JP2011202624A - Fuel injection control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection control device securing the accuracy of fuel injection amount to obtain desired torque while suppressing the adhesion of fuel spray irrespective of the displacement of a diesel engine.SOLUTION: An ECU 16 performs preliminary injection prior to pilot injection when an engine body 11 is in a compression stroke. In the compression stroke, since air sucked into a combustion chamber 22 is compressed, air density in the combustion chamber 22 becomes high compared with an intake stroke. Thereby, fuel injected from an injector 40 is not adhered to a piston 19 and a cylinder 21, and is mixed with the air in the combustion chamber 22. In the preliminary injection, the gradient of an injection rate in the early stage of the injection is set larger than at least either the main injection or pilot injection. Therefore, in the preliminary injection, the division of the injection is unnecessary as atomization is promoted, and the accuracy of the fuel injection amount from the injector 40 is easily secured. Thus, the desired torque in the engine body 11 is obtained irrespective of the displacement.

Description

  The present invention relates to a fuel injection control device, and more particularly to a fuel injection control device for a diesel engine.

  In a diesel engine, it is required to reduce combustion noise and PM (Particulate Matter) contained in exhaust gas while suppressing generation of nitrogen oxides. Therefore, a fuel injection device has been proposed that performs pilot injection that injects a small amount of fuel prior to main injection that injects most of the set fuel injection amount. Further, Patent Document 1 proposes preliminary injection in which fuel is injected into the fuel chamber at the beginning of the intake stroke immediately after the exhaust valve is closed, prior to pilot injection. In addition to pilot injection as in Patent Document 1, by performing preliminary injection in the intake stroke, the amount of fuel spray injected in each stage is reduced by reducing the amount of fuel injection in each stage of multistage injection. descend. Therefore, a lean air-fuel mixture is generated with almost no fuel spray adhering to the inner wall of the cylinder or the end face of the piston.

  However, in the case of a diesel engine with a small displacement and a small bore, when the pressure in the combustion chamber is small and the density is low as in the intake stroke, the reach of the fuel spray injected from the injector increases. Therefore, in order to suppress the fuel spray from adhering to the inner wall of the cylinder and the end face of the piston, the amount of fuel injected in one preliminary injection needs to be extremely small. As a result, there is a problem that it is difficult to ensure the accuracy of the fuel injection amount, and it is difficult to secure a desired torque in the diesel engine with a low accuracy fuel injection amount. Further, if the fuel injection amount in the preliminary injection is set to such an extent that the accuracy of the fuel injection amount can be ensured, the fuel spray adheres to the inner wall of the cylinder or the inner wall of the piston, which causes an increase in hydrocarbons contained in the exhaust. There is.

JP-A-10-141124

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a fuel injection control device that ensures the accuracy of the fuel injection amount that can obtain a desired torque while suppressing the adhesion of fuel spray regardless of the exhaust amount of the diesel engine. .

  In the first or second aspect of the invention, the preliminary injection prior to the pilot injection is performed in a compression stroke from the bottom dead center to the top dead center of the crankshaft. In the compression stroke, since the air sucked into the combustion chamber is compressed, the density of the combustion chamber is higher than that in the suction stroke. In the preliminary injection, the change in the fuel injection rate at the initial stage of injection is set to be larger than at least one of the main injection and the pilot injection. That is, the rise of the fuel injection rate in the preliminary injection becomes larger than at least one of the main injection and the pilot injection. Here, the fuel injection rate is a fuel injection amount per unit time.

  By the way, an injector that injects fuel intermittently injects fuel from an injection hole provided on the downstream side of the seat when the needle is seated on the seat formed on the nozzle or the needle is separated from the seat. Therefore, the fuel injected from the injector passes through a minute passage formed between the needle and the seat before reaching the injection hole. The gap formed between the needle and the seat increases as the change in the fuel injection rate increases, that is, as the rise increases. Further, as the gap formed between the needle and the seat increases, the flow rate of the fuel passing through the nozzle hole increases, and atomization of the fuel injected from the nozzle hole is promoted.

