JP2018123740A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably improve engine startability in ignition start control while accompanying with required minimum assist of rotation of a crank shaft by an electric motor, with respect to a control device of an internal combustion engine.SOLUTION: In an internal combustion engine 12 in which ignition start control is executed to start the internal combustion engine 12 by starting fuel injection and ignition from an expansion stroke cylinder in an expansion stroke in stopping an engine, rotation of a crank shaft 20 is assisted by an MG 28 so that any of other cylinders continued from the cylinder in which the combustion is executed finally just before start of fuel cut in accompany with engine stop request, is stopped in a next expansion stroke after the expansion stroke and an exhaust stroke are once executed during the period of fuel cut, in a case when a rotating speed Ne of the engine in outputting the engine stop request is lower than a prescribed value Ne0.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a control device for an internal combustion engine, and more specifically, controls an internal combustion engine in which an ignition start is performed to start an internal combustion engine by starting fuel injection and ignition from an expansion stroke cylinder in an expansion stroke while the engine is stopped. It is related with a suitable control device.

  For example, Patent Document 1 discloses a control device for an internal combustion engine. In a vehicle that performs S & S (Stop & Start) control, this control device injects fuel into a cylinder (expansion stroke cylinder) that is in an expansion stroke while the engine is stopped, and is ignited. It is disclosed that an air-fuel mixture is ignited by an apparatus.

JP 2007-218088 A JP 2010-007532 A

  As performed by the control device for an internal combustion engine described in Patent Document 1, ignition start control is known in which fuel injection and ignition are started from an expansion stroke cylinder in an expansion stroke while the engine is stopped to start the internal combustion engine. . If the engine speed when the engine stop request is issued is low, the crank angle that advances during the fuel cut period from the start of the fuel cut accompanying the engine stop request to the stop of the internal combustion engine becomes small. This means that the number of exhaust strokes for discharging the burned gas in the cylinder during the fuel cut period is reduced. For this reason, if the engine speed when the engine stop request is issued is low, a large amount of burned gas may remain inside the expansion stroke cylinder that becomes the first explosion cylinder when the engine is restarted by the ignition start control. . In such a case, since the amount of oxygen in the first explosion cylinder is reduced, there is a concern that the engine startability is lowered.

  The present invention has been made in view of the above-described problems, and is capable of stably improving the engine startability during ignition start control with the assistance of the minimum necessary rotation of the crankshaft by the electric motor. An object of the present invention is to provide a control device for an internal combustion engine.

  An internal combustion engine control apparatus according to the present invention includes an internal combustion engine that includes a fuel injection valve that directly injects fuel into a cylinder and an ignition device that ignites an air-fuel mixture, and a crankshaft of the internal combustion engine that can be driven to rotate. And an electric motor for controlling the internal combustion engine. The engine control performed by the control device includes ignition start control for starting the internal combustion engine by starting fuel injection and ignition from an expansion stroke cylinder in an expansion stroke while the engine is stopped. When the engine rotation speed when the engine stop request is issued is lower than a predetermined value, the control device continues to the cylinder that last burned immediately before the start of the fuel cut accompanying the engine stop request. The rotation of the crankshaft is assisted by the electric motor so that any one of the cylinders stops in the next expansion stroke after having once reached the expansion stroke and the exhaust stroke following the expansion stroke during the fuel cut period.

  According to the present invention, when the engine rotation speed when the engine stop request is issued is lower than the predetermined value, the cylinder following the last combustion is performed immediately before the start of the fuel cut accompanying the engine stop request. Control is performed to assist the rotation of the crankshaft by the electric motor so that any of the cylinders stops in the next expansion stroke after having once reached the expansion stroke and the exhaust stroke that follows during the fuel cut period. The As a result, even if there is a concern that scavenging of the burned gas in the cylinder will be insufficient, the electric motor will rotate the crankshaft with the minimum torque necessary to ensure startability by ignition start control. While assisting, scavenging of the first explosion cylinder by the ignition start control can be sufficiently performed. For this reason, the engine startability at the time of ignition start control can be stably improved.

It is a figure for demonstrating schematically the system configuration | structure of the vehicle which concerns on Embodiment 1 of this invention. It is a time chart showing an example of various operations in the process in which an internal-combustion engine stops in response to an engine stop request. It is a figure for demonstrating the outline | summary of the characteristic first explosion cylinder change control which concerns on Embodiment 1 of this invention. It is a flowchart which shows the routine of the process regarding the first explosion cylinder change control which concerns on Embodiment 1 of this invention. It is a figure for demonstrating the setting of the predetermined value Ne0 for determining whether an initial explosion cylinder corresponds to a scavenging completion cylinder. It is a figure for demonstrating the determination method of the presence or absence of progress of the last TDC. It is a figure for demonstrating the determination method of the assist torque by MG.

