined amount D and increase the injection amount of the main injection by the same amount as the predetermined amount D.

Next, with reference to FIG. 20, in the control when the opening degree of the EGR valve 45 becomes large, the control in the case where the calculated advance amount of the pre-injection P11 exceeds the predetermined advance limit will be described. Here, the advance limit is set to prevent injection at a stage where the in-cylinder temperature has not risen sufficiently, and when the injection is performed at a timing exceeding the advance limit, the injection is performed. The fuel may adhere to the wall surface of the cylinder. For this reason, in this control, the pre-injection P11 is divided into a plurality of parts to reduce the amount of one injection and reduce the risk of the injected fuel adhering to the wall surface of the cylinder.

In the embodiment shown in FIG. 20, when the opening degree of the EGR valve 45 is reduced from the base setting state shown in the upper stage, as shown in the middle stage, it is calculated to optimize the injection timing of the pre-injection P11. When the calculated value of the injection start timing exceeds the advance limit, the pre-injection P11 is divided into two pre-injections P111 and P112 and injected as shown in the lower stage. In this case, the injection of the divided first-stage pre-injection P111 is started just at the timing of the advance limit, and the second-stage pre-injection P112 is executed subsequent to the pre-injection P111. ing.

As described above, in the embodiment shown in FIG. 20, the advance limit is not changed even after the pre-injection is divided into a plurality, and the injection start timing of the pre-injection P111 of the first stage is adjusted to this advance limit. However, the present invention is not limited to such a form. For example, when the pre-injection is divided into a plurality of parts, the advance limit is also corrected (for example, the advance limit is advanced more than before the correction), and the injection start timing of the divided pre-injection is corrected. You may make it match with the advance limit.

[Control flow]
FIG. 21 is a flowchart showing an example of fuel injection control by the fuel injection control unit 71 (FIG. 7) of the processor 70. In the fuel injection control, first, in step S1, the fuel injection control unit 71 determines from the sensors SN1 to SN12 and other sensors (cylinder pressure sensor, etc.) shown in FIG. 7 that the operating region of the vehicle (the operating state of the engine body 1). ), and the environmental information that becomes the above combustion environment factor.

In the following step S2, the operating state determination unit 72 determines whether or not the current operating region corresponds to the PCI region in which the premixed compression ignition combustion is executed, based on the information regarding the operating region acquired in step S1. If the result of this determination is that it does not fall within the PCI region, then the flow of control proceeds to step S3, where the fuel injection control unit 71 executes other combustion control that has been preset for operating regions other than the PCI region. That is, the injection pattern selection unit 73 sets another fuel injection pattern for combustion control.

On the other hand, if the result of determination in step S2 is in the PCI region, the process proceeds to step S4, and the injection pattern selection unit 73 causes the pre-injection P1 (pre-stage injection) and the main injection P2 (post-stage injection) as illustrated in FIG. ) Is included in the divided injection pattern. In the following step S5, the injection setting unit 74 sets the fuel injection amount and the fuel injection timing of the pre-injection P1 and the main injection P2 so that the target heat release rate characteristic Hs illustrated in FIG. 8A can be achieved. Determine the base setting for the resulting ignition timing). In the following step S6, the correction unit 76 corrects the base setting in accordance with the various information (combustion environment factor) acquired in step S1.

FIG. 22 is a flowchart showing an example of control in the case where the opening degree of the EGR valve 45 is changed in the fuel injection control. Note that the control shown in FIG. 22 is executed as one of the controls (correction of the base setting by the correction unit 76) in step S6 of the flowchart of FIG.

In this control, first, in step S11, it is determined whether or not the opening degree of the EGR valve 45 has decreased. If it is determined that the opening degree of the EGR valve 45 has decreased, the process proceeds to step S12 and the EGR The heat release rate of the combustion by the pre-injection P1 is applied by applying the influence of the increase of the oxygen concentration in the combustion chamber 6 and the decrease of the gas temperature due to the decrease of the gas amount to the prediction formula (Arrhenius type prediction formula shown in FIGS. 12 and 13). Grasp the amount of retardation of the peak occurrence timing and the fluctuation (decrease amount) of the peak height.

In the following step S13, the advance amount of the pre-injection start timing for optimizing the generation timing of the heat release rate peak due to the pre-injection P1 is calculated based on the calculation result in step S12. In the following step S14, it is determined whether or not the calculated value of the injection start timing of the pre-injection P1 calculated in step S13 exceeds the advance limit, and if it does not exceed the advance limit, the process proceeds to step S16. .. On the other hand, when the pre-injection start timing exceeds the advance limit, in step S15, the process of dividing the pre-injection into plural parts is performed, and the process proceeds to step S16.

