Patent Description:
In hybrid vehicles, the engine is automatically stopped and automatically restarted based on a traveling state. In a controller for a hybrid vehicle disclosed in <CIT>, when a sufficient amount of electric power is available, only cranking by a motor is performed to start rotating the crankshaft and restart the engine. When a sufficient amount of electric power is not available, in addition to cranking by a motor, combustion is performed in a cylinder with the piston in a stopped state in the expansion stroke, and the combustion torque and the cranking torque are used to start rotating the crankshaft and restart the engine. In the following description, the cylinder with the piston in the stopped state in the expansion stroke is referred to as an "expansion stroke stopped cylinder.

In some hybrid vehicles, the clutch couples the engine to the motor by which cranking is performed, and the clutch is disengaged when the engine is in an automatically stopped state. In such a hybrid vehicle, restarting the engine using the above-described combustion torque and cranking torque may cause the following problem.

In some situations, variations in the response speed of the clutch may prevent cranking from being started by the timing of combustion in the expansion stroke stopped cylinder. The combustion torque generated by combustion in the expansion stroke stopped cylinder is small. Thus, when cranking cannot be started by the timing of combustion in the expansion stroke stopped cylinder, rotation of the crankshaft may not be able to be started, which may result in failure in the engine start, or the engine start may be delayed.

<CIT> relates to a 'Hybrid vehicle control apparatus'. <CIT> relates to a 'Control device for vehicle'.

The invention is defined in the appended independent claims.

In a controller for a hybrid vehicle according to an aspect of the present disclosure, the hybrid vehicle includes a motor arranged on a power transmission path between an engine and a wheel and includes a clutch arranged on a portion of the power transmission path between the engine and the motor. The controller is configured to switch between stopping operation of the engine with the clutch disengaged and operating the engine with the clutch engaged. The controller includes a restart control unit configured to select a start mode from multiple start modes and restart the engine in the selected start mode. The multiple start modes include a first start mode of commanding engagement of the clutch and starting combustion in the engine when the clutch starts transmitting torque and a second start mode of commanding engagement of the clutch and starting combustion in the engine after rotation of the engine is started by the torque transmitted from the motor through the clutch. The restart control unit is configured to, in a case in which the engine is restarted in the second start mode, measure a cranking start time from when engagement of the clutch is commanded to when transmission of the torque through the clutch is started, and only when measurement of the cranking start time has been completed after the vehicle is activated, restart the engine in the first start mode.

In a control method for a hybrid vehicle according to another aspect of the present disclosure, the hybrid vehicle includes a motor arranged on a power transmission path between an engine and a wheel and includes a clutch arranged on a portion of the power transmission path between the engine and the motor. The control method includes switching between stopping operation of the engine with the clutch disengaged and operating the engine with the clutch engaged. The control method also includes selecting a start mode from multiple start modes and restarting the engine in the selected start mode. The multiple start modes include a first start mode of commanding engagement of the clutch and starting combustion in the engine when the clutch starts transmitting torque and a second start mode of commanding engagement of the clutch and starting combustion in the engine after rotation of the engine is started by the torque transmitted from the motor through the clutch. The control method further includes, in a case in which the engine is restarted in the second start mode, measuring a cranking start time from when engagement of the clutch is commanded to when transmission of the torque through the clutch is started, and only when measurement of the cranking start time has been completed after the vehicle is activated, restarting the engine in the first start mode.

A controller and a control method for a hybrid vehicle according to a first embodiment will now be described with reference to <FIG>.

As shown in <FIG>, the hybrid vehicle includes an engine <NUM> that is a driving source for traveling. A shifting unit <NUM> is provided on a power transmission path of the hybrid vehicle from the engine <NUM> to left and right wheels <NUM>. The shifting unit <NUM> is coupled to the left and right wheels <NUM> by a differential apparatus <NUM> in a drivable manner.

The shifting unit <NUM> includes a clutch <NUM> and a motor generator <NUM> (M/G <NUM>). The M/G <NUM> is located on the power transmission path from the engine <NUM> to the wheels <NUM>. The clutch <NUM> is located on a portion of the power transmission path between the engine <NUM> and the M/G <NUM>. When supplied with hydraulic pressure, the clutch <NUM> becomes engaged to allow for power transmission between the engine <NUM> and the M/G <NUM>. When the supply of hydraulic pressure to the clutch <NUM> is stopped, the clutch <NUM> becomes disengaged to disconnect the power transmission between the engine <NUM> and the M/G <NUM>.

