US2987003A - Hydraulic pump system - Google Patents

Description

2,987,003 HYDRAULIC PUMP SYSTEM James H. Kress, Waterloo, Iowa, assignor, by mesne assignments, to Deere & Company, a corporation of Delaware 1 Filed Jan. 8, 1958, Ser. No. 707,816

7 Claims. (Cl. 103-38) I United States Patent This invention relates to a hydraulic pump system and strokes, and pilot pressure taken off the system in'g'eneral is used to oppose the bias and thereby to reduce the strokes and consequently to reduce the output. In other types of pumps, the pistons are moved forcibly on their discharge strokes and are returned on their intake strokes by relatively strong springs. One inherent disadvantage of that type of pump is that during low temperature operation, the pumping pistons may cling to their cylinder walls as a result of high viscosity of the fluid. Accord ing to the present invention, these and other disadvantages are overcome by means for positively returning the pistons on their full intake strokes or any increment thereof independent of oil viscosity and related factors. This feature is embodied in an improved pump in which the operationalcharacteristics of the pump are such as to impose on the pistons a bias tending to retain them at Y the outer ends of their discharge strokes, plus fluid means operative to vary the extent to which this inherent bias is overcome and thereby to vary the extent to which the pistons will return on their intake strokes, thus enabling variation in'pumpoutput from no-stroke 'to full-stroke. Another feature of the invention is to utilize relatively light return springs operative only in primingthe pump and having no efiect on control of the stroke regulation;

It is another object of the invention to provide an improved pumpin which pilot pistonsare respectively coaxial with pumping pistons, and fluid manifold means is provided for interconnecting the pilot cylinders for sup-.

plying fluid thereto. A significant feature of the invention resides in aregulating valve for automatically varying the volume inthe manifold in pilot cylinders in accordance with load requirements on whatever device is connectedto the pump.

The foregoing and other important objects and desirable features inherent in and encompassed by the invention'will become apparent to those versed in the art as a preferred embodiment of theinvention is disclosed, by Way ofcXample, in the single figure in the accompanying drawings and appended description.

The variable-displacement pump is indicated in its entirety by the numeral 10 and comprises means affording to drive an eccentric 16. The pump further includes a plurality of pump cylinders 18 disposed'radially as re- 14 and respectively ing valve to besubsequently described. However, this a crank case 12 in which acrank shaft 14 is operative L the like. ln'such systems, biasing means normally acts to increase the pump output by increasing the piston memo:

pistons are appropriately manifolde'd for connection to the line 24, in, a manner that will beobvious from the drawing without further description.

One of the pistons is shown in section so as to disclose the interior components thereof. From, this illustration it will be seen that the inner end of the piston has an in: take port 26 in communication with the crank case 12 and normally closed by a ball 28 under action of a relatively lightconical spring 30. As the top piston moves down on its intake stroke, the ball 28 lifts from the port 26, and fluid is taken into the interior of the piston for discharge via a discharge port 32 when the piston moves upwardly or outwardly on its discharge stroke. The

discharge port is controlled by a ball 34 spring loaded The outer or discharge end of each cylinder 18. is

' closed, as by athreaded plug 38, and this plug is hollow to afford a pilot chamber or cylinder 40. In the preferred construction illustrated, the pilot cylinder 40 is coaxial with the respective pump cylinder 18. A pilot piston 42-is reciprocable in the pilot cylinder 40 and is mechanically connected to theinterior of the pumping.

piston 20 as by an enlarged head 44 and snap ring 46. The head 44 is slotted at to enable fluidto pass from the intake port 26 to the discharge port 32 A relatively light spring 50 acts between the 'plug 38 and the pump'." v piston20 andnormally urges the pump piston-radially inwardly. However, this spring,. as. already stated, is relatively light and is instrumental primarily as means for facilitating the priming of the pump. This spring could be dispensed with if the arrangement involves a" reservoir'oil level higher than the pump and the regulatq detail. is of minor importance in the present disclosure.

Sufii'ce it to notethat the pump and pilot pistons 20 and 42 move in unison. The same construction is involved in the other two piston assemblies illustrated. The outer or upper end of the plug 38 is drilled'at 52 so that the pilot pistonsmay be connected by a manifold 54.

In the representative'system shown, the high pressure line 24 is connected to the inlet side 56 of a closed center control valve 58 which has a pair of motor ports 60 and 62 connected respectively to opposite endsofafluid in the regulating valve housing 74 carries a valve mem ber 86 biased to a closed position by a spring 88 which is adjustable at 90. When the valve is in its closed posi- I tion, the ports 76, 78, and are isolated from each other.

