US2669935A - Hydraulically actuated shift control for hydraulic pumps - Google Patents

Description

W. R. TUCKER Feb 23, 1954 HYDRAULICALLY ACTUATED SHIFT CONTROL FOR HYDRAULIC PUMPS 3 Sheets-Sheet l Filed Aug. 4, 1951 INVENTORl Warren JP. z'ccierv ATTORNEY Feb. 23, 1954 w. R. TUCKER 2,669,935

HYDRAULICALLY ACTUATED SHIFT CONTROL FOR HYDRAULIC PUMPS Filed Aug. 4, 1951 3 Sheets-Sheet 2 INVENTOR War/"cn J?. Tucer ATTORNEY W. R. TUCKER Feb. 23, 1954 HYDRAULICALLY ACTUATED SHIFT CONTROL FOR HYDRAULIC PUMPS 3 Sheets-Sheet 3 Filed Aug. 4, 1951 Y INVENTOR Warrenj?. Tucker BY WM ATTORNEY Patented Feb. 23, 1954 HYDRAULICALLY ACTATED'SHIFT CoN- TROL FORHYDRAULIC PUMPS Warren R.' Tucker,'ffMount Gilead; '01nd,' assignor to H-P-M. Development Corporation, Mount Gilead-, Ohio, a corporationv of Delaware A'pplicationfAugus'tL 1951, Serial No. 240,341

l y6 Claims.

1 IThe` present' invention" relates.- to hydraulic pumpsand more specificallyto an. improved mechanism for automatically controlling the volumetric output of 'variable delivery hydraulic pumps.

."Ordinarily, variable delivery hydraulicpumps; particularly those of the radial piston type, are provided with a'oW-controlling member movable Within the pump casing between positionsof 'concentric'ity and eccentricity with respect to the pu'mp' rotor,"whereby to 'vary the' stroke' ofithe associated pumping pistons to thuscontrolthe volume of iiuidv displaced by the pump. Movement of thelow-contrlling'member of the pump isoccasioned by forces applied thereto by a Variableitension compression springy arranged to act upon one side of the flow-controlling member to move'the same 'from a concentric or neutral position towarda full delivery'eccentric position. Positioned in opposing relationship to the 'spring are-one or more fluid-pressure-'responsive pistons or'plungers whichV are ordinarily arranged toreceive'fluid pressure from a .given pointwithin a. hydraulic circuitH to which pressure'uid is supplied by the pump. `Such pistons'or plungers function to shift the How-controlling member of theipump toward its neutral', no-deliyery position in vopposition to the spring,` and inresponse toI a predetermined high pressure. within""the hydraulic system vor circuit fed.. byrthe pump. Alternatively, the uid-pressure-responsive .pistons or plungersmay be arranged so as to receive pressure .iuid in response to. a predetermined movementv of ahydraulic'motoror ram connected within thehydraulic system in which the pump is-interposed,' in' order to automatically decrease the-volumetric output'of the pump in response toa-predetermined movement of theram or motor which is actuated by the pump.. Generally, thepistons or plungers of this character arerevferredjto as servo-motor controls.

