US3046895A

US3046895A - Variable displacement pump control

Info

Publication number: US3046895A
Application number: US717994A
Authority: US
Inventors: Berg Fritz; Wrabetz Karl
Original assignee: VEB ZENTRALE ENTWICKLUNG und KONSTRUKTION ZEK HYDRAULIK
Current assignee: VEB ZENTRALE ENTWICKLUNG und KONSTRUKTION ZEK HYDRAULIK
Priority date: 1957-02-27
Filing date: 1958-02-27
Publication date: 1962-07-31
Anticipated expiration: 1979-07-31

Description

July 31, 1962 F. BERG ETAL 3,046,895

VARIABLE DISPLACEMENT PUMP CONTROL Filed Feb. 27, 1958 3 Sheets-Sheet 1 INVENTORS: Fritz Berg Friedriclh Arndt Karl Wrobetz July 31, 1962 F. BERG ETAL VARIABLE DISPLACEMENT PUMP CONTROL 3 Sheets-Sheet 2 Filed Feb. 27, 1958 INVENTORS'. Fritz Berg Fnednch Arndr Karl Wrobetz July 31, 1962 F. BERG EIAL 3,046,895

' VARIABLE DISPLACEMENT PUMP CONTROL Filed Feb. 2'7, 1958 3 Sheets-Sheet 3 INVENTORS: Frirz Berg Ffledrich Arndt Karl Wrobetz VARIABLE DISPLACEMENT PUMP CONTRGL Fritz Berg, Friedrich Arndt, and Karl Wrabetz, Leipzig,

Germany, assignors, by mesne assignments, to VEB Zentrale Entwickiung und Konstmktion (Zek) Hydraulik, Leipzig, Germany Filed Feb. 27, 1958, Ser. No. 717,994 Claims priority, application Germany Feb. 27, 1957 8 Claims. ((31. 10337) The present invention relates to controls for variabledelivery pumps and more particularly for variable-andreversible-delivery pumps, such as radial plunger pumps of the type described in the book Oil Hydraulic lower and Its Industrial Application by Walter Ernst (1st Ed, New York, 1949, pages 120421), for use with hydraulic presses and the like.

The delivery of such pumps is varied by adjusting the eccentricity of a reactor ring or reaction rotor, arranged in a slide block which controls the stroke of the plungers and thereby permits variation of the delivery of the pump at constant motor speed. When the reactor ring or slide block is in a position concentric with the cylinder rotor in which the pistons are reciprocably supported, the pump is set for zero delivery. Shifting of the reaction rotor causes liquid to be pumped. A pump equipped for shifting of the reaction rotor into two eccentric positions on opposite sides of the zero-delivery position permits reversal of fluid flow Without change in the speed or direction of the pump motor and without external reversing valves.

To bring about a change in pump output and direction of flow requires substantial forces to be applied to the slide block holding the reaction rotor. It has, therefore, formerly been proposed to actuate shifting of the slide block by means of hydraulic servo motors equipped with pilot valves which can be adjusted by relatively small forces. The hydraulic servo motor acts against the restraint of a spring which exerts pressure on the slide block and therefore prevents back lash and actuates the return movement of the slide block when the hydraulic servo motor is deactivated.

It has, furthermore, been formerly proposed to have the pilot valve of the hydraulic servo motor actuated against the pressure of a return spring by means of a hydraulic pressure regulator, so that the output of the pump, and thereby the working speed of the hydraulic press or other device driven by the pump can be adjusted in a stepless manner by an operator from the control panel of the press. In this known arrangement, the pilot valve of the speed adjustment is additionally acted upon by a lever system connected to means for automatically reducing the oumut of the pump in proportion to the pressure developed when there is an increase of pressure on the delivery side of the pump. It is apparent that with such an arrangement the delivery of the pump is reduced to a minimum at maximum design pressure, even if the machine is set for its highest working speed by the operator. Delivery will only be adequate to compensate for leakage in the hydraulic system and to maintain the set maximum pressure. It is inconvenient to control a pump, which is usually mounted on the crosshead of the press, by remote control from the operating stand of the press if a hydraulic connection between the control actuating means at the operating stand and the controls themselves has to be provided. Hydraulic control lines have a fixed length and cannot be readily changed without requiring major alterations in the entire system. Additional control elements are required if the pump control cycle is to be changed, for example, in coordination with a programming system.

It is an object of the invention to permit locating the Patented July 31, 1962 mote controls by replacing the remote control feature of a hydraulic control with an electric servo system, comprising at least two coordinated electric synchros, the transmitter synchro being arranged at the operating station of the press or other device actuated by the pump, which pump is controlled by the device of the invention, and the receiver synchro being arranged to actuate the pump controls.

