Compression ignition engine control device

Abstract

To surely enhance fuel consumption performance and exhaustion performance, in an engine having a cavity of a top-and-bottom two-stage structure.SOLUTION: A fuel injection valve performs: pilot injection for injecting fuel at timing at which an injection shaft is oriented to a lip part in a compression stroke, in a first operation region in which an engine rotation number is equal to or lower than a switching rotation number and in a second operation region in which the engine rotation number is higher than the switching rotation number; and main injection for injecting the fuel after the pilot injection, and at timing at which the injection shaft is oriented to the lip part. In the first operation, the fuel injection valve is controlled so that the injection timing of the main injection is closer to an advance side in the case where the engine rotation number is high than in the case where the engine rotation number is low. In the second operation region, the fuel injection valve is controlled so that the injection timing of the pilot injection and the main injection is set closer to a retardancy side than the injection timing of the switching rotation number.SELECTED DRAWING: Figure 9

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 the top dead center of the compression stroke 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 points 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 the proportion of fuel distributed to the upper cavity by the pilot injection is configured to be higher than when the engine load is low. [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] According to the configuration of Patent Document 1, as described above, when fuel from the main injection tends to be distributed to the lower cavity, the proportion of fuel distributed to the upper cavity by the pilot injection is increased. As a result, the total fuel distribution proportions of the pilot injection and the main injection to each cavity are equal, and the fuel distribution throughout the combustion chamber after the main injection is completed is homogenized. However, with this configuration, the distribution of fuel from the main injection is still uneven, resulting in insufficient mixing of the fuel and air. This leaves room for improvement in terms of fuel economy and exhaust performance.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a control device for a compression ignition engine that can reliably improve fuel efficiency and exhaust performance in an engine in which part of the combustion chamber is defined by a piston crown surface having a cavity with a two-stage upper and lower structure. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a control device for an engine including an engine body having a cylinder, a piston reciprocating within the cylinder, a combustion chamber formed by a crown surface of the cylinder and the piston, a fuel injection valve disposed on a ceiling surface of the combustion chamber and configured to inject fuel along an injection axis, and a fuel injection control unit configured to control the fuel injection valve, wherein compression ignition combustion of an air-fuel mixture is performed within the combustion chamber, the piston having a lower cavity disposed in a radial center of the crown surface, an upper cavity disposed around the lower cavity and shallower than the lower cavity, and a lip portion connecting the lower cavity and the upper cavity, and the fuel injection control unit configured to control a fuel injection valve to inject a fuel into the compression stroke when the engine is operating in a first operating range where the engine speed is equal to or lower than a predetermined switching speed and a second operating range where the engine speed is higher than the switching speed. and a main injection valve that injects fuel after the pilot injection and at a timing when the injection shaft is directed toward the lip portion during at least a part of the injection period, and wherein, when the engine is operating in the first operating range during the distributed injection control, a first control is implemented to control the fuel injection valve so that the injection timing of the main injection is more advanced when the engine speed is high than when the engine speed is low, and a second control is implemented to control the fuel injection valve so that the injection timing of the pilot injection and the main injection are each more retarded than the injection timing at the switchover speed when the engine is operating in the second operating range.

[0008] According to this control device, by implementing distributed injection control, both the pilot injection and the main injection are performed at timings where the injection axis points toward the lip portion for at least part of each injection period, so that the fuel related to these injections can be distributed to both the upper and lower cavities.

[0009] Furthermore, when the engine is operating in the first operating range, where the engine speed is below the switching speed, the main injection timing is more advanced when the engine speed is high than when the engine speed is low. Therefore, in the above case, the fuel distribution ratio of the main injection to the upper and lower cavities can be adjusted appropriately, allowing the fuel from the main injection to be more evenly dispersed throughout the combustion chamber. Therefore, a homogeneous mixture that is well mixed with air can be formed throughout the combustion chamber near the top dead center of compression, which reliably achieves improved fuel economy and reduced soot generation, i.e., improved exhaust performance.

[0010] Specifically, as engine speed increases, piston speed increases. Therefore, if the injection timing of the main injection were constant regardless of engine speed, the piston position at the time when the main fuel from the main injection reaches the lip would be lower at high engine speeds than at low engine speeds, and the fuel from the main injection would not be biased toward the upper cavity at high engine speeds. In contrast, if the injection timing of the main injection is advanced at high engine speeds compared to low engine speeds, as described above, the piston position at that timing would be such that the fuel from the main injection that reaches the lip at each engine speed is appropriately distributed to the two cavities, upper and lower, and the fuel can be distributed in appropriate proportions to the two cavities.

