Hydraulic system having IMV ride control configuration

A hydraulic control system for a work machine is disclosed. The hydraulic control system has a source of pressurized fluid and at least one actuator having a first and a second chamber. The hydraulic control system also has a first independent metering valve disposed between the source and the first chamber, and a second independent metering valve disposed between the reservoir and the second chamber. The first and second independent metering valves each have a valve element movable from a flow blocking to a flow passing position to facilitate movement of the at least one actuator. The hydraulic control system further has an accumulator and a third independent metering valve disposed in parallel with the first independent metering valve and between the accumulator and the first chamber. The third independent metering valve is configured to selectively communicate the accumulator with the first chamber to cushion movement of the at least one actuator.

TECHNICAL FIELD

The present disclosure relates generally to a hydraulic system, and more particularly, to a hydraulic system having an IMV Ride Control configuration.

BACKGROUND

Work machines such as, for example, dozers, loaders, excavators, motor graders, and other types of heavy machinery use hydraulic actuators coupled to a work implement for manipulation of a load. Such work machines generally do not include shock absorbing systems and thus may pitch, lope, or bounce upon encountering uneven or rough terrain. The substantial inertia of the work implement and associated load may tend to exacerbate these movements resulting in increased wear of the work machine and discomfort for the operator.

One method of reducing the magnitude of the movements attributable to the work implement and associated load is described in U.S. Pat. No. 5,733,095 (the '095 patent) issued to Palmer et al. on Mar. 31, 1998. The '095 patent describes a work machine with a ride control system having a three-way solenoid-actuated directional control valve connected to move a hydraulic actuator in response to movements of a control lever, and a ride control arrangement. The ride control arrangement includes a valve mechanism associated with the hydraulic actuator and an accumulator. The valve mechanism includes a first valve and a second valve. The first valve is movable to selectively control fluid flow from the hydraulic actuator to the accumulator or to a reservoir. The second valve is controlled to move the first valve, thereby providing ride control. When the first valve is moved to communicate fluid from the hydraulic actuator to the accumulator, movement of a work implement connected to the hydraulic actuator is cushioned by flow between the hydraulic actuator and the accumulator. Consequently, the force of a load associated with the work implement is prevented from transference to a frame of the work machine to cause a jolt thereto and subsequently to wheels of the work machine, which could cause the work machine to lope or bounce.

Although the ride control system of the '095 patent may reduce some undesired movements of the work machine, it may be complex, expensive, and lack precision and responsiveness. In particular, because the '095 patent uses different types of valves to actuate the hydraulic actuator and to provide ride control, the system may be complex to control and expensive to build and maintain. Further, because the directional control valve is a three-position valve that controls both a filling function and a draining function associated with the hydraulic actuator, it may be costly and difficult to precisely tune.

The disclosed hydraulic system is directed to overcoming one or more of the problems set forth above.

SUMMARY OF THE INVENTION

In one aspect, the present disclosure is directed to a hydraulic control system for a work machine. The hydraulic control system includes a reservoir configured to hold a supply of fluid, a source configured to pressurize the fluid, and at least one actuator having a first chamber and a second chamber. The hydraulic control system also includes a first independent metering valve disposed between the source and the first chamber and a second independent metering valve disposed between the reservoir and the second chamber. The first independent metering valve has a valve element movable from a flow blocking position to a flow passing position to facilitate movement of the at least one actuator in a first direction. The second independent metering valve has a valve element movable from a flow blocking position to a flow passing position to facilitate movement of the at least one actuator in the first direction. The hydraulic control system also includes an accumulator and a third independent metering valve disposed in parallel with the first independent metering valve and between the accumulator and the first chamber. The third independent metering valve is configured to selectively communicate the accumulator with the first chamber to cushion movement of the at least one actuator.

In another aspect, the present disclosure is directed to a method of controlling a hydraulic system. The method includes pressurizing a supply of fluid and moving a first valve element of a first independent metering valve from a flow blocking position to a flow passing position to direct the pressurized fluid to a first chamber of an actuator, thereby facilitating movement of the actuator in a first direction. The method further includes moving a second valve element of a second independent metering valve from a flow blocking position to a flow passing position to drain fluid from a second chamber of the actuator, thereby facilitating movement of the actuator in the first direction. The method additionally includes moving a third valve element of a third independent metering valve from a flow blocking position to a flow passing position to direct pressurized fluid between the first chamber and an accumulator, thereby cushioning movement of the actuator.

