US2627232A

US2627232A - Hydraulic power unit

Info

Publication number: US2627232A
Application number: US47992A
Authority: US
Inventors: John A Lauck
Original assignee: Borg Warner Corp
Current assignee: Borg Warner Corp
Priority date: 1948-09-07
Filing date: 1948-09-07
Publication date: 1953-02-03
Anticipated expiration: 1970-02-03

Description

Feb. 3, 1953 J. A. LAUCK 2,627,232

HYDRAULIC POWER UNIT Filed Sept. 7, 194a s Sheets-Sheet 1 Feb. 3, 1953 J. A. LAUCK HYDRAULIC POWER UNIT Filed Sept. 7, 1948 3 Sheets-Sheet 2 Aw... H w m m \J E w Z J a m friveniof" 0/4, n l; came/ '13 I I I Feb. 3, 1953 J LAUCK 2,627,232

HYDRAULIC POWER UNIT Filed Sept. '7, 1948 5 Sheets-Sheet 5 a d/8f #0 j E ran] 1 Va/ve Patented Feb. 3, 1953 HYDRAULIC POWER UNIT JohnrA', Iia'uck; South Euclid, Ohio", assignorto Borg-Warner G'orporation, Chicago, 111., a a corporationoffIllinois Application September 7, 1948, Serial No. 47,992

5: Claims; 1

This inventiomrelates'to' powerunlt'sand more particularly to liquid pressure power units: 1m eluding" manually operablecontrol valve means;

Liquid pressure power units including-- acon tinuously driven pressuregenerator; an intermittently' operated" pressure" responsive motor; and" manually adjustable" control valvemeans have been proposed heretofore. However; previously known arrangements have lacked the refinement, sensitiveness; precision of control and' efliciency of" operation necessary; for'exampler under the" rigid requirements involvedin' raisingaml lower ing tractor" drawn agricultural implements:

In' previously available" arrangementsg it hasbeen foundvnecessary to either provide a very large flow capacity by-pass valvac'apable of lian dlingthe entire output of the 'pressuregenerator almost instantaneously 'when'the delivery-oi pressure liquid to the" motor is to'b'e' discontinued; or. alternatively, provide means effective" to throttle the inlet flow to the generator; The disadvantages and undesirable" aspects of each of these previous arrangements have" become well known.

It is an object of'thisinventiorr to providean improved efficientand effective power unit including' means for' selectively delivering liquid pressure to apressure'responsive.motor; holding; said pressure on said motor; andisubsequentlyf metering said liquid" pressure. away from said motor for controlling, the return. movement" thereof.

It is'uaifurtherl objectltoprovide anzarrangement of I the present character 7 employing, an". in? termeshing gear: type; pressure generator having. pressure loadable andunloadable endlplateandl gear, journal bearingdefining. means andmanm ally selective control .valve means for: maintaining; the pressure liquid actingonsaidend plate.-v means or. alternatively relievingthe same there from depending upon (the position ofrsaidmanual means.

It is a further and more-particularv objectto provide an arrangement ortheabove character incorporating, manually operable control valve means effective ina first :position thereofto. main-v tain said loading pressure on .saidend plate, to thus cause said pressure generator. to; deliver pressure liquidto said motor; the control valve means being movable a minute distance to a second position effective toinstantaneously relieve said loading pressureland cause said generator. to discontinue .thedelivery of pressure liquidto said motor, while-locking in placeethe'pressurer 2. liquid'i already delivered to" said motor ta thus maintain said motor'inth'e position to which the same has been moved; and the control valve means" being further movable to a third position" eiiectiveto' meter saiddelivere'dliquid awayfrom said motor ata precise rate dependent upon the extent of such movement, while at the same"- time continuing to relieve the pressure liquid" fromacting on said end" plate-bearing and-pumping seal defining means.

