Control device for internal combustion engine

Abstract

To provide a control device of an internal combustion engine which is suppressed in the lowering of the restartability of the internal combustion engine having a port injection valve.SOLUTION: A control device of an internal combustion engine having a port injection valve comprises: an intermittent operation control part for automatically stopping and automatically starting the internal combustion engine; a measurement part for measuring a stop time of the internal combustion engine when the internal combustion engine is automatically stopped, and newly remeasuring the stop time when there arises an automatic stop requirement once again after a start of the internal combustion engine; a port injection amount control part for increasing a fuel injection amount from the port injection valve after the start of the internal combustion engine as the stop time is longer, and gradually attenuating an increase amount; and a lower-limit guard part using the increase amount in the attenuation as a lower-limit value of the increase amount after the next start of the internal combustion engine.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

[0002] In an intermittent operation control in which an internal combustion engine equipped with a port injection valve automatically stops and starts, fuel injection is stopped when the internal combustion engine stops. As a result, the fuel adhering to the inner surface of the intake port dries up between the time the internal combustion engine stops and the time it is restarted, and part of the fuel injected from the port injection valve at the time of restart may adhere to the inner surface of the intake port, reducing the amount of fuel introduced into the cylinder. This may result in a decrease in the restartability of the internal combustion engine. For example, a technology is known in which the stop time of the internal combustion engine is measured, and the port injection amount is increased at the time of starting the internal combustion engine as the stop time increases, thereby improving the restartability of the internal combustion engine (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-124167 A Summary of the Invention [Problem to be solved by the invention]

[0004] If the increased amount of port injection is continued, the amount of fuel adhering to the inner surface of the intake port will gradually increase, and the amount of fuel introduced into the cylinder will also gradually increase. For this reason, it is possible to attenuate the increase in the port injection amount over time to return the port injection amount to the normal amount. Therefore, it is preferable to determine the attenuation rate of the port injection amount taking into account the amount of fuel adhering to the inner surface of the intake port.

[0005] However, while the increment of the port injection amount is decaying, the internal combustion engine may automatically stop again and restart in a short time. In this case, the stop time of the internal combustion engine is measured again, and the increment of the port injection amount is newly calculated based on this newly measured short stop time. Here, the increment that was decaying is updated to the newly calculated increment, but the newly calculated increment may be smaller than the increment during the decay before the update. In this case, the increment of the port injection amount may be insufficient, which may deteriorate the restartability of the internal combustion engine.

[0006] SUMMARY OF THE PRESENT DISCLOSURE In view of the above, an object of the present invention is to provide a control device for an internal combustion engine equipped with a port injection valve, which suppresses deterioration in the restartability of the internal combustion engine. [Means for solving the problem]

[0007] The above object is to provide a control device for an internal combustion engine equipped with a port injection valve, comprising: an intermittent operation control unit that executes automatic stopping and automatic starting of the internal combustion engine; a measurement unit that measures a stop time of the internal combustion engine when the internal combustion engine is automatically stopped, and when an automatic stop request is made again after the internal combustion engine is started, that re-measures the stop time; and a control unit that increases the amount of fuel injection from the port injection valve after the rotation speed of the internal combustion engine becomes equal to or greater than a threshold value after start control of the internal combustion engine is completed, and gradually attenuates the increased amount. and a lower limit guard unit that uses the attenuating increase as a lower limit guard value for the increase after the next start of the internal combustion engine, the threshold value being a rotation speed at which the internal combustion engine can operate autonomously plus a predetermined margin, the threshold value being a speed lower than an idle rotation speed, and when a second value obtained by adding a predetermined value to the rotation speed of the internal combustion engine at the start of start control of the internal combustion engine is greater than a first value, which is a predetermined fixed value, the threshold value is the second value, and the second value is the No.When the threshold value is equal to or less than one value, the threshold value is the first value, and the specified value is set to a value equal to or greater than the rotational speed at which the internal combustion engine increases from the rotational speed at which start control of the internal combustion engine begins to the rotational speed at which the internal combustion engine can operate autonomously, and equal to or less than the first value, which can be achieved by an internal combustion engine control device. Effect of the Invention

