JP7501273B2 - Control method and control device for internal combustion engine - Google Patents

Description

The present invention relates to a method for controlling an internal combustion engine and a control device for an internal combustion engine.

Idle stop control for an internal combustion engine is conventionally known, which automatically stops the internal combustion engine when a predetermined automatic stop condition is met during idling, and automatically restarts the internal combustion engine when a predetermined automatic restart condition is met during automatic stop.

For example, in Patent Document 1, when a request to restart the internal combustion engine is made while the engine speed is dropping after fuel injection has been stopped to automatically stop the internal combustion engine, the rate at which the engine speed is dropping is taken into consideration, and a predicted engine speed at the ignition timing for generating the first combustion is estimated from the timing at which the restart request is issued. A determination is made as to whether the predicted engine speed is equal to or greater than a preset reference threshold value to determine whether the engine can return to normal (can be started by resuming fuel injection).

JP 2011-157946 A

However, even if the automatic stop conditions are met and a decision (permission) is made to stop fuel injection, combustion in cylinders to which fuel was injected before the decision to stop fuel injection occurs after the decision to stop fuel injection, so the engine speed does not decrease immediately after the decision to stop fuel injection.

Therefore, immediately after it is determined that fuel injection should be stopped, combustion torque still remains in the internal combustion engine. Therefore, there is a risk that it is not possible to accurately predict how the engine speed will decrease from the rate at which the engine speed drops immediately after it is determined that fuel injection should be stopped.

In other words, when restarting an internal combustion engine whose engine speed has decreased due to automatic stopping, there is room for further improvement in determining whether restarting is possible by simply resuming fuel injection.

In the internal combustion engine of the present invention, when a restart request for the internal combustion engine is made while the engine speed is decreasing due to an automatic stop of the internal combustion engine, if the engine speed is equal to or higher than a predetermined rotation speed threshold at which the engine can be restarted only by fuel injection, the internal combustion engine is started by restarting fuel injection, and if the engine speed of the internal combustion engine is lower than the rotation speed threshold, the internal combustion engine is started by rotating the crankshaft of the internal combustion engine using an electric motor. The rotation speed threshold is set according to the deceleration of the engine rotation when the crankshaft of the internal combustion engine rotates by a predetermined angle or more after the fuel injection is stopped. The rotation speed threshold is also set according to the friction of the internal combustion engine until the crankshaft of the internal combustion engine rotates by the predetermined angle or more after the fuel injection is stopped.

According to the present invention, the rotation speed threshold is not based on the deceleration of the engine rotation immediately after fuel injection is permitted to be stopped, so it is possible to accurately determine (judge) how to restart an internal combustion engine that has been automatically stopped.

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; FIG. 4 is an explanatory diagram that illustrates an example of a map used when calculating a combustion recoverable rotation speed threshold value from a target power generation voltage and a coolant temperature. A timing chart showing the control state of the internal combustion engine after the automatic stop condition is satisfied. 3 is a flowchart showing a flow of control of an internal combustion engine according to the present invention.

Below, an embodiment of the present invention will be described in detail with reference to the drawings. Figure 1 is an explanatory diagram showing a schematic overview of the system configuration of an internal combustion engine 1 to which the present invention is applied.

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.

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.

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 when the engine is stopped, thereby starting the engine 1 (cranking start). The starter motor 2 is controlled by a control unit 21, which will be described later.

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

In other words, the internal combustion engine 1 transmits the rotation of a crankshaft (not shown) as a driving force to the drive wheels 7 of the vehicle.

The clutch 4 is located between the torque converter 3 and the CVT 5, and is engaged when the drive torque from the internal combustion engine 1 can be transmitted to the drive wheels 7. In other words, the clutch 4 is disposed on a power transmission path that transmits the drive force of the internal combustion engine 1 to the drive 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.

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.

CVT 5 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, thereby continuously changing the gear ratio.

Although a 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 using multiple frictional fastening elements in the stepped automatic transmission.

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), a catalyst temperature sensor 26 that detects the catalyst temperature of an exhaust purification catalyst (not shown) provided in the exhaust passage (not shown) of the internal combustion engine 1, and a water temperature sensor 27 that detects the coolant temperature (water temperature) of the internal combustion engine 1.

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.

The control unit 21 is capable of detecting the SOC (State of Charge), which is the ratio of the remaining charge to the charge capacity of the vehicle battery (not shown). In other words, the control unit 21 corresponds to a battery SOC detection unit.

The control unit 21 calculates the target generation voltage of an alternator (not shown) that generates electricity to charge the vehicle battery, etc., in accordance with the operating state of the vehicle battery, such as its SOC. The alternator is an auxiliary of the internal combustion engine 1.