It is a morespecific object to provide an arrangement ofthe above-character wherein said manually selectable control means is in the form" of a plunger or spool type valve having a cylindrical housing'forme'dwith a plurality ofaxially spaced ports and including a plunger" or spool. typevalve proper forme'dwithispecially' arranged axially spa'cedlperipheral valving surfaces'io'r coe operation with saidports;

Other objects, advantages and uses of the present invention will become apparent from. the reading of. the followingspecification taken in connection with. the appendeddrawings, which form a part thereof, and, wherein:

Fig. lis a... schematic layout view partially in section. showing a preferred embodiment of the invention;

Fig. 2. is anenl'argedlaxial cross-sectionalview takenlsubstantiallyon line 2-4 of. Fig. 3showing to advantage the: pressure loadable and uns loadable generator, and. the. associated. manually selectable control valvearrangement which in. combination forms the: particular subjectsmatter to which the-present invention is directed;

Fig. 3 is a cross-sectionalviewtaken substantially on line 3-3 of Fig. .2

Fig. lis a cross-sectional-viewtaken substantially on line-4-4-oftFig. 2;.

Fig. 5 is a cross-sectional view taken substan' tially on .1ine-5-5iof Fig. 2;.

Fig. 6 isan enlargedbroken away vie-wot a portion ofFig. 2 bringing out-to particular ad-- vantage the novel relationship and cooperation ,of. the precise form of pressure loaded: bushing assembly and the precise form of manuallyactu able control valvein combination; and

Fig. '7 is a schematic layoutview 'partially in section showing an alternative somewhat simplified embodiment of: the present invention;

Referring in greater detail to thedrawingsiand first to the preferredembodiment of the hydraulic power unit shown in Figs; 1. throughhd, it will be seen that a pump or 'liquid pressuregenerator a GI includes a unitary-housing: I Wenclosing gears H, l2, and manually actuatable control valve means Cl. Generator G! is adapted to be continuously driven, as for example, by having the usual geared connection 53 with the internal combustion engine of a tractor or other vehicle (not shown) requiring an intermittent supply of pressure liquid for operating a pressure responsive piston motor Ml associated with the vehicle. Liquid from a supply sump S is delivered by generator GE through conduit 14 to a one-way check valve V i thence through conduit 5%? to motor Mi, the latter being adapted to operate a device associated with the vehicle, the present arrangement being particularly suitable for the raising and lowering of a plow or for operating other agricultural implements drawn by a tractor (not shown).

In installations of the present character, it is important that there be provided a very sharp and precise control of the initiation and the discontinuance of pressure liquid delivery by pressure generator (ii. To this end the present invention provides in combination, a precise form of pressure generator comprising a liquid pressure loadable and unloadable bushing assembly or end plate means 13 subject to the novel and improved control valve unit Cl, both incorporated in the unitary housing Iii.

Manually actuatable control valve unit Cl comprises essentially bore ll formed in the unitary housing ill and having a plurality of axially spaced ports including a port 83 adapted to maintain the left-hand portion of bore il in continuous communication with the sump S through conduit 16a; a port 5 t in communication through conduit 59a with the pressure loading chamber of bushing assembly B; and port 29 in communication through conduit Zia with the pressure delivery line I 6 to motor M I. Axially adjustable valve plunger proper 23 cooperates with ports is and 2| to provide a plurality of operating conditions as will appear.

Port is is in the form of an annular recess in the wall of bore ll and has a generally rectangular cross section, including a forward wall 22 extending substantially at a right angle to the axis of the bore ll. Cooperating with annular port I 9 is cylindrical surface portion 23a of a plunger 23. This cylindrical surface portion 23a converges with a left end surface 232;, extends substantially at a right angle to the axis of bore H and forming with the cylindrical surface a very effective valve proper cooperating with the radial inner terminal of valve port wall 22 to provide a sharp opening and closing of port ill requiring only a very minute movement of the plunger. As will be apparent hereinafter, unloading of the pressure loadable bushing assembly 18 requires a flow capacity of only a few drops per second through port is, or only a very small fraction of the flow rate produced by the gears. It is very important as one of the more specific aspects of the embodiment of the invention disclosed that the opening and closing of port it require only a very small axial movement of plunger 23 as will appear from the description of the operation thereof in effecting the loading and unloading of pressure generator G-i Port fl is spaced axially to the right of port is and may likewise be in the form of an annular recess in cylindrical bore ll. Port ii is arranged to be closed by cylindrical valving surface 28 of plunger 23 when in opposed relation thereto, and is arranged to be gradually opened for permitting metered return flow therethrough, in accordance from generator Gi to motor Ml.

with the position of tapered metering surface it with respect to the port 2i.

