Combination Accumulator Charging, Flow Control And Relief Valve Assembly

Abstract

A control valve in a hydraulic system including an accumulator circuit and an open center circuit having a flow control valve member capable of delivering a generally constant volume of fluid to the accumulator while delivering any excess flow to the open center circuit. The same valve member is responsive to a pilot valve when the accumulator is charged to its maximum pressure for blocking the accumulator circuit and delivering full flow to the open center circuit.

Description

The present invention relates to hydraulic flow control valves particularly for use in a hydraulic system including an accumulator circuit and an open center circuit. Hydraulic systems employed in earth moving vehicles for example, commonly include an open center circuit and another circuit having an accumulator for insuring a constant supply of working fluid. The accumulator circuit is most often of the closed center type and may include a closed center brake control valve for regulating the flow of actuating fluid to hydraulic brakes. It is generally desirable to provide a control valve which is capable of delivering a substantially constant volume of fluid to the accumulator circuit. Since the output of an engine driven pump varies with the speed of the vehicle engine, the pump must have capacity sufficiently great to insure that the required volume of fluid is available to the accumulator circuit even at minimum pumping rates. The pump therefore operates much of the time with a volumetric output in excess of that required by the accumulator circuit. A basic function of the control valve is accordingly to insure the availability of constant volume flow to the accumulator circuit while delivering excess fluid into the open center circuit.

Prior art control valves employed in such systems generally include a flow control valve which is effective to divide fluid flow from a pump into the accumulator circuit and open center circuit as discussed above. A second valve is them employed for regulating fluid flow to the accumulator circuit and for blocking that circuit when the accumulator is charged to its maximum pressure. Separate relief means are also employed to protect the hydraulic system and control valve from accidental overpressures.

Within such an arrangement, the separate valves must each be capable of handling at least full volume flow for the accumulator circuit. The control valve therefore is generally large and bulky relative to the flow volume which it handles. In addition, the use of separate components for performing the various functions of the control valve tends to reduce the responsiveness of the control valve to the requirements of the hydraulic system.

The present invention overcomes these problems and provides a much more efficient control valve through use of single valve means which perform both the function of pressure compensated flow control and the function of accumulator charging control.

Accordingly it is an object of the present invention to provide a composite control valve for regulating fluid flow from a source to an accumulator circuit and an open center circuit.

It is a further object to provide single valve means in the control valve for functioning as a pressure compensated flow control valve and an accumulator charging control valve.

It is also an object of the invention to provide pilot means which are responsive to maximum accumulator pressure for causing the above valve means to block the accumulator circuit and deliver full flow to the open center circuit.

It is also an object of the invention to make the pilot means responsive to accumulator pressure substantially below its maximum value for causing the valve means to again place the source in communication with the accumulator circuit.

Additional objects and advantages of the invention are made apparent in the following description having referenced to the accompanying drawing.

The drawing is a generally schematic representation of a hydraulic system having an open center circuit and an accumulator circuit with a composite control valve shown in section.

The hydraulic system illustrated in the drawing includes a pump or source of fluid under pressure 11, an open center circuit 12, another circuit 13 including an accumulator 14 and a control valve 16 which embodies the novel concepts of the present invention. The hydraulic system is particularly contemplated for use within a vehicle such as an earthmoving dump truck. The accumulator circuit 13 is of the closed center type including a closed center brake valve 17 and a closed center steering valve 18 for regulating fluid flow to associated hydraulic equipment of the vehicle (not shown). In that circuit, the accumulator 14 tends to insure a sufficient amount of fluid under pressure in the circuit 13 for performing the steering and braking functions of the vehicle. The open center circuit 12 includes an open center valve 19 which may be employed to operate hydraulic hoist means for the vehicle (not shown). A relief valve 21 is also included in the open center circuit 12 to prevent overpressure.

To insure adequate fluid flow to both of the circuits 12 and 13, the fluid source 11 is desired to function as two pumps delivering two separate sources of fluid under pressure. In the present embodiment, the fluid source 11 is a double sectioned pump capable of delivering a relatively large volume of fluid under pressure to a conduit 22 which is in direct communication with the open center circuit 12. The pump 11 is also capable of delivering a smaller volume of fluid under pressure through a conduit 23 which is in communication with both the open center circuit 12 and the accumulator circuit 13 by means of the control valve 16.