The crank angle sensor 22 is capable of detecting the engine speed (engine revolutions per minute) of the internal combustion engine 1.

When a specific automatic stop condition is met while the vehicle is running or stopped, the internal combustion engine 1 automatically stops the fuel supply and stops. Then, when a specific automatic restart condition is met 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 a specific automatic stop condition is met, and automatically restarts the internal combustion engine 1 when a specific automatic restart condition is met.

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

The internal combustion engine 1 automatically stops when all of these automatic stop conditions are met. In other words, the control unit 21 automatically stops the internal combustion engine 1 when all of these automatic stop conditions are met while the internal combustion engine 1 is operating. 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 met. The control unit 21 allows the fuel injection to be stopped and stops the fuel injection when all of these automatic stop conditions are met while the internal combustion engine 1 is operating.

The conditions for automatic restart of the internal combustion engine 1 are, for example, that the accelerator pedal is depressed, that the battery SOC of the on-board battery is equal to or lower than a predetermined battery threshold SOCth, and that the catalyst temperature of the exhaust purification catalyst is equal to or lower than a predetermined first catalyst temperature threshold T1.

The internal combustion engine 1 is restarted if there is a restart request during automatic stop. In other words, the control unit 21 restarts the internal combustion engine 1 if any of the above-mentioned automatic restart conditions are met during automatic stop of the internal combustion engine 1. For example, during automatic stop, the internal combustion engine 1 is restarted when the battery SOC of the on-board battery falls below a battery threshold SOCth as a predetermined value.

Examples of automatic stopping of the internal combustion engine 1 include idle stop, coast stop, and sailing stop.

Idle stop is implemented when the vehicle is temporarily stopped, for example, if the automatic stop conditions described above are met. Idle stop is also released when, for example, any of the automatic restart conditions described above are met.

A coast stop is implemented when the automatic stop conditions described above are met while the vehicle is traveling. The coast stop is also released when any of the automatic restart conditions described above are met. Note that a coast stop is, for example, an automatic stop of the internal combustion engine 1 during deceleration at a low vehicle speed with the brake pedal depressed.

The sailing stop is implemented when the automatic stop conditions described above are met while the vehicle is traveling. The sailing stop is also released when any of the automatic restart conditions described above are met. Note that the sailing stop refers to automatically stopping the internal combustion engine 1 while the vehicle is coasting at medium to high vehicle speeds without the brake pedal being depressed.

When a request to restart the internal combustion engine 1 is made while the engine speed of the internal combustion engine 1 is decreasing due to automatic stopping, the control unit 21 starts the internal combustion engine 1 (combustion start) by resuming fuel injection if the engine speed of the internal combustion engine 1 is equal to or higher than a predetermined combustion recoverable rotation speed threshold (rotation speed threshold) at which the internal combustion engine 1 can be restarted by fuel injection alone, 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. In other words, the control unit 21 corresponds to a second control unit.

The combustion recoverable rotational speed threshold is set according to the deceleration of engine rotation when the crankshaft of the internal combustion engine 1 rotates by a predetermined angle or more after fuel injection is permitted to be stopped (after fuel injection is stopped). In addition, the combustion recoverable rotational speed threshold is set according to the friction of the internal combustion engine 1 until the crankshaft of the internal combustion engine 1 rotates by a predetermined angle or more after fuel injection is permitted to be stopped (after fuel injection is stopped).

The combustion recoverable rotational speed threshold is set by the control unit 21. In other words, the control unit 21 corresponds to the rotational speed threshold setting unit.

Immediately after fuel injection into the internal combustion engine 1 is permitted to stop, combustion occurs in the cylinder to which fuel was injected immediately before fuel injection was permitted to stop, so the engine speed does not drop (reduced) immediately.

In other words, immediately after it is determined that fuel injection has been stopped, there is still combustion torque remaining in the internal combustion engine 1, so it is not possible to predict how the engine speed (engine speed) will decrease due to friction in the internal combustion engine 1 from the rate at which the engine speed (engine speed) decreases (deceleration).

Therefore, when the combustion recoverable rotation speed threshold is set according to the deceleration of the engine rotation, the crankshaft of the internal combustion engine 1 has rotated a predetermined angle or more after fuel injection is permitted to be stopped.

As a result, the combustion recoverable rotational speed threshold is not based on the deceleration of the engine rotation immediately after fuel injection is permitted to stop, so it is possible to accurately determine (judge) how to restart the automatically stopped internal combustion engine 1. In other words, immediately after fuel injection is permitted to stop, a rotational speed threshold set according to the deceleration of the engine rotation is not used to determine whether restart is possible with fuel injection alone, so it is possible to accurately determine (judge) how to restart the automatically stopped internal combustion engine 1.

