Fuel injection control device for internal combustion engine

Abstract

To alleviate impact at the engagement of an on-off clutch arranged between an internal combustion engine and an electric motor when staring the internal combustion engine in a hybrid vehicle.SOLUTION: A fuel injection control device is given in a hybrid vehicle with an on-off clutch which is arranged at a power transmission path and disengaged in a release state between an internal combustion engine and an electric motor. The fuel injection control device performs, at the time of starting the internal combustion engine, fuel injection at the start time by use of a direct injection injector, and then shifts to fuel injection using a port injector using the port injector after the fuel injection at the start time. The fuel injection control device starts the fuel injection at the start time through the direct injection injector after receiving a start command of the internal combustion engine, and the fuel injection at the start time continues, when requested injection quantity of the internal combustion engine is less than minimum injection quantity of the direct injection injector, after the condition where the requested injection quantity of the internal combustion engine is less than the minimum injection quantity of the direct injection injector.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a fuel injection control device for an internal combustion engine.

Background Art

[0002] Conventionally, a fuel injection control device that includes a direct injection injector and a port injector and selectively uses these injectors according to the state of an internal combustion engine is known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since a direct injection injector injects fuel directly into a cylinder, it is necessary to enhance the atomization property of the fuel more than a port injector that inhales the fuel atomized in an intake port into the cylinder. The fuel injection pressure during fuel injection is high, and the combustion stability is high. For this reason, a direct injection injector can more easily obtain torque and can efficiently increase the engine speed compared to a port injector. For this reason, in an internal combustion engine equipped with a direct injection injector and a port injector, at the time of starting, first, starting fuel injection using the direct injection injector is performed. After that, the injection mode shifts to fuel injection using the port injector, in which the fuel injection amount corresponding to the required injection amount of the internal combustion engine is injected. When using the port injector, the rate of increase in the engine speed may decrease depending on the temperature of the port and the fuel properties, compared to the case where the required injection amount is injected using only the direct injection injector.

[0005] Incidentally, an internal combustion engine equipped with a direct injection injector and a port injector may be mounted on a hybrid vehicle together with an electric motor as a drive source. In a hybrid vehicle, a disconnect clutch for changing the connection state between the internal combustion engine and the electric motor is disposed between the internal combustion engine and the electric motor. In a hybrid vehicle, the internal combustion engine that has been stopped may start when the electric motor is rotating. The disconnect clutch is in a released state when the internal combustion engine is stopped, and is brought into an engaged state in accordance with the start of the internal combustion engine. At this time, if there is a difference between the rotational speed of the internal combustion engine and the rotational speed of the electric motor, an impact may occur when the disconnect clutch is engaged.

[0006] As described above, the internal combustion engine performs fuel injection at startup using only the direct injection injector, and then shifts to fuel injection using the port injector. Along with this shift in the injection mode, the rate of increase in the engine speed decreases. For this reason, depending on the timing of the shift in the injection mode, the period until the rotational speed of the internal combustion engine matches the rotational speed of the electric motor after the shift in the injection mode tends to become longer, and an impact at the time of engagement of the disconnect clutch is likely to occur.

[0007] Therefore, an object of the fuel injection control device for an internal combustion engine disclosed in this specification of the present invention is to mitigate the impact at the time of engagement of a disconnect clutch disposed between the internal combustion engine and the electric motor when the internal combustion engine in a hybrid vehicle starts.

Means for Solving the Problems

[0008] The above object is achieved by a fuel injection control device for an internal combustion engine in a hybrid vehicle, the device including: an internal combustion engine having a direct injection injector and a port injector; an electric motor connected to be power-transmittable to a power transmission path between the internal combustion engine and drive wheels; and a disconnect clutch provided in the power transmission path and disengaged to disconnect the connection between the internal combustion engine and the electric motor. When starting the internal combustion engine, the device performs starting fuel injection using the direct injection injector, and then shifts to port injector fuel injection using the port injector. The fuel injection control device starts the starting fuel injection by the direct injection injector in response to a start command of the internal combustion engine. After starting the starting fuel injection, when the required injection amount of the internal combustion engine becomes less than the minimum injection amount of the direct injection injector, the starting fuel injection is continued until after the time when the required injection amount of the internal combustion engine becomes less than the minimum injection amount of the direct injection injector, and then the device shifts to port injector fuel injection.

