JP2018105200A - Drive system of vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably start an internal combustion engine irrespective of a magnitude of a voltage of a battery for supplying drive power to an electric motor, in a drive system of a vehicle for imparting assist torque for assisting the rotation of a crankshaft at a start of the internal combustion engine from the electronic motor.SOLUTION: When a voltage of a battery at a start requirement is higher than a voltage V, normal control is selected. The voltage Vis a voltage value at which the voltage of the battery which lowers during the ignition start control of an ENG can stay within a non-output limit area which is indicated in Fig. 3. When the voltage of the battery at the start requirement is lower than the voltage V, low-voltage control is selected. Here, the low-voltage control is select only when the voltage of the battery at the start requirement is higher than a reference voltage V. When the voltage of the battery at the start requirement is lower than the reference voltage V, a starter is selected but not an MG.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a vehicle drive system.

  Japanese Patent Laying-Open No. 2006-033007 discloses a vehicle drive system equipped with an internal combustion engine having a plurality of cylinders. In this drive system, when the internal combustion engine is started, the start control for driving the injector and the spark plug of the target cylinder stopped in the expansion stroke and driving the electric motor for applying torque to the crankshaft is performed. According to this starting control, the rotation can be assisted by the torque applied from the electric motor while the crankshaft is rotated by the torque generated by driving the injector and the spark plug of the target cylinder. Therefore, the internal combustion engine can be started stably.

JP 2006-033007 A

  However, power supply from the battery is indispensable for driving the electric motor. Therefore, when the voltage of the battery at the start of the internal combustion engine is low in the first place, the output of the electric motor is restricted, or the operation of the electric motor is prohibited, and there is a possibility that the torque necessary for starting the internal combustion engine cannot be secured. The same applies to the case where the voltage of the battery drops to the above-described output limit range or operation prohibition range during the start control, and the internal combustion engine may not be started satisfactorily.

  The present invention has been made to solve the above-described problems. In a vehicle drive system in which assist torque for assisting rotation of a crankshaft is applied from an electric motor when the internal combustion engine is started, driving electric power is supplied to the electric motor. An object of the present invention is to stably start the internal combustion engine regardless of the voltage level of the battery.

In order to solve the above-mentioned problem, the first invention
An internal combustion engine including a plurality of cylinders, and an internal combustion engine including an injector for directly injecting fuel into a cylinder and an ignition device for igniting an air-fuel mixture for each cylinder;
An electric motor for applying torque to the crankshaft of the internal combustion engine;
A battery for supplying driving power to the electric motor;
When the internal combustion engine is restarted after being automatically stopped, the injector and ignition device of the first cylinder are driven on condition that the stop position of the piston of the first cylinder that is stopped in the expansion stroke is within a reference range. A control device configured to generate a torque for rotating the crankshaft, and to perform start control for driving the electric motor to generate torque for assisting the rotation of the crankshaft;
A vehicle drive system comprising:
When it is predicted that the voltage of the battery is lower than the first voltage during driving of the electric motor based on the start control, the control device performs low voltage start control instead of the start control. The low-voltage start control is configured to change a target value of assist torque by the electric motor to a value smaller than a target value in the case of performing the start control, and with the rotation of the crankshaft, The control is such that the ignition timing of the second cylinder that reaches the expansion stroke next to the first cylinder is advanced to the compression top dead center side as compared with the ignition timing in the case of performing the start control.

According to a second invention, in the first invention,
The control device is configured to permit execution of the low-voltage start control on condition that the stop position is in a piston position range narrower than the reference range.

According to a third invention, in the second invention,
The control device sets the piston position range to a narrower range as the voltage of the battery at the start request of the internal combustion engine is lower.

A fourth invention is any one of the first to third inventions,
The control device sets the ignition timing to a more advanced side as the voltage of the battery at the time of starting the internal combustion engine is lower.

According to a fifth invention, in any one of the first to fourth inventions,
The internal combustion engine further includes a crank angle sensor that detects a rotational speed of the crankshaft,
The rotation between the execution of the low voltage starting control and the start of the injector of the third cylinder that reaches the expansion stroke after the second cylinder with the rotation of the crankshaft. When the speed does not increase to a predetermined speed, the target value of the assist torque is continuously changed by the electric motor, and the additional low-voltage start is advanced to advance the ignition timing of the third cylinder to the compression top dead center side. It is configured to perform control.

A sixth invention is any one of the first to fifth inventions,
A second electric motor that receives driving power from the battery and applies torque to the crankshaft of the internal combustion engine, the second electric motor having a lower upper limit value of the voltage at which the output is limited than the electric motor;
When the control device is predicted that the voltage of the battery falls below a second voltage lower than the first voltage during driving of the electric motor based on the start control or the low voltage start control, It is characterized by performing 2nd start control which drives the said 2nd electric motor instead of an electric motor, It is characterized by the above-mentioned.

In order to solve the above-mentioned problem,
An internal combustion engine comprising an injector for directly injecting fuel into a cylinder and an ignition device for igniting an air-fuel mixture;
An electric motor for applying torque to the crankshaft of the internal combustion engine;
A battery for supplying driving power to the electric motor;
When the internal combustion engine is restarted after being automatically stopped, the crankshaft is driven by driving the injector and the ignition device of the cylinder on the condition that the stop position of the piston of the cylinder stopped in the expansion stroke is within a reference range. A control device configured to perform start control for generating torque for rotating the motor and generating torque for assisting rotation of the crankshaft by driving the electric motor;
A vehicle drive system comprising:
When it is predicted that the voltage of the battery is lower than the first voltage during driving of the electric motor based on the start control, the control device performs low voltage start control instead of the start control. And when the low voltage start control performs the start control on the target value of the assist torque by the electric motor on the condition that the stop position is in a piston position range narrower than the reference range. The control is characterized in that the control is changed to a value smaller than the target value.

In an eighth aspect based on the seventh aspect,
The control device sets the piston position range to a narrower range as the voltage of the battery at the start request of the internal combustion engine is lower.

