Compression ignition engine control device

Abstract

To enhance quietness performance while making power consumption performance and exhaustion performance favorable in an engine having a cavity of a top-and-bottom two-stage structure.SOLUTION: A fuel injection valve performs: main injection for injecting fuel at timing at which an injection shaft is oriented to a lip part during at least at a part of injection period so that fuel is distributed to a top cavity and a bottom cavity; and after-injection for injecting fuel after the main injection. The fuel injection valve is controlled so that the injection timing of the main injection is set to the timing on a retardancy side in the case where low-speed traveling is determined than in the case where high-speed traveling is determined. At least either of first control for controlling the fuel injection valve so that an injection amount of the after-injection becomes larger in the case of the low-speed traveling than in the high-speed traveling, and second control for controlling the fuel injection valve so that the injection timing of the after-injection is set to the timing closer to the retardancy side in the case of the low-speed traveling than in the case of the high-speed traveling, is performed.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to a control device for a compression ignition engine in which compression ignition combustion of an air-fuel mixture is carried out in a combustion chamber. [Background technology]

[0002] Further improvements in fuel economy and exhaust performance are required for engines for vehicles such as automobiles. In response to this, the applicant has developed a configuration in which the cavity formed on the piston crown surface has a two-tiered structure consisting of an upper cavity and a lower cavity, and fuel is collided with the lip connecting these two cavities to distribute the fuel throughout the combustion chamber, thereby shortening combustion time, improving fuel economy, and suppressing soot generation, as shown in Patent Document 1.

[0003] Specifically, Patent Document 1 discloses an engine having a piston with the above-mentioned two-stage cavity, in which a fuel injection valve that injects fuel toward the cavity performs a main injection near top dead center of compression and a pilot injection during the compression stroke, and the main injection and pilot injection are performed at a timing when the injection axis of the fuel injection valve is directed toward the lip. Also, in this engine, when the engine load is high, fuel from the main injection is likely to be distributed to the lower cavity, so by increasing the distribution rate of fuel from the pilot injection to the upper cavity compared to when the engine load is low, the total fuel supplied to the combustion chamber by the pilot injection and main injection is distributed evenly to the combustion chamber, thereby suppressing the generation of soot. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-122407 Summary of the Invention [Problem to be solved by the invention]

[0005] Engines installed in vehicles are required to have quietness in addition to fuel economy and exhaust performance. Specifically, when the vehicle is traveling at high speeds, the background noise is high, which minimizes the impact that the sound emitted from the engine, i.e., combustion noise, has on occupants. On the other hand, when the vehicle is traveling at low speeds, the background noise is low, which makes the combustion noise more noticeable to occupants, so it is particularly important to reduce the combustion noise. With the configuration of Patent Document 1, soot generation is suppressed and exhaust performance is improved as described above, but there is room for improvement in quietness.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a control device for a compression ignition engine that is mounted on a vehicle and has a piston crown surface with a two-stage cavity, where part of the combustion chamber is partitioned, and that can improve fuel efficiency and exhaust performance while also improving quietness. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a control device for an engine of a compression ignition engine mounted on a vehicle and including an engine body having a cylinder formed therein, a piston reciprocating within the cylinder, a combustion chamber formed by the cylinder and a crown surface of the piston in which compression ignition combustion of an air-fuel mixture is carried out, and a fuel injection valve disposed on a ceiling surface of the combustion chamber and injecting fuel along an injection axis, the control device comprising: a determination unit that determines whether the vehicle is traveling at a low speed or a high speed; and a fuel injection control unit that controls the fuel injection valve, wherein the piston has a lower cavity provided in a radial center of the crown surface, an upper cavity provided around the lower cavity and shallower than the lower cavity, and a lip portion that connects the lower cavity and the upper cavity, and the fuel injection control unit When the engine is operated in a medium load region where the engine load is higher than a predetermined first load and is equal to or lower than a predetermined second load set higher than the first load, a control for rapid multi-stage combustion is executed to cause the fuel injection valve to perform a main injection in which fuel is injected at a timing when the injection axis is directed toward the lip portion during at least a part of an injection period so that fuel is distributed to the upper cavity and the lower cavity, and an after-injection in which fuel is injected after the main injection; In the medium load rangeWhen the rapid multi-stage combustion control is executed, the fuel injection valve is controlled so that the injection timing of the main injection is more retarded when the judgment unit judges that the vehicle is traveling at a low speed than when the judgment unit judges that the vehicle is traveling at a high speed, and at least one of a first control that controls the fuel injection valve so that the injection amount of the after-injection is greater when the vehicle is traveling at a low speed than when the vehicle is traveling at a high speed, and a second control that controls the fuel injection valve so that the injection timing of the after-injection is more retarded when the vehicle is traveling at a low speed than when the vehicle is traveling at a high speed is executed.

[0008] With this control device, the injection timing of the main injection is retarded when the vehicle is traveling at low speeds compared to when the vehicle is traveling at high speeds. As a result, the combustion energy generated near the compression top dead center is increased when the vehicle is traveling at high speeds, improving fuel economy, and the combustion energy is reduced when the vehicle is traveling at low speeds, when the combustion noise is more noticeable to passengers, reducing the combustion noise, thereby improving both fuel economy and quietness.

[0009] Furthermore, the fuel from the main injection is distributed to both the upper and lower cavities, and the injection amount of the after-injection is increased and / or the injection timing of the after-injection is retarded when the engine is running at low speeds compared to when the engine is running at high speeds. This reduces soot generation and improves exhaust performance at both high and low speeds.

[0010] Specifically, distributing the fuel from the main injection to both the upper and lower cavities spreads the fuel throughout the combustion chamber, improving the homogeneity of the mixture and suppressing soot generation. However, as described above, when the vehicle is traveling at low speeds, the main injection is retarded, so the piston position is relatively low when the main fuel reaches the lip. Therefore, when traveling at low speeds, the fuel from the main injection is concentrated toward the upper part of the combustion chamber, reducing the homogeneity of the mixture and increasing the amount of soot generated by the combustion of that fuel. In contrast, when traveling at low speeds, the injection amount of the after-injection, which is performed after the main injection, is increased and / or the injection timing of the after-injection is retarded. This maintains the temperature of the combustion chamber after the main injection at a high temperature for a longer period, promoting the oxidation of soot generated by the combustion of the fuel from the main injection. Therefore, exhaust performance can be improved even when traveling at low speeds.

[0011] In the above control device, it is desirable that the judgment unit judges that the vehicle is traveling at a low speed when the gear stage of the transmission installed in the vehicle is equal to or lower than a predetermined judgment stage number, and judges that the vehicle is traveling at a high speed when the gear stage is higher than the judgment stage number (Claim 2).

[0012] This control device can determine whether the vehicle is traveling at a low speed or a high speed by utilizing the gear position of the transmission.

[0013] In the above control device, it is desirable that the fuel injection control unit executes the first control when the rapid multi-stage combustion control is executed, and when the first control is executed, controls the fuel injection valve so that the injection amount of the after-injection increases as the engine load increases (Claim 3).

[0014] According to this control device, when driving at low speeds, the amount of after-injection is increased when the engine load is high and the amount of soot generated after combustion of fuel from the main injection is more likely to increase, thereby suppressing the increase in soot that accompanies an increase in engine load.

