JP7480685B2 - Powertrain control method and control system - Google Patents

Description

The present invention relates to a control method and control system for a powertrain having an internal combustion engine, a motor, and a frictional fastening element that switches between connecting and disconnecting the driving force between the internal combustion engine and the motor.

In a powertrain system equipped with an internal combustion engine and a motor, there is known a system that can switch between running only on the motor and running at least using the internal combustion engine depending on the operating conditions. Furthermore, in a powertrain system having a clutch that switches between connecting and disconnecting the driving force between the internal combustion engine and the motor as described above, the output of the motor may be used to start the internal combustion engine while running only on the motor.

For example, Patent Document 1 discloses a technology in which, when switching from an EV mode, in which a target driving force based on the driver's request is realized by the motor alone, to an HEV mode, in which the target driving force is realized by the internal combustion engine and the motor, a clutch is engaged, and part of the output of the motor that outputs the torque to realize the target driving force in the EV mode is used to crank the internal combustion engine.

JP 2010-167899 A

However, in the technology of Patent Document 1, when starting the internal combustion engine using motor torque to transition from EV mode (hereinafter sometimes referred to as "second driving mode") to HEV mode (hereinafter sometimes referred to as "first driving mode"), the driving force may temporarily decrease. Specifically, the motor must output torque to achieve the target driving force while also outputting torque to crank the internal combustion engine, but if the sum of these two types of torque exceeds the torque the motor can generate, the driving force temporarily decreases. As a result, the vehicle deceleration occurs during cranking of the internal combustion engine. Note that deceleration is the acceleration in the front-rear direction that occurs in the vehicle when the vehicle speed decreases. Deceleration can be said to be negative acceleration.

In this manner, the internal combustion engine is cranked in a state where the driving force is reduced, and in the HEV mode after starting is complete, for example, the torque of the internal combustion engine generates a driving force equivalent to the driving force in the EV mode before starting, i.e., the target driving force. At this time, the vehicle acceleration also returns to the same level as before the internal combustion engine started, so the difference with the vehicle acceleration during the internal combustion engine cranking gives the driver an uncomfortable feeling of being pulled backwards during deceleration, and then lurching forward during acceleration. Furthermore, if the start of the internal combustion engine is due to a system request such as a low battery level, rather than the driver's depressing the accelerator pedal, the vehicle acceleration changes regardless of the driver's intention, increasing the sense of discomfort.

In response to this, it is possible to increase the size of the motor to increase the excess driving force when switching from EV mode to HEV mode, thereby preventing the vehicle from decelerating or accelerating; however, this could have an adverse effect on the layout of other components, for example.

As described above, in a powertrain system having an internal combustion engine, a motor, and a frictional fastening element that switches between connecting and disconnecting the driving force between the internal combustion engine and the motor, there is still room for improvement in the control during the transition from the second driving mode, which is the EV mode, to the first driving mode, which is the HEV mode.

The inventors of the present application conducted further intensive research to solve the above problem and discovered that if the amount of vehicle acceleration that changes at one time is kept below a predetermined value, the driver will not feel uncomfortable even if the absolute value of the amount of change in vehicle acceleration during the transition between driving modes becomes large. In other words, they came up with the idea that by gradually increasing the internal combustion engine output torque after the internal combustion engine start is complete, reducing the amount of acceleration that changes at one time, and keeping it within a range in which the driver does not feel the change in vehicle acceleration, it is possible to prevent the driver from feeling an uncomfortable acceleration.

The present invention is a method for controlling a powertrain that is mounted on a vehicle and includes a motor for driving drive wheels of the vehicle, an internal combustion engine mechanically connected to the drive wheels, a frictional engagement element capable of connecting and disconnecting power transmission between the internal combustion engine and the motor, and that is controlled to transmit driving force at least in a first driving mode in which the internal combustion engine is driven and to disconnect the driving force in a second driving mode in which the vehicle runs only on the power of the motor, and a controller that controls the internal combustion engine, the motor, and the frictional engagement element.

In order to realize the above idea, the control method includes a target driving force calculation process in which the controller calculates a target driving force based on the driver's operation, a driving mode selection process in which the controller selects either a first driving mode or a second driving mode based on at least the target driving force calculated in the target driving force calculation process, a target torque calculation process in which the controller calculates a target torque for the internal combustion engine, or the motor, or the internal combustion engine and the motor, in accordance with the target driving force calculated in the target driving force calculation process and the driving mode selected in the driving mode selection process, and an internal combustion engine start process in which the controller starts the internal combustion engine in accordance with the selection of the first driving mode by the driving mode selection process during the second driving mode by controlling the internal combustion engine, the motor, and the frictional engagement element. The internal combustion engine starting process further includes a cranking process in which the controller engages the frictional engagement element to crank the internal combustion engine using the power of the motor and start fuel supply to the internal combustion engine; a first internal combustion engine torque increase process in which, after the cranking process is completed, the controller controls the internal combustion engine so that the torque of the internal combustion engine is maintained at an intermediate value lower than the target internal combustion engine torque calculated by the target torque calculation process; and a second internal combustion engine torque increase process in which, after the first internal combustion engine torque increase process is completed, the controller controls the internal combustion engine so that the torque of the internal combustion engine increases to the target internal combustion engine torque calculated by the target torque calculation process.

According to the present invention configured in this manner, the internal combustion engine torque is increased stepwise from the cranking process where maximum deceleration occurs to the state where the target internal combustion engine torque is being output, divided into a first internal combustion engine torque increase process and a second internal combustion engine torque increase process. This allows the vehicle acceleration to be changed stepwise, and the amount of acceleration that changes at one time can be kept within a range of change that does not cause discomfort to the driver. When transitioning from the second driving mode to the first driving mode with a high target driving force, the vehicle acceleration may temporarily drop to negative values due to cranking of the internal combustion engine. Even if the vehicle acceleration drops to negative values and then returns to the original acceleration, the driver will not feel uncomfortable.

In one aspect of the present invention , when the selection is changed from the second driving mode to the first driving mode in the driving mode selection process, the controller controls the internal combustion engine so that the torque of the internal combustion engine increases to the target internal combustion engine torque without performing the first internal combustion engine torque increase process after the cranking process in response to the target driving force calculated in the target driving force calculation process increasing by a predetermined amount or more, and controls the internal combustion engine so that the first internal combustion engine torque increase process is performed after the cranking process to thereby execute the second internal combustion engine torque increase process in response to the target driving force calculated in the target driving force calculation process not increasing by a predetermined amount or more.

As a result, for example, if the driver presses the accelerator pedal harder and the target driving force increases significantly, it is determined that the vehicle's driving force is required to quickly follow the target driving force, and a large sudden change in acceleration is permitted, giving priority to the vehicle's driving force responsively achieving the target driving force. In this case, because the driver is pressing the accelerator pedal harder, the driver is less likely to feel uncomfortable even if there is a large sudden change in acceleration.

In one aspect of the present invention , when the amount of change in the target driving force becomes equal to or greater than a predetermined value after the start of the internal combustion engine starting process, the controller controls the internal combustion engine so that the torque of the internal combustion engine increases to the target internal combustion engine torque after the cranking process is completed without performing the first internal combustion engine torque increase process.

As a result, even if the decision to start the internal combustion engine is made due to a system request, such as a low battery level, and the driving mode is being switched, if the driver presses the accelerator harder, causing a large change in the target driving force due to the driver's request, a large sudden change in acceleration is permitted, and priority is given to ensuring that the vehicle's driving force responsively achieves the target driving force. Because the driver is requesting acceleration, the driver is unlikely to feel uncomfortable even if there is a large sudden change in acceleration.

In one aspect of the present invention, the controller further has a mode switching process in which at least a sports mode is selected and not selected based on a driver's operation, and if the sports mode is selected at the start of the internal combustion engine starting process, the controller controls the internal combustion engine in the internal combustion engine starting process so that the torque of the internal combustion engine increases to the target internal combustion engine torque after completion of the cranking process without performing the first internal combustion engine torque increasing process.

As a result, when driving in sports mode, where a fast response is required, acceleration is allowed to change suddenly and significantly, regardless of the amount of change in the target driving force based on the driver's request, and priority is given to ensuring that the vehicle's driving force responsively achieves the target driving force. Because the driver has selected sports mode, any discomfort felt by the driver due to a sudden, large change in acceleration is tolerated.

The controller may have a mode switching process for switching at least between selection and non-selection of the sports mode based on the driver's operation, and if the sports mode is selected at the start of the internal combustion engine starting process, the controller may control the internal combustion engine so that the period of the first internal combustion engine torque increase process is shorter than when the sports mode is not selected.

As a result, when driving in sports mode, where a fast response is required, it is possible to achieve a target driving force with better response than in normal mode, where sports mode is not selected, while minimizing the amount of change in vehicle acceleration.

Furthermore, in the first internal combustion engine torque increase process, the controller may control the internal combustion engine to set the torque of the internal combustion engine so that a difference between a minimum vehicle acceleration during the cranking process and a maximum vehicle acceleration during the first internal combustion engine torque increase process is within 0.02 G , and a difference between vehicle acceleration during the first internal combustion engine torque increase process and vehicle acceleration during the second internal combustion engine torque increase process is within 0.02 G.

As a result, the change in acceleration from the cranking process to the first internal combustion engine torque increase process, and the change in acceleration from the first internal combustion engine torque increase process to the second internal combustion engine torque increase process, can be made into vehicle acceleration change amounts that are not felt by humans, thereby reliably preventing any discomfort felt by the driver.

In the first internal combustion engine torque increase process, if the controller detects that the vehicle jerk is equal to or lower than a predetermined value, the controller may control the vehicle to end the retention of the internal combustion engine torque and transition to the second internal combustion engine torque increase process.

This allows the target driving force to be achieved quickly while preventing the driver from feeling uneasy. Note that "jerk" is the rate of change (or time derivative) of the vehicle's acceleration. If the jerk is small, the driver is less likely to feel changes in the vehicle's longitudinal acceleration.