[0008] According to the present invention, it is possible to provide a control device for an internal combustion engine that is equipped with a port injection valve and that suppresses deterioration in the restartability of the internal combustion engine. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of a hybrid vehicle. [Diagram 2] FIG. 2 is a schematic diagram of the engine. [Diagram 3] FIG. 3 is a timing chart showing an example of the control for increasing the port injection amount. [Figure 4] FIG. 4 is a timing chart showing an example of the control for increasing the port injection amount in a comparative example. [Diagram 5] FIG. 5 is a timing chart showing an example of the control for increasing the port injection amount in this embodiment. [Figure 6] FIG. 6 is a flowchart showing an example of the port injection amount increase control executed by the ECU. [Figure 7] FIG. 7 is a flow chart showing details of the control for increasing the port injection amount in this embodiment. [Figure 8] FIG. 8 is a map that defines the relationship between the engine stop time and the port injection amount increase coefficient. [Figure 9] FIG. 9 is a timing chart showing an example of the transition of the engine rotation speed during automatic start and during a change of mind. [Figure 10] FIG. 10 is a flowchart showing an example of threshold setting control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] [General configuration of hybrid vehicle] FIG. 1 is a schematic diagram of a hybrid vehicle. The hybrid vehicle is equipped with an engine 10 and a motor 15 as driving sources for traveling. The engine 10 is a spark-ignition gasoline engine, which will be described in detail later, and is an example of an internal combustion engine. A transmission unit 11 is provided in a power transmission path from the engine 10 to wheels 13. The transmission unit 11 and the left and right wheels 13 are drivingly connected via a differential 12.

[0011] The transmission unit 11 is provided with a K0 clutch 14 and a motor 15. In the transmission unit 11, the motor 15 is installed so as to be located on a power transmission path from the engine 10 to the wheels 13.

[0012] The K0 clutch 14 is disposed so as to be located between the engine 10 and the motor 15 in the power transmission path. The K0 clutch 14 is supplied with hydraulic pressure and enters an engaged state, connecting the power transmission between the engine 10 and the motor 15. The K0 clutch 14 enters a released state in response to the cessation of the hydraulic pressure supply, and interrupts the power transmission between the engine 10 and the motor 15. The K0 clutch 14 is in a slip state from the start of torque transmission until it is fully engaged. The ECU 50, which will be described later, can control the K0 clutch 14 to any one of a released state, a slip state, and an engaged state by adjusting the hydraulic pressure supplied to the K0 clutch 14 by a hydraulic control mechanism 22.

[0013] The motor 15 is connected to the battery 16 via an inverter 17. The battery 16 is a chargeable and dischargeable secondary battery such as a nickel-metal hydride battery or a lithium-ion battery. The motor 15 functions as a motor that generates driving force for the vehicle in response to power supplied from the battery 16, and also functions as a generator that generates electric power to charge the battery 16 in response to power transmission from the engine 10 and the wheels 13. The electric power exchanged between the motor 15 and the battery 16 is adjusted by the inverter 17.

[0014] The transmission unit 11 is provided with a torque converter 18, which is a fluid coupling having a torque amplifying function, and a stepped automatic transmission 19 that switches the gear ratio in multiple stages by changing the gear stage. In the transmission unit 11, the automatic transmission 19 is installed so as to be located at a portion of the power transmission path closer to the wheels 13 than the motor 15. The motor 15 and the automatic transmission 19 are connected via the torque converter 18. The torque converter 18 is provided with a lock-up clutch 20 that is supplied with hydraulic pressure and engages to directly connect the motor 15 and the automatic transmission 19.

[0015] 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 automatic transmission 19, and the lock-up clutch 20 via the hydraulic control mechanism 22. The hydraulic control mechanism 22 is provided with hydraulic circuits for each of the K0 clutch 14, the torque converter 18, the automatic transmission 19, and the lock-up clutch 20, and various hydraulic control valves for controlling the operating hydraulic pressures thereof.