[0011] However, if the advance of the main injection timing is increased, the thermal energy generated near the compression top dead center becomes excessive, resulting in an increase in the amount of NOx produced.In response to this, with this control device, when the engine speed becomes higher than the switching speed, the injection timing of the main injection and the pilot injection are retarded compared to the respective injection timings at the switching speed.

[0012] If the injection timing of the main injection is retarded, the piston position will be lower when the main fuel reaches the lip, which will tend to bias the fuel toward the upper cavity. On the other hand, if the injection timing of the pilot injection performed during the compression stroke is retarded, the fuel from the pilot injection will tend to bias toward the lower cavity. Therefore, by retarding both the main injection and the pilot injection as described above, the total fuel distribution supplied to the combustion chamber by these injections can be made more uniform. Therefore, with this control device, in the second operating range higher than the switching speed, the injection timing of the main injection is retarded from the switching speed, which can suppress the generation of NOx. Furthermore, the homogenization of the total fuel by the main injection and the pilot injection can suppress the generation of soot, thereby reliably improving exhaust performance in the second operating range.

[0013] In the above control device, it is desirable that, when the first control is performed, the fuel injection control unit controls the fuel injection valve so that the injection timing of the pilot injection is more advanced when the engine speed is high than when the engine speed is low (Claim 2).

[0014] According to this control device, when the engine is operating in the first operating range, the fuel distribution ratio between the two upper and lower cavities, including the fuel from the pilot injection as well as the fuel from the main injection, can be set to an appropriate ratio, thereby more reliably improving fuel economy and exhaust performance.

[0015] In the above control device, it is desirable that, when the distributed injection control is performed, the fuel injection control unit causes the fuel injection valve to perform a pre-injection, which injects fuel between the pilot injection and the main injection, and controls the fuel injection valve so that the time interval between the injection timing of the pre-injection and the injection timing of the main injection is constant (claim 3).

[0016] According to this control system, by performing a pre-injection in which fuel is injected between the pilot injection and the main injection, it is possible to prevent a large amount of fuel from being supplied to the combustion chamber at once by the main injection. Therefore, it is possible to suppress sudden combustion near the compression top dead center and suppress an increase in combustion noise. Furthermore, because the time interval between the injection timing of the pre-injection and the injection timing of the main injection is constant, it is possible to suppress interference between the fuel spray from the pre-injection and the fuel spray from the main injection, and it is possible to more appropriately distribute the fuel from the main injection to each cavity.

[0017] In the above control device, it is desirable that the control device further includes a gear stage detection unit capable of detecting the gear stage of a transmission provided in a vehicle equipped with the engine, and that the fuel injection control unit performs the first control and the second control when the gear stage detected by the gear stage detection unit is equal to or greater than a predetermined number set to two or more stages (Claim 4).

[0018] As described above, in the present invention, when the engine is operating in a high engine speed range in the first operating region during distributed injection control, the injection timing of the main injection is advanced, which may result in a higher combustion noise. In response to this, this control device implements distributed injection control when the gear is at a high speed greater than or equal to a predetermined number, that is, when the vehicle equipped with the engine is traveling at high speed. This prevents the occupants from feeling uncomfortable due to the combustion noise. [Effects of the Invention]

[0019] According to the present invention, a control device for a compression ignition engine can be provided that can reliably improve fuel efficiency and exhaust performance in an engine in which part of the combustion chamber is defined by a piston crown surface having a cavity with a two-stage upper and lower structure. [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 cross-sectional view of the combustion chamber showing the flow state of the fuel spray. [Figure 9] FIG. 9 is a cross-sectional view of the combustion chamber for explaining how fuel is distributed by main injection. [Figure 10] FIG. 10 is a cross-sectional view of the combustion chamber for explaining the distribution of fuel by pilot injection. [Figure 11] FIG. 11 is a graph showing the relationship between the engine speed and the main injection timing correction amount. [Figure 12] FIG. 12 is a graph showing the relationship between the engine speed and the pilot injection timing correction amount. 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. 8 , 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. 8 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.

[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] The 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 make 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 this 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 ridge 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 ridge portion 54 is a mountain-shaped protrusion located at the center of the crown surface 50 (lower cavity 51) in the radial direction B. The ridge portion 54 is protrudingly provided in a position directly below the nozzle 151 of the injector 15 (FIG. 8).

[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 recessed portion 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 cylinder axial direction), 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] The processor 70 receives detection signals from various sensors mounted on the vehicle. 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 gear position of the transmission 110. 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. The gear position sensor SN13 corresponds to the "gear position detection unit" in the claims.

