ciaim: 1. A fluid pressure servomo4lor comprisin.-: a body member havin- an axially extending power chamber therein, a movable wall in said power chamber constructed and arran.-ed to be driven toward one end of s,-,id body member, said body member also havin.- a g--nerally axially extending valve chamber adjacent the other erd thereof which valve chamber opens into and is generally concentric with said power chamber, a valve sleeve in slidinen.-a.@ement with the sidcwalls of said valve chamber ana capable of @-noving into abutment with said movable wall, abutment means limiting movement of said valve sleeve away from said movable wall, a valve spool in t',Ie ce.,@tral chamber of said valve sleeve, inlet means for said body member prov;ding fluid pressure communicatioii wilhin said body member, outlet means for fliiid pressure irom said body member, said valve sle--ve and valve's,,)ool co@istitutin@ a coacting valve structure which comm-Lin:,-ates said outl,-t riieans to the portion of said body j-.nemb,-r located between said sleeve and said movable wall when said valve spool is in a normal position i-,i said sl--eve and to communicate said inlet means to sa,.d poi-tion of said body member located between said sleeve and said movable wall when said valv-. spool is moved to an actuating position in sa-ld sleeve located in the direction of said movable wall from said normal pos:@'Lion, means for biasing.said valve spool toward its normal position, and actuating mcaiis projecting out of said s'@eeve for movin@ said valve spool, said actuating P-ica-@is -ncILiding a lost ;iotion connection for drivilig said valve sleeve in'co en,@agement with said movable wall, and said lost motion co-.inection being greater in le-@igth than the movement ol' said spool from its normal to its actuatin.- position; said means for biasing said valve spool being efi'ective to retaiii said sleeve against its abutme@-t durin.Q power actuation of the movable wall dtiring actuation of said valve spool tlirough said lost motioncoiinection and further movement of said actuating m,-ans efj'ectin,- abutment of said sleeve with said movable wall to obtain displacenient of said movable wall under power failure. 2. A fluid pressure servomotor comprising: a body member having an axially extend;ng power chamber therein, a movable wall in said power chamber constructed and arranged to be driven toward one end of said body member, said body member also having a generally axially extending valve chamber adjacent the other end thereof which valve chamber ope-,is into and is -enerally concentric with said power chariiber, a valve sleeve in sliding engagement with the side-walls o"' said valve chamber and capable of moving into abutment with said movable wall, abutment means limiting movement of said valve sleeve away from said movable wall, said body member having mcans forming an outlet connection, means forming pressure fluid inlet, atid means forming a flow through fluid path, said valve sleeve having a central chamber therein, a valve spool in said central chamber and having recesses therein which when said spool is in its normal positio-.1 communicates said @outl-@t means to the portion of said body r@iember betwee-@i said sleeve and said movable wall ,@,hile also communicating said mea-,is formin-, an inlet to said nieans form;ng a flow throu,,h path, and -@vhich when in an Pctuating position located in the direction of said movable wall from said normal pos;tion diverts at least a portion of fluid flow from said inlet means to said portion of said body member between said valve sl,- eve and said movable waH, said valve spool having an end adjacent said movable wall for receivir@g iluid pressure effective to bias it toward its norm-,il position, and actuating means projecting out of said sleeve for rnoving said valve spool, said actuating means including a Iost motion connection for driving said valve sleeve into engaement with said movable wall, and said lost motion connect;on having a greater amount 10 of lost motion than th.- movement of said spool from its no.-mal to its actuatiig position. 3. A unit comprising: a housing having fluid inlet port riieans and fluid outlet port means, said housin.- having a valve assembly chamber therein commun;cated with a 15 variable volume fluid chamber, said valve assembly comprising two relatively movable valve members slidably mounted in said valve assembly chamber, passage means communicatin.@ said valve assembly with said inlet and out]-,t port means, stop i-neans operatively connected to 20 said housing constructed for engagement by one of said valve members, means urging said one valve member into engageme@qt v;ith said stop means, said valve assembly being so arranged and constructed that when the other of said valve membcrs is in actuatipg position relative to 25 said one valve member fluid flow from said inlet port means will be corimunicated to said variable volume chamb--r and when in normal portion of s-,iid other valve member relative to said one valve member fluid flow commutiication from said inlet port means to said variable 30 volume f@Iiiid cl-@amber is cut off and said variable volume chamber is communicated with said outl.,t port means, movable n-iear@s oreratively connected to said valve members for movin,- said one valve member when said other valve member has traveled a predeternined distance rela35 tive tO said one valve member. 4. In a fl@,iid pressure motor: a housing having fluid inlet port means and fluid outlet port means, said housing having a longitudinally extending chamber therein, a valve assembly located at the rear of said chamber com40 prising two relatively movable valve members slidably mounted in said chamber, passag.