Isolation valve for a load-reaction steering system

1. A steering system comprising:

a fluid actuator;

a first steering circuit being in selective fluid communication with the fluid actuator; and

a second steering circuit being in selective fluid communication with the fluid actuator and being in parallel to the first steering circuit, the second steering circuit including a fluid controller having first and second control ports in fluid communication with the fluid actuator, the second steering circuit including a load-reaction feature, in which the first and second control ports are in fluid communication with a fluid meter of the fluid controller when the fluid controller is in a neutral position, and an isolation valve, the isolation valve being adapted to selectively enable and disable the load-reaction feature.

2. A steering system as claimed in claim 1 , wherein the first steering circuit is an electro-hydraulic steering circuit.

3. A steering system as claimed in claim 2 , wherein the electro-hydraulic steering circuit includes a first proportional valve that is pilot operated by a plurality of pilot valves.

4. A steering system as claimed in claim 3 , wherein each of the pilot valves are solenoid valves.

5. A steering system as claimed in claim 4 , wherein the electro-hydraulic steering circuit includes a microcontroller that controls the actuation of the plurality of pilot valves.

6. A steering system as claimed in claim 1 , wherein the second steering circuit includes a second proportional valve that is selectively actuated by a steering actuation member.

7. A steering system as claimed in claim 6 , wherein a neutral position of the second proportional valve includes the load-reaction feature.

8. A steering system as claimed in claim 7 , wherein the isolation valve is disposed between the second priority valve and the fluid actuator.

9. A steering system as claimed in claim 1 , wherein the second steering circuit includes a shuttle valve having a first inlet and a second inlet in fluid communication with the first control port and the second control port, respectively.

10. A steering system as claimed in claim 9 , wherein an outlet from the shuttle valve is used to pilot the isolation valve to a first position that enables the load-reaction feature of the second steering circuit.

11. A steering system as claimed in claim 10 , wherein the isolation valve is piloted by the first steering circuit to a second position that disables the load-reaction feature of the second steering circuit.

12. A steering system as claimed in claim 1 , wherein the isolation valve is biased to enable the load-reaction feature.

13. A steering system as claimed in claim 12 , wherein a spring acting on a first end of the isolation valve biases the isolation valve to enable the load-reaction feature.

14. A steering system comprising:

a first steering circuit in selective fluid communication with a fluid actuator, the first steering circuit defining a first flow path and having a first proportional valve disposed in the first flow path;

a second steering circuit in selective fluid communication with the fluid actuator, the second steering circuit defining a second flow path that is in a parallel flow configuration with the first flow path of the first steering circuit, the second steering circuit including:

a second proportional valve having a neutral position that is adapted to transmit a reaction load to a steering actuation member in response to an external load applied to the fluid actuator; and

an isolation valve disposed in the second flow path between the second proportional valve and the fluid actuator, wherein the isolation valve is adapted to disable the transmission of the reaction load when the first proportional valve is in fluid communication with the fluid actuator and enable the transmission of the reaction load when the second proportional valve is in fluid communication with the fluid actuator.

15. A steering system as claimed in claim 14 , wherein the isolation valve is actuated to enable the transmission of the reaction load in response to fluid communicated from the second steering circuit.

16. A steering system as claimed in claim 15 , wherein a sensor detects actuation of the second proportional valve.

17. A steering system as claimed in claim 16 , wherein the sensor is in electrical communication with a microcontroller of the first steering circuit.