  Therefore, in the first or second aspect of the invention, by increasing the gradient of the fuel injection rate in the preliminary injection, the flow velocity of the fuel injected from the nozzle hole is increased, and the atomization of the fuel injected from the nozzle hole is reduced. Promoting. Further, by performing this preliminary injection in a compression stroke in which the density of the combustion chamber is high, the reach of the fuel spray injected from the injection hole is reduced, and adhesion to the inner wall of the cylinder and the end face of the piston is suppressed. Therefore, it is possible to obtain a desired torque in the diesel engine without reducing the fuel injection amount in the preliminary injection and suppressing the fuel spray from adhering to the inner wall of the cylinder and the end face of the piston regardless of the exhaust amount of the diesel engine. it can.

The schematic diagram which shows the diesel engine system to which the fuel-injection control apparatus by one Embodiment of this invention is applied. Sectional view showing the outline of an injector of a diesel engine system It is sectional drawing which shows the principal part of the injector shown in FIG. 2, Comprising: The figure which shows the state in which the needle is seating on the nozzle It is sectional drawing which shows the principal part of the injector shown in FIG. 2, Comprising: The figure which shows the state which the needle | hook has separated from the nozzle The block diagram which shows the fuel-injection control apparatus by one Embodiment. The schematic diagram which shows the relationship between the angle of a crankshaft, and a fuel-injection rate in the fuel-injection control apparatus by one Embodiment. The schematic diagram which shows the relationship between the speed of a needle and the change of a fuel injection rate from the start of fuel injection in the fuel-injection control apparatus by one Embodiment. The schematic diagram which shows the relationship between a needle speed and the particle size of a spray in the fuel-injection control apparatus by one Embodiment. The schematic diagram which shows the relationship between a needle speed and the fuel combustion ratio in the fuel-injection control apparatus by one Embodiment. Schematic showing the relationship between needle speed and time variation of spray length

Hereinafter, a diesel engine system to which a fuel injection control device according to an embodiment of the present invention is applied will be described in detail with reference to the drawings.
First, the configuration of the diesel engine system 10 shown in FIG. 1 will be described. The diesel engine system 10 includes an engine body 11, an intake unit 12, an exhaust unit 13, an EGR unit 14, a fuel injection unit 15, and an ECU 16 as a fuel injection control device. The engine body 11 has a cylinder block 17, a cylinder head 18, and a piston 19. The cylinder block 17 has a plurality of cylinders 21 formed therein. The cylinder head 18 is provided at the upper end of the cylinder block 17. The piston 19 reciprocates in the axial direction inside the cylinder 21 formed by the cylinder block 17. A space surrounded by the end surface of the piston 19 on the cylinder head 18 side, the inner wall of the cylinder 21, and the end surface of the cylinder head 18 on the piston 19 side is a combustion chamber 22. The piston 19 is connected to a crankshaft (not shown). As the piston 19 moves in the axial direction of the cylinder 21, that is, in the vertical direction in FIG. 1, the crankshaft rotates. When the piston 19 moves to the uppermost position in FIG. 1 in the cylinder 21, that is, when the volume of the combustion chamber 22 is minimized, the rotation angle of the crankshaft is at the top dead center. On the other hand, when the piston 19 moves to the lowest position in FIG. 1 in the cylinder 21, that is, when the volume of the combustion chamber 22 becomes maximum, the rotation angle of the crankshaft is at the bottom dead center.

  The intake section 12 has an intake pipe member 23 and an intake valve (not shown). The intake pipe member 23 forms an intake passage 24. Atmosphere is introduced from one end of the intake passage 24 via an air cleaner (not shown). The other end of the intake passage 24 is connected to the combustion chamber 22. An intake valve (not shown) opens and closes between the intake passage 24 and the combustion chamber 22. A throttle valve 25 that adjusts the flow rate of intake air is provided in the intake passage 24. The exhaust part 13 has an exhaust pipe member 26 and an exhaust valve (not shown). The exhaust pipe member 26 forms an exhaust passage 27. The exhaust passage 27 is opened to the atmosphere via an exhaust purification device and a silencer (not shown). The other end of the exhaust passage 27 is connected to the combustion chamber 22. As a result, the exhaust from the combustion chamber 22 is discharged into the atmosphere via the exhaust passage 27. An exhaust valve (not shown) opens and closes between the combustion chamber 22 and the exhaust passage 27.