Control valve plunger 23 has a plurality of positions important to the operation of this unit including; a first position in which cylindrical valving surface 25a overlaps port it shutting off the relief of pressure from pressure loadable bushing or end plate assembly B of pressure generator GI, as will appear, and causes 0' e pressure liquid to hold the bushing B in pumping seal engagement with the adjacent gear side faces with the result that pressure generator is caused to deliver pressure liquid from sump B through check valve VI to motor M i. Control valve plung er 23 is movable axially a minute distance of the order of 5 to bi of an inch, to a second position thereof effective instantaneously to permit a sufficient number of drops of he lid. to .y from the rear of bushing B through port is past valving surfaces 22, 23a, 23b, and through port It to sump S thus permitting bushing B to move in the outward direction to reduce the pumping seal engagement with the gea face and dis continuing the further delivery of pressure liquid It will thus appear that upon cylindrical valving surface 230. uncovering the terminal of annular groove defining end surface 22, the entire periphery beech es instantly available for the flow of liquid there past. This feature, together with the loadable and unloadable bushing feature of generator 65, renders possible the sharp sensitive response with only a very minute axial travel of plunger 23. The fact that annular groove defining surface 22 is substantially parallel to the terminal surface 2% of plunger i2 also adds to the refined operation. In this second position valve plunger 23 continues to be effective through cylindrical surface 2% to maintain port 2! closed and this, together with the one-way action of valve VI, loclzs the pressure liquid in contact with the piston of motor Ml and thus holds the same in the position to which it has been previously moved. This locked condition continues to prevail throughout a limited further axial movement of valve plunger 23 which may be referred to as the first zone following the movement of the valve to the second position thereof. Control valve plunger 23 has a third position or range of movement which may more properly be referred to as a second zone of movement. When valve plunger 23 enters the second zone, conical metering valve surface begins to meter the liquid pressure away from motor Ml through conduits l6, 2 la, port 2i,

passages

28, 29 in valve 23, port itand conduit iila back to sump S, the rate at which this return metering is accomplished being determined by the extent of the axial movement of the valve plunger The limit of movement of motor Mt in the driven direction thereof may be controlled by the provision of a suitable stop 32 cngageable by a complementary stop 33 carried by the piston of motor Mi effective when engaged to move valving surface 23a axially to the right and relieve the loading pressure from acting on bushing B.