- means communicating s-,iid valve ass--mbly with sa-'-d inlet and outlet port ipcans, a pressure responsive mcinber slidably mounted in the front of said chamber, stop means operatively connected 45 to said housing constructed for en.-a.-epient by one @of said valve members, means urging said o-@ic vaiv,- member rearwardly into engagem--Pt with said stop ir@cans, said valve members being so arranged and constructed that when the other of said valve members is in actuating posi50 tion relative to said one valve member fluid flow from said inlet port means will be communicated to the rear of said pressure responsive member thereby providin.- a fl@iid force acting on said pressure responsive member for moving said pressure responsive member forwardly, 55 and when in normal position of said other valve member relative to said one valve meniber fluid flow communication from said inlet port means to the rear of said pressure responsive member is cut off and said rear of said pressure responsive niember is communicated with said 60 outl-.t port means, means at the front end 'of said one valve member for engaging the rear of said pressure responsive member, movable means operatively connected to said valve members for transferring force to said one valve memb@- r for moving said press,.ire responsive mem65 ber when said other valve member has traveled a predetermined distance relative to said one valve member. 5. The structure as recited in claim 4, wherein said movable means comprises actuatin.- means op.-ratively connected to said other valve niember for maving the 70 same, said actuating means having a lost motion connection with said one valve member for moving the same away from said stop means and thereby move said presstire responsive member forwards. 6. A unit coinprising: a housing having fILiid inlet port 75 means and fluid oultlet port meins, said housing having a

3,173,339 valve asse@nbly chamber therein comniunicated with a variable volume fluid chamber, said valve assembly comprising a first valve member slidably mounted in said chambers and a second valve member slidably mounted within said first valve member, passage m.ans communicating the interior of said first valve member with said inlet and outlet port means, stop means operatively connected to said housingconstructed for enga.-ement by said first valve member, means urging said first valve member into engagement with said stop means when said second valve member is in normal position, said valve assembly being so arranged and constructed that when said second valve member is in actuating position relative to said first valve member fluid flow from said inlet port means will be communicated to one end of said first valve member and to said variable volume chamber, thereby providing a fftiid force acting on said end of said first valve member for urging said first valve member against said stop means, and when in normal position of said second valve member relative to said first valve member fluid flow communication from said inlet port means to said one end -of said first valve member and said variable volume fluid chamber is cut off and said one end of said first valve meluber and said variable volume chamber is commi-,nicated with said outlet port means, movable means operatively connected to said valve mcinbers @Lor moving said first valve member when said other valve rr@ember has traveled a predetermined distance r-.Iative to said first valve member. 7. In a fluid pressure motor: a housing having fluid inlet port means and fluid outlet port mears, said housing having a longitudinally extending chamber therein, a valve assembly located at the rear of said chatiiloer comprising a first valve member slidably mounted in said chainber and a second valve member slidab'@y mounted within said first valve member, passage means communicating the interior of said first valve member with said inlet and outlet port means, a pressure responsive member slidably -mounted in the front portion of said chamber, stop means operatively connected to said housing constructed for engagement by said first valve member, means urging said first valve member rearwardly into enga,Cment with said stop means when said second valve member is in normal position, said valve assembly being so arranged and constructed that when said second valve member is in actuating position relative to said first valve meinber flu-' d flow from said inlet port means will be communicated to the front end of said first valve member and to the rear of said presslre responsive member thereby providing a fluid force acting on said first valve member front end for urging said first valve member rearwardly against said stop means and providing a fluid force acting on said pressure responsive member for moving said pressure responsive member forwardly, and when in normal position of said second valve member relative to said first valve member fluid flow communication from said inlet port means to said front end of said first valve me-@nber and the rear of said pressure responsive member is cut off and said front end of said first valve member and the rear of said pressure responsive member is communicated with said outlet port means, means at the front end of said first valve member for engaging the rear of said pressure responsive member, movable means operatively connected to said valve members for transferring force to said first valve member for moving said pressure responsive member when said other valve member has traveled a predetermined distance relative to said first valve mem. ber. 8. The structure as recited in claim 7, wherein said movable means comprises actuating me,,ins operat.;Vely conner-ted to said second valve meniber for rioving the same, said actuating means havin.a a lost motion connection with said second valve member for moving the,sa:n-le away from said stop meatis and thereby move said pressure responsive meinber forwards. 