Inkoperation, assuming that the pump is Vdriven at relatively highkspeeds and is arranged to vsup-- ply.pressure i'luid to a reciprocating hydraulic press-fram; the spring functions toinitiallyshift the now-'controlling member'of the pump toward its 'maximum' delivery position to initiate a relativelyyrapid closing cycle within the 'associated press'ram. During movement of the ram toward arWork-engagingposition, the pump is'conditione'd to deliver afmaximum'volume'of fluid; but as the raml approaches or engages a workpiece and 'resistanceY- isofferedthereby to'vcontinued mbifmentof the'r'am'j pressrevvithin thefout idlivery-ofthe pump' irc'reases,` andthe-'serveer motor' pistons or plungers 'thenv functionft?` 'shift the iiow-'controllingmember of the pump* back toward'aneutral, 11o-delivery position. actually," 'the flow-controlling 'member does not`-illy reach a neutral position, but avttainsarelatively short-stroke position, in ordertofmain'taina Tcofistant holding pressure within the'hydraulicicircuit to compensate for slippagevvithinthepulrp or yleakage Within the circuit controlled`Y thereby. The primary objection to controls of this type arises through their inability to properly-control the flow 'of Iiuid from the pump Whenith pump is idlingV at relatively low'speeds; Wherein'thei'fe is very'littl'e, if any;l pressure' exerted by'id being displacedby the'pump. tidling's'peeds, the spring which is kconditioned to shift thefilow controlling member of the pumptoWaifd'fits'full deliver'yposition is unop'posed byanyof the se'rivomotor pistons, due to the absence ofsui'ci'ent fluid pressurewithin they pump discharge to factuate the' servo-motor pistons, and; thereforethe flow-controlling membertis i'naintained'inaJ full delivery position when the pump is in an idling' condition. 5- "Accordingly, it :isthe primary objectf'of the present invention to provide, in associationiwith thev pressure-responsive pistons 'or plungers''df fa servo-motor ."controlfa "spring and pressureactuated` plunger which is" effectvet'naintan the now-controlling'fmembenof a pump" onpa short-stroke Y.delivery position when thepumpis idling at relatively low 4speeds insuflicient toese tablish a predetermined pressure.otputofthe pump, andv which; upon 'normal operating-ispeeds of the pump, is actuatedl by pressure yfluid-from the pump to permit the latter to bei conditioned to discharge pressure uid at full-delivery, and to permit'l normal operation `of thev :usual servo@4 motor pistons or plungers ofthe pump control....:-.

It is another object of the invention:tof-provider a "limitv stop|` forsthel piston stages-fofI ani servo-.r motor control which isarranged to r'shiftthe-ow'- controlling member ofithe pump tofa shortestroke delivery position in the: ;absence tof;a fpredeteral mined pressurewithin the dischargejof-ktherpnmpi to prevent undesired -di'splacement'of-'iiuid .f-roin' the; pump atvidling' speeds,fbut Whiclrlismovablei in response to "a build-up in.pressuretwithinthe pump discharge during-normal operating speeds of the pumpwto an inactiveposition permitting? actuation ofv the flow-controlling member ofthe pump by theusual spring'V and servo-motoncn-f trols-of`the pumps* 3*' W v-Forfaffurther and more' detailed lunderstanding' oimth'e* present*"invention l'and' the "variusadf-T tional objects and advantages realized therefrom, reference is made to the following description and the accompanying drawings, wherein:

Fig. 1 is a diagrammatic view of a hydraulic circuit including a variable delivery pump having the present pump control associated therewith;

Fig. 2 is an enlarged vertical sectional View taken through the piston end of the pump control;

Fig. 3 is a diagrammatic vertical sectional view of the pump conditioned on short-stroke idling position; and

Fig. 4 is a similar view showing the pump conditioned on high pressure neutral or holding position.

Referring now to the drawings, the numeral I designates generally the outer casing of a Variable delivery hydraulic pump. Enclosed within the casing Ill is a circular primary rotor II which `is. arranged to be driven in rotation by a drive shaft and motor assembly, not shown. The rotor I I is formed with a plurality of radially disposed cylinders I2 which open outwardly at the periphery of the primary rotor I I, and which terminate at their inner ends in relatively smaller diameter ports I3. The rotor II and its ports I3 are arranged to rotate about a relatively stationary valve pintle I4 in which are formed separate inlet and outlet passages, I5 and I5, respectively. In the position shown in the drawings, the pump is arranged to receive iiuid through the inlet passage I5 and to discharge uid from the outlet passage I6. Slidably carried within each of the cylinders I2 is a reciprocating pumping piston or plunger Il which terminates at its outer end in a crosshead I8 which is connected with an annular secondary rotor I9. In the usual manner, the secondary rotor is rotatably supported within an annular shift ring or now-controlling member 25 which is arranged to slide longitudinally of the lpump casing I0 between positions of concentricity and eccentricity with respect to the primary rotor Il.

