Steering System

A hydraulic steering system for a vehicle comprising a hydraulic steering actuator connected to provide a steering force to at least one steered wheel of a vehicle;

• a steering actuator control system configured to receive a first control input and provide a first control output to the steering actuator;
• a steering angle sensor mounted to detect a steering angle of the at least one steered wheel and to provide a steering angle signal indicative of the detected steering angle;
• the steering actuator control system comprising an electronic control unit configured to receive the steering angle signal from the angle sensor and a hydro-mechanical steering control unit;
• the steering system further comprising a hydraulic pump configured to pump a supply of hydraulic fluid from a tank to the hydro-mechanical steering control unit and a pressure limiting system for limiting the pressure of hydraulic fluid supplied to the actuator from the pump, wherein the pump is a variable displacement pump and the pressure limiting system includes at least one hydraulic line connected between a load sensing port LS of the hydro-mechanical steering control unit and the tank and at least one pressure limitation valve connected in the at least one hydraulic line, the pressure limiting system configured to limit the pressure of hydraulic fluid supplied to the steering actuator to a first pressure value;
• wherein the electronic control unit is configured to monitor the steering angle signal and to provide a second control output to control operation of the pressure limiting system so as to limit the pressure of hydraulic fluid provided to the steering actuator to a second pressure value which is lower than the first pressure value if the steering angle signal is indicative that the detected steering angle is greater than a first angle.

A method of operating a steering system comprising:

• first and second steerably mounted wheels;
• a hydraulic steering actuator connected to provide a steering force to the first and second wheels
• a steering actuator control system configured to receive a first control input and provide a first control output to the steering actuator;
• a steering angle sensor mounted to detect a steering angle of at least one of the first and second wheels and to provide a steering angle signal indicative of the detected steering angle;
• the steering control system comprising an electronic control unit configured to receive the steering angle signal from the steering angle sensor and to provide a second control output operative to reduce the steering force by reducing the pressure of fluid provided to the hydraulic steering actuator;
• the method comprising:
• the electronic control unit monitoring the steering angle signal from the angle sensor and providing the second control output operative to reduce the steering force applied by the steering actuator to the first and second wheels by reducing the pressure of fluid provided to the hydraulic steering actuator if the steering angle signal is indicative that the detected steering angle is greater than a first angle (α1).