[0015] In the above control device, it is desirable that, when the first control is executed, the fuel injection control unit controls the fuel injection valve so that the injection amount of injections other than the after-injection is smaller when the judgment unit determines that the vehicle is traveling at a low speed than when the judgment unit determines that the vehicle is traveling at a high speed (Claim 4).

[0016] This control device can achieve the above-mentioned effect obtained by increasing the amount of after-injection during low-speed driving, while suppressing changes in the total amount of fuel supplied to the combustion chamber in one combustion cycle, and therefore in engine torque, between low-speed driving and high-speed driving.

[0017] In the above control device, it is desirable that the fuel injection control unit executes the second control when the rapid multi-stage combustion control is being executed, and when the second control is being executed, controls the fuel injection valve so that the injection timing of the after-injection becomes more retarded as the engine load increases (Claim 5).

[0018] According to this control device, when driving at low speeds, the injection timing of the after-injection is retarded the more the engine load is high and the more likely the soot generated after combustion of fuel from the main injection is to increase, thereby suppressing the increase in soot that accompanies an increase in engine load. [Effects of the Invention]

[0019] According to the present invention, in an engine in which a portion of a combustion chamber is defined by a piston crown surface having a cavity with an upper and lower two-stage structure, it is possible to improve fuel economy and exhaust performance while also improving quietness. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a system diagram of a vehicle equipped with a diesel engine to which a control device for a compression ignition engine according to the present invention is applied. [Figure 2]FIG. 2(A) is a perspective view of the crown surface portion of the piston of the diesel engine shown in FIG. 1, and FIG. 2(B) is a perspective view with a cross section of the piston. [Figure 3] FIG. 3 is a block diagram showing the engine control system. [Figure 4] FIG. 4 is a map showing the operating range of the engine. [Figure 5] FIG. 5 is a flowchart showing the overall flow of injector control. [Figure 6] FIG. 6 is a time chart showing an example of the fuel injection timing and the heat release rate. [Figure 7] FIG. 7 is a flowchart showing the flow of injector control in the medium load range. [Figure 8] FIG. 8 is a graph showing the relationship between engine load and main injection timing when operating in a high gear and when operating in a low gear. [Figure 9] FIG. 9 is a graph showing the relationship between the engine load and the second after-injection timing when the engine is operating in a high gear and when the engine is operating in a low gear. [Figure 10] FIG. 10 is a graph showing the relationship between the engine load and the second after-injection amount when operating in a high gear and when operating in a low gear. [Figure 11] FIG. 11 is a cross-sectional view of a combustion chamber showing the flow state of fuel spray. [Figure 12] FIG. 12 is a cross-sectional view of a combustion chamber for explaining the relationship between the injection timing and the position of the piston. DETAILED DESCRIPTION OF THE INVENTION

[0021] [Overall configuration] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a control device for a compression ignition engine according to the present invention will be described in detail below with reference to the drawings. In this embodiment, an example in which the present invention is applied to a diesel engine system will be shown.

[0022] The diesel engine system according to this embodiment is mounted on a vehicle 100 as a driving source for traveling. FIG. 1 is a system diagram of the vehicle 100. Wheels 120 provided on the vehicle 100 are driven to rotate by the output of the diesel engine system. The vehicle 100 is equipped with a transmission 110 including a plurality of gear stages, and the output of the diesel engine system is transmitted to the wheels 120 while being speed-shifted by the transmission 110. The transmission 110 may be one with eight gear stages (eight-speed), for example.

[0023] [Overall engine configuration] The diesel engine system includes a four-stroke engine body 1 having a plurality of cylinders 2 and powered by a supply of fuel whose main component is diesel oil, an intake passage 30 through which intake air introduced into the engine body 1 flows, an exhaust passage 40 through which exhaust gas discharged from the engine body 1 flows, an EGR device 44 that recirculates a portion of the exhaust gas flowing through the exhaust passage 40 back into the intake passage 30, and a turbocharger 46 driven by the exhaust gas passing through the exhaust passage 40.

[0024] 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 plane of the paper on which FIG. 1 is drawn. The engine body 1 also includes a cylinder block 3 in which the cylinders 2 are formed, a cylinder head 4, and pistons 5. The cylinder head 4 is attached to the upper surface of the cylinder block 3. The pistons 5 are housed in the cylinders 2 so that they can slide back and forth, and are connected to a crankshaft 7 via a connecting rod 8. The crankshaft 7 rotates around its central axis in response to the reciprocating motion of the pistons 5. The structure of the pistons 5 will be described in detail below.

[0025] A combustion chamber 6 is formed above the piston 5. The combustion chamber 6 is formed by the underside of the cylinder head 4 (combustion chamber ceiling surface 6U, see FIG. 3), the cylinder 2, and a crown surface 50 of the piston 5. Fuel is supplied to the combustion chamber 6 by injection from an injector 15, which will be described later. The engine body 1 is a compression ignition engine in which compression ignition combustion of an air-fuel mixture is carried out in the combustion chamber 6, and the supplied fuel-air mixture is compressed by the piston 5 and self-ignites in the combustion chamber 6. The piston 5 is pushed down by the expansion force caused by the combustion of the air-fuel mixture, causing it to reciprocate up and down.

[0026] A crank angle sensor SN1 and a water temperature sensor SN2 are attached to the cylinder block 3. The crank angle sensor SN1 detects the rotation angle (crank angle) of the crankshaft 7 and the rotation speed (engine rotation speed) of the crankshaft 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.

[0027] The cylinder head 4 is formed with intake ports 9 and exhaust ports 10 that communicate with the combustion chambers 6. The underside of the cylinder head 4 is formed with an intake-side opening, which is the downstream end of the intake port 9, and an exhaust-side opening, which is the upstream end of the exhaust port 10. The cylinder head 4 is fitted with an intake valve 11 that opens and closes the intake-side opening, and an exhaust valve 12 that opens and closes the exhaust-side opening. Although not shown, the engine body 1 is a four-valve system (two intake valves and two exhaust valves), with two intake ports 9, two intake valves 11, two exhaust ports 10, and two exhaust valves 12 provided for each cylinder 2. The intake valves 11 and the exhaust valves 12 are opened and closed by valve trains 13 and 14 provided in the cylinder head 4 in conjunction with the rotation of the crankshaft 7. Each valve train 13 and 14 incorporates an S-VT, which continuously changes the opening and closing timing of the intake valves 11 and the exhaust valves 12.

[0028] An injector 15 (fuel injection valve) that injects fuel from its tip into the combustion chamber 6 is attached to the cylinder head 4, one for each cylinder 2. As shown in FIG. 11 , which will be described later, the injector 15 has a nozzle 151 at its tip. The injector 15 is attached to the cylinder head 4 so that the nozzle 151 protrudes downward toward the inside of the combustion chamber 6 from or near the radial center of the combustion chamber ceiling surface 6U. The nozzle 151 has an injection hole 152 that injects fuel into the combustion chamber 6. Although FIG. 11 shows one injection hole 152, in reality, a plurality of injection holes 152 are arranged at equal intervals around the circumferential direction of the nozzle 151. Fuel is injected from each injection hole 152 along an injection axis AX that substantially coincides with the hole axis of the injection hole 152.

