Recovery of calibrated center steering position after loss of battery power

An electric power assist steering (EPAS) system for a vehicle, said vehicle including a steering assembly providing a steering angle over a range of angles including a straight-ahead center steering position, said EPAS system comprising:

• 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 an inductive position sensor for generating pulses indicative of a rotational position of said electric motor within an electrical cycle at a first resolution, 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;
• and
• a controller for maintaining a steering angle indication, said controller including a nonvolatile memory for storing an instantaneous rotational position of said electric motor corresponding to a calibrated center steering position during a calibration process which locates said steering assembly at a steering angle corresponding to said center steering position, said controller including a position counter incremented 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 position counter and said rotational position within an electrical cycle.

A method of recovering center steering position of a steering assembly in a vehicle including an electric power assist steering (EPAS) system and a vehicle stability control (VSC) 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 and for providing a rotation signal to a position counter for maintaining a steering angle indication, and wherein said VSC system dynamically determines an estimated center steering position of said steering assembly, 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 rotational position of said electric motor corresponding to a calibrated center steering position during said calibration;
• operating said position counter during operation of said vehicle to maintain said steering angle indication with reference to said calibrated center steering position;
• detecting a loss of power to said position counter resulting in loss of said steering angle indication;
• after restoration of said power, then obtaining said estimated center steering position having been dynamically determined by said VSC system during subsequent operation of said vehicle;
• matching said estimated center steering position to said calibrated center steering position from said nonvolatile memory;
• updating said position counter in response to said estimated center steering position;
• and
• resuming operation of said position counter to maintain said steering angle indication.

Vehicle apparatus comprising:

• a steering assembly providing a steering angle over a range of angles including a straight-ahead center steering position;
• a vehicle stability control (VSC) system that dynamically determines an estimated center steering position of said steering assembly in response to sensed parameters during actual driving of said vehicle apparatus;
• an electric power assist steering (EPAS) system including 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 and wherein said electric motor includes a rotational position sensor for determining an instantaneous rotational position of said electric motor and for providing a rotation signal;
• and
• a controller for maintaining a steering angle indication, said controller including a nonvolatile memory for storing an instantaneous rotational position of said electric motor corresponding to a calibrated center steering position during a calibration process which locates said steering assembly at a steering angle corresponding to said center steering position, said controller including a position counter receiving said rotation signal and maintaining a count corresponding to an instantaneous steering angle relative to said center steering position, said controller including a power-loss detector for detecting a loss of power resulting in loss of said steering angle indication, and wherein, after restoration of power, said controller receives said estimated center steering position from said VSC system, matches said estimated center steering position to said calibrated center steering position from said nonvolatile memory, updates said position counter in response to said estimated center steering position, and resumes operation of said position counter to maintain said steering angle indication.

An electric power assist steering (EPAS) system for a vehicle, said vehicle including a steering assembly providing a steering angle over a range of angles including a straight-ahead center steering position and a vehicle stability control (VSC) system that dynamically determines an estimated center steering position of said steering assembly in response to sensed parameters during actual driving of said vehicle, said EPAS system comprising:

• 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 and wherein said electric motor includes a rotational position sensor for determining an instantaneous rotational position of said electric motor and for providing a rotation signal;
• and
• a controller for maintaining a steering angle indication, said controller including a nonvolatile memory for storing an instantaneous rotational position of said electric motor corresponding to a calibrated center steering position during a calibration process which locates said steering assembly at a steering angle corresponding to said center steering position, said controller including a position counter receiving said rotation signal and maintaining a count indicating an instantaneous steering angle relative to said center steering position, said controller including a power-loss detector for detecting a loss of power resulting in loss of said steering angle indication, and wherein, after restoration of power, said controller receives said estimated center steering position from said VSC system, matches said estimated center steering position to said calibrated center steering position from said nonvolatile memory, updates said position counter in response to said estimated center steering position, and resumes operation of said position counter to maintain said steering angle indication.