In the target driving force calculation process, the controller may further control the internal combustion engine to calculate the target driving force of the vehicle based on the gear position and the vehicle speed.

This allows the controller to more accurately calculate the target driving force, ensuring that any single change in vehicle acceleration is kept within a range that does not cause discomfort to the driver.

The internal combustion engine starting process may include a motor torque reduction process in which the controller controls the motor so that the output torque of the motor is reduced by a predetermined amount before the cranking process.

Before starting cranking of the internal combustion engine using the motor, control is performed to reduce the motor's output torque by a predetermined amount. In other words, before starting the internal combustion engine, control is performed to reduce the motor's output torque by a predetermined amount, thereby reducing the vehicle's forward acceleration by a predetermined amount in advance. The amount of reduction in acceleration is kept within a range in which the change in acceleration does not cause the driver to feel uncomfortable.

Then, the internal combustion engine is cranked using the motor's output torque. At that time, even if the acceleration in the vehicle's forward direction decreases to a deceleration corresponding to the shortage of the motor's output torque, the change in acceleration can be reduced because the acceleration has already been reduced. In other words, the amount of reduction in acceleration at this time falls within a range in which the change in acceleration does not cause the driver to feel uncomfortable. This makes it possible to prevent the driver from feeling uncomfortable as if the vehicle is suddenly being dragged backwards when the internal combustion engine is started following a switch from the second driving mode to the first driving mode.

The present invention relates to
A motor mounted on a vehicle and configured to drive a drive wheel of the vehicle;
an internal combustion engine mechanically connected to drive wheels of the vehicle;
a frictional fastening element that is disposed between the internal combustion engine and the motor and that switches between connection and disconnection to transmit and disconnect a driving force;
an accelerator opening sensor that detects an accelerator opening;
a controller electrically connected to the motor, the internal combustion engine, the frictional engagement element, and the accelerator position sensor;
It is a powertrain system equipped with.

The controller includes:
a target driving force calculation unit that calculates a target driving force of the vehicle based on at least the accelerator opening degree;
a driving mode selection unit that selects a driving mode of the vehicle from a first driving mode in which the frictional engagement elements are set to an engaged state and the vehicle is driven using at least the torque of the internal combustion engine, and a second driving mode in which the frictional engagement elements are set to a released state and the vehicle is driven using the torque of the motor without using the torque of the internal combustion engine;
a target torque calculation unit that calculates a target torque of the internal combustion engine, or the motor, or the internal combustion engine and the motor, in accordance with at least the target driving force calculated by the target driving force calculation unit and the driving mode selected by the driving mode selection unit;
an internal combustion engine control unit that controls the internal combustion engine so as to output the target internal combustion engine torque calculated by the target torque calculation unit;
a frictional engagement element control unit for controlling an engagement pressure of the frictional engagement element;
Equipped with
The internal combustion engine control unit further
by increasing the engagement pressure of the frictional engagement element by the frictional engagement element control unit in response to switching from the second driving mode to the first driving mode, cranking the internal combustion engine using the power of the motor and starting fuel supply to the internal combustion engine;
After the cranking is completed, an output torque of the internal combustion engine is maintained at an intermediate value lower than the target internal combustion engine torque calculated by the target torque calculation unit;
In response to the establishment of a release condition for the holding of the intermediate value, an output torque of the internal combustion engine is increased to the target internal combustion engine torque calculated by the target torque calculation unit ;
The internal combustion engine control unit further
When the selection is changed from the second driving mode to the first driving mode,
In response to the target driving force calculated by the target driving force calculation unit increasing by a predetermined amount or more, after the completion of the cranking, the internal combustion engine is controlled so that the output torque of the internal combustion engine is increased to the target internal combustion engine torque without maintaining the output torque of the internal combustion engine at an intermediate value lower than the target internal combustion engine torque;
In response to the target driving force calculated by the target driving force calculation unit not increasing by more than a predetermined amount, after completion of the cranking, the output torque of the internal combustion engine is maintained at an intermediate value lower than the target internal combustion engine torque, and in response to the establishment of a condition for releasing the maintenance at the intermediate value, the output torque of the internal combustion engine is increased to the target internal combustion engine torque .

According to the present invention configured in this way, the internal combustion engine torque from the occurrence of maximum deceleration to the state where the target internal combustion engine torque is being output is first held at an intermediate value lower than the target torque, and then increased to the value of the target torque. This allows the vehicle acceleration to be changed in stages, and the amount of change in the vehicle acceleration at one time can be kept within a range that does not cause discomfort to the driver.

The target driving force calculation unit may be further configured to calculate the target driving force according to the speed of the vehicle and the gear stage of a transmission disposed between the motor and the drive wheels.

This allows the target driving force to be calculated more accurately, ensuring that changes in vehicle acceleration are kept within a range that does not cause discomfort to the driver.

The powertrain control method and system of the present invention can prevent the driver from feeling uncomfortable due to the vehicle shock that occurs when the internal combustion engine is started while the vehicle is running on the motor alone, in a hybrid vehicle equipped with a frictional fastening element that switches between connecting and disconnecting the driving force between the internal combustion engine and the motor, without increasing the size of the motor.

1 is a schematic configuration diagram of a hybrid vehicle to which a powertrain control method and system according to an embodiment of the present invention is applied. 1 is a block diagram showing an electrical configuration of a hybrid vehicle to which a powertrain control method and system according to an embodiment of the present invention is applied; FIG. 4 is a characteristic diagram showing characteristics of a motor used in the embodiment of the present invention. FIG. 4 is a diagram showing an example of an acceleration characteristic map for each vehicle speed and gear position according to the present embodiment. 4 is a flowchart showing a driving force setting control for a hybrid vehicle according to an embodiment of the present invention. 4 is a flowchart showing an internal combustion engine torque setting control according to an embodiment of the present invention. 5 is a flowchart showing motor torque setting control according to an embodiment of the present invention. 4 is a flowchart illustrating a frictional engagement element control according to an embodiment of the present invention. 4 shows an example of a time chart when powertrain control is executed according to the embodiment of the present invention. 5 shows an example of a time chart when powertrain control is executed according to a second embodiment of the present invention. 4 shows an example of a time chart when powertrain control is executed according to the conventional technique or according to response-oriented control.

Hereinafter, a powertrain control method and system according to an embodiment of the present invention will be described with reference to the accompanying drawings.

<Overall system configuration>
First, the configuration of a hybrid vehicle will be described. Fig. 1 is an overall system diagram showing a powertrain system 1 of a hybrid vehicle to which a powertrain control method of an embodiment is applied. The powertrain system 1 includes an internal combustion engine 2, a motor 3, a first frictional engagement element CL1, and a controller 10.

The internal combustion engine 2 is, for example, a gasoline internal combustion engine, and the valve opening of the throttle valve and the like are controlled based on commands from the controller 10. The internal combustion engine 2 drives the drive wheels 7 of the vehicle.

Although not shown, the motor 3 is, for example, a synchronous motor generator with a permanent magnet embedded in the rotor and a stator coil wound around the stator, and is controlled by applying a three-phase AC current generated by the inverter 5 based on a control command from the controller 10. This motor 3 can operate as an electric motor that receives power from the battery 6 and drives it to rotate, or when the rotor is rotating due to an external force, it can function as a generator that generates an electromotive force at both ends of the stator coil and charge the battery 6. The rotor of this motor 3 is directly or indirectly connected to the input shaft of the automatic transmission 4. The motor 3 drives the drive wheels 7.

The first frictional engagement element CL1 connects the output shaft of the internal combustion engine 2 and the rotating shaft of the motor 3. The first frictional engagement element CL1 connects and disconnects the output shaft of the internal combustion engine 2 and the rotating shaft of the motor 3. This first frictional engagement element CL1 allows the transmission and interruption of torque between the internal combustion engine 2 and the motor 3 to be switched on and off. For example, the first frictional engagement element CL1 is a clutch. The first frictional engagement element CL1 is configured as a dry multi-plate clutch whose transmission torque capacity can be changed by the controller 10 continuously or stepwise controlling the clutch hydraulic oil flow rate and clutch hydraulic pressure by an oil pump (not shown).

The automatic transmission 4 changes the speed of the power from the internal combustion engine 2 and/or the motor 3 and outputs it to the drive wheels 7. Although detailed illustration is omitted, the automatic transmission 4 is configured with multiple planetary gear mechanisms, multiple brake mechanisms, and multiple clutch mechanisms. Based on a gear shift command output by the controller 10 and selected according to the vehicle speed and/or the rotation speed of the internal combustion engine 2, the automatic transmission 4 activates/deactivates the multiple brake mechanisms and/or engages/disengages the multiple clutch mechanisms. By switching the power transmission path configured to include the planetary gear mechanism, the automatic transmission 4 achieves the specified gear shift. The automatic transmission 4 is, for example, a transmission with six forward speeds and one reverse speed.

The automatic transmission 4 shown in FIG. 1 is equipped with a second frictional engagement element CL2. The second frictional engagement element CL2 collectively refers to multiple clutch mechanisms. In other words, the second frictional engagement element CL2 refers to a clutch mechanism that is in an engaged state when the automatic transmission 4 achieves a specified gear shift stage. When the second frictional engagement element CL2 is released while the hybrid vehicle is running, the automatic transmission 4 cuts off the transmission of torque between the upstream side (the internal combustion engine 2 and the motor 3) and the downstream side (the drive wheels 7).

The second frictional engagement element CL2, i.e., the multiple clutch mechanisms of the automatic transmission 4, are each configured as a dry multi-plate clutch whose transmission torque capacity can be changed by continuously or stepwise adjusting the clutch hydraulic oil flow rate and clutch hydraulic pressure supplied to the clutch mechanism.

The powertrain system 1 has an "EV mode" in which the vehicle runs using only the power of the motor 3, and an "HEV mode" in which the vehicle runs using at least the power of the internal combustion engine 2. The EV mode corresponds to the second driving mode, and the HEV mode corresponds to the first driving mode.