The M/G <NUM> is connected to an onboard power supply <NUM> by an inverter <NUM>. The M/G <NUM> functions as a motor that generates a drive force of the vehicle when powered by the onboard power supply <NUM> and also functions as a generator that generates electric power for charging the onboard power supply <NUM> when power is transmitted from the engine <NUM> or the wheels <NUM>. The electric power transmitted and received to and from the M/G <NUM> and the onboard power supply <NUM> is adjusted by the inverter <NUM>.

The shifting unit <NUM> also includes a torque converter <NUM> and a multi-speed automatic transmission <NUM>. The torque converter <NUM> is a fluid coupling that has a torque amplification function. The automatic transmission <NUM> switches the gear ratio in multiple stages by switching the gear stage. The automatic transmission <NUM> is located at a portion of the power transmission path between the M/G <NUM> and the differential apparatus <NUM>. The M/G <NUM> and the automatic transmission <NUM> are coupled to each other by the torque converter <NUM>. The torque converter <NUM> includes a lock-up clutch <NUM>. When supplied with hydraulic pressure, the lock-up clutch <NUM> becomes engaged to directly couple the M/G <NUM> to the automatic transmission <NUM>.

The shifting unit <NUM> further includes an oil pump <NUM> and a hydraulic pressure control unit <NUM>. The hydraulic pressure generated by the oil pump <NUM> is supplied by the hydraulic pressure control unit <NUM> to the clutch <NUM>, the torque converter <NUM>, the automatic transmission <NUM>, and the lock-up clutch <NUM>. The hydraulic pressure control unit <NUM> includes hydraulic circuits for the clutch <NUM>, the torque converter <NUM>, the automatic transmission <NUM>, and the lock-up clutch <NUM> and includes various types of hydraulic control valves for controlling the hydraulic pressures in these hydraulic circuits.

In addition, the hybrid vehicle includes a vehicle control unit <NUM>. The vehicle control unit <NUM> is an electronic control unit including a calculation processor that performs various types of calculation processes for travel control of the vehicle and a storage device that stores programs and data for control. The vehicle control unit <NUM> performs driving control of the engine <NUM> as one type of vehicle control. That is, the vehicle control unit <NUM> is also an engine controller. Further, the vehicle control unit <NUM> controls the inverter <NUM> and adjusts the amount of electric power transmitted and received to and from the M/G <NUM> and the onboard power supply <NUM> to perform torque control of the M/G <NUM>. The vehicle control unit <NUM> controls the hydraulic pressure control unit <NUM> to perform drive control of the clutch <NUM>, the lock-up clutch <NUM>, and the automatic transmission <NUM>. The vehicle control unit <NUM> receives various types of detection signals such as the vehicle speed and the depression amount of the accelerator pedal (accelerator operation amount).

As shown in <FIG>, the engine <NUM> includes a cylinder <NUM> in which air-fuel mixture is burned. For example, the engine <NUM> is a V6 engine with six cylinders <NUM>, only one of which is shown in <FIG>. Each cylinder <NUM> accommodates a piston <NUM> such that the piston <NUM> can reciprocate in the cylinder <NUM>. The piston <NUM> of each cylinder <NUM> is coupled to a crankshaft <NUM>, which is an output shaft of the engine <NUM>, by a connecting rod <NUM>. One end of the connecting rod <NUM> is pivotally coupled to the piston <NUM> by a piston pin 32A. The other end of the connecting rod <NUM> is pivotally coupled to the crankshaft <NUM> by a crank pin 32B. The connecting rod <NUM> and the crankshaft <NUM> configure a crank mechanism that converts reciprocating motion of the piston <NUM> into rotational motion of the crankshaft <NUM>. The engine <NUM> includes a crank angle sensor <NUM> that detects a rotation angle of the crankshaft <NUM>.

