Patent Description:
Work machines, such as off-highway vehicles, fork lifts, wheel loaders, track loaders, excavators, backhoes, bull dozers, and telehandlers are known. Work machines can be used to move material, such as pallets, dirt, and/or debris. The work machines typically include a work implement (e.g., a fork) connected to the work machine. The work implements attached to the work machines are typically powered by a hydraulic system. The hydraulic system can include a hydraulic pump that is powered by a prime mover, such as a diesel engine. Work machines are commonly provided with electronic control systems that rely upon a number of inputs and outputs, for example, pressure sensors, position sensors, and valve actuators. Electro-hydraulic valves often 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. To accurately control such valves, fluid properties must generally be input into the control system.

Some hydraulic systems, for example 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 methods to detect the functional state of safety elements. Real-time fault detection on safety elements can improve the overall safety rating for the system by reducing the number of dangerous faults which would remain undetected in the event of their failure. Oftentimes, the state of isolation functions on electro-hydraulic steering systems must be checked by way of a proxy or verification of flow downstream from the isolation spool. Such approaches can be undesirable as, in many cases, the system requires that wheel movement on the machine be verified (i.e. during machine startup). Improvements are desired.

<CIT> discloses a known hydraulic circuit.

This invention describes a method (hydraulic circuit) for detecting the functional state of a piloted or direct-operated isolation valve which is used to isolate flow output from an electro-hydraulic steering valve. The combination of an integrated diagnostic pressure signal and pressure sensor (i.e. pressure switch) is used to achieve real-time fault detection of the isolation element (i.e. pilot spool valve). This fault detection capability can be employed to raise the diagnostic coverage of the element in accordance with ISO <NUM> and IEC <NUM>. Direct measurement of the isolation functionality is preferable as it eliminates the need for undesirable conditions (such as wheel movement) during startup or normal operation. This invention presents a method of real-time detection for flow isolation valves which does not rely on moving parts of a machine's steering system.

In safety-applicable systems, it is often necessary to verify the functionality of the isolation valve (and pilot) at all times. It is common for the defined "safe state" of the system to be one in which the isolation valve is closed and there is no flow to and from the steering cylinders. One way to directly detect the isolation valve state is to measure the state using a spool position sensor, but another method is presented herein which involves an isolation valve design allowing for the valve state to be determined using a diagnostic pressure signal. A <NUM>-way / <NUM>-position isolation valve acts as a blocking valve for flow between the main-stage spool and the cylinder(s). An additional output pressure signal path (diagnostic signal) connects a dedicated diagnostic signal port to tank pressure when in the closed state (not actuated) and to reduced pilot pressure supply when in the open state (actuated). When the isolation valve is in the unactuated state (isolating), the pressure at the diagnostic port will be equal to tank pressure. When the isolation valve is in the actuated state (flowing), the pressure at the diagnostic port will be equal to reduced pilot supply pressure. The difference between the diagnostic port pressure in each of these two states is generally constant and roughly equal to the PRV pressure setting. Tank pressure variation will affect this somewhat but should be negligible compared to the PRV pressure.

In application, the concepts disclosed herein can be used to detect the state of the isolation valve at any given time. Given the situation when the isolation valve is stuck (or perhaps its pilot valve is stuck), the high-ranking system compares the command signal (i.e. PWM, current, etc.) with the measured pressure at the diagnostic port and determines that a failure has occurred which requires the system to take action (go to "safe" state). The failure would otherwise go undetected until a different part of the system detected the failure or a hazardous situation arose. As stated above, the advent of a diagnostic pressure signal for the isolation valve will allow a higher "diagnostic coverage," known as "DC" per ISO <NUM> and IEC <NUM>, to be claimed for the isolation valve component. This could increase the overall PL or SIL of the system in some cases.