In "EV mode," the first frictional engagement element CL1 is disengaged and torque transmission between the internal combustion engine 2 and the motor 3 is cut off. This allows the vehicle to run using only the power of the motor 3, without using the power of the internal combustion engine 2.

In "HEV mode", the first frictional engagement element CL1 is engaged and torque is transmitted between the internal combustion engine 2 and the motor 3. This allows the vehicle to run using at least the power of the internal combustion engine 2. In the HEV mode, the hybrid vehicle of this embodiment runs using only the power of the internal combustion engine 2. Note that the hybrid vehicle may also be configured to run using the power of both the internal combustion engine 2 and the motor 3 in the HEV mode.

Motor 3 is also used as a starter motor for internal combustion engine 2 for cranking when starting the internal combustion engine 2, as will be described in detail later.

<Electrical configuration>
Next, FIG. 2 is a block diagram showing an electrical configuration of the powertrain system 1 according to the embodiment of the present invention.

The controller 10 is a well-known microcomputer-based controller, and is configured as a computer having one or more processors 10a (typically a CPU), various programs interpreted and executed on the processor (including basic control programs such as an OS, and application programs that are started on the OS and realize specific functions), and memory 10b such as a ROM or RAM for storing programs and various data. The controller 10 functions as a means for executing the control method of the present invention.

The controller 10 receives a signal from an internal combustion engine speed sensor SN1 that detects the speed of the internal combustion engine 2, a signal from a motor speed sensor SN2 that detects the speed of the motor 3, a signal from an accelerator opening sensor SN3 that detects the accelerator opening corresponding to the amount of depression of the accelerator pedal by the driver, a signal from a vehicle speed sensor SN4 that detects the vehicle speed, a signal from an acceleration sensor SN5 that detects the acceleration in the forward and backward directions of the vehicle, a signal from an SOC sensor SN6 that detects the SOC (State of Charge) indicating the charging state of the battery 6, and a signal from a mode sensor SN7 that detects the driving mode selected by the driver. The "driving mode" includes a sports mode and a normal mode. The driver can switch between the selection of the sports mode and non-selection (i.e., the selection of the normal mode) by operating a switch not shown. When the driver selects the sports mode, the controller 10 controls the internal combustion engine 2, the motor 3, and/or the automatic transmission 4, for example, to increase the vehicle's responsiveness to the driver's accelerator pedal depression operation.

Furthermore, the controller 10 is configured to output control signals to the internal combustion engine 2, the automatic transmission 4, the inverter 5, and the first frictional engagement element CL1. For example, the controller 10 performs control to adjust the ignition timing, fuel injection timing, and fuel injection amount of the internal combustion engine 2, control to adjust the rotation speed and torque of the motor 3, and control to switch the first frictional engagement element CL1 between on and off. In reality, the controller 10 controls the ignition plug, fuel injection valve, throttle valve, etc. of the internal combustion engine 2, controls the motor 3 via the inverter 5, and controls the first frictional engagement element CL1 via a hydraulic control circuit.

<Powertrain system control>
Next, the contents of the control performed by the controller 10 in the embodiment of the present invention will be described. In this embodiment, the controller 10 performs control for starting the internal combustion engine 2 (internal combustion engine start control) when switching from a "second driving mode" (hereinafter referred to as EV mode) in which the hybrid vehicle is driven using the torque of the motor 3 to a "first driving mode" (hereinafter referred to as HEV mode) in which the hybrid vehicle is driven using at least the torque of the internal combustion engine 2. In this case, the controller 10 performs the internal combustion engine start control by controlling the internal combustion engine 2, the motor 3, and the first frictional engagement element CL1.

First, an overview of the internal combustion engine start control according to this embodiment will be described. The internal combustion engine start control can be divided into a first phase from a start request for the internal combustion engine 2, starting the internal combustion engine 2, and completing the start, and a second phase after the start of the internal combustion engine 2 is completed. The second phase is a phase that is performed when the forward acceleration decreases in the first phase, and is a phase from the completion of the start of the internal combustion engine 2 until the forward acceleration returns to the acceleration before the start of the internal combustion engine 2. If the forward acceleration does not decrease in the first phase, the second phase is not performed. Note that "the forward acceleration does not decrease in the first phase" includes a case where the acceleration change is to an extent that does not cause the driver to feel uncomfortable, as will be described later.

(First Phase)
As described above, when switching from the EV mode to the HEV mode, a relatively large deceleration may occur in the hybrid vehicle. This is because, when switching from the EV mode to the HEV mode while the hybrid vehicle is traveling, the first frictional engagement element CL1 is engaged and the torque of the motor 3 is transmitted to the internal combustion engine 2 to start the internal combustion engine 2 (i.e., the motor 3 performs cranking to start the internal combustion engine 2), but the motor 3 may not be able to generate a sufficient torque (torque including losses in the transmission, etc.; the same applies below) required to start the internal combustion engine 2. In this case, the kinetic energy of the traveling hybrid vehicle is used to start the internal combustion engine 2. As a result, in the hybrid vehicle, the acceleration in the traveling direction is reduced to a deceleration corresponding to the shortage of the output torque of the motor 3 relative to the torque required to start the internal combustion engine 2.

If the acceleration in the travel direction were to decrease significantly all at once, the driver would feel as if he or she were being pulled backwards, which could cause the driver to feel uncomfortable. In this embodiment, in the first phase of switching from EV mode to HEV mode, the controller 10 performs control to reduce the output torque of the motor 3 by a predetermined amount, and then transitions the first frictional engagement element CL1 from a released state to an engaged state, and cranks the internal combustion engine 2 using the motor 3 to start the internal combustion engine 2. In other words, in this embodiment, the controller 10 reduces the output torque of the motor 3 by a predetermined amount before starting the internal combustion engine 2 when switching from EV mode to HEV mode.

This allows the travel direction acceleration of the hybrid vehicle to be reduced in advance by a predetermined amount by reducing the output torque of the motor 3 before starting the internal combustion engine 2 to switch the driving mode. As a result, even if the motor 3 cannot generate sufficient torque required to start the internal combustion engine 2, it is possible to reduce the change in acceleration when the travel direction acceleration decreases to a deceleration corresponding to the shortfall in the output torque of the motor 3. This makes it possible to prevent the driver from feeling uncomfortable as if the hybrid vehicle is suddenly being dragged backwards when the internal combustion engine 2 is started in response to a switch from EV mode to HEV mode.

On the other hand, in this embodiment, even when switching from EV mode to HEV mode, if there is a driver operation related to the movement of the hybrid vehicle (typically, if the change in the accelerator opening corresponding to the driver's operation of the accelerator pedal is equal to or greater than a predetermined amount), the controller 10 does not perform control to reduce the output torque of the motor 3 by a predetermined amount as described above. In this case, the controller 10 transitions the first frictional engagement element CL1 from the released state to the engaged state without reducing the output torque of the motor 3, and cranks the internal combustion engine 2 by the motor 3 to start the internal combustion engine 2. This is because the internal combustion engine 2 is started quickly in order to prioritize responsiveness to the driver's operation over suppressing the acceleration change as described above. In addition, since the acceleration change occurs due to the driver's operation, the driver is unlikely to feel uncomfortable even if the acceleration change that occurs all at once is relatively large.

In this embodiment, even when switching from the EV mode to the HEV mode, if the change in acceleration when the acceleration in the travel direction decreases to the deceleration corresponding to the shortage of the output torque of the motor 3 is equal to or less than a predetermined value (for example, a change in acceleration that does not cause the driver to feel uncomfortable), the controller 10 does not perform control to reduce the output torque of the motor 3. That is, even in this case, the controller 10 transitions the first frictional engagement element CL1 from the released state to the engaged state without reducing the output torque of the motor 3, and cranks the internal combustion engine 2 by the motor 3 to start the internal combustion engine 2. For example, when the motor rotation speed is low and the motor 3 is in a state where it can generate almost maximum torque, and when the motor 3 alone can output the torque required for cranking the internal combustion engine 2 with the auxiliary equipment such as the air conditioner in a non-operating state, the controller 10 cranks the internal combustion engine 2 by the motor 3 without reducing the output torque of the motor 3 to start the internal combustion engine 2. In this case, the output torque of the motor 3 is not insufficient, so the acceleration in the travel direction does not decrease, and the driver does not feel uncomfortable.

In this embodiment, when a request to switch from EV mode to HEV mode is made, the controller 10 first controls the second frictional engagement element CL2 to transition from an engaged state to a slip state, both in cases where the output torque of the motor 3 is reduced in advance and in cases where it is not. The reason why the second frictional engagement element CL2 is put into a slip state in this way is that when starting the internal combustion engine 2, the kinetic energy of the traveling hybrid vehicle is transferred to the internal combustion engine side and used to start the internal combustion engine 2, and a decrease in the acceleration in the traveling direction is suppressed as much as possible.

By setting the second frictional engagement element CL2 to a completely released state, it is possible to reliably prevent the kinetic energy of the hybrid vehicle from being transmitted to the internal combustion engine 2. However, once the second frictional engagement element CL2 is set to a completely released state in this way, it takes time to switch the second frictional engagement element CL2 to an engaged state after the internal combustion engine 2 has finished starting, making it impossible to switch the driving mode quickly. Therefore, in this embodiment, when there is a request to switch from EV mode to HEV mode, the second frictional engagement element CL2 is set to a slip state. Note that the second frictional engagement element CL2 is fully engaged after the internal combustion engine 2 has finished starting.

However, even if the second frictional engagement element CL2 is set to a slip state, the inertia of the second frictional engagement element CL2 causes a decrease in the acceleration in the forward direction of the hybrid vehicle. Specifically, when a certain amount of torque is transmitted by the second frictional engagement element CL2 that is in a slip state rather than a completely released state, the kinetic energy of the hybrid vehicle is also used to increase the revolution speed of the planetary gears in the automatic transmission 4, and the acceleration in the forward direction decreases.