A ninth invention is the seventh or eighth invention, wherein
A second electric motor that receives driving power from the battery and applies torque to the crankshaft of the internal combustion engine, the second electric motor having a lower upper limit value of the voltage at which the output is limited than the electric motor;
When the control device is predicted that the voltage of the battery falls below a second voltage lower than the first voltage during driving of the electric motor based on the start control or the low voltage start control, It is characterized by performing 2nd start control which drives the said 2nd electric motor instead of an electric motor, It is characterized by the above-mentioned.

  According to the first aspect of the present invention, the low voltage start control can be performed when it is predicted that the battery voltage is lower than the first voltage during driving of the electric motor based on the start control. In the low voltage start control, the target value of the assist torque by the electric motor is changed to a value smaller than the target value in the case of performing the start control, and the ignition timing of the second cylinder is changed to the ignition in the case of performing the start control. This control is advanced to the compression top dead center side compared to the timing. If the target value of the assist torque by the electric motor is changed to a small value, it is possible to prevent the battery voltage from entering the operation prohibited area during the low voltage start control. Further, if the ignition timing of the second cylinder is advanced to the compression top dead center side, the combustion torque of the second cylinder can be increased, so that the torque that becomes insufficient due to the change in the target value of the assist torque is reduced to the combustion torque. Can be supplemented by. Therefore, even when the voltage of the battery is lower than the first voltage during driving of the electric motor based on the start control, it is possible to avoid the occurrence of a start failure of the internal combustion engine.

  According to the second aspect of the invention, the low voltage start control can be performed on the condition that it is within a narrower piston position range than when the start control is performed. If the piston position range is set to a narrow range, the piston can be effectively pushed down by the combustion energy generated in the first cylinder and the combustion torque of the first cylinder can be increased, which is insufficient when the assist torque target value is changed. Torque can be supplemented by the combustion torque. Therefore, it is possible to satisfactorily avoid the occurrence of starting failure of the internal combustion engine.

  According to the third aspect of the invention, the lower the battery voltage when the internal combustion engine is requested to start, the narrower the piston position range can be set. Therefore, even when the battery voltage at the time of the start request is low, the combustion torque of the first cylinder described above can be increased accordingly.

  According to the fourth aspect of the invention, the ignition timing of the second cylinder can be set to a more advanced side as the voltage of the battery at the start request of the internal combustion engine is lower. Therefore, even when the battery voltage at the time of the start request is low, the combustion torque of the second cylinder described above can be increased accordingly.

  According to the fifth aspect of the present invention, when the rotational speed has not increased to the predetermined speed after the low voltage start control is executed and before the drive of the injector of the third cylinder is started, the additional low voltage start is performed. Control can be performed. The additional low-voltage start control is a control for continuing the change of the target value of the assist torque by the electric motor and advancing the ignition timing of the third cylinder toward the compression top dead center side. If the ignition timing of the third cylinder is advanced to the compression top dead center side, the combustion torque of the third cylinder can be increased. Therefore, even when the rotational speed does not increase to the predetermined speed, it is possible to avoid the occurrence of a start failure of the internal combustion engine due to the combustion torque of the third cylinder.

  According to the sixth aspect of the present invention, when the voltage of the battery is predicted to fall below the second voltage lower than the first voltage during driving of the electric motor based on the start control or the low voltage start control, the second start control is performed. It can be performed. The second start control is a control for driving the second electric motor whose upper limit value of the voltage whose output is limited is lower than that of the electric motor. Therefore, according to the second start control, the internal combustion engine can be started even when the start control or the low voltage control cannot be selected.

  According to the seventh invention, when the voltage of the battery is predicted to be lower than the first voltage during driving of the electric motor based on the start control, it is within a narrower piston position range than that in the case of performing the start control. As a condition, low voltage start control can be performed. The low voltage start control is a control for changing the target value of the assist torque by the electric motor to a value smaller than the target value when the start control is performed. If the target value of the assist torque by the electric motor is changed to a small value, it is possible to prevent the battery voltage from entering the operation prohibited area during the low voltage start control. Further, if the piston position range is set to a narrow range, the combustion torque of the first cylinder can be increased, so that the torque that is insufficient due to the change of the assist torque target value can be compensated by the combustion torque. Therefore, it is possible to satisfactorily avoid the occurrence of starting failure of the internal combustion engine.

  According to the eighth aspect of the invention, the lower the battery voltage when the internal combustion engine is requested to start, the narrower the piston position range can be set. Therefore, even when the battery voltage at the time of the start request is low, the combustion torque of the first cylinder described above can be increased accordingly.

  According to the ninth invention, when the voltage of the battery is predicted to be lower than the second voltage lower than the first voltage during driving of the electric motor based on the start control or the low voltage start control, the second start control is performed. It can be performed. The second start control is a control for driving the second electric motor whose upper limit value of the voltage whose output is limited is lower than that of the electric motor. Therefore, according to the second start control, the internal combustion engine can be started even when the start control or the low voltage control cannot be selected.

It is a figure which shows the outline of the vehicle which comprises the drive system of Embodiment 1 of this invention. It is a figure which shows the outline of the control apparatus which comprises the drive system of Embodiment 1 of this invention. It is the figure which showed the relationship between the voltage of the battery which supplies drive electric power to MG, and the operating range of MG. It is the figure which showed the relationship between the control content at the time of restart of ENG, and the voltage of the battery at the time of a starting request | requirement. It is a figure which shows an example of the process routine of the ignition start control which ECU performs in Embodiment 1 of this invention. It is a figure explaining the change of the motor torque of MG in the low voltage control of Embodiment 1 of this invention. It is a timing chart explaining the low voltage control performed in Embodiment 1 of this invention. It is a figure which shows an example of the process routine of the low voltage control which ECU in Embodiment 1 of this invention performs. It is a timing chart explaining the low voltage control performed in Embodiment 2 of this invention. It is a figure which shows an example of the process routine of the low voltage control which ECU performs in Embodiment 2 of this invention. It is a figure explaining the piston position conditions of the 1st cylinder under low voltage control.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

Embodiment 1 FIG.
First, Embodiment 1 of the present invention will be described with reference to FIGS.