The sharply defined opening and closin of port l9 by cylindrical valving surface 23a is very in portant to the improved operation real present novel arrangement. The pre Are 1 able and unloadable bushing B, as will appear, is very sensitive to only a few drops of pressure liquid being relieved therefrom, thus making it ticable to effect the present refined and precise operation by an almost infinitesimal movement of manually actuatable valve plunger Generator: GI i includes; pressuresloadablez andf: unloadable. bushing B::andaisxgenerailyrsimilar. in: arrangement and": mode of: GDBIHJti'OIlCitOIZthGE gear"; pumpzconstructiorr disclosedxandzclaimed in": car her-Roth and Lauck PatentxNo;.2; l2fi;622;sdated: May 13,1947; except iorrthe structure providing; for the axial 1 movement soft theahushing making: practicableo the: loading and: unloading. thereof Essentially, .this preferredrformioff pressure gene erator: includes: the. intermeshing gears"; II;; I21, received'in .bores 13 6', 31 l with radial rend walls:- 3 8;", 39; M 42; said; gears; having; axially; oppositely? extending i'journalsni Ia, I Ib1;uI2a,e Zbnreceivedzzin t. reduced; housingbores 36a; 351313111; 3.301. Presesure loadable and; unloadable: bushings." B. are? preferablycprovidedon oneesidezofitheigears; the right side being-employed: in the; present: installae tion,. .while. onxther otherqside; of ftheigearsi there arelprovided fixed-:bushingsBZ. I Bushings Biarer cientdto permitestablishing the clesiredipnmpingn seahbetween .the-ainner faces,thereofzandjthegearw sidexfaces; and almotiveapressurechamberxMCria providedlto receive pressure generatedf by gears; I i I2 for: holding. I the bushings: in 2 engagement? 2:5 with'the gear i side faces. Bushings Beachyprefers ably comprises: an outwardly' extending; tubular: portion itrreceivedflahout ithescorrespondingugear; journal and within the corresponding:reduced housingzbore; Aafi'exibleaOuring seali lfiizisginter ex posed. between; the tubular: portion: 431 and: a: steppedzrecess Ma in theshousing'hore; Enlarged; radial inner) flange: 46; is coextensive. with; the. gearrteeth andu'has a forwardugeari side face. en-.- gaging surface area-ii] and: azrear pressure aetu+-- 3: ating surface; area d8 defining lrin; part 'a motive chamber Relief 'frecess. 49:3isrformedr; in the: forward facez-fl of the bushing:andciiseplaced in communication with BJIOW'LIH'BSSUYS' area hyaxia'l 1 groovei IL The bushingsB have:a:sufticient axialt movement:- to allow: a limitedislip or'sby pass 1 of? liquidz'hetween the *fOI'WHJCiZ i-ace- 1r anditheigear side.- face: under conditions Where the controll valve hassbeen OIJGIEttQditO discontinue :theadeliVGIYi'Ofl liquid'pressure to: motor: MI; ass will; appear; While;theapressurewmayhe directed tow motive a chamber: MC; from the. ldelivery side of L the gearteethin V aznumherof ways; it :is preferredi that: this be: accomplished" as: disclosedin the above :earli'er patentrby providing an axially; extendingrrestricted flow passaget= 52 i attheposition of convergence between 2 the. upper and lower bushings: Bion I the outlet side of' the gear teeth whilei-closing'the corresponding passagerhv means ofiaplug sfii onthe in'letsideof the'gear teeth to prevent recirculation.

For: the purpose of "maintaining: gears: I I and I 2e1iI11el1g9lg8IfleIlt withxthe inner-faces of "bushingsB2 when theloading pressurehasaheen re lievedfrom chamber: MC, the journals I lb; libare formed with cylindrical recesses 1 54 receiving coil compression spring 55 "and a floatingclosure plugPEG, the outer terminal of 'which plug is held in engagement witha fulcrumpin 51 axially supway,- check: valve: VI are, specially i chosen with referenceato:oneaanother; Sprirrgpitluarezgivsn: atcompressionzvaiueesuchzthat thea-pumpingaseai: effect: produced: therebyr will cause; the; gears: to: developta iverys'lowipressurezof :theazorden of abolit 50l2t0:.1001p, s, i.. In others-words, .thebushingss whenxiunloadedv, aresnottcompietel-ya "out 1of 5 liquid sealing-engagement :with ithe igearssideaf aces; this; relationship; beings: necessaryrin 1 order that: their. generator: will: respond immediately: to; aesliglit: movement of: valve; plunger: 23211154131181: direction: causing cylindrical surfaces 23m; to 1 overlap. I: ands close port I9. Coil compression=spring::;59,of onewayg'checkzvalve'll -I isrthereforexgiven a1.co-mpressioI-r.valuevsuflicientlyiabove thatzof coil compres sion; springsr58l to; assure thattvalve-t VI will not? open". in response I to; they range; of" pressure on valueof pressurexproducedzbyxthe/generator whom only' springs; 58. are a actings. tor urge the bushing? into-pumpingasseal engagement :vvith the gear :Sidfil? faces Underxzthis'z condition, the pressure gene erator -will. merely generate aapressure; withing-a range-oft'he: order 01350- to? p; s. iiandaany: tendency of thespressureto-rise ahovevthis.:valuewill result: in a sufiicient movement'of the::-bush-- ing saway "irom' the gear sideface: to'prevent any:

