Vacuum-power brake booster

Claim 2

For use as a brake booster, a vacuum-operated servomotor comprising structure defining a fluid chamber enclosure characterized by two separable cup-shaped members having spaced end walls with coaxial central openings, respectively, a source of presSure different from atmosphere, a source of atmospheric pressure, power-piston assembly including a coaxial cylindrically walled valve housing movable as a unit between said end walls from normal position in a pressure-applying direction under a pressure differential at opposite sides of said assembly, the latter serving to divide said chamber enclosure into a constant pressure chamber in continuous communication with said different source of pressure and a variable pressure chamber selectively communicable with said constant pressure chamber and said source of atmospheric pressure, a servo-motor output element, and a pedal-operated input element coaxially related to said output element: a follow-up control valve device characterized by an outer and an inner poppet-type fluid-controlling valve element in telescopic concentric relationship; a pair of axially-spaced annular valve faces defines opposite ends, respectively, of said inner valve element; an annular valve seat on said outer valve element normally in engagement with one of said valve faces to produce a closed ''''air-valve''''; an annular valve seat on said valve housing normally spaced from the other valve face to produce an open ''''vacuum-valve''''; a normally compressed spring operably effective between said valve elements to bias them apart to close said ''''air-valve,'''' said outer valve element being subsequently movable relatively to said inner valve element to engage said other valve face with the valve seat on said valve housing and disengage the valve seat aforesaid on said outer valve element from whereby said ''''vacuum-valve'''' is closed and the ''''air-valve'''' opened, respectively, corresponding to ''''applied'''' position of the control valve device to create said pressure differential across opposite sides of said piston assembly to move the same in said pressure-applying direction; fluid passage means incorporated in said piston assembly between said constant and variable pressure chambers under control of said ''''vacuum-valve normally open to balance pressures within said chambers; another fluid passage means incorporated in said outer valve element between said one valve face and a portion of said first-defined fluid passage means under control of said ''''air-valve'''' normally closed to block ingress of atmospheric pressure into said variable pressure chamber ; multilever force and reaction-transmitting mechanism adapted to mechanically connect said output element, said outer valve element and a thrust surface on said valve housing, the levers of said reaction mechanism being normally disposed normal to the axis of said output element to inhibit transmission of reaction from the latter to said input element; a variable work-load (resistance) initially produced in response to movement of said output element in said pressure-applying direction solely under manual operation of said pedal-operated input element effective to move said pair of valve elements as a unit short of ''''applied'''' position, such resistance upon reaching a predetermined magnitude being effective to substantially arrest movement of said output element and thereby conditioning said pair of valve elements for relative movement to said ''''applied'''' position and movement of said reaction mechanism to position its levers at an angle to the axis aforesaid of said output element effective to transmit reaction from the latter, under additional manual force exerted on said pedal-operated input element; a tubular extension coaxially connected to said outer valve element and operably projects through the opening in the end wall aforesaid of the cup-shaped member enclosing said variable pressure chamber, to the exterior thereof; mechanical means adapted to interconnect said tubular extension with said pedal-operated input element for actuation as a unit by the latter; and means for sealing and slidably supporting said tubular extension with respect to said lastdefined opening, the interior of said tubular extension cOntinuously communicates atmospheric pressure to said ''''airvalve.''''

Claim 3

The servomotor as claimed in claim 1 in which said fluid chamber enclosure comprises structure defining: a booster power-cylinder in which each of said cup-shaped members defines a metallic shell, said shells being of different depths with marginal portions of their respective confronting open ends characterized by a plurality of alternately interengaging segments, each of the latter having a terminal outstanding flange; an annular channel produced by said flanges around the exterior of the interengaging segments aforesaid; an auxiliary cup-shaped shell having an end wall and a peripheral flange normal thereto with an annular groove formed therein, said last-defined end wall being disposed contiguously with respect to the end wall of said shell of lesser depth and said last-defined flange being disposed in circular alignment with and in radially spaced relation with respect to the interior of said interengaging segments, to produce an annular space therebetween; means including a split-type metallic clamping ring adapted to interfit said annular channel between said flanges for radially impinging the interengaging segments aforesaid in cylindrical alignment; and means for attaching the end walls of said shell of lesser depth and said auxiliary shell, respectively, in a rigid unitary assembly.

Claim 4

The servomotor as claimed in claim 2 in which said clamping ring includes structure defining a pair of hollow axially aligned bosses with their respective confronting ends producing the split in said ring; and a fastening element projecting through said bosses to effect clamping pressure on said ring around the interengaging segments of said metallic shells.

Claim 5

The servomotor as claimed in claim 1 in which said piston assembly comprises structure defining : a cup-shaped member characterized by a wall having a central opening and a peripheral flange normal to the latter wall; an annular ported closure plate for said opening provided with a central opening, and an annular inturned flange defining the outer periphery of the latter opening which is offset from the confronting face portion on said last-defined wall to produce an annular entrance to an annular channel of similar configuration; a flexible power-diaphragm of annular configuration supported on said last-defined wall by means of an annular bead defining the inner periphery of said diaphragm in compressive engagement in the last-defined annular channel aforesaid under said last-defined peripheral flange and thereby effecting an airtight seal therebetween with its normal wall thickness radially extending outwardly through said entrance to encompass the exterior of said last-defined wall; a pair of radially spaced circularly aligned inner and outer looped segments defining the outer peripheral margin of said diaphragm; an annular bead defining the inner intermediate portion of said outer segment and adapted to engage the annular groove aforesaid formed in said peripheral flange of said auxiliary shell with said outer looped segment positioned in the annular space aforesaid between said peripheral flange and inner surface on said interengaging segments of said pair of metallic shells, whereby said outer looped segment is confined airtight within said last-defined annular space under compression effected by said clamping ring; and a normally compressed spring is operably disposed in said shell of greater depth to react between a stationary portion on said last-defined shell and the valve housing aforesaid to continuously bias said piston assembly toward normal released position.

