BACKGROUND

1. Field

The following description relates to a controller and a control method for a hybrid vehicle.

2. Description of Related Art

In some hybrid vehicles, a motor is arranged on a power transmission path between the engine and the wheels, and a clutch is arranged on a portion of the power transmission path between the engine and the motor. Such a hybrid vehicle has travel modes for the vehicle that include a first mode and a second mode. In the first mode, the vehicle travels using the power of the motor with the clutch disengaged and the engine stopped. In the second mode, the vehicle travels using the power of the engine with the clutch engaged and the engine operating. In a controller for a hybrid vehicle disclosed in Japanese Laid-Open Patent Publication No. 2009-208562, when the travel mode is switched from the first mode to the second mode, the engine is restarted by engaging the clutch and cranking the engine using the power of the motor. When the engine rotation speed increases to a value approximate to the motor rotation speed after the engine is restarted, the controller temporarily reduces the capacity of the torque transmitted by the clutch. This limits the generation of shock.

However, in a case in which the motor rotation speed is low, the engine rotation speed will exceed the motor rotation speed within a short period of time after the engine is restarted. Thus, in such a case, the capacity of the torque transmitted by the clutch cannot be timely reduced. This may cause the shock to be incompletely reduced.

SUMMARY

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

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 cause the hybrid vehicle to travel in a travel mode selected from multiple travel modes that include a first travel mode of traveling with the clutch disengaged and operation of the engine stopped and a second travel mode of traveling with the clutch engaged and the engine operating. The controller includes processing circuitry configured to restart the engine in a first start mode of starting combustion in the engine with the clutch non-fully engaged or a second start mode of starting combustion in the engine with the clutch fully engaged. The processing circuitry is configured to restart the engine in the first start mode when a rotation speed of the motor is greater than a determination value upon a request for switching from the first travel mode to the second travel mode and restart the engine in the second start mode when the rotation speed of the motor is less than or equal to the determination value upon the request for switching from the first travel mode to the second travel mode.

In a control method for a hybrid vehicle, 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 causing the hybrid vehicle to travel in a travel mode selected from multiple travel modes that include a first travel mode of traveling with the clutch disengaged and operation of the engine stopped and a second travel mode of traveling with the clutch engaged and the engine operating. The control method also includes restarting the engine in a first start mode of starting combustion in the engine with the clutch non-fully engaged when a rotation speed of the motor is greater than a determination value upon a request for switching from the first travel mode to the second travel mode. The control method further includes restarting the engine in a second start mode of starting combustion in the engine with the clutch fully engaged when the rotation speed of the motor is less than or equal to the determination value upon the request for switching from the first travel mode to the second travel mode.

Other features and aspects will be apparent from the following detailed description, the drawings, and the claims.