  The engine body 11 is a four-cycle diesel engine. The engine body 11 has an intake stroke for introducing intake air into the combustion chamber 22 when the piston 19 descends from top dead center to bottom dead center with the intake valve open and the exhaust valve closed. The engine body 11 is in a compression stroke in which the intake air taken into the combustion chamber 22 is compressed when the piston 19 rises from the bottom dead center to the top dead center with both the intake valve and the exhaust valve closed. In the second half of this compression stroke, fuel combustion occurs in the combustion chamber 22 and the pressure in the combustion chamber 22 rises. Therefore, the piston 19 descends again from the top dead center to the bottom dead center side. At this time, in the engine main body 11, the piston 19 descends from the top dead center to the bottom dead center with both the intake valve and the exhaust valve closed. Therefore, the engine body 11 is in a combustion stroke in which the volume of the combustion chamber 22 increases. The piston 19 lowered to the bottom dead center by the combustion stroke rises again to the top dead center side. At this time, the piston 19 moves in the engine body 11 with the intake valve closed and the exhaust valve opened. As a result, the engine body 11 performs an exhaust stroke in which the combustion gas in the combustion chamber 22 is discharged to the exhaust passage 27. The timing at which the intake valve and the exhaust valve are opened or closed, that is, the valve timing is shifted from the above timing to the advance side or the retard side according to the operating state of the engine body 11, or the intake valve is opened and closed and the exhaust valve is opened and closed. May overlap.

  The EGR unit 14 performs exhaust gas recirculation that recirculates a part of the exhaust gas to the intake air. The EGR unit 14 includes an EGR pipe unit 28 and an EGR valve 29. The EGR pipe portion 28 forms an EGR passage 31. The EGR passage 31 has one end connected to the exhaust passage 27 and the other end connected to the intake passage 24. The EGR valve 29 opens and closes the EGR passage 31 and controls the flow rate of exhaust gas recirculated from the exhaust passage 27 to the intake passage 24.

  The fuel injection unit 15 includes a common rail 32, an injector 40, and a supply pump (not shown). A supply pump (not shown) pressurizes fuel stored in a fuel tank (not shown) to a predetermined pressure. The fuel pressurized by the supply pump is stored in the common rail 32 while maintaining the pressure. The high-pressure fuel stored in the common rail 32 is injected from the injector 40 into the combustion chamber 22.

  The injector 40 has a well-known configuration, and mainly includes a body 41, a needle 42, a drive unit 43, and a drive force transmission unit 44 as shown in FIG. The body 41 includes a first body 45, a second body 46, a third body 47, and a nozzle 48, and accommodates a needle 42, a drive unit 43, and a drive force transmission unit 44 inside. The nozzle 48 is formed in a cylindrical shape, and has an injection hole 49 for injecting fuel at the tip while accommodating the needle 42 so as to be movable in the axial direction. The first body 45, the second body 46, the third body 47, and the nozzle 48 are integrally connected by a retaining nut 51.

  The needle 42, the needle stopper 52 and the balance piston 53 of the driving force transmission unit 44 are integrally movable in the axial direction inside the body 41. That is, the needle 42 slides with the cylindrical nozzle 48 on the drive unit 43 side, and the needle stopper 52 and the balance piston 53 slide with the cylindrical third body 47. High-pressure passage 54 that penetrates body 41 is supplied with high-pressure fuel from common rail 32. The high pressure passage 54 has an end opposite to the common rail 32 connected to the tip of the nozzle 48 and a high pressure chamber 55 on the drive unit 43 side of the balance piston 53. The body 41 forms a pressurizing chamber 57 at the end of the piezo piston 56 on the needle 42 side, and forms a lower chamber 58 at the end of the needle stopper 52 on the needle 42 side. The pressurizing chamber 57 and the lower chamber 58 are connected via a pressurizing passage 59. Further, the body 41 forms a low pressure chamber 61 on the drive unit 43 side of the piezo piston 56 and an upper chamber 62 on the drive unit 43 side of the needle stopper 52. The upper chamber 62 and the low pressure chamber 61 are connected via a low pressure passage 63. A piezoelectric actuator 64 of the drive unit 43 is accommodated in the low pressure chamber 61 of the body 41. The upper chamber 62 accommodates a spring 65 as an elastic member. The spring 65 presses the needle stopper 52 toward the needle 42. The piezo piston 56 has a connecting passage 66 that connects the pressurizing chamber 57 and the low pressure chamber 61 on the inside, and a check valve that blocks the flow of fuel from the pressurizing chamber 57 to the low pressure chamber 61 in the connecting passage 66. 67. The pressurizing chamber 57 accommodates a disc spring 68 as an elastic member. The disc spring 68 always presses the piezo piston 56 toward the piezo actuator 64.

