US Patent 8113307 Electric vehicle drive system

An electric powered vehicle includes a first drive unit and a second drive unit. The first drive unit and the second drive unit are coupled to one of the drive wheels. At its maximum power within the system, the second drive unit drives the vehicle at a higher speed than the first drive unit. A clutch automatically disengages the first drive unit from the drive wheel while the second drive unit is operating. The clutch may include a uni-directional device. An electronic control unit automatically adjusts the voltage supplied to the second drive unit to maintain the efficiency of the second electric drive unit within a predetermined efficiency range.