Patent Grant
9429175
The present invention relates to hydraulic systems. More particularly, the present invention relates to hydraulic systems for work vehicles and especially hydraulic systems that are compensated to regulate pressure differentials existing across metering orifices of control valves within the hydraulic systems.
Hydraulic systems are employed in many circumstances to provide hydraulic power from a hydraulic power source to multiple loads. In particular, such hydraulic systems are commonly employed in a variety of work vehicles such as excavators and loader-backhoes. In such vehicles, the loads powered by the hydraulic systems may include a variety of hydraulically actuated devices such as piston-cylinder assemblies that lower, raise and rotate arms, and lower and raise buckets, as well as hydraulically-powered motors that drive tracks or wheels of the vehicles. Although the various hydraulically actuated devices typically are powered by a single source (e.g., a single pump), the rates of fluid flow to the different devices typically are independently controllable, through the use of separate control valves (typically spool valves) that are independently controlled by an operator of the work vehicle.
The operation of the hydraulically actuated devices depends upon the hydraulic fluid flow to those devices, which in turn depends upon the cross-sectional areas of metering orifices of the control valves between the pressure source and the hydraulically actuated devices, and also upon the pressure differentials across those metering orifices.
To facilitate control, hydraulic systems often are pressure compensated, that is, designed to set and maintain the pressure differentials across the metering orifices of the control valves, so that controlling of the valves by an operator only tends to vary the cross-sectional areas of the orifices of those valves but not the pressure differentials across those orifices. Such pressure compensated hydraulic systems typically include pressure compensation valves positioned between the respective control valves and the respective hydraulically actuated devices. The pressure compensation valves control the pressures existing on the downstream sides of the metering orifices to produce the desired pressure differentials across the metering orifices.
Such pressure-compensated hydraulic systems normally ensure that the same particular pressure differential (e.g., a pump margin pressure) occurs across each of the control valves. Nevertheless, it may be desirable in some hydraulic systems to have a lower pressure differential across selected valves to reduce the hydraulic fluid flow through those valves. For example, in the case of an excavator, it may be desirable to provide normal hydraulic fluid flow to the cylinders that control lifting or other movement of an arm or bucket of the excavator, or to accessories of the excavator such as a trenching device, yet at the same time desirable to provide reduced hydraulic fluid flow to the hydraulic motors controlling the speeds of the tracks of the excavator so that the excavator travels at reduced speeds. Therefore, there is a need in some hydraulic systems to provide a pressure differential across metering orifices in selected control valves which is less than the pressure differential across other control valves.
This capability of providing adjustable control of the pressure differentials across multiple control valves in an even manner is desirable in many circumstances, since it is often desirable that multiple hydraulic devices of a hydraulic system should receive precisely identical amounts of hydraulic fluid flow when an operator sets the respective control valves identically. For example, with respect to the excavator discussed above, it would be desirable that the hydraulic motors corresponding to the left and right tracks of the excavator be driven at the exact same speed assuming that the operator of the excavator set the control valves for those motors to the same level.
U.S. Pat. No. 6,895,852 discloses an apparatus having a valve assembly with pressure compensated valve sections. The apparatus includes an adjustable pressure reducing valve that communicates pressure from a source (e.g., a pump) to the particular compensation valves that are coupled to the control valves for which adjustable control is desired. The opposing actuation ports of the adjustable pressure reducing valve are coupled, respectively, to the pressure applied to those particular compensation valves and to the highest load pressure plus an adjustment spring pressure. Consequently, the pressure applied to the particular compensation valves exceeds that of the highest load pressure by the adjustment spring pressure, which results in reduced pressure differentials across the control valves associated with those compensation valves. Because the adjustable pressure reducing valve is in communication with each of the particular compensation valves that are coupled to the control valves for which adjustable control is desired, and because the single adjustment spring pressure determines the operation of that adjustable pressure reducing valve, an operator only needs to make a single adjustment to the single adjustment spring pressure to produce the same changes to the pressure differentials across each of the control valves for which adjustable control is desired. Also disclosed is the use of another valve that is coupled between the adjustable pressure reducing valve, the highest load pressure and the particular compensation valves of interest. The reduction in the pressure differentials produced by the adjustable pressure reducing valve can be switched on and off by alternatively coupling the particular compensation valves to the output of the adjustable pressure reducing valve and to the highest load pressure, respectively.
The present invention provides a pressure compensated hydraulic system having differential pressure control that enables fluid flow through one or more valve sections to be adjusted, as may be in many applications. One or more principles of the invention may be applied to load sense and post-pressure compensated valves.