  As shown in FIGS. 3 and 4, the needle 42 has an annular seal portion 71 in the vicinity of the tip. The nozzle 48 has an annular sheet portion 72 on the inner peripheral surface. The nozzle hole 49 passes through the nozzle 48 and connects the inner peripheral wall and the outer wall of the nozzle 48 on the downstream side of the seat portion 72 in the fuel flow direction. The outer wall of the needle 42 and the inner wall of the nozzle 48 form a fuel passage 73 connected to the high-pressure passage 54 as shown in FIG. When the seal portion 71 is seated on the seat portion 72, the fuel passage 73 is closed. Therefore, the flow of fuel between the high-pressure passage 54 and the injection hole 49 is blocked, and the fuel is not injected from the injection hole 49. On the other hand, when the seal portion 71 is separated from the seat portion 72, the fuel passage 73 is opened. Therefore, the high-pressure passage 54 and the injection hole 49 are connected via the fuel passage 73, and fuel is injected from the injection hole 49.

  When drive energy is applied from the ECU 16 to the piezo actuator 64, the piezo actuator 64 extends in the axial direction. Therefore, as shown in FIG. 2, the piezo piston 56 in contact with the piezo actuator 64 is pushed by the piezo actuator 64 and moves to the needle 42 side, and the volume of the pressurizing chamber 57 is reduced. Since the check valve 67 blocks the flow of fuel from the pressurizing chamber 57 to the low pressure chamber 61, the lower chamber connected to the pressurizing chamber 57 via the pressure of the pressurizing chamber 57 and the pressurizing passage 59. The pressure at 58 increases. When the pressure in the lower chamber 58 rises, the balance of force between the balance piston 53 that receives the fuel pressure from the high pressure chamber 55 and the needle stopper 52 that receives the fuel pressure from the lower chamber 58 changes. That is, the force applied to the needle stopper 52 from the lower chamber 58 is greater than the sum of the force received by the balance piston 53 from the high pressure chamber 55 and the pressing force of the spring 65. As a result, the force pressing the needle 42 downward, that is, in the direction in which the seal portion 71 is seated on the seat portion 72 is reduced, and the needle 42 is raised upward, that is, toward the drive portion 43. As a result, the seal portion 71 is separated from the seat portion 72 and the fuel is injected from the injection hole 49.

On the other hand, when the drive energy from the ECU 16 to the piezo actuator 64 is recovered, the piezo actuator 64 contracts in the axial direction. Therefore, the piezo piston 56 in contact with the piezo actuator 64 moves to the drive unit 43 side together with the piezo actuator 64 by the pressing force of the disc spring 68. As a result, the volume of the pressurizing chamber 57 increases, and the pressure in the pressurizing chamber 57 and the lower chamber 58 decreases. When the pressure in the lower chamber 58 decreases, the force applied to the needle stopper 52 from the lower chamber 58 becomes smaller than the sum of the force received by the balance piston 53 from the high pressure chamber 55 and the pressing force of the spring 65. As a result, the force pressing the needle 42 downward, that is, in the direction in which the seal portion 71 is seated on the seat portion 72 increases, and the needle 42 moves downward, that is, on the side opposite to the drive portion 43. As a result, the seal portion 71 is seated on the seat portion 72, and fuel injection from the injection hole 49 is stopped.
Thus, according to the driving energy output from the ECU 16 to the piezo actuator 64, the needle 42 reciprocates in the axial direction. Thereby, the fuel injection from the injection hole 49 and its stop are controlled.

  As shown in FIG. 5, the ECU 16 includes a microcomputer 84 including a CPU 81, a ROM 82, and a RAM 83. The ECU 16 functions as a rotation angle acquisition unit 85, an operation state acquisition unit 86, an injection amount setting unit 87, and an injector control unit 88 by executing a computer program stored in the ROM 82. That is, the rotation angle acquisition unit 85, the operation state acquisition unit 86, the injection amount setting unit 87, and the injector control unit 88 are realized by software. In addition, you may implement | achieve these rotation angle acquisition parts 85, the driving | running state acquisition part 86, the injection quantity setting part 87, and the injector control part 88 in hardware.