[System Configuration of Embodiment 1]
FIG. 1 is a diagram showing an outline of a vehicle constituting the drive system according to the first embodiment of the present invention. 1 includes an internal combustion engine (hereinafter also referred to as “ENG”) 12, an automatic transmission (hereinafter also referred to as “T / M”) 14, an input shaft 16 of T / M 14, and a power source. An output shaft 18, a differential 20, an axle 22, and drive wheels 24 are provided.

  The ENG 12 is configured as a spark ignition type multi-cylinder engine (a four-cylinder engine as an example). The ENG 12 includes at least an in-cylinder injector and an ignition device (both not shown) for each cylinder. The in-cylinder injector is a known fuel injection valve that directly injects fuel into the cylinder. The ignition device is a known device that includes an ignition coil and an ignition plug and ignites an air-fuel mixture in a cylinder.

  The T / M 14 is a known transmission that can automatically change the gear ratio and that can be automatically set to the neutral state. A crankshaft (not shown) of the ENG 12 is connected to the input shaft 16 via a fluid transmission device (torque converter) so that power can be transmitted. Therefore, the power (engine torque) output from the ENG 12 is transmitted to the output shaft 18 via the input shaft 16 and the T / M 14. The output shaft 18 is connected to the axle 22 via a differential 20 so as to be able to transmit power. Therefore, the power transmitted to the output shaft 18 is transmitted to the drive wheels 24 via the differential 20 and the axle 22.

  The vehicle 10 shown in FIG. 1 also includes a motor generator (hereinafter also referred to as “MG”) 26, a transmission belt 28, and a battery 30. The MG 26 is configured by a permanent magnet type AC synchronous electric motor as an example. A rotation shaft (not shown) of the MG 26 is connected to the crank shaft of the ENG 12 via the transmission belt 28. The MG 26 applies the motor torque generated by the power running drive to the crankshaft of the ENG 12 via the transmission belt 28. The MG 26 also operates as a generator by regenerative driving.

  The battery 30 is comprised from the lithium ion battery as an example. The battery 30 is used as a power source that supplies driving power to the MG 26 when the MG 26 operates as a motor. The battery 30 is used as a battery that stores electric power generated by the MG 26 when the MG 26 operates as a generator.

  The vehicle 10 shown in FIG. 1 further includes a starter motor (hereinafter also referred to as “starter”) 32. The rotor shaft of the starter 32 is connected to the crank shaft of the ENG 12 through a known electric mechanism (none of which is shown) such as a belt mechanism so that power can be transmitted. The starter 32 is a well-known starter that receives the drive power from the battery 30 and cranks the ENG 12. The MG 26 is an electric motor having a generator function, whereas the starter 32 is a pure electric motor having no generator function.

  The starter 32 is mainly used for cranking when performing start control when the ENG 12 is cold. On the other hand, the MG 26 mainly stops the ENG 12 automatically without depending on the operation of the driver when a predetermined stop condition is satisfied, and restarts the ENG 12 in response to a subsequent start request (so-called stop-and-start control ( Hereinafter, it is also used for cranking when performing “S & S control”. Either one of the starter 32 and the MG 26 is selected and used for cranking the ENG 12. The selection of the starter 32 and the MG 26 will be described later.

  FIG. 2 is a diagram showing an outline of a control device constituting the drive system according to the first embodiment of the present invention. A control device (hereinafter also referred to as “ECU”) 40 shown in FIG. 2 includes a RAM, a ROM, a CPU, and the like. The ECU 40 captures and processes signals from various sensors mounted on the vehicle 10 shown in FIG. The various sensors include a crank angle sensor 42 that detects the crank angle and the engine rotation speed, a voltage sensor 44 that detects the voltage of the battery 30, a pressure sensor 46 that detects the in-cylinder pressure, and the temperature of the cooling water in the ENG 12. A temperature sensor 48 is included. The ECU 40 processes the signals of the various sensors taken in and operates the various actuators according to a predetermined control program. The actuator operated by the ECU 40 includes the ENG 12 (specifically, the in-cylinder injector and the ignition device described above), the MG 26 and the starter 32 (specifically, the inverter of the MG 26 and the starter 32).

[Control of Embodiment 1]
(Ignition start control)
The control executed by the ECU in the first embodiment includes ignition start control. The ignition start control is performed as one means for realizing the restart of ENG in the S & S control. The outline of the ignition start control is as follows. First, a cylinder stopped in the expansion stroke (hereinafter also referred to as “first cylinder”) is specified. Subsequently, the in-cylinder injector and the ignition device of the first cylinder are driven. Further, when the MG is driven substantially at the same time and the motor torque rises to the optimum torque TQ _A , the rotor shaft of the MG and the crank shaft of the ENG are connected. The optimum torque TQ _A is estimated based on the pressure in the cylinder of the cylinder stopped in the compression stroke (hereinafter also referred to as “second cylinder”) as the optimum torque for restarting the ENG.

Combustion torque (hereinafter, also referred to as “initial explosion torque”) generated by driving the in-cylinder injector and the ignition device of the first cylinder is applied to the ENG crankshaft, and the crankshaft rotates. Further, the motor torque of the MG increased by driving the MG at substantially the same time is applied to the crankshaft by the connection between the rotor shaft of the MG and the crankshaft of the ENG, and the crankshaft further rotates. That is, the rotation of the crankshaft is assisted by the application of the MG motor torque. When the engine speed increases to the threshold value N _TH, the driving of the MG is stopped to end the ignition start control, or the connection between the rotor shaft of the MG and the crank shaft of the ENG is released.

  Such ignition start control is performed in order to suppress the use frequency of the starter. S & S control can also be realized by a starter. Also in the first embodiment, when a predetermined MG use condition (hereinafter also referred to as “MG condition”) is not satisfied, S & S control using a starter is performed. However, when the starter is used, the power consumption is larger than when the MG is used. Therefore, according to the S & S control using MG, it is possible to suppress the power consumption and improve the fuel efficiency. In addition, the life of the starter can be extended.

