Integrated pressure diagnostic for off-highway steering isolation circuit

1. A hydraulic circuit comprising:

(a) an actuator having first and second ports;

(b) a metering valve assembly for controlling hydraulic flow into and out of the first and second ports; and

(c) an isolation valve assembly located between the actuator and the metering valve assembly, the isolation valve assembly including a first inlet port configured for fluid communication with a pressure source of the hydraulic circuit, a second inlet port configured for connection with a reservoir of the hydraulic circuit, and a pressure sensing port configured for connection with a pressure sensor;

(d) wherein the isolation valve assembly is movable between a first position, in which fluid flow between the metering valve and the actuator is enabled, and a second position, in which fluid flow between the metering valve and the actuator is blocked, and wherein the isolation valve assembly is spring biased into the second position;

(e) wherein when the isolation valve assembly is moved to one of the first and second positions, the first inlet port and the pressure sensing port are placed in fluid communication with each other, and wherein when the isolation valve assembly is moved to the other of the first or second position, the second inlet port and the pressure sensing port are placed in fluid communication.

2. The hydraulic circuit of claim 1 , wherein the isolation valve assembly is a spool valve assembly.

3. The hydraulic circuit of claim 1 , wherein when the isolation valve assembly is moved to the first position, the first inlet port and the pressure sensing port are placed in fluid communication with each other and wherein when the isolation valve assembly is moved to the second position, the second inlet port and the pressure sensing port are placed in fluid communication.

4. The hydraulic circuit of claim 1 , wherein the isolation valve assembly is actuated towards the second position by a solenoid actuator.

5. The hydraulic circuit of claim 1 , wherein the isolation valve assembly further includes a pilot valve assembly for selectively directing pressurized fluid to move the isolation valve assembly towards the second position.

6. The hydraulic circuit of claim 1 , further including a pressure sensor connected to the pressure sensing port.

7. An isolation valve assembly for use in a hydraulic circuit, the isolation valve assembly comprising:

(a) first and second ports configured for fluid communication with a metering valve assembly;

(b) third and fourth ports configured for fluid communication with an actuator;

(c) a fifth port configured for fluid communication with a pump side of the hydraulic circuit;

(d) a sixth port configured for fluid communication with a reservoir side of the hydraulic circuit; and

(e) a seventh port configured for fluid communication with a pressure sensor;

(f) wherein when the isolation valve is in a first position, the first and third ports are placed in fluid communication with each other, the second and fourth ports are placed in fluid communication with each other, the fifth and seventh ports are placed in fluid communication with each other, and the sixth port is blocked;

(g) wherein when the isolation valve is in a second position, the first through fifth ports are blocked and the sixth and seventh ports are placed in fluid communication with each other.

8. The isolation valve assembly of claim 7 , wherein the isolation valve assembly is a spool and sleeve type valve.

9. The isolation valve assembly of claim 7 , wherein the isolation valve assembly is spring biased towards the second position.

10. A method for determining a functional state of an isolation valve assembly, the method comprising the steps of:

(a) providing an isolation valve assembly in a hydraulic circuit that is movable between a first position in which fluid flow between a metering valve and an actuator is enabled and a second position in which fluid flow between the metering valve and the actuator is blocked;

(b) initiating an operation verification routine for the isolation valve assembly;

(c) reading a first diagnostic pressure value with the isolation valve assembly in the first position;

(d) moving the isolation valve assembly to the second position;

(e) reading a second diagnostic pressure value with the isolation valve assembly in the second position; and

(f) determining whether the isolation valve assembly is functional by comparing the first diagnostic pressure value to the second diagnostic pressure value.

11. The method of claim 10 , wherein the first position corresponds to a position in which the isolation valve assembly blocks flow between the metering valve and the actuator.

12. The method of claim 11 , wherein the second position corresponds to a position in which the isolation valve assembly enables flow between the metering valve and the actuator.

13. The method of claim 10 , wherein the step of reading a first diagnostic pressure value includes sensing a pressure associated with a reservoir of the hydraulic circuit.

14. The method of claim 13 , wherein the step of reading a second diagnostic pressure value includes sensing a pressure associated with a pump side of the hydraulic circuit.

15. The method of claim 14 , wherein the first position corresponds to a position in which the isolation valve assembly blocks flow between the metering valve and the actuator and the second position corresponds to a position in which the isolation valve assembly enables flow between the metering valve and the actuator.

16. The method of claim 10 , wherein the determining step includes comparing the difference between the first and second diagnostic pressure values.

17. The method of claim 16 , wherein the determining whether the isolation valve assembly is functional includes identifying the isolation valve assembly as being in a failed state when the difference between the first and second diagnostic pressure values is below a threshold value.

18. The method of claim 17 , wherein the threshold is a predetermined threshold value.