Integrated pressure diagnostics for off-highway steering isolation circuits

Abstract

The present invention provides a system and method for detecting the functional status of a pilot-operated or direct-acting isolation valve in a hydraulic circuit. In some examples, the hydraulic circuit is a steering circuit, and the isolation valve provides selective isolation between a hydraulic actuator and one or more metering valves. In some examples, 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. When the isolation valve assembly is moved to one of the first and second positions, the inlet port and pressure sensing port of the isolation valve assembly are in fluid communication with each other. When the isolation valve assembly is moved to the other of the first and second positions, the second inlet port and the pressure sensing port are in fluid communication.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Patent Application No. 62 / 968,745, filed January 31, 2020, the disclosure of which is incorporated herein by reference in its entirety. Background Art

[0003] Work machines such as off-highway vehicles, forklifts, wheel loaders, crawler loaders, excavators, backhoes, bulldozers and telehandlers are known. Work machines can be used to move materials such as pallets, soil and / or debris. Work machines typically include a work tool (e.g., a fork) connected to the work machine. The work tool attached to the work machine is typically powered by a hydraulic system. The hydraulic system may include a hydraulic pump powered by a prime mover (such as a diesel engine). Work machines are typically provided with electronic control systems that rely on a number of inputs and outputs, such as pressure sensors, position sensors and valve actuators. Electrohydraulic valves typically rely on sensed values (such as port pressure and / or valve position) to provide a stable, controlled flow to and from a hydraulic actuator (such as a linear actuator or motor). In order to accurately control these valves, fluid properties must typically be input into the control system.

[0004] Some hydraulic systems, such as some electro-hydraulic steering systems, require a specified level of functional safety (e.g. Performance Level (PL), Safety Integrity Level (SIL), Agricultural Performance Level (AgPL), etc.). Such systems typically employ a variety of methods to detect the functional status of safety elements. Real-time fault detection of safety elements can improve the overall safety level of the system by reducing the number of dangerous faults that remain undetected when the safety element fails. Typically, the status of the isolation function of an electro-hydraulic steering system must be checked by proxy or by verifying the flow downstream of the isolation spool. This approach may be undesirable because in many cases the system requires verification of the movement of the wheels on the machine (i.e. during machine startup). Improvements are therefore desired. Summary of the Invention

[0005] The present disclosure describes a method (hydraulic circuit) for detecting the functional status of a pilot-operated or direct-acting isolation valve used to isolate the flow output from an electro-hydraulic steering valve. Real-time fault detection of the isolation element (i.e., the pilot spool valve) is achieved using a combination of an integrated diagnostic pressure signal and a pressure sensor (i.e., a pressure switch). This fault detection capability can be used to improve the diagnostic coverage of the element in accordance with ISO 13849 and IEC61508. Direct measurement of the isolation function is preferred because it eliminates the need for undesirable conditions (such as wheel movement) during startup or normal operation. The present disclosure proposes a real-time detection method for a flow isolation valve that does not rely on moving parts of the machine steering system.

[0006] In a safe, functioning system, it is often necessary to verify the functionality of the isolation valve (and pilot valve) at all times. The defined "safe state" of the system is typically one in which the isolation valve is closed and there is no flow to or from the steering cylinder. While one way to directly detect the isolation valve's state is to measure it using a spool position sensor, this article proposes an alternative approach involving an isolation valve design that allows the use of a diagnostic pressure signal to determine the valve's state. A 7-way, 2-position isolation valve acts as a flow-blocking valve between the mainstage spool and the cylinder. An additional output pressure signal path (diagnostic signal) connects a dedicated diagnostic signal port to tank pressure in the closed state (unactuated) and to a reduced pilot pressure supply in the open state (activated). When the isolation valve is in the unactuated state (isolated), the pressure at the diagnostic port is equal to the tank pressure. When the isolation valve is in the actuated state (flowing), the pressure at the diagnostic port is equal to the reduced pilot supply pressure. The difference between the diagnostic port pressures in each of these two states is typically constant and approximately equal to the PRV pressure setting. Tank pressure changes will affect this somewhat, but this effect should be negligible compared to the PRV pressure.