  Here, the following conditions are included in the MG condition. The first condition includes that ENG is not in a cold state. Whether ENG is in the cold state is determined based on the detection value of the temperature sensor 48 shown in FIG. When ENG is in a cold state, the injected fuel is insufficiently vaporized and the air-fuel mixture in the first cylinder is difficult to burn. Further, when ENG is in a cold state, the influence of cooling loss is inevitable. Therefore, sufficient initial explosion torque is not applied to the crankshaft, and a sufficient increase in engine speed cannot be expected. Therefore, in this case, the S & S control is realized only by driving the starter without driving the in-cylinder injector, the ignition device, and the MG.

The second condition, the piston position of the first cylinder, and the like that are within the reference range CA _R. The piston position of the first cylinder is specified using the detection value of the crank angle sensor 42 shown in FIG. When the piston position of the first cylinder is at the top dead center side from the reference range CA _R, high compression pressure of the mixture gas in the cylinder, the combustion energy obtained by the combustion of the mixture of the first cylinder becomes large. However, the piston position of the second cylinder is in the top dead center side from the reference range CA _R, is required large combustion energy than this because the piston of the second cylinder is greater than the top dead center. On the other hand, when the piston position of the first cylinder is at the bottom dead center side from the reference range CA _R, the combustion energy decreases. Thus, when the piston position of the first cylinder is outside the reference range CA _R a sufficient initial explosion torque is not imparted to the crankshaft, it is not expected to be sufficient increase in the engine rotational speed. Therefore, also in this case, the S & S control is realized only by driving the starter.

The third condition, the voltage of a battery for supplying driving power to the MG, it can be mentioned higher than the reference voltage V _R. The battery voltage is specified using the detection value of the voltage sensor 44 shown in FIG. When the voltage of the battery is lower than the reference voltage V _R, the motor torque of the MG is reduced. Therefore, sufficient assist torque is not applied to the crankshaft, and a sufficient increase in engine speed cannot be expected. Therefore, in this case, the S & S control is realized by a combination of combustion of the first cylinder and driving of the starter at the same time. That is, S & S control is realized by a combination of initial explosion torque and starter motor torque.

(Problems of ignition start control)
Incidentally, the MG condition has the following problem related to the third condition. FIG. 3 is a diagram showing the relationship between the voltage of the battery that supplies driving power to the MG and the operating range of the MG. As shown in FIG. 3, the voltage of the battery is lower than the reference voltage V _R, the operation of the MG is prohibited. In this case, the third condition for realizing the S & S control by the combination of the initial explosion torque and the motor torque of the starter is as described above.

On the other hand, the voltage of the battery is higher than the reference voltage V _R, the operation of the MG is permitted. However, in FIG. 3, and a non-output limit range higher than the voltage V _{1 (>} reference voltage V _R), during the low operating prohibition area than the reference voltage V _R, the output restriction area is provided. The output limit area plays a role of buffering that the voltage of the battery that is decreasing suddenly enters the operation prohibited area from the non-output limit area. Of course, in the output restriction region, the motor torque of the MG is suppressed compared to the non-output restriction region.

It should be noted here that, as indicated by an arrow in the upper right of FIG. 3, the voltage of the battery that was in the non-output limit region at the time of the start request is lowered to the output limit region during the ignition start control. And when the fall of the voltage over such two operation permission area | regions actually occurs, the motor torque of MG will be suppressed and starting failure may generate | occur | produce. Therefore, in the first embodiment, when the ENG is restarted, the voltage of the battery at the start request is lower than the voltage V ₂ (> voltage V ₁ ) even when the MG condition is satisfied. Sometimes, control different from the ignition start control is executed. Hereinafter, for convenience of explanation, normal ignition start control performed when the voltage of the battery is higher than the voltage V ₂ is also referred to as “normal control”. Further, the ignition start control performed when the voltage of the battery is lower than the voltage V ₂ is also referred to as “low voltage control”.

FIG. 4 is a diagram showing the relationship between the control contents at the time of restarting ENG and the battery voltage at the start request. As shown in FIG. 4, the voltage of the battery at the time of the request for starting is higher than the voltage V ₂ is typically controlled is selected. Voltage V ₂ is the voltage of a battery decreases during the ignition start control of ENG is a voltage value which can remain in the non-output restricted zone described with reference to FIG. Voltage V ₂ can be set from voltages V ₁ described in FIG. 3, in advance by subtracting the reduction predicted value of the voltage caused by the driving of the MG.

On the other hand, the voltage of the battery at the time of the request for starting is lower than the voltage V _2, the low voltage control is selected. However, the low voltage control is selected, the voltage of the battery at the time of the request for starting is higher than the reference voltage V _R. When the voltage of the battery at the time of the request for starting is lower than the reference voltage V _R is the MG no starter is selected. The reason for selecting the starter is as described in the MG condition (third condition). Supplementally, the output limit range of the starter is set to be lower than the output limit range of the MG described in FIG. Therefore, the voltage of the battery at the start request is a lower than the reference voltage V _R of the MG, is higher than the output limit range of the starter, it is possible to realize a S & S control with high probability by the starter. Note that the reference voltage V _R, may be set to a voltage value obtained by subtracting the reduction predicted value of the voltage caused by the driving of MG (voltage V _3).

  FIG. 5 is a diagram showing an example of a processing routine for ignition start control executed by the ECU in the first embodiment of the present invention. This routine is repeatedly executed every predetermined control period after the predetermined stop condition is satisfied. Further, this routine is executed on the assumption that the first and second MG conditions described above are satisfied.

  In the routine shown in FIG. 5, first, the presence / absence of a start request is determined (step S10). The presence / absence of the start request is determined, for example, by the presence / absence of a driver operation such as a driver's foot coming off a brake pedal (not shown).