As will be understood, the elements of the pump heretofore described are those which normally comprise the usual radial piston Variable delivery hydraulic pump, whose operation will be well understood by those skilled in the art. So long as the shift ring 23 and the secondary rotor I9 occupy concentric positions with respect to the primary rotor II, there is no reciprocating motion of the pumping pistons I'I, and consequently, no displacement of uid between the inlet and outlet ports of the pump. However, as the shift ring 20 is displaced leftwardly, as viewed in the drawings, and as the primary and secondary rotors are rotated, the pistons I1 are forced to reciprocate within the cylinders I2 of the primary rotor to thus draw uid inwardly of the cylinders from the inlet passage I5 and to force fluid outwardly of the cylinders by way of the outlet passage I6. The greater the degree of eccentricity between the primary and secondary rotors, the greater the stroke of the pistons I7, andconsequently, a greater volume of fluid is displaced by the pump when the shift ring occupies its extreme lefthand position, as shown in Figs. 1 and 2 of the drawings, than when the shift ring occupies a slightly eccentric position leftwardly of the primary rotor, as shown in Fig. 3 of the drawing.

The pump casing I0 terminates on either side in relatively flat boss formations 2I in which is formed a shaft-receiving bore 22. Extending through and slidably carried within the bores 22 are stub shafts v23 which are suitably and rigidly 4 connected at their inner ends, in diametrically opposed relation, to the shift ring 20. Each of the stub shafts' 23 extends substantially outwardly from the pump casing I0 on either side thereof to be engaged by the flow-controlling mechanism, as will be hereinafter more fully described.

Secured to the right-hand boss formation 2I of the pump casing, as by means of capscrews 24, is a cylindrical spring housing 25 formed with an internal bore 26. Slidably carried in abutting relation to the right-hand stub shaft 23, and reciprocable within the internal bore 216 of the spring housing, is a piston-like end plate 2l which is engaged by one end of a coil compression spring 28. The opposite end of the spring 28 is abutted by a circular plate or collar 29 threadedly carried by the inner end of a screw-threaded adjusting shaft 30. The shaft 33 is rotatably carried in a bore 3| formed in the outer end wall of the spring housing 25. The shaft 33 extends outwardly from the housing and carries at its outer end a hand wheel 32 by which the shaft may be manually rotated. As will be understood, the rotation of the hand wheel functions to move the p-late or collar 29 longitudinally of the bore 25 in a manner to adjust the tension of the coil spring 28, and consequently, to increase or decrease the force exerted by the spring 28 upon the end plate 2'! and the right-hand .stub shaft 23. Thus, it will be seen that the spring 28 functions to resiliently urge the now-controlling shift ring 25 of the pump toward its extreme left-hand eccentric position, as shown in Figs. 1 and 2, providing for maximum displacement of uid by the pump.

Mounted on the left-hand boss formation 2I of the pump casing, and rigidly secured thereto, as by means of cap screws 33, is a cylindrical plate 34 which is formed with a rst cylinder bore 35 arranged in axial alignment with the shaft-receiving bore 22 of the casing I0. The bore 35 terminates at one end in a relatively diametrically enlarged annular port 36 which communicates with a radially extending inlet passage 3'I formed in the plate 34 and terminating in a screwthreaded connection opening 31a disposed on the outer surface of the plate 34. Adjoining the first cylinder bore and port 36 is a relatively smaller cylinder bore 38 which, in turn, terminates in an annular port 39. The port 39 also communicates with a second radially disposed passage 43 terminating at the periphery of the plate 34. Slidably carried within the larger cylinder bore 35 is a piston whose intermediate portion 4I' is maintained in close-fitting wiping engagement' with the walls of the bore 35, and which terminates at its inner end in a relatively reduced diameter projection 42 arranged'to abut the outer end of the stub shaft 23. At -its opposite end, the piston terminates lin a relatively reduced diameter portion 43 whichis carried in wiping engagement with the smaller diameter cylinder bore 38. The left-hand end faces of the pistons 4I and 43 provide pressure-responsive areas which are subject to fluid pressures introduced within the ports 35 and 39, respectively. As will be hereinafter more fully explained in connection with the operation of the present control, the pistons 4I and 43 function, in response to predetermined uid pressures, to shift the flow control ring 24V of the pumpfin oppositionr to the coil compression spring 28, and toward a neutral or no-delivery position.