The hydraulic circuit according to the invention includes an actuator having first and second ports, a metering valve assembly for controlling hydraulic flow into and out of the first and second ports, and an isolation valve assembly located between the actuator and the metering valve assembly, the isolation valve assembly including a first inlet port arranged in fluid communication with a pressure source of the hydraulic circuit, a second inlet port arranged in connection with a reservoir of the hydraulic circuit, and a pressure sensing port configured for connection with a pressure sensor. The hydraulic circuit further comprises a pressure sensor connected to the pressure sensing port. 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. The isolation valve assembly is spring biased into the second position. 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 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.

The system at hand 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 may be an open-center, closed center, or load-sensing (static or dynamic signal) valve. The system includes the use of a normally-closed isolation valve which blocks flow between the metering valve and steering cylinder(s). The isolation valve may be directly piloted (using solenoid coil) or hydraulically piloted (using pilot valve). In normal operation, the isolation valve is actuated to allow flow to pass between the metering valve and steering cylinders.

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

In some examples, 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.

In some examples, the isolation valve assembly is actuated towards the first position by a solenoid actuator.

In some examples, the isolation valve assembly further includes a pilot valve assembly for selectively directing pressurized fluid to move the isolation valve assembly towards the first position.

In one example, an isolation valve assembly of the hydraulic circuit includes first and second ports arranged in fluid communication with the metering valve assembly, and third and fourth ports arranged in fluid communication with the actuator. When the isolation valve is in the 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 first inlet port and the pressure sensing port are placed in fluid communication with each other, and the second inlet port is blocked. When the isolation valve is in the second position, the first through fourth and the first inlet port are blocked and the second inlet port and the pressure sensing port are placed in fluid communication with each other.

The method according to the invention for determining a functional state of an isolation valve assembly includes the steps of providing a hydraulic circuit defined in one of the claims, initiating an operation verification routine for the isolation valve assembly, reading by means of the pressure sensor of the hydraulic circuit a first diagnostic pressure value with the isolation valve assembly in the first position, moving the isolation valve assembly to the second position, reading by means of the pressure sensor of the hydraulic circuit a second diagnostic pressure value with the isolation valve assembly in the second position, and determining whether the isolation valve assembly is functional by comparing the first diagnostic pressure value to the second diagnostic pressure value.

In some examples, the step of reading by means of the pressure sensor of the hydraulic circuit a first diagnostic pressure value includes sensing a pressure associated with the reservoir of the hydraulic circuit.

In some examples, the step of reading by means of the pressure sensor of the hydraulic circuit a second diagnostic pressure value includes sensing a pressure associated with a pump side of the hydraulic circuit.

In some examples, the determining step includes comparing the difference between the first and second diagnostic pressure values.

In some examples, the determining 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.

In some examples, the threshold is a predetermined threshold value.

Non-limiting and non-exhaustive embodiments are 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.

Descriptions of a general system, an associated hydraulic system, related control systems, and methods follow.

As depicted at <FIG>, a work machine <NUM> is shown. Work machine <NUM> includes a work attachment <NUM> for performing a variety of lifting tasks associated with a load <NUM>. In one embodiment, work machine <NUM> is a telehandler having a telescoping boom <NUM> that supports the work attachment <NUM>. In one embodiment, the work attachment <NUM> includes a pair of forks. However, one skilled in the art will appreciate that work attachment may be any hydraulically powered work implement.

Work machine <NUM> is also shown as including at least one drive wheel <NUM> and at least one steer wheel <NUM>. In certain embodiments, one or more drive wheels <NUM> may be combined with one or more steer wheels <NUM>. The drive wheels are powered by a power plant <NUM>, for example an electric motor or an internal combustion engine. The power plant <NUM> is also configured to power a hydraulic system including a steering circuit <NUM> and a work circuit <NUM> of the work machine <NUM> via at least one hydraulic pump <NUM>. In one embodiment, pump <NUM> is mechanically coupled to the power plant <NUM>, such as by an output shaft or a power take-off. In one embodiment, pump <NUM> is powered indirectly by the power plant <NUM> via a hydraulic system with a hydraulic motor. The steering circuit <NUM> is controlled by operation of the pump <NUM> in cooperation with a number of hydraulic actuators and control valves. Likewise, the work circuit <NUM> actuates the work attachment <NUM> 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 for effectuating steering in addition to lifting, extending, tilting, and sideways motions of the work attachment <NUM>, powered by the work circuit <NUM>.

