Control method and control device for internal combustion engine

Abstract

An internal combustion engine (1) automatically shuts off through halting of fuel injection when an automatic shut-off condition is met. When there is a restart request while the engine rotation speed is reduced as a result of an automatic shut-off, the internal combustion engine (1) is started up through resuming of fuel injection if the engine rotation speed is equal to or greater than a combustion recoverable rotation speed threshold (R1) at which the engine rotation speed can be increased again simply by fuel injection, and, if the engine rotation speed is less than the combustion recoverable rotation speed threshold (R1), the internal combustion engine (1) is started up by means of a starter motor (2). When there is a restart request while a brake is being applied, the internal combustion engine (1) is started up by being rotated by the starter motor (2) instead of a start up through resuming of fuel injection.

Description

[Technical field]

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

[0002] Idle stop control of an internal combustion engine is conventionally known, which automatically stops the internal combustion engine when predetermined automatic stop conditions are met during idling, and automatically restarts the internal combustion engine when predetermined automatic restart conditions are met during the automatic stop.

[0003] For example, in Patent Document 1, when an automatic stop request is generated while the internal combustion engine is operating, fuel injection is stopped. In Patent Document 1, when a request to restart the internal combustion engine is generated while fuel injection is stopped due to the automatic stop request, the internal combustion engine is restarted by fuel injection only if the engine speed at that time is within a rotation speed range where restart is possible with fuel injection alone (above the lower limit of the rotation speed where starterless start is possible), and the internal combustion engine is restarted using a starter that rotates and drives the crankshaft as well if the engine speed at that time is outside the rotation speed range where restart is possible with fuel injection alone (below the lower limit of the rotation speed where starterless start is possible).

[0004] The lower limit of the engine speed at which restart is possible with fuel injection alone (lower limit of engine speed at which starterless start is possible) is set according to the deceleration of the internal combustion engine. However, when the driver depresses the brake pedal, the deceleration of the internal combustion engine changes depending on the magnitude (depression amount) of the brake pedal depression, making it difficult to determine the lower limit of the engine speed at which combustion start can be achieved. If the lower limit of the engine speed at which combustion start can be achieved is set assuming a situation in which the deceleration of the internal combustion engine due to sudden braking is large, the range in which combustion start is possible will be restricted when the deceleration of the internal combustion engine is normal (when no sudden braking is applied). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-223006 A Summary of the Invention

[0006] The internal combustion engine of the present invention comprises: When a predetermined automatic stop condition is met, fuel injection is stopped and the internal combustion engine is automatically stopped, When a request to restart the internal combustion engine is made during the engine speed reduction caused by this automatic stop, If the engine speed is equal to or higher than a predetermined engine speed threshold at which the engine can be restarted by fuel injection alone, the brake state is determined based on the brake state. If the brake is off, the internal combustion engine is started by restarting fuel injection without using the electric motor. If the brake is on, the electric motor is used to rotate the internal combustion engine to start it. When the engine rotation speed is lower than the rotation speed threshold, the electric motor is used to start the internal combustion engine.

[0007] This eliminates the need to set the engine speed threshold value for restarting the engine with fuel injection alone, taking into account the increase in deceleration of the internal combustion engine caused by the driver's braking operation. In other words, when a restart request is made with the brakes not being applied, the region in which restarting is possible with fuel injection alone can be expanded. [Brief description of the drawings]

[0008] [Figure 1] 1 is an explanatory diagram that illustrates a schematic overview of a system configuration of an internal combustion engine to which the present invention is applied; [Diagram 2] 5 is a timing chart showing an example of a state when an automatically stopped internal combustion engine is restarted. [Diagram 3] 5 is a timing chart showing an example of a state when an automatically stopped internal combustion engine is restarted. [Figure 4] 5 is a timing chart showing an example of a state when an automatically stopped internal combustion engine is restarted. [Diagram 5] 5 is a timing chart showing an example of a state when an automatically stopped internal combustion engine is restarted. [Figure 6] 3 is a flowchart showing a flow of control of an internal combustion engine according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described in detail with reference to the drawings, in which: Fig. 1 is an explanatory diagram showing a schematic outline of the system configuration of an internal combustion engine 1 to which the present invention is applied.

[0010] The internal combustion engine 1 is, for example, a multi-cylinder spark ignition gasoline engine that is installed as a drive source in a vehicle such as an automobile. Note that the internal combustion engine 1 may also be a diesel engine.