In accordance with the invention, a differential pressure controller (e.g. a differential pressure control valve) senses maximum regulated pressure (e.g. load sense pressure) downstream of one or more pressure compensating valves each associated with a respective control valve (or valves) that has a variable metering orifice through which hydraulic fluid flows between an inlet port providing for connection to a pump and a respective work port providing for connection to a respective actuator (e.g. a hydraulically actuated device such as a piston-cylinder assembly, hydraulic motor, etc.). The differential pressure controller produces an output pressure that may be supplied to a pump control port to which can be connected the control port of a variable displacement pump that produces an output pressure of the pump that is a predefined amount greater than the pressure supplied to the control port of the pump. Additionally or alternatively the output pressure of the differential pressure controller may be supplied to the pressure compensating valve of at least one of the control valves. The output pressure may be equal to the sum of the maximum regulated pressure (e.g., the load sense pressure) and a setting pressure of the differential pressure controller.
Accordingly, the differential pressure controller may supply an output pressure that is higher than the maximum regulated or load sense pressure to either or both the pump port and a work section compensator spring chamber to change a pressure differential. Consequently, either the inlet pressure and/or pressure downstream of the work section flow output controlling area increases. In other words, the system enables the hydraulic pressure differential between the control valve inlet and the work section with the highest work port pressure and/or across one or more work section flow areas to vary flow output of the control valve.
Hence, according to one aspect of the invention, a hydraulic control valve assembly comprises plural control valves each having a variable metering orifice through which hydraulic fluid flows between an inlet port providing for connection to a pump and a respective work port providing for connection to a respective actuator; a compensator that controls flow of fluid from the variable metering orifice to the work port of each control valve in response to a differential in pressures acting on opposite first and second sides of the compensator, wherein the first side receives a pressure at the downstream side of the variable metering orifice; a load sense passage connected to the control valves to provide a load sense pressure corresponding to the greatest pressure amongst the work ports; and a differential pressure controller having a first inlet connected to the pump supply port and a second inlet connected to the load sense passage, the differential pressure controller having a first operational mode in which load sense pressure at the second inlet is supplied to an outlet of the differential pressure controller and a second operational mode in which flow from the first inlet is metered to the outlet of the differential pressure controller to provide a differential control output pressure at the outlet of the differential pressure controller, and wherein the outlet of the differential pressure controller is connected to (a) a pump control port to which can be connected the control port of a variable displacement pump that produces an output pressure of the pump that is a predefined amount greater than the pressure supplied to the control port of the pump, and/or (b) to the second side of the pressure compensating valve of at least one of the plural control valves.
Each control valve may have a respective compensator, and each compensator that is not connected to the outlet of the differential pressure controller, has the second side connected to load sense passage.
The differential pressure controller may be configured to provide a differential control output pressure that is greater than the load sense pressure.
The differential pressure controller may include a controller valve that in the second operational mode provides a pressure drop corresponding to a control force applied to the controller valve. In a particular embodiment, the control force is selected to provide a predetermined pressure difference between the differential control output pressure and the load sense pressure.
The control force may be provided by a control device that may be configured to provide different control forces during shifting of the differential pressure controller between its first and second operation modes.
The controller valve is biased to a position corresponding the first operation mode.
According to another aspect of the invention, a method of controlling a hydraulic system wherein plural control valves each have a variable metering orifice through which hydraulic fluid flows between an inlet port providing for connection to a pump and a respective work port providing for connection to a respective actuator, comprises the steps of using a compensator to control flow of fluid from the variable metering orifice to the work port of each control valve in response to a differential in pressures acting on opposite first and second sides of the compensator, wherein the first side receives a pressure at the downstream side of the variable metering orifice; providing a load sense pressure corresponding to the greatest pressure amongst the work ports; and using a differential pressure controller having a first inlet connected to the pump supply port and a second inlet connected to the load sense passage, the differential pressure controller having a first operational mode in which load sense pressure at the second inlet is supplied to an outlet of the differential pressure controller and a second operational mode in which flow from the first inlet is metered to the outlet of the differential pressure controller to provide a differential control output pressure at the outlet of the differential pressure controller, and wherein the outlet of the differential pressure controller is connected to (a) a pump control port to which can be connected the control port of a variable displacement pump that produces an output pressure of the pump that is a predefined amount greater than the pressure supplied to the control port of the pump, and/or (b) to the second side of the pressure compensating valve of at least one of the plural control valves.