In contrast, in this embodiment, when switching from EV mode to HEV mode, the controller 10 reduces the output torque of the motor 3 by a predetermined amount before starting the internal combustion engine 2, thereby reducing the forward acceleration of the hybrid vehicle by a predetermined amount. As a result, even if the motor 3 cannot generate sufficient torque required to start the internal combustion engine 2 and increase the revolution speed of the planetary gears in the automatic transmission 4, it is possible to reduce the change in acceleration when the forward acceleration decreases to a deceleration equivalent to the shortfall in the output torque of the motor 3. This makes it possible to prevent the driver from feeling a strange sensation as if the hybrid vehicle is suddenly being dragged backwards when switching from EV mode to HEV mode.

(Second Phase)
In the first phase described above, if the traveling direction acceleration decreases, it is necessary to restore the traveling direction acceleration to the acceleration before the start of the internal combustion engine 2 after the start of the internal combustion engine 2 is completed. In this case, if the traveling direction acceleration increases significantly at once, the driver may feel a sense of jumping forward, which may cause the driver to feel uncomfortable. In this embodiment, the controller 10 controls the internal combustion engine 2 to hold at least the output torque at an intermediate value lower than the target internal combustion engine torque for a predetermined time in the second phase, and then increases the torque of the internal combustion engine 2 from the held intermediate value to the target internal combustion engine torque. That is, in this embodiment, the controller 10 increases the output torque of the internal combustion engine 2 in a stepwise manner after the internal combustion engine 2 is started when switching from the EV mode to the HEV mode.

This makes it possible to reduce the amount of acceleration that changes at one time when restoring the hybrid vehicle's travel direction acceleration, which was reduced due to the start of the internal combustion engine 2. This makes it possible to prevent the driver from feeling as if the hybrid vehicle is lurching forward after the start of the internal combustion engine 2 is complete.

On the other hand, in this embodiment, the controller 10 does not perform control to maintain the output torque of the internal combustion engine 2 at an intermediate value lower than the target in the second phase when there is a driver operation related to the movement of the hybrid vehicle (typically when the change in the accelerator opening corresponding to the driver's operation of the accelerator pedal is equal to or greater than a predetermined amount), as in the first phase. In this case, the controller 10 increases the output torque of the internal combustion engine 2 to the target internal combustion engine torque in one go. This is because responsiveness to the driver's operation is prioritized over suppression of acceleration changes as described above. Also, because the acceleration change occurs due to the driver's operation, the driver is unlikely to feel uncomfortable even if the acceleration change that occurs all at once is somewhat large.

Next, before explaining the internal combustion engine start control by the controller 10, the characteristics of the motor 3 and the method for calculating the target driving force of the hybrid vehicle will be explained with reference to the figures.

First, the characteristics of motor 3 will be described with reference to FIG. 3. In FIG. 3, the horizontal axis shows motor rotation speed, and the vertical axis shows motor torque. The solid line in FIG. 3 is a characteristic line showing the maximum torque of motor 3. The motor 3 used in this embodiment has a characteristic that the higher the rotation speed, the smaller the maximum torque that can be generated. In other words, motor 3 has a characteristic that the lower the rotation speed, the greater the maximum torque. In particular, motor 3 has a maximum torque that is generally greatest when the rotation speed is less than a predetermined value N1, and when the rotation speed is equal to or greater than the predetermined value N1, the maximum torque decreases as the rotation speed increases.

3 shows an example of an area in which the motor 3 operates when the hybrid vehicle is running in EV mode. The rotation speed of the motor 3 is approximately proportional to the vehicle speed of the hybrid vehicle. When the internal combustion engine 2 is requested to be started while the hybrid vehicle is running in EV mode, the torque of the motor 3 is used to start the internal combustion engine 2 as described above. As described above, the output torque of the motor 3 changes depending on the rotation speed of the motor 3. For example, when the rotation speed of the motor 3 is 1000 rpm, the output torque of the motor 3 is about 75 Nm. The torque obtained by subtracting the torque of the motor 3 used for running from the output torque of the motor 3 is the surplus torque of the motor 3, and this surplus torque is used to start the internal combustion engine 2. The arrow in FIG. 3 shows the magnitude of the surplus torque. When the rotation speed of the motor 3 is low, the surplus torque is large, and when the rotation speed of the motor 3 is high, the surplus torque is small. When the surplus torque is small, a torque shortage may occur in the first phase of starting the internal combustion engine 2 as described above.

Next, a method for calculating the target driving force of the vehicle will be described with reference to FIG. 4. FIG. 4 is a diagram showing an example of an acceleration characteristic map for each vehicle speed and gear position according to this embodiment. In each of FIGS. 4(A) to (C), the horizontal axis shows the accelerator opening, and the vertical axis shows the target acceleration.

Figure 4(A) shows an acceleration characteristic map to be applied at low speeds (e.g., a vehicle speed of 30 km/h), Figure 4(B) shows an acceleration characteristic map to be applied at medium speeds (e.g., a vehicle speed of 50 km/h), and Figure 4(C) shows an acceleration characteristic map to be applied at high speeds (e.g., a vehicle speed of 100 km/h). Graphs G11 to G16 shown in Figure 4(A) show acceleration characteristic maps to be applied to the first, second, third, fourth, fifth, and sixth gear stages, respectively, graphs G21 to G26 shown in Figure 4(B) show acceleration characteristic maps to be applied to the first, second, third, fourth, fifth, and sixth gear stages, respectively, and graphs G33 to G36 shown in Figure 5(C) show acceleration characteristic maps to be applied to the third, fourth, fifth, and sixth gear stages. As shown in Figures 4(A) to (C), in the acceleration characteristics map, the target acceleration is set to 0 when the accelerator opening is around 20%.

Note that Figure 4 shows acceleration characteristic maps applied at low, medium, and high speeds as an example, and in reality, acceleration characteristic maps applied to various other vehicle speeds are also prepared. Also, in Figure 4(C), the vehicle speed is relatively high, and the map applied to the low gears (1st and 2nd gears) at this vehicle speed is an exceptional one, so it is not shown.

As described below, the controller 10 uses the map in FIG. 4 to set a target acceleration based on the accelerator opening based on the detection signal of the accelerator opening sensor SN3 and the gear stage (i.e., the gear ratio) of the automatic transmission 4, and calculates a target driving force to achieve the target acceleration.

(Allowable Acceleration Change)
Here, the allowable acceleration change amount will be described. The allowable acceleration change amount means the maximum amount of acceleration change amount that does not make the driver feel uncomfortable during internal combustion engine start control. The allowable acceleration change amount is determined in advance based on the range of acceleration change amount that does not make the driver feel uncomfortable and the range of acceleration change amount required for the reliability of the hybrid vehicle. In this embodiment, for example, the allowable acceleration change amount is 0.02 G. If the acceleration change amount is 0.02 G or less, the driver is unlikely to feel uncomfortable.

The torque reduction of the motor 3 in the first phase described above reduces the torque of the motor 3 so that the acceleration change amount (in this case, the acceleration decrease amount) at the start of the internal combustion engine 2 does not exceed the allowable acceleration change amount. Therefore, in the first phase, the torque decrease amount of the motor 3 to be reduced before the start of the internal combustion engine 2 is determined based on the current acceleration of the hybrid vehicle, the estimated acceleration (i.e., the estimated deceleration) that is estimated to occur in the hybrid vehicle when the internal combustion engine start control is executed, and the allowable acceleration change amount. The estimated deceleration can be calculated by multiplying the torque balance obtained by subtracting the torque required to start the internal combustion engine 2 and the torque required to cancel the running resistance from the torque that the motor 3 can output, by a predetermined coefficient. This predetermined coefficient is determined based on the current gear stage of the automatic transmission 4, the tire diameter, the weight of the hybrid vehicle, etc. In this embodiment, for convenience, it is assumed that a torque balance of 10 Nm corresponds to an acceleration of 0.01 G of the hybrid vehicle. That is, for example, when the torque balance is -15 Nm, the estimated deceleration is -0.015 G. In addition, the controller 10 can determine the torque that the motor 3 can output based on the rotation speed of the motor 3 detected by the motor rotation speed sensor SN2 by referring to a map (prestored in the memory 10b of the controller 10) that shows the relationship between the rotation speed of the motor 3 and the torque that can be output. In addition, in this embodiment, for the sake of convenience, the torque required to start the internal combustion engine 2 is set to 90 Nm, and the torque required to cancel the running resistance is set to 10 Nm, but these values can be set appropriately depending on the configuration of the internal combustion engine 2 of the hybrid vehicle, the vehicle speed, etc.

The torque of the motor 3 is maintained in the second phase as described above by keeping the torque of the internal combustion engine 2 low so that the amount of acceleration change (in this case, the amount of acceleration increase) after the internal combustion engine 2 has completed starting does not exceed the allowable amount of acceleration change. The allowable amount of acceleration change in the second phase is the same as the allowable amount of acceleration change in the first phase. The allowable amount of acceleration change in the first phase and the allowable amount of acceleration change in the second phase can also be made different.

(Specific Configuration of Internal Combustion Engine Start Control)
Next, the internal combustion engine start control according to the embodiment of the present invention will be specifically described with reference to FIGS.

Figure 5 shows a flow for setting the driving force of a vehicle according to an embodiment of the present invention. First, when the driving force setting control shown in Figure 5 is started, in step S11, the controller 10 acquires various information about the vehicle, including information corresponding to the detection signals from the above-mentioned sensors SN1 to SN7. Then, the process proceeds to step S12.

In step S12, the controller 10 sets the target driving force of the vehicle based on the acceleration characteristics map of FIG. 4 described above. For example, when the hybrid vehicle is traveling at a speed of 60 km/h in third gear, the controller 10 sets the target driving force (acceleration) according to the accelerator opening based on the graph of G23 in FIG. 4(B). The process then proceeds to step S13.

In step S13, the controller 10 selects either the EV mode or the HEV mode based on the target driving force set in step S12. As an example, when the target driving force is large, the HEV mode is selected, and when the target driving force is small, the EV mode is selected.