DETAILED DESCRIPTION

FIG. 1illustrates an exemplary work machine10. Work machine10may be a mobile machine that performs some type of operation associated with an industry such as mining, construction, farming, transportation, or any other industry known in the art. For example, work machine10may be an earth moving machine such as a loader, a dozer, an excavator, a backhoe, a motor grader, a dump truck, or any other earth moving machine. Work machine10may include a frame12, a work implement14movably attachable to work machine10, an operator interface16, a power source18, and one or more hydraulic actuators20.

Frame12may include any structural member that supports movement of work machine10and work implement14. Frame12may embody, for example, a stationary base frame connecting power source18to work implement14, a movable frame member of a linkage system, or any other structural member known in the art.

Numerous different work implements14may be attachable to a single work machine10and controllable via operator interface16. Work implement14may include any device used to perform a particular task such as, for example, a bucket, a fork arrangement, a blade, a shovel, a ripper, a dump bed, a broom, a snow blower, a propelling device, a cutting device, a grasping device, or any other task-performing device known in the art. Work implement14may be connected to work machine10via a direct pivot, via a linkage system, or in any other appropriate manner. Work implement14may be configured to pivot, rotate, slide, swing, lift, or move relative to work machine10in any manner known in the art.

Operator interface16may be configured to receive input from a work machine operator indicative of a desired work implement movement. Specifically, operator interface16may include an operator interface device22.

Operator interface device22may embody, for example, a single- or multi-axis joystick located to one side of an operator station. Operator interface device22may be a proportional-type controller configured to position and/or orient work implement14. It is contemplated that additional and/or different operator interface devices may be included within operator interface16such as, for example, wheels, knobs, push-pull devices, switches, buttons, pedals, and other operator interface devices known in the art.

Power source18may be an engine such as, for example, a diesel engine, a gasoline engine, a gaseous fuel-powered engine such as a natural gas engine, or any other type of engine known in the art. It is contemplated that power source18may alternatively embody another source of power such as a fuel cell, a power storage device, an electric or hydraulic motor, or another source of power known in the art.

As illustrated inFIG. 2, work machine10may include a hydraulic control system24having a plurality of fluid components that cooperate together to move work implement14. Specifically, hydraulic control system24may include a tank26holding a supply of fluid, and a source28configured to pressurize the fluid and to direct the pressurized fluid to hydraulic actuator20.

Hydraulic control system24may also include a rod end supply valve32, a rod end drain valve34, a head end supply valve36, a head end drain valve38, an accumulator40, and an accumulator valve42. Hydraulic control system24may further include a controller48in communication with the fluid components of hydraulic control system24. It is contemplated that hydraulic control system24may include additional and/or different components such as, for example, check valves, pressure relief valves, makeup valves, pressure-balancing passageways, and other components known in the art.

Tank26may constitute a reservoir configured to hold a supply of fluid. The fluid may include, for example, a dedicated hydraulic oil, an engine lubrication oil, a transmission lubrication oil, or any other fluid known in the art.

One or more hydraulic systems within work machine10may draw fluid from and return fluid to tank26. It is also contemplated that hydraulic control system24may be connected to multiple separate fluid tanks.

Source28may be configured to produce a flow of pressurized fluid and may embody a pump such as, for example, a variable displacement pump, a fixed displacement variable delivery pump, a fixed displacement fixed delivery pump, or any other suitable source of pressurized fluid. Source28may be drivably connected to power source18of work machine10by, for example, a countershaft50, a belt (not shown), an electrical circuit (not shown), or in any other appropriate manner. Alternatively, source28may be indirectly connected to power source18via a torque converter, a gear box, or in any other manner known in the art. It is contemplated that multiple sources of pressurized fluid may be interconnected to supply pressurized fluid to hydraulic control system24.