[0007] In application, the concepts disclosed herein can be used to detect the state of an isolation valve at any given time. Considering a situation where the isolation valve is stuck (or perhaps its pilot valve is stuck), the high-level system compares the command signal (i.e., PWM, current, etc.) with the measured pressure at the diagnostic port and determines that a fault has occurred that requires the system to take action (enter a "safe" state). This fault would otherwise remain undetected until a different part of the system detects the fault or a hazardous condition occurs. As described above, the presence of the isolation valve diagnostic pressure signal will result in a higher "diagnostic coverage" (referred to as "DC" according to ISO13849 and IEC 61508) of the isolation valve component. In some cases, this may increase the overall PL or SIL of the system.

[0008] In one example, a hydraulic circuit includes an actuator having a first port and a second port; a metering valve assembly for controlling hydraulic flow into and out of the first port and the second port; and an isolation valve assembly positioned 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 to a reservoir of the hydraulic circuit, and a pressure sensing port configured for connection to a pressure sensor. In one aspect, 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. 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 in fluid communication with each other, and when the isolation valve assembly is moved to the other of the first and second positions, the second inlet port and the pressure sensing port are in fluid communication with each other.

[0009] The current system represents a typical electro-hydraulic steering circuit for off-highway vehicles, in which a pilot-operated proportional metering valve is used to meter flow to and from a set of one or more steering cylinders. The metering valve can be an open-center valve, a closed-center valve, or a load-sensing (static or dynamic signal) valve. The system includes the use of a normally closed isolation valve that blocks flow between the metering valve and the steering cylinders. The isolation valve can be directly piloted (using a solenoid coil) or hydraulically piloted (using a pilot valve). In normal operation, the isolation valve is actuated to allow flow to pass between the metering valve and the steering cylinders.

[0010] In some examples, the isolation valve assembly is a spool valve assembly.

[0011] In some examples, when the isolation valve assembly is moved to the first position, the first inlet port and the pressure sensing port are 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 in fluid communication.

[0012] In some examples, the isolation valve assembly is spring biased to one of the first position and the second position.

[0013] In some examples, the isolation valve assembly is spring biased to the second position.

[0014] In some examples, the isolation valve assembly is actuated toward the second position by a solenoid actuator.

[0015] In some examples, the isolation valve assembly further includes a pilot valve assembly for selectively directing pressurized fluid to move the isolation valve assembly toward the second position.

[0016] In some examples, the isolation valve assembly further includes a pressure sensor connected to the pressure sensing port.

[0017] In one example, an isolation valve assembly for a hydraulic circuit includes: a first port and a second port configured for fluid communication with a metering valve assembly; a third port and a fourth port configured for fluid communication with an actuator; a fifth port configured for fluid communication with a pump side of the hydraulic circuit; a sixth port configured for fluid communication with a reservoir side of the hydraulic circuit; and a seventh port configured for fluid communication with a pressure sensor. When the isolation valve is in a first position, the first and third ports are in fluid communication with each other, the second and fourth ports are in fluid communication with each other, the fifth and seventh ports are in fluid communication with each other, and the sixth port is blocked. When the isolation valve is in a second position, the first through fifth ports are blocked, and the sixth and seventh ports are in fluid communication with each other.

[0018] In some examples, the isolation valve assembly is a spool and sleeve valve.

[0019] In some examples, the isolation valve assembly is spring biased toward the second position.

[0020] In one example, a method for determining the functional status of an isolation valve assembly includes the following steps: providing an isolation valve assembly in a hydraulic circuit, the isolation valve assembly being capable of moving between a first position and a second position, wherein in the first position, fluid flow between a metering valve and an actuator is enabled, and in the second position, fluid flow between the metering valve and the actuator is blocked; initiating an operational verification routine for the isolation valve assembly; reading a first diagnostic pressure value when the isolation valve assembly is in the first position; moving the isolation valve assembly to a second position; reading a second diagnostic pressure value when the isolation valve assembly is in the second position; and determining whether the isolation valve assembly is functional by comparing the first diagnostic pressure value and the second diagnostic pressure value.