  Embodiments of the present invention will be described below with reference to the drawings. However, in the embodiment shown below, when referring to the number of each element, quantity, quantity, range, etc., unless otherwise specified or clearly specified in principle, the reference However, the present invention is not limited to these numbers. Further, the structures, steps, and the like described in the embodiments below are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

Embodiment 1 FIG.
1. System Configuration According to Embodiment 1 FIG. 1 is a diagram for schematically explaining the system configuration of a vehicle 10 according to Embodiment 1 of the present invention. A vehicle 10 shown in FIG. 1 includes a spark ignition type internal combustion engine 12 as a power source. As an example, the internal combustion engine 12 is an in-line four-cylinder engine.

  The internal combustion engine 12 includes a fuel injection valve 14 and an ignition device 16. The fuel injection valve 14 is disposed in each cylinder and injects fuel directly into the cylinder. The ignition device 16 uses a spark plug disposed in each cylinder to ignite the air-fuel mixture in the cylinder. The internal combustion engine 12 includes a crank angle sensor 18. The crank angle sensor 18 outputs a signal corresponding to the rotational position of the crankshaft 20. The crank angle sensor 18 can acquire the engine rotation speed, and can also acquire the stop position (piston stop position) of the crankshaft 20 when the engine is stopped.

  Torque generated by the internal combustion engine 12 (crankshaft 20 torque) is transmitted to the drive wheels 26 via the transmission 22 and the differential gear 24. The vehicle 10 also includes a motor generator (hereinafter also referred to as “MG”) 28. The MG 28 is connected to the crankshaft 20. In the configuration shown in FIG. 1, the MG 28 is connected to the crankshaft 20 via a belt 30 as an example.

  The MG 28 is electrically connected to the battery 32. The MG 28 has a function as a generator that converts the torque of the crankshaft 20 generated by combustion into electric power. The battery 32 stores the electric power generated by the MG 28. The MG 28 also has a function as an electric motor that rotationally drives the crankshaft 20 using the electric power of the battery 32.

  The system according to this embodiment includes an electronic control unit (ECU) 34. The ECU 34 includes at least an input / output interface, a memory, and a processor, and is mounted on the vehicle 10 in order to control the operation of the internal combustion engine 12. In addition to the crank angle sensor 18 described above, the ECU 34 is electrically connected to various sensors for acquiring the operating state of the vehicle 10 including the operating state of the internal combustion engine 12. The ECU 34 is electrically connected to various actuators for controlling the operation of the internal combustion engine 12, such as the fuel injection valve 14, the ignition device 16, and the MG 28 described above. In the memory, various control programs and maps for controlling the operation of the internal combustion engine 12 are stored. The processor reads the control program from the memory and executes it, and generates operation signals for various actuators based on the acquired sensor signals. Thereby, the function of the “control device for an internal combustion engine” according to the present embodiment is realized.

2. Engine control according to Embodiment 1 2-1. Ignition start control The engine control performed by the ECU 34 includes ignition start control. The ignition start control is to start the internal combustion engine 12 in a warm state by starting fuel injection and ignition from a cylinder in an expansion stroke (hereinafter referred to as “expansion stroke cylinder”) while the engine is stopped. is there. More specifically, in the present embodiment, the ignition start control is used when the internal combustion engine 12 is restarted during the execution of S & S (Stop & Start) control. In the S & S control, when a predetermined engine automatic stop condition is satisfied while the vehicle 10 is temporarily stopped, the operation of the internal combustion engine 12 is automatically stopped by stopping the fuel supply, and then a predetermined engine start condition is satisfied. When this happens, the internal combustion engine 12 is restarted.

2-2. FIG. 2 is a time chart showing an example of various operations in the process in which the internal combustion engine 12 stops in response to an engine stop request. Note that the waveform of the crank angle signal in FIG. 2 fluctuates at a 180 ° CA period.

  A time point t0 in FIG. 2 corresponds to when an engine stop request is issued. In a period before time t0, fuel injection and ignition are performed in order in each cylinder. When the engine stop request is issued at time t0, the fuel injection is stopped lastly in the cylinder (# 2 cylinder in the example shown in FIG. 2) for which the fuel injection command is issued immediately before issuing the engine stop request.