[0011] The internal combustion engine 1 has a fuel injection valve (not shown). The fuel injection amount of the fuel injection valve, the fuel injection timing of the fuel injection valve, the pressure of the fuel supplied to the fuel injection valve, etc. are optimally controlled by a control unit 21 described later.

[0012] The internal combustion engine 1 also has a starter motor 2 as an electric motor. The starter motor 2 rotates a crankshaft (not shown) of the internal combustion engine 1 in a stopped state to start (crank start) the internal combustion engine 1. The starter motor 2 is controlled by a control unit 21, which will be described later.

[0013] The driving force of the internal combustion engine 1 is transmitted to a CVT (continuously variable transmission) 5 serving as a transmission via a torque converter 3 and a clutch 4, and the driving force transmitted to this CVT 5 is transmitted to driving wheels 7 of the vehicle via a final gear 6.

[0014] That is, the internal combustion engine 1 transmits the rotation of a crankshaft (not shown) as a driving force to driving wheels 7 of the vehicle.

[0015] The clutch 4 is located between the torque converter 3 and the CVT 5, and is engaged when the driving torque from the internal combustion engine 1 can be transmitted to the driving wheels 7. In other words, the clutch 4 is disposed on a power transmission path that transmits the driving force of the internal combustion engine 1 to the driving wheels 7. The operation of engaging / disengaging the clutch 4 is performed based on a control command from a control unit 21, which will be described later. The clutch 4 is disengaged, for example, during a coast stop, which will be described later.

[0016] The CVT 5 has a primary pulley 8 on the input side, a secondary pulley 9 on the output side, and a belt 10 that transmits the rotation of the primary pulley 8 to the secondary pulley 9.

[0017] CVT 5, for example, uses hydraulic pressure to change the width of the V-grooves (not shown) of primary pulley 8 and secondary pulley 9 around which belt 10 is wound, thereby changing the contact radius between belt 10 and primary pulley 8 and secondary pulley 9, and thereby continuously changing the gear ratio.

[0018] Although the CVT 5 is used as the transmission, it is also possible to use a stepped automatic transmission instead of the CVT 5. In this case, the clutch 4 is configured by utilizing a plurality of frictional engagement elements in the stepped automatic transmission.

[0019] The control unit 21 receives detection signals from various sensors, such as a crank angle sensor 22 that detects the crank angle of the crankshaft, an accelerator opening sensor 23 that detects the amount of depression of an accelerator pedal (not shown), a vehicle speed sensor 24 that detects the vehicle speed, a brake sensor (brake switch) 25 that detects the amount of depression of a brake pedal (not shown), and a catalyst temperature sensor 26 that detects the catalyst temperature of an exhaust purification catalyst (not shown) provided in an exhaust passage (not shown) of the internal combustion engine 1.

[0020] The control unit 21 calculates the required load (engine load) of the internal combustion engine 1 using the detection value of the accelerator opening sensor 23.

[0021] The control unit 21 is also capable of detecting a state of charge (SOC) that is a ratio of the remaining charge to the charge capacity of an in-vehicle battery (not shown). In other words, the control unit 21 corresponds to a battery SOC detector.

[0022] The crank angle sensor 22 is capable of detecting the engine rotation speed (engine rotation number) of the internal combustion engine 1.

[0023] When a predetermined automatic stop condition is satisfied while the vehicle is running or stopped, the internal combustion engine 1 automatically stops the fuel supply and stops. Then, when a predetermined automatic restart condition is satisfied while the internal combustion engine 1 is automatically stopped, the internal combustion engine 1 restarts. In other words, the control unit 21 automatically stops the internal combustion engine 1 when the predetermined automatic stop condition is satisfied, and automatically restarts the internal combustion engine 1 when the predetermined automatic restart condition is satisfied.

[0024] The automatic stop conditions for the internal combustion engine 1 include, for example, the accelerator pedal being not depressed, the battery SOC of the vehicle battery being greater than a predetermined battery threshold SOCth, and the catalyst temperature of the exhaust purification catalyst being higher than a predetermined first catalyst temperature threshold T1.

[0025] The internal combustion engine 1 is automatically stopped when all of these automatic stop conditions are satisfied. In other words, the control unit 21 automatically stops the internal combustion engine 1 when all of these automatic stop conditions are satisfied while the internal combustion engine 1 is in operation. In other words, the control unit 21 corresponds to a first control unit that stops fuel injection and automatically stops the internal combustion engine 1 when a predetermined automatic stop condition is satisfied.

