US2936712A - Variable displacement pump - Google Patents

Description

May 17, 1960 H. W. VAN GERPEN VARIABLE DISPLACEMENT PUMP Filed Jan. 20, 1958 FIG.

H.W.VAN GERPEN United States .PatentO "ice 2,936,712 VARIABLE DISPLACEMENT PUMP Harlan W. Van Gerpen, Waterloo, Iowa, assignor, by

me sne assignments, to Deere 8: Company, a corporation of Delaware Application January 20, 1955, Serial No. 110,119

' 7 Claims. cl'. 103-3 This invention relates "to a variable displacement pump and more particularly to pilot-pressure control means for regulating the stroke of the pump and therefore for incurring variations in pump output. I 'Although variable displacement pumps with means for varying pump output are known, most of these operate on the principle of varying the eccentricity of the driving member relative to radial pistons, for example, while others use various types of means for pressurizing the pump itself so as to regulate the stroke of the pistons. According to the present invention, a pilot-pressure control regulating means is afforded which acts on variablelength piston assemblies by introducing fluid to and withdrawing fluid from the components of the assemblies so that, although one component of each assembly may be driven on a fixed stroke, the other component is regulated as to stroke length. It is a feature of the invention to provide a pump having a plurality of variable-length piston assemblies .in which drive and pumping pistons in each assembly are constructed to afford a fluid-receiving chamber therebetween, together with manifold means interconnecting the chambers of all piston assemblies so that the fluid in the manifold means and chambers may circulate from one chamber to another'as the piston assemblies are consecutively operated. Superimposed on this is means for varying the fluid in the manifold so as to incur variations in the intake strokes of the pumping parts of the piston assemblies. This arrangement enables full-time contact between the driving means and the 'drive pistons, thus eliminating noise, wear, etc. The invention features piston-control port means operative between the manifold outlet and the associated chamber for trapping a cushioning amount of'fluid between the pistons so as to prevent direct pistonto-piston contact. It is another object of the invention to provide each variable-length piston assemblyas a pumping piston havinga tubular skirt which telescopically receives the associated drive piston, together with controlled passage and port means for controlling the conduction of fluid to and from the chamber formed within the skirt portion of the pumping piston.

The foregoing and other important objects and desirable features inherent in and encompassed by the invention will become apparent as a preferred embodiment thereof is. disclosed in detail in the ensuing specification and accompanying sheet of drawings, the several figures of which are described immediately below.

Fig. 1 is a schematic view partly in section, showing the improved pump assembly in circuit with hydraulic mechanism including a pair of fluid motors.

Figs. 2, 3 and 4 are enlargedsectional views showing various stages in the operation of the pump as respects one of the plurality of variable lengthpiston assemblies.

The pump selected for purposes of illustration comprises pump housing 10 having a plurality of cylinders, here a pair of diametricallyopposed cylinders .12 and 14 respectively having outer ends 16 and 18. The cylinder end 16 is connected at one side to-an intake passage 2,936,712 Patented May 17, 1960 2 20 and at its other side to a discharge passage 22. The cylinder end 18 is similarly connected to intake and discharge passages 24 and 26 respectively. The intake passages 20 and 24 are connected in common to an intake line 28 leading to reservoir at 30. The discharge passages 22 and 26 are connected in common to a high pressure line 32.

The pump cylinders 12 and 14 respectively carry variable- length piston assemblies 34 and 36 which are reciprocated consecutively by drive means, here taking in the form of a crankshaft 38 having fixed thereto an eccentric 40. It should be noted at this point that this is in general merely representative of many arrangements that the pump could take.

The hydraulic system to which the pump is connected by the high pressure line 32 and a high pressure branch 42 embodies a two-way fluid motor 44 and a one-way fluid motor 46. The motor 44 is under control of a control valve illustrated schematically at 48, and a control valve for the motor 46 is illustrated schematically at.50. Flow control valves at 52 and 54 respectively are embodied in the high pressure line 32 and high pres sure branch 42 for obvious purposes. The valves 48 and 50 may be manually and/or servo operated, as suggested schematically at 56 and 58 respectively. Both control valves are shown in their neutral positions and are of the closed center type. The valve 48 is connected by motor lines 60' to the motor 44, and the valve 50 is connected to the motor 46 via a motor line 62, a return line 64 and a supply line 66, the latter incorporating a non-return valve 68 of conventional construction and illustrated schematically here.