If the EV mode is selected, the process proceeds to step S14. In step S14, the controller 10 determines the output torque of the motor 3. In this step, the controller 10 sets the output torque of the motor 3 to achieve the target driving force set in step S12.

In step S15, the controller 10 controls the motor 3 based on the output torque of the motor 3 set in step S14, and outputs the required torque.

If the HEV mode is selected, the process proceeds to step S16. In step S16, the controller 10 determines the output torque of the internal combustion engine 2. In this step, the controller 10 sets the output torque of the internal combustion engine 2 so that the hybrid vehicle meets the target driving force set in step S12.

In step S17, the controller 10 controls the throttle valve of the internal combustion engine 2 based on the output torque of the internal combustion engine 2 set in step S16, and outputs the required torque.

When step S15 or step S17 is completed, the process returns to the start. This flow is always executed while the vehicle is running.

Next, the driving mode switching control of the internal combustion engine 2, the motor 3, and the first frictional engagement element CL1 according to an embodiment of the present invention will be specifically described with reference to Figures 6, 7, and 8. Figure 6 is a flowchart showing the internal combustion engine torque setting control according to an embodiment of the present invention, which is executed in step S16 of Figure 5.

The internal combustion engine torque setting control is always executed while the vehicle is traveling. First, in step S21, the controller 10 determines the traveling mode. That is, it determines whether the internal combustion engine 2 is driven. If the vehicle is traveling in HEV mode, in other words, if the internal combustion engine 2 is driven, the output torque of the internal combustion engine 2 is set taking into account mechanical losses occurring in the automatic transmission 4, etc. (step S29), and the process proceeds to step S17 described above. If the vehicle is traveling in EV mode, in other words, if the internal combustion engine 2 is not driven, the vehicle is traveling only with the output torque of the motor 3. In this case, the process proceeds to step S22.

In step S22, the controller 10 determines whether or not there is a request to start the internal combustion engine. If there is no request to start the internal combustion engine (step S22: No), it is decided to continue running using only the motor 3, and the process returns to start without setting the output torque of the internal combustion engine 2. If there is a request to start the internal combustion engine (step S22: Yes), it is decided to start the internal combustion engine 2, and the process proceeds to step S23. In step S23, cranking of the internal combustion engine 2 is started by utilizing part of the output torque of the motor 3 along with engagement control of the first frictional engagement element CL1.

In the next step S24, the controller 10 determines the type of trigger for the internal combustion engine start request determined in step S22. Specifically, it is determined whether to prioritize suppression of vehicle shock or to prioritize responsiveness of internal combustion engine start. A specific example of prioritizing responsiveness of internal combustion engine start is described below.

When the target driving force of the vehicle set in Fig. 5 changes by a predetermined value or more, priority is given to responsiveness. For example, when the internal combustion engine is started by detecting that the value of the accelerator opening sensor SN3 has reached a predetermined value or more, the driver is depressing the accelerator pedal heavily, and it is determined that the internal combustion engine is started to increase the driving force responsively, and the starting responsiveness is prioritized. Furthermore, when the internal combustion engine is started by the driver's intention to manually change gears by operating a paddle switch (not shown) or a shift lever (not shown), it is determined that the driver is requesting quick acceleration/deceleration by changing gears, and the starting responsiveness is prioritized. In addition, when the internal combustion engine is started under the following conditions, the starting responsiveness may be prioritized.
- When the amount of brake operation or the amount of change in operation exceeds a certain value - When the steering amount of steering wheel operation exceeds a certain value - When the sports mode is selected when starting the internal combustion engine - When switching to the sports mode is performed before the start of the internal combustion engine is completed On the other hand, when the internal combustion engine is started due to a system request such as a low battery level based on the detection signal of the SOC sensor SN6, the controller 10 determines that the emphasis is on shock reduction.

If the controller 10 determines in step S24 that shock reduction is important, the process proceeds to step S25. If the controller 10 determines that response is important, the process proceeds to step S29 without proceeding to step S25. In this case, after cranking of the internal combustion engine 2 is completed, the controller 10 sets the torque of the internal combustion engine 2 to a value corresponding to the target vehicle driving force. The output torque of the internal combustion engine 2 increases, and the driving force of the vehicle quickly becomes the target vehicle driving force. However, this may cause the driver to feel uncomfortable.

In step S25, the controller 10 determines whether or not cranking of the internal combustion engine 2 has been completed. If cranking has not been completed (step S25: No), the controller 10 remains in step S25 until cranking is completed. If cranking has been completed (step S25: Yes), the controller 10 proceeds to step S26.

In step S26, it is determined whether or not a trigger for prioritizing responsiveness as described in step S24 (including a change in the target driving force of the vehicle by a predetermined value or more) has occurred during the internal combustion engine start process from the request to start the internal combustion engine 2 to the start of the internal combustion engine 2 and the completion of the start. For example, if the accelerator pedal is depressed further while cranking is being performed in steps S23 to S25, or if the accelerator pedal is depressed further during steps S27 or S28 described below (step S26: No), the process proceeds to step S29 in which the internal combustion engine torque is set to a value corresponding to the target driving force of the vehicle even during shock reduction-oriented internal combustion engine start control. The driving force of the vehicle quickly becomes the target driving force of the vehicle. If a trigger for prioritizing responsiveness has not occurred (step S26: Yes), the process proceeds to step S27.

In step S27, the controller 10 sets the internal combustion engine torque to an intermediate target value lower than the value corresponding to the vehicle target driving force. The intermediate target value is set so that the change in the acceleration in the traveling direction of the hybrid vehicle does not exceed the allowable acceleration change amount. More specifically, the difference between the vehicle acceleration α corresponding to this intermediate target value and the vehicle acceleration α1 immediately after the start of the internal combustion engine 2 is approximately 0.02 G or less, and the difference between the vehicle acceleration α corresponding to the intermediate target value and the vehicle acceleration α2 in a state in which the vehicle target driving force is satisfied is approximately 0.02 G or less. As described above, this is determined because the maximum allowable acceleration change amount that does not give the driver a sense of discomfort is 0.02 G. After the intermediate target value is set, the output torque of the internal combustion engine 2 increases and the vehicle acceleration becomes the intermediate target value. The change in the vehicle acceleration at this time does not exceed the allowable acceleration change amount. The process proceeds to step S28.

In step S28, the controller 10 determines whether a predetermined time has elapsed since the intermediate target value was set in step S27, the output torque of the internal combustion engine 2 increased, and the vehicle acceleration became the intermediate target value. If the predetermined time has not elapsed (step S28: No), the process returns to before step S26. If the predetermined time has elapsed (step S28: Yes), the process proceeds to step S29, where the internal combustion engine torque is set to a value corresponding to the vehicle target driving force. The output torque of the internal combustion engine 2 increases again, and the vehicle driving force becomes the vehicle target driving force. The amount of change in the vehicle acceleration at this time also does not exceed the allowable amount of acceleration change. The process returns to the start.

Steps S26 to S28 correspond to a first internal combustion engine torque increase process in which, after the cranking process is completed, the controller 10 maintains the torque of the internal combustion engine 2 at an intermediate value lower than the target internal combustion engine torque. Steps S28 to S29 correspond to a second internal combustion engine torque increase process in which the controller 10 increases the torque of the internal combustion engine 2 to the target internal combustion engine torque.

In addition, in step S28, the controller 10 may determine whether the jerk of the hybrid vehicle is less than a predetermined value. "Jerk" is the rate of change (or time derivative) of the acceleration of the vehicle. When the jerk becomes small, the driver is less likely to feel the change in the longitudinal acceleration of the vehicle.

Figure 7 is a flow chart showing the motor torque setting control according to an embodiment of the present invention, which is executed in step S14 of Figure 5. First, in step S31, the controller 10 determines the current driving mode. If the current driving mode is HEV mode (step S31: HEV mode), the vehicle is driven by the power of the internal combustion engine 2, so the process returns to start without setting the torque. Note that in this embodiment, the motor 3 does not output torque while the internal combustion engine 2 is running, but this is not the only case, and the motor 3 may output auxiliary torque depending on the target driving force of the vehicle and the current driving force of the internal combustion engine 2. If the current driving mode is EV mode (step S31: EV mode), the process proceeds to step S32.

In step S32, the controller 10 determines whether or not there is a request to start the internal combustion engine. If there is no request to start the internal combustion engine (step S32: No), the process proceeds to step 33, where the motor output torque is set to achieve the target driving force of the vehicle. The process then proceeds to step S15, where the controller 10 controls the motor 3 based on the set motor torque.

On the other hand, if there is a request to start the internal combustion engine in step S32 (step S32: Yes), the process proceeds to step S34.

In steps S34 and S35, the controller 10 calculates the surplus torque of the motor 3. As described above, the surplus torque refers to the torque obtained by subtracting the torque of the motor currently being used for driving from the torque that can be output by the motor 3. The torque that can be output by the motor 3 is determined according to the rotation speed of the output shaft of the motor 3, as shown in FIG. 3.

Next, in step S35, the controller 10 predicts and determines whether the vehicle acceleration change at the start of the internal combustion engine will be equal to or greater than a predetermined value. Specifically, it determines whether the value (i.e., the torque difference) obtained by subtracting the torque required to crank the internal combustion engine 2 from the margin torque calculated in step S34 is equal to or greater than a predetermined threshold value. The predetermined threshold value used here is determined from the torque corresponding to 0.02G, which is the maximum vehicle acceleration change that gives the driver a sense of discomfort. If it is determined that the predicted vehicle acceleration change is greater than 0.02G (step S35: No), in step S36, the controller 10 reduces the set torque of the motor 3 and returns to step S35 again. If it is determined in step S35 that the predicted vehicle acceleration change is less than 0.02G (step S35: Yes), the controller 10 proceeds to step S37. For example, if the estimated acceleration change associated with the cranking of the internal combustion engine 2 is 0.03G and the allowable acceleration change is 0.02G, the difference (i.e., the excess of the estimated acceleration change) is 0.01G. In this case, the torque corresponding to this difference of 0.01 G is 10 Nm, so the controller 10 reduces the output torque of the motor 3 by 10 Nm.