The port 76 is 'connectedto the high pressure line bya control line portion 92 and the outlet port 78 is connectcd to the manifold by a communicating control line portion 94. The end of the regulating valve bore 84 opposite to the spring 88 affords a chamber 96 which is connected by a line 98 to the-high pressure line 24 upstream of the control valve 58.

The arrangement is such that when pressure in the line 24 is at a predetermined value, the valve 86 is hal anccd between this pressure and the spring 88. to incur the closed position shown in the drawing, whereby the olume of fluid in the manifold 5'4 is constant. Thus, althoughjthe pilot pistons 42 move with the pump pistons 28 and have a pumping action, the fluid in'the manifold merely circulates from one pilot cylinder 40 to the other.

Whenthe'control valve 58 is in neutral, as shown, the 7 pressure in the line 24 is that predetermined by'the spring 88, and the pistons 20 are reciprocated on strokes Patented Juno 6,'i961 will overcome fluid pressure in the line 98 and chamber 96 and thevalve member 86 will move to the right,,in-

terconnecting ports 76 and 78 and thus supplying fluid from the high pressureline 24 to the manifold 54 via 9Z-76--7894. This fluid will of course enter the pilot cylinders 40 and will increase the stroke of each piston 20 for the following reason: during operation of the pump, rotation is so rapid that the pistons 20 tend to stay out to their discharge ends and consequently fail to completely return on their intake strokes. -Thus, their effective strokes are, shorter than their predeterminedmaximum strokes. If this condition persists, and the regulating valve member 86'is in its closed position as shown, the volume of fluid in the manifold 54 and pilot chambers or cylinders '40 is constant, and the intake stroke cannot be increased. Thus, the volumetric output.

of the-pump will depend upon the extent to which the pumping pistons 20 return on their intake strokes.

In the example just assumed, with the pressure drop in the line 24 because of opening of the control valve 58, fluid from the line 24 is supplied to the manifold 54 and thus forces the pistons further on their intake strokes, which consequently means an increase in their discharge strokes as well, thereby increasing the volumetric output. The pressure in the line 24 depends of course upon-the load encountered by the motor 64, and when this pressure increases enough to overcome the spring 88, the regulating valve member 86will return to neutral and will maintain the constant volume of fluid in the manifold 54 and pilot cylinders 40 as long as the volumetric requirement remains unchanged. -If the requirement increases, the valve member 86 will again shift to the right and add fluid. In the event that the line 24 achieves an instantaneous pressure rise, as by the motor 64 reaching the end of its stroke or encountering an obstacle that it cannot overcome, pressure rise in the regu- 'lating valve chamber 96 will cause the valve member 86 to shift to the left, thus interconnecting ports 78 and 80, whereby fluid will be subtracted from the manifold and pilot cylinder volume via 94--78-:8082.'

The valve bore 84 is connected behind the valve member 86 to reservoir by a drain line 100 for accepting leakage past this valve member.

In short, and assuming a stabilized pump running condition, wherein fluid viscosityand pump'speed are considered constant, 'an increase in pump stroke follows decrease of line pressure in line 24, which of course entails decrease in pressure acting via the line 98 on the right hand end .of the valve member 86 in the chamber 96. Likewise, a decrease in pump stroke follows an increase in the pilot pressure inthe chamber 96 as a result of a decrease in line pressure. For any constant volumetric output, the total quantity of fluid remains approximately constant in the pilot manifold 54 and pilot cylinders 40, since the pilot fluid circulates from one pilot cylinder to another. If an external cont-rolmeans, such as the control valve 58, incurs a situation in which more oil flows into the pilot manifold line, the pilot pistons, which act integrally-with the pump pistons 20, must move toward the center of the pump, consequently forcibly moving the pump pistons 20 on their intake strokes so that the output of the pump isincreased.

From the foregoing, it will be'seen that the pump construction itself is compact and simple, and in a preferred embodiment the pilot cylinders and pistons are respectively coaxial with the pump cylinders and pistons. The regulating valve 72 affords means forautomatic regulation of the volume of fluid in the pilot manifold, and

this regulating valve controls pump displacement according to volumetric requirements of the hydraulic motor 64, for example. Other features not categorically enumerated will readily occur to those versed in the art, as will many modifications and alterations 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:

