Patent Application
20120152629
The present disclosure relates generally to a hydraulic system, and more particularly, to a hydraulic system having a load lock valve.
Motor graders are commonly used in earth leveling applications such as road maintenance or surface contouring, where the motor graders are required to follow a defined course while scraping a work tool such as a blade or a ripper against a work surface to remove material from the work surface. A motor grader typically has a front frame containing a front axle with steerable wheels, and a rear frame containing tandem rear axles with non-steerable and driven wheels. The front frame is connected to the rear frame by an articulation joint. Steering of a motor grader is accomplished by pivoting the front wheels relative to the front axle, by actuating articulation cylinders located on either side of the articulation joint to pivot the front frame relative to the rear frame, or by both pivoting the front wheels and articulating the front frame at the same time.
When steering by turning the front wheels while simultaneously articulating the front frame, overrunning loads can be induced within the articulation cylinders that cause voiding of the cylinders. That is, the articulation cylinders, because of steering at the front wheels, could be forced to extend or retract faster than normally possible by articulation steering alone. This overrunning condition can cause a significant pressure differential across the cylinders (voiding) that could damage the cylinders and/or valving associated with the cylinders. For this reason, some articulation cylinders are provided with load lock valves that restrict fluid flows exiting the cylinders to thereby reduce the likelihood of voiding. Unfortunately, it may be possible for these load lock valves to stick and thereby cause undesired instabilities in machine steering and travel.
An example of a load lock valve is disclosed in U.S. Pat. No. 5,960,814 (the '814 patent) issued to Kot on Oct. 5, 1999. Specifically, the '814 patent discloses a load lock valve for use with a hydraulic cylinder of a load handling system. The load lock valve includes a body having a bore therein, a valve stem disposed within the bore, and a relief piston located end-to-end with the valve stem. The valve stem includes a poppet that is spring-biased to engage a seat when a failure of the load handling system causes a loss of pressure at a rod-end of the hydraulic cylinder. When the poppet engages the seat, no fluid from a head-end of the cylinder is allowed to leave the cylinder. The relief piston holds the poppet away from the seat for normal cylinder movement as long as pressurized fluid is directed into the head end of the cylinder. In this manner, during a failure that causes a sudden drop in pressure at the head end of the cylinder, a load previously lifted by the cylinder is kept from lowering until pressure at the head end is restored.
Although the system of the '814 patent may be applicable to a load handling system, it may lack applicability to a steering system. In particular, the load lock valve of the '814 patent may only function during a failure situation and, in response to the failure, may stop all movement of the cylinder. In addition, the load lock valve of the '814 patent may need to be manually reset before the cylinder can again start functioning. Accordingly, the load lock valve of the '814 patent may do little to reduce the likelihood of voiding during a non-failure situation, and may possibly result in the instabilities described above if applied to a steering system.
The hydraulic system of the present disclosure addresses one or more of the needs set forth above and/or other problems of the prior art.
In one aspect, the present disclosure is directed to a load lock valve. The load lock valve may include a block having a first bore, and a body disposed within the first bore. The body may include a second bore with a first opening at a first end of the body and a second opening at an opposing second end of the body, a first radial port located at the first end of the body in fluid communication with the second bore, a second radial port located between the first radial port and the second end of the body in fluid communication with the second bore, and a valve seat disposed between the first and second radial ports. The load lock valve may also include a poppet disposed within the body and having a nose end, a control end, a balance passage extending from the control end toward the nose end and terminating short of the nose end, and a third radial port located at the nose end in fluid communication with the balance passage. The load lock valve may additionally include a spring located at the control end and configured to bias the poppet toward the first opening. The control end of the poppet is fluidly communicated with the first radial port when a sealing surface at the nose end is against the valve seat.
In another aspect, the present disclosure is directed to a hydraulic control system. The hydraulic control system may include a tank, a pump configured to draw fluid from the tank and pressurize the fluid, and an actuator having a first chamber and a second chamber and being configured to receive the pressurized fluid and discharge fluid to the tank. The hydraulic control system may also include at least one valve disposed between the actuator and the pump and tank and being configured to selectively allow pressurized fluid into the first and second chambers and out of the first and second chambers to move the actuator, and a load lock valve associated with the first chamber. The load lock valve may include a valve element movable against a spring bias from a flow-blocking position toward a flow passing position, and at least one piston movable by a pressure of fluid discharged from the pump into the second chamber to push the valve element against the spring bias. The valve element may be fluidly communicated at opposing ends with a pressure of fluid passing from the first chamber through the load lock valve.