An intake passage <NUM>, into which intake air is drawn, is connected to each cylinder <NUM> via an intake valve <NUM>. An exhaust passage <NUM>, out of which exhaust gas is discharged, is connected to each cylinder <NUM> via an exhaust valve <NUM>. The intake passage <NUM> includes an airflow meter <NUM> and a throttle valve <NUM>. The airflow meter <NUM> detects an intake air flow rate GA, which is the flow rate of intake air flowing through the intake passage <NUM>. The throttle valve <NUM> adjusts the flow rate of intake air. Further, the engine <NUM> is provided with a fuel injection valve <NUM> in correspondence with each cylinder <NUM>. The fuel injection valve <NUM> injects fuel into the cylinder <NUM>. Each cylinder <NUM> includes an ignition device <NUM> that ignites, with spark discharge, air-fuel mixture of the intake air drawn in through the intake passage <NUM> and the fuel injected by the fuel injection valve <NUM>. The exhaust passage <NUM> includes a catalyst device <NUM> that purifies exhaust gas.

The above-described vehicle control unit <NUM> receives detection signals of the crank angle sensor <NUM> and the airflow meter <NUM>. Further, the vehicle control unit <NUM> calculates an engine speed NE from the detection signal of the crank angle sensor <NUM> as an interruption process executed whenever the crankshaft <NUM> is rotated by an angle corresponding to a given angle. The vehicle control unit <NUM> performs an open degree control of the throttle valve <NUM>, a fuel injection control of the fuel injection valve <NUM>, and an ignition control of the ignition device <NUM> to perform driving control of the engine <NUM>.

Further, the vehicle control unit <NUM> switches between a first travel mode of traveling by stopping the operation of the engine <NUM> and a second travel mode of traveling by operating the engine <NUM> depending on traveling situations, thereby intermittently driving the engine <NUM>. In the first travel mode, the vehicle travels using the power of the M/G <NUM> with the operation of the engine <NUM> stopped and the clutch <NUM> disengaged. In the second travel mode, the vehicle travels using the power of the engine <NUM> with the engine <NUM> operated and the clutch <NUM> engaged. In the second travel mode, travel assist with power driving of the M/G <NUM> and regenerative power generation with regenerative driving of the M/G <NUM> are performed depending on traveling situations of the vehicle. For example, the travel mode is switched based on a requested drive force of the vehicle obtained from the vehicle speed and the accelerator operation amount and based on a charge state of the onboard power supply <NUM>.

In the present embodiment, when switching from the second travel mode to the first travel mode, the vehicle control unit <NUM> increases the open degree of the throttle valve <NUM> immediately before the crankshaft <NUM> stops rotating. This causes the crankshaft <NUM> to stop rotating with the piston <NUM> located in the proximity of the intake bottom dead center in one of the cylinders <NUM> of the engine <NUM>. Thus, when the travel mode is switched from the first travel mode to the second travel mode, the engine <NUM> is started from a state in which the rotation of the crankshaft <NUM> is in a stopped state with the piston <NUM> located in the proximity of the intake bottom dead center in one of the cylinders <NUM> of the engine <NUM>. In the following description, the cylinder <NUM> with the piston <NUM> located in the proximity of the intake bottom dead center when the rotation of the crankshaft <NUM> is in the stopped state is referred to as an "intake bottom dead center stopped cylinder.

Further, the vehicle control unit <NUM> performs a restart control of the engine <NUM> when switching from the first travel mode to the second travel mode. The vehicle control unit <NUM>, which is a restart control unit, selects a start mode from multiple start modes including a first start mode and a second start mode and restarts the engine <NUM> in the selected start mode.

Restarting of the engine <NUM> in the first start mode will now be described with reference to <FIG>. In <FIG>, C3 indicates the position of the crank pin 32B in the intake bottom dead center stopped cylinder with reference to a rotation center axis O of the crankshaft <NUM>. In <FIG>, C2 indicates the position of the crank pin 32B of a cylinder that is burned one time before the intake bottom dead center stopped cylinder, and C1 indicates the position of the crank pin 32B of a cylinder that is burned two times before the intake bottom dead center stopped cylinder. When the rotation of the crankshaft <NUM> is in the stopped state, the piston <NUM> is located in the compression stroke in the cylinder that is burned one time before the intake bottom dead center stopped cylinder, and the piston <NUM> is located in the expansion stroke in the cylinder that is burned two times before the intake bottom dead center stopped cylinder. In the following description, the cylinder with the piston <NUM> located in the compression stroke when the rotation of the crankshaft <NUM> is in the stopped state is referred to as a "compression stroke stopped cylinder," and the cylinder with the piston <NUM> located in the expansion stroke when the rotation of the crankshaft <NUM> is in the stopped state is referred to as an "expansion stroke stopped cylinder.