In step S16, a correction for advancing the injection start timing of the pre-injection P1 is performed based on the advance amount calculated in step S13. In the following step S17, the injection amount of the pre-injection is increased and the injection amount of the main injection is reduced by the increase amount of the pre-injection amount so as to optimize the heat fluctuation rate characteristic grasped by the prediction formula. .. In the following step S18, the control based on the correction set in step S16 and step S17 is continued until the injection with the new target fuel injection amount is started, and the process is ended.

On the other hand, when it is determined in step S11 that the opening degree of the EGR valve 45 has not decreased, the process proceeds to step S19, and it is determined whether the opening degree of the EGR valve 45 has increased. If it is determined in step S19 that the opening degree of the EGR valve 45 has not increased, it is determined that the EGR valve opening degree has not changed, and the process ends.

When it is determined in step S19 that the opening degree of the EGR valve 45 has increased, the process proceeds to step S20, and the prediction formula (the effect of the decrease in oxygen concentration in the combustion chamber 6 and the increase in gas temperature due to the increase in the EGR gas amount ( Applying to the Arrhenius type prediction formula shown in FIG. 12 and FIG. 13, the advance amount of the peak generation timing of the heat release rate of combustion by each injection (particularly the pre-injection P1) and the fluctuation of the peak height (increase amount) Figure out. In the following step S21, the retard amount of the pre-injection start timing for optimizing the heat generation rate peak generation timing by the pre-injection P1 is calculated based on the calculation result in step S20.

In the following step S22, the injection start timing of the pre-injection P1 is corrected to be retarded based on the retard amount calculated in step S19. In a succeeding step S22, the injection amount of the pre-injection is reduced and the injection amount of the main injection is increased by the reduction amount of the pre-injection amount so as to optimize the heat fluctuation rate characteristic grasped by the prediction formula. .. In the following step S18, the control based on the correction set in steps S21 and S22 is continued until the injection with the new target fuel injection amount is started, and the process is ended.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and appropriate modifications can be made within the scope of the claims. For example, in the control shown in FIG. 20, the pre-injection P1 is divided into two pre-injections (pre-injection P111, P112), but the present invention is not limited to such a form, and the pre-injection P1 is It may be divided into three or more pre-injections.

1 Engine Body 2 Cylinder 5 Piston 50 Crown 5C Cavity 51 First Cavity Section 512 First Bottom 52 Second Cavity 522 Second Bottom 525 Standing Wall Region 53 Connection 6 Combustion Chamber 15 Injector (Fuel Injection Valve)
44 EGR device 45 EGR valve 70 Processor (fuel injection control device for diesel engine)
71 Fuel injection control unit (split injection control unit, setting unit, prediction unit, correction unit)
72 Operation state determination unit 73 Injection pattern selection unit (split injection control unit)
74 Injection setting section (setting section)
75 prediction unit 76 correction unit 77 storage unit P1 pre-injection (pre-stage injection)
P2 main injection (post-stage injection)
H Heat release rate characteristic Hs Target heat release rate characteristic Hp Predicted heat release rate characteristic HAp 1st peak HBp 2nd peak

Claims (9)