An exemplary embodiment of a machine 10 is illustrated in
One or more hydraulic actuators 30 may be associated with machine 10 to facilitate articulation of front frame 12 relative to rear frame 14. In the disclosed embodiment, two substantially identical hydraulic actuators 30 are associated with machine 10 and disposed in opposition to each other at the sides of articulation joint 16. Each of hydraulic actuators 30 may be attached at a head end 32 to front frame 12 and at a rod end 34 to rear frame 14. To articulate front frame 12 in a counterclockwise direction relative to rear frame 14 (as viewed from above machine 10), the hydraulic actuator 30 located at the left side of machine 10 (as viewed from an operator's perspective) may be retracted to bring the corresponding head and rod ends 32, 34 closer together, while at the same time the hydraulic actuator 30 located at the right side of machine 10 may extend to push the corresponding head and rod ends 32, 34 farther apart.
As shown in
Head- and rod-end pressure chambers 40, 42 may each be selectively supplied with pressurized fluid and drained of the pressurized fluid to cause piston assembly 38 to displace within tube 36, thereby changing an effective length of hydraulic actuators 30. A flow rate of fluid into and out of head- and rod-end pressure chambers 40, 42 may relate to a velocity of hydraulic actuators 30, while a pressure differential between head- and rod-end pressure chambers 40, 42 may relate to a force imparted by hydraulic actuators 30 on the associated frame members.
Machine 10 may include a hydraulic control system 44 having a plurality of fluid components that cooperate to cause the extending and retracting movements of hydraulic actuators 30 described above. Specifically, hydraulic control system 44 may include a tank 46 holding a supply of fluid, and a source 48 configured to pressurize the fluid and direct the pressurized fluid to each of hydraulic actuators 30. Source 48 may be connected to tank 46 via a tank passage 50, and to each hydraulic actuator 30 via a common supply passage 52 and separate head- and rod-end passages 54, 56. Tank 46 may be connected to each hydraulic actuator 30 via a common drain passage 58 and head- and rod-end passages 54, 56. Hydraulic control system 44 may also include a plurality of valves located between hydraulic actuators 30 and tank 46 and source 48 to regulate flows of fluid through passages 52-58.
Source 48 may be configured to draw fluid from one or more tanks 46 and pressurize the fluid to predetermined levels. Specifically, source 48 may embody a pumping mechanism such as, for example, a variable displacement pump having a displacement actuator that adjusts a displacement thereof based on a pressure of hydraulic control system 44, a fixed displacement pump (shown in
In one embodiment, a pressure compensating valve 60 and/or a check valve 62 may be disposed within common supply passage 52 downstream of source 48 to provide a unidirectional supply of fluid having a substantially constant flow from source 48 into the passages of hydraulic control system 44. It is contemplated that, in some applications, pressure compensating valve 60 and/or check valve 62 may be omitted, if desired.
Tank 46 may constitute a reservoir configured to hold a low-pressure 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 machine 10 may draw fluid from and return fluid to tank 46. It is contemplated that hydraulic control system 44 may be connected to multiple separate fluid tanks or to a single tank, as desired.
The valves of hydraulic control system 44 may be disposed within a valve block 63 and include, for example, a head-end supply valve 64, a head-end drain valve 66, a rod-end supply valve 68, and a rod-end drain valve 70. Head-end supply valve 64 may be disposed between common supply passage 52 and head-end passage 54, which may lead to head-end pressure chamber 40 of hydraulic actuator 30. Head-end drain valve 66 may be disposed between head-end passage 54 and common drain passage 58. Rod-end supply valve 68 may be disposed between common supply passage 52 and rod-end passage 56, which may lead to rod-end pressure chamber 42. Rod-end drain valve 70 may be disposed between rod-end passage 56 and common drain passage 58. Each of valves 64-70 may include a variable-position, spring-biased valve element, for example a poppet or spool element, that is solenoid actuated and configured to move to any position between a first end-position at which fluid is allowed to flow through the respective valve, and a second end-position at which fluid flow is blocked.