Referring to <FIG>, an example of a steering circuit <NUM> of the work machine <NUM> is shown. Steering circuit <NUM> is for controlling the steering of the work machine <NUM> via one or more actuators <NUM>. As depicted the actuator <NUM> is shown as being a linear acting actuator. However, the invention is not limited to only this type of actuator and can be used with other types of actuators, such as rotary type actuators. As depicted, the steering circuit <NUM> also includes a metering valve assembly <NUM>, an isolation valve assembly <NUM>, first and second pressure reducing valve assemblies <NUM>, <NUM>, a and a pressure reference valve assembly <NUM>. Various interconnecting hydraulic passageways and/or lines are also provided with the steering circuit <NUM>. The steering circuit <NUM> is also connected to the hydraulic pump <NUM> and a reservoir or tank <NUM>.

In one aspect, the hydraulic actuator <NUM> includes a first chamber 22a and a second chamber 22b separated by a piston 22c. The hydraulic actuator <NUM> is shown as further including a first port 22d in fluid communication with the first chamber 22a and a second port 22e in fluid communication with the second chamber 22b. Accordingly, as fluid enters the first chamber 22a via the first port 22d, the piston 22c is forced in a first direction which in turn causes fluid to exit the second chamber 22b via the second port 22e. Likewise, as fluid enters the second chamber 22b via the second port 22e, the piston is forced in a second direction opposite the first direction which in turn causes fluid to exit the first chamber 22a. In one aspect, the first direction is associated with steering the work machine <NUM> in one direction while the second direction is associated with steering the work machine <NUM> in the opposite direction.

Fluid into and out of the ports 22d, 22e of the actuator <NUM> is controlled by the metering valve assembly <NUM>. In operation, the metering valve assembly <NUM> selectively places pumped fluid from the pump <NUM> with either the first or second chamber 22a, 22b via the first or second port 22d, 22e and also selectively places the other chamber 22a, 22b via the first or second port 22d, 22e in fluid communication with the tank or reservoir <NUM> such that fluid can exit the opposite chamber 22a, 22b. As shown, the metering valve assembly <NUM> is a three position, four-way valve having ports 102a through 102d. In the first position A of the metering valve assembly <NUM>, pumped fluid from the pump <NUM> flows through ports 102a, 102c of the metering valve assembly <NUM> and into the first chamber 22a via port 22d to drive the piston 22c in the first direction. Concurrently, fluid exiting the second chamber 22b via port 22e flows through ports 102b, 102d of the metering valve assembly <NUM> and to the reservoir or tank <NUM>. In a second position B of the metering valve assembly, pumped fluid from the pump <NUM> flows through ports 102a, 102d of the metering valve assembly <NUM> and into the second chamber 22b via port 22e to drive the piston 22c in the second direction. Concurrently, fluid exiting the first chamber 22a via port 22d flows through ports 102b, 102e of the metering valve assembly <NUM> and to the reservoir or tank <NUM>. In the third position C of the metering valve assembly <NUM>, which is the neutral or open center position, fluid flow out of the chambers 22a, 22b of the actuator <NUM> is blocked at ports 102c, 102d of the metering valve assembly <NUM> while ports 102a, 102b redirect pumped fluid from the pump <NUM>. In the example shown, the pressure reducing pilot valves <NUM>, <NUM> are provided to provide pilot pressure to move the metering valve assembly <NUM> into the first or second positions A, B while centering springs <NUM>, 102n bias the metering valve assembly <NUM> into the center or neutral position C. Although a particular metering and pilot valve assembly is shown, other arrangements are possible. For example, the metering valve assembly <NUM> could also be configured to have a closed-center or configured as a load-sensing (static or dynamic) proportional metering valve utilizing, for example, variable solenoid actuators instead of hydraulic pilot pressure.