  The periods described as “expansion”, “exhaust”, “intake”, and “compression” in FIG. 2 correspond to the strokes of the cylinder (ie, # 2 cylinder) in which fuel was injected last. . In the example shown in FIG. 2, the firing period ends at the end of the combustion performed in the “expansion” stroke of the # 2 cylinder, and the fuel cut period starts. When shifting to the fuel cut period, the engine rotation speed Ne decreases with time and eventually becomes zero (that is, the internal combustion engine 12 stops).

  Part of the combustion gas generated by the last combustion of each cylinder immediately before the end of the firing period remains in the cylinder without being discharged from the cylinder in the cycle in which the last combustion was performed. The burned gas remaining in the cylinder is scavenged by fresh air newly introduced into the cylinder during the subsequent fuel cut period. However, if the engine rotational speed Ne at the time of the engine stop request is low, the crank angle advanced during the fuel cut period becomes small. This means that the number of exhaust strokes for discharging the burned gas in the cylinder during the fuel cut period is reduced. As a result, scavenging of burned gas may be insufficient.

  In more detail, FIG. 2 shows that only about one cycle has elapsed in each cylinder during the fuel cut period because the engine speed Ne at the time of the engine stop request is low, and as a result, the combustion last occurs before the fuel cut starts. This shows an example in which the # 2 cylinder in which the operation is performed stops in the expansion stroke. In this example, the # 2 cylinder in which combustion was performed last corresponds to the first explosion cylinder when the ignition start control is performed thereafter. For this reason, in this example, there is a possibility that the ignition start control may be started in a state where the scavenging of the burned gas is insufficient, and there is a concern that the engine startability is deteriorated. The predetermined value Ne0 of the engine speed Ne in FIG. 2 will be described later with reference to FIG.

2-3. Characteristic First Explosion Cylinder Change Control According to Embodiment 1 FIG. 3 is a diagram for explaining an outline of characteristic initial explosion cylinder change control according to the first embodiment of the present invention. In the present embodiment, in order to make a cylinder in which scavenging of burned gas is sufficiently completed (hereinafter referred to as “scavenging completion cylinder”) as an initial explosion cylinder in the ignition start control, the following initial explosion cylinder change is performed. Control is performed as needed.

  Specifically, other cylinders following the cylinder that was last burned immediately before the start of the fuel cut accompanying the engine stop request can once undergo the expansion stroke and the exhaust stroke that follows this during the fuel cut period. In such a case, such other cylinders correspond to the scavenging completion cylinder. The reason is that combustion does not occur when the expansion stroke is reached during the fuel cut period, and therefore, the combustion gas generated during the combustion of the previous cycle can be sufficiently scavenged in the exhaust stroke following the expansion stroke (that is, This is because a large amount of oxygen in the cylinder can be secured). Therefore, if such a scavenging completion cylinder can always be used as the first explosion cylinder, the engine startability by the ignition start control can be stably improved.

  In the operation example shown in FIG. 3, the # 3 cylinder (that is, the first explosion cylinder) in the expansion stroke when the internal combustion engine 12 stops without the assistance of the rotation of the crankshaft 20 by the MG 28 is the above-described scavenging completed cylinder. This is an example that does not exist. The reason for this is that the # 3 cylinder in this example corresponds to the cylinder that was burned last just before the start of the fuel cut, and the combustion generated by the last combustion only in the exhaust stroke that reaches once during the fuel cut period. This is because part of the gas remains in the cylinder and scavenging becomes insufficient. For this reason, in such an example, there is a concern that the engine startability by the ignition start control is lowered.

  Therefore, in the present embodiment, when an engine stop request is issued, it is determined whether or not the first explosion cylinder in the ignition start control is a scavenging completion cylinder. Specifically, this determination is made based on whether or not the engine speed Ne when the engine stop request is issued is equal to or higher than a predetermined value Ne0 (see FIG. 5).

  In addition, in this embodiment, when it is determined that the initial explosion cylinder does not become the scavenging completion cylinder because the engine rotation speed Ne when the engine stop request is issued is lower than the predetermined value Ne0, the scavenging completion cylinder is Rotation assistance of the crankshaft 20 using the MG 28 is performed so as to become the first explosion cylinder.

  The above-mentioned assist is any of the other cylinders following the cylinder that was last burned immediately before the start of the fuel cut accompanying the engine stop request (in this embodiment, the cylinder next to the cylinder that was burned last) ) Is executed in order to stop in the next expansion stroke after the expansion stroke and the subsequent exhaust stroke are once received during the fuel cut.