Rigidly secured to the outer surface of the plate 34, as by means of cap screws 44, is the inner end wall A45 of an elongated cylindrical `spring formed in a uid-pressiire-responsive piston |,z

and is rigidly secured to the piston 5| by means of a threaded nut 52. The piston 5|'is arranged to slide within the bore 46a of the housing 46 and is engaged on its rear side by one end of'a coil compression spring 53. The spring53 is some-- what heavier than the coil compression spring 28, which is mounted within the opposite hous.

ing 25, and functions'in the absence of counteracting uid pressures, to urge the plunger. 48 rightwardly .into close abutment with.. the outer end face of the piston 43 to shift'the flow control ring29 to a slightly left-hand eccentric position as shown in Fig. 3, atfwhich position'the piston 5| abuts 'the stationary end wall 45. -The opposite end'of the spring 53 engages a retaining'collar 54 which is threadedly carried within a' screwth'rea'ded bore 55 formed in the outer end of the housing 46. For convenience, the cylindrical retaining collar 54 is provided centrally with a hexagonal bolt head 56' by which the collar 54 may be rotated through the use of the ordinary wrench, and the collar 54 may be locked'in any adjusted position by means of an annular Spanner nut 55a.

' The piston 5| is formed on its opposite side with a relatively large pressure face or area 5|a adjacent the end wall 45 which is responsive to pressure fluid introduced Within the inner end of the housing 46 by way of a port 5|b formed in the end wall 45 and having a radially extending passage or channel 5|c terminating at the periphery of the housing 45. Thus, the piston 5| and its plunger or stop member'48 vare arranged for movement inwardly of the pump assembly under action of the spring 53, but aresubject" to movement in the opposite direction in response to the introduction of fluid into the passage 5'|c and the inner end of the cylinder 48a under pressure sui'licient to overcome the forces exerted upon the piston by the spring 53. 'A i The end wall 45 is further formed in its central region with a leakage chamber or port 5|d communicating centrally'with `the bore`41 inthe end wall. The chamber 5|cl 'is provided witha radial outlet passage 5|@4 which communicates with a reservoir, not shown. The chamber'5ld serves to prevent the passage of iiuid between the port 39 and the inner end of the cylinder 43a around the piston 48, and thus isolates the larger piston 5| from the smaller high pressure pistons or plungers 4| and 43.

yAs .will be seen in Figs. 1 and 2, the inlet passage 40 communicating with the port-39 receives one end of a remotely extending conduit 41 whose opposite end communicates with one ofthe motor ports 58 of aspool-type distributing valve 59. The opposite motor port 69 of the valve 59 is connected by means of a conduit BI with the passage 31 for the larger cylinder bore 35. The-'valve 59 is further'provided with an inlet port 552which is connected tov receive iiuidthrough a pilotline 63 -communicatingwith a main pump discharge line- |59 connected with the pump outlet `p assage l5. `Further, the valve 59 is provided withvan outletor exhaustkport 64 having a conduit 6,5

