Method to detect hydraulic valve failure in hydraulic system

1. A hydraulic system comprising:

a controller connected to an operator interface;

a pump operable in a first direction for supplying pressurized fluid;

a load-holding valve connected between the pump and a port for connection to an actuator, the load-holding valve controlled by the controller and operative in a first position to allow flow to the actuator to operate the actuator against a load and operative in a second position to block load-induced return flow from the actuator to the pump; and

an electric machine configured to operate the pump;

wherein the controller is configured to receive a requested actuator stop, to control the load-holding valve to move to the second position in response to the requested actuator stop, to monitor a system condition in response to the requested actuator stop, to evaluate the monitored system condition with a prescribed criteria, and to determine whether or not to initiate a back-up control routine based on the evaluation; and

wherein the monitored system condition is the electric machine's torque.

2. The hydraulic system of claim 1 , wherein the back-up routine includes operating the pump to control load-induced movement of the actuator.

3. The hydraulic system of claim 1 , wherein the controller is further configured to generate an alert indicating failure of the load-holding valve.

4. The hydraulic system of claim 1 , wherein the controller is further configured to run the pump to depressurize hydraulic fluid between the pump and the load-holding valve after the load-holding valve is controlled to close.

5. The hydraulic system of claim 1 , further comprising a second valve selectively fluidly connecting a hydraulic fluid passage between the pump and the load-holding valve to a reservoir, and

wherein the controller is further configured to connect the hydraulic fluid passage to the reservoir after the load-holding valve is controlled to close.

6. The hydraulic system of claim 1 , wherein the pump is a bi-directional pump operable in a first direction for supplying pressurized fluid through the load-holding valve to the actuator for operating the actuator in one direction, and operable in a second direction opposite the first direction for supplying pressurized fluid through a second valve to the actuator for operating the actuator in a direction opposite the first direction.

7. The hydraulic system of claim 1 , further wherein the actuator is operable in opposite directions in response to hydraulic fluid being supplied to and returned from the actuator.

8. The hydraulic system of claim 1 , further comprising:

a boost system for accepting fluid from or supplying fluid to a hydraulic circuit of the hydraulic system,

wherein the boost system includes:

a boost pump for supplying fluid to a fluid make-up/return line that selectively is in fluid communication with the actuator, and a boost electric machine for driving the boost pump, the boost electric machine connected to a boost electric power source through a boost inverter.

9. The hydraulic system of claim 1 , wherein the electric machine is an electric motor operated by the controller and connected to an electrical source through an inverter to drive the pump.

10. The hydraulic system of claim 1 , wherein the monitored system condition further includes pressure between the pump and the load-holding valve.

11. A method of detecting a failure of hydraulic valve configured to control flow between a pump and an actuator in a hydraulic system, the method comprising the steps of:

receiving a requested stop of the actuator;

controlling the valve to close in response to the requested stop of the actuator;

monitoring a system condition in response to the requested stop of the actuator;

evaluating the monitored system condition with a prescribed criteria; and

determining whether or not the valve has failed based on the evaluation;

wherein an electric machine operates the pump; and

wherein the monitoring a system condition includes monitoring the electric machine's torque.

12. The method of claim 11 , further comprising:

determining whether or not to operate the pump to stop the actuator based on the evaluation.

13. The method of claim 11 , wherein the monitoring a system condition further includes monitoring pressure between the pump and the valve.

14. The method of claim 11 , further comprising operating the pump to reduce pressure between the pump and the hydraulic valve after the controlling.

15. The method of claim 11 , further comprising opening a bleed valve to reduce pressure between the pump and the hydraulic valve after the controlling.

16. The method of claim 11 , further comprising:

operating the pump in one direction for supplying pressurized fluid through the valve to the actuator for operating the actuator in a first direction, and operating the pump in a second direction opposite the first direction for supplying pressurized fluid through a second valve to the actuator for operating the actuator in a direction opposite the first direction.

17. The method of claim 11 , further comprising:

driving the pump via the electric machine connected to an electrical source through an inverter.

18. The method of claim 11 , further comprising:

generating an alert indicating failure of the hydraulic valve based on the determination.