According to a further aspect of the invention, a valve assembly comprises multiple working sections, each working section having a movable control spool and a compensator, an input conduit for supplying fluid to the working sections, a load sense conduit adapted to receive a pressure signal from the working section outputting a highest pressure, and a control mechanism connected to the input conduit and the load sense conduit and provide an output pressure in response to actuation of an associated input.
The associated input may be a proportional solenoid, and/or the output pressure may be provided to one of a pump, a pressure gain mechanism, or a compensator of at least one of the working sections.
A control valve assembly employing a control mechanism according to the present invention has numerous applications. For example, with reference to a mini-excavator such as those often available for rental, a device that is actuatable by an operator for either increasing or decreasing fluid flow through one or more sections of a valve assembly may allow the mini-excavator to have multiple operating modes. In one example, the mini-excavator may have a novice operating mode and an expert operating mode, where selection of the operating mode is provided by a switch within a cab of the mini-excavator. Actuation of the switch into the novice operating mode operates to slow the speed associated with each function of the mini-excavator; whereas actuation of the switch into the expert operating mode operates to increase the speed associated with each function of the mini-excavator as compared to the speed in novice mode.
Further features and advantages of the invention will become apparent from the following detailed description when considered in conjunction with the drawings.
The valve assembly 10 forms a portion of a hydraulic system 100. The hydraulic system 100 also includes a variable displacement hydraulic pump 102, a reservoir 104, and hydraulically actuated devices (not shown) (also herein referred to as actuators), one of which is associated with each working section 16 and 18 of the valve assembly 10. The hydraulically actuated devices may be piston-cylinder assemblies, hydraulic motors, etc. The hydraulically actuated devices may be those used to lower, raise and rotate arms, lower and raise buckets, or to power drive tracks or wheels of vehicles, in particular excavators.
The hydraulic pump 102 is responsive to a pressure signal at load sense port 103 for controlling a pressure at its outlet port. For example, the hydraulic pump 102 may be designed to provide a 300 psi margin pressure. In such an example, the hydraulic pump 102 is operable to maintain an outlet pressure that is 300 psi greater than the received pressure. The pump 102 adjusts its displacement so as to maintain the margin pressure based outlet pressure.
In other embodiments, other types of load sensing margin pressure sources may be used. For example, a fixed displacement pump may be used with a bypass valve that modulates flow bypassed back to the reservoir in response to a pressure signal, whereby the pressure supplied at the outlet of the pressure source maintains a pressure that is greater than the pressure signal by a prescribed amount. Such a load sensing margin pressure source may be used interchangeably with the herein illustrated load sensing margin pressure sources using variable displacement pumps.
The outlet port of the hydraulic pump 102 is in fluid communication with the inlet section 12 of the valve assembly 10. An inlet conduit 24 of the valve assembly 10 includes an inlet port 25 preferably located in the inlet section 12. The inlet conduit 24 extends through the inlet section 12, through each working section 16 and 18, and into the outlet section 14 of the valve assembly 10.
Each of the working sections 16 and 18 of the valve assembly 10 includes an associated control spool 26 and an associated compensator 28. In the embodiment illustrated in
The inlet conduit 24 provides fluid to the control spool 26 of each working section 16 and 18. The control spools 26 are independently actuatable to move from a neutral, closed position to a position for directing hydraulic fluid toward the compensator 28 of the associated working section.
In response to movement of a control spool 26 of a working section 16 and 18, fluid flows from the inlet conduit 24 across the control spool 26 and into a metered cavity of the working section located immediately upstream of the compensator 28. A pressure drop occurs as the fluid passes across the control spool 26 to the metered cavity.