10 9. The stracture as reeited in claim 8 wherein said means urging said first valve menijber rearwardly into engagement with said stop means when said second valve member is in normal T)osition -comprises sprin.- mearis urging said pressure responsive member rearwardly into en,@agement xvith said front end of said first valve meiriber. 10. Tho structure as recited in claim 9 wherein said spring means en.-ages the front oj' said pressure responsive member. 10 II. The structure a-s re-,ited in claim IO wherein means are provided for communicating pressure acting on the rear of said pressure responsive member to the @front end of said second valve meniber whereby said pressure is transferred to said actuating means by said second valve 15 member. 12. The structure as recited in claim 10 wherein sa@id first valve member comprises a valve sleeve having an annular inlet pot-t and an annular outlet port in t-he interior wall thereof communicated with said housing inlet 20 and Dutlet port means, resperfively, said second valve member comprising a spool valve member having at least one land so arranged to cooperate with said annular groov,-s for effecting the above said functions when said spool valve member is in normal and ar-tuatiilg persitions. 25 13. The structure as recited in claim 10 wherein said hoti-sing has a second outlet port n-leans, said first valve member comprising a hollow valve sleeve havin.- an annular inlet port and two annular outlet ports in the interior wall thereof, means communicating said @annular 30 inlet port with said housing i-,ilet port means and each of said anntilar oiitlet ports wi@th a respective one of said hous;ng outlet port means, said second valve member comprising a !spool valve member having lands so arranged to cooperate with said annular grooves for effect35 ing the above said functions when said spool valve member is in normal and acttiating positions in addition to providin- fluid flow from said inlet port means to said second outlet port means via said annular inlet port ar@d the respective annular outlet port of said second outlet 40 port means when said spool valve member is in normalposit-ion. 14. The structure as recited in clai-m 13 wherein means are provided for communicatin.- pressure acting on the rear of said pressure resdonsive member to the -front 45 end of said spool valve whereby said presstire is transferred to said actuating means by said spool valve. 15. The istructure as reeited in claim 14 wherein said a@ctuating ineans and the 16st motion -onnection thereof with said valve sleeve comprises a rod engaging the rear 50 end of said spool valve -m-.mber and extendin.- in a direction rearwardly therefrom, a longitudinal sleeve e-@icompassing said rod, said rod and longitudinal s'@eeve being int-@rconnected for relative movement therebetween after a predetern@ ined force has been reached, the front end of 55 said sleeve being spaced lorigitudinally from the rear end of said valve sleeve whereby the front end of said longitudinal sleeve engages the valve sleeve to move the same and which valve sleeve in turn engages the rear of said pressure responsive member to -pove the same when said 60 longitlidinal sleeve is moved relative to said valve sleeve beyond the normal displacement reqiiired thereof for hydraulic actuation of said pressure responsive member. 16. A unit comprising: a housin.- providing an expansible cbamber therein, a fluid pressure responsive mem65 ber received in said chaniber, a valve assembly chaniiber conimunicated with said expansible chamber, said valve assembly incILiding two relatively movable valve menibers, said housing having inlet p,ort means and two outlet port means, passage means communicating sa-id inlet 4 o and outlet port @means to said valve members, said valve assembly being so constructed and arranged that in operating position of one of said valve members relative to the other of said valve members said inlet port means is communicated to said expansible chamber to provide 75 fluid flow thereto for moving said presstire res@Donsive

member a-@id when in normal position of said one vilve men,ber relative to sa;d other valve merriber comrwanicates sa:@d expansible chamber and i)rcss-are responsive rr.ember to one of the otitict port means and commur-.icates said inlet port means with the other outlet port means, said other valve meniber havin.- means for orcratively en.- aging said pressure responsive member, movable means ,operatively connected to sa;d valve members for moving said otlier valve member when said one valve member has traveled a predetermined distance relative to said other valve member. 17. The structure as reci'Led in clair@i 16 wherein said movable means comprises actuating means operatively connected to sad one valve member for moving the same, said actuating means having a lost motion connection with said other valve - niemb.-r for moving the s,,ime and thereby said p.-essure responsive member. 18. A unit comprising: a hotising prov:@ding a variab'@e volum-- ebamber therein, a valve assembly charnber communicat-@d withsaid variable voltime ch-,tmber, said valve asscip-bly -1-ii-,Iuding two re'@-@ttively movable valve memloers, said hous:lng havin.- iiilet port means and tnvo o-,itlet port nieans, passa.-c m--ans co@- nmunicatiii- said inlet and outlet port means to -said valv.- members, sa-ld valve assembly be,ng so co-@istructed and arranged that in operating POs, @ 'tion of on-. of said valve memb-,rs relative to the other of s,,i@'d valve members said inlet port means is communicated to sa;d varitble voli-ime chan-iber and when in norm-,il pcsitiln ol' said one valve member relative to said other valve iiicirber co.,iimunicates said var;able vol@,ime ch,imber to one of the outlet port mcans and communicates said inlet port means with the other outlet poi-t m-,ans, movable means op@-ratively co@-inected to sa-.d valve men-@oers for moving said other valve member when sa;d or@e valve meni@ber has traveled a predeerinii,@-d d:lstance relative to siid other valve member. 