Hydraulic actuator20may embody a fluid cylinder that connects work implement14to frame12via a direct pivot, via a linkage system with hydraulic actuator20being a member in the linkage system (referring toFIG. 1), or in any other appropriate manner. It is contemplated that a hydraulic actuator other than a fluid cylinder may alternatively be implemented within hydraulic control system24such as, for example, a hydraulic motor or another appropriate hydraulic actuator. As illustrated inFIG. 2, hydraulic actuator20may include a tube52and a piston assembly54disposed within tube52. One of tube52and piston assembly54may be pivotally connected to frame12, while the other of tube52and piston assembly54may be pivotally connected to work implement14. It is contemplated that tube52and/or piston assembly54may alternatively be fixedly connected to either frame12or work implement14. Hydraulic actuator20may include a rod chamber56and a head chamber58separated by a piston60. Rod and head chambers56,58may be selectively supplied with pressurized fluid from source28and selectively connected with tank26to cause piston assembly54to displace within tube52, thereby changing the effective length of hydraulic actuator20. The expansion and retraction of hydraulic actuator20may function to assist in moving work implement14.

Piston assembly54may include piston60being axially aligned with and disposed within tube52, and a piston rod62connectable to one of frame12and work implement14(referring toFIG. 1). Piston60may include a first hydraulic surface64and a second hydraulic surface66opposite first hydraulic surface64. An imbalance of force caused by fluid pressure on first and second hydraulic surfaces64,66may result in movement of piston assembly54within tube52. For example, a force on first hydraulic surface64being greater than a force on second hydraulic surface66may cause piston assembly54to retract within tube52to decrease the effective length of hydraulic actuator20. Similarly, when a force on second hydraulic surface66is greater than a force on first hydraulic surface64, piston assembly54will displace and increase the effective length of hydraulic actuator20. A flow rate of fluid into and out of rod and head chambers56and58may determine a velocity of hydraulic actuator20, while a pressure of the fluid in contact with first and second hydraulic surfaces64and66may determine an actuation force of hydraulic actuator20. A sealing member (not shown), such as an o-ring, may be connected to piston60to restrict a flow of fluid between an internal wall of tube52and an outer cylindrical surface of piston60.

Rod end supply valve32may be disposed between source28and rod chamber56and configured to regulate a flow of pressurized fluid to rod chamber56in response to a command velocity from controller48. Specifically, rod end supply valve32may be an independent metering valve (IMV) having a proportional spring-biased valve element that is solenoid actuated and configured to move between a first position at which fluid flow is blocked from rod chamber56and a second position at which fluid is allowed to flow into rod chamber56. The valve element of rod end supply valve32may be movable to any position between the first and second positions to vary the rate of flow into rod chamber56, thereby affecting the velocity of hydraulic actuator20. It is contemplated that rod end supply valve32may be configured to allow fluid from rod chamber56to flow through rod end supply valve32during a regeneration event when a pressure within rod chamber56exceeds a pressure directed from source28to rod end supply valve32.

Rod end drain valve34may be disposed between rod chamber56and tank26and configured to regulate a flow of fluid from rod chamber56to tank26in response to the command velocity from controller48. Specifically, rod end drain valve34may be an IMV having a proportional spring-biased valve element that is solenoid actuated and configured to move between a first position at which fluid is blocked from flowing from rod chamber56and a second position at which fluid is allowed to flow from rod chamber56. The valve element of rod end drain valve34may be movable to any position between the first and second positions to vary the rate of flow from rod chamber56, thereby affecting the velocity of hydraulic actuator20.

Head end supply valve36may be disposed between source28and head chamber58and configured to regulate a flow of pressurized fluid to head chamber58in response to the command velocity from controller48. Specifically, head end supply valve36may be an IMV having a proportional spring-biased valve element configured to move between a first position at which fluid is blocked from head chamber58and a second position at which fluid is allowed to flow into head chamber58. The valve element of head end supply valve36may be movable to any position between the first and second positions to vary the rate of flow into head chamber58, thereby affecting the velocity of hydraulic actuator20. It is further contemplated that head end supply valve36may be configured to allow fluid from head chamber58to flow through head end supply valve36during a regeneration event when a pressure within head chamber58exceeds a pressure directed to head end supply valve36from source28or during a ride control mode.