In step S37, the controller 10 sets the motor torque to the sum of the torque required to crank the internal combustion engine 2 and the torque used to run the vehicle. The process then proceeds to step S15 described above. In step S15, the controller 10 controls the motor 3 based on the set motor torque.

Figure 8 is a flowchart showing the control of the first frictional engagement element CL1 when starting the internal combustion engine according to an embodiment of the present invention. The first frictional engagement element CL1 basically switches the state of engagement of the driving force when transitioning from HEV mode to EV mode, or from EV mode to HEV mode. In this example, the flow of control in the case of transition from EV mode to HEV mode, which involves starting the internal combustion engine 2, is described.

First, in step S41, the controller 10 determines the current driving mode. If the current driving mode is the HEV mode (step S41: HEV mode), the internal combustion engine 2 is already running, so the process returns to START without controlling the first frictional engagement element CL1. If the current driving mode is the EV mode (step S41: EV mode), the process proceeds to step S42. In step S42, the controller 10 determines whether or not there is an internal combustion engine start request. If there is no internal combustion engine start request (step S42: No), it is decided to continue driving using only the motor 3, and the process returns to START without controlling the first frictional engagement element CL1. If there is an internal combustion engine start request (step S42: Yes), it is decided to start the internal combustion engine 2, and the process proceeds to step S43.

In step S43, the controller 10 increases the fastening force of the first frictional fastening element CL1 and transitions to a slip state in order to start transmitting driving force between the internal combustion engine 2 and the motor 3. At this stage, because the difference in rotation speed between the internal combustion engine 2 and the motor 3 is large, full fastening is not performed, and a slip state is entered to prevent the generation of large vehicle acceleration and damage to each component.

In step S44, the controller 10 determines whether or not ignition of the internal combustion engine 2 has been performed. If ignition of the internal combustion engine 2 has not been performed (step S44: No), the process does not proceed to the next step, and is returned to step S44 again. If ignition of the internal combustion engine 2 has been performed (step S44: Yes), the controller 10 controls the first frictional engagement element CL1 to transition from a slip state to a fully engaged state (step S45).

<Action and effect>
Next, the operation and effects of the powertrain system and the control method according to the embodiment of the present invention will be described.

Figure 9 shows an example of a time chart when control of a powertrain system according to an embodiment of the present invention is executed, and Figure 10 shows an example of a time chart when control of a powertrain system according to another embodiment of the present invention is executed. Furthermore, Figure 11 shows an example of a time chart when driving mode switching is performed by conventional technology. Figure 11 also corresponds to a time chart when control that emphasizes responsiveness is executed in control of a powertrain system according to an embodiment of the present invention.

The graphs in Figures 9, 10, and 11 show the changes over time in the following parameters:

Graph G40: internal combustion engine start request flag Graph G41: vehicle acceleration Graph G42: output torque of motor 3 Graph G43: torque (negative value) required to counteract running resistance
Graph G44: Torque (negative value) at the first frictional engagement element CL1 before the start of the internal combustion engine 2
Graph G45: Output torque of the internal combustion engine 2 after starting Graph G46: Torque balance (total value of G41 to G45)
Graph G50: internal combustion engine start request flag Graph G51: vehicle acceleration Graph G52: output torque of motor 3 Graph G53: torque (negative value) required to counteract running resistance
Graph G54: Torque (negative value) at the first frictional engagement element CL1 before the start of the internal combustion engine 2
Graph G55: Output torque of the internal combustion engine 2 after starting Graph G56: Torque balance (total value of G51 to G55)
Graph G57: Accelerator opening Graph G60: Internal combustion engine start request flag Graph G61: Vehicle acceleration Graph G62: Output torque of motor 3 Graph G63: Torque (negative value) required to counteract running resistance
Graph G64: Torque (negative value) at the first frictional engagement element CL1 before the start of the internal combustion engine 2
Graph G65: Output torque of the internal combustion engine 2 after starting Graph G66: Torque balance (total value of G61 to G65)
In the following description, the vehicle acceleration corresponding to a torque balance of 10 Nm is 0.01 G.

In the example of the conventional technology shown in Figure 11, from before time t1 when the vehicle is running in EV mode until after time t5 when the vehicle is running in HEV mode, the torque required to counteract the running resistance is constant at -10 Nm (see graph G63). Furthermore, before time t1, the output torque of the motor 3 is 25 Nm (see graph G62). Therefore, the torque balance is 15 Nm (see graph G66), and the acceleration of the hybrid vehicle corresponding to this torque balance is 0.015 G (see graph G61).

In the example of the conventional technology in FIG. 11, when it is determined at time t1 that there is a request to switch from EV mode to HEV mode (see graph G60), internal combustion engine startup control is started immediately from time t1. That is, as soon as engagement control of the first frictional engagement element CL1 is started (see graph G64), the torque of the motor 3 increases (see graph G63). The torque of the first frictional engagement element CL1 is the torque supplied to the internal combustion engine 2 before ignition, and corresponds to the torque required to start the internal combustion engine 2.

Then, between time t1 and time t3, the magnitude of the torque required to start the internal combustion engine 2 increases to 90 Nm (see graph G64. The torque required to start the internal combustion engine 2 is shown as a negative value, so it decreases on the graph). Between time t1 and time t2, the output torque of the motor 3 also increases in accordance with the increase in the torque required to start the internal combustion engine 2 (see graph G62), so the torque balance is kept constant at 15 Nm (see graph G66). That is, there is no change in the acceleration of the hybrid vehicle. However, after the output torque of the motor 3 reaches the maximum value of 85 Nm at time t2, the output torque of the motor 3 does not increase. Therefore, between time t2 and time t3, the torque balance decreases in accordance with the increase in the torque required to start the internal combustion engine 2 (see graph G66). Then, when the magnitude of the torque required to start the internal combustion engine 2 reaches the maximum value of 90 Nm at time t3, the torque balance becomes 85-10-90=-15 Nm (see graph G66). The acceleration of the hybrid vehicle corresponding to this torque balance is -0.015 G (see graph G61). Therefore, the amount of acceleration decrease from the acceleration of 0.015 G at time t1 when the internal combustion engine start control is initiated is 0.03 G. In other words, in the conventional technology illustrated in FIG. 11, the amount of decrease in the traveling direction acceleration of the hybrid vehicle during the internal combustion engine start control exceeds the allowable acceleration change amount of 0.02 G that does not cause the driver to feel uncomfortable, and therefore there is a possibility that the driver will feel uncomfortable.

Also, at time t4, after the cranking of the internal combustion engine 2 is completed, the controller 10 immediately sets the target torque of the internal combustion engine 2 toward the output torque for achieving the target driving force of the vehicle. The target torque of the internal combustion engine 2 is the torque required for the vehicle acceleration to return to the vehicle acceleration before the start of the internal combustion engine 2, and is 25 Nm, which corresponds to the output torque of the motor 3 at that time (see graphs G61, G62, and G65). The output torque of the internal combustion engine 2 increases to 25 Nm, and the output torque of the motor 3 gradually decreases to zero. Between time t4 and time t5, the torque balance changes from -15 Nm to 15 Nm (see graph G65). The acceleration of the vehicle corresponding to the torque balance of -15 Nm at time t4 is -0.015 G, and the acceleration of the vehicle corresponding to the torque balance of 15 Nm at time t5 is 0.015 G, and the increase in the acceleration in the traveling direction of the vehicle between time t4 and time t5 is 0.015-(-0.015)=0.03 G. That is, in the conventional technology illustrated in FIG. 11, the increase in the vehicle's acceleration in the forward direction after the internal combustion engine starts exceeds 0.02 G, which is the allowable acceleration change amount that does not cause the driver to feel uncomfortable, and this may cause the driver to feel uncomfortable.

On the other hand, even in this embodiment illustrated in FIG. 9, the torque required to counteract the running resistance from before time t1 when the vehicle is running in EV mode until after time t5 when the vehicle is running in HEV mode is constant at -10 Nm (see graph G43). Also, before time t1, the output torque of motor 3 is 25 Nm (see graph G42). Therefore, the torque balance before time t1 is 15 Nm (see graph G46), and the vehicle acceleration corresponding to this torque balance is 0.015 G (see graph G41).

In the example of this embodiment in FIG. 9, as in the example of the conventional technology shown in FIG. 11, it is determined that there is a request to switch from EV mode to HEV mode at time t1 (see graph G40). However, if the internal combustion engine start control is started immediately at time t1 as in the example of the conventional technology, the amount of decrease in the acceleration in the traveling direction of the hybrid vehicle during the internal combustion engine start control reaches 0.03 G, which may cause the driver to feel uncomfortable. Therefore, in the example of this embodiment in FIG. 9, the controller 10 reduces the output torque of the motor 3 by a predetermined amount between times t1 and t1' before executing the internal combustion engine start control. In the example of FIG. 9, the amount of acceleration that decreases due to cranking of the internal combustion engine 2 can be estimated to be the same as in the example of FIG. 11. The estimated acceleration decrease amount is 0.03 G and the allowable acceleration decrease amount is 0.02 G, so the difference (i.e., the excess of the estimated acceleration decrease amount) is 0.01 G. That is, the torque corresponding to this difference of 0.01 G is 10 Nm, so the controller 10 reduces the output torque of the motor 3 by 10 Nm between time t1 and t1' to 15 Nm (see G42). As a result, the torque balance at time t1' is 15-10=5 Nm, and the vehicle acceleration corresponding to this torque balance is 0.005 G (see graph G41).