[0016] The hybrid vehicle is provided with an ECU (Electronic Control Unit) 50 as a control device for the vehicle. The ECU 50 is an electronic control unit including a calculation processing circuit that performs various calculation processes related to vehicle driving control, and a memory that stores control programs and data. The ECU 50 is an example of a control device for an internal combustion engine, and functionally realizes an intermittent operation control unit, a measurement unit, a port injection amount control unit, and a lower limit guard unit, which will be described in detail later.

[0017] The ECU 50 controls the operation of the engine 10 and the motor 15. For example, the ECU 50 controls the inverter 17 to adjust the amount of electric power exchanged between the motor 15 and the battery 16, thereby controlling the torque of the motor 15. The ECU 50 controls the operation of the K0 clutch 14, the lock-up clutch 20, and the automatic transmission 19 through the control of the hydraulic control mechanism 22. The ECU 50 receives detection signals such as an accelerator pedal opening degree, which is the amount of depression of the accelerator pedal by the driver.

[0018] The ECU 50 drives the hybrid vehicle in one of the driving modes of the motor driving mode, the hybrid driving mode, and the engine driving mode. In the motor driving mode, the ECU 50 releases the K0 clutch 14 to rotate the wheels 13 with the power of the motor 15. In the hybrid driving mode, the ECU 50 engages the K0 clutch 14 to rotate the wheels 13 with the power of the engine 10 and the motor 15. In the engine driving mode, the ECU 50 engages the K0 clutch 14 to rotate the wheels 13 with the power of the engine 10. The ECU 50 selects the motor driving mode when the remaining charge of the battery 16 is sufficient. The ECU 50 selects the hybrid driving mode or the engine driving mode when the remaining charge of the battery 16 is low, when the vehicle speed exceeds the upper limit in the motor driving mode, or when the vehicle accelerates rapidly.

[0019] The ECU 50 executes intermittent operation control in which the engine 10 is automatically stopped when a predetermined stop condition is satisfied in the hybrid driving mode or the engine driving mode, and the engine 10 that has been automatically stopped is restarted when a predetermined restart condition is satisfied. For example, in the hybrid driving mode or the engine driving mode, when the vehicle speed is equal to or lower than zero or a speed slightly higher than zero and the brake pedal is depressed, the ECU 50 determines that the automatic stop condition is satisfied and automatically stops the engine 10. In addition, when the brake pedal is released, the ECU 50 determines that the automatic start condition is satisfied and automatically restarts the engine 10. When the engine 10 is automatically stopped, the ECU 50 releases the K0 clutch 14 to stop fuel injection. When the engine 10 is automatically started from a stopped state, the ECU 50 controls the K0 clutch 14 to a slip state, cranks the engine 10 using the motor 15, starts fuel injection and ignition from the in-cylinder injection valve 41d to cause the engine 10 to fully explode, and maintains the K0 clutch 14 in the slip state or transitions it to an engaged state.

[0020] [Engine outline] FIG. 2 is a schematic diagram of the engine 10. The engine 10 has cylinders 30, pistons 31, connecting rods 32, a crankshaft 33, an intake passage 35, an intake valve 36, an exhaust passage 37, and an exhaust valve 38. The cylinders 30 burn an air-fuel mixture. FIG. 2 shows only one of the multiple cylinders 30 of the engine 10. The pistons 31 are accommodated in each cylinder 30 so as to be capable of reciprocating, and are connected to a crankshaft 33, which is an output shaft of the engine 10, via a connecting rod 32. The connecting rod 32 and the crankshaft 33 constitute a crank mechanism that converts the reciprocating motion of the pistons 31 into the rotational motion of the crankshaft 33. The engine 10 is provided with a crank angle sensor 34 that detects the rotation angle of the crankshaft 33.