In an engine control device provided in a compression ignition engine in which multi-stage injection of fuel into a combustion chamber is executed,
A pre-injection executed on the advance side of the compression top dead center of the compression ignition engine, and a fuel injection executed on the retard side of the pre-injection while the fuel injected by the pre-injection is burning. A fuel injection unit for injecting injection into the combustion chamber,
An injection control unit that controls the injection timing and injection amount of each injection executed by the fuel injection unit,
An EGR valve control unit that controls an opening degree of an EGR valve of an EGR device included in the compression ignition engine,
The injection control unit,
The interval between the first peak of the heat release rate caused by the combustion of the fuel injected by the pre-injection and the second peak of the heat release rate caused by the combustion of the fuel injected by the main injection is the pre-injection and the main injection. A base setting determination means for determining the base setting of the injection timing and the injection amount of each injection so that the pressure waves generated by the combustion of the respective fuels have intervals that cancel each other out,
Injection timing variation calculation means for calculating a variation in the injection timing of the pre-injection due to a change in the oxygen concentration and gas temperature in the combustion chamber due to a change in the opening degree of the EGR valve,
When the opening degree of the EGR valve is reduced by the EGR valve control unit, the injection start timing of the pre-injection is calculated by the injection timing variation calculation means while maintaining the injection timing of the main injection at the base setting. Setting correction means for changing the base setting from the base setting to the advance side, increasing the injection amount of the pre-injection from the base setting, and decreasing the injection amount of the main injection by the increase amount of the injection amount of the pre-injection according to And an engine control device including. In the engine control device according to claim 1,
The base setting determination means determines the base setting based on the target fuel injection amount,
When the target fuel injection amount is changed, the EGR valve control unit sets the opening degree of the EGR valve to the changed target fuel injection before starting the injection based on the changed target fuel injection amount. Change the opening according to the amount,
The setting correction means, during the period from when the opening degree of the EGR valve is changed to when the injection based on the changed target fuel injection amount is started, the injection start timing of the pre-injection and the pre-injection and An engine control device that executes control for correcting the injection amount of the main injection. The engine control device according to claim 1 or 2, wherein the advance amount of the injection start timing of the pre-injection by the setting correction means is based on the pre-injection resulting from the advance angle of the injection timing of the pre-injection. The advance amount of the generation timing of the first peak of the heat generation rate is the retard amount of the generation timing of the first peak of the heat generation rate by the pre-injection due to the reduction of the opening degree of the EGR valve. The engine control device according to claim 1, wherein the control device is set to be smaller than the above. The engine control device according to any one of claims 1 to 3, wherein an increase amount of the injection amount of the pre-injection by the setting correction unit is a heat generation rate by the pre-injection caused by the increase amount. Of the engine so that the amount of increase in the first peak of the EGR valve does not exceed the amount of decrease in the first peak of the heat generation rate due to the pre-injection due to the reduction in the opening degree of the EGR valve apparatus. The engine control device according to any one of claims 1 to 4, wherein when the injection start timing of the pre-injection set by the setting correction unit exceeds a predetermined advance angle limit, An engine control device that divides the injection into a plurality of pre-injections executed during the advance limit and the injection timing of the main injection. In an engine control device provided in a compression ignition engine in which multi-stage injection of fuel into a combustion chamber is executed,
A pre-injection executed on the advance side of the compression top dead center of the compression ignition engine, and a fuel injection executed on the retard side of the pre-injection while the fuel injected by the pre-injection is burning. A fuel injection unit for injecting injection into the combustion chamber,
An injection control unit that controls the injection timing and injection amount of each injection executed by the fuel injection unit,
An EGR valve control unit that controls an opening degree of an EGR valve of an EGR device included in the compression ignition engine,
The injection control unit,
The interval between the first peak of the heat release rate caused by the combustion of the fuel injected by the pre-injection and the second peak of the heat release rate caused by the combustion of the fuel injected by the main injection is the pre-injection and the main injection. A base setting determination means for determining the base setting of the injection timing and the injection amount of each injection so that the pressure waves generated by the combustion of the respective fuels have intervals that cancel each other out,
Injection timing variation calculation means for calculating a variation in the injection timing of the pre-injection due to a change in the oxygen concentration and gas temperature in the combustion chamber due to a change in the opening degree of the EGR valve,
When the opening degree of the EGR valve is increased by the EGR valve control unit, the injection start timing of the pre-injection is calculated by the injection timing variation calculation means while maintaining the injection timing of the main injection at the base setting. Setting correction means for changing from the base setting to the retard angle side according to the above, decreasing the injection amount of the pre-injection from the base setting, and increasing the injection amount of the main injection by the decrease amount of the injection amount of the pre-injection. And an engine control device including. The engine control device according to claim 6,
The base setting determination means determines the base setting based on the target fuel injection amount,
When the target fuel injection amount is changed, the EGR valve control unit changes the opening degree of the EGR valve to the changed target fuel injection amount before starting the injection based on the changed target fuel injection amount. Change the opening according to the amount,
The setting correction means, during the period from when the opening degree of the EGR valve is changed to when the injection based on the changed target fuel injection amount is started, the injection start timing of the pre-injection and the pre-injection and An engine control device that executes control for correcting the injection amount of the main injection. The engine control device according to claim 6 or 7, wherein the retard amount of the injection start timing of the pre-injection by the setting correction means is due to the pre-injection caused by the retard angle of the injection timing of the pre-injection. The retard amount of the generation timing of the first peak of the heat generation rate is the advance amount of the generation timing of the first peak of the heat generation rate due to the pre-injection due to the opening degree of the EGR valve being increased. Engine control unit that is set to be smaller than. The engine control device according to any one of claims 6 to 8, wherein a reduction amount of the injection amount of the pre-injection by the setting correction unit is a heat generation rate by the pre-injection caused by the reduction amount. The engine control is set so that the amount of decrease in the first peak of does not exceed the amount of increase in the first peak of the heat generation rate due to the pre-injection due to the increase in the opening degree of the EGR valve. apparatus.

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