In the first start mode, when the switching from the first travel mode to the second travel mode is requested, the transmission of torque from the M/G <NUM> through the clutch <NUM> to the crankshaft <NUM> (i.e., increase in clutch hydraulic pressure to start cranking) is commanded. In addition to this command, fuel is injected into the expansion stroke stopped cylinder. The fuel injection to the expansion stroke stopped cylinder is performed with the rotation of the crankshaft <NUM> in the stopped state before cranking is started. After the fuel injection, ignition is performed in the expansion stroke stopped cylinder at a timing on which cranking is started, and the rotation of the crankshaft <NUM> is started using the combustion torque generated in the expansion stroke stopped cylinder and the torque of the M/G <NUM> transmitted through the clutch <NUM>. Subsequently, fuel injection and ignition are performed in each cylinder <NUM> in accordance with a given sequence to restart the engine <NUM>. In the following description, the torque of the M/G <NUM> transmitted to the crankshaft <NUM> through the clutch <NUM> before the engine <NUM> starts is complete is referred to as a "cranking torque.

Restarting of the engine <NUM> in the second start mode will now be described with reference to <FIG>. In the second start mode, when the switching from the first travel mode to the second travel mode is requested, an increase in the clutch hydraulic pressure to start cranking is commanded. In the second start mode, the fuel injection to the expansion stroke stopped cylinder is not performed at this time, and the rotation of the crankshaft <NUM> is started using only the cranking torque. After the cranking is started, in the compression stroke stopped cylinder, fuel injection is performed before the piston <NUM> reaches the compression top dead center. Further, ignition is performed after the piston <NUM> passes through the compression top dead center. Subsequently, fuel injection and ignition are performed in each cylinder <NUM> in accordance with a given sequence to restart the engine <NUM>.

As described above, both in the first start mode and the second start mode, when the switching from the first travel mode to the second travel mode is requested, an increase in the clutch hydraulic pressure to start cranking is commanded. In the first start mode, the engine <NUM> is restarted by starting combustion in the expansion stroke stopped cylinder at the same time (or almost at the same time) as when cranking is started. In the second start mode, the engine <NUM> is restarted by starting combustion in the compression stroke stopped cylinder after cranking is started. As compared to the second start mode of starting rotation of the crankshaft <NUM> using only cranking torque, the cranking torque required for restarting the engine <NUM> is small in the first start mode of starting rotation of the crankshaft <NUM> using the cranking torque and the combustion torque generated in the expansion stroke stopped cylinder. During traveling in the first travel mode, room needs to be left to increase the torque of the M/G <NUM> by an amount corresponding to the cranking torque required for restarting the engine <NUM> such that the travel mode can be switched to the second travel mode. Thus, when the engine <NUM> is restarted in the first start mode, the traveling region where the vehicle can travel in the first travel mode is broader than when the engine <NUM> is restarted in the second start mode. However, restarting the engine <NUM> in the first start mode causes the following problem.

<FIG> shows changes in the clutch hydraulic pressure and engine speed when the engine <NUM> is restarted in the first start mode. At time t1, when the switching from the first travel mode to the second travel mode is requested, an increase in the clutch hydraulic pressure to start cranking is commanded. A hydraulic pressure P2 in <FIG> indicates a target value of the clutch hydraulic pressure during cranking. In the present embodiment, a hydraulic pressure P1, which is higher than the hydraulic pressure P2, is set as a command value of the clutch hydraulic pressure over a fixed period of time after the command of increasing the pressure is started. Then, the command value of the clutch hydraulic pressure is set to the hydraulic pressure P2, which is a target value. This shortens the time for the clutch hydraulic pressure to reach the hydraulic pressure P2.