[0021] The intake passage 35 is an intake passage for intake air, and is connected to an intake port 35p of each cylinder 30 via an intake valve 36. The exhaust passage 37 is an exhaust passage for exhaust air, and is connected to an exhaust port 37p of each cylinder 30 via an exhaust valve 38. The intake passage 35 is provided with an airflow meter 39 for detecting the amount of intake air, and a throttle valve 40 for adjusting the flow rate of intake air.

[0022] An in-cylinder injection valve 41d is provided in the cylinder 30. The in-cylinder injection valve 41d injects fuel directly into the cylinder 30. The intake passage 35 is provided with a port injection valve 41p that injects fuel toward the intake port 35p. Note that the in-cylinder injection valve 41d may not be provided and only the port injection valve 41p may be provided. Each cylinder 30 is provided with an ignition device 42 that ignites a mixture of the intake air introduced through the intake passage 35 and the fuel injected by the in-cylinder injection valve 41d and the port injection valve 41p by spark discharge. A catalyst 43 for purifying exhaust gas is provided in the exhaust passage 37, and an air-fuel ratio sensor 44 for detecting the air-fuel ratio is provided upstream of the catalyst 43.

[0023] The ECU 50 receives detection signals from the crank angle sensor 34, the air flow meter 39, and the air-fuel ratio sensor 44. The ECU 50 calculates the engine speed from the detection signal from the crank angle sensor 34. The ECU 50 controls the operation of the engine 10 through control of the opening of the throttle valve 40, control of the fuel injection of the in-cylinder injection valve 41d and the port injection valve 41p, control of ignition of the ignition device 42, etc.

[0024] [Port injection volume increase control] The ECU 50 executes an increase control for increasing the fuel injection amount from the port injection valve 41p when the engine 10 is restarted, taking into consideration the drying of the inner surface of the intake port 35p while the engine 10 is automatically stopped by the intermittent operation control. Specifically, the ECU 50 measures the stop time S of the engine 10, calculates an increase coefficient K of the port injection amount based on the stop time S, and increases the port injection amount based on the increase coefficient K after the start control for restarting the engine 10 is completed. The increase coefficient K is a value of 1 or more, and is a value for multiplying a basic port injection amount determined by the operation amount of the accelerator pedal by the driver, etc., and setting the injection amount obtained by multiplying the increase coefficient K by the basic port injection amount determined by the operation amount of the accelerator pedal by the driver, etc., as a target port injection amount. The increase coefficient K is calculated to be larger as the stop time S of the engine 10 is longer. This is because the longer the stop time S of the engine 10 is, the more likely the inner surface of the intake port 35p becomes dry, and the less likely the fuel injected from the port injection valve 41p is to be introduced into the cylinder 30 when the engine 10 is restarted.

[0025] Here, the ECU 50 determines that the engine 10 is stopped when the engine speed is less than the rotation speed (complete combustion rotation speed) at which the engine 10 can operate autonomously. Also, the ECU 50 determines that the engine 10 is after starting and the start control of the engine 10 is completed when the engine speed is equal to or higher than the rotation speed at which the engine 10 can operate autonomously. The start control is a control that is performed from the stopped state of the engine 10 until the engine 10 completes combustion and becomes capable of operating autonomously. Specifically, from the stopped state of the engine 10, cranking is started by the motor 15 while putting the K0 clutch 14 into a slip state, fuel is injected from the in-cylinder injection valve 41d to complete combustion, and the start control is completed. The stop time S of the engine 10 is the time during which the engine 10 is stopped as determined above. The rotation speed at which the engine 10 can operate autonomously is a speed slower than the idle rotation speed INe.

[0026] Fig. 3 is a timing chart showing an example of the port injection amount increase control. Fig. 3 shows the engine rotation speed, the driving state of the engine 10, the stop time S of the engine 10, and the increase coefficient K. The driving state of the engine 10 indicates whether the engine 10 is stopped or has been started.