1. A hydraulic system, comprising: a variable-die placement pump having a discharge line and further having a plurality of consecutively reciprocable pumping elements for pressurizing said line, each element being movable on intake and discharge strokes of predotermined length and conditioned by forces during operation to tend toward the end of its discharge stroke whereby the length of the intake stroke is less than said predetermined length; means connected to the pump and providing a plurality of fluid chambers, one for each element; a plurality of pistons, one in each chamber and connected to and movable with the pumping element in that chamber; a fluid manifold interconncctdecrease in the volumetric requirements imposed on the ment pump having a discharge line and further having a plurality'of pump cylinders and a plurality of consecutively reciprocable pump pistons respectively in said cylinders for pressurizing said line, each pump piston being movable on intake and discharge strokes of predetermined length and conditioned by forces during operation to tend toward the end of the discharge stroke whereby the length of the intake stroke is less than said predetermined length; means connected to the pump and providinging aplurality of pilot cylinders, one coaxial with and at the discharge end of each' pump cylinder; a pluralityof pilot pistons, one in each pilotcylinder and connected to and movable with the associated pump piston; a fluid manifold interconnecting the pilot cylinders; supply means connected between the discharge line and manifold for supplying fluid to the pilot cylinders viathe manifold in opposition to the aforesaid condition to increase the return of the pump pistons on their intake strokes; and means connected to and operative on the supply means in response to variations in the volumetric requirements imposed on the discharge line to vary the amount of fluid in said manifold and pilot cylinders and thus to incur intake strokes of the elements respectively according to increase and decrease in the volumetric requirements imposed on the discharge line.

3. A hydraulic system, comprising: a variable-displacement pump having a plurality of consecutively reciprocable pumping elements, each movable on intake and exhaust strokes of predetermined lengthand conditioned by forces during operation to tend toward the end of the discharge stroke whereby the length of the intake stroke is less than said predetermined length; a high-pressure line connected to the discharge side of said pumping elements; means connected to the pump and providing a plurality of fluid chambers, one for each element; a plurality of pistons, one in each chamber and connected to and movable with the associated pumping element; a fluid manifold interconnecting the chambers; a control line connected to the high-pressure line and to the manifold for supplying fluid to the chambers via said manifold to move the pistons and thereby to return the elements forcibly on their intake strokes in opposition to the aforesaid condition; and a regulating valve in said control line having open and closed positions respectively opening and blocking said control line and including a piston portion open to the high-pressure line, said regulating valve being operative toincur its'closed position in response to a predetermined pressure in said high-pressure line so as to maintain a constant predetermined fluid volume in the manifold and chambers and to incur its open position in response to a decrease inpressure in said high-pressure line'to add fluid to said manifold and chambers.

4. The invention defined in claim 3, in which: the regulating valve has a dump position achievable in response to a predetermined increase in pressure in the high-pressure line to dump fluid from the manifold and chambers.

5. A hydraulic system, comprising: a variable-displacement pump having a discharge line and further having a plurality of consecutively reciprocable pumping elements for pressurizing said line, each element being movable on intake and exhaust strokes of predetermined length and conditioned by forces during operation to tend toward the end of the discharge stroke whereby the length of the intake stroke is less than said predetermined length; means connected to the pump and providing a plurality of fluid chambers, one for each element; a plurality of pistons, one in each chamber and connected to and movable with the associated pumping element; a fluid manifold interconnecting the chambers; a control line interconnecting the discharge line and manifold for supplying fluid to the chambers via said manifold to move the pistons and thereby to return the elements forcibly on their intake strokes in opposition to the aforesaid condition; a regulating valve in said control line having open and closed positions respectively opening and blocking said control line and including a fluid-receivable portion communicating with the discharge line, said regulating valve being operative to incur its closed position in response to a predetermined pressure in said discharge line so as to maintain a constant predetermined fluid volume in the manifold and chambers and to incur its open position in response to a decrease in pressure in said dis charge line to add fluid to said manifold and chambers! 6. The invention defined in claim 5, in which: the regulating valve has a dump position achievable in response to a predetermined increase in pressure in the discharge line to dump fluid from the manifold and chambers.

7. A hydraulic system, comprising: a variable displacement pump having a plurality of consecutively reciprocable pumping elements, each movable on intake and discharge strokes of predetermined length and conditioned by forces during operation to tend toward the end'of its discharge stroke whereby the length of the intake stroke is less than said predetermined length; means connected to the pump and providing a plurality of fluid chambers, one for each element;a plurality 'ofpistons, one in each chamber and connected to and movable with the pumping element in that chamber; a fluid manifold interconnecting the chambers; supply means connected between the discharge side of the pump and manifold for supplying fluid to the chambers via said manifold to move the pistons and thereby to return the elements forcibly on their intake strokes in opposition to theaforesaid condition; and means connected to and," operative on the supply means for varying the amount of fluid in said manifold and chambers and thus to vary the extent to which the elements are returned on their intake strokes.

References Cited in the file of this patent UNITED STATES PATENTS

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