[0026] The conditions for automatic restart of the internal combustion engine 1 include, for example, the accelerator pedal being depressed, the battery SOC of the vehicle battery being below a predetermined battery threshold SOCth, and the catalyst temperature of the exhaust purification catalyst being below a predetermined first catalyst temperature threshold T1.

[0027] The internal combustion engine 1 is restarted when there is a restart request during the automatic stop. In other words, the control unit 21 restarts the internal combustion engine 1 when any of the above-mentioned automatic restart conditions is satisfied during the automatic stop of the internal combustion engine 1. For example, the internal combustion engine 1 during the automatic stop is restarted when the battery SOC of the vehicle-mounted battery becomes equal to or lower than the battery threshold SOCth as a predetermined value.

[0028] The automatic stopping of the internal combustion engine 1 includes, for example, an idle stop, a coast stop, and a sailing stop.

[0029] The idle stop is implemented when the automatic stop condition as described above is satisfied while the vehicle is temporarily stopped. The idle stop is released when any of the automatic restart conditions as described above is satisfied.

[0030] The coast stop is implemented when, for example, the above-mentioned automatic stop conditions are satisfied while the vehicle is traveling. The coast stop is also released when, for example, any of the above-mentioned automatic restart conditions is satisfied. Note that the coast stop refers to, for example, automatically stopping the internal combustion engine 1 during deceleration at a low vehicle speed with the brake pedal depressed.

[0031] The sailing stop is implemented when the automatic stop condition as described above is satisfied while the vehicle is traveling. The sailing stop is released when any of the automatic restart conditions as described above is satisfied. The sailing stop is, for example, the automatic stopping of the internal combustion engine 1 while the vehicle is coasting at a medium to high vehicle speed without the brake pedal being depressed.

[0032] When a request to restart the internal combustion engine 1 is made during a decrease in the engine speed of the internal combustion engine 1 due to an automatic stop, the control unit 21 starts the internal combustion engine 1 by restarting fuel injection (combustion start) if the engine speed of the internal combustion engine 1 is equal to or higher than a predetermined combustion recoverable rotation speed threshold R1 (rotation speed threshold) at which the internal combustion engine 1 can be restarted only by fuel injection, and starts the internal combustion engine 1 (cranks) by rotating the crankshaft using the starter motor 2 if the engine speed of the internal combustion engine 1 is lower than the combustion recoverable rotation speed threshold R1. Furthermore, when a request to restart is made with the brake pedal depressed and the brake on, the control unit 21 does not start the internal combustion engine 1 by restarting fuel injection, but starts the internal combustion engine 1 by rotating the starter motor 2 after the engine speed becomes "0". In other words, the control unit 21 corresponds to a second control unit.

[0033] The combustion recoverable rotation speed threshold R1 is set in consideration of the time difference between the timing when the fuel injection start command is issued for the internal combustion engine 1 during automatic stop and the timing when the fuel is ignited in the cylinder (the timing of the first combustion after the fuel injection is restarted). In other words, the combustion recoverable rotation speed threshold R1 is set in consideration of the reduction in the engine speed between the timing when the fuel injection start command is issued and the timing when the fuel is ignited in the cylinder, so that the engine speed at the timing of the first combustion after the fuel injection is restarted is not lower than the rotation speed at which the internal combustion engine 1 can be started by restarting the fuel injection. The combustion recoverable rotation speed threshold R1 is set in accordance with the deceleration of the internal combustion engine 1, and is, for example, a value of about 600 rpm.

[0034] When the internal combustion engine 1 that has been automatically stopped is started (combustion start) by resuming fuel injection, there is a time difference between the timing when the command to start fuel injection is issued and the timing when the fuel is ignited in the cylinder (the timing of the first combustion after fuel injection is resumed). In other words, the timing when combustion starts in the internal combustion engine 1 is delayed from the timing when the command to start fuel injection is issued. This is because fuel is supplied to the cylinder that is in the intake stroke after the command to start fuel injection is issued, and the fuel in this cylinder is ignited (combusted) after passing through the compression stroke.

[0035] When the internal combustion engine 1 that has been automatically stopped is started (combustion start) by resuming fuel injection, if the deceleration of the vehicle increases due to further depression of the brake pedal at the timing when a command to start fuel injection is issued, the engine speed may drop significantly before the ignition timing of the cylinder in which fuel is first burned. If the deceleration of the vehicle increases due to further depression of the brake pedal, the engine speed of the internal combustion engine 1 is dragged along by the deceleration of the vehicle, and the rate at which the engine speed drops increases.