[0027] As shown in FIG. 3, when the engine 10 is automatically stopped by the intermittent operation control and the stop time S of the engine 10 is being measured, the start control is started by the driver releasing the brake pedal, and at time t1, it is determined that the start control of the engine 10 is completed and the measurement of the stop time S of the engine 10 is stopped. The example of FIG. 3 shows a case where a value k1 of the boost coefficient K corresponding to the time s1 which is the stop time S of the engine 10 is calculated. After the start control of the engine 10 is completed, when the engine rotation speed is equal to or higher than the threshold A, the boost coefficient K decays at a constant rate from the value k1. The threshold A is a rotation speed which is a predetermined value higher than the rotation speed at which the engine 10 can operate autonomously and is slower than the idle rotation speed INe. Note that the example of FIG. 3 shows a state in which the engine 10 is automatically started and the driver depresses the accelerator pedal, causing the engine rotation speed to be higher than the idle rotation speed INe, and the stop time S of the engine 10 is held even after the engine 10 is started.

[0028] At time t2, the engine speed is maintained at the idle speed INe, and when the automatic stop condition is subsequently satisfied, at time t3, the engine 10 drops below the rotation speed at which it can be operated autonomously and automatically stops. When the engine 10 automatically stops, the stop time S of the engine 10 is measured again, and the boost coefficient K is maintained. When the engine 10 is restarted thereafter, the boost coefficient K is newly calculated based on the stop time S of the engine 10.

[0029] [Port injection amount increase control in comparison example] Fig. 4 is a timing chart showing an example of the control for increasing the port injection amount in the comparative example. Fig. 4 corresponds to Fig. 3. Specifically, Fig. 4 is the same as Fig. 3 up to time t3. Fig. 4 shows a case where the engine 10 is started by the driver depressing the accelerator pedal immediately after the engine speed drops to a speed lower than the speed at which the engine can be operated autonomously at time t3, that is, the engine 10 is started by a so-called change of mind. As a result, the ECU 50 executes the start control of the engine 10, and at time t4, the start control is completed, the engine speed becomes equal to or higher than the speed at which the engine can be operated autonomously, and the engine 10 is restarted.

[0030] In this case, the stop time S of the engine 10 is measured again at time t3. The stop time S from time t3 to the restart of the engine 10 at time t4 is set as time s2. The boost coefficient K is also newly calculated as a small value k2 corresponding to this short time s2, and the boost coefficient K starts to decay from the value k2 at time t4. However, the value k2 of the boost coefficient K is smaller than the value k1a of the boost coefficient K during decay just before time t4. Therefore, although the port injection amount is increased based on the value k1 of the boost coefficient K set based on the time s1 up to time t1, the boost coefficient K is set to an even smaller value during decay at time t4. Therefore, the port injection amount may be insufficient after time t4, and the restartability of the engine 10 may be deteriorated.

[0031] [Increasing control of port injection amount in this embodiment] Fig. 5 is a timing chart showing an example of the increase control of the port injection amount in this embodiment. Fig. 5 corresponds to Fig. 4. In this embodiment, the increase coefficient K being attenuated is updated as needed as a lower limit guard value in the memory of the ECU 50. Therefore, when the engine 10 is restarted at time t4, the updated value k1a as the lower limit guard value becomes the initial value of the newly calculated increase coefficient K. Therefore, after time t4, the newly calculated increase coefficient K attenuates from the value k1a, and the shortage of the port injection amount can be eliminated.

[0032] FIG. 6 is a flow chart showing an example of the control of increasing the port injection amount executed by the ECU 50. The ECU 50 judges whether the engine 10 has automatically stopped based on whether the engine speed has become lower than the rotation speed at which the engine can be operated autonomously (step S1). If the answer is Yes in step S1, the ECU 50 starts measuring the stop time S of the engine 10 (step S2). Next, the ECU 50 judges whether the engine 10 has started based on whether the engine speed has become equal to or higher than the rotation speed at which the engine can be operated autonomously (step S3). The start of the engine 10 includes not only automatic start but also change of mind as described above. Even if the answer is No in step S1, step S3 is executed. If the answer is No in step S3, this control is terminated. If the answer is Yes in step S3, the ECU 50 stops measuring the stop time S (step S4). Steps S1 and S3 are examples of the processing executed by the intermittent operation control unit. Steps S2 and S4 are examples of the processing executed by the measurement unit.

