Vehicle steering system
A vehicle steering system includes an input configured to receive a signal representing a target steering angle, an output configured to provide a torque output command to a steering motor based on the target steering angle, and a torque limiter module configured to receive the torque output command and apply a torque limit thereto, prior to the torque output command being provided to the steering motor. The torque limit is configurable dynamically based on at least one vehicle parameter.
1. A vehicle steering system comprising
a power assisted steering module including
a steering motor and
a motor controller for:
receiving a signal representing a target steering angle to automatically maintain a position of the vehicle on a road;
calculating, from the target steering angle, a motor torque value to be applied to the steering motor for controlling the steering motor;
maintaining the motor torque value while a driver-applied steering input parameter is below a non-zero first threshold;
limiting the motor torque value to reduce an influence of the signal in linear proportion to an increase in the driver-applied steering input parameter when the driver-applied steering input parameter is above the first threshold and below a second threshold that is higher than the first threshold; and
reducing the motor torque value substantially to zero when the driver-applied steering input parameter reaches or exceeds the second threshold,
wherein limiting the motor torque value is further dependent on a steering angle error comprising a difference between the target steering angle and an actual steering angle provided to a steering wheel of the steering system.
2. The vehicle steering system of claim 1 , wherein the driver-applied steering input parameter is a torque parameter communicated to the power assisted steering module.
3. The vehicle steering system of claim 1 , wherein if the driver-applied steering input parameter corresponds to a divergence from a current path of the vehicle according to the target steering angle, the motor torque value is reduced to zero.
4. The vehicle steering system of claim 1 , wherein the first threshold is based on the driver-applied steering input parameter resulting from a steering input from the driver that corresponds, within a predetermined tolerance, to the target steering angle.
5. The vehicle steering system of claim 1 , wherein the driver-applied steering input parameter is based on an output from a torsion bar sensor of the steering system, the torsion bar sensor being operable in response to a driver input at the steering wheel.
6. A vehicle comprising a vehicle steering system as claimed in claim 1 .
7. A vehicle steering system comprising
a power assisted steering module including
a steering motor and
a motor controller for:
receiving a signal representing a target steering angle to automatically maintain a position of the vehicle on a road;
calculating, from the target steering angle, a motor torque value to be applied to the steering motor for controlling the steering motor;
maintaining the motor torque value while a driver-applied steering input parameter is below a non-zero first threshold;
limiting the motor torque value to reduce an influence of the signal in linear proportion to an increase in the driver-applied steering input parameter when the driver-applied steering input parameter is above the first threshold and below a second threshold that is higher than the first threshold; and
reducing the motor torque value substantially to zero when the driver-applied steering input parameter reaches or exceeds the second threshold,
wherein the first threshold is based on the driver-applied steering input parameter resulting from a steering input from the driver that corresponds, within a predetermined tolerance, to the target steering angle.
8. The vehicle steering system of claim 7 , wherein the driver-applied steering input parameter is a torque parameter communicated to the power assisted steering module.
9. The vehicle steering system of claim 7 , wherein limiting the motor torque value is further dependent on a steering angle error comprising a difference between the target steering angle and an actual steering angle provided to a steering wheel of the steering system.
10. The vehicle steering system of claim 7 , wherein if the driver-applied steering input parameter corresponds to a divergence from a current path of the vehicle according to the target steering angle, the motor torque value is reduced to zero.
11. The vehicle steering system of claim 7 , wherein the driver-applied steering input parameter is based on an output from a torsion bar sensor of the steering system, the torsion bar sensor being operable in response to a driver input at the steering wheel.
12. A vehicle comprising a vehicle steering system as claimed in claim 7 .