After that, between time t1' and time t3, the magnitude of the torque required to start the internal combustion engine 2 increases to 90 Nm (see graph G44). Between time t1' and time t2, the output torque of the motor 3 also increases in accordance with the increase in the torque required to start the internal combustion engine 2 (see graph G42), so the torque balance is kept constant at 5 Nm (see graph G46). That is, there is no change in the acceleration of the hybrid vehicle. However, after the output torque of the motor 3 reaches a maximum value of 85 Nm at time t3, the output torque of the motor 3 does not increase. Therefore, between time t2 and time t3, the torque balance decreases in accordance with the increase in the torque required to start the internal combustion engine 2 (see graph G46). Then, when the magnitude of the torque required to start the internal combustion engine 2 reaches a maximum value of 90 Nm at time t3, the torque balance becomes 85-10-90=-15 Nm (see graph G46). The acceleration of the hybrid vehicle corresponding to this torque balance is -0.015 G (see graph G41). Therefore, the amount of acceleration reduction from the acceleration of 0.005 G at time t1' is 0.02 G. That is, in the example of this embodiment shown in FIG. 9, the amount of reduction in the acceleration in the traveling direction of the hybrid vehicle at one time is equal to or less than 0.02 G, which is the allowable acceleration reduction amount that does not cause the driver to feel uncomfortable, so the discomfort felt by the driver can be suppressed.

The amount of acceleration reduction between time t1 and time t1' is 0.01 G, which is less than the allowable amount of acceleration reduction of 0.02 G, so the discomfort felt by the driver during this deceleration can be reduced.

After time t3, the internal combustion engine 2 is ignited at time t4. After time t4, the controller 10 sets the target torque of the internal combustion engine 2 to a torque (i.e., an intermediate target value) that is lower than the output torque for achieving the target driving force of the vehicle. The original target torque of the internal combustion engine 2 is 25 Nm, and when the torque balance changes from -15 Nm to 15 Nm, the increase in the acceleration in the vehicle's forward direction becomes 0.015-(-0.015)=0.03 G, which exceeds the allowable acceleration change amount. The controller 10 sets the intermediate target value of the torque of the internal combustion engine 2 to 15 Nm. This intermediate target value is the torque at which the acceleration change amount becomes the largest without exceeding the allowable acceleration change amount of 0.02 G. The vehicle acceleration corresponding to a torque balance of -15 Nm is -0.015 G, and the vehicle acceleration corresponding to a torque balance of 5 Nm at time t4' is 0.005 G, so the increase in the vehicle's forward acceleration between time t4 and time t4' (i.e., the amount of increase at one time) is 0.015 - (-0.005) = 0.02 G. This prevents the driver from feeling uncomfortable.

For a predetermined period of time from time t4' to time t4", the controller 10 maintains the intermediate target value of the torque of the internal combustion engine 2 at 5 Nm. During this period, the jerk of the hybrid vehicle (i.e., the time derivative of the acceleration) falls below a predetermined threshold value.

When the predetermined time has elapsed, the controller 10 ends holding the intermediate target value of the torque of the internal combustion engine 2. The period from time t4 to t4" corresponds to the first internal combustion engine torque increase process.

After time t4", the controller 10 increases the torque of the internal combustion engine 2 once again (second internal combustion engine torque increase step). Specifically, the controller 10 sets the target torque of the internal combustion engine 2 to 25 Nm, which is the output torque for achieving the target driving force of the vehicle. Between time t4" and time t5, the torque balance changes from 5 Nm to 15 Nm (see graph G66). The vehicle acceleration corresponding to a torque balance of 5 Nm at time t4" is 0.005 G, and the vehicle acceleration corresponding to a torque balance of 15 Nm at time t5 is 0.015 G. The increase in the vehicle's forward acceleration between time t4" and time t5 (i.e., the amount of increase at one time) is 0.015 - 0.005 = 0.01 G, which is below the allowable acceleration change amount of 0.02 G that does not cause the driver to feel uncomfortable. This suppresses the driver from feeling uncomfortable.

Here, the predetermined time from time t4' to time t4" can be set to an appropriate length. If the predetermined time is too short, the change in acceleration from time t4 to time t4' and the change in acceleration from time t4" to time t5 will be continuous, and a single change in acceleration will essentially exceed the allowable amount of acceleration change, which may cause the driver to feel uncomfortable. On the other hand, if the predetermined time is too long, the driving force of the hybrid vehicle will remain below the target driving force for a long period of time, which may cause the driver to feel uncomfortable.

In addition, instead of waiting for a predetermined time from time t4' to time t4" to elapse, the controller 10 may determine that the jerk of the hybrid vehicle has fallen below a threshold based on the detection signal of the acceleration sensor SN5, and if the jerk falls below the threshold, set the target torque of the internal combustion engine 2 to an output torque for achieving the target driving force of the vehicle.

The period for holding the intermediate target value may also be adjusted based on both waiting for a predetermined time from time t4' to time t4" to elapse and the magnitude of the jerk of the hybrid vehicle based on the detection signal of acceleration sensor SN5. In other words, if the jerk falls below the threshold before the predetermined time has elapsed, holding of the intermediate target value is terminated and the target torque of internal combustion engine 2 is set to the output torque for achieving the target driving force of the vehicle. If the jerk does not fall below the threshold before the predetermined time has elapsed, the target torque of internal combustion engine 2 is set to the output torque for achieving the target driving force of the vehicle once the predetermined time has elapsed.

In contrast to the shock reduction-emphasis control illustrated in FIG. 9, the example in FIG. 11 omits the reduction in motor torque from time t1 to t1' in FIG. 9, and omits the holding of the intermediate target value from time t4' to time t4". The example in FIG. 11 corresponds to an example of responsiveness-emphasis control.

In addition, in the responsiveness-oriented control, rather than omitting to hold the intermediate target value from time t4' to time t4" (i.e., setting the holding time to zero), the holding time may be relatively short. In other words, the time for holding the intermediate target value from time t4' to time t4" is made shorter in the responsiveness-oriented control than in the shock reduction-oriented control. In this way, it is possible to both increase responsiveness and suppress the sense of discomfort felt by the driver.

The example embodiment in FIG. 10 shows a case where a responsiveness priority trigger (in this example, the accelerator operation amount is equal to or greater than a predetermined value) occurs during the internal combustion engine start process. In this example, an internal combustion engine start request occurs at time t1 (see graph G50), and the accelerator is depressed further while shock reduction start control is being performed from time t1 to t3, causing the responsiveness priority flag to be set at time t2' (see graph G57).

In this case, the controller 10 switches from shock reduction emphasis control to responsiveness priority control. However, in the example of FIG. 10, the timing of the control switch is after the torque of the motor 3 has already been reduced by the passage of time from t1 to t1', so responsiveness priority control is not performed before the cranking of the internal combustion engine 2 is completed, and is performed after the cranking of the internal combustion engine 2 is completed. Therefore, the time t1 to time t3 in FIG. 10 is the same as the time t1 to time t3 in FIG. 9.

After cranking is completed (time t4), a trigger that prioritizes responsiveness occurs (corresponding to step S26 in FIG. 6), so the controller 10 immediately increases the torque of the internal combustion engine 2 to the vehicle target driving force (time t5, see G55). This results in a change in vehicle acceleration of 0.03 G, but it is possible to prioritize satisfying the driver's responsiveness requirements. Time t4 to time t5 in FIG. 10 is substantially the same as time t4 to time t5 in FIG. 11.

Note that, unlike FIG. 10, if the timing of switching from shock reduction emphasis control to responsiveness priority control occurs before time t1' has elapsed, the controller 10 may immediately execute responsiveness priority control even before cranking of the internal combustion engine 2 is completed.

As described above, in this embodiment, when switching from EV mode to HEV mode, the controller 10 increases the output torque of the internal combustion engine 2 in two stages after cranking of the internal combustion engine 2 by the motor 3 is completed. Since the vehicle acceleration can be changed in stages, even if the vehicle driving force temporarily falls below the target driving force and then returns to the original target driving force, the change in acceleration can be kept within a range that does not cause the driver to feel uncomfortable. In other words, when the internal combustion engine 2 is started due to a change in driving mode, it is possible to prevent the driver from feeling uncomfortable as if the vehicle is suddenly jumping forward.

In addition, according to this embodiment, when the target driving force increases significantly due to the driver depressing the accelerator pedal, for example, the controller 10 does not gradually change the vehicle acceleration, but rather quickly increases the output torque to the target driving force after cranking of the internal combustion engine 2 is completed. This makes it possible to responsively achieve the target driving force when the driver requests that the internal combustion engine 2 be started quickly, and thus to appropriately meet the driver's request.

In addition, according to this embodiment, when switching from EV mode to HEV mode, the controller 10 reduces the output torque of the motor 3 by a predetermined amount, and then engages the first frictional engagement element CL1 and cranks the internal combustion engine 2 using the motor 3 to start the internal combustion engine 2. This makes it possible to reduce the vehicle's forward acceleration in advance, thereby reducing the sudden change in vehicle acceleration. In other words, it is possible to prevent the driver from feeling uncomfortable as if the vehicle is suddenly being dragged backwards when the internal combustion engine 2 is started due to switching from EV mode to HEV mode.