[0036] As a result, the engine speed of the internal combustion engine 1 drops significantly before the ignition timing of the cylinder in which fuel is first burned, and there is a risk that the fuel will not be burned and the engine will stall (stalling), making it impossible to start the internal combustion engine 1 by resuming fuel injection.

[0037] Therefore, when a restart request is made with the brake pedal depressed in the brake-on state, the internal combustion engine 1 is started using the starter motor 2, rather than starting by resuming fuel injection.

[0038] A restart request when the brake pedal is depressed and the brake is on is not due to an acceleration request by the driver. Therefore, when a restart request is made when the brake is on, there is little need to restart the internal combustion engine 1 early. Therefore, when a restart request is made with the brake pedal depressed, the internal combustion engine 1 is not started by resuming fuel injection, but is started using the starter motor 2 after the engine speed becomes "0".

[0039] Therefore, the lower limit of the engine speed at which the engine can be restarted by fuel injection alone (combustion recoverable speed threshold R1) does not need to be set in consideration of an increase in deceleration of the internal combustion engine 1 caused by the driver's braking operation.

[0040] In other words, when a restart request is made with the brake pedal not depressed, the region in which the engine can be restarted by fuel injection alone can be expanded.

[0041] FIG. 2 is a timing chart showing the state when the automatically stopped internal combustion engine 1 is restarted, and shows the case where the internal combustion engine 1 is restarted in the brake-on state.

[0042] Time t1 in Fig. 2 is the timing when the automatic stop condition of the internal combustion engine 1 is satisfied. In Fig. 2, the automatic stop condition is satisfied at time t1 when the brake is applied and the vehicle speed is decreasing, and the automatic stop of the internal combustion engine 1 is permitted.

[0043] Time t2 in Fig. 2 is the timing when a restart request is made to the automatically stopped internal combustion engine 1. In other words, time t2 in Fig. 2 is the timing when any one of the above-mentioned automatic restart conditions is satisfied.

[0044] 2, the engine speed is greater than the combustion recoverable speed threshold R1, but the brake is on. Therefore, the internal combustion engine 1 is not restarted by combustion start, but is restarted by the starter motor 2 after waiting for the engine speed to become "0".

[0045] 2 is the timing when the engine speed becomes "0" after a restart request. The starter motor 2 starts (is turned on) at time t3. The period from time t3 to time t4 in FIG 2 is a cranking period during which the crankshaft of the internal combustion engine 1 is rotated by the starter motor 2.

[0046] FIG. 3 is a timing chart showing the state when the automatically stopped internal combustion engine 1 is restarted, and shows the case where the brake is turned off and the engine accelerates again when the automatically stopped internal combustion engine 1 is restarted.

[0047] Time t1 in Fig. 3 is the timing when the automatic stop condition of the internal combustion engine 1 is satisfied. In Fig. 3, the automatic stop condition is satisfied at time t1 when the brake is applied and the vehicle speed is decreasing, and the automatic stop of the internal combustion engine 1 is permitted.

[0048] Time t2 in Fig. 3 is the timing when a restart request is made to the internal combustion engine 1 that is automatically stopped due to depression of the accelerator pedal. That is, time t2 in Fig. 3 is the timing when any of the above-mentioned automatic restart conditions is satisfied due to depression of the accelerator pedal. Time t2 in Fig. 3 is also the timing when the driver's foot is released from the brake pedal, resulting in the brake-off state.

[0049] At time t2 in Fig. 3, the brake is off and the engine speed is higher than the combustion recoverable speed threshold R1. Therefore, at time t2 in Fig. 3, restart of the internal combustion engine 1 by combustion start is started. Time t3 in Fig. 3 is the timing of the first combustion after fuel injection is resumed.

[0050] In addition, when a restart request is made while the clutch 4 is released and the driving force of the internal combustion engine 1 is not being transmitted to the drive wheels 7, if the engine speed of the internal combustion engine 1 is equal to or higher than the combustion recoverable rotational speed threshold R1 (rotational speed threshold), the control unit 21 starts the internal combustion engine 1 by resuming fuel injection even if the brake is on with the brake pedal depressed.

