Patent Grant
6871574
Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to hydraulic systems, and more particularly to valve assemblies for controlling the flow of hydraulic fluid to and from an actuator to produce bidirectional motion.
2. Description of the Related Art
Various types of mobile equipment are operated by a hydraulic system that drives an actuator, such as a hydraulic cylinder and piston arrangement, which receives pressurized fluid controlled by a hydraulic valve. A typical four-position control valve selectively applies the pressurized fluid to one of two cylinder chambers and drains the hydraulic fluid from the other chamber, thereby driving the actuator in one of two directions depending upon which chamber receives the pressurized fluid. Usually a proportional control valve is employed, which can be opened to varying degrees to control the rate of fluid flow to and from the associated actuator, thereby moving the element of the machine that is connected to the actuator at different speeds.
Mobile equipment often incorporate auxiliary hydraulic valves for optional or lower usage type functions. A relatively low flow control valve usually acceptable for these auxiliary functions. If electrohydraulic operation is required, simple on/off valve can be used. For example, direct acting solenoids often are utilized to shift conventional spools in a manner similar to that employed in manual valves. On/off cartridge valves also may be utilized for this purpose, but in applications that require a three-position, four-way valve arrangement, cartridge valves become relatively large and complex, so as to not be cost effective.
Conventional three-position spool valves, that are commonly used to control auxiliary functions, have a center or neutral position which blocks the flow of fluid from the pump, as well as blocking the connection of the workports to tank. In hydraulic circuits that provide load sensing to control the supply pressure from the pump, these spool valves also require a bleed connection in the neutral position to relieve the load sense pressure signal. For bidirectional operation, a load sense signal must be provided, regardless of the direction of the valve motion. This is often accomplished with a bridge type connection through which the workport pressure flows in both directions of valve operation.
Thus, it is desirable to duplicate the function of a three-position, four-way control valve with solenoid operated valves in an assembly which is as cost effective as possible.
A control valve assembly is provided for a hydraulic system having a pump supply line, a tank return line, and a double acting actuator. The control valve assembly has a first workport and a second workport for connection to the double acting actuator. A first control valve is connected to the pump supply line and the tank return line, one of which at a time is connected by different operating positions of the first control valve to a first common port. A second control valve also is connected to the pump supply line and the tank return line, one of which at a time is connected to a second common port in different operating positions of the second control valve.
A first pilot operated check valve is connected between the first common port and the first workport and has a free flow direction from the first common port to the first workport. The first pilot operated check valve has a pilot inlet connected to the second common port, wherein sufficient pressure at the pilot inlet opens the first pilot operated check valve to fluid flow from the first workport to the first common port. A second pilot operated check valve has another pilot inlet connected to the first common port, wherein sufficient pressure at the pilot inlet opens the second pilot operated check valve to fluid flow from the second workport to the second common port.
To drive the actuator in one direction, the first control valve is placed in the position in which the pump supply line is connected to the first common port and the second control valve is placed in the position in which the tank return line is connected to the second common port. The pressure at the first common port opens the first pilot operated check in the free flow direction so that fluid is supplied to the actuator via the first workport. The pressure at the first common port also is applied to the pilot inlet of the second pilot operated check valve and causes that check valve to open allowing fluid to drain to tank from the actuator via the second workport.
To drive the actuator in the opposite direction, the positions of the first and second control valves are reversed to apply fluid from the supply line to the second workport and drain fluid from the second workport to tank. Pressure at the second common port of the second control valve, when applied to the first pilot operated check valve opens that valve.
A load sense circuit preferably is provided to receive the pressures at the first and second common ports and produce a load sense signal corresponding to the greater of those pressures.
With initial reference to
The valve assembly 18 has a pair of two-position, three-way control valves 28 and 30 which have a spool that is operated by a solenoid 29 and 31, respectively. Each control valve 28 and 30 selectively connects either the supply line 16 or the tank return line 24 to a common port 32 or 33 of the valve. When energized, the first solenoid 29 drives the first control valve 28 into a first position in which the supply line 16 is connected to the first common port 32 which is coupled to a first intermediate passage 34. When the first solenoid 29 is de-energized, a spring biased the first control valve into a second position in which the first intermediate passage 34 is connected to the tank return line 24. Similarly, the second control valve 30 has a first position in which the pump supply line 16 is connected via the second common port 33 to a second intermediate passage 35 of the valve assembly 18. A spring biases the second control valve 30 into a second position where the tank return line 24 is connected to the second common port 33.
The first intermediate passage 34 is coupled by a first pilot operated check valve 36 to a first workport 38 of the valve assembly 18, which workport is connected to the first chamber 21 of the cylinder 20. The first pilot operated check valve is oriented to have a free-flow direction from the first intermediate passage 34 to the first workport 38. The flow in the opposite direction is normally blocked by the first pilot-operated check valve 36, unless the valve receives a pilot signal from the second intermediate passage 35 which is sufficient to unseat the check valve, as will be described. A second pilot operated check valve 40 is connected between the second intermediate passage 35 and a second workport 42 of the valve assembly 18, which in turn, is connected to the second chamber 22 of cylinder 20. The free flow direction of the second pilot operated check valve 40 is oriented to permit flow from the second intermediate passage 35 to the second workport 42. The second pilot operated check valve 40 blocks flow in the opposite direction unless it receives a sufficient pilot signal from the first intermediate passage 34.