[0021] In some examples, the first position corresponds to a position in which the isolation valve assembly blocks flow between the metering valve and the actuator.

[0022] In some examples, the second position corresponds to a position of the isolation valve assembly enabling flow between the metering valve and the actuator.

[0023] In some examples, reading the first diagnostic pressure value includes sensing a pressure associated with a reservoir of the hydraulic circuit.

[0024] In some examples, reading the second diagnostic pressure value includes sensing a pressure associated with a pump side of the hydraulic circuit.

[0025] In some examples, 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.

[0026] In some examples, the determining step includes comparing a difference between the first diagnostic pressure value and the second diagnostic pressure value.

[0027] In some examples, the determining includes identifying the isolation valve assembly as being in a fault condition when a difference between the first diagnostic pressure value and the second diagnostic pressure value is below a threshold.

[0028] In some examples, the threshold is a predetermined threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Non-limiting and non-exhaustive embodiments will be described with reference to the following figures, which are not necessarily drawn to scale, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

[0030] Figure 1 is a schematic diagram of a work machine having exemplary features according to various aspects of the principles of the present disclosure.

[0031] Figure 2 is a schematic diagram of a portion of an electro-hydraulic system comprising a Figure 1 The steering circuit and actuator of a work machine are shown.

[0032] Figure 3 yes Figure 2 Schematic diagram of a portion of the system shown in .

[0033] Figure 4 yes Figure 2 Schematic diagram of a variation of a portion of the electrohydraulic system shown in .

[0034] Figure 5 yes Figure 2 Schematic diagram of the electronic control system of the hydraulic circuit shown in .

[0035] Figure 6 is shown for detection Figure 2 and Figure 4 Flowchart of a method for isolating functional states of a system shown in FIG. DETAILED DESCRIPTION

[0036] Various embodiments will be described in detail with reference to the accompanying drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the claims appended hereto. Furthermore, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments of the appended claims.

[0037] The following is a description of the overall system, associated hydraulic system, related control systems, and methods.

[0038] Overall system description

[0039] like Figure 1 As depicted, a work machine 10 is shown. Work machine 10 includes a work attachment 12 for performing various lifting tasks associated with a load 44. In one embodiment, work machine 10 is a telehandler having a telescopic arm 42 supporting work attachment 12. In one embodiment, work attachment 12 includes a pair of forks. However, those skilled in the art will recognize that the work attachment may be any hydraulically powered work implement.

[0040] The work machine 10 is also shown as including at least one drive wheel 14 and at least one steering wheel 16. In some embodiments, one or more drive wheels 14 can be combined with one or more steering wheels 16. The drive wheels are powered by a power unit 18 (e.g., an electric motor or an internal combustion engine). The power unit 18 is also configured to provide power to the hydraulic system of the work machine 10, including the steering circuit 100 and the working circuit 200, via at least one hydraulic pump 20. In one embodiment, the pump 20 is mechanically coupled to the power unit 18, such as via an output shaft or a power take-off. In one embodiment, the pump 20 is indirectly powered by the power unit 18 via a hydraulic system having a hydraulic motor. The steering circuit 100 is controlled by operation of the pump 20, in cooperation with a number of hydraulic actuators and control valves. Similarly, the working circuit 200 actuates the work attachment 12 by operation of the pump, in cooperation with a number of hydraulic actuators and control valves. In one embodiment, the work machine includes hydraulic actuators and valves powered by the work circuit 200 for achieving steering in addition to lift, extend, tilt, and side-to-side movement of the work attachment 12 .

