EP0059712B1 - Improved load-plus valve for variable displacement pumps - Google Patents

Improved load-plus valve for variable displacement pumps Download PDF

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Publication number
EP0059712B1
EP0059712B1 EP81901353A EP81901353A EP0059712B1 EP 0059712 B1 EP0059712 B1 EP 0059712B1 EP 81901353 A EP81901353 A EP 81901353A EP 81901353 A EP81901353 A EP 81901353A EP 0059712 B1 EP0059712 B1 EP 0059712B1
Authority
EP
European Patent Office
Prior art keywords
pressure
spool
pump
control
load
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP81901353A
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0059712A1 (en
EP0059712A4 (en
Inventor
Walter Z. Ruseff
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Caterpillar Inc
Original Assignee
Caterpillar Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Caterpillar Inc filed Critical Caterpillar Inc
Publication of EP0059712A1 publication Critical patent/EP0059712A1/en
Publication of EP0059712A4 publication Critical patent/EP0059712A4/en
Application granted granted Critical
Publication of EP0059712B1 publication Critical patent/EP0059712B1/en
Expired legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B1/00—Multi-cylinder machines or pumps characterised by number or arrangement of cylinders
    • F04B1/12—Multi-cylinder machines or pumps characterised by number or arrangement of cylinders having cylinder axes coaxial with, or parallel or inclined to, main shaft axis
    • F04B1/26—Control
    • F04B1/30—Control of machines or pumps with rotary cylinder blocks
    • F04B1/32—Control of machines or pumps with rotary cylinder blocks by varying the relative positions of a swash plate and a cylinder block
    • F04B1/324—Control of machines or pumps with rotary cylinder blocks by varying the relative positions of a swash plate and a cylinder block by changing the inclination of the swash plate
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B49/00—Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00
    • F04B49/08—Regulating by delivery pressure

