Method and apparatus for controlling an electric assist motor

摘要

An apparatus for controlling an electric assist steering system (10) having an electric assist motor (26) operatively connected to a steerable member. Energization of the motor provides steering assist to the steering member. The apparatus includes a steering torque sensor (27) for sensing applied steering torque and providing a torque signal indicative thereof. A first switching device (72) is operative coupled between one terminal of the electric assist motor (26) and a first terminal of a source of electrical energy. A second switching device (98) is operative coupled between a second terminal of the electric assist motor and a second terminal of the source of electrical energy. A controller (76) periodically switches the first and second switching devices between ON and OFF conditions so that the ON condition of each the first and second switching devices is less than one-hundred percent of a period and a portion of the ON condition of the first and second switching devices overlap. Electrical current flows through the electric assist motor (26) during an overlap portion of ON conditions. The amount of the overlap controls current in the electric assist motor. The controller (76) controls the overlap in response to the sensed applied steering torque.