[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 current gear position of the transmission 110 is a high gear position. The determination unit 71 determines that the gear position is a high gear position when the current gear position detected by the gear position sensor SN13 is equal to or greater than a preset reference gear position (predetermined number of gear positions). The reference gear position is set in advance to a value equal to or greater than second gear (second speed) and stored in the storage unit 78. For example, if the transmission 110 has eight gear positions, the reference gear position is set to seventh gear (seventh 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] [Injector control in the medium load range] The control of the injector 15 when the engine is operating in the medium load range A2 will be described.

[0060] FIG. 6 is a graph showing an example of the injection rate (amount of fuel injected from the injector 15 per unit time) and the heat generation rate when the engine is operating in the medium load range A2 (when the determination unit 71 determines that the engine is operating 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 the following injections: 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. The main injection P3 is the main injection for obtaining engine torque, and its injection amount is set to be larger than the other four injection amounts.

[0062] 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).

[0063] [Control configuration when high-gear multi-stage combustion conditions are met] Next, a description will be given of the control of the injector 15 when the conditions that the engine is operating in the medium load range A2 and the gear position is a high gear position are met (when the determination unit 71 determines that the gear position is a high gear position), which is a characteristic configuration of the present invention. Hereinafter, the above condition will be referred to as a high gear multi-stage combustion condition.

[0064] (Pilot injection and main injection) The injection timing (injection start timing) of the pilot injection P1 and the main injection P3 when the high gear multi-stage combustion condition is met will be explained below. In the following, the injection timing of the pilot injection P1 will be referred to as the pilot injection timing, and the injection timing of the main injection will be referred to as the main injection timing, as appropriate.

[0065] When the high gear multi-stage combustion condition is met, the fuel injection control unit 72 (injection timing setting unit 74) performs distributed injection control by setting the pilot injection timing and the main injection timing to timings at which the injection axis AX of the injector 15 points toward the lip portion 53 for at least a part of the injection period (the period from the injection timing to the end of injection). Note that the timing at which the injection axis AX of the injector 15 points toward the lip portion 53 differs depending on the specifications of the injector 15, but is, for example, within a range from about 20° CA (CA: crank angle) before BTDC (compression top dead center) to about 20° CA after ATDC (compression top dead center).

[0066] This injection control allows part of the fuel from the pilot injection P1 and part of the fuel from the main injection P3 to collide with the lip portion 53 when the high gear multi-stage combustion conditions are met, and as shown in Figure 6, it becomes possible to achieve rapid multi-stage combustion in which the heat generation caused by the pilot injection P1 and the heat generation caused by the main injection P3 occur in gradual succession, with the heat generation rate reaching a peak near the top dead center (TDC) of compression.

[0067] This will be explained in detail using Figure 8. Figure 8 is a simplified partial cross-sectional view of the combustion chamber 6. Figure 8 shows the piston 5 at a position where the injection axis AX of the injector 15 is directed toward the lip portion 53, and a portion of the fuel (fuel spray Df) injected from the injector 15 collides with the lip portion 53.

[0068] Fuel is injected from the injection hole 152 of the injector 15 along the injection axis AX. The injection axis AX substantially coincides with the axis of the injection hole 152. The injected fuel (fuel spray) Df diffuses at a spray angle θ. FIG. 8 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.

[0069] When the fuel spray Df injected from the injector 15 collides with the lip portion 53, the fuel spray Df separates into a portion (arrow F11) heading toward the lower cavity 51 (downward) and a portion (arrow F12) heading toward the upper cavity 52 (upward).

[0070] 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.

[0071] 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 522 (a squish space on the peripheral flat surface portion 55), as shown by arrow F23, and mixes with the air in that space.

[0072] By colliding the fuel spray Df with the lip portion 53 and distributing it between the lower cavity 51 and the upper cavity 52 in this manner, the fuel can be dispersed throughout the combustion chamber 6. Therefore, by colliding the fuel from the pilot injection P1 (fuel injected from the injector 15 in response to the execution of the pilot injection P1) with the lip portion 53, the fuel from the pilot injection P1 is dispersed throughout the combustion chamber 6, forming a homogeneous mixture with a low fuel concentration throughout the combustion chamber 6. This allows the mixture to burn slowly, thereby increasing the temperature throughout the combustion chamber 6. Furthermore, by colliding the fuel from the main injection P3 (fuel injected from the injector 15 in response to the execution of the main injection P3) with the lip portion 53, the fuel from the main injection P3 is dispersed throughout the combustion chamber 6, forming a homogeneous mixture with a high fuel concentration throughout the combustion chamber 6. This allows the mixture to combust rapidly following the combustion associated with the pilot injection P1. Therefore, the heat release rate shown in FIG. 6 is achieved. This combustion mode improves fuel economy due to the short combustion period, and also improves exhaust performance by suppressing soot generation due to the homogeneous mixture, i.e., by promoting the mixing of air and fuel.