, As will be brought out below, the output of the pump varies according to the demand of the hydraulic system in response to a signal given by the system through the medium of demand valve means 70 and various pilot pressure lines to be presently described. The valve means 70 comprises-a bore 72 separated by a piston valve 74 into pilot and pressure chambers 76 and 78 respectively. The pressure chamber 78 is connected to the high pressure'line 32 by a supply line 80. Pressure against the {demand valve piston 74 via 8078 is opposed by a relatively strong spring 82, plus pilot pressure supplied to the pilot chamber 76 by a pilot line 84 having. branches 86 connected respectively to the motor lines 60 and a branch 88 connected to the supply line 66 between the valve 50 and the motor 46. The pilot line branches 86 incorporate individual non-return valves 90, and a similar non-return valve 92 is incorporated in the pilot line branch 88. These valves may be of any c onventional type and are therefor illustrated schematlcally. The purpose of these valves is to prevent reverse flow from one pilot branch to the-other.

The demand valve piston 74 controls a port 94 which 1s connected at 96 to pilot pressure manifold means '98 having outlets 100 and 102 to the cylinders 12 and 14, respectively, independently of the intake and discharge passages 20, 22, 24 and 26. The port 94 and consequently the manifold means 98 is connected to reservoir via a line 104 having a restricted orifice 106 therein.

thevariable- lngth pistonassemblies 34 and 36, it will be seen that the output of the pump is controlled by the 'demand valve means 70 responsive to the demand of the hydraulic system in the following manner: when both control valves 48 and 50 are closed, there is no pressure in the pilot line 84, since fluid trapped therein and in the pilot chamber 76 will bleed to reservoir throughthe orifice 112. --Consequently, the only force opposing the piston 74 is the spring 82, and pressure inthe high pressure line 32 and supply line 80 will balance against the spring 82 so as to open the port 94 to afford a small steady flow to the pilot line or manifold 98. Suffice it for the moment to note that this flow and pressure are sutficient .to minimize the intake strokes of the piston assemblies, so that the output of the pump is relatively low, suflicient only to maintain the flow just described. When the valve 48, for example, is opened or moved to one or the other of its active positions, pressure in the line 3280 will drop, and the spring 82 will close the demand valve piston 74 on the port 94, with the result that fluid in the pilot manifold 98 will bleed to reservoir via 96104 and the orifice 106. This, in a manner to be brought out below, will bring about an increase of the strokes of the piston assemblies 34 and 36, with the result that the output in the line 32 will increase until the pressure is high enough to overcome the resistance encountered by the motor 44. As pressure builds up in one or the other of the motor lines 60, flow begins in the pilot line via whichever branch 86 is connected to the pressurized motor line 60, and this pressure builds up below the demand valve piston 74 to act with the spring 82 against the piston 74. However, because of the metering effect across the control valve 48, the resulting pressure drop means that the pressure at 78 will be higher than the pilot pressure combined with the force of the spring 82, as long as the motor 44 is moving, whereupon the port 94 will open and fluid will be supplied to the pilot manifold 98 to again reduce the stroke of the pump and therefore to reduce its output. When the motor 44 encounters increased resistance, flow stops and pressure builds up, in the pilot line to again close the demand valve and thereby to cut off supply of fluid to the pilot manifold 98 with the result that the output of the pump is increased as the strokes of the piston assemblies 34 and 36 are increased. The particular demand valve means forms no part of the present invention and any other signal system or feedback arrangement could be used. That illustrated forms the subject matter of ass-ignees Patent Number 2,892,312, issued June 30, 1959.

As best shown in Figs. 2, 3 and 4, each variable-length piston assembly comprises an outer pumping piston 114 and an inner drive piston 116. Since the components of the piston assembly 36 are the same as those of the assembly 34, only the assembly 34 will be described.