It is contemplated that one or more of valves 64-70 may include a different number and/or type of elements than described above such as, for example, a fixed-position valve element and/or a valve element that is hydraulically actuated, mechanically actuated, pneumatically actuated, or actuated in another suitable manner. It is further contemplated that some or all of valves 64-70 may be combined and include a fewer number of valve elements, as desired. For example a single spool valve (not shown) may be utilized to regulate all head-end flows associated with hydraulic actuator 30, while another spool valve (not shown) may be utilized to regulate all rod-end flows. In another example, a single spool valve (not shown) may be utilized to regulate all head- and rod-end flows associated with hydraulic actuators 30. It is yet further contemplated that valves 64-70 may be associated with only one of hydraulic actuators 30, or that valves 64-70 may be common to both of hydraulic actuators 30, as desired. When control valves 64-70 are common to both of hydraulic actuators 30, each supply valve (i.e., head-end or rod-end supply valves 64, 68) and each drain valve (i.e., head-end or rod-end drain valves 66, 70) may be associated with head-end pressure chamber 40 of one hydraulic actuator 30 and rod-end pressure chamber 42 of the other hydraulic actuator 30, such that when a particular chamber of one hydraulic actuator 30 is filling, the same chamber of the other hydraulic actuator 30 is draining and vice versa.
As described above, when machine 10 is steered via simultaneous wheel turning and frame articulation, an overrunning condition may be generated that causes voiding of hydraulic actuator 30. For the purposes of this disclosure, the overrunning condition may be considered the condition that exists when piston assembly 38 of hydraulic actuator 30 is mechanically forced to move in a particular direction faster than possible through normal fluid supply to the expanding chamber of hydraulic actuator 30. When piston assembly 38 is moved faster than normally possible, piston assembly 38 may mechanically force one of head- or rod- chambers 40, 42 to contract and discharge fluid at a very high-pressure, while simultaneously drawing down the pressure of the expanding chamber to a very low level (e.g., while creating a near vacuum in the expanding chamber). As piston assembly 38 is forced to move faster by the mechanical interactions of machine 10 during steering, a low-pressure threshold within the expanding chamber of hydraulic actuator 30 will eventually be crossed that could result in damage to hydraulic actuator 30. This state is known as voiding.
To help reduce the likelihood of voiding during the overrunning condition, hydraulic actuator 30 may be provided with a set of load lock valves 72. In particular, a first or head-end load lock valve 72 may be associated with head-end pressure chamber 40 of hydraulic actuator 30, while a second substantially identical load lock valve 72 (i.e., a rod-end load lock valve 72) may be associated with rod-chamber 42. Each of load lock valves 72 may include a valve element 74 moveable by a piston 76 from a flow-blocking position, against the bias of a spring 78, toward a flow-passing position. When valve element 74 is in the flow-blocking position, flow through the respective head- or rod-end passage 54, 56 may be inhibited. When valve element 74 is in the flow-passing position, flow through the respective head- or rod-end passage 54, 56 may be allowed substantially unimpeded by load lock valve 72. Valve element 74 may be moved to any position between the flow-blocking and flow-passing positions to affect a variable restriction on the flow of fluid through load lock valve 72. The restriction on the flow of fluid through load lock valve 72 may function to limit the corresponding movement of piston assembly 38 within hydraulic actuator 30. By limiting the movement of piston assembly 38 during the overrunning condition, source 48 can supply pressurized fluid into the expanding chamber of hydraulic actuator 30, thereby reducing the likelihood of voiding therein. In this manner, regardless of the direction of machine steering (i.e, regardless of whether hydraulic actuators 30 are extending or retracting), both head- and rod-end pressure chambers 40, 42 of each hydraulic actuator 30 may be protected from voiding by its associated load lock valve 72 during over-running loads.