[0073] However, in order to fully obtain the above effect, it is necessary to appropriately distribute the fuel between the lower cavity 51 and the upper cavity 52.

[0074] Specifically, regardless of the engine speed, if the main injection timing is set to a predetermined timing at which fuel can be appropriately distributed to the lower cavity 51 and the upper cavity 52 at the lowest engine speed in the medium load range A2, the higher the engine speed, the more the fuel from the main injection will be biased toward the upper cavity 52.

[0075] This is because, while the time it takes for the fuel spray to travel from the nozzle 151 to the lip portion 53 is substantially constant regardless of engine speed, the higher the engine speed, the faster the moving speed of the piston 5; and, in the main injection P3 performed near the top dead center of the compression stroke, the piston 5 is descending at the time when the main fuel spray reaches the lip portion 53. In other words, when the main injection timing is set to the above-mentioned predetermined time, as shown in Fig. 9, the position of the piston 5 at the time when the fuel spray Df from the main injection P3 reaches the lip portion 53 is the position indicated by the dashed line when the engine speed is low, but is the position indicated by the solid line, which is lower than the dashed line, when the engine speed is high. Therefore, when the engine speed is high, the fuel spray Df collides with a higher part of the lip portion 53, and more fuel is distributed to the upper cavity 52.

[0076] In contrast to this, if the main injection timing is set to be more advanced (earlier in crank angle) when the engine speed is high than when it is low, the position of the piston 5 at the time when the fuel from the main injection P3 reaches the lip portion 53 can be made higher, thereby suppressing the bias of fuel to the upper cavity 52.

[0077] Furthermore, pilot injection P1 is performed during the compression stroke, before main injection P3, while the piston 5 is rising. Therefore, if the pilot injection timing is maintained at a constant timing regardless of engine speed, the position of the piston 5 at the time when the fuel spray Df from pilot injection P1 reaches the lip portion 53 will be the position indicated by the dashed line in Fig. 10 when the engine speed is low, but will be the position indicated by the solid line in Fig. 10, which is above the dashed line, when the engine speed is high. Therefore, if the pilot injection timing is set to a constant timing regardless of engine speed, when the engine speed is high, the fuel spray Df will impinge on a lower part of the lip portion 53, and more fuel will be distributed to the lower cavity 51.

[0078] In contrast, if the pilot injection timing is set to be more advanced when the engine speed is high than when it is low, the position of the piston 5 at the time when the fuel from the pilot injection P1 reaches the lip portion 53 can be made lower, thereby suppressing the bias of fuel to the lower cavity 51.

[0079] From the above, it is considered preferable to set the main injection timing and the pilot injection timing so that the injection axis AX of the injector 15 is directed toward the lip portion 53 for at least a part of each injection period, and so that the timing becomes more advanced as the engine speed increases.

[0080] However, the inventors of the present application have found that the amount of NOx generated increases when the main injection timing is advanced as the engine speed increases. Specifically, as the engine speed increases, the wall temperature of the combustion chamber 6 increases, and the amount of NOx generated increases. However, when the main injection timing is advanced as the engine speed increases, the amount of NOx generated increases even more than the above increase. This is thought to be because when the main injection timing is advanced, the amount of heat generated near the compression top dead center increases, causing the temperature inside the combustion chamber 6 to rise.

[0081] As a result of extensive research into the above problem, the inventors of the present application have discovered that when the engine speed is high, retarding the pilot injection timing rather than advancing the main injection timing can improve exhaust performance, although fuel economy performance is slightly reduced.

[0082] Specifically, if the pilot injection timing is retarded, the fuel from pilot injection P1 collides with the lip 53 when the piston 5 is in an upper position. As a result, the fuel from pilot injection P1 is biased toward the lower cavity 51. If the fuel from pilot injection P1 is biased toward the lower cavity 51, the degree of homogeneity of the fuel throughout the combustion chamber 6 decreases. Therefore, the temperature rise throughout the combustion chamber 6 before the start of main injection P3 is suppressed, which lengthens the combustion period of the mixture after the start of main injection P3, resulting in a slight decrease in fuel economy. However, if the main injection timing is retarded in this case and the fuel from main injection P3 is biased toward the upper cavity 52, the total fuel from pilot injection P1 and main injection P3 is distributed throughout the combustion chamber 6, suppressing the generation of soot, and retarding the main injection timing suppresses the generation of NOx.

