1. Field of the Invention
The present invention relates to a system and method for monitoring torque in an electric motor.
2. Background Art
With the increasing use of electric motors to drive mechanical systems—e.g., as an alternative to an internal combustion engine to power a vehicle—the need for effective motor control systems is increasingly important. A motor control system may monitor various system components, such as the electric motor itself, sensors used to monitor and provide information about the operation of the electric motor, or both. One such controller arrangement is described in U.S. Pat. No. 5,670,856 issued to Le et al. on Sep. 23, 1997. Le et al. describes a motor controller arrangement for an apparatus that is driven by a number of redundant electric motors. Various motor parameters such as position, speed, and current, are monitored by a plurality of controllers which exchange data over a data bus. The redundant arrangement is configured such that each control channel carries a portion of the overall system load. If one of the channels fails, the remaining channels increase their operational capacity to allow full operation of the driven apparatus.
In order for a motor control system to be effective, the associated monitoring systems must be equally effective. When an electric motor is used to drive a vehicle, monitoring a number of motor parameters is important. For example, knowing the motor speed may be important for accurately determining the speed of the vehicle. The motor speed may also be used to determine the overall power output by the motor. Another important motor parameter is the motor torque. A vehicle operator commands the vehicle to provide a certain acceleration; this acceleration is processed into a motor torque command. The torque output of the motor should closely match the torque command; otherwise, the vehicle operator may receive unexpected results. Therefore, there exists a need for monitoring torque in an electric motor, thereby helping to ensure the accuracy of motor torque determinations, so that motor driven systems can be effectively operated.