The control valve 16 performs at least three functions within the illustrated hydraulic system. A first function is that of pressure compensated flow control for delivering a generally constant volume of fluid to the accumulator circuit 13 while passing excess fluid to the open center circuit 12. A second function is that of accumulator charging control whereby fluid is permitted to pass from the pump 11 to the accumulator circuit 13 until the accumulator 14 is charged to its maximum pressure. The accumulator circuit is then blocked from the pump 11 and complete flow from the pump 11 is directed to the open center circuit 12. A spool 24 reciprocably disposed in a bore 26 defined by the control valve housing 27 accomplishes both of these functions in a manner described below. The combined function of the valve spool 24 enables operation of the control valve 16 with the spool 24 being the only basic valve element which need be sized to transmit full flow from the conduit 23 into the circuit 12 and controlled flow into circuit 13, when needed. This feature permits very compact sizing for the control valve 16 relative to the quantity of fluid which it is capable of directing to the hydraulic circuits. The combined functions of the spool 24 also enable a more positive response to meet requirements of the hydraulic system. The control valve 16 also includes a relief pilot means 28 which is in communication with the spool bore 26 for relieving excessive overpressures within the control valve 16.

Describing the control valve 16 in greater detail, the spool 24 is urged rightwardly as seen in the drawing by a spring 29 seated upon a spring retainer 31. The spool 24 defines a first chamber 32 and a second chamber 33 which are in communication by means of a restrictive orifice 34. An inlet port 36 is defined by the housing 27 for communicating the conduit 23 with the first chamber 32. Crossdrilled passages 37 in the spool 24 permit selective and variable communication of fluid from the second chamber 33 into a passage 38 in the housing 27. The passage 38 is in communication with the accumulator circuit 13 across a check valve 39 and through an outlet port 41 in the housing 27. The spool 24 also defines another set of crossdrilled passages 42 for selectively and variably communicating the first chamber 32 with an outlet port 43 which is in communication with the open center circuit 12.

The effect of the orifice 34 in restricting flow of fluid thereacross causes the spool 24 to respond as a full, pressure compensated flow control valve. the volume of fluid delivered by the pump through the conduit 23 is generally greater than the volume of fluid which can pass through the orifice 34. A pressure drop therefore exists across the orifice 34 which tends to shift the spool 24 leftwardly against the spring 29. As the spool 24 shifts leftwardly, the passages 42 are placed in at least partial communication with the outlet port 43 while the passages 37 remain in at least partial communication with the chamber 38. Proper selection of the spring 29 permits the orifice 34 to establish a relatively constant volume flow into the chamber 33 and then to the accumulator circuit through the passage 38.

If volumetric flow from the conduit 23 increases, the pressure drop across the orifice 34 also increases and the spool 24 is moved further leftwardly. Thus, flow continues at a generally constant volume rate into the passage 38 while excess fluid from the conduit 23 is directed to the open center circuit 12 through the ports 42 and the outlet passage 43. A decrease in fluid flow through the conduit 23 results in rightward motion of the spool 24 which decreases flow through the passages 42 and maintains constant volume flow into the passage 38.

The accumulator charging control function of the spool 24 is accomplished in combination with a pilot spool 44 reciprocably arranged in a bore 46 which is also defined by the housing 27. The relief spool 44 is urged upwardly as seen in the drawing by a spring 47. A plunger or piston 48 having a smaller cross section than the relief spool 44 is reciprocably disposed in a smaller bore 49 in coaxial alignment with the relief spool 44 opposite its spring 47.

As fluid crosses the orifice 34 and enters the second chamber 33, it is also directed through a smaller restrictive orifice 51 in the spool 24. The orifice 51 communicates fluid from the second chamber 33 into the spring chamber 52 at the left hand of the bore 26. The spring retainer 31 is generally tubular so that a passage 53 defined by the housing 27 communicates the spring chamber 52 with the relief spool bore 46. The relief spool 44 (in the position shown in the drawing) functions to block the passage 53 and the spring chamber 52 until the accumulator 14 is charged to its maximum pressure.

As fluid under pressure from the conduit 23 passes through the spool 24 and enters the chamber 38, it is initially blocked from entering the accumulator circuit by the poppet-type check valve 39. Accordingly fluid in the passage 38 is pressurized. When fluid pressure in the passage 38 equals fluid pressure behind the check valve 39 plus force of a spring 54 tending to close the poppet valve, the valve 39 opens and the passage 38 is placed in communication with the accumulator circuit. In this condition, the spool 24 permits regulated fluid flow to the accumulator circuit until the accumulator 14 is charged to a predetermined maximum pressure.

Maximum pressure in the accumulator circuit and in the port 41 is communicated through a passage 56 in the check valve 39, the spring chamber 57 behind the poppet valve 39 and passages 58 and 59 in the housing 27 to a chamber 61 adjacent the plunger 48. Maximum accumulator pressure in the chamber 61 is sufficient to urge the plunger 48 and the relief spool 44 downwardly so that a groove 62 in the relief spool 44 is in communication both with the passage 53 and the spring chamber 63 below the relieve spool 44. Fluid under pressure in the spring chamber 52 is then permitted to drain through the passage 53, the groove 62, the spring chamber 63 and an outlet drain port 64. Pressure reduction in the spring chamber 52 permits the spool 24 to move sufficiently to the left to block communication between the passages 37 and the passage 38. In this manner, the spool 24 is effective to terminate flow into the accumulator circuit 13 and direct full flow from the conduit 23 into the open center circuit 12 through the cross drill passages 42 and the outlet port 43.

