Abstract:
A pressure compensated hydraulic valve (2) is provided with a housing (4) having a reciprocal spool (6) for communicating hydraulic fluid to work ports (8,10). Pressure compensating means (58) is provided in the same housing with the valve and senses work port pressure by hydraulic fluid flow through the spool from the work port and creates a substantially fixed differential pressure across the spool by controlling the pressure after the flow has passed through the spool.

Description:
This is a continuation of application Ser. No. 06/579,394 filed Feb. 13, 1984, now abandoned. 
    
    
     BACKGROUND AND SUMMARY 
     The invention relates to pressure compensated hydraulic valves, wherein a fixed differential pressure is maintained, to maintain a uniform flow rate. 
     In a hydraulic valve having a reciprocal spool for communicating hydraulic fluid to work ports, it is known to create a fixed differential pressure across the spool by controlling the pressure before the flow has passed through the spool. For example in Wilke U.S. Pat. No. 3,881,512, the hydraulic fluid is preconditioned before it flows across control spool 13 by an initial pressure compensating valve mechanism 15 which divides flow from inlet 18 to either feeder 20 or bypass 19 to keep the flow through work port 22 constant for any given position of spool 13 regardless of fluxuations in pump or load pressure. 
     In the present invention, a fixed differential pressure is created by controlling pressure after hydraulic flow has passed through the spool. 
     The present invention evolved from cost reduction efforts to minimize the number and complexity of parts, particularly those requiring machining. This is accomplished in part by marrying certain open flow circuit structure with pressure compensated circuit structure. In an open flow circuit, the flow rate changes in response to load pressure. Unitary open flow hydraulic valves are known having check valves in the same housing as the control spool, typically in the area of a bridge passage between work ports through the spool. 
     The present invention provides a unitary pressure compensated hydraulic valve, eliminating a separate discreet pressure compensating module. The pressure compensating means of the invention is in the same housing as the control spool. Furthermore, the invention enables known check valve structure and location from open flow circuitry to be applied and used in pressure compensating and shuttle circuits. This facilitates economy of manufacture by enabling use of existing manufacturing steps and assembly line sequences for as much of the valve as possible. The use of check valve structure for pressure compensating and shuttle circuits is further desirable because it typically involves a less expensive stamping operation, as opposed to machining or the like. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional side view of a valve constructed in accordance with the invention. 
     FIG. 2 is a sectional top view of the valve of FIG. 1. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, valve 2 includes a housing 4 having a reciprocal control spool 6 moveable left-right for communicating hydraulic fluid to work ports 8 and 10. Spool 6 is shown in the neutral position, and bridge passage 12 is vented to reservoir passage or tank 14 through bridge vent passage 16 in the control spool as shown at dashed line vent passages 16a, 16b and 16c. 
     When spool 6 is moved leftwardly by the operator, bridge vent passage 16 is blocked, and bridge passage 12 is placed in communication with work port 8 through control spool passage 20, such that the work port pressure is sensed in bridge passage 12 by hydraulic fluid flow through the spool bore. This applied work port pressure pressurizes a pilot system for load sensing and pressure compensation. 
     Bridge passage 12 is in communication with a sensing shuttle passage 22, FIG. 2. If the valve is a single section or monoblock valve, the hydraulic flow in passage 22 continues past shuttle check valve 24 and into crossing passage 26 and through-shuttle passage 28. If the valve is a multi-section valve, then a plurality of identical valve sections are aligned side by side, for example as shown cut away at 30 and 32. If the work port pressure of central section 31 in sensing shuttle passage 22 is greater than the work port pressure in through-shuttle passage 34 of the previous section 30, then shuttle check valve 24 moves downwardly to close passage 34 and the higher pressure from passage 22 is communicated through crossing passage 26 to through shuttle passage 28. If the work port pressure in sensing shuttle passage 22 of present valve section 31 is less than the work port pressure in the through-shuttle passage 34 of the previous section 30, then shuttle check valve 24 moves upwardly to close passge 22 and enable the higher pressure in passage 34 to be communicated to through-shuttle passage 28. Likewise, shuttle check valve 36 of the next section 32 operates to apply the higher pressure of through-shuttle passage 28 of the present section 31 and sensing shuttle passage 38 of the next section 32 to the through-shuttle passage 40 of next section 32. In this manner, the highest work port pressure of all the valve sections is communicated to a sense line 52 connected to the input 44 of hydraulic pump 46 and to a communication passage 48 which extends through all of the valve sections, as shown through respective passages 50, 52 and 54. 