With continued reference to <FIG>, the steering circuit <NUM> is shown as further including an isolation valve assembly <NUM>. As arranged, the isolation valve assembly <NUM> is located between the metering valve assembly <NUM> and the actuator <NUM>. Accordingly, the isolation valve assembly <NUM> can operate to block fluid into and out of the actuator chambers 22a, 22b regardless of the position of the metering valve assembly <NUM>. The isolation valve assembly <NUM> can thus provide a safety function in the event of an operational fault associated with the metering valve assembly <NUM> and/or related components, whereby the position of the actuator <NUM> is safely held in place and prevented from moving until the fault is resolved.

As most easily viewed at <FIG>, the isolation valve assembly <NUM> is a two-position, seven-way valve having ports 104a through <NUM>. In a first position A of the isolation valve assembly <NUM>, the port 104a is blocked; the ports 104b and 104e are connected to each other such that fluid communication is opened between the pressure referencing valve assembly <NUM> and a pressure sensor <NUM>; the ports 104c and 104f are open to each other such that fluid communication is opened between the actuator port 22d and the port <NUM> of the metering valve assembly <NUM>; and the ports 104d and <NUM> are open to each other such that fluid communication is opened between the actuator port 22e and the port <NUM> of the metering valve assembly <NUM>. In a second position B of the isolation valve assembly <NUM>, the ports 104a and 104e are open to each other such that fluid communication is opened between the tank or reservoir <NUM> and the pressure sensor <NUM> while the remaining ports 104b, 104c, 104d, 104f, and <NUM> are blocked.

In the example shown at <FIG> and <FIG>, the isolation valve assembly <NUM> is biased toward the second position B by a biasing spring <NUM> and is operated toward the first position A by a pilot valve assembly <NUM> acting on an end 104i of the isolation valve assembly <NUM>. As shown, the pilot valve assembly <NUM> is a three-way, two position valve having ports 105a to 105c. In a first position A of the pilot valve assembly <NUM>, the ports 105a and 105c are connected to each other such that fluid communication is opened between the pressure reducing valve assembly <NUM> and the end 104i of the isolation valve assembly <NUM> and such that the port 105b is blocked. Accordingly, in the first position A of the pilot valve assembly <NUM>, fluid pressure equivalent to the downstream side of the pressure reducing valve assembly <NUM> acts on the end of the isolation valve assembly <NUM> to move the isolation valve assembly <NUM> to the first position A. In a second position B of the pilot valve assembly <NUM>, the port 105a is blocked while the ports 105b and 105c are connected to each other such that fluid communication is open between the reservoir or tank <NUM> and the end 104i of the isolation valve assembly <NUM>. Accordingly, in the second position B of the pilot valve assembly <NUM>, the spring force from the spring <NUM> is greater than any force generated by the fluid pressure from the tank or reservoir <NUM>, thereby allowing the spring <NUM> to act on the end of the isolation valve assembly <NUM> to move the isolation valve assembly <NUM> to the second position B. In the example shown, the pilot valve assembly <NUM> is operated between the 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 <NUM> into the second position B.

In an alternative example, the isolation valve assembly <NUM> can be provided without a pilot valve assembly <NUM>. Such an example is shown at <FIG>, wherein the steering circuit <NUM> is shown as being the same as depicted in <FIG>, but with the exception that the isolation valve assembly <NUM> is provided with an actuator 104j, such as a solenoid, instead of the pilot valve assembly <NUM>. Accordingly, the actuator 104j can be energized to operate the isolation valve assembly towards the first position A.

