m the interaction force between the synchronizer and the gear in the transmission 20 at the current gear position is approximately zero and therefore it is easy to disengage them without injury to the mechanical parts at that moment the signal processing unit 32 instructs the transmission 20 to disengage while when the rotation speed of the motor 10 is regulated to s k the rotation speed difference between the synchronizer and the gear in the transmission 20 at the target gear position is approximately zero and therefore it is easy to engage them without injury to the mechanical parts at that moment the signal processing unit 32 instructs the transmission 20 to shift to the target gear position according to a preferred embodiment the components in said control device 30 are further configured as follows said signal processing unit 32 is configured to send the instruction for regulating motor torque to said motor control unit 33 firstly and choose said target gear position according to the current gear position with reference to or not with reference to the changing trend of the current rotation speed s said motor control unit 33 is configured to receive the instruction for regulating motor torque from said signal processing unit 32 regulate the torque of said motor 10 to m and send a feedback signal indicating the torque synchronization is completed to said signal processing unit 32 said signal processing unit 32 is configured.