The DC traction motor features great instantaneous power, higher over-loading torque (over-loading ratio is 3 or 4), long life cycle, high reliability and quick acceleration. According to actual working conditions, the speed of the electric motor can be adjusted in a wide scope either via constant power variance or via constant torque variance. The constant power variance regulates the current of excitation (separating) to change magnetic flux (normally weak magnet), thus changing the speed. This is suitable for battery powered vehicles driven on a level road because it makes the motor run with high speed at low torque when in constant power. The constant torque variance regulates the armature of excitation (shut, series), keeping the current of excitation constant. This is useful for starting and climbing because of low speed at great torque in constant power. Also, the motor can work as a generator, recharging the battery when the vehicle is decelerated and thus using the limited energy supply more efficiently. The motor抯 excitation is either separating (shut) or series; its insulation grade is class H; and its work duty is short-term S2.