In the depicted examples, the valve assemblies <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are generally shown as being sleeve and spool type valve assemblies. However, other types of valve assemblies may be used without departing from the concepts presented herein. Additionally, while the valve assemblies are schematically shown as separate valve assemblies, some or all of the depicted valve assemblies can be provided in a single physical housing assembly, optionally including other valve assemblies associated with the work circuits <NUM>. In some examples, multiple housing assemblies are assembled together such that all of the valves associated with the work and steering sections are provided as an overall assembly, as is the case for some models of the Eaton CMA Advanced Mobile Valve. It is also noted that the use of the isolation valve assembly <NUM> is not limited to use in conjunction with a single metering valve assembly <NUM> for a steering application. For example, the isolation valve assembly <NUM> could be used with two independent metering valves, for example two three-position, three-way valves, with one valve controlling flow into and out of the actuator port 22d and the other valve controlling flow into and out of the actuator port 22e. For example, the isolation valve assembly <NUM> could be used with an actuator associated with a section of the work circuit <NUM> (e.g. a lift, tilt, or side actuator) or with another portion of the work machine <NUM>, such as with a brake circuit.

In one aspect, the work machine <NUM> can be provided with a control system to operate the aspects of the hydraulic system, as shown schematically at <FIG>, <FIG>, and <FIG>. In one aspect, the control system includes a controller <NUM> that receives input signals and generates output signals for controlling the work machine <NUM>. In the example presented, the controller <NUM> is only shown as receiving inputs and sending outputs in relation to the isolation valve assembly <NUM>. However, a skilled person will appreciate that the other control functions of the work machine <NUM> (e.g. control of pump <NUM>, work circuit <NUM>, valve assemblies <NUM>, <NUM>, <NUM>, etc.) can be incorporated into the controller <NUM>, or that the functions relating to the isolation valve assembly <NUM>, described below, can be incorporated into a larger system controller that controls all functions of the work machine <NUM>.

Referring to <FIG>, the electronic controller <NUM> is schematically shown as including a processor 50A and a non-transient storage medium or memory 50B, such as RAM, flash drive or a hard drive. Memory 50B is for storing executable code, the operating parameters, the input from the operator interface while processor 50A is for executing the code.

Electronic controller <NUM> may have a number of inputs and outputs that may be used for operating the isolation valve assembly <NUM>. For example, 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 the other valve assemblies, which may be provided as a direct inputs into the electronic controller <NUM> or may be received from another portion of the control system via a control area network (CAN). One input into the electronic controller <NUM> is the diagnostic pressure signal <NUM> received from the pressure sensor <NUM> of the isolation valve assembly <NUM>. One output from the electronic controller <NUM> is the isolation valve position signal <NUM> sent to either the actuator 104j or 105d, depending upon the configuration of the system.

The electronic controller <NUM> may also include a number of algorithms or control schemes to correlate the inputs and outputs of the controller <NUM>. In one embodiment, the controller <NUM> includes an algorithm to verify functionality of the isolation valve assembly <NUM>, as described further in the Method of Operation section below. The electronic controller <NUM> may also store a number of predefined and/or configurable parameters and offsets for such purposes. As used herein, the term "-configurable" refers to a parameter or offset value that can either be selected in the controller (i.e. via a dipswitch) or that can be adjusted within the controller.

Referring to <FIG>, the operation <NUM> of the isolation valve assembly <NUM> is shown. In an initial step <NUM>, an isolation valve assembly operation verification algorithm or routine is initiated. This step can be performed automatically by the system or upon request, for example by a user input. When the isolation valve assembly <NUM> is in its biased state in position B, for example before or shortly after the work machine <NUM> or the circuit associated with the isolation valve assembly <NUM> is activated, the controller <NUM> receives and records the diagnostic pressure signal <NUM> sensed at the pressure sensor <NUM>. For purposes herein, this reading can be referred to as the first reference pressure signal and is shown as being performed at step <NUM> in <FIG>. As explained previously, when the isolation valve assembly <NUM> is in position B, the ports 104a and <NUM> are connected to each other such that the pressure sensor <NUM> is in fluid communication with the reservoir or tank. Accordingly, the first reference pressure signal will generally correspond to the hydraulic pressure at the reservoir or tank.