19. A unit comprisin-: a housing providiiig a variabie volume chamber therein, a valve assembly chainb-,r communicated with said variable volume chamber, said valve assembly includ;ng two relatively movable valve members said housin.@ havi-.ig inlet port means and two outlel Port means, passage means conimuiiicating said inlet and outlet pc)@-t means to said valve rf@embers, said valve assenibiy being so constriieted and arran@ed that in operatin- position of ore of said valve members relative to th-- other of said valve irembers said inlet poit means is communicated to said v-,triable volume chamber and when in norr@ial position of sa:ld one valve member relatine to said other valve member communicates said variable volume 3,173,339 12 chan-iber to one of the outlet port means and communicates said i-iilet por, nicans with tli-. other outlet port means, actuatiig means for moving said one valve member from normal to operating position, movable means operatively connected to said valve members for moving s,,iid other valve memb.-r when said one valve mem-ber has travel@ed 4a predeterinined distaice relative to said other valve merr@ber. 20. A udill comprisin.-: a housing havinf,@ fluid -inlet port 10 rileans and fluid outlet port means, said housing havi@-@g a valve assembly cbainber thercin conimunicated ivith a variable volume fluid c'@ian-iber, said valve assembly comprisin- two relatively movable valve members slidlbly iiiounted in said valve ,issembly chamber, p,,issa-e mea@-is 15 communicatino, said valve assembly wiih said inlet and outlet po.,t means, s'lop means operatively cor@nected to sa;d housin.- constructed for en.-agement by one of said valve meiiibers,. means tirging said one valve member i@ito enga,,ement with said !stop means, said valve assembly 20 bc,n.- so arraiig-,d and constru-.ted that when the Gther of said valve members is in actuatin.- position relative to said ope valve ri,-mb@-r fluid flow from said inlet port nieii-is will be conitnunicated to said var@iable volume cbamber aid when L-i normal position of said other valve 25 me@liber relative to said on-, valve member fluid flo7,v communic,-ttio-i from sa@d inlet nort means to said variable volume flliid c@liamber is cut off ind said variab!e vollime claniber ;s coinmuii--ated witli-said outlet port means, actuatin.@ means for moving said other valve member from 30 iiormal to actuating position, rilovable Tneans operatively connected to said valve meir@bers for movin.- said one valve m-,mber vvben said other valve memb-,r has traveled a predeterrpined dista-@ice relative to said one valve meml,)er. 35 21. The structure as recitcd in claim 18 wherein said niovabl,- m-,ans comprises acttiating means operatively connected to said one valve member for movi-@i.- the same, said ac,uatin,@ means hav;ng a lost motion connection v,,itli siid other valve memb-,r for mechanically moving 4( sai-i oticr valve meri-lber when said one valve memb,-r has traveled a predetern-i@ned distance relative to said other valve r@iember. References Cited in the file.of this patent 45 UNITED STATES PATENTS 2,331,238 Schnell ---------------- Oct. 5, 1943 2,360,578 Porter ----------------- Oct. 17, 1944 2,517,005 MacDuff -------------- Aug. 1, 1950 31101,032 Randol ---------------- Aug. 20, 1963

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,173,339 March 16., 1965 Lester J. Larsen et al. It is hereby certified that error appears in tl@e abo-7e numbered patent re@quiring correction and that the said Lettei-s Patent shoald read as corre--ted belod. Column 8,, li@ne 27,, for "portion" read -- position column 10, lines 10, 16 and 2S for the claim reference numeral 1110111, each occurrence., read -- 8 Signed and sealed this 14th day of September 1965. .SEAL) A.ttest: ERNEST W. SWIDER EDWARD J. BRENNER @ttesting Officer Commissioner of Patents

Uni'ted States Patent Office 3@173,339 3,173,339 POWER CONTROL VALVE Lester J. Larsen and Eugene M. Roganson, both of St. Joseph, Mich., assignors to The Bendix Corporation, St. Joseph, Mich., a corporation of Delaware Confintiation of application Ser. No. 777,242, Dec. 1, 1958. This application Sept. 28, 1961, Ser. No. 141,463 21 Claims. (Cl. 91-391) The present invention relates to fluid pressure servomotors of the type which can be actuated manually when no pressure fluid is available to actuate the same; and more particularly to a fluid pressure servomotor of the above described type wherein no follow-up of the servomotor's control member is exper;enced - ,vhen pressure fluid is available to actuate the unit, but which automatically provides follow-up when the unit is actuated manually. The present application is a continuation of U.S. application Serial No. 777,242 filed December 1, 1958, now abandoned. An object of the present invention is the provision of a new and improved fluid pressure servomotor which is caused to operate in the above stated manner by reason of a novel and uiique arrangement of its parts. A further object of the present invention is the provision of a new and improved servomotor of the above described typ-- which is simple in design, rugged in its construction, and inexpensive to be manufactured on a mass production basis. A still further object of the present inventioii is the provision of a new and improved arrangement for a ffuid pressure motor of the above described type comprising: a power piston, a valve sleeve spaced a-ially of said power piston, a slide valve in said sleeve for controlling the pressure between the