Head end drain valve38may be disposed between head chamber58and tank26and configured to regulate a flow of fluid from head chamber58to tank26in response to a command velocity from controller48. Specifically, head end drain valve38may be an IMV having a proportional spring-biased valve element configured to move between a first position at which fluid is blocked from flowing from head chamber58and a second position at which fluid is allowed to flow from head chamber58. The valve element of head end drain valve38may be movable to any position between the first and second positions to vary the rate of flow from head chamber58, thereby affecting the velocity of hydraulic actuator20.

Accumulator40may be selectively communicated with head chamber58by way of accumulator valve42to selectively receive pressurized fluid from and direct pressurized fluid to hydraulic cylinder20. In particular, accumulator40may be a pressure vessel filled with a compressible gas and configured to store pressurized fluid for future use as a source of fluid power. The compressible gas may include, for example, nitrogen or another appropriate compressible gas. As fluid within head chamber58exceeds a predetermined pressure while accumulator valve42and head end supply valve36are in a flow passing condition, fluid from head chamber58may flow into accumulator40. Because the nitrogen gas is compressible, it may act like a spring and compress as the fluid flows into accumulator40. When the pressure of the fluid within head chamber58then drops below a predetermined pressure while accumulator valve42and head end supply valve36are in the flow passing condition, the compressed nitrogen within accumulator40may urge the fluid from within accumulator40back into head chamber58.

To smooth out pressure oscillations within hydraulic cylinder20, the hydraulic system24may absorb some energy from the fluid as the fluid flows between head chamber58and accumulator40. The damping mechanism that accomplishes this may include a restrictive orifice44disposed within either accumulator valve42, or within a fluid passageway between accumulator40and head chamber58. Each time work implement14moves in response to uneven terrain, fluid may be squeezed through restrictive orifice44. The energy expended to force the oil through restrictive orifice44may be converted into heat, which may be dissipated from hydraulic system24. This dissipation of energy from the fluid essentially absorbs the bouncing energy, making for a smoother ride of work machine10.

Accumulator valve42may be disposed in parallel with head end supply valve36and between accumulator40and head chamber58. Accumulator valve42may be configured to regulate a flow of pressurized fluid between accumulator40and head chamber58in response to a command velocity from controller48. Specifically, accumulator valve42may be an IMV having a proportional spring-biased valve element configured to move between a first position at which fluid is blocked from flowing between head chamber58and accumulator40, and a second position at which fluid is allowed to flow between head chamber58and accumulator40. When in ride control mode, it is contemplated that instead of a fixed restrictive orifice44, the valve element of accumulator valve42may be controllably moved to any position between the flow passing and the flow blocking position to vary the restriction and associated rate of fluid between head chamber58and accumulator40, thereby affecting the cushioning of hydraulic actuator20during travel of work machine10. It is further contemplated that, when in an operational mode other than ride control mode, accumulator valve42may be further configured to supply fluid to head chamber58for intended movements of hydraulic actuator20, when source28has insufficient capacity to produce a desired velocity of hydraulic actuator20.

Rod and head end supply and drain valves32–38and accumulator valve42may be fluidly interconnected. In particular, rod and head end supply valves32,36may be connected in parallel to a common supply passageway68extending from source28. Rod and head end drain valves34,38may be connected in parallel to a common drain passageway70leading to tank26. Rod end supply and drain valves32,34may be connected to a common rod chamber passageway72for selectively supplying and draining rod chamber56in response to velocity commands from controller48. Head end supply and drain valves36,38and accumulator valve42may be connected to a common head chamber passageway74for selectively supplying and draining head chamber58in response to the velocity commands from controller48.

Controller48may embody a single microprocessor or multiple microprocessors that include a means for controlling an operation of hydraulic control system24. Numerous commercially available microprocessors can be configured to perform the functions of controller48. It should be appreciated that controller48could readily embody a general work machine microprocessor capable of controlling numerous work machine functions. Controller48may include a memory, a secondary storage device, a processor, and any other components for running an application. Various other circuits may be associated with controller48such as power supply circuitry, signal conditioning circuitry, solenoid driver circuitry, and other types of circuitry.