[0029] The injectors 15 are connected via fuel supply pipes to a common rail (not shown) for accumulating pressure, which is common to all cylinders 2. High-pressure fuel pressurized by a fuel pump (not shown) is stored in the common rail. The fuel stored in this common rail is supplied to the injectors 15 of each cylinder 2, and the fuel is injected from each injector 15 at high pressure (approximately 50 MPa to 250 MPa) into the combustion chamber 6. A fuel pressure regulator 16 (not shown in FIG. 1, see FIG. 3) is provided between the fuel pump and the common rail to change the injection pressure, which is the pressure of the fuel injected from the injectors 15.

[0030] The intake passage 30 is connected to one side of the cylinder head 4 so as to communicate with the intake port 9. Air (fresh air) taken in 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. In the intake passage 30, an air cleaner 31, a compressor 47 of a turbocharger 46, a throttle valve 32, an intercooler 33, and a surge tank 34 are arranged in this order from the upstream side.

[0031] The air cleaner 31 removes foreign matter from the intake air. The throttle valve 32 opens and closes the intake passage 30 to adjust the flow rate of intake air in the intake passage 30. The compressor 47 is rotationally driven by a turbine 48 provided in the exhaust passage 40, and compresses (supercharges) the intake air flowing through the intake passage 30. The intercooler 33 cools the intake air compressed by the compressor 47. The surge tank 34 provides a space for evenly distributing the intake air to the multiple cylinders 2.

[0032] An air flow sensor SN3, an intake air temperature sensor SN4, an intake air pressure sensor SN5, and an intake O2 sensor SN6 are arranged in the intake passage 30. The air flow sensor SN3 is arranged downstream of the air cleaner 31 and detects the flow rate of the intake air passing through that section. The intake air temperature sensor SN4 is arranged downstream of the intercooler 33 and detects the temperature of the intake air passing through that section. The intake air pressure sensor SN5 and the intake O2 sensor SN6 are arranged near the surge tank 34 and detect the pressure and oxygen concentration of the intake air passing through that section, respectively.

[0033] An exhaust passage 40 is connected to the other side of the cylinder head 4 so as to communicate with the exhaust port 10. Burned gas (exhaust gas) generated in the combustion chamber 6 is discharged to the outside of the vehicle through the exhaust port 10 and the exhaust passage 40. In the exhaust passage 40, a turbine 48 of a turbocharger 46 and an exhaust purification device 41 are provided in this order from the upstream side. The exhaust purification device 41 incorporates an oxidation catalyst 42 and a DPF (diesel particulate filter) 43 for capturing particulate matter. Note that a NOx catalyst that reduces NOx to render it harmless may also be provided downstream of the exhaust purification device 41 in the exhaust passage 40.

[0034] An exhaust O2 sensor SN8 and a differential pressure sensor SN9 are arranged in the exhaust passage 40. The exhaust O2 sensor SN8 is arranged between the turbine 48 and the exhaust purification device 41 and detects the oxygen concentration of the exhaust passing through that section. The differential pressure sensor SN9 detects the differential pressure between the upstream end and downstream end of the DPF 43.

[0035] The EGR device 44 includes an EGR passage 44A that connects the exhaust passage 40 and the intake passage 30, and an EGR valve 45 that is provided in the EGR passage 44A and adjusts the flow rate of exhaust gas (EGR gas) that flows through the EGR passage 44A. The EGR passage 44A connects a portion of the exhaust passage 40 upstream of the turbine 48 with a portion of the intake passage 30 between the intercooler 33 and the surge tank 34. An EGR cooler (not shown) that cools the EGR gas passing through the EGR passage 44A is disposed in the EGR passage 44A.

[0036] [Detailed structure of the piston] Next, the structure of the piston 5, particularly the structure of the crown surface 50, will be described in detail. Fig. 2(A) is a perspective view mainly showing the upper portion of the piston 5. Fig. 2(A) shows a piston head that forms the upper part of the piston 5 and has the crown surface 50 as its top surface. Fig. 2(B) is a perspective view with a radial cross section of the upper part (piston head) of the piston 5. Note that in Figs. 2(A) and 2(B), the cylinder axial direction A and the radial direction B of the combustion chamber are indicated by arrows. In the following description of the piston 5, the sliding direction of the piston 5 is considered to be the vertical direction, and the plane perpendicular to this is considered to be the horizontal plane.

[0037] The piston 5 includes a cavity 5C, a peripheral flat surface 55, and a side circumferential surface 56. A portion (bottom surface) of the combustion chamber wall surface that defines the combustion chamber 6 is formed by a 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 axial direction A, and receives the spray of fuel injected by the injector 15. The peripheral flat surface 55 is an annular flat portion located in a region near the outer periphery of the crown surface 50 in the radial direction B. The cavity 5C is located in a central region in the radial direction B of the crown surface 50 excluding the peripheral flat surface 55. The side circumferential surface 56 is a surface that comes into sliding contact with the inner wall surface of the cylinder 2.

[0038] The cavity 5C is a so-called egg-shaped two-stage cavity, and has upper and lower cavities each having an egg-shaped cross section wall.

[0039] Specifically, the cavity 5C includes a lower cavity 51, an upper cavity 52, a lip portion 53, and a peak portion 54. The lower cavity 51 is a recessed portion located in the radial center of the crown surface 50, i.e., in the central region in the radial direction B. The upper cavity 52 is an annular recessed portion located on the outer circumferential side of the lower cavity 51 in the crown surface 50. The lip portion 53 is a portion connecting the lower cavity 51 and the upper cavity 52 in the radial direction B. The peak portion 54 is a mountain-shaped protrusion located at the central position of the crown surface 50 (lower cavity 51) in the radial direction B. The peak portion 54 is protruded directly below the nozzle 151 of the injector 15 (FIG. 9).

[0040] The lower cavity 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 located at the highest position in the lower cavity 51 and is connected to the lip portion 53. The first bottom portion 512 is the most recessed area in the lower cavity 51 and has an annular shape in a top view. The first bottom portion 512 is also the deepest part of the cavity 5C as a whole. In a top view, the first bottom portion 512 is located close to the lip portion 53 on the inside in the radial direction B.

[0041] The first upper end portion 511 and the first bottom portion 512 are connected by a radially recessed portion 514 that curves outward in the radial direction B. The radially recessed portion 514 has a portion that is recessed further outward in the radial direction B than the lip portion 53. The first inner end portion 513 is located at the radially innermost position in the lower cavity 51, and is continuous with the lower end of the peak portion 54. The first inner end portion 513 and the first bottom portion 512 are connected by a curved surface that curves gently in a skirt-like shape.

[0042] The upper cavity 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 radially innermost position in the upper cavity 52 and is connected to the lip portion 53. The second bottom portion 522 is the most recessed region in the upper cavity 52. ​​The second bottom portion 522 of the upper cavity 52 has a depth in the cylinder axial direction A that is shallower than that of the first bottom portion 512. In other words, the upper cavity 52 is a recess located above the lower cavity 51 in the cylinder axial direction A. The second upper end portion 523 is located at the highest position and radially outermost in the upper cavity 52 and is connected to the peripheral flat portion 55. The tapered region 524 extends from the second inner end portion 521 toward the second bottom portion 522 and has a surface shape that slopes downward radially outward.