The above-mentioned predetermined rotation angle is at least the angle at which combustion in the cylinder where fuel is injected ends before fuel injection is permitted to be stopped.

This makes it possible to switch as quickly as possible to the combustion recovery speed threshold value according to the engine rotation deceleration, making it possible to widen (expand) the range in which an automatically stopped internal combustion engine 1 can be started by resuming fuel injection.

When the combustion recoverable rotational speed threshold is set according to the deceleration of the engine rotation, it is set to be larger as the deceleration of the engine rotation increases.

By setting the combustion recovery rotation speed threshold higher as the engine rotation deceleration increases, the internal combustion engine 1 that has been automatically stopped can be reliably started by resuming fuel injection.

The combustion recoverable rotational speed threshold is set according to the friction of the internal combustion engine 1 from when fuel injection is permitted to be stopped until the crankshaft of the internal combustion engine 1 rotates by a predetermined angle or more.

This allows the internal combustion engine 1 to be started by resuming fuel injection even before the combustion recovery rotation speed threshold can be set according to the deceleration of the engine rotation.

Here, when the combustion recoverable rotational speed threshold is set according to the friction of the internal combustion engine 1, for example, the auxiliary load or the coolant temperature of the internal combustion engine 1 may be used as a substitute characteristic for friction. In other words, when the combustion recoverable rotational speed threshold is set according to the friction of the internal combustion engine 1, it may be set according to the auxiliary load or the coolant temperature of the internal combustion engine 1. The auxiliary load is, for example, the target power generation voltage of the alternator.

By using the auxiliary load or coolant temperature as a proxy characteristic for friction, the combustion recovery engine speed threshold can be finely adjusted according to friction.

The combustion recoverable rotational speed threshold may be calculated using, for example, the target power generation voltage and coolant temperature of the alternator, using a map such as that shown in FIG. 2 stored in the control unit 21. FIG. 2 is an explanatory diagram that shows a schematic example of a map used when calculating the combustion recoverable rotational speed threshold from the target power generation voltage and coolant temperature.

The combustion recoverable rotation speed threshold is set to be higher as the target power generation voltage (auxiliary load) of the alternator increases or the coolant temperature decreases. The friction of the internal combustion engine 1 increases as the target power generation voltage (auxiliary load) of the alternator increases or the coolant temperature decreases.

By setting the combustion recovery rotational speed threshold higher as friction increases, the internal combustion engine 1 that has been automatically stopped can be reliably started by resuming fuel injection.

The combustion recoverable rotational speed threshold may be set using only the auxiliary load of the internal combustion engine 1 (the target power generation voltage of the alternator). In this case, the combustion recoverable rotational speed threshold is set to be higher as the auxiliary load (the target power generation voltage of the alternator) increases. The combustion recoverable rotational speed threshold may also be set using only the cooling water temperature. In this case, the combustion recoverable rotational speed threshold is set to be higher as the cooling water temperature decreases.

Figure 3 is a timing chart showing the control state of the internal combustion engine 1 after the automatic stop condition is met.

In FIG. 3, the automatic stop condition for the internal combustion engine 1 is met at time t1. In other words, fuel injection is permitted to be stopped at the timing of time t1. Time t2 in FIG. 3 is the timing at which the crankshaft of the internal combustion engine 1 has rotated a predetermined angle after fuel injection is permitted to be stopped. Time t3 in FIG. 3 is the timing at which the engine speed of the internal combustion engine 1 becomes equal to or lower than the combustion recoverable speed threshold. Time t4 in FIG. 3 is the timing at which the engine speed becomes "0".

The dashed characteristic line A in Figure 3 shows the change in the combustion recoverable rotational speed threshold.

The engine rotation deceleration is calculated from time t2 to time t4 when the engine rotation speed of the internal combustion engine 1 becomes "0". Therefore, the combustion recoverable rotation speed threshold is calculated from a map (see FIG. 2) that is assigned according to the target power generation voltage of the alternator and the coolant temperature between time t1 and time t2.

The combustion recoverable rotation speed threshold is calculated according to the deceleration of the engine rotation between time t2 and time t4. The combustion recoverable rotation speed threshold between time t2 and time t4 is set to be larger as the deceleration of the engine rotation is larger.
Therefore, characteristic line A (combustion recoverable rotational speed threshold) in Figure 3 is a curve that is convex downward as a whole in Figure 3, since the deceleration of the engine rotation in Figure 3 is a curve that is convex upward as a whole.

In FIG. 3, the period from time t1 to time t3 when the engine speed is equal to or higher than the combustion recoverable speed threshold is the region where the engine can be restarted by fuel injection alone. In FIG. 3, the period from time t3 onwards when the engine speed is lower than the combustion recoverable speed threshold is the region where the internal combustion engine 1 is started by rotating it using the starter motor 2.