Definitions

  • This invention relates generally to a load-plus valve for use in the servo-system of a variable displacement pump, and more particularly to a load-plus valve having a load piston normally isolated from a modulating spool and movable into contact therewith to control pump displacement.
  • Variable displacement pumps are employed in the hydraulic control circuits of construction vehicles to control fluid actuators, such as double-acting hydraulic cylinders.
  • the servo-systems employed for such pumps oftentimes include a flow-pressure compensated or "load-plus” valve which functions to maintain pump discharge pressure above a minimum pressure level and also above a load pressure generated in the cylinder.
  • This type valve is fully disclosed in U.S.-A-4 116 587, issued on Septemper 26, 1978 to Kenneth P. Liesener and assigned to the assignee of this application.
  • the "load-plus" valve functions to sense load pressure and to automatically actuate a swash plate of the pump in response to such pressure to maintain a desired pump discharge pressure.
  • the load pressure is received by a piston which controls the movements of a modulating spool through a relatively large compression coil spring.
  • a second, smaller spring acting in conjunction with the larger spring establishes a margin pressure, whereas the larger spring establishes a stand-by pressure for the system. Since the piston must travel a substantial distance and due to the associated arrangement of the springs, substantial space for such components is required, resulting in a relatively large pump package.
  • the piston and spool are continually interconnected by the springs, the system remains continuously dynamic and close calibration of the springs is required to ensure the desired margin and stand-by pressures.
  • the invention further comprises means for isolating the second means from the first means freeing the first means to function independently of the second means in response to the load pressure falling below a pre-determined level, and for interconnecting the first and second means to modulate the control pressure by. the second means in response to the load pressure exceeding such predetermined level.
  • the improved fluid circuit will thus function efficiently to establish margin and stand-by pressures with the above first means, which may include a modulating valve spool, being enabled to establish a stand-by pressure independent of the second means which is responsive to load pressure.
  • Such isolation improves the working efficiency of the system and provides for the utilization of a relatively small and compact pump package.
  • Figure 1 illustrates a fluid circuit 10 comprising a variable displacement pump 11 for communicating pressurized fluid from a reservoir or tank 12 to a fluid actuator 13 under the control of a standard directional control valve 14.
  • the engine- driven pump may take the form of a hydraulic pump of the type shown in Figure 2 of the drawings.
  • actuator 13 constitutes a double-acting hydraulic cylinder adapted for use on a construction vehicle or the like in a conventional manner.
  • directional control valve 14 Upon upward movement of directional control valve 14 in Figure 1, the head end of cylinder 13 will be pressurized via lines 16 and 17, whereas the rod end thereof will be vented to tank 12 via lines 18 and 19. Downward shifting of directional control valve 14 will pressurize the rod end of cylinder 13 via lines 16 and 18 and exhaust the head end of the cylinder via lines 17 and 19.
  • a line 20 When either the head or rod end of cylinder 13 is pressurized with hydraulic fluid, a line 20 will communicate a load pressure signal PL to a servo-system 21 for pump 11.
  • servo-system 21 includes a flow-pressure compensated or "load-plus” valve 22 for maintaining pump discharge pressure P o in line 16 at a predetermined level above the required load pressure P L in line 20 and the active line 17 or 18, as depicted by the "MARGIN" in Figure 3.
  • load-plus valve 22 includes first means 23 for varying a control pressure P c in a control or actuating chamber 24 in proportion to discharge pressure P o of pump 11, and second means 25 for controlling the first means to modulate the control pressure P c in response to variations in load pressure P L ,
  • hydraulic pump 11 comprises a barrel 26 adapted to be driven by an output shaft 27 of an engine, a plurality of reciprocal pistons 28 connected to a control member or swash plate 29, and a housing 30 enclosing the pump assembly.
  • the displacement of pump 11 is determined by the rotational orientation of swash plate 29, having opposite sides thereof connected to first and second biasing means 31 and 32 which are interrelated by rods 33 and 34 and pistons 35 and 36.
  • swash plate 29 will effect maximum pump displacement, whereas horizontal orientation of the swash plate in Figure 2 will effect zero or minimum displacement of the pump upon engagement of the swash plate with a stop 37.
  • First biasing means 31 may be considered to comprise the fluid pressure communicated to an actuating chamber 38 above piston 35, a first compression coil spring 39 mounted in the chamber and disposed between housing 30 and the piston, and a second compression coil spring 40 mounted between swash plate 29 and housing 30.
  • Second biasing means 32 may be considered to comprise the control pressure P c prevalent in chamber 24, above piston 36 which has a substantially larger effective diameter than piston 35.
  • first biasing means functions to urge swash plate 29 towards its first or maximum displacement position
  • second biasing means 32 functions to urge the swash plate towards its second or minimum displacement position in opposition to the first biasing means and in response to the variable control pressure P c in chamber 24.
  • “Load-plus” valve 22 generally functions similar to the corresponding valve disclosed in above-referenced U.S.-A-4 116 587.
  • Pump discharge pressure P o in a main discharge passage 41 communicates to chamber 38 of first biasing means 31 via a branch passage 42, an annulus 43, and a passage 44, whereas a second branch passage 45 communicates pump discharge pressure to first means 23 of load-plus valve 22.
  • Branch passage 45 communicates a control pressure P c to a control chamber 46 via an annulus 47 and a restricted passage 48 formed in a tubular member secured in housing 30.
  • a spool 49 of first means 23 will move upwardly to the position shown to straddle and controllably modulate a passage 50 which communicates with chamber 24, by a land 51 defined on the spool.
  • Second means 25 of load-plus valve 22 will control the position of spool 49 between a first position communicating pressurized fluid from chamber 46 to control chamber 24 and a second position at least partially venting control chamber 24 through passage 54, under certain operating conditions and in response to variations in load pressure P L in line 20.
  • this invention is directed to an isolation means 55 which functions to improve the operation and physical makeup of load-plus valve 22.
  • Isolation means 55 functions to isolate second means 25 from first means 23 to permit the first means to function independently of the second means in response to load pressure P L falling below a predetermined level. When the load pressure exeeds such level, isolation means 55 will function to permit mechanically interconnection of first and second means 23 and 25 to modulate control pressure P c .
  • isolation means 55 may be considered to comprise the arrangement of first and second means 23 and 25 wherein they are physically separated during certain phases of operation of servo-system 22 and moved into physical contact with each other during other phases thereof.
  • An upper end of spool 49 of first means 23 has an annular retainer 49' secured thereon and a stand-by pressure establishing means 56, shown in the form of a compression coil spring, is mounted between the retainer and housing 30.
  • Second means 25 for controlling first means 23 to modulate control pressure P c in response to variations in load pressure P L includes a piston 57 reciprocally mounted in a tubular guide 58 forming part of housing 30 with an upper-flared end 57' of the piston being mounted in a cup-shaped and slotted retainer 59.
  • a margin pressure establishing means 60 shown in the form of a second compression coil spring, is mounted between retainer 59 and housing 30 to provide a biasing and margin force opposing downward movement of piston 57 in Figure 2 in response to increases in load pressure P L .
  • the load pressure is communicated to an actuating chamber 61 via line 20 and through a restricted orifice 62, defined in housing 30.
  • spool 49 will shift upwardly against the opposed biasing force of spring 56 towards a position S, substantially as illustrated, to alternately communicate control chamber 46 and vent passage 53 with chamber 24 to establish a stand- by pressure, primarily for establishing a pressure- flow potential for any implement motion in the fluid circuit and for making-up any leakage that may exist therein.
  • Control pressure P c in chamber 24 will move piston 36 downwardly to pivot swash plate 29 towards its minimum displacement position at or near stop 37.
  • spring 56 which is independent of second means 25, provides a load-plus function in conjunction with margin spring 60 by exerting a substantially constant force on spool 49 whereby pump discharge pressure P o is always maintained above load pressure P L , as indicated by the "MARGIN" in Figure 3.
  • pump discharge pressure is always above the load pressure and, once the pump discharge pressure exceeds a preselected minimum pressure level, the pressure differential between the pump discharge and load pressure will remain substantially constant throughout the higher pressure ranges.
  • Figure 2 further illustrates a poppet-type relief valve 63 which establishes a maximum fluid pressure in the circuit.
  • the relief valve will open to communicate chamber 61 with a drain passage 64, via slotted retainer 59 and a passage 65.
  • the effective area of piston 36 is substantially larger than that of piston 35 whereby first biasing means 32 is enabled to overcome the opposing combined forces of first biasing means 31 to effect the desired control of the displacement of pump 11 between its minimum and maximum displacements.
  • first and second biasing means 31 and 32 may have the various spring and related arrangements varied, depending on the particular design of the pump package.
  • swash plate 29 could be initially biased to its minimum displacement position (rather than its maximum displacement position illustrated in Figure 2), depending on the particular application for the pump.
  • Fluid circuit 10 finds particular application to hydraulic circuits for construction vehicles and the like wherein close and efficient control of one or more fluid actuators 13 is required for work purposes.
  • spool 49 When a stand-by pressure, such as 6 895 kPa, is prevalent in main discharge passage 41, spool 49 will move up towards position S and continuously modulate between these two positions to maintain such stand-by pressure, which is set and controlled by spring 56 which functions independently of spring 60.
  • a stand-by pressure such as 6 895 kPa
  • Control pressure P c and load pressure P L are thus in direct opposition across the "solid" mechanical connection between the spool and piston.
  • the direct opposition of these pressures will provide for close control of any modulation effected across land 51 of spool 49 when the spool is shifted downwardly by piston 57 to at least partially vent control chamber 24, via passages 50, 54, and 53.
  • the reduced control pressure in chamber 24 will allow swash plate 27 to once again move towards its maximum displacement position illustrated in Figure 2.
  • Fluid pressure in chamber 46 will rise a like amount since the displacement of pump 11 has increased to, in turn, increase discharge pressure P o whereafter swash plate 29 will again move towards its minimum or some intermediate displacement position, depending upon flow requirements.
  • relief valve 63 will function to prevent system pressures from exceeding a maximum pressure level.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Control Of Positive-Displacement Pumps (AREA)
  • Fluid-Pressure Circuits (AREA)
  • Reciprocating Pumps (AREA)
EP81901353A 1980-09-12 1980-09-12 Improved load-plus valve for variable displacement pumps Expired EP0059712B1 (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US1980/001193 WO1982001045A1 (en) 1980-09-12 1980-09-12 Improved load-plus valve for variable displacement pumps