[0041] hydraulic system

[0042] Reference Figure 2, shows an example of a steering circuit 100 for a work machine 10. The steering circuit 100 is used to control the steering of the work machine 10 via one or more actuators 22. As depicted, the actuator 22 is shown as a linear-acting actuator. However, the present disclosure is not limited to this type of actuator and may also be used with other types of actuators, such as rotary actuators. As depicted, the steering circuit 100 also includes a metering valve assembly 102, an isolation valve assembly 104, a first pressure reducing valve assembly 106, a second pressure reducing valve assembly 108, and a pressure reference valve assembly 110. Various interconnected hydraulic channels and / or pipelines are also provided along with the steering circuit 100. The steering circuit 100 is also connected to a hydraulic pump 20 and a reservoir or tank 24.

[0043] In one aspect, hydraulic actuator 22 includes a first chamber 22a and a second chamber 22b separated by a piston 22c. Hydraulic actuator 22 is shown as further including a first port 22d in fluid communication with first chamber 22a, and a second port 22e in fluid communication with second chamber 22b. Thus, when fluid enters first chamber 22a through first port 22d, piston 22c is forced in a first direction, which in turn causes fluid to exit second chamber 22b through second port 22e. Similarly, when fluid enters second chamber 22b through second port 22e, the piston is forced in a second direction, opposite the first direction, which in turn causes fluid to exit first chamber 22a. In one aspect, the first direction is associated with turning work machine 10 in one direction, while the second direction is associated with turning work machine 10 in the opposite direction.

[0044] Metering valve assembly 102 controls the flow of fluid into and out of ports 22d, 22e of actuator 22. In operation, metering valve assembly 102 selectively places pumped fluid from pump 20 into first chamber 22a or second chamber 22b via first port 22d or second port 22e, and also selectively places the other chamber 22a, 22b in fluid communication with tank or reservoir 24 via first port 22d or second port 22e, allowing fluid to exit the opposing chamber 22a, 22b. As shown, metering valve assembly 102 is a three-position, four-way valve having ports 102a to 102d. In a first position A of metering valve assembly 102, pumped fluid from pump 20 flows through ports 102a, 102c of metering valve assembly 102 and into first chamber 22a through port 22d to drive piston 22c in a first direction. At the same time, fluid exiting second chamber 22b through port 22e flows through ports 102b, 102d of metering valve assembly 102 and into reservoir or tank 24. In the second position B of the metering valve assembly, pumped fluid from pump 20 flows through ports 102a, 102d of metering valve assembly 102 and into second chamber 22b through port 22e to drive piston 22c in a second direction. Simultaneously, fluid exiting first chamber 22a through port 22d flows through ports 102b, 102e of metering valve assembly 102 and into reservoir or tank 24. In the third position C of metering valve assembly 102, i.e., the neutral or open center position, fluid flow from chambers 22a, 22b of actuator 22 is blocked at ports 102c, 102d of metering valve assembly 102, while ports 102a, 102b redirect pumped fluid from pump 20. In the example shown, the pressure reducing pilot valves 106, 108 are configured to provide a pilot pressure to move the metering valve assembly 102 to either the first position A or the second position B, while the centering springs 102m, 102n bias the metering valve assembly 102 to a center or neutral position C. While specific metering and pilot valve assemblies are shown, other arrangements are possible. For example, the metering valve assembly 102 can also be configured to have a closed center, or as a load-sensing (static or dynamic) proportional metering valve utilizing, for example, a variable solenoid actuator rather than a hydraulic pilot pressure.

[0045] Continue to refer to Figure 2, the steering circuit 100 is shown as further including an isolation valve assembly 104. As arranged, the isolation valve assembly 104 is located between the metering valve assembly 102 and the actuator 22. Thus, regardless of the position of the metering valve assembly 102, the isolation valve assembly 104 can be operated to block fluid flow into and out of the actuator chambers 22a, 22b. Thus, the isolation valve assembly 104 can provide a safety function in the event of an operational malfunction associated with the metering valve assembly 102 and / or related components, whereby the position of the actuator 22 is securely maintained in place and prevented from moving until the malfunction is resolved.