[0083] Based on the above findings, in this embodiment, when the high gear multi-stage combustion condition is met and the engine is operating in a region where the engine speed is equal to or lower than a predetermined switching speed N10, the fuel injection control unit 72 (injection timing setting unit 74) sets the main injection timing to a timing at which the injection axis AX of the injector 15 points toward the lip portion 53 for at least a portion of the injection period of the main injection P3, and sets the main injection timing to a timing that is more advanced as the engine speed increases. Also, when the high gear multi-stage combustion condition is met and the engine is operating in a region where the engine speed is higher than the switching speed N10, the fuel injection control unit 72 sets the main injection timing to a timing at which the injection axis AX of the injector 15 points toward the lip portion 53 for at least a portion of the injection period of the main injection P3, and sets the main injection timing to a timing that is more retarded than the injection timing at the switching speed N10.

[0084] Furthermore, when the high gear multi-stage combustion condition is met and the engine is operating in a region where the engine speed is equal to or lower than a predetermined switching speed N10, the fuel injection control unit 72 (injection timing setting unit 74) sets the pilot injection timing to a time when the injection axis AX of the injector 15 is directed toward the lip portion 53 for at least a part of the injection period of the pilot injection P1, and sets the timing to be more advanced as the engine speed increases. Furthermore, when the high gear multi-stage combustion condition is met and the engine is operating in a region where the engine speed is higher than the switching speed N10, the fuel injection control unit 72 (injection timing setting unit 74) sets the pilot injection timing to a time that is more retarded than when the engine speed is at the switching speed N10.

[0085] Specifically, when the high gear multi-stage combustion condition is met, the fuel injection control unit 72 (injection timing setting unit 74) first sets the main injection timing (hereinafter referred to as the reference main injection timing) at the lowest engine speed N0 (hereinafter referred to as the reference speed) in the medium load range A2 and the pilot injection timing (hereinafter referred to as the reference pilot injection timing) at the reference speed, based on the engine load. The reference main injection timing and the reference pilot injection timing are each set in advance for the engine load and stored in the storage unit 78. The reference main injection timing and the reference pilot injection timing are each set to a timing at which the injection axis AX of the injector 15 points toward the lip portion 53 for at least a part of the injection period.

[0086] Next, the fuel injection control unit 72 (injection timing setting unit 74) sets a main injection timing correction amount, which is the correction amount for the main injection timing, and a pilot injection timing correction amount, which is the correction amount for the pilot injection timing, based on the engine load and engine speed. Thereafter, the fuel injection control unit 72 (injection timing setting unit 74) corrects the reference main injection timing with the main injection timing correction amount and sets the corrected value as the main injection timing, and also corrects the reference pilot injection timing with the pilot injection timing correction amount and sets the corrected value as the pilot injection timing. The main injection timing correction amount and the pilot injection timing correction amount are each set in advance for the engine load and engine speed and stored in the memory unit 78.

[0087] Fig. 11 is a graph showing the relationship between the main injection timing correction amount and engine speed. Fig. 12 is a graph showing the relationship between the pilot injection timing correction amount and engine speed. In Fig. 11 and Fig. 12, the vertical axis represents the injection timing advance amount (advance side correction amount). Note that Fig. 11 and Fig. 12 show the above relationship at a specified engine load, but the relationship between each correction amount and engine speed when the high gear multi-stage combustion condition is met has a similar tendency at other engine loads.

[0088] 11, in the region where the engine speed is equal to or lower than the switching speed N10, the main injection timing correction amount (advance amount) is set to a larger value as the engine speed increases, and is set to a maximum amount Tm_10 (hereinafter referred to as maximum advance correction amount Tm_10) when the engine speed is at the switching speed N10. On the other hand, in the region where the engine speed is higher than the switching speed N10, the main injection timing correction amount (advance amount) is gradually reduced from the maximum advance correction amount Tm_10 as the engine speed increases.