[0043] The standing wall region 525 is a wall surface formed to rise relatively steeply radially outward from the second bottom portion 522. In the cross-sectional shape in the radial direction B, from the second bottom portion 522 to the second upper end portion 523, the wall surface of the upper cavity 52 is a curved surface that curves from the horizontal direction to the upward direction, and the standing wall region 525 is a portion that is a wall surface close to a vertical wall near the second upper end portion 523. A lower portion of the standing wall region 525 is located inside in the radial direction B relative to the upper end position of the standing wall region 525.

[0044] The lip portion 53 has a hump-like shape that protrudes radially inward in a cross section in the radial direction B between the lower cavity 51 located on the lower side and the upper cavity 52 located on the upper side. The lip portion 53 has a lower end portion 531, a third upper end portion 532 (the upper end portion in the axial direction of the cylinder), and a central portion 533 located in the middle between them. The lower end portion 531 is a portion connected to the first upper end portion 511 of the lower cavity 51. The third upper end portion 532 is a portion connected to the second inner end portion 521 of the upper cavity 52.

[0045] In the cylinder axial direction A, the lower end 531 is the lowest portion of the lip portion 53, and the third upper end 532 is the highest portion. The tapered region 524 described above is also a region that extends from the third upper end 532 toward the second bottom portion 522. The second bottom portion 522 is located below the third upper end 532. In other words, the upper cavity 52 of this embodiment does not have a bottom surface that extends horizontally from the third upper end 532 outward in the radial direction B. In other words, the third upper end 532 is not connected to the peripheral flat portion 55 by a horizontal plane, but has the second bottom portion 522 that is recessed below the third upper end 532.

[0046] The ridge portion 54 protrudes upward, but the protruding height is the same as the height of the third upper end portion 532 of the lip portion 53, and is located at a position recessed from the peripheral flat surface portion 55. The ridge portion 54 is located at the center of the circular lower cavity 51 in a top view, and this makes the lower cavity 51 annular groove formed around the ridge portion 54.

[0047] [Control configuration] Next, the control configuration of the diesel engine system will be described with reference to the block diagram of Fig. 3. The diesel engine system of this embodiment is comprehensively controlled by a processor 70 (engine control device). The processor 70 is composed of a CPU, ROM, RAM, etc.

[0048] Detection signals from various sensors mounted on the vehicle are input to the processor 70. In addition to the sensors SN1 to SN9 described above, the vehicle is equipped with an accelerator position sensor SN10 that detects the accelerator position, an atmospheric pressure sensor SN11 that measures the atmospheric pressure in the vehicle's driving environment, an outside air temperature sensor SN12 that measures the air temperature in the vehicle's driving environment, and a gear position sensor SN13 that detects the current position of the transmission 110, i.e., the current gear position. Information detected by these sensors SN1 to SN13, namely, information such as crank angle, engine speed, engine water temperature, intake air flow rate, intake air temperature, intake air pressure, intake oxygen concentration, injection pressure of the injector 15, exhaust oxygen concentration, accelerator position, outside air temperature, air pressure, and gear position, is sequentially input to the processor 70.

[0049] The processor 70 controls each part of the engine while executing various determinations and calculations based on input signals from the sensors SN1 to SN13, etc. That is, the processor 70 is electrically connected to the injector 15 (fuel pressure regulator 16), the throttle valve 32, the EGR valve 45, etc., and outputs control signals to these devices based on the results of the calculations, etc.

[0050] The processor 70 operates so as to be provided with a determining unit 71, a fuel injection control unit 72 that controls the operation of the injector 15, and a storage unit 78, by executing a predetermined program.

[0051] The determination unit 71 sets a target engine torque, which is a target torque for the engine, based on the engine speed detected by the crank angle sensor SN1 and the accelerator opening detected by the accelerator opening sensor SN10.

[0052] The determination unit 71 determines the engine operating range (determines in which operating range the engine is operating). FIG. 4 is a map diagram showing operating ranges set according to the engine speed and the target engine torque, i.e., the engine load. The engine operating ranges are roughly divided into a low load range A1, a medium load range A2, and a high-speed, high-load range A3 depending on the combustion mode. The low load range A1 is a range in which the engine speed is equal to or lower than a predetermined first speed N1 and the engine load is equal to or lower than a predetermined first load T1. The medium load range A2 is a range in which the engine speed is equal to or lower than the first speed N1 and the engine load is equal to or lower than a predetermined second load T2, excluding the low load range A1. The high-speed, high-load range A3 is the remaining range other than the low load range A1 and the medium load range A2. The determination unit 71 determines the engine operating range based on the set target engine torque (engine load) and engine speed.

[0053] The determination unit 71 determines whether the vehicle 100 is traveling at a low speed or a high speed, that is, whether the vehicle 100 is traveling at a speed equal to or lower than a predetermined speed or higher than a predetermined speed. The determination unit 71 makes this determination based on the current gear position. If the current gear position detected by the gear position sensor SN13 is equal to or lower than a preset reference gear position (number of determination positions), the determination unit 71 determines that the vehicle 100 is traveling at a low speed. On the other hand, if the current gear position is higher than the reference gear position, the determination unit 71 determines that the vehicle 100 is traveling at a high speed. The reference gear position is set in advance and stored in the memory unit 78. For example, if the transmission 110 has eight gear positions, the reference gear position is set to fourth position (fourth speed).

[0054] The fuel injection control unit 72 controls the fuel injection operation by the injector 15. The fuel injection control unit 72 operates to have the functions of an injection amount setting unit 73 and an injection timing setting unit 74 by executing a predetermined program.

[0055] The injection amount setting unit 73 sets the injection amount, which is the amount of fuel injected from the injector 15. In this embodiment, in any gear position and in any of the regions A1 to A3, multi-stage injection is performed in which fuel is injected from the injector 15 in multiple injections during one combustion cycle. Thus, the injection amount setting unit 73 sets the injection amount of each injection performed during one combustion cycle. The injection amount setting unit 73 sets each injection amount according to the determination result of the determination unit 71, the engine speed, and the engine load. The injection amount setting unit 73 sets each injection amount so that the total of the set injection amounts, which is the sum of the injection amounts of the injections performed during one combustion cycle, matches the injection amount necessary to achieve the target engine torque.

[0056] The injection timing setting unit 74 sets the injection timing of each injection (the timing at which fuel injection from the injector 15 starts). The injection timing setting unit 74 sets the injection timing of each injection depending on the determination result of the determination unit 71, the engine speed, and the engine load.

[0057] The fuel injection control unit 72 controls the injector 15 so that the amount of fuel set by the injection amount setting unit 73 is injected at the injection timing set by the injection timing setting unit 74 .