One or more maps relating interface device position and command velocity information for hydraulic actuator20may be stored in the memory of controller48. Each of these maps may be in the form of a table, a map, an equation, or in another suitable form. The relationship maps may be automatically or manually selected and/or modified by controller48to affect actuation of hydraulic actuator20.

Controller48may be configured to receive input from operator interface device22and to command a velocity for hydraulic actuator20in response to the input. Specifically, controller48may be in communication with rod and head end supply and drain valves32–38of hydraulic actuator20via communication lines80–86respectively, with operator interface device22via a communication line88, and with accumulator valve42via a communication line90. Controller48may receive the interface device position signal from operator interface device22and reference the selected and/or modified relationship maps stored in the memory of controller48to determine command velocity values.

These velocity values may then be commanded of hydraulic actuator20causing rod and head end supply and drain valves32–38and/or accumulator valve42to selectively fill or drain rod and head chambers56and58associated with hydraulic actuator20to produce the desired work implement velocity.

Controller48may also be configured to initiate a ride control mode. In particular, controller48may either be manually switched to ride control mode or may automatically enter ride control mode in response to one or more inputs. For example, a button, switch, or other operator control device (not shown) may be associated with operator station16that, when manually engaged by a work machine operator, causes controller48to enter the ride control mode. Conversely, controller48may receive input indicative of a travel speed of work machine10, a loading condition of work machine10, a position or orientation of work implement14, or other such input, and automatically enter the ride control mode. When in ride control mode, controller48may cause the valve elements of rod end supply valve32and head end drain valve38to move to or remain in the flow blocking positions. Controller48may then move the valve elements of rod end drain valve34, head end supply valve36, and accumulator valve42to the flow passing position. As described above, accumulator valve42may be moved to the flow passing position to allow fluid to flow between head chamber58and accumulator40for absorption of energy from the fluid each time the fluid passes through restrictive orifice44. Head end supply valve36may be moved to the flow passing position to allow fluid flow between accumulator valve42and head chamber58. Rod end drain valve34may be moved to the flow passing position to prevent hydraulic lock during an up-bounce of work implement14as fluid is flowing from accumulator40into head chamber58. It is also contemplated that the valve elements of rod end drain valve34and head end supply valve36may be selectively positioned between the flow passing and flow blocking positions to vary the restriction of the fluid exiting and/or entering head and rod chambers56and58, thereby increasing dampening during ride control mode.

One or more sensors92,94may be associated with controller48to facilitate precise pressure control of the fluid within accumulator40. Pressure sensor92may be located to monitor the pressure of fluid within head chamber58, while sensor94may be located to monitor the pressure of fluid entering accumulator40. Sensors92and94may be in communication with controller48by way of communication lines96and98, respectively. To minimize undesired movement of work implement14upon initiation of the ride control mode, the pressure of the fluid within accumulator40may be substantially matched to the pressure within head chamber58. The pressure within accumulator40may be varied by moving accumulator valve42to the flow passing position and selectively moving head end supply and drain valves32,34between the flow passing and blocking positions, and/or by operating source28. Head end supply and drain valves32,34may be selectively moved in response to a pressure differential between the fluids monitored by sensors92and94to drain accumulator40while source28may be selectively operated to fill accumulator40, thereby substantially balancing the pressures of the fluid within accumulator40and head chamber58.

INDUSTRIAL APPLICABILITY

The disclosed hydraulic control system may be applicable to any work machine that includes a hydraulic actuator connected to a work implement.

The disclosed hydraulic control system may improve ride control of the work machine by minimizing undesired movements of the work machine that are attributable to inertia of the work implement and an associated load. The operation of hydraulic control system24will now be explained.

During operation of work machine10, a work machine operator may manipulate operator interface device22to create a movement of work implement14. The actuation position of operator interface device22may be related to an operator expected or desired velocity of work implement14. Operator interface device22may generate a position signal indicative of the operator expected or desired velocity and send this position signal to controller48.