Since the receiver of an electric servo system is capable of furnishing only a relatively weak torque, the receiving synchro of the control device of the invention is directly coupled to a first hydraulic servo motor acting on a lever which actuates the pilot valve of a second hydraulic servo motor, which in turn is in operative engagement with the slide block or reaction rotor of the variable-delivery pump. The second hydraulic servo motor is furthermore acted upon by a pressure compensating control adapted to adjust delivery of the pump, so as to maintain the predetermined fluid pressure. The device of the invention permits adjustment of this pressure compensating control from the operating stand for altering maximum fluid pressure and delivery.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which,

FIG. 1 is a diagrammatic view, partly in vertical section and partly in side elevation, of the control device according to the invention,

FIG. 2 is an enlarged vertical section of the pressure compensating control of FIG. 1, equipped with remote control mechanism, and

FIG. 3 is an electric wiring diagram of the control de vice as applied to a variable-displacement pump which actuates a hydraulic press.

Referring now to FIG. 1, there is shown .a variableand-reversible delivery pump 2 of the radial plunger type having a slide block 1 carrying the reaction rotor of the pump and shiftable between extreme eccentric positions e and 2 corresponding to maximum delivery for power stroke and return stroke, respectively, of a coordinated hydraulic machine, such as a hydraulic press actuated by a piston 3 connected to the pump 2 by a feed line 25 and a return line 29. The position of slide block 1 is shifted by means of a hydraulic servo motor 5 of conventional design and mode of operation, having a power piston 4 and a piston-type pilot valve 6 axially arranged in power piston 4 and equipped With a stop 6a limiting the stroke of valve 6 and thereby of piston 4 which follows the servo valve 6 in proportion to the servo valve movement. 7

A gear pump, schematically indicated at 7, provides auxiliary control fluid for the hydraulic control elements and make-up fluid for leakage losses in the main hydraulic system of pump 2 in a well-known manner. A springloaded relief valve 8 maintains constant pressure in the auxiliary hydraulic system.

Hydraulic servo motor 5 is controlled by an electric servo system consisting of a transmitting electric servo motor or synchro 9, the angular position of which is set 2Q a lever 21 pivotally supported in the case of the by the operator, or by an automatic programming device and a receiving synchro 10 which follows the angular movement of transmitter 9 in aewell known manner, and which displaces the axial pilot valve 13 in a power piston 14 of a hydraulic servo motor 15. The rotary movement of-Ireceiving servomotor is transformed'into translatory movement of the valve 13 by means of an internally threaded bushing 11, fixedly mounted on'the shaft of motor 10, cooperating with a threaded plug 12 mounted'on valve 13. Hydraulic servo motor 15 actuates a rack 16 which engages a gear segment on one end of' a lever 17.

' The other end of lever 17 is forked and is adapted to move the-stem'of pilot valve 6 of hydraulic servo motor 5 towards piston 4 by abutting against collar 13.

A shifting movement of valve 6 in response to an upward movement of power piston 14 in hydraulic seryo motor 15 is opposed by acompression spring 19. Spring 19, by means of 'a linkage consisting of one end of a piston control device at 22 urges collar 18 towards the forked 20 end of lever 17 with a fixed pressure. Piston 20 is integral with a differential piston 23, one surface of which is exposed in cylinderspace 24 to the pressure in feed line 25 of the, main hydraulic system with which it is connected by conduit 26. Cylinder space 28, in which 25 'the' lar ger surface of differential piston 20 is exposed, is

connected 'selectiyely with. the pressure system ofv gear 7 orwith the sump of pump 7 by a slide valve 27 actuated bya solenoid 34.

Theinitial stress of compression spring 19 can be adjustably fixed byr changing the po'sitionof a threaded spring cover 30'. Electrical means for remote control of the adjustment of spring 19 is illustrated in FIG. 2 which shows on an enlarged scale. the forked end of lever 17 engaging the collar 18, supported on the stem of, valve 6.,which is equipped with stop 6a. Lever 21, which is supportedon pivot 22, mounted-in the housing of the control device, slidably engages rings pivotally mountedpn valve. 6 and piston 2 0, respectively, piston 20 being acted upon by compression spring 19, the, initial" stress of, which is adjustable by meansof a threaded co'ver 30. Cover-30 is adaptedto be'rotatedby. the gear train 38a of a gear motor38, which is 'furthermoreconnected to a potentiometer 36 by, means of reduction gearsfitlb.

"Operation of thedevice of FIGS. '1 and 2 will now bedescribed, together with FIGI3 which illustrates thc flelectric circuit of a pump control device of the. invention as applied tolahydraulic system operating a hydraulic press. In order to provide for several diflerent working speeds ofpistonfi. of the press, there arevprovided. in, addition to'transmitting synchro 9, shownlin Fl G 1 additional,

synchros 9a. and 9b.

