Steering system
A steering system includes a mechanism configured to turn a steer wheel of a vehicle, a motor configured to generate driving force that is applied to the mechanism, and a controller configured to control the motor according to a steering status. The controller includes a limiting control circuit configured to limit a current that is supplied to the motor to a limiting value, a determining circuit configured to determine whether the steer wheel is in contact with an obstacle by using at least a comparison between a value of the current that is supplied to the motor and a threshold, and a threshold computing circuit configured to compute the threshold that is used by the determining circuit, the threshold computing circuit being configured to compute a value less than the limiting value according to the limiting value as the threshold.
1. A steering system comprising:
a mechanism configured to turn a steer wheel of a vehicle;
a motor configured to generate driving force that is applied to the mechanism; and
a controller configured to control the motor according to a steering status, wherein the controller includes:
a limiting control circuit configured to limit a current that is supplied to the motor to a limiting value,
a determining circuit configured to determine whether the steer wheel is in contact with an obstacle by using at least a comparison between a value of the current that is supplied to the motor and a threshold such that, when the value of the current supplied to the motor exceeds the threshold, it is determined that the steer wheel is in contact with the obstacle, and
a threshold computing circuit configured to compute the threshold that is used by the determining circuit, wherein the threshold is set to be less than the limiting value by a fixed amount in a range where the limiting value is equal to or above a predetermined value.
2. The steering system according to claim 1 , wherein the threshold computing circuit is configured to compute the threshold such that the threshold does not fall within a practical current range that is a range of the value of the current that is supplied to the motor in a normal usage state of the vehicle.
3. The steering system according to claim 1 , wherein:
the mechanism includes a steering shaft configured to rotate in conjunction with an operation of a steering wheel and a wheel steering shaft provided such that power transmission between the steering wheel and the wheel steering shaft is separated; and
the motor includes a reaction motor configured to generate a steering reaction force based on a first command value that is computed according to the steering status and a steering motor configured to generate a wheel steering force based on a second command value that is computed according to the steering status, the steering reaction force is a torque in a direction opposite from a direction of steering of the steering shaft, the wheel steering force is a torque for turning the steer wheel and is applied to the wheel steering shaft.
4. The steering system according to claim 3 , wherein:
the controller includes a limiting axial force computing circuit configured to compute a limiting axial force as control for, when the determining circuit determines that the steer wheel is in contact with the obstacle, informing a driver that the steer wheel is in contact with the obstacle; and
the limiting axial force is an axial force of the wheel steering shaft to be incorporated into the first command value for the reaction motor to virtually limit the operation of the steering wheel.
5. The steering system according to claim 3 , wherein:
the controller includes
an ideal axial force computing circuit configured to compute an ideal axial force that is an ideal axial force of the wheel steering shaft based on a target rotational angle of a rotor that rotates in conjunction with a turning motion of the steer wheel,
an estimated axial force computing circuit configured to compute an axial force of the wheel steering shaft as an estimated axial force based on a current value of the steering motor, the current value reflecting a vehicle behavior, a road surface condition, or the steering status, and
an allocation computing circuit configured to compute a combined axial force as the axial force of the wheel steering shaft to be incorporated into the first command value for the reaction motor by combining the estimated axial force and the ideal axial force according to the vehicle behavior, the road surface condition, or the steering status; and
the allocation computing circuit is configured to, when the determining circuit determines that the steer wheel is in contact with the obstacle, switch the axial force of the wheel steering shaft to be incorporated into the first command value for the reaction motor from the combined axial force to the estimated axial force as control for informing a driver that the steer wheel is in contact with the obstacle.