If it is determined in step S10 that there is a start request, it is determined whether or not normal control can be executed (step S12). Whether normal control is executable, it is determined based on the magnitude relationship between the detected value of the voltage sensor 44 shown in FIG. 2, the voltage V ₂ described in FIG. If the sensor detection value is determined to be higher than the voltage V _2, it can be determined that the normal control is feasible. Therefore, it progresses to step S14 and normal control is selected.

In step S12, the detection value of the voltage sensor 44 when it is determined to be lower than the voltage V ₂ is whether a low voltage control can be performed is determined (step S16). The processing in step S16 is for determining whether the above-described third MG condition is successful. Whether or not the low voltage control can be executed is determined based on the magnitude relationship between the detection value of the voltage sensor 44 used in step S12 and the reference voltage V _R (or voltage V ₃ ) described in FIG. The If the sensor detection value is determined to be higher than the reference voltage V _R, it can be determined that the low-voltage control can be performed. Therefore, it progresses to step S18 and low voltage control is selected.

In step S16, when the sensor detection value is determined to be lower than the reference voltage V _R, it can be determined that the low-voltage control is not feasible. Therefore, it progresses to step S20 and the start by a starter is selected. As already described, the starter start is based on the combination of the initial explosion torque and the starter motor torque.

(Low voltage control)
As described above, in the ignition start control, when the MG motor torque rises to the optimum torque TQ _A , the MG rotor shaft and the ENG crankshaft are connected. This connection operation is common to normal control and low voltage control. However, in the case of the normal control, the target value of the MG motor torque is maintained at the optimum torque TQ _A even after the coupling operation, whereas in the case of the low voltage control, the target value is the optimum torque TQ _A after the coupling operation. Is changed to a smaller value. By changing the target value of the motor torque to a small value, it is possible to reduce the amount of decrease in the battery voltage that accompanies the driving of the MG. Therefore, the voltage of the battery during low voltage control falls below the reference voltage V _R, it can be prevented from being entered to the operation prohibition area described in FIG. The change of the target value will be described with reference to FIG.

The horizontal axis in FIG. 6 corresponds to the vertical axis in FIG. That is, when the voltage of the battery at the start request is higher than the reference voltage V _R (or voltage V ₃ ) and lower than the voltage V ₂ , the low voltage control is selected. As shown in FIG. 6, at a low voltage control, the target value of the motor torque of MG is set between the torque TQ ₁ and the torque TQ _2. In FIG. 6, the torque TQ ₁ is set to a value smaller than the optimum torque TQ _A. However, the torque TQ ₁ may be equal to the optimum torque TQ _A. Torque TQ ₂ is the minimum value of the motor torque that can assist the rotation of the crankshaft. As shown in FIG. 6, in the low voltage control, the target value of the motor torque of the MG is set to a smaller value as the battery voltage at the start request is smaller.

  However, if the MG motor torque target value is changed to a small value, the MG assist torque also decreases. Therefore, in the low voltage control, the ignition timing of the cylinder that reaches the expansion stroke next to the first cylinder, that is, the above-described second cylinder is changed to the compression top dead center (TDC) side. During the ignition control, the ignition timing of each cylinder is set to be retarded from TDC. In the low voltage control, the ignition timing of the first cylinder is set at the same time as the normal control, while the ignition timing of the second cylinder is advanced to the TDC side. The combustion torque can be increased by advancing the ignition timing of the second cylinder to the TDC side. Therefore, it becomes possible to compensate for the decrease in the assist torque of the MG by the combustion torque of the second cylinder and to avoid the start failure of the ENG.

  FIG. 7 is a timing chart illustrating low voltage control performed in the first embodiment of the present invention. In FIG. 7, it is assumed that the first cylinder is the first cylinder # 1 and the second cylinder is the third cylinder # 3.

In the chart shown in FIG. 7, an ENG start request is issued at time t ₀ , and the target value of the MG motor torque (hereinafter also referred to as “MG torque” in the description of FIG. 7) is set to the optimum torque TQ _A. Is done. The actual motor torque of MG (hereinafter also referred to as “output torque” in the description of FIG. 7) increases with a time delay and reaches the optimum torque TQ _A. Upon reaching the output torque optimum torque TQ _A, connects the crank shaft of the rotor shaft and ENG of MG, starts the low voltage control. The low voltage control, first, at time t ₁ by driving the No. 1 cylinder injector cylinders # 1 to inject fuel, then the ignition air mixture drives the ignition device in the same cylinder.

Combustion torque is generated with the combustion of the air-fuel mixture in the first cylinder # 1, and the engine speed starts to increase. In the low voltage control, the MG torque is changed from the optimum torque TQ _A to the torque TQ ₃ at time t ₂ when the engine speed starts to increase. Torque TQ ₃ is set according to the voltage of the battery at time _{t 0.} By changing the MG torque from the optimum torque TQ _A torque TQ _3, the voltage of the battery during low voltage control falls below the reference voltage V _R, in advance from being entered to the operation prohibition area described in FIG. 3 Can be prevented. The torque TQ ₃ is not less than the torque TQ _{2 and not} more than the torque TQ ₁ shown in FIG. 5 (TQ ₂ ≦ TQ ₃ ≦ TQ ₁ ).

The low voltage control, after changing the MG torque, by driving the cylinder injector at time t ₃ in the third cylinder # 3 to inject fuel air mixture in a subsequent time t ₄ by driving the ignition device in the same cylinder Ignition. FIG. 7 shows the ignition timing (time t ₅ ) of the cylinder under normal control as a comparison of the ignition timing (time t ₄ ) of the third cylinder # 3 under low voltage control. As can be seen by comparing the two, time t ₄ is earlier than time t ₅ . By advancing the third ignition timing of the cylinder # 3 from time t ₅ to time t _4, it is possible to increase the combustion torque generated due to combustion of the mixture in the cylinder. Therefore, according to the low-voltage control, a decrease in the time t ₂ after the output torque, supplemented by the combustion torque of the third cylinder # 3, it is possible to avoid a poor starting of the ENG.