[0089] In the example of FIG. 11, in the region where the engine speed is equal to or lower than the switching speed N10, the main injection timing correction amount (advance amount) increases approximately in proportion to the increase in engine speed. In the region where the engine speed is higher than the switching speed N10 and equal to or lower than a predetermined speed N12, the main injection timing correction amount (advance amount) decreases approximately in proportion to the increase in engine speed from the maximum advance correction amount Tm_10. In the region where the engine speed is higher than the predetermined speed N12, the main injection timing correction amount (advance amount) decreases approximately in proportion to the increase in engine speed (however, at a slower rate than in the region from the switching speed N10 to the predetermined speed N12), and the main injection timing correction amount (advance amount) becomes 0 at the first speed N1 (the maximum speed in the medium load region A2). The maximum advance correction amount Tm_10 is set to a value of, for example, 5° CA or less.

[0090] By setting the main injection timing correction amount (advance amount) as described above, in the region where the engine speed is equal to or less than the switching speed N10, the main injection timing is set to a timing that is more advanced as the engine speed increases, and in the region where the engine speed is higher than the switching speed N10, the main injection timing is set to a timing that is more retarded than the timing when the engine speed is at the switching speed N10. Also, in the region where the engine speed is higher than the switching speed N10, the main injection timing is set to a timing that is more advanced when the engine speed is high than when it is low.

[0091] As shown in Fig. 12, in the region where the engine speed is equal to or lower than the switching speed N10, the pilot injection timing correction amount (advance amount) is set to a larger value as the engine speed increases, and is set to a maximum amount Tpl_10 (hereinafter referred to as maximum advance correction amount Tpl_10) when the engine speed is at the switching speed N10. On the other hand, in the region where the engine speed is higher than the switching speed N10, the pilot injection timing correction amount (advance amount) is gradually reduced from the maximum advance correction amount Tpl_10 to a smaller advance amount Tpl_12 as the engine speed increases, and when the engine speed exceeds a predetermined speed N12, the pilot injection timing correction amount (advance amount) is maintained at the timing Tpl_12 for that speed N12.

[0092] 12, in the region where the engine speed is equal to or lower than the switching speed N10, the pilot injection timing correction amount (advance amount) increases approximately in proportion to the increase in engine speed. Also, in the region where the engine speed is higher than the switching speed N10 and equal to or lower than a predetermined speed N12, the pilot injection timing correction amount (advance amount) decreases approximately in proportion to the increase in engine speed, and in the region higher than the above-mentioned speed N12, the pilot injection timing correction amount (advance amount) is maintained at the above-mentioned predetermined speed N12 regardless of the engine speed. For example, the maximum advance correction amount tpl_10 of the pilot injection P1 is set to a value similar to the maximum advance correction amount Tm_10 of the main injection P1 (a value of 5° CA or less).

[0093] By setting the pilot injection timing correction amount (advance amount) as described above, in the region where the engine speed is equal to or less than the switching speed N10, the pilot injection timing is set to a timing that is more advanced as the engine speed increases, and in the region where the engine speed is higher than the switching speed N10, the pilot injection timing is set to a timing that is more retarded than the timing when the engine speed is at the switching speed N10. Also, in the region where the engine speed is higher than the switching speed N10, the pilot injection timing is set to a timing that is more advanced when the engine speed is high than when it is low.

[0094] Here, as described above, fuel economy performance is slightly reduced in the range higher than the switching speed N10 due to the implementation of the above-described injection control. For this reason, in this embodiment, the switching speed N10 is set to the maximum speed in the normal rotation range so as to obtain high fuel economy performance during normal operation (frequent operation). For example, the switching speed N10 is set to 1800 rpm when the first speed N1, which is the maximum speed in the medium load range A2, is 2200 rpm. Note that the range in the medium load range A2 where the engine speed is equal to or lower than the switching speed N10 corresponds to the "first operating range" in the claims, and the range in the medium load range A2 where the engine speed is higher than the switching speed N10 corresponds to the "second operating range" in the claims.

[0095] Furthermore, among the above-mentioned injection controls, the control in which the main injection timing is set to be more advanced when the engine speed is high than when it is low in the range where the engine speed is equal to or lower than the switching speed N10 corresponds to the "first control" in the claims. Furthermore, the control in which the pilot injection timing and the main injection timing are set to be more retarded than the injection timing at the switching speed N10 in the range where the engine speed is higher than the switching speed N10 corresponds to the "second control" in the claims.

[0096] (Pre-injection, first after-injection and second after-injection) The pre-injection P2, the first after-injection P4, and the second after-injection P5 when the high gear multi-stage combustion condition is met will be described.

[0097] Pre-injection P2 is an injection to prevent excessive combustion noise. In other words, if a large amount of fuel is supplied to the combustion chamber 6 at once by main injection P3, the fuel-air mixture will burn rapidly, which is likely to cause excessive combustion noise. Therefore, a portion of the fuel to be burned near the compression top dead center is supplied to the combustion chamber 6 by pre-injection P2 before main injection P3.