ends of said valve sleeve and spool and said power piston to bias the same away from said power piston, stop limits limiting movement of said sleeve away from said power piston, and valve actuating means including a rod for actuating said slide valve, a second sleeve adapted to abut said valve sleeve and normally spaced a sufficient distance therefrom to accommodate valve actuating movement, and a spring positioned between said rod and said second sleeve which limits the valve actuating force that can be applied to said valve slide before the second sleeve abuts said valve sleeve. The inveiition resides in certain constructions, and combinations, and arrangements of parts; and further objects and advantages of the invention will become apparent to those skilled in the art to vvhich the invention relates from the following description of the preferred embodiment described with reference to the accompanying drawing forming a part of this specification, and in which: FIGURE I is a cross sectional view of a fluid pressure servomotor embodying principles of the present invention; and FIGURE 2 is a fra.-mentary cross sectional view of a portion of the unit shown in FIGURE 1. The fltiid pressure servomotor shown in @the drawing is what rnight be called a power operated master cylinder of a type which is power actuated by means of hydraulic pressure fluid. Although the servomotor unit will have other uses, it is b.-lieved to have particular advantages when used to actuate the hydraulic braking system of aii automotive vehicle. The servomotor unit shown in the drawing generally comprises a fluid pressurizing chamber or a master cylinder A from which fluid is displaced by means of a driven movable wall or piston member B, and an axially aligned control valve section C which controls the hydraulic fluid pressure that is supplied to the piston member B when fli-iid pressure is available, and which automatically drives the piston member B by the n-ianually Patented Mar. 16, 1965 2 applied control force when fluid pressure is not available to actuate the piston member B. The fluid pressurizing chamber A shown in the drawing is formed by means of a master cylinder housing section 10 that is cast with an internal fluid pressurizing chamber 12 therein. The master cylinder housing section 10 is bolted to a servomotor housing section 14 containing the power piston B, and one end of the power piston B projects into the fluid pressurizing chamber 12 to dis10 place fluid therefrom through an outlet opening 16 in the opposite end of the housing section 10. A suitable seal 18 is provided between the piston B and the housing section 10, and a suitable residual pressure check valve structure 20 is provided in a counterbored section of 15 the outlet opening 16 in order to hold a slight positive pressure upon the system actuated by the servomotor units. The residual pressure check valve structure 20 shown in the drawing is of the type shown and described in the Goepfrich Reissue Patent No. 24,664, and for details of 20 its construction and operation, reference may be had to that patent. Suffice it to say that the check valve structure 20 is formed by a dished plate 24 having a membrane 26 tensiolied over its outer surface. Suitable offset openings are provided in the plate 24 and membrane 26 25 so that the openings in the plate will normally be covered by the membrane and such that when fluid is displaced from the chamber 12, the membrane is moved away from the openings in the plate to pass out through the central opening in the membrane 26. The residual pressure check 30 valve structure 20 is normally biased into sealing engagement with the shoulder 28 formed by the counterbored section 22 by means of a coil spring 30 interpositioned between the check valve structure 20 and the end of the piston member B to hold pressure upon the driven sys35 tem. When th@- pressure in the chamber 12 drops below the pressure in the driven system by a generaby predetermined amount, coil spring 30 yields to permit the check valve structure 20 to move away from the shoulder 28 and thereby permit return flow into the chamber 12 40 around the outer periphery of the check valve structure 20. The piston member B is normally urged into its normal retracted position shown in the drawing by means of an additional coil spring 32 that is compressed between the end of the piston me@nber B and the opposite end of the fluid pressurizing chamber 12. A conventional 45 bleed screw arrangement 34 is provided in the housing section 10 to remove all air from the pressurizing chamber 12. As previously indicated, the piston member B is normally adapted to be actuated by means of hydraulic fluid 50 pressure, and accordingly the head end 36 of the piston member that is carried in the servomotor housing section 14 is provided with a cast iron piston ring 42 positioned in a piston ring groove 44 to effect a suitable seal with respect to the cylinder walls of the power chamber 38. 55 Hydraulic pressure is admitted and exhausted from the power chamber 38 by means of the control valve section C which will now be described. The control valve section C is formed within a bore 46 in the servomotor housing 14, which bore is axially 60 aligned with, and opens into, the power chamber 38. The control valve structure is generaly of the slide valve type; and is formed by means of a valve sleeve 48 slidingly received within the bore 46, and a valve spool 50 that is slidingly received within the longitudinal opening 52 65 through the valve sleeve 48. The servomotor unit shown in the drawing is specifically designed to be placed in hydraulic series circuit with an open center power steering unit so that fluid flow from a continually driven pump will be received by the servo70 motor unit and passed on to the power steering unit without there being created any appreciable back pressure in