Then, at time t ₆ to the engine rotational speed is increased to the threshold value N _TH, to change the MG torque to zero from the torque TQ _3, and terminates the low voltage control.

  FIG. 8 is a diagram showing an example of a low voltage control processing routine executed by the ECU in the first embodiment of the present invention. This routine is executed as a subroutine of step S18 described in FIG.

In the routine shown in FIG. 8, first, the optimum torque TQ _A is determined (step S22). The optimum torque TQ _A is estimated based on the in-cylinder pressure of the second cylinder as a target value of the motor torque of the MG. The detected value of the pressure sensor 46 shown in FIG. 2 is used for the pressure in the cylinder of the second cylinder.

Following step S22, the actual motor torque MG is calculated (step S24), and whether the motor torque exceeds the optimum torque TQ _A is determined (step S26). The actual motor torque of MG is calculated based on, for example, the rotation speed of MG and the detected value of voltage sensor 44 used in step S16 of FIG. The processing of step S24, S26, at step S26 until the motor torque of MG is determined to exceed the optimum torque TQ _A, is repeatedly executed.

If it is determined in step S26 that the actual motor torque of the MG exceeds the optimum torque TQ _A , execution of the low voltage control is permitted (step S28). By the processing in step S28, the in-cylinder injector and the ignition device of the first cylinder are driven, and combustion torque is applied to the crankshaft. Further, the MG rotor shaft and the ENG crankshaft are connected to each other, and MG assist torque is applied to the crankshaft.

Subsequent to step S28, the target value of the motor torque of the MG is changed from the optimum torque TQ _A to the torque TQ ₃ (step S30). The torque TQ ₃ is as already described in FIG. Torque TQ ₃ is set in accordance with the detected value of the voltage sensor 44 used in step S16 in FIG. 5.

  Following step S30, the ignition timing of the second cylinder is advanced to the TDC side (step S32). The advance angle of the ignition timing of the second cylinder is set separately according to the ENG specifications. Then, it is determined whether or not the set ignition timing has been reached (step S34), and the ignition device for the second cylinder is driven (step S36). By the process of step S36, the combustion torque of the second cylinder is increased.

Following step S36, whether the engine rotational speed threshold value _{N TH} or more is determined (step S38). The process of step S38 is repeatedly executed until it is determined that the engine speed is equal to or higher than the threshold value _NTH . When it is determined that the engine speed is equal to or higher than the threshold value N _TH , the target value of the MG motor torque is changed from the torque TQ ₃ to 0 (step S40). Execution of the low voltage control is completed by the process of step S40.

As described above, according to the routine shown in FIG. 8, it is possible to lower the target value of the motor torque of the MG torque TQ ₃ by the processing of step S30. Therefore, it is possible to reduce the amount of decrease in battery voltage that accompanies MG driving. Accordingly, the voltage of the battery during low voltage control falls below the reference voltage V _R, it can be prevented from being entered to the operation prohibition area described in FIG. Further, according to the routine shown in FIG. 8, the ignition timing of the second cylinder can be advanced to the TDC side by the processing of steps S32 to S36. Therefore, it is possible to avoid the ENG start failure by compensating for the decrease in the target value of the MG motor torque with the combustion torque of the second cylinder.

  In the first embodiment described above, the MG is low in the “motor” of the first and seventh inventions, the ECU is in the “control device” in the invention, and the normal control is low in the “startup control” of the invention. The voltage control corresponds to the “low voltage start control” of the present invention.

  In the first embodiment described above, the starter is controlled by a combination of the first cylinder combustion and the starter driving at the same time in the “second electric motor” of the sixth and ninth inventions. This corresponds to “second start control”.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS. The configuration of the drive system according to the second embodiment is the same as the configuration of the drive system shown in FIGS. Further, the basic configuration of the ignition start control is common to the control configuration described with reference to FIGS. Therefore, the description of the configuration of the drive system and the ignition start control is omitted.

[Control of Embodiment 2]
In the low voltage control of the first embodiment described above, the combustion torque is increased by changing the ignition timing of the second cylinder to the TDC side, and the engine speed is increased to the threshold value N _TH . However, for some reason, even if the combustion torque of the second cylinder is high, the engine rotation speed may not rise to the threshold value _NTH . Therefore, in the low voltage control of the second embodiment, the ignition timing of the cylinder that reaches the expansion stroke next to the second cylinder (hereinafter also referred to as “third cylinder”) is also changed to the TDC side. The combustion torque of the third cylinder can be increased by advancing the ignition timing of the third cylinder to the TDC side. Therefore, it becomes possible to compensate for a decrease in the assist torque of the MG accompanying the execution of the low voltage control with the combustion torque of the second and third cylinders, and to avoid a start failure of the ENG.

  FIG. 9 is a timing chart for explaining the low voltage control performed in the second embodiment of the present invention. In FIG. 9, it is assumed that the first cylinder is the first cylinder # 1, the second cylinder is the third cylinder # 3, and the third cylinder is the fourth cylinder # 4.

In the chart shown in FIG. 9, an ENG start request is issued at time t ₀ , and the target value of the MG motor torque (hereinafter also referred to as “MG torque” in the description of FIG. 9) is set to the optimum torque TQ _A. Is done. The actual motor torque of MG (hereinafter also referred to as “output torque” in the description of FIG. 9) increases with a time delay and reaches the optimum torque TQ _A. Upon reaching the output torque optimum torque TQ _A, connects the crank shaft of the rotor shaft and ENG of MG, starts the low voltage control. The low voltage control, first, at time t ₁ by driving the No. 1 cylinder injector cylinders # 1 to inject fuel, then the ignition air mixture drives the ignition device in the same cylinder.

Further, in the low voltage control changes the MG torque from the optimum torque TQ _A at time _{t 2} to the torque TQ _3. Further, in the low voltage control drives the cylinder injector at time t ₃ in the third cylinder # 3 to inject fuel and ignite the mixture to drive the ignition device in the same cylinder in the subsequent time t _4. Up to this point, it is the same as the low voltage control of the first embodiment described above.