  As shown in FIGS. 1 and 5, the ECU 16 performs various operations such as an accelerator opening sensor 91, an intake air amount sensor 92, a crank angle sensor 93, a pressure sensor 94, an intake air temperature sensor 95, a water temperature sensor 96, and an intake air pressure sensor 97. Connected to the sensor. The accelerator opening sensor 91 detects the amount of depression of an accelerator pedal (not shown) and outputs the detected amount of depression to the ECU 16 as an electrical signal. The intake air amount sensor 92 detects the flow rate of air flowing through the intake passage 24 and outputs the detected flow rate of air to the ECU 16 as an electrical signal. The crank angle sensor 93 detects a rotation angle of a crankshaft (not shown), and outputs the detected rotation angle to the ECU 16 as an electric signal. The pressure sensor 94 detects the pressure of the fuel stored in the common rail 32 and outputs the detected fuel pressure to the ECU 16 as an electrical signal. The intake air temperature sensor 95 detects the temperature of intake air flowing through the intake passage 24 and outputs the detected intake air temperature to the ECU 16 as an electrical signal. The water temperature sensor 96 detects the temperature of the cooling water in the engine body 11 and outputs the detected temperature of the cooling water to the ECU 16 as an electrical signal. The intake pressure sensor 97 detects the pressure of the air flowing through the intake passage 24 and outputs the detected pressure of the air to the ECU 16 as an electrical signal.

  The rotation angle acquisition unit 85 realized by the ECU 16 acquires the rotation angle of the crankshaft of the engine body 11 based on the electric signal output from the crank angle sensor 93. Based on the crankshaft rotation angle acquired by the rotation angle acquisition unit 85 and the electrical signal output from the accelerator opening sensor 91, the operation state acquisition unit 86 determines the operation state such as the load and rotation speed of the engine body 11. get. The injection amount setting unit 87 sets the fuel injection amount from the injector 40 as a basic injection amount based on the operation state of the engine body 11 acquired by the operation state acquisition unit 86. At the same time, the injection amount setting unit 87 uses the set basic injection amount as the intake air amount output from various sensors such as the intake air amount sensor 92, the intake air temperature sensor 95, the water temperature sensor 96, and the intake pressure sensor 97, Correction is made based on the intake air temperature, the coolant temperature, the intake air pressure, and the like, and the final determined injection amount Qd is set.

  The injector control unit 88 intermittently injects fuel from the injector 40 based on the crankshaft rotation angle acquired by the rotation angle acquisition unit 85 and the fuel injection amount set by the injection amount setting unit 87. That is, the injector control unit 88 controls the injection of fuel from the injection hole 49 by controlling the driving energy output to the injector 40. The ECU 16 also determines the common rail based on the fuel pressure in the common rail 32 detected by the pressure sensor 94, the operating state of the engine body 11 acquired by the operating state acquisition unit 86, and the determined injection amount set by the injection amount setting unit 87. 32 pressures are feedback controlled. That is, the ECU 16 controls the fuel pressure in the common rail 32 to a target pressure by controlling the flow rate of fuel discharged from a supply pump (not shown).

Next, the injector control unit 88 will be described in detail including the operation.
The injector control unit 88 controls the fuel injection from the injector 40 by controlling the drive energy output to the piezo actuator 64 of the injector 40 as described above. Specifically, the injector control unit 88 executes fuel injection from the injector 40 at a predetermined time in accordance with the rotation angle of the crankshaft. In the present embodiment, the injector controller 88 performs at least three fuel injections of the preliminary injection 101, the pilot injection 102, and the main injection 103 as shown in FIG. 6 for one combustion stroke in the combustion chamber 22. Execute. That is, the injector control unit 88 performs the preliminary injection amount Qs during the preliminary injection 101, the pilot injection amount Qp during the pilot injection 102, and the main injection 103 during the main injection 103 based on the fuel determined injection amount Qd set by the injection amount setting unit 87. An injection amount Qm is injected. That is, the determined injection amount Qd is Qd = Qs + Qp + Qm.