The operating cycle of the press is startedby pushing, starter" button 40,. which energizesrelay.1 i1,thus .closing self-holding contact 31f and connectingthe statorswindings of synchros 9 and 10, comp nsatin currents, willflow: between therotors of synchros 9and 10, until the rotor of receiving synchro 10. wi11 assume the position corre: sponding to that for. which the" rotor of transmitting synch'ro. '9 isseto'nlthe. dial. Powenforoperation ,of. the servo system is derived from a. three-'wire main line, generally indicated by reference numeralSQ, i i

The rotary movementof synchrolfl, induced bytransmitting ,synchro I 9, causesftransla tory :movement of I pilot valve'13'and of the coordinated power piston 14, which.

- -by means of rack.16 and lever 17 pushes collar 18 and therefore the pilotvalve6-towards.theright (FIG.- 1). This causes slide blockl to. shift towardsthe eccentric position e1. 'l 7 i 1 The piston 3 of the. hydraulic press, whiclris setby 7 synchro 9 for rapid forward feed, willthus ,move, down ward until cam 41 actuates switchiivz which hasamormally closed'contact 32' arrangedin. the hOldlIlgfihfCllltj of; relay 3,1. "Relayj 31, is. derener'gized and the, circuit; connecting synchros 9 and 10 is interrupted. A normally is de-energized and relay 31b actuated, and] receiving synchro 10 is disconnected from transmitting synchro, 9a and connected to synchr'o 9b, which is assumed. to, be set for the actual working speed. The pressure in

lines

25 and 26 is increased because of the resistance of the work, which is transmitted to piston 3.- As long as the Working pressure of the main hydraulic system which; is

, transmitted to space 24 is too low to overcome the pressure of' spring 19, piston 20 remains in a positionrdetermined by the abutment of collar 18 against the forked end of lever 17. The position of lever 17,, whichis set bysynchro 10, therefore determines the eccentricity of slide block 1 which controls the delivery of pump 2 and thereby sets the. traveling speed of piston 3. the pressure in lines 25 and 2 6-, and therefore in cylinder space 24, increases further, it becomes sufficiently high to overcome the opposing force of spring 1 9. 'Leverll then shifts the pilot valve 6 and slide block 1 to the left to maintain the pressure in cylinder space 28 necessary to balance the force of spring 19. If the pressure inline 25 reaches the maximum rated value, the slide block 1 is set for approximately zero eccentricity and therefore,

zero pressing fluid delivery. d

When the pressure in the main hydraulic system drops,

lever 21 is again urged into abutment against collar 18.

by spring 19 and the stem of pilot valve 6 is movedv away from power piston 4 as far as the pressure in line] 26 and cylinder space 24 will; permit. If this pressure is.

low enough, the collar 18 will abut against the forked.

head of'the lever 17 and'the speed of; main piston 3 will again be determined, by the setting of servo "motors;

9 and 10.

The speed of the working stroke of, a press equipped with the control device of the invention can therefore be,

controlled at will by. setting. of transmitting. servo motors. 9, 9a, 9b, etc. When a. pressure set by adjustment of, the stress of spring 19is exceeded, the traveling; speed of.

the press piston 3 is reduced to that. value which, is a compatible with the'maximum pressureset. It is, apparcut that a complex working cycle may be automaticallycontrolled by an arrangement comprising the. necessary number of cam-actuated switches and transmittinggservo; motors.

, Aftencompletion of the work stroke, switch, 33, is,"

in f; orm l am.

actuated by earn 41. contact of switch 33 initiates the rapid return strokeof; piston 3 by energizing solenoid 3.4. of slide valve 27 (HQ 1). The slide valve is shiftedtogwards the right dp i u om s ar P 1 12 s dm ttm othe cyl n der space 28, exerting suflicient force; on piston 2049;

overcome. the pressure of spring;19. The hydraulic servo motor 5 therefore moves the slide block 1 into the en:

treme left position a; for reverse flow of fluii n h main hydraulicsystem. The, speed ofthereturn stroke;

of piston 3 is determined by; theposition of stop 6a which limits the leftward movement of. pilot valve.6 and.)

thereby of slide block 1. The returnstroke is. notconz. trolled by the electric servo. motor system. It is per-. formed atmaximum speed, that is atmaximumidelivery: of the pump 2. The positionrof the lever 17 and. the. setting of servo motorsr9', 9a, 9b, andrllltremainsuna. changed during the returnstroke.

The position of the spring cap 30 can-be changed, by.

0 means of the gearmotor 38, for adjusting the initial'tension of, spring 19, and thereby the maximum. working.-

pressure of thermain hydraulic system. lt-isunderstood that the cap 30 may-also beadjustedby a system include mg an electric. servo. motor actuating. a hydraulic servo motor, whereby a visual indication of the position of the spring cap 30 may be had on the control board from the position of the rotor of the transmitting electric servo motor.