In low voltage control of the second embodiment, at time t ₇ by driving the fourth cylinder injector for cylinder # 4 to inject fuel air mixture in a subsequent time t ₈ drives the ignition device in the same cylinder Ignition. FIG. 9 shows the ignition timing (time t ₉ ) of the cylinder under normal control as a comparison of the ignition timing (time t ₈ ) of the fourth cylinder # 4 under low voltage control. As can be seen by comparing the two, time t ₈ is earlier than time t ₉ . The fourth ignition timing of the cylinder # 4 that advancing from time t ₉ to the time t _8, it is possible to increase the combustion torque generated due to combustion of the mixture in the cylinder. Therefore, according to the low voltage control in the second embodiment, a reduction in the time t ₂ after the output torque, supplemented by the combustion torque of the third cylinder # 3 and fourth cylinder # 4, avoiding startup failure of the ENG It becomes possible to do.

Then, at time _{t 10} to the engine rotational speed she is increased to the threshold value _{N TH,} to change the MG torque to zero from the torque TQ _3, and terminates the low voltage control.

  FIG. 10 is a diagram illustrating an example of a low voltage control processing routine executed by the ECU according to the second embodiment of the present invention. This routine is executed as a process replacing steps S38 and S40 described in FIG.

In the routine shown in FIG. 10, it is first determined whether or not the engine speed is equal to or higher than a threshold value N _TH (step S42). This step S42 is the same as the process of step S38 of FIG. If it is determined that the engine speed is equal to or higher than the threshold value N _TH , the target value of the MG motor torque is changed from the torque TQ ₃ to 0 (step S44). Execution of the low voltage control is completed by the processing in step S44.

On the other hand, if it is determined in step S42 that the engine rotation speed is less than the threshold value _NTH, it can be determined that the engine rotation speed has not _fully increased to the threshold value _NTH despite the ignition advance angle of the second cylinder. Therefore, the ignition timing of the third cylinder is advanced to the TDC side (step S46). The advance angle of the ignition timing of the third cylinder is set equal to the advance angle of the second cylinder. Then, it is determined whether or not the ignition timing set in step S46 has been reached (step S48), and the third cylinder ignition device is driven (step S50). By the process of step S50, the combustion torque of the third cylinder is increased.

  As described above, according to the routine shown in FIG. 10, the ignition timing of the third cylinder can be advanced to the TDC side by the processes of steps S46, S48, and S50. Therefore, it becomes possible to compensate for the decrease in the target value of the MG motor torque accompanying the low voltage control with the combustion torque of the second and third cylinders, and to avoid the ENG start failure.

  In the second embodiment described above, the “additional low voltage start control” of the fifth invention is realized by advancing the ignition timing of the third cylinder to the TDC side.

Embodiment 3 FIG.
Next, Embodiment 3 of the present invention will be described with reference to FIG. The configuration of the drive system according to the third embodiment is common to the configuration of the drive system shown in FIGS. Further, the basic configuration of the ignition start control is common to the control configuration described with reference to FIGS. Therefore, the description of the configuration of the drive system and the ignition start control is omitted.

[Control of Embodiment 3]
In the ignition start control of the first and second embodiments described above, that the piston position of the first cylinder is in the reference range CA _R is the second MG condition. Of course, this MG condition applies to both normal control and low voltage control. However, a low voltage control of the third embodiment, stringent conditions are applied to the MG conditions than reference range CA _R. FIG. 11 is a diagram for explaining the piston position condition of the first cylinder during the low voltage control. As shown in FIG. 11, in the third embodiment, the piston position of the first cylinder, a condition that in the narrow range CA ₁ than the reference range CA _R, the low voltage control is permitted to run.

As in the first embodiment described above, in the low voltage control of the third embodiment is changed to a value smaller than the optimum torque TQ _A target value of the motor torque. Therefore, it is possible to reduce the amount of decrease in the voltage of the battery accompanying the driving of the MG, and to prevent the battery voltage from entering the operation prohibited area described with reference to FIG. 3 during the low voltage control. On the other hand, if the MG motor torque target value is changed to a small value, the MG assist torque also decreases.

In this regard, in the third embodiment, and that the piston position of the first cylinder is in the range CA ₁ as a condition for permitting execution of the low-voltage control. If the piston position of the first cylinder is in the range CA _1, it is possible to obtain a large initial explosion torque than when the piston position is within the reference range CA _R. This is because as the range of the piston position of the first cylinder is narrowed, the piston can be effectively pushed down by the combustion energy generated in the first cylinder. Therefore, if voltage control is executed under such conditions, it is possible to compensate for a decrease in the MG assist torque with a relatively large initial explosion torque and to avoid a start failure of the ENG. In low voltage control of the third embodiment, as the voltage of the battery at the time of the request for starting is small, the range CA ₁ is set to a narrower range.

The permission condition for low voltage control according to the third embodiment may be applied as the permission condition for low voltage control according to the first and second embodiments. In this case, in step S16 shown in FIG. 5, in addition to the determination as to the third MG conditions described above, the determination as to whether the piston position of the first cylinder is in the range CA ₁ shown in FIG. 11 Just do it.

DESCRIPTION OF SYMBOLS 10 Vehicle 12 Internal combustion engine 14 Automatic transmission 16 Input shaft 18 Output shaft 20 Differential 22 Axle 24 Drive wheel 26 Motor generator 28 Transmission belt 30 Battery 32 Starter 40 Control device 42 Crank angle sensor 44 Voltage sensor 46 Pressure sensor 48 Temperature sensor

A fourth invention is any one of the first to third inventions,
The control device sets the ignition timing of the second cylinder to a more advanced side when performing the low-voltage start control as the voltage of the battery at the start request of the internal combustion engine is lower. .