  In the main injection 103, most of the determined injection amount Qd set by the injection amount setting unit 87 is injected. That is, Qm> Qs and Qm> Qp. Further, the main injection 103 is near the top dead center when the rotation angle of the crankshaft of the engine body 11 is from the end of the compression stroke to the beginning of the combustion stroke, that is, when the piston 19 rises from the bottom dead center to the top dead center in the compression stroke. This is executed when the piston 19 descends from the top dead center to the bottom dead center in the combustion stroke. The timing for executing the main injection 103 varies to the advance side or the retard side depending on the load state of the engine body 11 and the like. The pilot injection 102 is executed prior to the main injection 103. That is, the pilot injection 102 is executed when the rotation angle of the crankshaft is on the more advanced side than the main injection 103 time. The preliminary injection 101 is performed prior to the pilot injection 102. That is, the preliminary injection 101 is executed when the crankshaft rotation angle is on the more advanced side than the pilot injection 102 time. In the case of the present embodiment, the preliminary injection amount Qs in the preliminary injection 101 is set larger than the pilot injection amount Qp in the pilot injection 102.

  The injector control unit 88 executes the preliminary injection 101 when the rotation angle of the crankshaft is in the compression stroke, that is, when the piston 19 is in the stroke that rises from the bottom dead center to the top dead center. For example, in the case of the engine body 11 having a displacement of about 2 liters, if ATDC = 0 is set as the top dead center when shifting from the compression stroke to the combustion stroke, the preliminary injection 101 is executed in the compression stroke of −60 ° to −25 °. Is done. The timing of the preliminary injection 101 is the change in the compression ratio of the engine body 11, the supercharging pressure, the change in density and temperature of the combustion chamber 22 due to changes in the intake air temperature, and the distance to the cylinder due to the change in bore. It changes based on changes. Accordingly, the timing of the preliminary injection 101 is set to an appropriate time according to the characteristics of the engine body 11.

  Here, if the time interval from the preliminary injection 101 to the pilot injection 102 is I1, and the time interval from the pilot injection 102 to the main injection 103 is I2, I1> I2. In this case, I1 is set sufficiently longer than I2. As described above, the preliminary injection 101 is executed at a time sufficiently preceding the pilot injection 102. That is, the pilot injection 102 is intended to form a nucleus serving as a fire type that promotes the ignition of fuel in the subsequent main injection 103. Therefore, the pilot injection 102 is executed immediately before the main injection 103. On the other hand, the preliminary injection 101 aims to supply the fuel to be injected in the main injection 103 to the combustion chamber 22 in advance as an air-fuel mixture in order to reduce the generation of PM in the main injection 103. That is, it is desirable that the fuel injected in the preliminary injection 101 is diffused in the combustion chamber 22 without burning up to the main injection 103. Therefore, the preliminary injection 101 is executed at the beginning of the compression stroke where the fuel does not ignite.

  As shown in FIG. 6, the injector control unit 88 changes the fuel injection rate in the initial injection in the preliminary injection 101, that is, the rate of increase more than at least one of the fuel injection rates in the initial injection of the main injection 103 or the pilot injection 102. Set larger. Here, the initial injection means the time from when the fuel injection is started from the injector 40 until the injection rate reaches the maximum (peak). The fuel injection rate is the fuel injection amount per unit time. As shown in FIG. 6, when fuel injection is performed from the injector 40, the fuel injection rate increases from the start of injection and decreases after reaching the maximum value. In the case of the present embodiment, the gradient of the fuel injection rate at the initial stage of the preliminary injection 101, that is, the increase rate of the fuel injection rate is larger than that of the pilot injection 102 or the main injection 103. That is, the rise of the fuel injection rate at the initial stage of the preliminary injection 101 is larger than at least one of the pilot injection 102 and the main injection 103.

  In order to increase the gradient of the fuel injection rate at the initial stage of injection, the driving speed of the needle 42 of the injector 40 needs to be increased. That is, the voltage of the drive signal applied to the piezo actuator 64 is increased, and the extension speed of the piezo actuator 64 is increased. As the driving speed of the needle 42 increases, the change in the fuel injection rate per time, that is, the gradient of the fuel injection rate increases as shown in FIG.