[0058] [Overall control flow of injector 15] FIG. 5 is a flowchart showing the overall flow of control of the injector 15 performed by the fuel injection control unit 72 (processor 70). The processor 70 first reads information detected by the sensors SN1 to SN13 (step S1). Next, the processor 70 (determination unit 71) determines whether the engine is operating in the medium load range A2 (step S2). If the determination is YES and the engine is operating in the medium load range A2, the processor 70 controls the injector 15 to achieve rapid multi-stage combustion (step S3). Rapid multi-stage combustion will be described later. If the determination in step S2 is NO and the engine is not operating in the medium load range A2, the processor 70 determines whether the engine is operating in the low load range A1 (step S4). If the determination is YES and the engine is operating in the low load range A1, the processor 70 controls the injector 15 to perform premixed combustion of the air-fuel mixture (step S5). For example, the injector 15 is caused to perform four-stage injection. On the other hand, if the determination in step S4 is NO, that is, if the engine is operating in the high-speed, high-load range A3, the processor 70 controls the injector 15 so that the mixture is diffusively burned (step S6). For example, the processor 70 causes the injector 15 to perform two to six-stage injection.

[0059] [Control in the medium load range A2] We will now explain the control of the injector 15 performed by the fuel injection control unit 72 (processor 70) when the engine is operating in the medium load range A2 (when the judgment unit 71 determines that the engine is operating in the medium load range A2), which is a characteristic configuration of the present invention.

[0060] FIG. 6 is a graph showing an example of the injection rate of the injector 15 (the amount of fuel injected from the injector 15 per unit time) and the heat release rate in the medium load range A2.

[0061] 6, in the medium load range A2, the fuel injection control unit 72 performs five-stage injection. Specifically, the fuel injection control unit 72 causes the injector 15 to perform a pilot injection P1 that injects fuel during the compression stroke, a pre-injection P2 that injects fuel during the compression stroke and at a timing later than the pilot injection P1, a main injection P3 that injects fuel near the compression top dead center (TDC) and at a timing later than the pre-injection P2, a first after-injection P4 that injects fuel during the expansion stroke and at a timing later than the main injection P3, and a second after-injection P5 that injects fuel during the expansion stroke and at a timing later than the first after-injection P4. Here, the second after-injection P5 that is performed last corresponds to the "after-injection" in the claims.

[0062] Hereinafter, the injection timings of pilot injection P1, pre-injection P2, main injection P3, first after-injection P4, and second after-injection P5 will be referred to as pilot injection timing, pre-injection timing, main injection timing, first after-injection timing, and second after-injection timing, respectively. Also, the injection quantities of pilot injection P1, pre-injection P2, main injection P3, first after-injection P4, and second after-injection P5 will be referred to as pilot injection quantity, pre-injection quantity, main injection quantity, first after-injection quantity, and second after-injection quantity, respectively.

[0063] The main injection P3 is the main injection for obtaining engine torque, and the main injection amount is set to be larger than the other four injection amounts. Also, the higher the engine load (target engine torque), the larger the main injection amount becomes.

[0064] 7 is a flowchart showing an outline of the control of the injector 15 performed by the fuel injection control unit 72 when the engine is operating in the medium load range A2. As shown in FIG. 7, the fuel injection control unit 72 sets the pilot injection amount and pilot injection timing (step S12), and also sets the main injection amount and main injection timing (step S13). The fuel injection control unit 72 also sets the pre-injection amount and, as described later, sets the pre-injection timing based on the main injection timing (step S14). The fuel injection control unit 72 also sets the first after-injection amount and the second after-injection amount, and, as described later, sets the first after-injection timing and the second after-injection timing based on the main injection timing (steps S15 and S16).

[0065] [Control in the medium load range during high-speed driving] Even when the engine is operating in the same medium load range A2, the fuel injection control unit 72 performs different controls depending on whether the vehicle 100 is traveling at a high speed or a low speed.

[0066] First, a description will be given of the control performed by the fuel injection control unit 72 when the engine is operating in the medium load range A2 and the vehicle 100 is traveling at high speed (when the determination unit 71 determines that the vehicle 100 is traveling at high speed). Hereinafter, operation when the engine is operating in the medium load range A2 and the vehicle 100 is traveling at high speed will be referred to as high gear operation, where appropriate.

[0067] (Injection timing) During high gear operation, the fuel injection control unit 72 (injection timing setting unit 74) sets the main injection timing based on the engine speed and engine load within a range in which the injection axis AX of the injector 15 is oriented toward the lip portion 53 during at least a portion of the injection period (the period from the injection timing to the end of injection) and the fuel injected from the injector 15 is distributed to the upper cavity 52 and the lower cavity 51. Hereinafter, the injection timing in which the injection axis AX of the injector 15 is oriented toward the lip portion 53 during at least a portion of the injection period and the fuel injected from the injector 15 is distributed to the upper cavity 52 and the lower cavity 51 will be referred to as the fuel distribution possible timing, as appropriate. Note that the fuel distribution possible timing differs depending on the specifications of the injector 15, but is, for example, a timing within a range from approximately 20° CA (CA: crank angle) before BTDC (compression top dead center) to approximately 20° CA after ATDC (compression top dead center).

[0068] Specifically, the main injection timing during high gear operation is set in advance in a map to a time within a range in which fuel distribution is possible for the engine speed and engine load, and is stored in the memory unit 78. The fuel injection control unit 72 (injection timing setting unit 74) extracts from this map a value corresponding to the current engine speed (engine speed detected by the crank angle sensor SN1) and the current engine load (target engine torque set by the determination unit 71), and sets it as the main injection timing.

[0069] Fig. 8 is a graph showing an example of the relationship between the engine load and the main injection timing at a predetermined engine speed during high gear operation (line L1) and during low gear operation (line L2), which will be described later. As shown by line L1 in Fig. 8, for example, at a predetermined engine speed, the main injection timing during high gear operation is set to a timing on the advanced side as the engine load increases up to a predetermined load, and once the predetermined load is exceeded, the main injection timing is set to a timing on the retarded side as the engine load increases.

[0070] When operating in a high gear, the fuel injection control unit 72 also sets the pilot injection timing based on the engine speed and engine load within the range in which the fuel distribution timing is possible. As with the main injection timing, the pilot injection timing is also set by extracting values ​​corresponding to the current engine speed and engine load from a map that is preset and stored in the memory unit 78.

[0071] When operating in a high gear, the fuel injection control unit 72 sets the pre-injection timing so that the time interval between the pre-injection timing and the main injection timing is approximately constant regardless of the engine speed or engine load. This interval is set in advance and stored in the memory unit 78, and the fuel injection control unit 72 calculates a timing that is advanced by this interval from the previously set main injection timing and sets it as the pre-injection timing.

[0072] When operating in a high gear, the fuel injection control unit 72 sets the first post-injection timing so that the time interval between the first post-injection timing and the main injection timing is approximately constant. This interval is set in advance and stored in the memory unit 78. The fuel injection control unit 72 calculates the timing to be retarded by this interval from the previously set main injection timing and sets it as the pre-injection timing.

[0073] During high gear operation, the fuel injection control unit 72 sets the second after-injection timing based on the engine speed and engine load. Specifically, the fuel injection control unit 72 sets the interval between the main injection timing and the second after-injection timing based on the engine speed and engine load, calculates a timing that is retarded from the set main injection timing by that interval, and sets this as the second after-injection timing. The interval between the main injection timing and the second after-injection timing is set in advance for the engine speed and engine load and stored in the memory unit 78 as a map, and the fuel injection control unit 72 calculates a timing that is retarded from the previously set main injection timing by that interval and sets this as the pre-injection timing.