[0046] like Figure 3 Most easily seen, the isolation valve assembly 104 is a two-position, seven-way valve having ports 104a to 104g. In the first position A of the isolation valve assembly 104, port 104a is blocked; ports 104b and 104e are connected to each other, allowing fluid communication between the pressure reference valve assembly 110 and the pressure sensor 112; ports 104c and 104f are connected to each other, allowing fluid communication between the actuator port 22d and port 102k of the metering valve assembly 102; and ports 104d and 104g are connected to each other, allowing fluid communication between the actuator port 22e and port 102l of the metering valve assembly 102. In the second position B of isolation valve assembly 104, ports 104a and 104e open to each other such that fluid communication between tank or reservoir 24 and pressure sensor 112 is open, while the remaining ports 104b, 104c, 104d, 104f, and 104g are blocked.

[0047] exist Figure 2 and Figure 3In the illustrated example, isolation valve assembly 104 is biased to a second position B by biasing spring 104h and is operated toward a first position A by pilot valve assembly 105 acting on end 104i of isolation valve assembly 104. As shown, pilot valve assembly 105 is a three-way, two-position valve having ports 105a to 105c. In first position A of pilot valve assembly 105, ports 105a and 105c are connected, allowing fluid communication between pressure-reducing valve assembly 110 and end 104i of isolation valve assembly 104, while port 105b is blocked. Therefore, in first position A of pilot valve assembly 105, fluid pressure on the downstream side of pressure-reducing valve assembly 100 acts on the end of isolation valve assembly 104, causing isolation valve assembly 104 to move to first position A. In the second position B of the pilot valve assembly 105, port 105a is blocked, while ports 105b and 105c are connected to each other, allowing fluid communication between the reservoir or tank 24 and the end 104i of the isolation valve assembly 104. Thus, in the second position B of the pilot valve assembly 105, the spring force from spring 104h is greater than any force generated by fluid pressure from the tank or reservoir 24, thereby allowing spring 104h to act on the end of the isolation valve assembly 104 to move the isolation valve assembly 104 to the second position B. In the example shown, the pilot valve assembly 105 is operated between positions A and B by an actuator 105d (such as a variable solenoid). Although not shown, a spring may be provided on the opposite end to bias the pilot valve assembly 105 to the second position B.

[0048] In an alternative example, the isolation valve assembly 104 may be provided without the pilot valve assembly 105 . Figure 4 An example of this is shown, where the steering circuit 100 is shown with Figure 2 The same is depicted, except that the isolation valve assembly 104 is provided with an actuator 104j (such as a solenoid) rather than the pilot valve assembly 105. Thus, the actuator 104j can be energized to operate the isolation valve assembly toward the first position A.

[0049] In the depicted examples, valve assemblies 102, 104, 105, 106, and 108 are generally shown as sleeve- and spool-type valve assemblies. However, other types of valve assemblies may be used without departing from the concepts presented herein. Furthermore, while the valve assemblies are schematically shown as separate valve assemblies, some or all of the valve assemblies depicted may be provided within a single physical housing assembly, optionally including other valve assemblies associated with the working circuit 200. In some examples, multiple housing assemblies are assembled together so that all valves associated with the working and steering sections are provided as a single assembly, as is the case with some models of Eaton's CMA Advanced Mobility Valve. It should also be noted that the use of the isolation valve assembly 104 is not limited to use in conjunction with a single metering valve assembly 102 for steering applications. For example, the isolation valve assembly 104 may be used with two independent metering valves, such as two three-way, three-position valves, where one valve controls flow to and from actuator port 22d and the other valve controls flow to and from actuator port 22e. For example, isolation valve assembly 104 may be used with an actuator associated with a section of work circuit 200 (eg, a lift, tilt, or side actuator) or another portion of work machine 10 (such as a brake circuit).

[0050] Electronic control systems

[0051] In one aspect, work machine 10 may be provided with a control system to operate various aspects of the hydraulic system, such as Figure 2 、 Figure 4 and Figure 5 Schematically shown. In one aspect, the control system includes a controller 50 that receives input signals and generates output signals for controlling the work machine 10. In the example presented, the controller 50 is shown only as receiving and sending inputs and outputs related to the isolation valve assembly 104. However, a skilled artisan will recognize that other control functions of the work machine 10 (e.g., control of the pump 20, the work circuit 200, the valve assemblies 102, 106, 108, etc.) can be incorporated into the controller 50, or that functions related to the isolation valve assembly 104 (described below) can be incorporated into a larger system controller that controls all functions of the work machine 10.