Publications (3)

Publication Number Publication Date
EP0059712A1 EP0059712A1 (en) 1982-09-15
EP0059712A4 EP0059712A4 (en) 1984-06-13
EP0059712B1 true EP0059712B1 (en) 1986-12-03

Family

ID=22154541

Family Applications (1)

Application Number Title Priority Date Filing Date
EP81901353A Expired EP0059712B1 (en) 1980-09-12 1980-09-12 Improved load-plus valve for variable displacement pumps

Country Status (5)

Country Link
EP (1) EP0059712B1 (enrdf_load_stackoverflow)
JP (1) JPS57501397A (enrdf_load_stackoverflow)
BE (1) BE890199A (enrdf_load_stackoverflow)
DE (1) DE3071852D1 (enrdf_load_stackoverflow)
WO (1) WO1982001045A1 (enrdf_load_stackoverflow)

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3797245A (en) * 1972-08-25 1974-03-19 Caterpillar Tractor Co Dual range pressure dependent variable flow fluid delivery system
US4124333A (en) * 1977-10-12 1978-11-07 Caterpillar Tractor Co. Externally adjustable load plus pump control assembly

Also Published As

Publication number Publication date
EP0059712A1 (en) 1982-09-15
DE3071852D1 (en) 1987-01-15
JPS57501397A (enrdf_load_stackoverflow) 1982-08-05
WO1982001045A1 (en) 1982-04-01
EP0059712A4 (en) 1984-06-13
BE890199A (fr) 1982-01-04

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