[0074] Fig. 9 is a graph showing an example of the relationship between the engine load and the second after-injection timing at a predetermined engine speed during high gear operation (line L1) and during low gear operation (line L2), which will be described later. As shown by line L1 in Fig. 9, for example, at a predetermined engine speed, the second after-injection timing during high gear operation is set to a timing that is more advanced as the engine load increases up to a predetermined load, and is set to a timing that is more retarded as the engine load increases once the predetermined load is exceeded, in substantially the same manner as the main injection timing.

[0075] (Injection amount) When operating in a high gear, the fuel injection control unit 72 sets the injection amount of each injection (pilot injection amount, pre-injection amount, main injection amount, first after-injection amount, second after-injection amount) based on the engine speed and engine load. Each injection amount when operating in a high gear is set in advance in a map for the engine speed and engine load and stored in the memory unit 78, and the fuel injection control unit 72 (injection amount setting unit 73) extracts each value corresponding to the current engine speed and current engine load from each map and sets it as each injection amount.

[0076] Fig. 10 is a graph showing an example of the relationship between the engine load and the second after-injection amount at a predetermined engine speed during high gear operation (line L1) and during low gear operation (line L2), which will be described later. As shown by line L1 in Fig. 10, for example, at a predetermined engine speed, the second after-injection amount during high gear operation is set to increase as the engine load increases. In the example of Fig. 10, the second after-injection amount during high gear operation is increased approximately in proportion to the engine load.

[0077] (Combustion type) In this embodiment, the above-described injection control improves fuel economy and exhaust performance during high gear operation.

[0078] A more detailed explanation will be given using Figure 11. Figure 11 is a partial cross-sectional view of the combustion chamber 6 showing the state of fuel when it is injected at the fuel distribution possible period. The fuel (fuel spray) Df injected from the injector 15 along the injection axis AX diffuses at a spray angle θ. Figure 11 shows an upper diffusion axis AX1 indicating upward diffusion relative to the injection axis AX, and a lower diffusion axis AX2 indicating downward diffusion. The spray angle θ is the angle formed by the upper diffusion axis AX1 and the lower diffusion axis AX2.

[0079] When fuel is injected from the injector 15 during the fuel distribution period, part of the fuel Df collides with the lip portion 53. When the fuel Df collides with the lip portion 53, the fuel Df separates into a portion (arrow F11) flowing toward the lower cavity 51 (downward) and a portion (arrow F12) flowing toward the upper cavity 52 (upward).

[0080] The fuel heading toward the lower cavity 51 flows along the wall surface of the lower cavity 51, thereby mixing with the air in the radial center of the lower cavity 51 and the combustion chamber 6. Specifically, the fuel heading in the direction of arrow F11 (downward) enters the radial recess 514 of the lower cavity 51 while mixing with the air, then changes its flow direction from downward to inward in the radial direction B, and flows along the first bottom 512 as shown by arrow F12. Furthermore, the fuel flowing in the direction of arrow F12 is lifted upward, and flows radially outward from the combustion chamber ceiling surface 6U as shown by arrow F13, mixing with the air in the radial center of the combustion chamber 6.

[0081] On the other hand, the fuel flowing toward the upper cavity 52 flows along the wall surface of the upper cavity 52 and mixes with the air in the upper cavity 52. ​​Specifically, the fuel flowing in the direction of arrow F21 (upward) enters the tapered region 524 of the upper cavity 52 while mixing with the air, flows obliquely downward along the tapered region 524 as shown by arrow F22, and reaches the second bottom portion 522. Thereafter, the fuel is lifted upward by the rising curved surface between the second bottom portion 522 and the standing wall region 525, and flows radially inward from the combustion chamber ceiling surface 6U. In addition, a portion of the fuel lifted upward also flows into a space radially outward of the standing wall region 525 (a squish space on the peripheral flat surface portion 55) as shown by arrow F23, and mixes with the air in that space.

[0082] In this way, when fuel is injected during the fuel distribution period, the injected fuel diffuses throughout the combustion chamber 6 and mixes with the air throughout the combustion chamber 6, forming a homogeneous mixture in the combustion chamber 6. The homogeneous mixture rapidly burns near the top dead center of compression. This shortens the combustion time, thereby improving fuel economy. Furthermore, the promotion of air-fuel mixing also reduces soot generation. Therefore, when the engine is driven in a high gear, the above-described injection control improves fuel economy and exhaust performance. In particular, in this embodiment, the pilot injection timing is also set to the fuel distribution period, so the fuel from the pilot injection P1 also diffuses throughout the combustion chamber 6. As a result, as shown in FIG. 6 , the fuel from the pilot injection P1 is burned slowly, and rapid multi-stage combustion is achieved in which the heat generation from the pilot injection P1 and the heat generation from the main injection P3 gradually continue, resulting in a peak heat release rate near the top dead center of compression (TDC). This reduces combustion noise while improving fuel economy and exhaust performance.

[0083] Furthermore, when operating in a high gear, the first after-injection P4 and the second after-injection P5 are performed after the main injection P3, which maintains a high temperature in the combustion chamber 6 after the main injection P3 is completed, promoting the oxidation of soot produced during the combustion of fuel by the main injection P3, thereby reliably reducing soot emissions from the engine.

[0084] [Control in the medium load range during low speed driving] Next, a description will be given of the control performed by the fuel injection control unit 72 when the engine is operating in the medium load range A2 and the vehicle 100 is traveling at a low speed (when the determination unit 71 determines that the vehicle 100 is traveling at a low speed). Hereinafter, operation when the engine is operating in the medium load range A2 and the vehicle 100 is traveling at a low speed will be referred to as low gear operation, where appropriate.

[0085] When driving in a low gear, the main injection timing is set to a time when fuel distribution is possible, as in driving in a high gear, to achieve rapid multi-stage combustion. As described above, setting the main injection timing to a time when fuel distribution is possible can suppress combustion noise while improving exhaust performance. However, when the vehicle 100 is traveling at low speeds, background noise such as wind noise is low, making it easier for occupants to detect combustion noise. Therefore, to further improve the quietness of the vehicle 100, it is desirable to further reduce combustion noise when traveling at low speeds. In response to this, retarding the main injection timing can lower the peak value of combustion pressure and reduce combustion noise.

[0086] Therefore, in this embodiment, when operating in a low gear, the fuel injection control unit 72 (injection timing setting unit 74) sets the main injection timing to a timing within a range in which fuel distribution is possible and that is more retarded than the main injection timing during high gear operation (the main injection timing is set to be more retarded during low gear operation than during high gear operation at an operating point where the engine speed and engine load are the same). Specifically, the main injection timing during low gear operation is set in advance for the engine speed and engine load to a timing within a range in which fuel distribution is possible and that is more retarded than the main injection timing during high gear operation, and is stored in a map. The fuel injection control unit 72 extracts values ​​corresponding to the current engine speed and engine load from this map and sets the main injection timing.

[0087] As shown by line L2 in FIG. 8, for example, at a predetermined engine speed, the main injection timing during low gear operation is set to be more retarded than the main injection timing during high gear operation shown by line L1, and is set to become more retarded as the engine load increases.

[0088] Here, if the main injection timing is retarded as described above, the combustion noise can be reduced, but the fuel from the main injection P3 may be concentrated in the upper part of the combustion chamber 6, which may increase the amount of soot generated by the combustion of the fuel from the main injection P3.