As described above, in the first start mode, the rotation of the crankshaft <NUM> is started by performing ignition in the expansion stroke stopped cylinder at time t2, at which cranking is started by an increase in the clutch hydraulic pressure to a value that allows for the transmission of torque after time t1. Variations occur in the time from when an increase in the clutch hydraulic pressure is commanded to when cranking is started, that is, the time from when engagement of the clutch <NUM> is commanded to when torque can be transmitted through the clutch <NUM>. Particularly, this time is long when the temperature of oil is low and the viscosity of the oil is high. In such a case, cranking cannot be started by the timing of combustion in the expansion stroke stopped cylinder. The combustion torque generated by combustion in the expansion stroke stopped cylinder is small. Thus, when cranking cannot be started by the timing of combustion in the expansion stroke stopped cylinder, rotation of the crankshaft <NUM> may not be able to be started, which may result in failure in starting of the engine <NUM>, or starting of the engine <NUM> may be delayed. In the following description, the time from when engagement of the clutch <NUM> is commanded to when cranking is started is referred to as a "cranking start time TCR.

In the present embodiment, restarting of the engine <NUM> is controlled in the following manner.

<FIG> shows a flowchart of a start mode selection routine for selecting the start mode of the engine <NUM> when switching from the first travel mode to the second travel mode. The vehicle control unit <NUM> executes the processing of the routine when the switching from the first travel mode to the second travel mode is requested. When the routine is started, in step S100, the vehicle control unit <NUM> first determines whether a permission flag has been set. The permission flag indicates whether starting of the engine <NUM> in the first start mode is permitted. When the permission flag has been set (YES), the vehicle control unit <NUM> selects restarting of the engine <NUM> in the first start mode in step S110. When the permission flag has not been set (NO), the vehicle control unit <NUM> selects restarting of the engine <NUM> in the second start mode in step S120. The engine <NUM> is restarted in the selected start mode. The permission flag has been cleared when the vehicle is activated and set as a result of the processing of a first start mode permission determination routine, which will be described later. The vehicle is activated by, for example, turning on a start switch of the vehicle.

<FIG> shows a flowchart of the first start mode permission determination routine. The vehicle control unit <NUM> executes the processing of <FIG> during restarting of the engine <NUM> in the second start mode that is performed when the second start mode is selected in the start mode selection routine.

After the processing of the routine is started, when engagement of the clutch <NUM> is commanded (S200: YES), the vehicle control unit <NUM> starts measuring the cranking start time TCR (S210). When confirming from the detection result of the crank angle sensor <NUM> that the rotation of the crankshaft <NUM> has been started (i.e., that cranking has been started) (S220: YES), the vehicle control unit <NUM> ends measuring the cranking start time TCR (S230). That is, the time from when engagement of the clutch <NUM> is commanded to when the transmission of torque through the clutch <NUM> is started is obtained as a measurement value of the cranking start time TCR.

Subsequently, in step S240, the vehicle control unit <NUM> determines whether the measurement value of the cranking start time TCR is less than or equal to a determination value. When determining that the measurement value of the cranking start time TCR is less than or equal to the determination value (S240: YES), the vehicle control unit <NUM> sets the permission flag in step S250 and then ends the routine. When determining that the measurement value of the cranking start time TCR exceeds the determination value (S240: NO), the vehicle control unit <NUM> ends the processing of the routine without operating the permission flag (i.e., ends the processing of the routine by keeping the permission flag cleared).

In the present embodiment, when the engine <NUM> is restarted in the first start mode, engagement of the clutch <NUM> is commanded. Then, when a fixed time has passed, ignition in the expansion stroke stopped cylinder is performed. In the following description, the fixed time is referred to as a "combustion start time. " The same time as the combustion start time is used for the determination value.

The operation and advantages of the present embodiment will now be described.

In the present embodiment, since the permission flag has been cleared when the vehicle is activated, the first restarting of the engine <NUM> after the activation of the vehicle is performed in the second start mode. When the engine <NUM> is restarted in the second start mode, the cranking start time TCR is measured. When the time exceeding the combustion start time is measured as the cranking start time TCR, the permission flag is not set. Thus, the next restarting of the engine <NUM> is performed in the second start mode to measure the cranking start time TCR again. When the time less than or equal to the combustion start time is measured as the cranking start time TCR, the permission flag is set to restart the engine <NUM> in the first start mode after the next time.

