Vehicle steering system

Abstract

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 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. Aspects of the disclosure also relate to a method, a controller configured to implement the method, and a vehicle incorporating the controller or the system.

1 . A vehicle steering system comprising;
 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 prior to the torque output command being provided to the steering motor, wherein the torque limit is configurable dynamically based on at least one vehicle parameter.   
     
     
         2 . The vehicle steering system of  claim 1 , wherein the at least one vehicle parameter includes a driver-applied steering input parameter. 
     
     
         3 . The vehicle steering system of  claim 2 , wherein the torque limit reduces in proportion to the magnitude of the driver-applied steering input parameter. 
     
     
         4 . The vehicle steering system of  claim 2 , wherein the torque limit is further dependent on a steering angle error which is the difference between the target steering angle and an actual steering angle provided to a steering wheel of the steering system. 
     
     
         5 . The vehicle steering system of  claim 4 , where the steering angle error is used to calculate a weighting function which is used to vary a proportion to which the torque limit is applied compared to an upper torque threshold. 
     
     
         6 . The vehicle steering system of  claim 2 , 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. 
     
     
         7 . The vehicle steering system as claimed in  claim 1 , wherein the target steering angle is provided an automated driving controller. 
     
     
         8 . A method of controlling the torque output from a vehicle steering system, the method comprising:
 receiving a signal indicative of a target steering angle;   providing a torque output command to a steering motor based on the target steering angle; and   applying a torque limit to the torque output command, prior to the torque output command being provided to the steering motor, wherein the torque limit is configurable dynamically based on at least one vehicle parameter.   
     
     
         9 . A controller for a steering system for carrying out the steps of the method as claimed in  claim 8 . 
     
     
         10 . A vehicle comprising a vehicle steering system as claimed in  claim 1 . 
     
     
         11 . A vehicle steering system comprising;
 an automated driving controller for generating a signal representing a target steering angle; and   a power assisted steering module for receiving the signal representing the target steering angle and calculating, from the target steering angle, a motor torque value for controlling a steering motor;   wherein the power assisted steering module comprises means for regulating the motor torque value that is to be applied to the steering motor when the driver applies a steering input.   
     
     
         12 . The vehicle steering system of  claim 11 , wherein the motor torque value is regulated based on a driver-applied steering input parameter. 
     
     
         13 . The vehicle steering system of  claim 12 , wherein the driver-applied steering input parameter is a torque parameter calculated at the automated driving controller and communicated to the power assisted steering module. 
     
     
         14 . The vehicle steering system of  claim 12 , wherein the influence of the automated driving controller is reduced as the driver-applied steering input parameter increases. 
     
     
         15 . The vehicle steering system of  claim 12 , wherein the regulation of the motor torque value is further dependent on a steering angle error which is the difference between the target steering angle and an actual steering angle provided to a steering wheel of the steering system. 
     
     
         16 . The vehicle steering system of  claim 12 , wherein if a driver-applied steering input parameter resulting from a significant steering input from the driver corresponds to a divergence from a current path of the vehicle according to the target steering angle, the motor torque value is regulated to reduce the influence of the automated driving controller to zero. 
     
     
         17 . The vehicle steering system of  claim 12 , wherein if a driver-applied steering input parameter resulting from a steering input from the driver corresponds, within a certain tolerance, to the target steering angle, the influence of the automated driving controller is not reduced. 
     
     
         18 . The vehicle steering system of  claim 11 , wherein the driver-applied steering input 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. 
     
     
         19 . A vehicle comprising a vehicle steering system as claimed in  claim 11 .