[0089] Specifically, during main injection P3, the piston 5 is descending at the timing when the main fuel spray reaches the lip portion 53. Therefore, when the main injection timing is retarded, the position of the piston 5 is lower when the fuel spray Df reaches the lip portion 53. In other words, when the main injection timing is a predetermined timing, the position of the piston 5 when the main fuel Df from the main injection P3 reaches the lip portion 53 is as shown by the dashed line in FIG. 12 . However, when the main injection timing is retarded from the predetermined timing, the position of the piston 5 at the timing is lower than the dashed line position, as shown by the solid line in FIG. 12 . Therefore, when the main injection timing is retarded, the main fuel Df from the main injection P3 collides with a higher portion of the lip portion 53, and more fuel is distributed to the upper cavity 52. ​​As a result, the diffusion of the fuel from the main injection P3 throughout the combustion chamber 6 is suppressed, the homogeneity of the mixture decreases, and soot is more likely to be generated. In addition, the amount of soot produced also increases because the oxidation of soot is suppressed by the fact that a larger amount of fuel from the main injection P3 flows into the squish space (the space on the peripheral flat surface portion 55 radially outward of the standing wall region 525) defined by the relatively low temperature inner surface (cylinder liner) of the cylinder 2.

[0090] On the other hand, if the temperature inside the combustion chamber 6 can be maintained at a high temperature for a longer period after the end of the main injection P3, the oxidation of soot produced during the combustion of fuel by the main injection P3 can be promoted, thereby suppressing an increase in soot emissions from the engine.

[0091] Therefore, in this embodiment, as shown by line L2 in Fig. 9, the second after-injection timing during low gear operation is set to a timing that is more retarded than the main injection timing during high gear operation, as shown by line L1. In other words, during low gear operation, the fuel injection control unit 72 (injection timing setting unit 74) sets the second after-injection timing to a timing that is more retarded than the second after-injection timing during high gear operation (the second after-injection timing is set to be more retarded during low gear operation than during high gear operation at an operating point where the engine speed and engine load are the same). If the second after-injection timing is retarded, the combustion chamber 6 is heated by the combustion of fuel by the second after-injection P5, and the combustion chamber 6 is maintained at a high temperature for a longer period after the end of the main injection P3, thereby further promoting the oxidation of soot.

[0092] Specifically, the fuel injection control unit 72 sets the interval between the main injection timing and the second after-injection timing based on the engine speed and engine load when operating in a low gear, just as when operating in a high gear. The fuel injection control unit 72 calculates the delay of the previously set main injection timing by the interval and sets the second after-injection timing. However, the fuel injection control unit 72 sets the interval between the main injection timing and the second after-injection timing when operating in a low gear to be equal to or greater than the interval when operating in a high gear. As a result, since the main injection timing is set to a more retarded timing when operating in a low gear than when operating in a high gear, the second after-injection timing is set to a more retarded timing when operating in a low gear than when operating in a high gear. In this embodiment, the interval when operating in a low gear is set longer than the interval when operating in a high gear, and the second after-injection timing is retarded by a larger amount than the retard of the main injection timing. The interval when operating in a low gear is determined in advance for each engine speed and engine load and is stored in the memory unit 78 as a map.

[0093] Furthermore, as described above, the higher the engine load, the larger the main injection amount. A larger main injection amount also increases the amount of soot produced. Therefore, as shown by line L2 in FIG. 9, the fuel injection control unit 72 sets the second after-injection timing during low gear operation to a more retarded timing as the engine load increases. In other words, the intervals are set so as to satisfy this relationship.

[0094] In addition, during low gear operation, the fuel injection control unit 72 (injection timing setting unit 74) sets the main injection timing to a timing that is more retarded than that during high gear operation, and also sets the pilot injection timing to a timing that is more retarded than that during high gear operation.

[0095] On the other hand, when operating in a low gear, the fuel injection control unit 72 (injection timing setting unit 74) sets the pre-injection timing and the first after-injection timing so that the time interval between each injection timing and the main injection timing is a predetermined interval, regardless of the engine speed and engine load, just as when operating in a high gear.

[0096] (Injection amount) To address the problem of soot being more likely to be generated after combustion by the main injection P3 when operating in a low gear, increasing the second after-injection amount can also suppress an increase in soot emissions from the engine. In other words, increasing the second after-injection amount increases the combustion energy of the fuel by the second after-injection P5, making it possible to raise the temperature in the combustion chamber 6 after the end of the main injection P3, and thereby lengthening the period during which the temperature in the combustion chamber 6 is maintained at a high temperature, further promoting the oxidation of soot.

[0097] Therefore, in this embodiment, as shown by line L2 in FIG. 10, the second after-injection amount during low gear operation is set to be greater than the main injection amount during high gear operation shown by line L1. Large amountIn other words, when operating in a low gear, the fuel injection control unit 72 (injection amount setting unit 73) sets the second after-injection amount to an amount greater than the second after-injection amount when operating in a high gear (the second after-injection amount is set to be greater when operating in a low gear than when operating in a high gear at an operating point where the engine speed and engine load are the same). Also, when operating in a low gear, the fuel injection control unit 72 (injection amount setting unit 73) sets the second after-injection amount to an amount that increases as the engine load increases. For example, as shown by line L2 in FIG. 10, at a predetermined engine speed, the second after-injection amount when operating in a low gear increases in approximately proportion to the increase in engine load.

[0098] On the other hand, when operating in a low gear, the fuel injection control unit 72 sets each of the other injection amounts (pilot injection amount, pre-injection amount, main injection amount, first after-injection amount) to an amount smaller than each of the injection amounts when operating in a high gear (the injection amounts of the other injections except for the second after-injection P5 are set to be smaller when operating in a low gear than when operating in a high gear at an operating point where the engine speed and engine load are the same). Specifically, the fuel injection control unit 72 sets each of the other injection amounts (pilot injection amount, pre-injection amount, main injection amount, first after-injection amount) so that the total value of the reduction amounts of each injection amount when operating in a high gear is approximately equal to the increase amount of the second after-injection amount when operating in a high gear. In this embodiment, vinegar The other injection amounts are set so that the reduction amounts thereof approximately match the increase amount of the second after-injection amount relative to high gear operation divided into four equal parts.

[0099] Each injection amount (pilot injection amount, pre-injection amount, main injection amount, first after-injection amount, second after-injection amount) is set in advance for the engine speed and engine load so that the above relationship is satisfied, and is stored in a map in the memory unit 78. The fuel injection control unit 72 extracts values ​​corresponding to the current engine speed and engine load from this map and sets them as each injection amount, both when operating in a low gear and when operating in a high gear.

[0100] Among the above controls performed by the fuel injection control unit 72 in the medium load range A2, the control of causing the injector 15 to perform the main injection P3 and the second after-injection P5 and setting the main injection timing to a timing at which fuel can be distributed corresponds to the "control for rapid multi-stage combustion" in the claims. Furthermore, the control of making the second after-injection amount during low gear operation greater than the second after-injection amount during high gear operation corresponds to the "first control" in the claims. Furthermore, the control of setting the second after-injection timing during low gear operation to a timing that is more retarded than the second after-injection timing during high gear operation corresponds to the "second control" in the claims.