Figure 4 is a flowchart showing the flow of control of the internal combustion engine 1 in the above-mentioned embodiment.

In step S1, it is determined whether or not fuel injection is being stopped due to automatic stopping of the internal combustion engine 1. If fuel injection is being stopped due to automatic stopping of the internal combustion engine 1 in step S1, the process proceeds to step S4. If fuel injection is not being stopped due to automatic stopping of the internal combustion engine 1 in step S1, the process proceeds to step S2.

In step S2, it is determined whether or not an automatic stop of the internal combustion engine 1 has been initiated. In other words, it is determined whether or not an automatic stop condition for the internal combustion engine 1 has been established during fuel injection. If an automatic stop of the internal combustion engine 1 has been initiated in step S2, the process proceeds to step S3. If an automatic stop of the internal combustion engine 1 has not been initiated in step S2, the current routine is terminated.

In step S3, fuel injection into the internal combustion engine 1 is stopped.

In step S4, it is determined whether the crankshaft of the internal combustion engine 1 has rotated a predetermined angle or more after fuel injection has stopped.

If in step S4 the crankshaft of the internal combustion engine 1 has rotated a predetermined angle or more after fuel injection has been stopped, proceed to step S5. If in step S4 the crankshaft of the internal combustion engine 1 has not rotated a predetermined angle or more after fuel injection has been stopped, proceed to step S6.

In step S5, the combustion recoverable rotation speed threshold is set according to the deceleration of the engine rotation.

In step S6, the combustion recoverable rotational speed threshold is set according to the friction of the internal combustion engine 1.

Although an embodiment of the present invention has been described above, the present invention is not limited to the above-mentioned embodiment, and various modifications are possible without departing from the spirit of the present invention.

The above-mentioned embodiments relate to a method for controlling an internal combustion engine and a control device for an internal combustion engine.

1... internal combustion engine 2... starter motor 3... torque converter 4... clutch 5... CVT
6... final gear 7... driving wheel 8... primary pulley 9... secondary pulley 10... belt 21... control unit 22... crank angle sensor 23... accelerator opening sensor 24... vehicle speed sensor 25... brake sensor 26... catalyst temperature sensor 27... water temperature sensor

Claims (6)

When a predetermined automatic stop condition is satisfied, fuel injection is stopped to automatically stop the internal combustion engine, and when a request to restart the internal combustion engine is made while the engine speed of the internal combustion engine is decreasing due to this automatic stop, if the engine speed of the internal combustion engine is equal to or higher than a predetermined engine speed threshold at which the internal combustion engine can be restarted by fuel injection alone, the internal combustion engine is started by resuming fuel injection, and if the engine speed of the internal combustion engine is lower than the engine speed threshold, the internal combustion engine is started by rotating it using an electric motor;
The control method for an internal combustion engine, characterized in that the rotational speed threshold is set according to a deceleration of engine rotation when the crankshaft of the internal combustion engine rotates by more than a predetermined angle after fuel injection is stopped, and is set according to friction of the internal combustion engine until the crankshaft of the internal combustion engine rotates by more than the predetermined angle after fuel injection is stopped. The method for controlling an internal combustion engine according to claim 1, characterized in that the predetermined angle is at least the angle at which combustion in the cylinder to which fuel is injected ends before fuel injection is permitted to be stopped. The method for controlling an internal combustion engine according to claim 1 or 2, characterized in that the rotational speed threshold is set to be larger as the deceleration of the engine rotational speed increases. 2. The method for controlling an internal combustion engine according to claim 1 , wherein the rotation speed threshold value is set using an auxiliary load or a coolant temperature of the internal combustion engine as the substitute characteristic for the friction. 5. The method for controlling an internal combustion engine according to claim 4 , wherein the rotation speed threshold value is set to be larger as the auxiliary load increases or as the coolant temperature decreases. 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, when a restart request for the internal combustion engine is made while the engine speed of the internal combustion engine is decreasing due to the automatic stop, starts the internal combustion engine by resuming fuel injection if the engine speed of the internal combustion engine is equal to or higher than a predetermined engine speed threshold value at which the internal combustion engine can be restarted by fuel injection alone, and starts the internal combustion engine using the electric motor if the engine speed of the internal combustion engine is lower than the engine speed threshold value;
a rotation speed threshold setting unit that sets the rotation speed threshold in accordance with a deceleration of engine rotation when a crankshaft of the internal combustion engine rotates by a predetermined angle or more after fuel injection is stopped ,
The control device for an internal combustion engine , wherein the rotation speed threshold setting unit sets the rotation speed threshold in accordance with friction of the internal combustion engine until a crankshaft of the internal combustion engine rotates by a predetermined angle or more after fuel injection is stopped .

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