type .valve member 56 which may be eitherme` chanically. or electrically controlled to establish communication between the inlet port 62s and either vof the motor ports 58 or 60 while connecting the opposite motor port with the exhaust port 64, or may provide for the simultaneous connection of both motor ports with therninlet port B2. It will be understood that when it is desired that the pump be shifted toward its neutral position in response to a relatively extreme highA pressure Within the discharge or outletpf the pump, the valve 59 should be conditioned to establish communication between the pump discharge and the smaller port 39, as shown in Fig'fl, in vview of the yfact that the pressure-responsive face of thepiston 43 is of smaller area than the pressureeresponsivei face ofthe larger piston, andconsequently, `a ahigher vpressure withinffthe pump dischargeis necessary to force the pistons riglitwardlyA and the f'iiow' control ring` 2nite-sa neutral position in 'opposition' to thefspringl 28 wlienf'pr'essure is acting uponthe smaller piston 43 alone.' When'it isv desired to shift the pump automatically toward 'a neutral positionfin re' sponse to a lesser pressure Within fthe `pump vdis'- charge,vl the valve 59 may be conditioned-toes# tablish" communication between the pumpdischarge and the larger port 36 wherefsuch .pres. sure may act upon the relatively larger-'area pro".- vided by the piston 4|. In the 'event-'that-'it i'sl desired to shift the pumptoward af rio-delivery position in response to a still lesser pressure buildeupwithin the discharge of the pump, the va1ve59 may be conditioned to introduce'lfluid pressure" into both-ports 35 and 39 toreact upon -thecms' posite areas of the pistons 4 l 'and 43.' In; operation, Yassuming that the pump is corfnectedto' supply pressure'luid to a double=acting` ram, as shown at liyandwhichA may be'e'mployed to'frec'iprocate one 'of the Adies of a hydraulic press, the outlet passage l5 of the pump isfconnected with the main delivery line B9. lInterposed within the line 59 is -a reversing valve 1|l"ha'ving motor port's connected, respectively, with the-rain"-A advancing and retracting area-s of the ram '58,'v and operable selectively to introduce pressure'i'fluid into'either the ram-advancing area or'tli" ram-1 retractirigk area while connecting the oppositev area' with"exhaust.v The port 5|b and pistonSI. areico'nnect'ed by way of a conduit 1| With""th"e linev 69." 'The'distribu'ting 'Valve '59"'isz'connected to"`re'ceivefpressure fluid from the 'main pu"p discharge line 99 `through thecondu'it 63. 4744When the pump is idling at relativelylbwsped, the'va'rious parts of the control and pump'ocupy npositions as f shownI in' Fig. 3, wherein"`- the ilow control yring 20 is' maintained' in a sli'g'fhtllyy left-hand eccentric position providing for arelal` tively short pumping stroke of the? pistons |11 anda substantially small displacement offilu'id from the pump 'at low pressure.v v'Thisshortf-il stroke position is obtained due to the forces exerted by th relatively heavy spring 53"4 through the plunger 88. pistons 4|' and 43, andthe'"left` hand'r stub shaft 23 to the Aflow controlring'' 2|l.v The force-exerted by thel spring" 53 overcomes that exerted bythe relatively"lighterspring 28 until the piston 5| abuts the end wall 45, and further ri'ghtward movement of the oW'control-rilig 29 under influence of the spring v53 'is prevented. Thus, the pump is permittedfto idlev with 4littleior nol displacement of vfluid 'by' the-p-istonsll11'51r 'q Assuming that 'it lis desired to initiatecan fads' vancin'g stroke Within `the 'ram' 683;:.the valve .0 sflcondtipnedto establish..'communicatiqnfrbge tween the ram-advancing area and the main discharge line of the pump and the speed of the pump is increased. Upon increase in the driving speed of the pump, the pistons I 'l increase the pressure of fluid being discharged from the pump into the line 69. This increased pressure is transmitted to the face |a of the piston 5I by way of the conduit 7l, and when the pressure reaches a predetermined amount, say 150 p. s. i., sufficient to overcome the force exerted by the spring 53, the piston 5l and plunger 48 are shifted leftvvardly to permit the spring 28 to shift the flow control ring leftwardly to its full delivery position as shown in Figs. 1 and 2. The valve 59 may be conditioned so as to connect the smaller port 39 of the servo-motor control with the pilot line 63. 'Ihe pump discharges pressure fluid through the main supply line 69 at full volume in View of the displacement of the ow control ring 20, the pistons 4l and 43, and the plunger 48 to their extreme left-hand positions by the spring 28. The ram 68 advances rapidly under the relatively high volumetric output of the pump until the same encounters resistance to further travel. As this resistance is encountered, the pressure in the pump discharge immediately increases, and this pressure is transmitted by way of the pilot line 63, valve 59, and conduit 51 to the smaller piston face 43. As the pressure within the smaller port 39 increases to a predetermined high pressure, the force exerted upon the smaller piston 43 overcomes the forces exerted through the variable tension spring 28 to move the flow control ring 28 rightwardly toward a neutral pressure-holding position, as indicated in Fig. 4. In this position the pump supplies suiiicient fluid to the system to compensate for slippage or leakage and maintains a given high pressure throughout the circuit Without endangering the pump or the various other elements in the circuit. At this time, the reversing valve 10 may be conditioned to introduce fluid pressure within the retracting area of the ram 68 and to exhaust the advancing area thereof to permit the ram to retract out of engagement with the work. Upon shifting of the valve Il), the pressure within the main discharge line 69 drops sharply to decrease the pressure acting upon the piston 43, thus permitting the spring 28 to once again shift the flow control ring from its neutral position to full stroke position while sufficient pressure is maintained within the pump discharge to hold the piston 5l and plunger 48 in their left-hand positions. Thus, the ram 68 is retracted rapidly until reaching its upper position, at which time the pressure build-up within the pump discharge is transmitted to the piston face 4| and/or 43 of the servo-motor control to once again shift the pump to a no-delivery or holding position.