A plurality of pilot passages may be associated with valve element 74 and piston 76. In particular, a first pilot passage 80 of each load lock valve 72 may direct fluid pressure from a corresponding one of head- or rod-end passages 54, 56 at a side of each load lock valve 72 opposite hydraulic actuator 30 (i.e., from an upstream side if the associated chamber is expanding or from a downstream side if the associated chamber is contracting) to push on a spring-end of each valve element 74. Simultaneously, a second pilot passage 82 may direct fluid from the same location within the corresponding one of head- or rod-end passages 54, 56 to push on an end of each valve element 74 opposite spring 70. First and second pilot passages 80, 82 may together substantially hydraulically balance valve element 74 (i.e., first and second pilot passages 80, 82 may function as balance passages for valve element 74). A third pilot passage 84 in each load lock valve 72 may also communicate fluid from second pilot passage 82 to an internal end of piston 76 and thereby urge piston 76 away from the associated valve element 74. A fourth pilot passage 86 may extend from common supply passage 52 to distal ends of each piston 76 and thereby urge pistons 76 toward the associated valve elements 74. It is contemplated that fourth pilot passage 86 may be omitted in some situations, as will be explained in greater detail below.
The cross-sections of
Valve element 74, in the embodiments of
Piston 76, in the embodiment of
Piston 76, in the embodiment of
The disclosed load lock valve may be used with any hydraulic system that is operable under overrunning conditions. The disclosed load lock valve may be particularly useful in steering system applications, where varying levels of flow control are beneficial and manual valve resetting is undesired. The disclosed load lock valves may help to reduce instability that tends to occur when acting to increase the restriction to return flow to prevent the potential increase in cylinder speed of an associated actuator during the overrunning condition and thereby reduce the likelihood of voiding. Operation of hydraulic control system 44 will now be explained.
As shown in
For example, if a retraction of hydraulic actuator 30 is requested, rod-end supply valve 68 may be moved toward the flow-passing position (shown in
As the pressurized fluid from rod-end supply valve 68 flows toward rod-end pressure chamber 42 via rod-end passage 56 during a normal retraction (i.e., during a non-overrunning retraction), the fluid may enter the rod-end load lock valve 72 (right-most load lock valve 72 shown in
During steering of machine 10, when wheels 20 (referring to
During the overrunning extension of hydraulic actuator 30, the pressure of the fluid discharged from hydraulic actuator 30 may be elevated and, in some situations, exceed the pressure of the fluid entering hydraulic actuator 30. That is, the pressure within rod-end pressure chamber 42 may be greater than the pressure within head-end pressure chamber 40 during the overrunning extension of hydraulic actuator 30. In order to limit the movement of hydraulic actuator 30 and reduce the likelihood of voiding in head-end pressure chamber 40, the rod-end load lock valve 72 may be activated to selectively restrict the flow of fluid exiting rod-end pressure chamber 42.
During a normal extension of hydraulic actuator 30, the pressure of the fluid from source 48 entering head-end pressure chamber 40 and space 116 between pistons 76 may be high enough to move the rod-end piston 76 (right-most piston 76 illustrated in
Because valve element 74 may be substantially hydraulically balanced, the likelihood of sticking during the overrunning condition may be reduced. That is, second pilot passage 82, together with third radial port 106, may fluidly communicate both ends of valve element 74 with the same fluid pressure, thereby substantially hydraulically balancing valve element 74 in both the flow-passing and flow-blocking positions. Because valve element 74 may be substantially hydraulically balanced, the likelihood of a pressure differential developing between nose end 102 and control end 104 that causes sticking of valve element 74 may be low. In addition, the larger cross-sectional area at nose end 102, as compared to control end 104, may help ensure that valve element 74 is capable of opening.
It will be apparent to those skilled in the art that various modifications and variations can be made to the hydraulic control system of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the hydraulic control system disclosed herein. For example, it is contemplated that, if the single integral piston 76 is used to move valve elements 74 of both load lock valves 72 (as in the embodiment of
This application is based on and claims the benefit of priority from U.S. Provisional Application No. 61/423,303 by Daniel T. MATHER et al., filed Dec. 15, 2010, the contents of which are expressly incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61423303 | Dec 2010 | US |