[0098] When the high gear multi-stage combustion condition is met, the fuel injection control unit 72 (injection timing setting unit 74) sets the injection timing of the pre-injection so that the time interval between the injection timing of the pre-injection and the injection timing of the main injection is constant regardless of the engine speed.

[0099] The first after-injection P4 and the second after-injection P5 are both injections for burning soot. That is, after the fuel from the main injection P3 is burned, fuel is supplied to the combustion chamber 6 and burned, thereby burning the soot generated by the combustion of the fuel from the main injection P3. When the high gear multi-stage combustion condition is met, the fuel injection control unit 72 (injection timing setting unit 74) sets the interval between the main injection timing and the injection timing of the first after-injection and the time between the main injection timing and the injection timing of the second after-injection based on the engine speed and engine load, and sets the injection timing of the first after-injection and the injection timing of the second after-injection to times delayed by each interval from the already set main injection timing, respectively. For example, when the high gear multi-stage combustion condition is met, the fuel injection control unit 72 (injection timing setting unit 74) sets the injection timing of the first after-injection P4 so that the time interval between the main injection timing and the injection timing of the first after-injection P4 is constant regardless of the engine speed. On the other hand, the injection timing of the second after-injection P5 is set so that the time interval between the injection timing of the first after-injection P4 and the injection timing of the second after-injection P5 is shorter when the engine speed is high than when it is low.

[0100] [Control configuration for low-gear multi-stage combustion conditions] A brief description will be given of the control of the injector 15 when the condition that the engine is operating in the medium load range A2 and the gear position is a low gear position is met (when the determination unit 71 determines that the gear position is a low gear position). Hereinafter, the above condition will be referred to as a low gear multi-stage combustion condition.

[0101] When the low gear multistage combustion condition is satisfied, as when the high gear multistage combustion condition is satisfied, the fuel injection control unit 72 performs the distributed injection control described above, setting the pilot injection timing and the main injection timing so that the injection axis AX of the injector 15 points toward the lip portion 53 for at least a portion of the injection period. This allows rapid multistage combustion to be achieved even when the low gear multistage combustion condition is satisfied. However, when the low gear multistage combustion condition is satisfied, the fuel injection control unit 72 does not perform the following control: when the engine speed is equal to or less than the switching speed N10, the fuel injection control unit 72 sets the pilot injection timing and the main injection timing to more advanced timings when the engine speed is high than when the engine speed is low; and when the engine speed is higher than the switching speed N10, the fuel injection control unit 72 does not set the pilot injection timing and the main injection timing to more retarded timings than the injection timings at the switching speed. For example, when the low gear multistage combustion condition is satisfied, the fuel injection control unit 72 sets the pilot injection timing and the main injection timing to approximately constant timings regardless of the engine speed.

[0102] [Effect, etc.] As described above, according to the control device for a compression ignition engine according to the above embodiment, when the high gear multi-stage combustion condition is established, both the pilot injection timing and the main injection timing are set to timings in which the injection axis AX points toward the lip portion 53 during 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.

[0103] Furthermore, when the high gear multi-stage combustion condition is met and the engine is operating at an engine speed below the switching speed N10, the pilot injection timing and main injection timing are set to be more advanced when the engine speed is high than when it is low. This allows the fuel from both the pilot injection P1 and the main injection P3 to be distributed to the upper and lower cavities 51, 52 at appropriate ratios. This improves both fuel economy and exhaust performance.

[0104] Furthermore, when the high gear multi-stage combustion condition is met and the engine is operating in a range where the engine speed is higher than the switching speed, the pilot injection timing is set to a time that is more retarded than the time at the switching speed, and the main injection timing is set to a time that is more retarded than the time at the switching speed. Therefore, when the engine speed is higher than the switching speed, the generation of soot and NOx can be reliably suppressed, and exhaust performance can be reliably improved.

[0105] In the above embodiment, the pre-injection P2 is performed between the pilot injection P1 and the main injection P3. This allows the above-mentioned effects to be achieved while suppressing an increase in combustion noise. Furthermore, when the high gear multi-stage combustion condition is met, the time interval between the injection timing of the pre-injection P2 and the main injection timing is constant regardless of the engine speed. This prevents interference between the fuel sprays of the pre-injection P2 and the main injection P3, ensuring that the fuel from the main injection P3 is properly distributed and separated into the cavities 51 and 52.