The compensator 28 of each working section 16 and 18 is adapted to maintain a set pressure drop within the working section. The set pressure drop is related to a received pressure signal, commonly called a load sense signal. As illustrated in
Thus, with reference to the exemplary embodiment of
In addition to receiving the load sense signal from the load sense conduit 34, each compensator 28 also includes a spring 36 having a preset spring force for biasing a poppet of the compensator 28 into a closed position, as is illustrated schematically in
The outlet section 14 of the valve assembly 10 according to the embodiment of
The control mechanism 40 includes a first position, illustrated schematically in
The control mechanism 40 moves in response to a controlled input from the first position to a position in which the input conduit 24 is in communication with the control conduit 42. The pressure drop across the control mechanism 40 may be controlled when the input conduit 24 is in communication with the control conduit 42. For example, in one embodiment, the controlled input is provided by an input device 48 such as a proportional solenoid (or a hydraulic or pneumatic pressure source 48a either within the hydraulic system or separate from the hydraulic system, an adjustable spring mechanism 48b, or a stepper motor or similar device) that is adapted to adjust the pressure drop across the control mechanism 40, for example in the range of 0 to 300 psi. A return spring 50 may act to return the control mechanism 40 to the first position in the absence of a higher force from the proportional solenoid 48 or other input device. Additional alternatives for the controlled input may include an adjustable pressure input from a hydraulic or pneumatic pressure source either within the hydraulic system or separate from the hydraulic system, an adjustable spring mechanism, or a bi-directional pilot valve, stepper motor or similar devices that avoid the need for the return spring, or similar devices in general. The input device may be controlled by a suitable controller such as a microprocessor, programmable controller or the like, with one or more inputs, such as a selector input for enabling selection between different modes of operation of the control mechanism. The controller may have other inputs for receiving signals from one or more sensors that report system pressures, fluid flows, states, etc. to the controller. This may include end-of-stroke sensors for use in connection with one or more of the different embodiments for automatic cylinder speed reduction at the end of stroke, as discussed further below. The controller may also provide for proportional control of the controlled input for providing desired functionality. The controller may even simply be a mode selector switch.
During operation of the hydraulic system 100 of
For example, assume that working section 16 is actuated for providing fluid at 2000 psi to its working port B and working section 18 is actuated for providing fluid at 1000 psi to its working port B. The load sense signal pressure, i.e., the highest working port pressure, will be 2000 psi. With the control mechanism 40 in the first position, as illustrated in
Now, assume that the proportional solenoid 48 is actuated and the control mechanism 40 shifts to a position for connecting the inlet conduit 24 to the control conduit 42, this corresponding to a second operational mode. When first actuated, the proportional solenoid 48 controls the control mechanism 40 to provide a first pressure drop between the inlet conduit 24 and the controlled conduit 42. The proportional solenoid 48 then adjusts the pressure drop across the control mechanism 40 to provide the desired pressure in the control conduit 42.
For example, still assume that working section 16 is actuated for providing fluid at 2000 psi to its working port B and working section 18 is actuated for providing fluid at 1000 psi to its working port B. The proportional solenoid 48 controls the control mechanism 40 for providing the desired pressure in the control conduit 42. In this example, assume that the desired pressure in the control conduit 42 is 2100 psi (100 psi higher than the load sense signal pressure). Thus, when initially actuated, the proportional solenoid 48 controls the control mechanism 40 to provide a 200 psi pressure drop (2300 psi pump outlet pressure to the 2100 psi control conduit 42 pressure). In response to the 2100 psi pump control conduit pressure, the pump 102 applies its margin pressure to attempt to maintain an outlet pressure of 2400 psi. As the pump outlet pressure increases to 2400 psi, the proportional solenoid 48 adjusts to increase the pressure drop across the control mechanism 40 to 300 psi for maintaining the 2100 psi pressure in the control conduit 42. In response to the pump outlet pressure increasing to 2400 psi, the pressure drop across the control spool 26 of each working section 16 and 18 increases (in this example, the pressure drop increases by 100 psi as the pump outlet pressure increases from 2400 psi to 2300 psi). As a result of the increase pressure drop across the control spool 26 of each working section 16 and 18, flow to the associated hydraulically actuated devices increases and thus, the actuation speed of the associated hydraulically actuated devices increases.
As will be appreciated, the hydraulic system shown in
Before leaving
The valve assembly 10a of
In the
Another embodiment is shown in
Although
Although
For example, in the valve assembly 10d shown in
The valve assembly 10e of
As shown in
The control mechanism 40 can also be used to provide a programmed damping mode by providing automatic cylinder speed ramp-down near the end of stroke, thereby extending the component and overall machine life. That is, cylinder movement can be gradually or quickly slowed near the end of stroke to prevent hard impact. This can be effected by varying the control input to the control mechanism 40 such as by means of a proportional control. In the
Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.
This application is a national phase of International Application No. PCT/US2011/036047 filed May 11, 2011 and published in the English language which claims the benefit of U.S. Provisional Application No. 61/333,389 filed May 11, 2010, each of which is hereby incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2011/036047 | 5/11/2011 | WO | 00 | 2/28/2013 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2011/143301 | 11/17/2011 | WO | A |
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| Number | Date | Country | |
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| 20130146162 A1 | Jun 2013 | US |
| Number | Date | Country | |
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