  When the drive speed of the needle 42 is increased, the particle size of the spray formed by the fuel injected from the injection hole 49 is reduced as shown in FIG. That is, when the driving speed of the needle 42 is increased, atomization of the fuel is promoted. This is because when the driving speed of the needle 42 increases, the fuel easily passes through the fuel passage 73 between the needle 42 and the nozzle 48. That is, the fuel supplied to the high-pressure passage 54 flows into the nozzle hole 49 via the gap between the needle 42 and the nozzle 48, that is, the fuel passage 73 as the needle 42 rises. Therefore, the fuel flowing from the high-pressure passage 54 into the nozzle hole 49 flows into the nozzle hole 49 after the flow path is restricted by the fuel passage 73. Here, when the drive speed of the needle 42 increases, the cross-sectional area of the fuel passage 73 rapidly increases and becomes larger than the cross-sectional area of the injection hole 49. As a result, the flow velocity of the fuel flowing into the injection hole 49 increases early from the start of injection, and atomization of the fuel spray is promoted.

  As the atomization of the fuel is promoted, the fuel injected into the combustion chamber 22 has a reduced combustion rate as shown in FIG. The reason for this is as follows. That is, by promoting atomization of the fuel injected into the combustion chamber 22, the fuel particles injected from the injector 40 are quickly dispersed into the combustion chamber 22. Therefore, the air-fuel mixture formed by air and fuel in the combustion chamber 22 is in a very lean state. As a result, the combustion chamber 22 is compressed as the piston 19 rises, and even if the temperature of the combustion chamber 22 rises, the lean air-fuel mixture becomes difficult to ignite.

  In this way, the injector control unit 88 increases the gradient of the fuel injection rate in the preliminary injection 101, thereby atomizing the fuel and avoiding the ignition of the fuel injected by the preliminary injection 101 while generating the air-fuel mixture. I am trying. In addition to this, the injector control unit 88 executes the preliminary injection 101 in the compression stroke as described above. In the compression stroke, the density in the combustion chamber 22 is greater than in the intake stroke. Therefore, the reach distance of the fuel spray injected from the injection hole 49, that is, the spray length is smaller than the intake stroke. Thereby, the fuel spray injected from the injection hole 49 of the injector 40 is less likely to reach the inner wall of the cylinder 21 and the end face of the piston 19 due to the increase in the density of the combustion chamber 22.

  Here, when the driving speed of the needle 42 is increased, the total length of the fuel spray injected from the injector 40 is larger than that when the driving speed of the needle 42 is small as long as it is limited to the initial stage of fuel injection as shown in FIG. . However, the total length of the final fuel spray, that is, the reach distance is hardly affected by the driving speed of the needle 42. On the other hand, at the initial stage of fuel injection, the piston 19 is located closer to the bottom dead center, and the distance from the injection hole 49 of the injector 40 to the end face of the piston 19 is relatively large. Therefore, the fuel injected from the injection hole 49 does not easily reach the end face of the piston 19.

  As described above, in the present embodiment, by performing the preliminary injection 101 having a large initial gradient of the fuel injection rate in the compression stroke, a lean air-fuel mixture that does not cause combustion is generated in the combustion chamber 22, and Adherence of fuel spray to the inner wall of the cylinder 21 and the end face of the piston 19 is substantially prevented. After the lean air-fuel mixture is generated by the preliminary injection 101 in this way, a small amount of pilot injection 102 is executed, whereby a nucleus serving as a fire type is formed in the combustion chamber 22. Then, by executing the main injection 103 in the combustion chamber 22 in which nuclei are formed by the pilot injection 102, ignition of fuel by the main injection 103 is promoted, and generation of noise due to combustion delay can be prevented.

  Further, by executing the preliminary injection 101 prior to the pilot injection 102, the fuel injection amount in the main injection 103 is reduced by the preliminary injection amount Qs in the preliminary injection. Therefore, air shortage at the time of combustion in the main injection 103 hardly occurs, and PM contained in the exhaust gas is reduced. Furthermore, by performing the preliminary injection 101 in the compression stroke, it is possible to increase the preliminary injection amount Qs while avoiding the fuel spray in the preliminary injection 101 from adhering to the cylinder 21 and the piston 19. Thereby, it is not necessary to control the minute injection amount in the preliminary injection 101. Thereby, even when the preliminary injection 101 and the pilot injection 102 are executed, the injection amount in each injection and the total amount of fuel finally burned, that is, the determined injection amount Qd are precisely controlled. Therefore, the output torque of the engine body 11 can also be controlled with high accuracy.