[0009] In the fuel injection control device for the internal combustion engine, the fuel injection control device compares a determination value set using the minimum injection amount and the required injection amount of the direct injection injector with the required injection amount. When it is determined that the required injection amount is less than the determination value, the device shifts from the starting fuel injection to the injector fuel injection.

Advantages of the Invention

[0010] According to the present invention, at the start of an internal combustion engine in a hybrid vehicle, the impact at the time of engagement of a disconnect clutch arranged between the internal combustion engine and the electric motor can be mitigated.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, in the drawings, the dimensions, ratios, etc. of each part may not be illustrated so as to be exactly the same as the actual ones. Also, depending on the drawings, details may be omitted. Furthermore, the scales of the elements drawn between the drawings may be different.

[0013] [Schematic Configuration of Hybrid Vehicle] Figure 1 is a schematic configuration diagram of a hybrid vehicle 1. In the hybrid vehicle 1, a K0 clutch 14, a motor 15, a torque converter 18, and a transmission 19 are sequentially provided in the power transmission path from the corresponding engine 10 to the drive wheels 13. The engine 10 and the motor 15 are mounted as driving sources for the running of the hybrid vehicle 1. The engine 10 is an example of an internal combustion engine, and is, for example, a V-type 6-cylinder gasoline engine, but the number of cylinders is not limited to this, and it may be an in-line gasoline engine. The K0 clutch 14, the motor 15, the torque converter 18, and the transmission 19 are provided in the transmission unit 11. The transmission unit 11 and the left and right drive wheels 13 are drivingly connected via a differential 12.

[0014] The K0 clutch 14 is provided between the engine 10 and the motor 15 on the power transmission path. The K0 clutch 14 receives hydraulic pressure supply from the released state and enters the engaged state, connecting the power transmission between the engine 10 and the motor 15. The K0 clutch 14 enters the released state in response to the stop of the hydraulic pressure supply, cutting off the power transmission between the engine 10 and the motor 15. The engaged state means that both engaging elements of the K0 clutch 14 are connected and the engine 10 and the motor 15 have the same rotational speed. The released state means that both engaging elements of the K0 clutch 14 are separated. Note that the K0 clutch 14 corresponds to a disconnect clutch.

[0015] The motor 15 is connected to the battery 16 via the inverter 17. The motor 15 functions as a motor that generates the driving force of the vehicle in response to the power supply from the battery 16, and also functions as a generator that generates electric power for charging the battery 16 in response to the power transmission from the engine 10 or the drive wheels 13. The electric power exchanged between the motor 15 and the battery 16 is adjusted by the inverter 17. Note that the motor 15 corresponds to an electric motor.

[0016] The inverter 17 is controlled by the ECU 100 described later, converts the DC voltage from the battery 16 into an AC voltage, or converts the AC voltage from the motor 15 into a DC voltage. In the case of the power running operation where the motor 15 outputs torque, the inverter 17 converts the DC voltage of the battery 16 into an AC voltage and adjusts the power supplied to the motor 15. In the case of the regenerative operation where the motor 15 generates electricity, the inverter 17 converts the AC voltage from the motor 15 into a DC voltage and adjusts the power supplied to the battery 16.

[0017] The torque converter 18 is a fluid coupling having a torque amplification function. The transmission 19 is a stepped automatic transmission that switches the gear ratio in multiple steps by switching the gear stage, but is not limited thereto and may be a continuously variable automatic transmission. The transmission 19 is provided between the motor 15 and the drive wheels 13 on the power transmission path. The motor 15 and the transmission 19 are connected via the torque converter 18. The torque converter 18 is provided with a lock-up clutch 20 that receives the supply of hydraulic pressure and engages to directly connect the motor 15 and the transmission 19.