[0051] When the clutch 4 is released (clutch off), the internal combustion engine 1 is not affected by an increase in deceleration caused by the driver's brake operation. Therefore, even if the brake is on when a restart request is made, the control unit 21 restarts the internal combustion engine 1 by resuming fuel injection if the engine speed of the internal combustion engine 1 is equal to or higher than the combustion recoverable speed threshold value R1 with the clutch 4 released.

[0052] This enables the internal combustion engine 1 to expand the region in which it can be restarted by fuel injection alone.

[0053] FIG. 4 is a timing chart showing the state when the automatically stopped internal combustion engine 1 is restarted, and shows the case where the clutch 4 is released when the automatically stopped internal combustion engine 1 is restarted.

[0054] Time t1 in Fig. 4 is the timing when the automatic stop condition of the internal combustion engine 1 is satisfied. In Fig. 4, the automatic stop condition is satisfied at time t1 when the brake is applied and the vehicle speed is decreasing, and automatic stopping (coast stop) of the internal combustion engine 1 is permitted. At the timing of time t1 in Fig. 4, the clutch 4 is released with the start of the coast stop.

[0055] Time t2 in Fig. 4 is the timing when a restart request is made to the internal combustion engine 1 during automatic stop. In other words, time t2 in Fig. 4 is the timing when any one of the above-mentioned automatic restart conditions is satisfied.

[0056] At time t2 in Fig. 4, the brake is on, but the clutch 4 is released and the engine speed is higher than the combustion recoverable speed threshold R1. Therefore, at time t2 in Fig. 4, restart of the internal combustion engine 1 by combustion start is started.

[0057] 4 is the timing of the first combustion after the fuel injection is restarted. 4 is the timing of the clutch 4 being engaged after the internal combustion engine 1 starts combustion.

[0058] When a restart request is made while the internal combustion engine 1 is stopped, or when a restart request is made while the vehicle speed is below a predetermined low vehicle speed threshold V1 where the effect of deceleration of the internal combustion engine 1 is small regardless of whether the brake is on, the control unit 21 starts the internal combustion engine 1 by resuming fuel injection even when the brake is on.

[0059] When the vehicle is stopped or the vehicle speed is equal to or lower than a predetermined low vehicle speed threshold V1, the internal combustion engine 1 is not affected by an increase in deceleration caused by the driver's braking operation. Therefore, in such a state, even if the brake is applied, the control unit 21 restarts the internal combustion engine 1 by resuming fuel injection.

[0060] This enables the internal combustion engine 1 to expand the region in which it can be restarted by fuel injection alone.

[0061] FIG. 5 is a timing chart showing the state when the automatically stopped internal combustion engine 1 is restarted, and shows the case where the vehicle speed is equal to or lower than the low vehicle speed threshold V1 when the automatically stopped internal combustion engine 1 is restarted.

[0062] Time t1 in Fig. 5 is the timing when the automatic stop condition of the internal combustion engine 1 is satisfied. In Fig. 5, the automatic stop condition is satisfied at time t1 when the brake is applied and the vehicle speed is decreasing, and the automatic stop of the internal combustion engine 1 is permitted.

[0063] Time t2 in Fig. 5 is the timing when a restart request is made to the internal combustion engine 1 during automatic stop. In other words, time t2 in Fig. 5 is the timing when any one of the above-mentioned automatic restart conditions is satisfied.

[0064] At time t2 in Fig. 5, the brake is on, but the vehicle speed is equal to or lower than the low vehicle speed threshold V1, and the engine speed is higher than the combustion recoverable speed threshold R1. Therefore, at time t2 in Fig. 5, restart of the internal combustion engine 1 by combustion start is started. Time t3 in Fig. 5 is the timing of the first combustion after fuel injection is resumed.

[0065] FIG. 6 is a flowchart showing the flow of control of the internal combustion engine 1 in the above-described embodiment.

[0066] In step S1, it is determined whether or not a restart request for the internal combustion engine 1 has occurred. That is, it is determined whether or not an automatic restart condition has been established during the automatic stop of the internal combustion engine 1. If it is determined in step S1 that a restart request has occurred, the process proceeds to step S2. If it is not determined in step S1 that a restart request has occurred, the current routine is terminated.

[0067] In step S2, it is determined whether the engine speed is equal to or higher than the combustion recoverable speed threshold R1. If the engine speed is equal to or higher than the combustion recoverable speed threshold R1 in step S2, the process proceeds to step S3. If the engine speed is not equal to or higher than the combustion recoverable speed threshold R1 in step S2, the process proceeds to step S7.