[0052] Reference Figure 3 , the electronic controller 50 is schematically shown as including a processor 50A and a non-transitory storage medium or memory 50B, such as RAM, a flash drive, or a hard drive. The memory 50B is used to store executable code, operating parameters, and input from an operator interface, while the processor 50A is used to execute the code.

[0053] The electronic controller 50 may have a number of inputs and outputs that can be used to operate the isolation valve assembly 104. For example, the inputs and outputs may be in the form of pressure and position sensors. Other examples of inputs are vehicle status, engine status / speed, pump status / displacement / demand, and the positions of other valve assemblies, which may be provided as direct inputs to the electronic controller 50 or received from another part of the control system via a control area network (CAN). One input to the electronic controller 50 is a diagnostic pressure signal 52 received from the pressure sensor 112 of the isolation valve assembly 104. One output of the electronic controller 50 is an isolation valve position signal 54 that is sent to actuator 104j or actuator 105d (depending on the system configuration).

[0054] The electronic controller 50 may also include a plurality of algorithms or control schemes that relate the inputs and outputs of the controller 50 to each other. In one embodiment, the controller 50 includes an algorithm for verifying the functionality of the isolation valve assembly 104, as further described in the method of operation section below. The electronic controller 50 may also store a number of predefined and / or configurable parameters and offsets for these purposes. As used herein, the term "configurable" refers to parameters or offset values that can be selected in the controller (i.e., via a dip switch) or adjusted within the controller.

[0055] How to operate

[0056] Reference Figure 4 , illustrates operation 1000 of the isolation valve assembly 104. In an initial step 1002, an isolation valve assembly operation verification algorithm or routine is initiated. This step may be performed automatically by the system, or, for example, upon request, such as through user input. When the isolation valve assembly 104 is in its biased state in position B, such as shortly before or after start-up of the work machine 10 or a circuit associated with the isolation valve assembly 104, the controller 50 receives and records the diagnostic pressure signal 52 sensed at the pressure sensor 112. For purposes herein, this reading may be referred to as the first reference pressure signal and is illustrated as being at Figure 4 1004 is executed in step 1006. As previously explained, when the isolation valve assembly 104 is in position B, ports 104a and 104g are connected to each other, placing the pressure sensor 112 in fluid communication with the reservoir or tank. Thus, the first reference pressure signal will generally correspond to the hydraulic pressure of the reservoir or tank.

[0057] After obtaining the first reference pressure signal, the controller 50 moves the isolation valve assembly 104 to position A by sending an output signal to the actuator 104 j or the actuator 105 d in step 1006 .

[0058] Once the isolation valve assembly 104 is in position A, the controller 50 receives and records the diagnostic pressure signal 52 sensed at the pressure sensor 112 at step 1008. For the purposes of this document, this reading may be referred to as the second reference pressure signal. As previously explained, in position A of the isolation valve assembly 104, ports 104b and 104e are connected to each other, placing the pressure sensor 112 in fluid communication with the downstream side of the pressure reducing valve 110. Generally speaking, the pressure reducing valve 110 reduces the fluid pressure provided by the pump 20 to a pressure of approximately 20 bar and provides a relatively constant fluid pressure to the downstream components. Therefore, it can generally be expected that the second reference pressure signal is equal to the downstream pressure of the pressure reducing valve 110.

[0059] In step 1010, the first reference pressure signal and the second reference pressure signal are compared to each other. In one example, if the system and isolation valve assembly 104 are operating correctly, the second reference pressure signal should be significantly higher than the first reference pressure signal; for example, a difference of 20 bar can be expected. If isolation valve assembly 104 fails to enter position A or position B and does not move to the commanded position, the difference between the first and second pressure signals will result in zero, as pressure sensor 112 will simply read the same signal in both cases. Therefore, correct operation of isolation valve assembly 104 can be verified by observing the difference between the first and second reference pressure signals. In one example, a threshold difference is defined such that when the difference between the first and second reference pressure signals is equal to or greater than the threshold difference, isolation valve assembly 104 can be identified as operating normally, and when the difference between the first and second reference pressure signals is less than the threshold difference, isolation valve assembly 104 can be identified as not opening and in a faulty state. The threshold difference can be a fixed value or a calculated value.