When the spool 24 blocks fluid flow into the passage 38, the poppet valve 39 is returned to its closed position by the spring 54 to prevent loss of fluid from the accumulator circuit while the spool 24 is shifting or when the pump 11 is not in operation. The pilot spool 44 maintains the spool 24 in its full leftward position until pressure in the accumulator circuit is substantially reduced from its maximum value. Accordingly, the relief spool 44 determines a maximum and minimum working pressure for the accumulator 14 so that the spool 24 is not continually opening and closing whenever pressure is discharged from the accumulator 14 through the steering and brake valves 18 and 17.

The manner in which the relief spool 44 functions to establish the maximum and minimum working pressures for the accumulator 14 is best seen with reference to the drawing. As the relief spool 44 is shifted downwardly by the piston 48, fluid from the passage 58 is communicated across the spool 44 by a groove 66 into another passage 67 which is in communication with a chamber 68 at the upper end of the relief spool bore 46 adjacent the piston 48. In this manner, pressure in the accumulator circuit acts against the larger cross section of the spool 44 so that the spring 47 cannot reposition the relief spool 44 until pressure in the accumulator is substantially reduced.

When accumulator pressure is reduced below its minimum value, for example, by operation of the steering or brake valves, the relief spool 44 is shifted upwardly by the spring 47 to again block the spring chamber 52. As the relief spool is shifted upwardly by the spring 47, an internal passage 50 in the spool 44 communicates the chamber 68 with the drain port 64 to insure full return of the pilot spool 44. The spool 24 is accordingly made responsive to the pressure drop across its orifice 34 and it again acts as a flow control valve for delivering a constant volume of fluid to the accumulator circuit as described above.

The poppet-type relief valve 28 protects the accumulator charging circuit in the event that either relief spool 44 or check valve 39 becomes stuck in the position shown in the drawing. In either event, excessive pressure builds up in passage 38 and second chamber 33 and accordingly is communicated into the spring chamber 52. Excessive pressure in the spring chamber 52 shifts the poppet valve 28 leftwardly against its spring 69 and permits fluid from the spring chamber 52 to enter the chamber 71 behind the poppet valve 28. The chamber 71 is in communication with the spring chamber 63 beneath the relief spool 44 by means of a passage 72 so that fluid from the spring chamber 52 may pass to drain through the outlet port 64. When the spring chamber 52 is thus drained, a pressure drop exists across the orifice 51 sufficient to shift the spool 24 leftwardly so that substantially full flow from the conduit 23 is directed to the open center circuit through the outlet port 43.

Claims

I claim:

1. A control valve for a system including a first source of hydraulic fluid under pressure, an open center circuit, a second source of hydraulic fluid under pressure in communication with said open center circuit, and a circuit including a fluid accumulator comprising:

a valve body;

a valve spool reciprocally arranged in the valve body, the spool including a first chamber, a second chamber and a restrictive orifice therebetween;

means communicating the first source with the first chamber;

means for communicating the second chamber with the accumulator circuit and delivering fluid directly to the accumulator circuit at a rate at least partially determined by the orifice;

means for communicating the first chamber with the open center circuit and delivering excess fluid thereinto;

pilot means associated with the accumulator circuit and in communication through another more restrictive orifice in the valve spool with the second chamber of said valve spool, the pilot means being responsive to maximum accumulator pressure for providing fluid pressure relief for the valve spool downstream of its restrictive orifice and causing the spool to divert fluid flow from the source to the open center circuit, the pilot means being responsive to substantial reduction of accumulator pressure from its maximum value for terminating fluid relief for the valve spool;

passage means communicating the valve spool downstream of its more restrictive orifice to a fluid drain, the pilot means comprising a spool; and

spring means for urging said pilot spool into blocking relation with the passage, piston means of smaller cross section than the pilot spool, the piston means in coaxial alignment with the pilot spool and in communication with the accumulator circuit, the piston means responsive to maximum accumulator pressure for urging the pilot spool toward unblocking relation with the passage and means for communicating an end surface of the pilot spool with the accumulator circuit when the pilot spool is shifted by the piston means.

2. The invention of claim 1 wherein the accumulator circuit includes a hydraulic closed center brake control valve.

3. The invention of claim 2 wherein the hydraulic system is suitable for use in a vehicle, the accumulator circuit also including a hydraulic closed center steering control valve and the open center circuit including a hydraulic open center valve for providing fluid flow to a hydraulic motor.

4. The invention of claim 1 further comprising a spring for acting upon the valve spool and urging it against fluid pressure from the source, a check valve arranged between the valve spool and the accumulator circuit and relief means for communicating the valve spool downstream of its second chamber with a drain.