Controller48may be configured to determine a command velocity for hydraulic actuator20that results in the operator expected or desired velocity. Specifically, controller48may be configured to receive the operator interface device position signal and to compare the operator interface device position signal to the relationship map stored in the memory of controller48to determine an appropriate velocity command signal. Controller48may then send the command signal to rod and head end supply and drain valves32–38to regulate the flow of pressurized fluid into and out of rod and head chambers56,58, thereby causing movement of hydraulic actuator20that substantially matches the operator expected or desired velocity.

In some situations, such as during an operational mode other than ride control, the flow of pressurized fluid from source28may be insufficient to extend hydraulic actuator20at the operator-desired velocity. In these situations, controller48may move the valve elements of accumulator valve42and head end supply valve36to the flow passing position to allow pressurized fluid to flow from accumulator40to head chamber58.

Accumulator40may also be used during ride control mode. Specifically, when controller48either automatically enters or is manually caused to enter ride control mode, controller48may move the valve elements of rod end supply valve32and head end drain valve38to the flow blocking position (or retain them in the flow blocking position if already in the flow blocking position) and move the valve elements of accumulator valve42, head end supply valve36, and rod end drain valve34to the flow passing position. When in ride control mode, fluid may be allowed to drain from rod chamber56and flow into and out of head chamber58. As fluid both leaves rod chamber56and flows into and out of head chamber58, bounce energy may be absorbed as the fluid flow is restricted.

The pressure of fluid within accumulator40and head chamber58may be substantially balanced before fluid is allowed to flow between accumulator40and head chamber58during ride control mode. In particular, if the fluids within accumulator40and head chamber58are not substantially balanced prior to the direction of fluid between accumulator40and head chamber58, work implement14may move undesirably upon initiation of ride control mode. For example, if the pressure of the fluid within accumulator40exceeds the pressure of the fluid within head chamber58, upon moving the valve elements of head end supply valve36and accumulator valve42to the flow passing positions to initiate ride control mode operation, the fluid within accumulator40may flow into head chamber58and raise work implement14. Conversely, if the pressure of the fluid within head chamber58exceeds the pressure of the fluid within accumulator40, upon moving the valve elements of head end supply valve36and accumulator valve42to the flow passing positions, the fluid within head chamber58may flow into accumulator40causing work implement14to drop.

The pressure of the fluid within accumulator40and head chamber58may be balanced by selectively moving the valve elements of rod end supply and drain valves32,34between the flow passing and flow blocking positions, and/or by operating source28. For example, if a reduction of the pressure of the fluid within accumulator40is desired, the valve elements of both rod end and supply and drain valves32,34may be moved to the flow passing position to allow fluid from accumulator40to flow through rod end supply and drain valves32,34to tank26. Similarly, if an increase in the pressure of the fluid within accumulator40is desired, the valve elements of rod and head end supply valves32,36may be moved to the flow blocking position and then source28caused to produce a flow of pressurized fluid. When the valve elements of both of head and rod end supply valves32,36are in the flow blocking position and source28is creating a flow of pressurized fluid, the flow may be forced into accumulator40, thereby increasing the pressure of the fluid within.

Because hydraulic control system24may utilize five substantially identical independent metering valves, the cost and complexity of hydraulic control system may be low. In particular, because of the commonality of the IMVs, the cost to build and service hydraulic control system24be low compared to a system having different types of control valves. For example the cost to produce a single type of valve, to stock a single type of valve, to train a technician to assemble or service a single type of valve, and other associated costs may be much less than those costs associated with a system having multiple valve types. In addition, because the IMVs are substantially identical, the control strategies governing operation of the IMVs may also be similar, potentially resulting in less software related expense and complexity.

In addition, because the IMVs are only two position valves, the cost of the IMVs may be low. Specifically, a valve having more than two positions requires additional machining processes and material, which increases the base price of the IMV. In addition, the difficulty of precisely tuning a valve having more than two positions increases at a rate proportional to the number of positions.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed hydraulic control system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed hydraulic control system. For example, hydraulic cylinder20may be differently oriented such that accumulator40and accumulator valve42are more appropriately associated with rod chamber56rather than head chamber58for effective use during ride control mode. In addition, accumulator40and accumulator valve42may be associated with multiple hydraulic actuators20and/or multiple hydraulic circuits. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.