[0060] The various embodiments described above are provided by way of illustration only and should not be construed as limiting the appended claims. Those skilled in the art will readily recognize various modifications and changes that may be made without following the exemplary embodiments and applications shown and described herein and without departing from the true spirit and scope of the present disclosure.

Claims

1. A hydraulic circuit comprising: (a) an actuator having a first port and a second port; (b) a metering valve assembly for controlling hydraulic flow into and out of the first port and the second port; as well as (c) an isolation valve assembly positioned between the actuator and the metering valve assembly, the isolation valve assembly comprising a first inlet port configured for fluid communication with a pressure source of the hydraulic circuit, a second inlet port configured for connection to a reservoir of the hydraulic circuit, and a pressure sensing port configured for connection to a pressure sensor; (d) a pressure sensor connected to the pressure sensing port; (e) 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 the isolation valve assembly is spring biased to the second position; and (f) wherein the first inlet port and the pressure sensing port are in fluid communication with each other when the isolation valve assembly is moved to one of the first position and the second position, and wherein the second inlet port and the pressure sensing port are in fluid communication when the isolation valve assembly is moved to the other of the first position or the second position.

2. The hydraulic circuit according to claim 1, wherein: The isolation valve assembly is a spool valve assembly.

3. The hydraulic circuit according to claim 1, wherein: When the isolation valve assembly is moved to the first position, the first inlet port and the pressure sensing port are 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 in fluid communication.

4. The hydraulic circuit according to claim 1, wherein: The isolation valve assembly is actuated toward the second position by a solenoid actuator.

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

6. The hydraulic circuit according to claim 1, wherein: The isolation valve assembly includes: (a) a first port and a second port configured to be in fluid communication with a metering valve assembly; (b) a third port and a fourth port configured to be in fluid communication with the actuator; and (c) wherein, when the isolation valve is in the first position, the first port and the third port are in fluid communication with each other, the second port and the fourth port are in fluid communication with each other, the first inlet port and the pressure sensing port are in fluid communication with each other, and the second inlet port is blocked; (d) wherein, when the isolation valve is in the second position, the first port to the fourth port and the first inlet port are blocked, and the second inlet port and the pressure sensing port are in fluid communication with each other.

7. A method for determining the functional status of an isolation valve assembly in a hydraulic circuit according to claim 1, the method comprising the steps of: (a) providing a hydraulic circuit as claimed in any one of the preceding claims; (b) initiating an operational verification routine for the isolation valve assembly in the hydraulic circuit; (c) reading a first diagnostic pressure value via a pressure sensor in the hydraulic circuit when the isolation valve assembly is in the first position; (d) moving the isolation valve assembly to the second position; (e) reading a second diagnostic pressure value via a pressure sensor in the hydraulic circuit when the isolation valve assembly is in the second position; and (f) Determining whether the isolation valve assembly is functioning properly by comparing the first diagnostic pressure value and the second diagnostic pressure value.

8. The method of claim 7, wherein: The step of reading a first diagnostic pressure value includes sensing a pressure associated with a reservoir of the hydraulic circuit.

9. The method of claim 8, wherein: The step of reading a second diagnostic pressure value includes sensing a pressure associated with a pump side of the hydraulic circuit.

10. The method of claim 7, wherein: The determining step includes comparing a difference between the first diagnostic pressure value and the second diagnostic pressure value.

11. The method according to claim 10, wherein: The determining includes identifying the isolation valve assembly as being in a fault condition when a difference between the first diagnostic pressure value and the second diagnostic pressure value is below a threshold value.

12. The method of claim 11, wherein: This threshold is a predetermined threshold.

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