[0018] The transmission unit 11 is further provided with an oil pump 21 and a hydraulic control mechanism 22. The hydraulic pressure generated by the oil pump 21 is supplied to the K0 clutch 14, the torque converter 18, the transmission 19, and the lock-up clutch 20 via the hydraulic control mechanism 22, respectively. The hydraulic control mechanism 22 is provided with respective hydraulic circuits for the K0 clutch 14, the torque converter 18, the transmission 19, and the lock-up clutch 20, and various hydraulic control valves for controlling their operating hydraulic pressures. Incidentally, a wet clutch may be provided instead of the torque converter 18.

[0019] The hybrid vehicle 1 is provided with an ECU (Electronic Control Unit) 100 as a control device for the vehicle. The ECU 100 is an electronic control unit including an arithmetic processing circuit that performs various arithmetic processes related to vehicle running control, and a memory in which control programs and data are stored. The ECU 100 also functions as a fuel injection control device.

[0020] The ECU 100 controls the driving of the engine 10 and the motor 15. Specifically, the ECU 100 controls the throttle opening, ignition timing, and fuel injection amount of the engine 10 to control the torque and rotational speed of the engine 10. The ECU 100 controls the inverter 17 to adjust the amount of power transfer between the motor 15 and the battery 16, thereby controlling the torque and rotational speed of the motor 15. Also, the ECU 100 performs drive control of the K0 clutch 14, the lock-up clutch 20, and the transmission 19 through the control of the hydraulic control mechanism 22.

[0021] Signals from the ignition switch 71, crank angle sensor 72, motor rotational speed sensor 73, accelerator opening sensor 74, air flow meter 75, air-fuel ratio sensor 76, water temperature sensor 77, and fuel pressure sensor 78 (see Figure 2) are input to the ECU 100. The crank angle sensor 72 detects the rotational speed of the crankshaft of the engine 10. The motor rotational speed sensor 73 detects the rotational speed of the output shaft of the motor 15. The accelerator opening sensor 74 detects the accelerator pedal opening, which is the amount of depression of the driver's accelerator pedal. The air flow meter 75 detects the intake air amount of the engine 10. The air-fuel ratio sensor 76 detects the air-fuel ratio of the exhaust gas flowing into the catalyst 43. The water temperature sensor 77 detects the temperature of the cooling water of the engine 10. The fuel pressure sensor 78 detects the pressure (fuel pressure) of the fuel in the high-pressure delivery pipe 54 described later. The ECU 100 calculates the minimum injection amount Qmin of the direct injection injector 41d described later based on the detection value of the fuel pressure sensor 78. Also, the ECU 100 stores the value of the rich limit injection amount in the preset engine 10. Further, the ECU 100 calculates a determination value set using the minimum injection amount of the direct injection injector 41d and the required injection amount of the engine 10, and compares the calculated determination value with the rich limit injection amount. Then, the injection pattern is set based on the comparison result. The setting of the injection pattern will be described in detail later.

[0022] The ECU 100 drives the hybrid vehicle in either the motor mode or the hybrid mode. In the motor mode, the ECU 100 releases the K0 clutch 14 and runs on the power of the motor 15. At this time, the engine 10 may be in a stopped state. In the hybrid mode, the ECU 100 switches the K0 clutch 14 to the engaged state and runs at least on the power of the engine 10. When switching from the state where the engine 10 is stopped to the hybrid mode, or when the engine 10 starts. The switching of the driving mode is performed based on the required driving force of the vehicle obtained from the vehicle speed and the accelerator opening, the state of charge of the battery 16, etc. Note that when charging the battery 16 by operating the engine 10, the engine 10 also starts even when the engine 10 is in a stopped state.

[0023] [Schematic Configuration of Engine] Figure 2 is a schematic configuration diagram of the engine 10. The engine 10 has cylinders 30, pistons 31, connecting rods 32, a crankshaft 33, an intake passage 35, intake valves 36, an exhaust passage 37, and exhaust valves 38. Only one of the plurality of cylinders 30 of the engine 10 is shown in Figure 2. Combustion of the air-fuel mixture takes place in the cylinder 30. The piston 31 is reciprocally accommodated in each cylinder 30 and is connected to the crankshaft 33, which is the output shaft of the engine 10, via the connecting rod 32. The connecting rod 32 converts the reciprocating motion of the piston 31 into the rotational motion of the crankshaft 33.