In the particular form of the invention illustrated, the pumping piston 114 has thereon a tubular skirt 118 which telescopically receives the drive piston 116 soas to afford between the pistons a fluid chamber 120. The pumping piston is constantly opposed by biasing means in the form of a compression spring 122 so that thepumping piston is constantly urged in the direction of its intake stroke or downwardly or toward the drive means 3840. The drive piston 116 is in constant contact with the eccentric 40 of the drive means and is positively moved on an out stroke as the eccentric moves from the position of Fig. 2 to that of Fig. 4. I

The skirt 11.8 of the pumping piston has therein an aperture .124 which remains in communication with the outlet 1% throughout the range of movement of the pumping piston. The interior radial face of the pumping 130, an axial passage 132, and a second cross passage 134 intersecting the axial passage 132 above a springloaded check valve 136 in said axial passage.

Looking now at Fig. 2 and assuming that there is little or no fluid in the manifold 98, it will be seen that the piston assembly 34 is collapsed or relatively short, because its length is compressed between the spring 122 and the drive'means 38-40.

One feature of the arrangement as shown in Fig. 2 is that a cushioning amount of fluid is trapped'in the chamber 120 between the two pistons 114and 116. As will be seen, the cross passage 134 is out of register at this time with the skirt aperture 124 and, since the check valve 136 closes the intersection of the axial passage 132 and the other cross passage 130, the fluid in the chamber cannot escape. It should be noted also that the projections are slightly out of contact with the top face of the drive piston 116. This trapped volume of fluid prevents piston-to-piston contact. Of course, if there is any vleakagein the system, as between the passage 134 and the aperture 124, the projections 126 will contact the top face of the piston 116 and will maintain a slight space between the two pistons so as to improve the ability of the chamber to receive fluid.

Considering again the assumption that there is no fluid pressure in the line 98, the only fluid in the chamber 120 will be that trapped by the non-register of the passage 134 and aperture 124. The piston 114 is then at the end of its intake stroke, having taken in a maximum quantity of fluid at the cylinder end 16 so that when the drive means 38-40 turns to the position of Fig. 4, fluid is expelled past the check valve in the discharge line 22. Simultaneously, the components of the other piston assembly 36 are acting in a reverse manner; that is to say, the spring for that piston assembly is moving that pump ing piston inwardly on its full intake stroke. Accordingly, Fig. 2 represents what might be considered full stroke or maximum output of the pump. This maximum output will be maintainedas long as the status of fluid in the manifold 98 ismaintained.

During normal or standby operation, as previously described, output of the pump is based only on an amount of pressure sufficient to balance the demand valve piston 74 against the spring 82. Therefore, it is desirable that the output of the pump be considerably reduced. This is achieved by introducing fluid to the line 98 so as to extend the lengths of the piston assemblies 34 and 36. This occurs Via the pilot manifold 98 which, as previously described, is connected to the piston assembly chambers at the outlets 1G0 and 102v Fig. 3represents a condition in which maximum volumehas been supplied, tothe chamber 120 with the eccentric 40 in its down position. The result of the introduction of fluid to the chamber 120 via the cross passages 134 and 130 (see Fig.2) pushesthe pumping piston 114 outwardly to its maximum outward position while the drive piston 116 is at its maximum in stroke position. It should be appreciated, of course, that the rapidly rotating drive means 38-40 causes a constant change between the two pistons 114 and 116, but,

piston 114 has thereon a plurality of axial projections 126 which prevent face-to-fac-e contact betweenthe two pistons, thus improving the fluid-receiving statusof the the drive piston 116 starts up, a communicating register is effected between the passage 134 and the skirt aperture 124. This apertureis still in communication with the outlet 100, and fluid escapes throughthe port means just described so that the position. of the pumping piston 114 remains substantially fixed and-the entire assembly collapses as the drive piston 116 moves outwardly.

The small steady flow to the pilot line 98 across the port 94 in the demand valve means is calibrated relative to the orifice 106 so that for any given situation it may be assumed that the volume of fluid in the line 98 and the piston assembly chambers is constant. Hence, as one piston assembly is moving on its out stroke, the other is moving on its in stroke and the fluid exhausted from the chamber 120, for example, as the Fig. 4 position is achieved, is circulated through the manifold to the chamber in the other assembly, which is increasing as the chamber 120 is decreasing.