After the first reference pressure signal is obtained, the controller <NUM> moves the isolation valve assembly <NUM> to the position A by sending an output signal to the actuator 104j or 105d in a step <NUM>.

Once the isolation valve assembly <NUM> is in the position A, the controller <NUM> receives and records the diagnostic pressure signal <NUM> sensed at the pressure sensor <NUM> at a step <NUM>. For purposes herein, this reading can be referred to as the second reference pressure signal. As explained previously, in position A of the isolation valve assembly <NUM>, the ports 104b and 104e are connected to each other such that the pressure sensor <NUM> is in fluid communication with the downstream side of the pressure reducing valve <NUM>. In general terms, the pressure reducing valve <NUM> reduces the fluid pressure supplied by the pump <NUM>, for example down to a pressure of about <NUM> bar, and provides a relatively more constant fluid pressure to the downstream components. Accordingly, the second reference pressure signal generally can be expected to be equal to the downstream pressure at the pressure reducing valve <NUM>.

In a step <NUM>, the first and second reference pressure signals are compared to each other. In one example, if the system and isolation valve assembly <NUM> are operating correctly, the second reference pressure signal should be well above the first second reference pressure signal, for example a difference of <NUM> bar could be anticipated. In instances where the isolation valve assembly <NUM> has failed into either position A or B and does not move to the commanded position, the difference between the first and second pressure signals would resultantly be zero as the pressure sensor <NUM> will simply be reading the same signal in both instances. Accordingly, the proper operation of the isolation valve assembly <NUM> can be verified by observing the difference between the first and second reference pressure signals. In one example, a threshold difference value is defined such that when the difference between the first and second reference pressure signals is equal to or above the threshold difference value, the isolation valve assembly <NUM> can be identified as operating properly and such that when the difference between the first and second reference pressure signals is below the threshold difference value, the isolation valve assembly <NUM> can be identified as not having opened and in a failure state. The threshold difference value can be a fixed value or a calculated value.

Claim 1:
A hydraulic circuit (<NUM>) comprising:
(a) an actuator (<NUM>) having first and second ports (22d, 22e);
(b) a metering valve assembly (<NUM>) for controlling hydraulic flow into and out of the first and second ports (22d, 22e);
(c) an isolation valve assembly (<NUM>) located between the actuator (<NUM>) and the metering valve assembly (<NUM>), the isolation valve assembly (<NUM>) including a first inlet port (104b) arranged in fluid communication with a pressure source (<NUM>) of the hydraulic circuit (<NUM>), a second inlet port (104a) arranged in connection with a reservoir (<NUM>) of the hydraulic circuit (<NUM>), and a pressure sensing port (104e) configured for connection with a pressure sensor (<NUM>); and
(d) a pressure sensor (<NUM>) connected to the pressure sensing port (104e);
wherein
(a) the isolation valve assembly (<NUM>) is movable between a first position, in which fluid flow between the metering valve (<NUM>) and the actuator (<NUM>) is enabled, and a second position, in which fluid flow between the metering valve (<NUM>) and the actuator (<NUM>) is blocked; and
(b) when the isolation valve assembly (<NUM>) is moved to one of the first and second positions, the first inlet port (104b) and the pressure sensing port (104e) are placed in fluid communication with each other and when the isolation valve assembly (<NUM>) is moved to the other of the first or second position, the second inlet port (104a) and the pressure sensing port (104e) are placed in fluid communication, characterized in that the isolation valve assembly (<NUM>) is spring biased into the second position.