[0024] The intake passage 35 is connected to the intake ports of the respective cylinders 30 via the intake valves 36. The exhaust passage 37 is connected to the exhaust ports of the respective cylinders 30 via the exhaust valves 38. The intake passage 35 is provided with an air flow meter 75 and a throttle valve 40 for adjusting the intake air amount. The exhaust passage 37 is provided with an air-fuel ratio sensor 76 and a catalyst 43 for exhaust purification.

[0025] The cylinder 30 is provided with a direct injection injector 41d. The direct injection injector 41d directly injects fuel into the cylinder 30. The intake passage 35 is provided with a port injector 41p that injects fuel toward the intake port. Each cylinder 30 is provided with a spark plug 42 that ignites an air-fuel mixture of intake air introduced through the intake passage 35 and fuel injected by the direct injection injector 41d and the port injector 41p by spark discharge.

[0026] The port injector 41p is connected to a low-pressure delivery pipe 52. The low-pressure delivery pipe 52 is supplied with fuel in the fuel tank 50 pumped up by the low-pressure pump 51. Since the inside of the low-pressure delivery pipe 52 is maintained at a relatively low fuel pressure, the port injector 41p injects fuel with a relatively small injection amount. The low-pressure pump 51 is an electric pump driven by the supply of electric power.

[0027] The direct injection injector 41d is connected to a high-pressure delivery pipe 54. The high-pressure delivery pipe 54 is supplied with fuel pumped up from the fuel tank 50 by the low-pressure pump 51 and boosted to a high fuel pressure by the high-pressure pump 53. Since the inside of the high-pressure delivery pipe 54 is maintained at a relatively high fuel pressure, the direct injection injector 41d injects fuel with a relatively large injection amount. That is, the minimum injection amount Qmin of the direct injection injector 41d is larger than the minimum injection amount of the port injector 41p. Here, the minimum injection amount is the amount of fuel injected during the minimum valve opening period that the injector can achieve. The high-pressure pump 53 is a mechanical pump driven in conjunction with the rotation of the engine 10. A fuel pressure sensor 78 is attached to the high-pressure delivery pipe 54. The fuel pressure detected by the fuel pressure sensor 78 is the fuel pressure inside the high-pressure delivery pipe 54 as described above, and is the fuel pressure supplied to the direct injection injector 41d.

[0028] [Engine Stop and Start] For the engine 10 configured as described above, when a predetermined stop condition is satisfied in the hybrid mode or the engine mode, the ECU 100 executes intermittent operation control to automatically stop the engine, and when a predetermined automatic restart condition is satisfied, the ECU 100 executes intermittent operation control to automatically restart the engine. The automatic stop condition is, for example, when the accelerator opening becomes 0 in the hybrid mode or the engine mode. The automatic restart condition is, for example, when the accelerator opening becomes greater than 0 and the required torque for the engine 10 becomes greater than 0 after the engine 10 has been automatically stopped.

[0029] In this way, when the automatic restart condition is satisfied during the intermittent operation of the engine 10, a start is requested. When there is a start request for the engine 10, the ECU 100 controls the K0 clutch 14 to be in a slip state and starts cranking the engine 10 with the motor 15 and starts combustion in the engine 10.

[0030] Specifically, the ECU 100 executes compression stroke injection by the direct injection injector 41d a predetermined number of target times, and then switches to intake stroke injection by the direct injection injector 41d and executes it a predetermined number of target times. The compression stroke injection is fuel injection executed during the compression stroke for the cylinder 30 that becomes the compression stroke in order with the start of cranking. By executing the compression stroke injection, the torque of the engine 10 can be increased early. The intake stroke injection is fuel injection executed during the intake stroke for the cylinder 30 that becomes the intake stroke in order. By executing the intake stroke injection, the torque of the engine 10 can be stabilized. When the compression stroke injection and the intake stroke injection have each been executed the target number of times, it is considered that the operating state of the engine 10 has stabilized and the start of the engine 10 is completed. Hereinafter, this series of injection patterns will be referred to as fuel injection at startup. In the fuel injection at startup, only the direct injection injector 41d is used, but after the fuel injection at startup is performed, it shifts to port injector used fuel injection using the port injector 41p. In the port injector used fuel injection, only the port injector 41p may be used, or both the port injector 41p and the direct injection injector 41d may be used.