[0106] Here, when the high gear multi-stage combustion condition is met and the engine speed is equal to or less than or close to the switching speed N10, the main injection timing is set to the advance side, which tends to increase the combustion noise. In contrast, in the above embodiment, the injection control is performed when the gear is in a high gear, that is, when the vehicle 100 is traveling at high speed. This allows the combustion noise to blend in with the traveling noise, preventing the occupants from detecting the combustion noise and feeling uncomfortable.

[0107] [Variations] In the above embodiment, when the high gear multi-stage combustion condition is met, the pilot injection timing as well as the main injection timing are controlled so that, when the engine speed is equal to or lower than the switching speed N10, the timing is advanced as the engine speed increases, and when the engine speed is higher than the switching speed N10, the timing is retarded relative to the timing at which the engine speed is at the switching speed N10. Here, because the injection amount of the main injection P3 is greater than the injection amount of the pilot injection P1, an inappropriate distribution of fuel from the main injection P3 to the upper and lower cavities 51, 52 has a greater impact on fuel economy and exhaust performance. For this reason, the above control may be limited to the main injection P3, and the pilot injection timing may be maintained at a constant timing regardless of the engine speed.

[0108] In the above embodiment, when the transmission is in a high-speed gear position, control is performed to switch the pilot injection timing and main injection timing between when the engine speed is equal to or less than the switching speed N10 and when it is higher than the switching speed N10 (control in which, when the engine speed is equal to or less than the switching speed N10, the pilot injection timing and main injection timing are set to be more advanced when the engine speed is high than when the engine speed is low, and when the engine speed is higher than the switching speed N10, the pilot injection timing and main injection timing are set to be more retarded than the injection timing at the switching speed). However, regardless of the gear position of the transmission, the above control may also be performed when the engine is operating in the medium load range A2. However, if control is performed to advance the main injection timing as the engine speed increases, as described above, combustion noise tends to increase when the engine speed is equal to or less than the switching speed N10 or close to it. Therefore, the above control, including advancing the main injection timing as the engine speed increases, is preferably performed while the engine is operating in a high-speed gear position.

[0109] Furthermore, the control when the engine is operating in the medium load region A2 and the transmission is in a low gear, the control when the engine is operating in the low load region A1, and the control when the engine is operating in the high speed, high load region A3 are not limited to the above.

[0110] 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.

[0111] Furthermore, the pre-injection P2, the first after-injection P4, and the second after-injection P5 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, which includes an engine body having a cylinder, a piston that reciprocates within the cylinder, a combustion chamber formed by the cylinder and a crown surface of the piston, a fuel injection valve disposed on a ceiling surface of the combustion chamber and that injects fuel along an injection axis, and a fuel injection control unit that controls the fuel injection valve, and in which compression ignition combustion of an air-fuel mixture is performed within the combustion chamber, 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 first operating range where the engine speed is equal to or lower than a predetermined switching speed and in a second operating range where the engine speed is higher than the switching speed, a distributed injection control is performed in which the fuel injection valve performs a pilot injection in which fuel is injected during a compression stroke and at a timing where the injection shaft is directed toward the lip portion for at least a part of an injection period, and a main injection in which fuel is injected after the pilot injection and at a timing where the injection shaft is directed toward the lip portion for at least a part of an injection period, When the distribution injection control is performed, When the engine is operated in the first operating range, a first control is performed to control the fuel injection valve so that the injection timing of the main injection is more advanced when the engine speed is high than when the engine speed is low, a control device for a compression ignition engine, wherein, when the engine is operated in the second operating range, a second control is performed to control the fuel injection valve so that the injection timings of the pilot injection and the main injection are each retarded relative to the injection timings at the switchover rotation speed.

2. 2. The control device for a compression ignition engine according to claim 1, a fuel injection control unit that controls the fuel injection valve so that the injection timing of the pilot injection is more advanced when the engine speed is high than when the engine speed is low, when the first control is performed.

3. 3. The control device for a compression ignition engine according to claim 1, the fuel injection control unit, when performing the distributed injection control, causes the fuel injection valve to perform a pre-injection in which fuel is injected between the pilot injection and the main injection, and controls the fuel injection valve so that the time interval between the injection timing of the pre-injection and the injection timing of the main injection is constant.

4. The control device for a compression ignition engine according to any one of claims 1 to 3, a gear position detection unit capable of detecting a gear position of a transmission provided in a vehicle equipped with the engine, a fuel injection control unit that performs the first control and the second control when the gear position detected by the gear position detection unit is equal to or greater than a predetermined number of gear positions set to two or more.

Images