Patent ID: 7295907
Filing Date: 2007-11-13
Classification: B62D

Abstract:
1. A method of maintaining an absolute steering angle of a steering assembly in a vehicle including an electric power assist steering (EPAS) system, wherein said steering assembly has a steering angle over a range of angles including a center steering position, wherein said EPAS system includes an electric motor for applying torque to said steering assembly, wherein said electric motor passes through a plurality of rotations over said range of angles of said steering assembly, wherein said electric motor includes a rotational position sensor for determining an instantaneous rotational position of said electric motor at a first resolution within a current electrical cycle of said electric motor, and wherein said electric motor includes a Hall-effect sensor for sensing rotation past predetermined rotational positions of said electric motor at a second resolution lower than said first resolution, said Hall-effect sensor generating a predetermined transition of Hall states with a measuring range greater than said electrical cycle, said method comprising the steps of: locating said steering assembly at a steering angle corresponding to said center steering position in a controlled calibration; storing in nonvolatile memory an instantaneous one of said Hall states and said instantaneous rotational position within an electrical cycle corresponding to a calibrated center steering position during said calibration; incrementing an electrical cycle position counter in response to said predetermined transition of Hall states; and maintaining an instantaneous steering angle relative to said center steering position in response to said electrical cycle position counter and said instantaneous rotational position within an electrical cycle.