1 Powertrain System 1
2 internal combustion engine 3 motor CL1 first frictional fastening element 10 controller

Claims (10)

A motor mounted on a vehicle and configured to drive a drive wheel of the vehicle;
an internal combustion engine mechanically connected to the drive wheels;
a frictional engagement element capable of connecting and disconnecting power transmission between the internal combustion engine and the motor, the frictional engagement element being controlled to transmit a driving force at least in a first traveling mode in which the internal combustion engine is driven, and to disconnect the driving force in a second traveling mode in which the vehicle travels only by the power of the motor;
a controller that controls the internal combustion engine, the motor, and the frictional engagement element;
A method for controlling a powertrain comprising:
a target driving force calculation step in which the controller calculates a target driving force based on an operation of a driver;
a driving mode selection step in which the controller selects either a first driving mode or a second driving mode based on at least the target driving force calculated in the target driving force calculation step;
a target torque calculation step in which the controller calculates a target torque of the internal combustion engine, or the motor, or the internal combustion engine and the motor, in accordance with the target driving force calculated in the target driving force calculation step and the driving mode selected in the driving mode selection step;
an internal combustion engine starting step in which the controller starts the internal combustion engine in response to selection of the first traveling mode by the traveling mode selection step during the second traveling mode by controlling the internal combustion engine, the motor, and the frictional engagement element,
The internal combustion engine starting process further includes:
a cranking process in which the controller engages the frictional engagement element to crank the internal combustion engine using power of the motor and start fuel supply to the internal combustion engine;
a first internal combustion engine torque increasing step in which, after completion of the cranking step, the controller controls the internal combustion engine so that a torque of the internal combustion engine is maintained at an intermediate value lower than the target internal combustion engine torque calculated in the target torque calculating step;
a second internal combustion engine torque increasing step in which, after completion of the first internal combustion engine torque increasing step, the controller controls the internal combustion engine so that a torque of the internal combustion engine increases to the target internal combustion engine torque calculated in the target torque calculating step;
Equipped with
When the selection is changed from the second driving mode to the first driving mode in the driving mode selection step, the controller:
controlling the internal combustion engine so that the torque of the internal combustion engine increases to the target internal combustion engine torque without performing the first internal combustion engine torque increasing step after the cranking step in response to the target driving force calculated in the target driving force calculating step increasing by a predetermined amount or more;
a first internal combustion engine torque increasing step after the cranking step, and a second internal combustion engine torque increasing step after the cranking step, in response to the target driving force calculated in the target driving force calculation step not increasing by a predetermined amount or more. A motor mounted on a vehicle and configured to drive a drive wheel of the vehicle;
an internal combustion engine mechanically connected to the drive wheels;
a frictional engagement element capable of connecting and disconnecting power transmission between the internal combustion engine and the motor, the frictional engagement element being controlled to transmit a driving force at least in a first traveling mode in which the internal combustion engine is driven, and to disconnect the driving force in a second traveling mode in which the vehicle travels only by the power of the motor;
a controller that controls the internal combustion engine, the motor, and the frictional engagement element;
A method for controlling a powertrain comprising:
a target driving force calculation step in which the controller calculates a target driving force based on an operation of a driver;
a driving mode selection step in which the controller selects either a first driving mode or a second driving mode based on at least the target driving force calculated in the target driving force calculation step;
a target torque calculation step in which the controller calculates a target torque of the internal combustion engine, or the motor, or the internal combustion engine and the motor, in accordance with the target driving force calculated in the target driving force calculation step and the driving mode selected in the driving mode selection step;
an internal combustion engine starting step in which the controller controls the internal combustion engine, the motor, and the frictional engagement element to start the internal combustion engine in response to selection of the first traveling mode by the traveling mode selection step during the second traveling mode,
The internal combustion engine starting process further includes:
a cranking process in which the controller engages the frictional engagement element to crank the internal combustion engine using power of the motor and start fuel supply to the internal combustion engine;
a first internal combustion engine torque increasing step in which, after completion of the cranking step, the controller controls the internal combustion engine so that a torque of the internal combustion engine is maintained at an intermediate value lower than the target internal combustion engine torque calculated in the target torque calculating step;
a second internal combustion engine torque increasing step in which, after completion of the first internal combustion engine torque increasing step, the controller controls the internal combustion engine so that a torque of the internal combustion engine increases to the target internal combustion engine torque calculated in the target torque calculating step;
Equipped with
When an amount of change in the target driving force becomes equal to or greater than a predetermined value after the start of the internal combustion engine starting process,
The powertrain control method, wherein the controller controls the internal combustion engine so that a torque of the internal combustion engine increases to the target internal combustion engine torque after the cranking process is completed, without performing the first internal combustion engine torque increasing process. A motor mounted on a vehicle and configured to drive a drive wheel of the vehicle;
an internal combustion engine mechanically connected to the drive wheels;
a frictional engagement element capable of connecting and disconnecting power transmission between the internal combustion engine and the motor, the frictional engagement element being controlled to transmit a driving force at least in a first traveling mode in which the internal combustion engine is driven, and to disconnect the driving force in a second traveling mode in which the vehicle travels only by the power of the motor;
a controller that controls the internal combustion engine, the motor, and the frictional engagement element;
A method for controlling a powertrain comprising:
a target driving force calculation step in which the controller calculates a target driving force based on an operation of a driver;
a driving mode selection step in which the controller selects either a first driving mode or a second driving mode based on at least the target driving force calculated in the target driving force calculation step;
a target torque calculation step in which the controller calculates a target torque of the internal combustion engine, or the motor, or the internal combustion engine and the motor, in accordance with the target driving force calculated in the target driving force calculation step and the driving mode selected in the driving mode selection step;
an internal combustion engine starting step in which the controller controls the internal combustion engine, the motor, and the frictional engagement element to start the internal combustion engine in response to selection of the first traveling mode by the traveling mode selection step during the second traveling mode,
The internal combustion engine starting process further includes:
a cranking process in which the controller engages the frictional engagement element to crank the internal combustion engine using power of the motor and start fuel supply to the internal combustion engine;
a first internal combustion engine torque increasing step in which, after completion of the cranking step, the controller controls the internal combustion engine so that a torque of the internal combustion engine is maintained at an intermediate value lower than the target internal combustion engine torque calculated in the target torque calculating step;
a second internal combustion engine torque increasing step in which, after completion of the first internal combustion engine torque increasing step, the controller controls the internal combustion engine so that a torque of the internal combustion engine increases to the target internal combustion engine torque calculated in the target torque calculating step;
Equipped with
The controller has a mode switching step of switching at least between selection and non-selection of a sports mode based on an operation of a driver,
If the sports mode is selected at the start of the internal combustion engine starting process,
A powertrain control method, in which, in the internal combustion engine starting process, the controller controls the internal combustion engine so that the torque of the internal combustion engine increases to the target internal combustion engine torque after the cranking process is completed, without performing the first internal combustion engine torque increasing process. a mode switching step in which the controller switches between at least a sports mode selection and a non-selection based on an operation of a driver;
3. The powertrain control method according to claim 1, wherein when a sport mode is selected at the start of the internal combustion engine starting process, the controller makes the period of the first internal combustion engine torque increasing process shorter than when the sport mode is not selected. In the first internal combustion engine torque increasing step, the controller
5. A powertrain control method according to claim 1, further comprising the step of setting a torque of the internal combustion engine so that a difference between a minimum value of vehicle acceleration during the cranking process and a maximum value of vehicle acceleration during the first internal combustion engine torque increasing process is within 0.02 G, and a difference between a vehicle acceleration during the first internal combustion engine torque increasing process and a vehicle acceleration during the second internal combustion engine torque increasing process is within 0.02 G. 6. A powertrain control method according to claim 1, wherein, in the first internal combustion engine torque increasing process, when the controller detects that a jerk of vehicle acceleration has become equal to or lower than a predetermined value, the controller ends the holding of the internal combustion engine torque and transitions to the second internal combustion engine torque increasing process. The powertrain control method according to claim 1 , wherein in the target driving force calculation step, the controller further calculates the target driving force of the vehicle based on a gear position and a vehicle speed. 8. The powertrain control method according to claim 1, further comprising a motor torque reduction step of controlling the motor such that an output torque of the motor is reduced by a predetermined amount before the cranking step in the internal combustion engine starting step. A motor mounted on a vehicle and configured to drive a drive wheel of the vehicle;
an internal combustion engine mechanically connected to drive wheels of the vehicle;
a frictional fastening element that is disposed between the internal combustion engine and the motor and that switches between connection and disconnection to transmit and disconnect a driving force;
an accelerator opening sensor that detects an accelerator opening;
a controller electrically connected to the motor, the internal combustion engine, the frictional engagement element, and the accelerator position sensor;
A powertrain system comprising:
The controller includes:
a target driving force calculation unit that calculates a target driving force of the vehicle based on at least the accelerator opening degree;
a driving mode selection unit that selects a driving mode of the vehicle from a first driving mode in which the frictional engagement elements are set to an engaged state and the vehicle is driven using at least the torque of the internal combustion engine, and a second driving mode in which the frictional engagement elements are set to a released state and the vehicle is driven using the torque of the motor without using the torque of the internal combustion engine;
a target torque calculation unit that calculates a target torque of the internal combustion engine, or the motor, or the internal combustion engine and the motor, in accordance with at least the target driving force calculated by the target driving force calculation unit and the driving mode selected by the driving mode selection unit;
an internal combustion engine control unit that controls the internal combustion engine so that the internal combustion engine outputs the target internal combustion engine torque calculated by the target torque calculation unit;
a frictional engagement element control unit for controlling an engagement pressure of the frictional engagement element;
Equipped with
The internal combustion engine control unit further
by increasing the engagement pressure of the frictional engagement element by the frictional engagement element control unit in response to switching from the second driving mode to the first driving mode, cranking the internal combustion engine using the power of the motor and starting fuel supply to the internal combustion engine;
After the cranking is completed, an output torque of the internal combustion engine is maintained at an intermediate value lower than the target internal combustion engine torque calculated by the target torque calculation unit;
In response to the establishment of a release condition for the holding of the intermediate value, an output torque of the internal combustion engine is increased to the target internal combustion engine torque calculated by the target torque calculation unit ;
The internal combustion engine control unit further
When the selection is changed from the second driving mode to the first driving mode,
In response to the target driving force calculated by the target driving force calculation unit increasing by a predetermined amount or more, after the completion of the cranking, the internal combustion engine is controlled so that the output torque of the internal combustion engine is increased to the target internal combustion engine torque without maintaining the output torque of the internal combustion engine at an intermediate value lower than the target internal combustion engine torque;
a control unit for controlling the output torque of the internal combustion engine to be increased to the target internal combustion engine torque when a condition for releasing the holding of the intermediate value is satisfied, the ... 10. The powertrain system according to claim 9 , wherein the target driving force calculation unit further calculates the target driving force in accordance with a speed of the vehicle and a gear stage of a transmission disposed between the motor and the driving wheels.

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