For example, a patent document 1 discloses a hybrid electric vehicle provided with an engine and a motor-generator as drive sources, wherein a first clutch whose transmitted torque capacity is adjustable is disposed between the engine and the motor-generator, and wherein a second clutch whose transmitted torque capacity is adjustable is disposed between the motor-generator and driving wheels of the vehicle.
According to patent document 1, the engine is started by applying the first clutch in response to a request issued when the vehicle is running while being driven only by the motor-generator with the engine stopped, wherein the request is a request for shifting to an operating mode in which the engine is started and the vehicle runs while being driven by both of the engine and the motor-generator. Patent document 1 discloses a technique that when a battery for supplying electric power to the motor-generator can output a sufficient power at such engine start during vehicle running, namely, when a maximum possible output torque of the motor-generator is sufficient to cover vehicle-driving torque and engine-starting torque, then the transmitted torque capacity of the first clutch is increased, and a target torque of the motor-generator is increased with increase of the transmitted torque capacity of the first clutch, thereby increasing a cranking torque transmitted from the motor-generator to the engine through the first clutch, and quickly completing the engine start.
However, in patent document 1, control of the transmitted torque capacity of the first clutch when the engine is started from rest while the vehicle is running, is the same in situations where the engine is started in response to driver's accelerator operation as in situations where the engine is started in response to a factor other than driver's accelerator operation.
Namely, the control of the transmitted torque capacity of the first clutch during engine cranking is not based on whether the engine start is in response to driver's accelerator operation, i.e. in response to a driver's request, or in response to a factor other than driver's accelerator operation, i.e. not based on driver's intention.
Accordingly, when the engine is started from rest in response to a factor other than driver's accelerator operation, a driver tends to sensitively feel shocks caused by torque fluctuation resulting from application of the first clutch, because the engine start is not intended by the driver.
USPTO Backgrounds
USPTO Backgrounds