either the fluid pressure servomotor unit shown in the drawing, or in the power steering unit. Accordin,-Iy the control valve str@icture C is provided with a@i exhaust connettion 54 that communicates with an exhaust groove 56 in the longitudinal opening 52, a pressure connection (not shown) that continually commuiicates with an ie@et groove 58 in the longitudinal opening 52, and a flow through connection (not shown) that is continually in coinmunication with a flow through recess 60 in the longitudinal opening 52. The valve sleeve 48 is adapted to be moved longitudinally of its receiving bore 46 as will later be explained; and in order that the exhaust, and inlet, conn6etions will continually communicate with their respective recesses,- lon,@itudinal grooves 62 (oiily on-, of vvhich is shown) are spaced around the val-,,e slceve in an appropriate inanner to continually communica,e the respe--'Live connections with their respective grooves during longitudinal movement of the valve sleeve 438 in the bore 46. In order that the longitudinal gtooves will b-. held in ali.-nment with the respective connections, an additional Ibngitudinal groove 64 is provided in the bore 46 in a manner to receive a portion of a -.1-lide ball 66 that projects out bf an opening 68 in the hotising section 40, and which ball 66 is held in place by another ball 70 tnat is pressed into opening 68 to effect a seal the@-efor. The valve spool 50 is provided with saitable land portions 72 and 74 that are spaced apart by a recess 76 having a width which is less than the spacin.- between tlle recesses 56 @nd 58 in the longitudinal opening 52 of th-. valve sleeve 43. In the normal position of the valve spool 50, shown in the drawing, land portion 72 uncovers th,-@ exhaust groove 56 by an amount which is less than the overlap between the land portion 74 and the inlet recess 56, which land 74 is of such a width as to provide ai underlap with respect to the land portion 78 in the longitudinal opening 52 that separates its inlet recess 58 and i's flow through recess 60. The recess 76 of the spool 59 is communicated to the face of the pis' on B i-@l the power chamber 38 by means of a transverse drilling '00 and a longitl,.dinal drilling 82 in the valve spool 50. In the position shown in the drawing, therefore, the exbaiist groove 56 will be communicated wilh the head of the piston member B while the inlet -.roove 58 is communicated to the flow throu.-h groove 60. Inasmuch as the inner edge of the land portion 74 of the valve spool 50 provides an underlap with respect to the sidewall portion 78 of the longitudinal opening 52 between grooves 58 and 60, ivhich und@rlap is greater in aniount than its overlap with respect to the sidewall portion of opening 52 betvi,-en grooves 56 and'53, vihich overlap in tum is greater than the underlap of the land portion 72 with respect to the exhaust groove 56, adtuatin.- movement of the valve spool 50 towards the ponver piston B will effect a sequential operation wherein the exhaust groove 56 is first closed off with respect to the control recess 76, the control recess is th-,reafter opened with respect to the inlet groove 58, and the inlet groove 58 is thereafter closed with respect to the flow through groove 60. At any time, therefore, that the power @teering unit that is connected to the flow through groove 60 is being actuated to provide a back pressure, the valve spool 50 need only be longitudinally moved suffici6ntly to close off exb@aust groove 56 and open the control recess 76 to the inlet groove 58 to supply the back pressure created by the power steering unit against the face of the power piston B, and thereby power actuate the servomotor unit. If the power steering unit that is connected to the flow through groove 60 is not being actuated, contihued movement of the valve spool 50 toward tile power piston B decreases the space b.-tween the land portion 74 with the sidewall portion 78 to create a back pressure in inlet groove 58 to thereby supply actuatina. pressure to the control recess 76 and hence to the face of the power piston B to power aettiate the servonlotor unit. In order that sudden sur.-cs of fluid pressure will not be applied directly tQ the, face of the power. piston B, 3,173,339 4 a cbeck valve and orifice arran-ement 84 is provided in the longitudinal opening 52 of the valve spool 50 between the end of the valve spool 50 and the power piston B. The check valve and orifice arrangement 84 is formed by means of an automatic screw machine made part 86 thit is received in a counterbore 8'0 and is held in place by snap rin- 90. Pressure flow from the valve spool 52 to the face of the power piston B is controlled by a longitudinal orifice bore 92; and @'n order that fluid can be con10 ducted quickly away from the face of the power piston B, a longitudinal opening 94 thit is counterbored to provid,a valve seat facing the valve spool 50 for a ball valve 96 is also providcd in the part $6. The ball valve 96 is held in place by means of a welch plug 93 having suitable 15 openings therethrou.-h and which is pressed in the counterbore of the opening 94. A suitable seal 100 is provided between the land portion 72 and the outer end of the valve sleeve 48 and a coil spring 102 is positioned between the inner end of the valve 20 spool 50 and the part 86 to help to bias the valve spool 50 to its normal nosition shown in the drawing. Actuation of the valve si-)ool 50 is had by means of a yieldable control link D that ab,,its the end of the valve spool 50 ar,.d projects outwardly of the housing of the 25 servomotor unit. The yieldable control link comprises an actuating pin or rod 104 having a ball end 106 which abuts the end of ,he valve spool 50 and which is held within the longitudinal openin.