It will be understood that the differential pressure-responsive areas provided by the pistons 4I and 43, together with the distributing valve 59, provide a convenient means for adjusting the pressure at which the pump may be shifted from its full delivery position toward its neutral or pressure-holding position. As heretofore explained, the distributing valve 59 may be conditioned to supply pressure fiuid selectively to either one of the pistons 4l or 43, or simultaneously to both pistons, and the greater the effective area subjected to the pressure of iiuid discharged by the pump, the greater the force acting to shift the flow control member of the pump rightwardly against the action of the spring 28 at a given pressure. Thus, if the discharge of the pump is connected to supply pressure uid to the larger piston 4 I, a lesser pressure in the discharge' of the pump is necessary to shift the pump toward its short-stroke position than is required when the discharge of the pumpis directed to the smaller piston 43. By the same token, if both of the pistons 4l and 43 are subjected to pressures developed within the pump discharge, the pump VWill be shifted toward its short-stroke or no-delivery position at a still lesser pressure. It should here be noted that the plunger 48, which is under action of the spring 53, .functions only when the pump is Vidling at relatively low speeds to maintain the flow control ring in its shortstroke position as shown in Fig. 3 and to provide for a small displacement of fluid from the pump when idling. The pistons '4| and 43 are sized in accordance with given Vdesired pressure conditions, and in shifting the pump from a full delivery position to a neutral pressure-holding position, the same function independently of the plunger 48. Ordinarily, the tension of the spring 53 is adjusted so as to overcome the tension of the spring 28. However, as soon as the pressure build-up within the discharge of the pump reaches a predetermined amount, the piston 5I compresses the spring 53 and permits the flow control ring 2S to shift leftwardly in response to the forces exerted thereon by the spring 28.

In view of the foregoing, it will be seen that the present invention provides an improved and simplified uid-pressure-responsive limit stop for the servo-motor controls of a variable delivery hydraulic pump which functions automatically when the pump is idling to maintain the flow control member of the pump in an intermediate short-stroke position until the speed of the pump is increased to attain a predetermined pressure.,

While a single preferred form of the invention has been disclosed in detail, it will be understood that various modifications with regard to oonstructional details may be employed without departing from the spirit of the invention or thek scope of the following claims.

I claim:

i. In a control for regulating the volumetric output of a variable delivery hydraulic pump automatically in response to pressure conditions within the discharge of the pump, a flow-control'- ling member movable within said pump between a no-delivery position and a full delivery position; spring means arranged on one side of the flow-controlling member of the pump and urging the latter toward its full delivery position; a

uid-pressure-responsive member engaging the flow-controlling member on the side thereof opposite said spring means; means for establishing communication between said fiuid-pressure-responsive member and the discharge of the pump, said pressure-responsive member being operable, in response to the attainment of a given high pressure Within the discharge of the pump', to move the now-controlling member of the pump from its full delivery position to its rio-delivery position; and other resiliently compressible spring means engageable with said pressure-respon. ive member oniy when the pressure within the charge of said pump is below a given low pressure for causing said pressure-responsive member to move the now-controlling member of the pump from its full delivery position to an intermediate delivery position.