  More specifically, in the example shown in FIG. 3, when the last compression top dead center (hereinafter also referred to as “final TDC”) that has arrived during the fuel cut period has elapsed, the target assist is executed. . As a result, as shown in FIG. 3, the # 4 cylinder following the # 3 cylinder that was burned last just before the start of the fuel cut performs the expansion stroke and the exhaust stroke that follows this once during the fuel cut period. After being greeted, it will stop at the next expansion stroke. Thereby, scavenging can be promoted by extending the time until the engine stop is completed by the assistance of the MG 28. As a result, the # 4 cylinder that did not correspond to the scavenging completion cylinder can be changed to the first explosion cylinder that satisfies the requirements for the scavenging completion cylinder when the engine is stopped.

2-4. FIG. 4 is a flowchart showing a routine of processing related to initial explosion cylinder change control according to Embodiment 1 of the present invention. Note that this routine is repeatedly executed during the operation of the internal combustion engine 12.

  In the routine shown in FIG. 4, the ECU 34 first determines whether or not there is an engine stop request (step S101). More specifically, it is determined whether or not a predetermined engine automatic stop condition is established by S & S control. As a result, when this determination is not satisfied, the process at the time of starting the current routine is immediately terminated.

  On the other hand, when it is determined in step S101 that there is an engine stop request, the ECU 34 determines whether or not the engine speed Ne is lower than a predetermined value Ne0 (step S102). When it is determined that there is an engine stop request, fuel injection to each cylinder is stopped.

  FIG. 5 is a diagram for explaining setting of a predetermined value Ne0 for determining whether or not the first explosion cylinder corresponds to a scavenging completion cylinder. The vertical axis in FIG. 5 is the engine rotation speed Ne when the engine stop request is issued, and the horizontal axis is the time from when the engine stop request is issued until the engine stop is completed. As shown in FIG. 5, the higher the engine speed Ne when the engine stop request is issued, the longer the time until the engine stops. The time T1 in FIG. 5 corresponds to the minimum value of the elapsed time that can be determined that scavenging has been completed. The predetermined value Ne0 used in the determination in step S102 corresponds to a value of the engine rotation speed Ne that can set the time until engine stop to the time T1. Therefore, if the engine speed Ne when the engine stop request is issued is equal to or higher than the predetermined value Ne0, it can be said that the first explosion cylinder can be a scavenging completed cylinder, while the engine speed Ne is lower than the predetermined value Ne0. As it is, it can be said that the first explosion cylinder cannot be a scavenging completed cylinder.

  When the determination in step S102 is not established, that is, when it can be determined that the first explosion cylinder corresponds to the scavenging completion cylinder, the ECU 34 immediately ends the process at the time of starting this routine.

  On the other hand, if the determination in step S102 is established, that is, if it can be determined that the initial explosion cylinder does not correspond to the scavenging completion cylinder, the ECU 34 proceeds to step S103. In step S103, it is determined whether or not the final TDC has been exceeded during the fuel cut period accompanying the engine stop request.

  FIG. 6 is a diagram for explaining a method for determining whether or not the final TDC has elapsed. Whether or not the final TDC has been exceeded during the fuel cut period can be determined based on the current engine speed Ne and the crank angle. Specifically, the number of remaining compression TDCs during the fuel cut period can be known from the engine speed Ne. A predetermined value Ne1 in FIG. 6 is a value indicating a boundary between a rotational speed region in which the remaining number of TDCs is greater than 1 and a rotational speed region in which the remaining number of TDCs is 1. Therefore, it can be determined whether or not the final TDC has been exceeded by determining, based on the crank angle, that the compression TDC has arrived after the current engine rotational speed Ne has fallen below the predetermined value Ne1.

  The ECU 34 repeatedly executes the process of step S103 while determining that the final TDC is not yet exceeded in step S103. On the other hand, when it is determined that the final TDC has been exceeded, the ECU 34 calculates an assist torque for the rotation of the crankshaft 20 by the MG 28 (step S104). The assist torque is obtained by adding another cylinder (here, as an example, the cylinder next to the cylinder where combustion was last performed) following the cylinder where combustion was last performed immediately before the start of fuel cut accompanying the engine stop request. This is the torque value of the MG 28 necessary to make the first explosion cylinder (expansion stroke cylinder) after the expansion stroke and the subsequent exhaust stroke are once met during the fuel cut period.