The wiring diagram of FIG. 3 shows the circuitry used in the device of the invention for electrical remote control of the initial tension of spring 19 by means of gear motor 38 and potentiometer 36. A bridge circuit 37 of a type known per se is employed between a master potentiometer 35 and a slave potentiometer 36 connected with spring cap 30.

When the master potentiometer 35 is set for a desired working pressure, a zero voltage relay 42, which is an element of the bridge circuit 37 between the slave potentiometer 36 and the master potentiometer 35 energizes contactor 44, which starts gear motor 38 to rotate in one direction. Let it be assumed, for example, that this be clockwise rotation and that it cause reduction of the initial stress of compression spring 19 which causes a decrease of the working pressure of the main hydraulic system. Movement of motor 38 continues until the slave potentiometer 36, which is moved by means of the gears 38b, reaches a position corresponding to that of transmitting potentiometer 35. The bridge circuit reaches equilibrium, and zero voltage relay 4-2 returns to its neutral center position. Contactor 44 is deenergized and the gear motor 38 stops. When it is desired to increase the working pressure, it is necessary to increase the stress of spring 19. This is done by adjusting the master potentiometer 35 in the opposite direction, whereby the zero voltage relay energizes the contactor 43 for counterclockwise rotation of gear motor 38 until the positions of the two

potentiometers

35 and 36 are again brought into agreement and the bridge circuit is balanced.

While the control device of the invention has been illustrated by an embodiment controlling a variable-andreversible displacement pump of the radial plunger type having a reaction rotor contained within a slide block, it will be understood by those skilled in the art that the device of the invention is equally applicable to variable displacement pumps of different types which require substantial forces for the shifting of their reaction-rotors, whereby the pump delivery is adjusted,

Various modifications are contemplated and may obviously be resorted to by those skilled in the art without departing from the spirit and scope of the invention as hereinafter defined by the appended claims, as only a preferred embodiment thereof has been disclosed.

What is claimed is: i

1. A variable delivery pump comprising, in combination, a coordinated fluid motor, conduit means between said pump and'said motor for a fluid circulated by said pump, reactor ring means shiftable for the adjustment of delivery and direction of flow of said fluid in said conduit means, a control device including first hydraulic servo motor means having a first movable portion connected to said reactor ring means for shifting the position thereof, movable control means connected to said first hydraulic servo motor means and elfective to move the latter and said reactor ring means an amount in proportion to movement of said movable control means, second hydraulic servo motor means having a second movable portion connected to said movable control means for movement of the latter in response to movement of said second movable portion, and supplemental control means acting at the connection of said second servo motor means and said movable control means, and including a sliding member, a predetermined biasing force means biased against one side of said member to urge said memher in one direction, and means communicating the other side of said member with said conduit means to bias this side in the opposite direction by means of said fluid delivered by said pump.

2. A variable delivery pump according to claim 1 wherein said sliding member has at least two difierential piston area portions at said other side, one portion being exposed to discharge pressure from said conduit means, further comprising constant pressure control fluid means, the other one of said differential piston area portions being adapted to be selectively exposed to the positive and negative pressure sides of said control fluid means.

3. A variable delivery pump according to claim 2 wherein said one differential piston area portion is smaller than said other portion, said discharge pressure applied to said one portion normally balancing the action of said biasing force means, while upon connecting said positive pressure side to said other portion said biasing force means is overcome, said sliding member is shifted in the direction of said one side and said supplemental control means may act by shifting said reactor ring means to reverse the direction of flow of said fluid delivered by said pump.

4. A variable delivery pump according to claim 1, further including remote control means for adjusting said predetermined biasing force means.

5. A variable delivery pump according to claim 1 wherein said predetermined biasing force means is a spring.

6. A variable delivery pump according to claim 5 wherein said remote control means includes electric motor means for adjusting the tension of said spring, master potentiometer means settable for a predetermined pressure of said spring, slave potentiometer means operatively coupled to said electric motor means for coordinated setting movement therewith, and bridge circuit means re sponsive to the relative settings of said master and said slave potentiometer means for controlling the movement of said electric motor means.

7. A variable delivery pump according to claim 4 wherein said remote control means further includes an electric servo system having transmitter'means and receiver means, and a hydraulic servo motor connected to said predetermined biasing force means, said receiver means being adapted to actuate said hydraulic servo motor for adjusting said predetermined biasing force means.

8. A variable delivery pump according to claim 7 wherein said electric servo'system includes a plurality of transmitter means, and control means operatively connected to said fluid motor for selectively and individually connecting said transmitter means to said receiver means.

References Cited in the file of this patent UNITED STATES PATENTS Marshall et al Nov. 3, 1959