The two intermediate passages 34 and 35 also are connected by a load sense circuit 37 and specifically are coupled by a shuttle valve 44 to a load sense passage 46. A load sense signal, corresponding to the greater of the two pressures at those intermediate passages, is produced in the load sense passage 46 and is used to control the output pressure of the pump 12. The exemplary hydraulic system 10 uses a variable displacement hydraulic pump 12 with the load sense passage 46 connected to the control input of the pump. Alternatively, a fixed displacement pump could be employed along with a conventional unloader valve controlled by the load sense signal.
The first and second intermediate passages 34 and 35 open into a check valve bore 53 into which the workports 36 and 40 also open. A pilot plunger 54, which also forms the shuttle valve 44, is slidably received a central portion of the check valve bore 53 and has longitudinal grooves in its surface extending from each end to one of two annular notches 59 and 60, thereby allowing fluid to flow from either intermediate passage 34 or 35 into one of those notches. A central land 76 on the pilot plunger 54 between the two annular notches 59 and 60 tightly engages the inner surface of the check valve bore 53 when the pilot plunger is displaced left or right from the neutral position illustrated in FIG. 2. In the neutral position both of the annular notches 59 and 60 open into the load sense passage 46 in the valve assembly body 50.
The pilot plunger 54 engages both of the pilot operated check valves 36 and 40 located in opposite ends of the check valve bore 53. The first pilot operated check valve 36 with a first poppet 56 that abuts a first seat formed in the check valve bore 53. The first poppet 56 has a central aperture there through into which a pin 58 of the pilot plunger 54 extends. A first sphere 61 is received within the poppet aperture and is urged against a second seat within that aperture by a piston 62 which is biased by a spring 64 to place the first check 36 valve in the closed position. The second pilot operated check valve 40 has an identical structure comprising a second poppet 66 that engages a second third seat in the check valve bore 53. The second poppet 66 has an aperture there through into which a second pin 68 of the pilot plunger 54 extends. A second sphere 70 is urged against a fourth seat in this second poppet's aperture by a piston 72 that is biased by a second spring 74. In the neutral position of the pilot plunger 54 as illustrated in
To operate the actuator 20, one of the two solenoid valves 28 or 30 within the assembly 18 will be energized depending upon the desired direction of movement of the piston 26. For example, the first solenoid actuated valve 28 is energized to extend the piston's rod from the cylinder 20. Doing so connects the pump supply line 16 to the first intermediate passage 34 thereby applying pressurized fluid to a nose chamber 84 of the first pilot operated check valve 36. Pressure from that fluid forces the first pilot operated check valve 36 to open in the free-flow direction and allows the fluid to flow to the first workport 38 and the first cylinder chamber 21.
The pressure in the nose chamber 84 also shifts the pilot plunger 54 to the right, toward the second pilot operated check valve 40. This motion forces the second plunger pin 68 against the second sphere 70 of the second pilot operated check valve 40, thereby unseating that sphere. When the second sphere 70 is unseated, pressure within a rear chamber 86 of the second pilot operated check valve 40 is vented to tank which reduces the pressure within that chamber. A small transverse aperture 80 provides a path through the second check valve poppet 66 from the second workport 40 into a cavity between that poppet 66 and piston 71, thereby applying the workport pressure to an annular surface on the piston. This causes the second check valve piston 71 to move away from engagement with the second sphere 70 so that the force from the plunger pin 68 also unseats the second check valve poppet 66. This action opens a path into the second intermediate passage 35 through which fluid from the second workport 42 drains to the second control valve 30 and onward into the tank passage 24.
As the second pilot operated check valve 35 opens fully, the pilot plunger 54 moves farther toward it (rightward in the drawing) and into a position where pressure from the first intermediate passage 34 is communicated through the plunger's longitudinal grooves and notch 59 into the load sense passage 46. Thus, the pressure in the first workport 38 is applied to the load sense passage 46. At the same time, the position of the plunger 54 is such that the land 76 engages the wall of the check valve bore 53 and blocks pressure in the second intermediate passage 35 from reaching the load sense passage 46.
In order to move the cylinder piston 26 in the opposite direction within the cylinder 20, pressurized hydraulic fluid must be applied to the second cylinder chamber 22 through the second workport 42. To accomplish this, the second control valve 30 is activated to couple the pump supply line 16 to the second intermediate passage 35 while the first control valve 28 is de-energized. This action reverses the operation described previously with respect to activating the first control valve 28. That is, pressure within the second intermediate passage 35 drives the pilot plunger 54 toward the first pilot operated check valve 36 (leftward in the drawings) which opens that check valve. This motion of the pilot plunger 54 also opens a path between the second intermediate passage 35 and the load sense passage 46 and blocks communication between the first intermediate passage 34 and the load sense passage. This generates a load sense signal from the pressure at the second intermediate passage 34.
The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.
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| Number | Date | Country | |
|---|---|---|---|
| 20040237768 A1 | Dec 2004 | US |