- 52 of the valve sleeve 48 by means of wire snap rin- 108. The outer end of the rod 30 104 is received within one end of an aetuating slccve 110, and a threaded plug 112 is screwed into the outer end of the actuating sleev-, 110 for the rec--ption of linkage that is cor@nected to the brake pedal lever of the vehicle. From the above description of the control valve structure 35 C, it will be apparent that the hydraulic pressure which is supplied to actuate the power piston B also supplies a reactive force upon the inner end of the valve spool 50 tendin,@ to move it to its nornial or released position shown in the -drawing. In order that the maximum hydra-tilic 40 pressure which can be applied to the power piston B will be limited to a predel@ermined val,,ic, a compression spring 114 is interpositioned between the actuatin- sleeve 110 and the actuating rod 104 to li-ii-iit the force whicii the operator can supply to the valve spool 50 and in turn 45 thereby limit the maximum hydraulic pressure wlil:ch can be delivered against the power piston B. Conpressioii spring 114 also serves the purpose during power actlicition of permitting the spool 50 to shift back and forth slightly w;thout transferring objectionable movement to th-. foot '50 of the operator. A suitable shoulder 116 is providcd ori the rod 104 adjacent the ball end 106, and the annular washer 118 is biased tliereagainst by one end of the coil spring 1IL4. The other end of the coil spring 114 is positioned against a sii-nilar annular wash-,r 120 which in tu-n 55 is abutted by the threaded plug 112. The rod 104 is prevented from being withdrawn from the sleeve 110 by means of a snap ring 122 which abuts the washer 120, and by a similar snap ring 124 which abi,-ts the washer 120, and by a similar snap ring 124 which prevents the actuat60 ing sleeve 110 from being withdrawn past the inner annular wasiler 118. in the normal condition of the servomotor unit shown in the drawing, pressure froni a liydraulic pump is admitted to the groove 58 in the valve sleeve 48 and thence 65 passes directly to the flow through groove 60 to an opencenter hydraulic ste,-ring unit without producing any appreciable pressure drop across the control valve structure C. Actuation of the Lnit is had by depressing a foot pedal lever, not shown, to move the yieldable co-@itrol link D inwaxdly causin@ force to be transmitted 70 throu.-h the compressicii si)ring 114 to the actuating rod 104 to thereby produce iwvard movemert of the valve spool 50 with respect to the valve sleeve 43. As previously hidicated the control recess 76 is coritini-ially in 75 communication with the face of th-- ioower piston B

5 through drilli-iigs 80 ,ind 82, and the initial movement of valve spool 50 closes off the exhaList groove 56 from the control recess 76 and thereafter opens the control recess 76 to the inlet groove 58 of the valve to communicate the inlet groove 53 to the face of the power piston B. As previously indicated, the land 74 is of such an axial len.-th that it will remain slightly open with respect to the land 78 of the valve sleeve 48 when its other end just becomes underlapped with respect to the inlet groove 58, so that if back pressure is bein.- produced in the flow through groove 60 by a power steering unit, this pressure will be immediately communicated to the control recess 76 and hence to the power piston B when the land 74 becomes underlai)ped with respect to the groove 58. If back pressure is not being produced in the flow through groove 60, continued inward movement of the vilve spool 50 with respect to th.- valve sleeve 48 causes the space between the land 74 and the sidewall portion 78 to decrease and thereby restrict flow through the valve to create a back pressure in the inlet groove 58, which then is transmitted ,hi-ough th-e control recess 76 and drillings 80 and 82 to the top face of the po-v@,er piston B. As previously indicated, the control drilling 82 opens into the end of the valve spool 59 such that the control pressure produces a reactio@n against the valve sPOOl which reaction pressure will be transmitted back through the rod 104 and actuating sleeve 110 to apprise the operator of the amount of presslire which is being delivered to the power piston B. It has f-arther been indicated that the control pressure passing through the control drilling 82 must flow through an orifice drilling 92 in the check valve and orifice arrangei-nent 34 so that a rapid build-up in pressure against the power piston B wiR not be produced. An increase in pressure upon the ponver piston B ca,,ises it to be forced inwardly into the fli,id pressurizing charnber A, thereby compressing springs 30 and 32, and displacing flu:ld out thiough the residual pressure check valve structure 20 t(y the braking system which the unit operates. A safety feature is provided in the unit by incorporation of the compression spring 114 which limits the amount of valve actv-ating force that can be transmitted to th@- valve spool 50, such that after a predetermined amount of valve actuat-in,- force has been transmitted to the valve spool 50, the coil sprirg 114 will yield under the i-eactio-@l pressure, previously described, that is produced upon t,@e valve spool 50. Yielding of the compression spring 114 wiR i3ermit the valve spool 50 to move towards its released condition under the reaction pressures to cause the land 74 to close oiT the control recess 76 Nvith respect to the inlet gro@ove 58, and thereafter bleed sufficient control pressure out tirough tile exhaust groove 56 to maintain a pressure against the power piston B which corresponds to tiie maximum thrust that can be transmitted thorugh the coil spriiig 114. The maximum force that can be transrlitted through the conpression spring 114 is in tum limited by the force that is required to corrpress the spring 114 sufficiently to accomplish the above referred to valve movement, @,vhen the end of the actuating sleeve 110 has been moved into engagement with the valve sleeve 48. A retraction of the yieldable control link D will, of course, pernu 't the land 74 to become underlapped with respect to the sidewall portio,@i 73. If no back pressure is b.