[0033] Next, the ECU 50 determines whether or not there is a port injection request (step S5). In general, when the engine 10 is operating at low speed and low load, port injection is performed, when the engine 10 is operating at high speed and high load, in-cylinder injection is performed, and when the engine 10 is operating at medium speed and medium load, both port injection and in-cylinder injection are performed. If the answer is No in step S5, the control ends. If the answer is Yes in step S5, the ECU 50 executes control to increase the port injection amount (step S6).

[0034] Fig. 7 is a flowchart showing details of the port injection amount increase control of this embodiment. The ECU 50 calculates the port injection amount increase coefficient K based on the stop time S of the engine 10 (step S11). Fig. 8 is a map that specifies the relationship between the stop time S of the engine 10 and the port injection amount increase coefficient K. The horizontal axis indicates the stop time S, and the vertical axis indicates the increase coefficient K. As described above, the longer the stop time S of the engine 10, the larger the port injection amount increase coefficient K calculated to be.

[0035] Next, the ECU 50 judges whether the boost coefficient K is equal to or greater than the lower limit guard value (step S12). If the answer is Yes in step S12, the ECU 50 judges whether the engine rotation speed is equal to or greater than a threshold value A (step S13). The threshold value A is a rotation speed at which the engine can be operated autonomously and a predetermined margin is added, and is a speed lower than the idle rotation speed INe. If the answer is Yes in step S13, the boost coefficient K calculated in step S11 is attenuated as an initial value (step S14). Next, the ECU 50 updates the attenuating boost coefficient K as a lower limit guard value as needed (step S15). If the answer is No in step S13, this control ends.

[0036] If the answer is No in step S12, the ECU 50 sets the boost coefficient K calculated in step S11 to the lower limit guard value (step S16). Next, if the answer is Yes in step S13, the ECU 50 attenuates the boost coefficient K set to the lower limit guard value in step S16 as an initial value (step S14). Next, the ECU 50 updates the attenuating boost coefficient K as the lower limit guard value as needed (step S15).

[0037] In this way, by continually updating the value of the increase coefficient K during decay as a lower limit guard value, even when the engine 10 automatically stops while the increase in the port injection amount is decaying and is restarted in a short time, as in the case of a change of mind described above, it is possible to prevent a deficiency in the port injection amount and to suppress a deterioration in the restartability of the engine 10. Furthermore, by using simple control such as continually updating the value of the increase coefficient K during decay as a lower limit guard value, it is possible to effectively suppress a deterioration in the restartability of the engine 10 without significantly changing the control of the decay of the increase coefficient K, the measurement of the stop time S, etc.

[0038] Next, the threshold value A will be described. The threshold value A is a variable value that is set to different values ​​during automatic start and during a change of mind. FIG. 9 is a timing chart showing an example of the transition of the engine rotation speed during automatic start and during a change of mind. For ease of understanding, FIG. 9 shows the engine rotation speed during automatic start and during a change of mind at the same time. In addition, both during automatic start and during a change of mind, the case where the start control of the engine 10 is started at time t11 is shown.

[0039] During automatic start, the engine speed increases from zero at time t11, and at time t13, the engine becomes capable of independent operation and start control is completed. After that, when the engine speed reaches or exceeds a value a1 at time t14, the boost coefficient K is attenuated as described above. The value a1 is a predetermined fixed value.

[0040] During a change of mind, the start control is started at time t11 when the driver depresses the accelerator pedal and the engine speed is equal to or lower than a predetermined value but before it becomes zero. At time t12, the engine becomes capable of independent operation and the start control is completed. Even in this case, if the decay of the boost coefficient K is started uniformly on the condition that the engine speed is equal to or higher than the value a1, the decay will start during execution of the start control during a change of mind. Thus, the decay of the boost coefficient K should be performed after the completion of the start control, but the decay starts during execution of the start control, so that the port injection amount may be insufficient. Therefore, in this embodiment, as shown in FIG. 9, a value a2 is calculated in addition to the value a1, and the larger of the values ​​a1 and a2 is set as the threshold A, so that the timing of the start of the decay of the boost coefficient K can be appropriately controlled even during a change of mind. Specifically, the ECU 50 sets the threshold A as follows.