     Transfer passage 52 communicates through cross passage 56 with a pressure compensating check valve 58, such as a spring biased poppet. The bottom side 60 of check valve 58 is thus applied with the pressure from passage 52, which is the highest work port pressure of the valve sections. The top side 62 of valve 58 is of the same area as the bottom side and thus the same pressure is applied in passage 64 above valve 58. Passage 64 around the top of valve 58 is a feeder passage which also has a section around spool 6, FIG. 1. The pressure in feeder passage 64 is thus the highest work port pressure of the multiple valve sections. 
     The above noted description explains pressurization of the system in response to initial movement of spool 6. This pressurization occurs before metering notch or passage 66 in the spool comes into communication with feeder passsage 64. 
     Further leftward movement of spool 6 brings metering passage 66 into communication with feeder passage 64. Supply passage 68 then communicates with feeder passage 64 through metering passage 66. Metering passage 70 and supply passage 72, effective during rightward movement of spool 6, are comparable. Supply passages 68 and 72 are suppled from pump 46 which outputs hydraulic flow pressure on output 74 which is a predetermined amount greater than the flow pressure input to the pump at 44. Since the pressure at 44, FIGS. 1 and 2, is the highest work port pressure of the valve sections, the pressure in supply passages 68 and 72 is the noted predetermined amount greater than the highest work port pressure. As above noted, the initial pressurization of the system causes the pressure in feeder passage 64 to be the same as the highest work port pressure. There is thus a fixed differential pressure across metering passage 66 from supply passage 68 to feeder passage 64. 
     Hydraulic fluid can flow from supply passage 68 through metering passage 66 to feeder passage 64. Feeder passage 64, FIG. 2, communicates with the left side of bridge passage 12 through cross passage 76 and an orifice 78 opened by downward movement of pressure compensating check valve 58. The flow rate in feeder passage 64 is such as to provide sufficient fluid to afford the same amount of pressure on the top side 62 as on the bottom side 60 of valve 58. Valve 58 can move up and down to control the size of orifice 78, such that should the load increase, causing work port pressure to increase, the shuttle system responds to impose the increased load pressure on the bottom of the check valves 58 in all of the valve sections so that the poppets 58 can operate as load holding check valves. This increased pressure is also sensed at port 44 of the pump to effect an increase in the output pressure of the pump and thereby increase the pressure in the inlet passage 68 (or 72) sufficiently to maintain the pressure differential across the metering notches 66. In as much as this same increased load pressure is manifested at the bottoms of the poppets 58 in the stack of valve sections, the desired pressure differential will be maintained across the metering notches in any of the spools in adjacent sections that have been actuated to operating positions. 
     Load 80 is raised via outlet and inlet work ports 8 and 10 and their respective connection lines 82 and 84. Further leftward movement of spool 6 by the operator further raises load 80 by increasing the area of metering passage 66 which is exposed to feeder passage 64. Flow rate is equal to the product of the area and the square root of the differential pressure. Since the differential pressure across metering passage 66 is constant, flow rate is a direct linear function of the area of metering passage 66 which is in communication with feeder passage 64. This area is increased during further leftward movement of spool 6, thus supplying more fluid and raising load 80. Standard pressure relief valves 86 and 88 are provided for the work ports and reservoir passage. A standard spring centering mechanism 90 is provided on the end of spool 6 for locating the latter&#39;s neutral position. 
     From the foregoing description it will be appreciated that one of the outstanding features of the invention resides in the fact that the valve mechanism can act as a flow divider due to the maintenance of the same pressure differential across the metering notches of all the spools that have been shifted to operating positions. This is achieved regardless of pump output, even if the demands of the various systems exceed pump output capacity. 
     It is recognized that various modifications are possible within the scope of the appended claims.