As the volume of fluid is varied in the line 98, the ability of the pistons 114 and 116 to extend and collapse will vary. For example, a volume introduced tothe chamber 120 less than that assumed in Fig. 3, will result in a position of the pumping piston 114 somewhat below that illustrated. Consequently, the fluid trapped in the chamber 120 will act as a column or driving connection between the two pistons and, as the stroke of the piston 116 is constant, the column of fluid will carry the pumping piston 114 from the assumed position short of that in Fig. 3 to the maximum position of Fig. 4, discharging a comparable amount of fluid at the discharge passage 22.

Several features of the invention will be apparent from the foregoing description. One significant feature is the shear action as the port 134 goes out of register with the port 124 to establish the cushioning volume of oil in the chamber 120 (Fig. 2). Another feature is the circulation or interchange of fluid from the chamber of one assembly 34 to the other assembly 36 via the pilot manifold 98, plus means for varying the volume in the line 98 so as to achieve variations in the strokes of the pumping pistons 114'Wi1iCh of course results in variations in output of the pump. Features in addition to those already enumerated will readily occur to those versed in the art, as will variations in the preferred embodiment disclosed, all of which may be achieved without departure from the spirit and scope of the invention.

What is claimed is: I p

1. A variable displacement pump, comprising: a pump housing having intake and exhaust passages and a plurality of cylinders each connected at one end to said passages; a plurality of drive pistons, one in each cylinder and movable toward and away from said cylinder end respectively on out and in strokes of'fixed length; drive 7 infinitely variable-volume fluid chamber between said two associated pistons; a fluid pressure manifold means having outlets leading to the chambers for incurring circulation of fluid among the chambers as the drive pistons move consecutively on their out strokes and as the pumping pistons are biased on their return strokes so that a given volume of fluid trapped in the manifold means and chambers will produce a given length of travel of the pumping pistons on their intake and discharge strokes; and volume-regulatingmeans connected to said manifold and chambers for trapping fluid therein to effectuate said drive connections, said means includingan adjustable element and an associated fluid port for selectively causing increase and decrease in the volume of trapped fluid to vary the length of travel of the pumping pistons on their intake and discharge strokes.

2. The invention defined in claim 1, including-pistoncontrolled port means ateach outlet operative to cut off manifold from the chamber between associated pistons and thus trap a cushioning amount'of fluid between the two' associated drive and pumping pistons to prevent complete exhaustion of the associated chamber and there; by to prevent piston-to-piston contact between said associated pistons.

3. The invention defined in claim 1, in which: each pumping. piston has a face portiontransverse to its axis and facing its associated drive piston and said drive piston has a face portion transverse to its axis and facing the face on said pumping piston, said faces defining opposite ends of the associated chamber, and one of said faces has an axial projection preventing face-to-face contact between said two pistons.

4. The invention defined in claim 1, in which: each drive piston has a passage therein leading to the associated chamber and registrable with the associated outlet for carrying fluid to and from the chamber, and said piston passage and outlet are so arranged as to go out .of register upon predetermined movement of said drive piston so as to cut off the chamber from the'manifold and thus to trap fluid in said chamber as a cushion preventing direct piston-to-piston contact. 1

5. The invention defined in claim 1, in which: each pumping piston includes a coaxial tubular skirt extending toward and telescopically receiving the associated drive piston, and the associated chamber is afforded within said skirt and between said pistons, said skirt having an aperture therethrough for register with the associated outlet.

6. The invention defined in claim 5, in which: said aperture is so constructed as to retain communication with said outlet throughout the full stroke of the pumping piston; the associated drive piston has a passage therein leading atone end to the chamber and registrable at its other. end with the skirt aperture; and said passage other end and said aperture so arranged as to go out of register upon predetermined movement of said drive piston so as to trap fluid in said chamber as a cushion preventing direct piston-to-piston contact.

7. The invention defined in claim 1, in which: each drive piston has a first cross passage therein opening to the associated outlet, an axial passage extending from said cross passage to the chamber between the associated pistons, a check valve operative on the axial passage to prevent return flow from the axial passage to the cross passage, a second cross passage leading to the axial passage beyond the check valve and opening to the associated outlet, and said second cross passage and outlet being so arranged as to go out of register upon predetermined movement of said drive piston so as to trap fluid in said chamber as a cushion preventing direct piston-to-piston contact.

References Cited in the fileof this patent UNITED STATES PATENTS France Oct. 29, 1956

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