[0031] When the engine 10 is in a stopped state, the K0 clutch 14 is in a released state, but the ECU 100 executes control to engage the K0 clutch 14 in accordance with a start command for the engine 10.

[0032] [Fuel injection control at startup] Hereinafter, with reference to FIGS. 3 to 6, an example of control when the engine 10 starts will be described. FIG. 3 is a flowchart showing an example of fuel injection control executed by the ECU 100, and FIG. 4 is a time chart showing an example of the transition of each value when fuel injection control is performed. FIG. 5 is a graph illustrating the relationship between the minimum injection fuel pressure and the fuel pressure of the injector, and FIG. 6 is a time chart showing an example of the transition of each value when the required injection amount is less than the rich limit injection amount in the fuel injection control device.

[0033] FIG. 4 shows the transition of the hydraulic pressure for engaging the K0 clutch 14, the transition of the fuel pressure supplied to the direct injection injector 41d, the transition of the minimum injection amount Qmin of the direct injection injector 41d, the transition of the rich limit injection amount, the transition of the required injection amount of the engine 10, the transition of the motor speed, the transition of the engine speed, and a signal instructing the switching of the injection mode.

[0034] In the following description, a situation where the engine 10 is started from a state where the hybrid vehicle 1 (see FIG. 1) is traveling at a predetermined speed with the motor 15 as the driving source for traveling will be described. For this reason, as shown in FIG. 4, it is assumed that the motor 15 is operated while maintaining a substantially constant motor speed according to the traveling speed of the hybrid vehicle 1. The engine 10 is stopped before time t1 in FIG. 4, and thus the engine speed before time t1 is 0. At time t1, the start condition of the engine 10 is satisfied, and control for starting the engine 10 is started.

[0035] The minimum injection quantity Qmin of the direct injection injector 41d changes according to the change in the fuel injection pressure supplied to the direct injection injector 41d. This is because, as shown in FIG. 5, the minimum injection quantity in the injector changes according to the injection pressure.

[0036] The rich limit injection quantity means the limit fuel injection quantity that the engine 10 can tolerate as a rich combustion state caused by the required injection quantity falling below the minimum injection quantity Qmin. When the required injection quantity falls below the minimum injection quantity Qmin, the actual fuel injection quantity becomes more than the required injection quantity, and the combustion mode becomes a rich state. When the deviation between the required injection quantity and the minimum injection quantity Qmin becomes large, the rich state progresses and the engine 10 misfires. Therefore, the rich limit injection quantity is obtained in advance through experiments or the like. The rich limit injection quantity is a determination value set using the minimum injection quantity Qmin and the required injection quantity of the direct injection injector 41d. In the present embodiment, the value calculated by the minimum injection quantity Qmin÷the required injection quantity is the injection quantity that is the allowable limit deviation quantity. For example, if the value allowed as the minimum injection quantity Qmin÷the required injection quantity is α (α is a value of 1 or more), when the value of the minimum injection quantity Qmin÷the required injection quantity becomes larger than α, the required injection quantity becomes smaller than the minimum injection quantity Qmin÷α (=rich limit injection quantity). That is, when the required injection quantity falls below the rich limit injection quantity, the engine 10 misfires. The determination value set using the minimum injection quantity Qmin and the required injection quantity may be set by other methods.

[0037] Note that in the time chart shown in FIG. 4, for the sake of easily understanding the characteristics of the control in the present embodiment, the transitions of the respective values in the comparative example are also shown together.

[0038] Referring to FIG. 3, first, in step S1, the ECU 100 determines whether there is a starting request for the engine 10. For example, based on the detected value of the accelerator opening sensor 74 (see FIG. 1), when it is detected that the accelerator opening becomes larger than 0 and the required torque for the engine 10 becomes larger than 0, a negative determination (No determination) is made. The ECU 100 repeats the process of step S1 until a positive determination is made in step S1. When the ECU 100 makes a positive determination (Yes determination) in step S1, it proceeds to step S2.