[0041] FIG. 10 is a flow chart showing an example of the setting control of the threshold value A. This control is repeatedly executed during the execution of the intermittent operation control. The ECU 50 acquires the engine rotation speed at the start of the start control of the engine 10 (step S21). Next, the ECU 50 calculates the value a2 (step S22). The value a2 is a value obtained by adding a predetermined value Δa to the acquired rotation speed at the start of the start control. Here, the predetermined value Δa is equal to or higher than the rotation speed at which the engine 10 increases from the engine rotation speed at the start of the start control of the engine 10 to the rotation speed at which the engine 10 can operate autonomously, and is determined in advance by an experiment. FIG. 9 shows the value a2 calculated by adding the predetermined value Δa to the engine rotation speed at the start of the start control during a change of mind.

[0042] Next, the ECU 50 determines whether the value a2 is greater than the value a1 (step S23). If the answer is Yes in step S23, the ECU 50 sets the value a2 as the threshold A (step S24). If the answer is No in step S23, the ECU 50 sets the value a1 as the threshold A (step S25).

[0043] As described above, by comparing the value a2 with the value a1 and setting the larger value as the threshold A, it is possible to prevent the attenuation of the boost coefficient K from starting during execution of the start control, and to prevent the port injection amount from becoming insufficient. The control shown in FIG. 10 is also executed during automatic start. During automatic start, the value a2 is calculated by adding a predetermined value Δa to zero, which is the engine speed at the start of the start control. In this case, the predetermined value Δa is set so that a1 ≧ a2. That is, the predetermined value Δa is set to a value equal to or less than the value a1.

[0044] Furthermore, the engine speed at which start control is initiated during a change of mind is a variable value that depends on the vehicle speed at that time, etc. In this case as well, the value a2 is calculated based on the engine speed at the start of start control, so that the timing of attenuation of the boost coefficient K can be appropriately controlled.

[0045] In this embodiment, a hybrid vehicle is controlled by a single ECU 50, but this is not limited to the above, and the above-mentioned control may be performed by multiple 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.

[0046] In the above embodiment, a hybrid vehicle has been described as an example, but the present invention is not limited to this, and the vehicle may have only an engine as a drive source for the vehicle.

[0047] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0048] 10 Engine 14 K0 clutch 15 Motor 30 cylinders 35p Intake port 41p Port injection valve 50 ECU (internal combustion engine control unit)

Claims

[Claim 1] A control device for an internal combustion engine equipped with a port injection valve, an intermittent operation control unit that executes automatic stopping and automatic starting of the internal combustion engine; a measurement unit that measures a stop time of the internal combustion engine when the internal combustion engine is automatically stopped, and that re-measures the stop time when an automatic stop request is made again after the internal combustion engine is started; a port injection amount control unit that increases the amount of fuel injection from the port injection valve after the rotation speed of the internal combustion engine becomes equal to or higher than a threshold value after completion of the start control of the internal combustion engine as the stop time is longer, and gradually attenuates the increased amount; a lower limit guard unit that uses the attenuated increase as a lower limit guard value of the increase after the next start of the internal combustion engine, the threshold value is a rotation speed at which the internal combustion engine can operate autonomously plus a predetermined margin, and is a speed lower than an idle rotation speed, When a second value obtained by adding a predetermined value to the rotation speed of the internal combustion engine at the start of the start control of the internal combustion engine is greater than a first value, which is a predetermined fixed value, the threshold value is the second value, and when the second value is equal to or less than the first value, the threshold value is the first value. A control device for an internal combustion engine, wherein the specified value is set to a value equal to or higher than the rotational speed at which the internal combustion engine increases from the rotational speed at which start control of the internal combustion engine begins to a rotational speed at which the internal combustion engine can operate autonomously, and equal to or lower than the first value.

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