The present embodiment has the following advantages.

A controller and a control method for a hybrid vehicle according to a second embodiment will now be described with reference to <FIG>. In the second embodiment, the same reference numerals are given to those components that the same as the corresponding components of the above-described first embodiment and detailed description thereof is omitted.

In the first embodiment, the combustion start time in the first start mode is fixed. In the second embodiment, the combustion start time is variably set based on the measurement result of the cranking start time TCR when the engine <NUM> is restarted in the second start mode.

<FIG> shows a flowchart of the combustion start time setting routine. In the present embodiment, the vehicle control unit <NUM> executes the processing of <FIG> instead of the first start mode permission determination routine of <FIG> during restarting of the engine <NUM> in the second start mode that is performed when the second start mode is selected in the start mode selection routine of <FIG>.

After the processing of the routine is started, when engagement of the clutch <NUM> is commanded (S300: YES), the vehicle control unit <NUM> starts measuring the cranking start time TCR (S310). When confirming that cranking has been started (S320: YES), the vehicle control unit <NUM> ends measuring the cranking start time TCR (S330).

Subsequently, in step S340, the vehicle control unit <NUM> sets the combustion start time based on the measurement value of the cranking start time TCR. For example, the time that is slightly shorter than the measurement value of the cranking start time TCR is set as the value of the combustion start time. Then, in the subsequent step S350, the vehicle control unit <NUM> sets the permission flag and then ends the processing of the routine.

In the present embodiment, the first restarting of the engine <NUM> after activation of the vehicle is performed in the second start mode. During the restarting of the engine <NUM> in the second start mode, the cranking start time TCR is measured and the combustion start time is set based on the measurement value.

Restarting of the engine <NUM> after the second time subsequent to the activation of the vehicle is performed in the first start mode. The restarting of the engine <NUM> in the first start mode is performed based on the combustion start time that is slightly shorter than the cranking start time TCR that has been measured earlier. That is, the combustion start time is set to be longer as the time measured as the cranking start time TCR is longer.

The above-described embodiments may be modified as follows. The above-described embodiments and the following modifications can be combined as long as the combined modifications remain technically consistent with each other.

Instead of the multi-speed automatic transmission, a continuously variable transmission may be employed.

In addition to the first travel mode and the second travel mode, the travel mode may include an additional travel mode.

In addition to the first start mode and the second start mode, the start mode may include an additional start mode.

Claim 1:
A controller for a hybrid vehicle, the hybrid vehicle including a motor (<NUM>) arranged on a power transmission path between an engine (<NUM>) and a wheel (<NUM>) and including a clutch (<NUM>) arranged on a portion of the power transmission path between the engine (<NUM>) and the motor (<NUM>), the controller being configured to switch between stopping operation of the engine (<NUM>) with the clutch (<NUM>) disengaged and operating the engine (<NUM>) with the clutch (<NUM>) engaged, wherein
the controller comprises a restart control unit (<NUM>) configured to select a start mode from multiple start modes and restart the engine (<NUM>) in the selected start mode,
the multiple start modes include a first start mode of commanding engagement of the clutch (<NUM>) and starting combustion in the engine (<NUM>) when a fixed combustion start time has passed after engagement of the clutch (<NUM>) is commanded and a second start mode of commanding engagement of the clutch (<NUM>) and starting combustion in the engine (<NUM>) after rotation of the engine (<NUM>) is started by the torque transmitted from the motor (<NUM>) through the clutch (<NUM>), and
the restart control unit (<NUM>) is configured to:
in a case in which the engine (<NUM>) is restarted in the second start mode, measure a cranking start time (TCR) from when engagement of the clutch (<NUM>) is commanded to when transmission of the torque through the clutch (<NUM>) is started; and
only when measurement of the cranking start time (TCR) has been completed and the measured cranking start time (TCR) is less than or equal to the fixed combustion start time after the vehicle is activated, restart the engine (<NUM>) in the first start mode.