Maximum power efficiency in electric vehicles is achieved when each wheel is driven by its own motor. That is, in this maximally efficient arrangement, power is applied directly to each wheel rather than via connections via a mechanical shaft and gears to a single motor. In typical designs, each wheel acts as a stand-alone unit, and the power drawn by each wheel is drawn from the battery according to the needs of the motor driving that wheel. Thus, the power required by each wheel is not synchronized with the best flow of current from the battery. This design can wear out the battery and reduce the battery lifetime due to increased internal dynamic resistance within the battery.
U.S. Pat. No. 5,241,250 discloses a servomotor system for multiple-axis motors. It teaches the use of pulse-width modulation for controlling the current delivered to the motors, but does not consider the problem of having to orient simultaneously multiple motors. Numerous patents (e.g. U.S. Pat. Nos. 5,869,946; 5,955,851; 6,297,610; 6,774,600; 6,812,656; 6,936,982; U.S. Pat. Appl. 2003-0160586) teach methods of regulating the total current delivered to a multi-phase DC motor, e.g. by pulse-width modulation, such that no individual phase is overloaded. U.S. Pat. No. 7,154,300 discloses a servo-motor system for multiple axes, but does not provide any specific means for preventing excessive demands being made on the power source as described above, nor does it teach a method for insuring that the motors reach their desired positions.
U.S. Pat. No. 6,057,664 (henceforth '664) discloses a motor driving control unit and method that comprises inter alia a current control section that takes a measured output current and then outputs a voltage instruction to a PWM section from the detected current value, a current instruction from an external device, and from a positional signal of an encoder connected to a motor. The apparatus and method disclosed in '664 do not provide any means for low-level synchronization of multiple motors (or of multiple windings of a single motor). Additionally, as the apparatus disclosed in '664 reads current as a parameter, it provides no means for superposition of phases. Nor does the apparatus disclosed in '664 provide a central PWM controller; every PWM in the system is a separate unit.
Thus, there is a long-felt need for a method for synchronizing the power demands of the wheels of the vehicle with the optimal current output of the battery.
Furthermore, there exists a long-felt need for an apparatus that can provide simultaneous, independent, accurate axial speed and positional control to a plurality of motors, said apparatus also designed to optimize the amount of current delivered to the servomotor system that controls the speeds and/or positions of the motors. Similarly, there exists a long-felt need for a method of controlling the speeds and/or 1 positions of a plurality of motors such that the axial position or speed of each motor can be controlled independently and accurately, which optimizes the current delivered to each servomotor system, and which ensures that the maximum total current required by the system never exceeds the maximum current that the power source can provide without experiencing a significant voltage drop.