  As described above, in one embodiment, the preliminary injection 101 prior to the pilot injection 102 is performed in the compression stroke. In the compression stroke, since the air sucked into the combustion chamber 22 is compressed, the density of the combustion chamber 22 is higher than that in the suction stroke. In the preliminary injection 101, the change in the fuel injection rate at the initial stage of injection is set to be larger than at least one of the main injection 103 or the pilot injection 102. That is, the gradient of the fuel injection rate in the preliminary injection 101 is larger than at least one of the main injection 103 or the pilot injection 102. For this reason, the fuel injection amount increases in a short period of time, and it is not necessary to further divide the fuel injection in the preliminary injection 101 in order to secure a desired fuel injection amount. As a result, it is not necessary to reduce the fuel injection amount in the preliminary injection 101, and it is easy to ensure the accuracy of the fuel injection amount. Therefore, a desired torque can be obtained in the engine body 11 regardless of the displacement.

  Further, by increasing the gradient of the fuel injection rate in the preliminary injection 101, the flow rate of the fuel injected from the injection hole 49 is increased, and the atomization of the fuel injected from the injection hole 49 is also promoted. As described above, by performing the preliminary injection 101 in the compression stroke in which the density of the combustion chamber 22 is high, the reach of the fuel spray injected from the injection hole 49 becomes small, and the inner wall of the cylinder 21 and the end face of the piston 19 are reduced. Adhesion is suppressed. Therefore, it is possible to suppress the discharge of unburned HC accompanying the fuel spray regardless of the displacement.

The present invention described above is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.
For example, in the above embodiment, the rising of the fuel injection rate in the preliminary injection 101 is set large by changing the drive speed of the needle 42 in the injector 40. However, the pressure of the fuel stored in the common rail 32 may be changed between the preliminary injection 101, the pilot injection 102, and the main injection 103. The fuel injection rate of the fuel injected from the injector 40 varies depending on the pressure of the fuel stored in the common rail 32. Therefore, the rising of the fuel injection rate may be changed by changing the fuel pressure between the preliminary injection 101, the pilot injection 102, and the main injection 103.

  In the drawings, 11 is an engine body (diesel engine), 16 is an ECU (fuel injection control device), 22 is a combustion chamber, 40 is an injector, 85 is a rotation angle acquisition unit (rotation angle acquisition means), and 86 is an operation state acquisition unit. (Operating state acquisition means), 87 denotes an injection amount setting section (injection amount setting means), 88 denotes an injector control section (injector control means), and 93 denotes a crank angle sensor (rotation angle acquisition means).

Claims (2)

A fuel injection control device that controls injection of fuel from an injector to a combustion chamber in a diesel engine,
Rotation angle acquisition means for acquiring the rotation angle of the crankshaft of the diesel engine;
An operation state acquisition means for acquiring an operation state of the diesel engine;
An injection amount setting means for setting an amount of fuel to be injected from the injector based on the operation state of the diesel engine acquired by the operation state acquisition means;
Injector control means for intermittently injecting fuel from the injector based on the rotation angle of the crankshaft acquired by the rotation angle acquisition means and the fuel injection amount set by the injection amount setting means;
The injector control means injects most of the fuel injection amount set by the injection amount setting means when the rotation angle of the crankshaft acquired by the rotation angle acquisition means is at the end of the compression stroke of the diesel engine. Main injection, pilot injection for injecting fuel prior to the main injection when the rotation angle of the crankshaft is more advanced than the main injection, and the rotation angle of the crankshaft is advanced than the pilot injection. Performing preliminary injection for injecting fuel prior to the pilot injection when the rotation angle of the crankshaft is on the corner side and in the compression stroke from bottom dead center to top dead center;
The change in fuel injection rate at the initial stage of injection from the start of fuel injection in the preliminary injection to the maximum injection amount is expressed as the fuel injection rate at the initial stage of injection of the main injection or the fuel at the initial stage of injection of the pilot injection. A fuel injection control device characterized in that it is larger than at least one of changes in injection rate. When the time interval from the preliminary injection to the pilot injection is I1, and the time interval from the pilot injection to the main injection is I2,
I1> I2
The fuel injection control device according to claim 1, wherein

Images