[0101] [Effect, etc.] As described above, according to the control device for a compression ignition engine according to the above embodiment, in the medium load range A2, both the pilot injection timing and the main injection timing are set to timings in which the injection axis AX is directed toward the lip portion 53 for at least a part of each injection period. Therefore, the fuel related to these injections can be made to collide with the lip portion 53 and distributed to both the upper cavity 52 and the lower cavity 51, thereby realizing rapid multi-stage combustion with excellent fuel economy and exhaust performance.

[0102] Furthermore, when the engine is operating in a low gear (when the engine is operating in the medium load range A2 and the vehicle 100 is traveling at a low speed), the main injection timing is set to be more retarded than when the engine is operating in a high gear (when the engine is operating in the medium load range A2 and the vehicle 100 is traveling at a high speed). As a result, when the engine is operating in a high gear, the combustion energy generated near the compression top dead center is increased to improve fuel economy, and when the engine is operating in a low gear and the combustion noise is easily noticeable by the passengers, the combustion energy is kept small to reduce the combustion noise, thereby improving both fuel economy and quietness.

[0103] Furthermore, when the engine is in a low gear, the second after-injection timing is retarded compared to when the engine is in a high gear, and the second after-injection amount is increased, so that the temperature in the combustion chamber 6 after the fuel combustion by the main injection P3 is maintained at a high temperature for a longer period of time. Therefore, when the engine is in a low gear, the soot that has increased after the main injection due to the retarded main injection timing can be reliably oxidized. This ensures that the amount of soot emitted from the engine is kept low and good exhaust performance is ensured.

[0104] In the above embodiment, when the engine is operated in a low gear, the second after-injection timing is set to a more retarded timing and the second after-injection amount is increased as the engine load increases and soot is more likely to be generated by the combustion of fuel in the main injection P3. This makes it possible to more reliably reduce the amount of soot emissions.

[0105] In the above embodiment, when the engine is in a low gear, the second after-injection amount is greater than the second after-injection amount when the engine is in a high gear, while the injection amounts of the other injections are reduced compared to the amounts when the engine is in a high gear. Therefore, when the engine is in a low gear, the increase in the second after-injection amount provides the above-described effect, while suppressing changes in the total amount of fuel supplied to the combustion chamber in one combustion cycle, and therefore in the engine torque, between when the engine is in a low gear and when the engine is in a high gear.

[0106] [Variations] In the above embodiment, a case has been described in which both control is performed to retard the second after-injection timing during low gear operation compared to the second after-injection timing during high gear operation, and control is performed to increase the second after-injection amount compared to the second after-injection amount during high gear operation, but only one of these may be performed.

[0107] In addition, the control to retard the second after-injection timing as the engine load increases during low gear operation, and the control to increase the second after-injection amount as the engine load increases during low gear operation may be omitted.

[0108] Furthermore, the specific method of determining whether vehicle 100 is traveling at a low speed or a high speed is not limited to the above. For example, if the vehicle speed detected by a vehicle speed sensor or the like is equal to or greater than a predetermined speed, it may be determined that vehicle 100 is traveling at a high speed, and if the vehicle speed is less than the predetermined speed, it may be determined that vehicle 100 is traveling at a low speed.

[0109] In addition, in the above embodiment, the current stage number (current gear stage) of the transmission 110 is detected using the gear stage sensor SN13, but the stage number (gear stage) may also be calculated from the vehicle speed, engine speed, etc.

[0110] In addition, in the above embodiment, a case has been described in which all other injection amounts (pilot injection amount, pre-injection amount, main injection amount, first after-injection amount) except for the second after-injection amount during low gear operation are made smaller than the respective amounts during high gear operation, but it is also possible to configure only one of the other injection amounts except for the second after-injection amount to be smaller than the amount during high gear operation.

[0111] Furthermore, the pilot injection P1, pre-injection P2, and first after-injection P4 may be omitted. [Explanation of symbols]

[0112] 1 Engine body 2 cylinders 5 pistons 6 Combustion chamber 6U Combustion chamber ceiling (ceiling) 15 Injector (fuel injection valve) 5C cavity 50 Crown surface 51 Lower cavity 52 Upper cavity 53 Lip 70 Processor (control device) 72 Fuel injection control unit P1 pilot injection P2 Pre-injection P3 main injection

Claims

1. A control device for a compression ignition engine mounted on a vehicle, the control device comprising: an engine body having a cylinder formed therein; a piston reciprocating within the cylinder; a combustion chamber formed by the cylinder and a crown surface of the piston in which compression ignition combustion of an air-fuel mixture is carried out; and a fuel injection valve disposed on a ceiling surface of the combustion chamber and injecting fuel along an injection axis, a determination unit that determines whether the vehicle is traveling at a low speed or a high speed; a fuel injection control unit that controls the fuel injection valve, The piston has a lower cavity provided at the radial center of a crown surface of the piston, an upper cavity provided around the lower cavity and shallower than the lower cavity, and a lip portion connecting the lower cavity and the upper cavity, The fuel injection control unit when the engine is operated in a medium load region where the engine load is higher than a predetermined first load and is equal to or lower than a predetermined second load set higher than the first load, a control for rapid multi-stage combustion is executed in which the fuel injection valve performs a main injection in which fuel is injected at a timing where the injection axis is directed toward the lip portion during at least a part of an injection period so that fuel is distributed to the upper cavity and the lower cavity, and an after-injection in which fuel is injected after the main injection, When the rapid multi-stage combustion control is executed in the medium load region, controlling the fuel injection valve so that the injection timing of the main injection is more retarded when the determination unit determines that the vehicle is traveling at a low speed than when the determination unit determines that the vehicle is traveling at a high speed; A control device for a compression ignition engine, characterized by executing at least one of a first control that controls the fuel injection valve so that the injection amount of the after-injection is larger when the engine is running at low speed than when the engine is running at high speed, and a second control that controls the fuel injection valve so that the injection timing of the after-injection is more retarded when the engine is running at low speed than when the engine is running at high speed.

2. 2. The control device for a compression ignition engine according to claim 1, The control device for a compression ignition engine, characterized in that the determination unit determines that the vehicle is traveling at a low speed when the gear stage of a transmission installed in the vehicle is equal to or lower than a predetermined determination number, and determines that the vehicle is traveling at a high speed when the gear stage is higher than the determination number.

3. 3. The control device for a compression ignition engine according to claim 1, The control device for a compression ignition engine, characterized in that the fuel injection control unit executes the first control when the rapid multi-stage combustion control is executed, and when the first control is executed, controls the fuel injection valve so that the injection amount of the after-injection increases as the engine load increases.

4. The control device for a compression ignition engine according to any one of claims 1 to 3, A control device for a compression ignition engine, characterized in that, when the first control is executed, the fuel injection control unit controls the fuel injection valve so that the injection amount of injections other than the after-injection is smaller when the judgment unit determines that the vehicle is traveling at a low speed than when the judgment unit determines that the vehicle is traveling at a high speed.

5. 3. The control device for a compression ignition engine according to claim 1, a control device for a compression ignition engine, characterized in that the fuel injection control unit executes the second control when the rapid multi-stage combustion control is being executed, and when the second control is being executed, controls the fuel injection valve so that the injection timing of the after-injection becomes more retarded as the engine load increases.

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