2. In a control for regulating the volumetric output of a variable delivery hydraulic pump automatically in response to pressure conditions Within the discharge of the pump, 4a now-controlling member movable within said pump between a no-delivery position and a full delivery position; spring means arranged on one side of the now-controlling member of the pump and urging the latter toward its full delivery position; a fluidpressure-responsive member engaging the flow1 controlling member on the side thereof opposite said spring means; means for establishingI communication between said fluid-pressure-responsive member and the discharge of the pump, said pressure-responsive member being operable, in response to the attainment of a given high pressure Within the discharge of the pump, to move the now-controlling member of the pump from its full delivery position to its no-delivery position; other resiliently compressible spring means engageable with said pressure-responsive member only when the pressure Within the discharge of said pump is below a given low pressure for causing said pressure-responsive member to move the flow-controlling member of the pump from its full delivery position to an intermediate delivery position; and means connected with vsaid other spring means for varying the tension there- 0f and thereby to vary the given low pressure at which said other spring means is effective.

3. In a variable delivery hydraulic pump having a pressure outlet a flow control member movable in said pump between no-delivery and maximum delivery positions; spring means urging said flow control member toward its maximum delivery position; fluid-pressure-responsive piston means arranged to move said now control member in opposition to said spring means, said piston means being in fluid communication with control member toward a neutral position; a r

uid-actuated plunger engageable with said piston means and movable between a irst position,

10 operable, in the absence of said lower pressure acting on the face of said plunger, to shift said plunger to its irst position in opposition to said first-named spring means.

fl. In a variable delivery hydraulic pump; a now-control member movable in said pump between no-delivery and maximum delivery positions; spring means engageable With said flowcontrol member on one side thereof for urging the latter toward its full delivery position; piston means engageable with the opposite side of said now-control member and responsive to a predetermined high pressure output of said pump for shifting said flow-control member from a maximum delivery position toward its no-delivery position; a movable spring-pressed plunger engageable with said piston means to limit shifting movement oi said now-control member under inuence of said spring means to an intermediate position between its no-delivery position and its maximum delivery position; and Huid-pressure-l responsive means -connected with said plunger and responsive to a given low pressure output of said pump substantially less than said firstnamed pressure output for moving said plunger to a position permitting shifting movement of said flow-control member by said spring means to its maximum delivery position.

5. in a variable speed, variable delivery hydraulie pump having a pressure outlet; a flowcontrol member movable between neutral and maximum delivery positions; spring means normally urging said flow-control member toward its maximum delivery position; a plunger arranged on the side of said flow-control member opposite said spring means and movable to shift said flow-control member from a maximum delivery position to an intermediate position short of said neutral position; a second spring means engaging said plunger and urging the latter to shift said flow-control member to said intermediate position in opposition to said rst-named spring means; and uid-pressure-responsive means connected with said plunger and responsive to a given low .pressure at the outlet of said pump for moving said plunger to a position permitting free shifting movement of said flow-control member to its maximum delivery position under iniiuence of said rst-named springmeans.

6. In a variable speed, variable delivery hydraulic pump; a iiow control member movable in said pump between no-delivery and maximum delivery positions; spring means urging said ow control member toward its maximum delivery position; iiuid pressure-responsive piston means connected with the iiow control member of said pump and responsive to a predetermined high pressure within the discharge of said pump for shifting the flow control member of the pump to a no-delivery position in opposition to said spring means; and other spring means engageable with said piston means and operable when said pump is idling to cause said piston means to shift the ow control member of the pump to an intermediate delivery position.

- WARREN R. TUCKER.

No references cited.

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