Thermal current limiting apparatus and method for vehicle system with electric motor actuator

摘要

An electric motor actuator used in an environment of varying loads for varying time periods is efficiently designed to a predetermined specification in terms of both motor load and time and operated up to but not exceeding this specification over the full expected operating range. A motor load signal is low pass filtered with a plurality of time constants spanning a range of expected motor operation to generate a plurality of filtered motor load signals each associated with one of the time constants. Each of these filtered motor load signals is compared with a predetermined reference value corresponding to the associated time constant. If one or more of the filtered motor load signals exceeds the predetermined reference value with which it is compared, the one that so exceeds by the greatest margin is selected. A command current limit factor is derived from the selected filtered motor load signal and used to limit the commanded motor current. The motor load signal preferably indicates motor operating current and may be derived from a motor current sensor or from the limited command current signal, motor speed and operating voltage to compensate for a decrease of current with motor speed due to inductance/slope compensation and voltage limit effects.