further rise; the liquid thenicirculating from" the outlet-side i of the gear teeth backto the inlet: side thereof, b'etween the gear sidiyfaee-and the associated bushing; Check valveVI will be?- openedaonly when it is desired totransmit liquid i pressure to-motor-"MI as'indicated by 'the opera tor moving valve plunger'flto the left and clos ing port I 9-with the-result that the liquid pressurebuilds up within motive" chamber" MC, which" causes the pressure generated by the gearsto-sup plement the pressure. ofnsprings- 58 in holding the 1 bushings in" pumping seal engagement with: thegear side faces: The combined pressures? will have a value'sufficiently high to cause openeing'of valve VI and-the"delivery of "pressure'liquidi" to motorlM I TurningxtaFig: 7, there disclosed" a -some= W-hat simplifiedembodiment of'the presentinvention asapphed to apower" unit incorporating both a. rotary gear typef pressure generator G2 and'acorresponding form-of rotary motorrMI. Sincethe-liquidpressure foroperatingkm-otor M2- is supplied. continuously" and directed therefrom back'to the sump; S2, when" the same isheingpa driven; there isnoneed for; the special'provision'" of means for efl'ectingthe return-offthis-pressure. liquid fromthe-motor: Therefore; the tapered? metering surface; important to the modification= ofFig; l; isnotrequiredin-thissimplified con"- structionz.

It will" be seen; however, that the" broaderaspects of the'present inventionare incorporated inFig. 7- incl-uding" the pressure loadable anduniloadable" gear-typegenerator G2 one vv'ay check:- valve V2, and-the special construction" ofjcontrol valve C2 for-selectively causing the loading and r unloading of the-generator withonly avery small" or-minute-travel-of plunger--l23;- Port H9; including-radially" extending terminal surface" I 2 2, corresponds to port '23-- and radiallyextending surf-ace 22*ofthe-modification disclosed in- Figs: 1 through 65 Valving: surfaces I2 3a and- I 2312' of plunger" I 23' correspond tosurfaces- 23a,- 23b* of valve plunger-"2'3 of theabove =modifi'cation:

ltlwill' b'e again noted in this alternative *form of the invention that due'tothe uniquechar acteristics ofthe :pressure generator incorporat ing loadablen and: unloadab'le bushings: under the control of valve-w C22: having? the specially-i COIL- structedgiport I I 9 an-dz cooperatingszplunger valv ing surface i23a, there results a very sharp and refined control of the transition between the on and off delivery condition of the generator G2 with only a very small axial movement of valve plunger I23 of the order of to 1% of an inch.

While the present invention has been described in connection with certain specific embodiments thereof, it is to be understood that this is by Way of example and that the invention is to be defined by the appended claims, which should be given a scope commensurate with the prior art.

What is claimed is:

1. In an arrangement for generating liquid pressure including a housing containing intermeshing gears adapted to be continuously driven, said housing being formed with a pair of adjoining substantially cylindrical chambers having generally radially extending endwalls, said gears being received within said chambers, a low pressure liquid inlet leading to and a high pressure liquid outlet leading from said chambers, reduced bores in the end walls of said housing chambers forming co-axial extensions of said cylindrical chambers, said gears having journal extending from the opposite sides thereof into said reduced bores, axially adjustable bearing and pumping seal defining bushings in said housing on at least one side of said gear members embracing said journals, said bearing and pumping seal defining bushings including outwardly extending tubular portions received in sealed relation. within said reduced bores and radially enlarged substantially annular flange portions received in said cylindrical chambers, said annular flange portions each having a front face engageable with the adjacent gear side face from a position below the roots of the teeth to the radially outer extremities of said teeth throughout the circumferential extent thereof, said front face and said side face constituting a pair of adjacent faces which provide a surface area forming a pumping seal between the respective gears and the corresponding annular flange portions, said front faces being subject to the gear generated pressures in said cylindrical chambers in communication with the gear teeth, each of said annular portions also having a back face spaced from the adjacent radial end wall of the housing to provide an annular control pressure space at the back of each of said annular portions, an annular relief recess formed in said front face radially inwardly of the roots of said gear teeth, means placing said relief recess in communication with a zone of relatively low pressure with relation to the generated pressure, passage defining means placing said space in re stricted flow communication with the outlet pressure from said gears for causing the same to act on said pressure responsive surface for pressure loading said bushings in pumping seal engagement, and selectively controllable means including a cylindrical valve bore formed in said housing, port means in the side wall of said valve bore having a flow capacity only a small fraction of the total flow produced by said gears, said port means comprising an annular recess formed in the wall of said valve bore, Said annular recess being defined in part by a generally radially extending side wall, a passage in said housing placing said port in communication with said annular control pressure space, a cylindrical spool valve proper received in said valve bore for manual adjustment therein, a relief port in said valve bore in communication with a zone of low pressure relative to said generated pressure and spaced from said port means, said spool valve including a terminal piston portion defined by a first cylindrical surface area and a radial extending terminal surface converging therewith, whereby said cylindrical surface is effective to close said port means when moved into overlapping relation thereto, and is further effective upon a minute movement in the opening direction to uncover the port means, of the order of ,4 to ,5 of an inch, to thus cause flow to said relief port from said port means about the complete periphery of said piston terminal portion resulting immediately in suflicient relief of loading pressure from said motive chamber to cause the unloading of pressure liquid from further acting on said back face of said annular flange.

