Variable speed drive unit for electric vehicle and variable speed driving method

A variable speed driving method for an electric vehicle provided with an electric motor for propelling, a motor drive circuit for controlling the drive power of the motor, and a control circuit section for outputting an operation command to the motor drive circuit, comprising the steps of:

• providing a transmission apparatus which engages or disengages a drive shaft which receives the drive force from the propelling motor and a driven shaft which is interconnected with propelling wheels by an electromagnetic clutch, wherein said electromagnetic clutch comprised of a first clutch interconnected with the drive shaft, a second clutch having a rotational speed different from the first clutch, and an output side clutch interconnected with the driven shaft;
• releasing an operation command to said motor drive circuit at a time of shifting gears to release clutch engagement,
• reissuing an operation command to said motor drive circuit to increase the rotational speed of said first or second clutch slightly higher than the rotational speed of the output side clutch, and
• engaging said first or second clutch with the output side clutch.