[0039] In step S2, the ECU 100 executes fuel injection at startup. The time t1 in FIG. 4 is the start point of fuel injection at startup. As shown by the injection pattern in the embodiment of FIG. 4, the ECU 100 uses the direct injection injector 41d to execute compression stroke injection a predetermined number of target times, and then switches to intake stroke injection and executes it a predetermined number of target times. At this time, the ECU 100 controls the values of the fuel pressure and the required injection amount. The fuel pressure is controlled so that a predetermined value is maintained, and the required injection amount rapidly rises at time t1 and then gradually decreases.

[0040] After rapidly rising, the required injection amount gradually decreases and falls below the minimum injection amount Qmin of the direct injection injector 41d at time t2. In this embodiment, as shown in FIG. 4, the fuel injection at startup using only the direct injection injector 41d continues after time t2. Focusing on the engine speed in the embodiment of FIG. 4, the engine speed smoothly rises after time t1 and reaches the same speed as the motor speed at time t4.

[0041] Here, referring to the transition of each value in the comparative example in FIG. 4, the fuel injection control of the comparative example will be described. In the comparative example, at time t2 when the required injection amount falls below the minimum injection amount Qmin, the injection mode shifts from the injection mode using only the direct injection injector 41d to the port injector used fuel injection using the port injector 41p. This shift in the injection mode is a measure to avoid the situation where the fuel injection by the direct injection injector 41d results in an injection amount larger than the required injection amount due to the high fuel pressure, leading to a rich state. By shifting the injection mode to the mode using the port injector 41p, the fuel injection amount decreases, and accordingly, the rising speed of the engine speed decreases. As a result, the time when the engine speed reaches the same speed as the motor speed becomes time t5, which is later than time t4 in the embodiment.

[0042] Next, the engagement of the K0 clutch 14 will be described. The K0 clutch is in a released state when the engine 10 is stopped. Then, at time t3 after time t1 when a start command is issued to the engine 10, the ECU 100 instructs the hydraulic control mechanism 22 to increase the hydraulic pressure for engaging the K0 clutch 14. And at time t4, the engagement of the K0 clutch 14 is completed. At this time, the engine speed in the embodiment has risen to the same speed as the motor speed. Therefore, the impact at the time of engagement of the K0 clutch 14 is suppressed. In contrast, the engine speed in the comparative example has a slow rising speed due to the shift of the injection mode to the mode using the port injector 41p, and has not reached the motor speed at time t4. As a result, in the comparative example, an impact occurs at time t4 when the K0 clutch 14 engages.

[0043] As described above, the impact during the engagement of the K0 clutch 14 in the comparative example occurs because the injection mode switches to the port injector usage injection mode at the time t2 when the required injection amount falls below the minimum injection amount Qmin of the direct injection injector 41d. Therefore, in the present embodiment, the fuel injection at startup using only the direct injection injector 41d is continued even after the time point (time t2) when the required injection amount becomes less than the minimum injection amount Qmin of the direct injection injector 41d. As a result, the engine speed can linearly increase until it reaches the same speed as the motor, and the K0 clutch 14 is engaged when the engine speed and the motor speed become equal. Thereby, the impact during the engagement of the K0 clutch 14 is mitigated.

[0044] Note that since the rising speed of the hydraulic pressure for engaging the K0 clutch 14 slightly varies depending on conditions such as the temperature of the hydraulic oil, etc., the timing (time t3) of the hydraulic pressure rising instruction for the K0 clutch 14 is determined in consideration of this. That is, regardless of the rising speed of the hydraulic pressure for engaging the K0 clutch 14, the time t3 is set so that the engagement of the K0 clutch 14 can be completed as late as possible after the time t4.

[0045] Referring to FIG. 3 again, in step S3, the ECU 100 determines whether the number of injection times of the fuel injection at startup has reached a preset target number. When the ECU 100 makes an affirmative determination in step S3, it proceeds to step S5. In step S5, the ECU 100 ends the fuel injection at startup, and thereafter, appropriately selects the port injector 41p and shifts to the port injector usage fuel injection that realizes the fuel injection amount corresponding to the intake air amount in the engine 10. By executing step S5, a series of controls at the startup of the engine 10 ends. On the other hand, when the ECU 100 makes a negative determination in step S3, it proceeds to step S4.