-ing supplied against the flow through groave 60 by the downstream power steering unit, this underlap will bleed pressure from the inlet groove 50 and hence the control recess 76, inasmuch as the land 74 is underlapped with respect to the outer edge of the groove 58 at this time, and the pressure against the power piston B is thereby reduced. If back pressure is being held against the ,-ro@ove 60, it will be necessary to further retract the yieldable control link D to p--rmit the land 74 to become lapped with resinect to tbe outer end of the inlet groove 58 before a reduc@ion of pressure can be experienced w@thin 3,173,339 6 the control recess 76. It will be understood that during pow-@r operation of the unit, control pressure upon the inner end of the valve sleeve 48 holds it stationary into abutment with the wire snap ring 126 so that the only travel 'Lhat is required of the yieldable control link D is that necessary to stroke the valve spool 50 with respect to the stationary valve sleeve 48. A r-omplete release of pressure upon the yieldable control link D will, of course, permit the val-,@e land 72 to become underlapped I 0 with t@le exhaust groove 56, the ball valve 96 to move off of its seat in the part 86, and fluid to rapidly flow from the power chamber 38 through drillings 80 and 82, recess 76 and the exhaust groove 56. During an emergency when hydraulic pressure does 15 not exist to power operate the unit, the unit can be or)erated @nalijally by forcing the yieldable control link 6 into the servomotor unit 1'n tle same maniier previously described for its power actuation. Since now no pressure will exist against the end of the valve spool 50, 20 the valve spool 50 will be moved inwardly easily against th-@ slight amount of force exerted by the coil spripg 102 to perniit the inner end ol' the actuating sleeve 110 to abut th-- outer end -of the valve sle@ve, 48. Thereafter continued in-@vard movement of the actuating sleeve 110 25 causes tne valve sleeve 48 to be moved inwardly against the face of the power piston B, to therea-fter mechanically force the uower piston B into the fluid pressulizing chamber 12 to cause fluid to be displaced therefrom in the same manner as described above for the ur@it's power 3o operation. in order that a vacuum will not be created withiii the power chamber 38 during manu@-d actualion of the power r)iston B, communication of the po-wer charpber 38 is h@d with tle exiiaust con-iiection 54 through a siitable check valve structure 128. The check valve 35 structure 128 shown in the drawing is 'Lormed by means of a boring that is counterbored to provide a valve seit against which a ball valve 132 abuts to prevent pressure flow out of the chamber 33 during t@he power operation. DLring manuil actuation, the ball valve 132 is easily 40 lifted off its seat by flow from exhaust connection 54 i@ito the power chamber 38, and the ball valve 132 is retained w;thin its counterbore by means of a welch plug 134 havin.- suitable openings theretlrough. The portion of the po-,ver chamber 33 forwardly of the piston head 36 45 is also cornmunicated to the exhaust connection 54 through suitable drillings in the housi.-ig section 40. In ord-,r to compensate for any leakage which m6y occur in the hydraulic system to which the outlet 16 is communicated, a suitable drilling 136 is provided between 5o the froiit and back faces of the power piston B to permit fluid flow from th-- power chamber 38 to the fluid pressurizing chamber 12 durin- the released condition of the servomotor un;t. Control of flow throug'@i the drilling 136 is had by meails of a check valve structure 138 in 55 the passage 136. The end of the passage 136 adjacent tl-ie valve spool 50 is counterbored to provide a shoulder 140 against which an annular valve seat member 1-42 is held by an agnular men-iber 144 which is simultaneously defornied nto a groove 146 ;.I the sidewalls of the counter60 bored section, and deformed against the valve seat member 142 to hold it in seali-iig enga.- ement with the shoulder 140. A suitable opening 148 is provided through the valve seat member 142, and the inner end of the openin@ 148 is chamfered to provide a valve seat 150 against which 65 a ball valve 152 abuts to pr@-vent flow from the cliamber 12 to the chamber 38 during actuation of the unit. In order that the ball valve 152 will be held out of engagement w,.th its seat 150 during the released condition of the servomotor Linit, a stem 154 is resistance welded 70 to the ball 152 and extends throtigh the opening 148 to abtit the end of the chamber 38 and hold the ball valve 152 off of ifs seat when the povver piston B is in its normal released condition adjacent the valve spool 50. Actuatior. of the unit, of course, either manually or with 75 power, causes the piston B to move awry from the end

3,173,339 7 of the power chaniber 38, ar,.d thereby permits tl-ie ball valve 152 to be forced against its seat 150 by reason of the greater hydraulic pressure that is prodliced in the fluid pressurizin@ chamber 12 than is produced in the power chamber 38. While the invention has been described in considerable detail, I do not wish to be limited to the exact construction shown and described, and it is our intention to cover hereby all novel adaptations, modifications and arrang.--ments thereof which come within the practice of those skilled in the art to which th-- invent;on rela'Les. We