[0068] In step S3, it is determined whether or not the brake is off. If the brake is off in step S3, the process proceeds to step S4. If the brake is not off in step S3, the process proceeds to step S5.

[0069] In step S4, the internal combustion engine 1 is started by restarting fuel injection.

[0070] In step S5, it is determined whether or not the clutch is off. If it is off in step S5, the process proceeds to step S4. If it is not off in step S5, the process proceeds to step S6.

[0071] In step S6, it is determined whether the vehicle speed is equal to or less than the low vehicle speed threshold V1. In step S6, if the vehicle speed is equal to or less than the low vehicle speed threshold V1, the process proceeds to step S4. In step S6, if the vehicle speed is not equal to or less than the low vehicle speed threshold V1, the process proceeds to step S7.

[0072] In step S7, the internal combustion engine 1 is started by cranking using the starter motor 2.

[0073] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

[0074] For example, the rotation speed threshold is set according to the deceleration of the internal combustion engine, but it is also possible to consider a response in which the rotation speed threshold is not set according to the deceleration of the internal combustion engine when the brake is on. Also, when a restart request is made with the brake on while the engine rotation speed of the internal combustion engine is decreasing due to automatic stop, the rotation speed threshold may not be set or may be set to infinity, and the internal combustion engine may be started by rotating it using the electric motor. Furthermore, the rotation speed threshold may be set to a constant value when the brake is on.

[0075] The above-described embodiment relates to a control method for an internal combustion engine and a control device for an internal combustion engine.

Claims

1. When a predetermined automatic stop condition is met, fuel injection is stopped and the internal combustion engine is automatically stopped, When a request to restart the internal combustion engine is made during the engine speed reduction caused by this automatic stop, If the engine speed is equal to or higher than a predetermined engine speed threshold at which the engine can be restarted by fuel injection alone, the brake state is determined based on the brake state. If the brake is off, the internal combustion engine is started by restarting fuel injection without using the electric motor. If the brake is on, the electric motor is used to rotate the internal combustion engine to start it. starting an internal combustion engine using the electric motor when the engine rotation speed is lower than the rotation speed threshold value; A method for controlling an internal combustion engine.

2. When the restart request is made, if the engine speed is equal to or higher than the engine speed threshold and the brake is on, If the clutch on the power transmission path that transmits the driving force of the internal combustion engine to the drive wheels is released and the driving force of the internal combustion engine is not transmitted to the drive wheels, Even when the brake is on, the internal combustion engine is started by restarting fuel injection without using an electric motor.

2. A method for controlling an internal combustion engine according to claim 1.

3. When the restart request is made, if the engine speed is equal to or higher than the engine speed threshold and the brake is on, If the vehicle is stopped, Even when the brake is on, the internal combustion engine is started by restarting fuel injection without using an electric motor.

3. A method for controlling an internal combustion engine according to claim 1 or 2.

4. When the restart request is made, if the engine speed is equal to or higher than the engine speed threshold and the brake is on, If the vehicle speed is equal to or lower than a predetermined low vehicle speed threshold, Even when the brake is on, the internal combustion engine is started by restarting fuel injection without using an electric motor. The method for controlling an internal combustion engine according to any one of claims 1 to 3.

5. The rotation speed threshold is set according to the deceleration of the internal combustion engine. A method for controlling an internal combustion engine according to any one of claims 1 to 4.

6. 5. The method for controlling an internal combustion engine according to claim 2, wherein the rotational speed threshold value is set to a constant value when the brake is on.

7. an electric motor capable of starting an internal combustion engine; A first control unit that stops fuel injection and automatically stops the internal combustion engine when a predetermined automatic stop condition is satisfied; A second control unit that restarts the internal combustion engine based on a request to restart the internal combustion engine; having The second control unit is When a request to restart the internal combustion engine is received during the engine speed reduction due to the automatic stop, If the engine speed is equal to or higher than a predetermined engine speed threshold at which the engine can be restarted by fuel injection alone, the brake state is determined based on the brake state. If the brake is off, the internal combustion engine is started by restarting fuel injection without using the electric motor. If the brake is on, the electric motor is used to rotate the internal combustion engine to start it. starting an internal combustion engine using the electric motor when the engine rotation speed is lower than the rotation speed threshold value; A control device for an internal combustion engine.

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