[0046] In step S4, the ECU 100 determines whether the required injection amount is smaller than the rich limit injection amount. As described above, the rich limit injection amount means the limit fuel injection amount that the engine 10 can tolerate. However, in the time chart shown in FIG. 4, the required injection amount exceeds the rich limit injection amount. Therefore, if the required injection amount is in the state shown in FIG. 4, the ECU 100 makes a negative determination in step S4, repeats the process from step S2, and continues the fuel injection at startup using only the direct injection injector 41d.

[0047] On the other hand, as shown in FIG. 6, when the required injection amount falls below the rich limit injection amount at time t2´, the ECU 100 makes an affirmative determination in step S4 and proceeds to step S5. In step S5, the ECU 100 shifts from the injection mode using only the direct injection injector 41d to the injection mode using the port injector 41p as well. Since the port injector 41p has a lower fuel pressure and a smaller minimum injection amount compared to the direct injection injector 41d, the required injection amount can be achieved by using the port injector 41p. As a result, misfire of the engine 10 can be avoided.

[0048] Note that by shifting to the injection mode using the port injector 41p at time t2´, the rate of increase in the engine speed decreases. Therefore, the engine speed becomes equal to the motor speed at time t5´, which is after the time t4 when the engagement of the K0 clutch 14 is completed. However, the difference between the engine speed and the motor speed at time t4 is smaller compared to the difference between the engine speed and the motor speed at time t4 in the comparative example shown in FIG. 4. Therefore, even in a situation like the time chart shown in FIG. 6, the impact during the engagement of the K0 clutch 14 is mitigated.

[0049] By executing step S5, a series of controls during the startup of the engine 10 is completed.

[0050] In this embodiment, in order to continue the fuel injection at startup using only the direct injection injector 41d until after the time when the required injection amount becomes less than the minimum injection amount Qmin of the direct injection injector 41d, it is possible to mitigate the impact at the time of engagement of the K0 clutch 14.

[0051] However, when the required injection amount falls below the rich limit injection amount, by shifting to an injection mode using the port injector 41p, it is possible to avoid misfires in the engine 10.

[0052] In the above-described embodiment, the case of controlling a hybrid vehicle by a single ECU 100 was illustrated, but it is not limited thereto. For example, the above-described control may be executed by a plurality of ECUs such as an engine ECU that controls the engine 10, a motor ECU that controls the motor 15, and a clutch ECU that controls the K0 clutch 14.

[0053] As described above in detail with respect to the embodiments of the present invention, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Explanation of Reference Numerals

[0054] 1 Hybrid vehicle 10 Engine 11 Transmission unit 12 Differential 13 Drive wheels 14 K0 clutch 15 Motor 41d Direct injection injector 41p Port injector 100 ECU

Claims

1. In a hybrid vehicle comprising an internal combustion engine having a direct injection injector and a port injector, an electric motor power-transmissibly connected to a power transmission path between the internal combustion engine and drive wheels, and a disconnect clutch provided in the power transmission path and disengaged to disconnect the connection between the internal combustion engine and the electric motor, a fuel injection control device for an internal combustion engine that performs starting fuel injection using only the direct injection injector at the start of the internal combustion engine and then shifts to port injector use fuel injection using the port injector after the starting fuel injection, the fuel injection control device is configured to: start the starting fuel injection by only the direct injection injector by the start command in parallel with control to engage the disconnect clutch started in association with the start command of the internal combustion engine; when the required injection amount of the internal combustion engine becomes less than the minimum injection amount of the direct injection injector after starting the starting fuel injection, continue the starting fuel injection until after the time when the required injection amount of the internal combustion engine becomes less than the minimum injection amount of the direct injection injector, and then shift to the port injector use fuel injection; engage the disconnect clutch while the starting fuel injection is being performed; A fuel injection control device for an internal combustion engine.

2. The fuel injection control device is configured to: compare a determination value set using the minimum injection amount and the required injection amount of the direct injection injector with the required injection amount, and when it is determined that the required injection amount is less than the determination value, shift from the starting fuel injection to the port injector use fuel injection regardless of the engagement state of the disconnect clutch started in association with the start command of the internal combustion engine; The fuel injection control device for an internal combustion engine according to Claim 1.

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