2. In an arrangement for generating liquid pressure including a housing containing intermeshing gears adapted to be continuously driven, axially adjustable end plate means within said housing engageable with the gear side faces from a position below the roots of the teeth to the radial outer extremities of said teeth throughout the circumferential extent thereof, said end plate means including an outwardly facing pressure responsive surface area effective in response to pressure generated by said gears for pressure loading said end plate means in pumping seal engagement, selectively controllable means including a manually actuatable valve effective when moved into closed position to confine said loading pressure in contact with said pressure responsive surface for causing liquid pressure generating action and effective when moved into open position to relieve said loading pressure for causing discontinuance of said liquid pressure generating action by venting said loading pressure to a zone of lower than discharge pressure, said valve having a flow capacity only a small fraction of the liquid flow produced by said gears, said valve having very sharp opening and closing characteristics and requiring a very short travel distance, said valve comprising means defining a cylindrical bore, a first port formed in the wall of said valve bore, a passage placing said port in communication with said pressure responsive surface area, a cylindrical plunger valve proper received in said valve bore for axial adjustment therein, a relief port in said valve bore in communication with a zone of low pressure relative to said loading pressure and spaced from said first port, said plunger having a first cylindrical valving surface merging with the inner terminal of said plunger for cooperation with said first port, and manual means for selectively operating said plunger to control communication between said first and second ports.

3. A hydraulic power unit for generating liquid pressure including a housing containing intermeshing gears adapted to be continuously driven, axially adjustable end plate means within said housing engageable with the gear side faces in sealing relation, compression spring means positioned between the housing and the end plate means effective to urge said end plate means in the direction of said gear side faces with a first predetermined force to assure an initial pumping seal, an outwardly facing motive area on said end plate means effective in response to liquid pres sure generated by the gears and applied thereto to urge said end plate means into pumping seal engagement with a certain force supplementing said first force, conduit defining means placing said motive area in restricted flow communication with the outlet from said gears, a one-way check valve in the outlet from said intermeshing gear pressure gcnerating means,- a second coiled compression spring associated With said check valverforrurging the check 'valvein closingdirecztion asaidspring being selected to haveaacompression value exceeding i that required to hold said check valve closed against-the pressure de- -veloped by said intermeshing ,gears by virtue of the initial pumping sealprovi'ded by 'the first mentioned compression spring means, and valving' means effective when moved into open posi tion to relieve the liquid pressure from acting on said motive area, said valving means comprising a selectively controllable valve including a cylindrical valve chamber, said valve chamber having a first port formed therein communicating with said motive area and a second port formed therein communicating with a zone of lower than generated pressure, and a valve plunger disposed in said chamber and mam'ally operable to a first position uncovering said first port and placing said motive area in communication with said zone of relatively low pressure through said second port to thus limit the pumping seal with the gear side faces to that produced by the compression spring, the plunger being manually shiftable to a second position overlapping the first port to maintain loading pressure on the motive area to supplement the action of the compression spring means.