According to a fifth invention, in any one of the first to fourth inventions,
Further comprising a crank angle sensor for detecting a rotational speed of the crankshaft,
The rotation between the execution of the low voltage starting control and the start of the injector of the third cylinder that reaches the expansion stroke after the second cylinder with the rotation of the crankshaft. When the speed does not increase to a predetermined speed, the target value of the assist torque is continuously changed by the electric motor, and the additional low-voltage start is advanced to advance the ignition timing of the third cylinder to the compression top dead center side. It is configured to perform control.

According to the sixth aspect of the present invention, when the voltage of the battery is predicted to fall below the second voltage lower than the first voltage during driving of the electric motor based on the start control or the low voltage start control, the second start control is performed. It can be performed. The second start control is a control for driving the second electric motor whose upper limit value of the voltage whose output is limited is lower than that of the electric motor. Therefore, according to the second start control, the internal combustion engine can be started even when the start control or the low voltage start control cannot be selected.

According to the seventh invention, when the voltage of the battery is predicted to be lower than the first voltage during driving of the electric motor based on the start control, it is within a narrower piston position range than that in the case of performing the start control. As a condition, low voltage start control can be performed. The low voltage start control is a control for changing the target value of the assist torque by the electric motor to a value smaller than the target value when the start control is performed. If the target value of the assist torque by the electric motor is changed to a small value, it is possible to prevent the battery voltage from entering the operation prohibited area during the low voltage start control. Further, if low-voltage start control is performed on the condition that the piston position range is narrow, the combustion torque generated in the cylinder having the piston stopped in the expansion stroke after the automatic stop can be increased, so that the assist torque The torque that is insufficient due to the change in the target value can be compensated by the combustion torque. Therefore, it is possible to satisfactorily avoid the occurrence of starting failure of the internal combustion engine.

According to the eighth aspect of the invention, the lower the battery voltage when the internal combustion engine is requested to start, the narrower the piston position range can be set. Therefore, even if the battery voltage at the time of the start request is low, the above-described combustion torque can be increased accordingly.

Claims (9)

An internal combustion engine including a plurality of cylinders, and an internal combustion engine including an injector for directly injecting fuel into a cylinder and an ignition device for igniting an air-fuel mixture for each cylinder;
An electric motor for applying torque to the crankshaft of the internal combustion engine;
A battery for supplying driving power to the electric motor;
When the internal combustion engine is restarted after being automatically stopped, the injector and ignition device of the first cylinder are driven on condition that the stop position of the piston of the first cylinder that is stopped in the expansion stroke is within a reference range. A control device configured to generate a torque for rotating the crankshaft, and to perform start control for driving the electric motor to generate torque for assisting the rotation of the crankshaft;
With
When it is predicted that the voltage of the battery is lower than the first voltage during driving of the electric motor based on the start control, the control device performs low voltage start control instead of the start control. The low-voltage start control is configured to change a target value of assist torque by the electric motor to a value smaller than a target value in the case of performing the start control, and with the rotation of the crankshaft, Driving the vehicle, characterized in that the ignition timing of the second cylinder, which reaches the expansion stroke next to the first cylinder, is advanced to the compression top dead center side as compared with the ignition timing when the start control is performed. system.   The control device is configured to permit execution of the low-voltage start control on condition that the stop position is in a piston position range narrower than the reference range. The vehicle drive system according to claim 1.   3. The vehicle drive system according to claim 2, wherein the control device sets the piston position range to a narrower range as the voltage of the battery at the time of starting the internal combustion engine is lower.   4. The vehicle according to claim 1, wherein the control device sets the ignition timing to a more advanced side as the voltage of the battery at the time of starting the internal combustion engine is lower. 5. Drive system. The internal combustion engine further includes a crank angle sensor that detects a rotational speed of the crankshaft,
The rotation between the execution of the low voltage starting control and the start of the injector of the third cylinder that reaches the expansion stroke after the second cylinder with the rotation of the crankshaft. When the speed does not increase to a predetermined speed, the target value of the assist torque is continuously changed by the electric motor, and the additional low-voltage start is advanced to advance the ignition timing of the third cylinder to the compression top dead center side. The vehicle drive system according to any one of claims 1 to 4, wherein the vehicle drive system is configured to perform control. A second electric motor that receives driving power from the battery and applies torque to the crankshaft of the internal combustion engine, the second electric motor having a lower upper limit value of the voltage at which the output is limited than the electric motor;
When the control device is predicted that the voltage of the battery falls below a second voltage lower than the first voltage during driving of the electric motor based on the start control or the low voltage start control, 6. The vehicle drive system according to claim 1, wherein the vehicle start system is configured to perform a second start control for driving the second electric motor instead of the electric motor. 6. An internal combustion engine comprising an injector for directly injecting fuel into a cylinder and an ignition device for igniting an air-fuel mixture;
An electric motor for applying torque to the crankshaft of the internal combustion engine;
A battery for supplying driving power to the electric motor;
When the internal combustion engine is restarted after being automatically stopped, the crankshaft is driven by driving the injector and the ignition device of the cylinder on the condition that the stop position of the piston of the cylinder stopped in the expansion stroke is within a reference range. A control device configured to perform start control for generating torque for rotating the motor and generating torque for assisting rotation of the crankshaft by driving the electric motor;
With
When it is predicted that the voltage of the battery is lower than the first voltage during driving of the electric motor based on the start control, the control device performs low voltage start control instead of the start control. And when the low voltage start control performs the start control on the target value of the assist torque by the electric motor on the condition that the stop position is in a piston position range narrower than the reference range. A drive system for a vehicle, characterized in that the control is to change the value to be smaller than a target value.   8. The vehicle drive system according to claim 7, wherein the control device sets the piston position range to a narrower range as the voltage of the battery at the time of starting the internal combustion engine is lower. A second electric motor that receives driving power from the battery and applies torque to the crankshaft of the internal combustion engine, the second electric motor having a lower upper limit value of the voltage at which the output is limited than the electric motor;
When the control device is predicted that the voltage of the battery falls below a second voltage lower than the first voltage during driving of the electric motor based on the start control or the low voltage start control, 9. The vehicle drive system according to claim 7, wherein the second start control for driving the second electric motor instead of the electric motor is performed.

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