  FIG. 7 is a diagram for explaining an assist torque determination method by the MG 28. In the example shown in FIG. 7, the assist torque is determined so as to increase as the engine speed Ne when the final TDC is reached is lower. The lower the engine speed Ne when the final TDC is reached, the smaller the crank angle that travels between the final TDC and the engine stop. For this reason, in order to realize the target engine stop position with high accuracy while suppressing the influence of the engine rotational speed Ne when the final TDC is reached, the lower the engine rotational speed Ne is, the lower the engine rotational speed Ne is, as shown in FIG. It is better to increase the assist torque. The ECU 34 stores a map (not shown) that defines the relationship as shown in FIG. In step S104, referring to such a map, an assist torque corresponding to the magnitude of the engine speed Ne when the final TDC is reached is calculated.

  Next, the ECU 34 drives the MG 28 so that the assist torque determined in step S104 is output (step S105).

2-5. Effect of First Explosion Cylinder Change Control According to Embodiment 1 According to the routine processing shown in FIG. 4 described above, the engine rotation speed Ne when the engine stop request is issued is lower than the predetermined value Ne0, so that it remains as it is. Then, when it is determined that the first explosion cylinder does not become the scavenging completion cylinder, the MG 28 assists the rotation of the crankshaft 20. This assist is performed after the other cylinder following the cylinder where the combustion was last performed just before the start of the fuel cut in response to the engine stop request once after the expansion stroke and the exhaust stroke that followed during the fuel cut period. It is executed in order to stop in the expansion stroke. That is, the assist is executed to assist the rotation of the crankshaft 20 with the minimum torque necessary for ensuring startability by the ignition start control. For this reason, according to the control of the present embodiment, there is a concern that scavenging of the burned gas in the cylinder becomes insufficient because the engine speed Ne when the engine stop request is issued is lower than the predetermined value Ne0. Even under circumstances, engine startability can be improved while minimizing power consumption by assist.

  Further, according to the above routine, the assistance by the MG 28 is performed when the final TDC is exceeded (that is, immediately before the engine is stopped). If the engine rotation speed Ne is high, the subsequent rotation behavior is likely to deviate from the expectation due to fluctuations in the friction of the internal combustion engine 12 or the like. As a result, the engine stop position may deviate from the target stop position. On the other hand, the engine stop position is not easily displaced immediately before the engine is stopped. For this reason, it is not always necessary to perform the assist after the final TDC has been exceeded. However, if the assist is performed when the final TDC is exceeded (that is, immediately before the engine is stopped) as in the example shown in the routine, the first explosion is performed. It becomes possible to accurately change to the scavenging completion cylinder targeting the cylinder.

  By the way, in the first embodiment described above, when the engine speed Ne when the engine stop request is issued is lower than the predetermined value Ne0, the MG 28 assists immediately before the start of the fuel cut accompanying the engine stop request. The cylinder (# 4 cylinder in the example shown in FIG. 3) next to the cylinder (# 3 cylinder in the example shown in FIG. 3) in which the combustion was performed last is the expansion stroke and the exhaust following this during the fuel cut period. This is executed to stop the next expansion stroke after the stroke has been reached once. However, in the case of the example shown in FIG. 3, the target of such initial explosion cylinder change control is any of the other cylinders following the # 3 cylinder that was last burned immediately before the start of fuel cut. For example, it is not limited to the # 4 cylinder next to the # 3 cylinder, and may be the # 2 cylinder or the # 1 cylinder.

DESCRIPTION OF SYMBOLS 10 Vehicle 12 Internal combustion engine 14 Fuel injection valve 16 Ignition device 18 Crank angle sensor 20 Crankshaft 28 Motor generator (MG)
32 Battery 34 Electronic control unit (ECU)

Claims (1)

An internal combustion engine comprising a fuel injection valve for directly injecting fuel into a cylinder, and an ignition device for igniting an air-fuel mixture;
An electric motor capable of rotationally driving the crankshaft of the internal combustion engine;
And a control device for controlling the internal combustion engine.
The engine control performed by the control device includes ignition start control for starting the internal combustion engine by starting fuel injection and ignition from an expansion stroke cylinder in an expansion stroke while the engine is stopped.
When the engine rotation speed when the engine stop request is issued is lower than a predetermined value, the control device continues to the cylinder that last burned immediately before the start of the fuel cut accompanying the engine stop request. Assisting the rotation of the crankshaft by the electric motor so that one of the cylinders stops in the next expansion stroke after having once reached the expansion stroke and the exhaust stroke that follows during the fuel cut period. A control device for an internal combustion engine.

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