4:. In an arrangement for generating liquid pressure including a housing containing intermeshing gears adapted to be continuously driven, said housing being formed with a pair of adjoining, substantially cylindrical chambers having generally radially extending end walls, said gears being received within said chambers, a low pressure liquid inlet leading to and a high pressure liquid outlet leading from said chambers, reduced bores in the end walls of said housing chambers forming co-axial extensions of said cylindrical chambers, said gears having journals extending from the opposite sides thereof into said reduced bores, axially adjustable bearing and pumping seal defining bushings in said housing on at least one side of said gear members embracing said journals, said bearing and pumping seal defining bushings including outwardly extending, tubular portions received in sealed relation within said reduced bores and radially enlarged, substantially annular flange portions received in said cylindrical chambers, said annular flange portions each having a front face engageable with the adjacent gear side face from a position below the roots of the teeth to the radially outer extremities of said teeth throughout the circumferential extent thereof, said front face and said side face constituting a pair of adjacent faces which provide a surface area forming a pumping seal between the respective gears and the corresponding annular flange portions, said front faces being subject to the gear generated pressures in said cylindrical chambers in communication with the gear teeth, each of said annular portions also having a back face spaced from the adjacent radial end wall of the housing to provide an annular control pressure space at the back of each of said annular portions, an annular relief recess formed in said front face radially inwardly of the roots of said gear teeth, means placing said relief recess in communication with a zone of relatively low pressure with relation to the generated pressure, passage defining means placing said space in restricted flow communication with the outlet pressure from said gears for causing the same to act on said pressure responsive surface for pressure loading raeavgeca -1 0 *sai'dbu'shings' inpumping seal engagement, and selectively controllable. means i including :acylindrical WalVe bore formed in J said housing, port means in the side wall of said valve borelhavin'g a fiow capacity only a small fraction of the total flow produced by said gears, said port means comprising an annular recessformed in the Wall of isa-idcbore, l-saidl annular trecess being rdefined in part by a generally radially extending-side "wall ja passage in said housing placing said port in communicationwith said annular control pressure space, a relief port in said valve bore in communication with a zone of lower than said generated pressure and spaced from said port means, a cylindrical spool valve proper received in said valve bore for manual adjustment therein, said spool valve including a terminal piston portion defined by a first cylindrical surface area and a radial extending terminal surface converging therewith, whereby said cylindrical surface is effective to close said first port when moved into overlapping relation thereto, and is further effective upon a minute movement in the opening direction to uncover the first port, of the order of to & of an inch, to thus cause flow to said relief port from said first port about the complete periphery of said piston terminal portion resultingimmediately in sufficient relief of loading pressure from said motive chamber to cause the unloading of pressure liquid from further acting on said back face of said annular flange, said spool valve being movable to a further variable position whereby return flow through said high pressure liquid outlet may be metered.

5. In an arrangement for generating liquid pressure including a housing containing intermeshing gears adapted to be continuously driven, said housing having an inlet and an outlet port formed therein, axially adjustable end plate means within said housing engageable with the gear side faces from a position below the roots of the teeth to the radial outer extremities of said teeth throughout the circumferential extent thereof, said end plate means including an outwardly facing pressure responsive surface area effective in response to pressure generated by said gears for pressure loading said end plate means in pumping seal engagement, selectively controllable means including a manually actuatable valve effective when moved into closed position to confine said loading pressure in contact with said pressure responsive surface for causing liquid pressure generating action and effective when moved into open position to relieve said loading pressure for causing discontinuance of said liquid pressure generating action, said valve having a flow capacity only a small fraction of the liquid flow produced by said gears, said valve having very sharp opening and closing characteristics and requiring a very short travel distance, said valve comprising means defining a cylindrical valve bore, a first port formed in the wall of said valve bore, a passage placing said port in. communication with said pressure responsive surface area, a relief port formed in said valve bore and communicating with a zone of lower than said generated pressure and spaced from said first port, a cylindrical plunger valve proper received in said valve bore for axial adjustment therein, said plunger having a first cylindrical valving surface merging with the inner terminal of said plunger for cooperation with said first port and for controlling flow from said first port to said relief port, and manual means for selectively operating said plunger, a third port formed in the 1 1 wall of said bore, and a tapered metering surface on said plunger arranged to cooperate with said third port to control return flow from said third port to said relief port.

JOHN A. LAUCK.

REFERENCES CITED The following references are of record in the file of this patent:

Number Roth, et a1. Mar. 16, 1948