Claim 6

The servomotor as claimed in claim 4 in which the valve housing aforesaid is of cylindrically-walled configuration comprising structure defining a wall closing said one end thereof and its other open end being defined by an annular outstanding flange having a peripheral offset producing an annular shoulder which projects through the central opening in the wall oF said last-defined cup-shaped member; a plurality of circumferentially spaced holes in said peripheral offset; matching patterns of holes in the outer and inner peripheral margins of the aforesaid xlosure plate and power-diaphragm, respectively; a like-plurality of fasteners projecting through said plurality and patterns of hokes to produce a rigid airtight unitary assembly of said valve housing, last-defined cup-shaped member, inner annular bead on said power-diaphragm, and the closure plate aforesaid, said valve housing and closure plate being disposed in coaxial relationship to produce a ''''valve-cage''''; a plurality of radially disposed circumferentially spaced cylindrical chambers formed in the end wall of said valve housing; a central opening through the end wall of said valve housing; and an annular thrust-transmitting surface coaxially disposed on the exterior of the end wall of said valve housing and through which the last-defined central opening passes.

Claim 7

The servomotor as claimed in claim 5 in which each of said cylindrical chambers is adapted to carry a complemental resilient element, and each of said seal-containing chamber is formed with a closed end and an open end with a hole through the closed end coaxially positioned with respect to a hole defining an annular configuration of said sealing element; and means for stabilizing each sealing element in its associated chamber.

Claim 8

The servomotor as claimed in claim 5 in which said outer fluid-controlling valve element comprises structure defining : an elongated cylindrical valve sleeve having an annular outstanding flange at one end and radially spaced from the interior of the cylindrical wall of said valve housing to produce an annular air-vacuum chamber therebetween; a normally compressed spring encircling said valve sleeve is operably disposed in said air-vacuum chamber to react between said sleeve flange and confronting face portion on the closed end of said valve housing whereby said valve sleeve is biased toward normal ''''unapplied'''' position wherein said sleeve flange abuts the confronting face portion on the inturned flange of said closure plate; a threaded counterbore is provided in the sleeve flange; an annular wall projects radially inwardly from an intermediate portion of said valve sleeve, and is adapted to provide on one side the first-defined valve seat; an axial bore passes through said last-defined wall; an annular spring chamber defines the the other side of said last-defined wall, said spring chamber being adapted to contain the first-defined spring; said inner fluid-controlling valve element comprising structure defining: another elongated cylindrical valve sleeve slidably disposed in the latter axial bore in airtight sealed relationship therewith; an outstanding flange defines one end of said inner valve sleeve; a peripheral resilient element defines the one valve face carried by said last-defined flange, adapted to normally engage said last-defined valve seat to produce said ''''air-valve'''' in closed condition, the other end of said inner valve sleeve is provided with a reduced diameter threaded portion terminating in an annular shoulder which threadingly receives an annular collar in engagement therewith; an annular flange radially outstands from the engaging end of said collar and is provided with a peripheral offset for reception of a complemental resilient element defining the other valve face normally spaced from the valve seat aforesaid on the closed end of said valve housing to produce said ''''vacuum-valve'''' in open condition; an annular cavity formed coaxially in the interior of the closed end of said valve housing, said other end of said inner valve sleeve being normally spaced from the bottom of said cavity;.

Claim 9

The servomotor as claimed in claim 7 in which the first-defined fluid passage means aforesaid include structure defining a plurality of vacuum passages through the end wall of said valve housing, the cavity aforesaid in the latter, the annular air-Vacuum chamber aforesaid and the ports in the closure plate aforesaid which place the said constant and variable pressure chambers on opposite sides, respectively, of said piston assembly in communication with each other when said ''''vacuum-valve'''' is open and said ''''air-valve'''' closed to produce equivalent pressures therein; said other fluid passage means including structure defining a plurality of intersecting passages embodied in the intermediate wall aforesaid of the outer valve sleeve, said air-vacuum chamber and ports in said closure plate aforesaid to admit atmospheric pressure into said variable pressure chamber to create said pressure differential across opposite sides of said piston assembly to move the same in said pressure-applying direction when said ''''vacuum-valve'''' is closed to isolate said constant and variable pressure chambers and said ''''air-valve'''' open to admit said atmospheric pressure continuously present as a source within the tubular extension aforesaid having an outstanding annular flange at its forward end provided with a cylindrical threaded portion adapted to engage the threaded counterbore aforesaid in said outer valve sleeve to produce a coaxial unitary assembly thereof; and an air chamber adjacent said ''''air-valve'''' in continuous communication therewith and said source of atmospheric pressure.

Claim 10

The servomotor as claimed in claim 7 in which said annular valve seats on the closed end of said valve housing and the intermediate wall aforesaid of said outer valve sleeve, respectively, each comprises structure defining : an annular groove fitted with a complemental resilient element, and their respective cooperative annular valve faces carried by the inner valve sleeve aforesaid are devoid of resiliency.

Claim 11

The servomotor as claimed in claim 7 in which said valve spring in said spring chamber comprises structure defining : a pair of Belleville (dished) spring washers in face-to-face relationship and normally under a predetermined tension.

Claim 12

The servomotor as claimed in claim 7 in which said valve spring in said spring chamber comprises structure defining : a conical-type helical spring normally under a predetermined tension.

Claim 13

The servomotor as claimed in claim 7 in which said multi-lever force and reaction-transmitting mechanism comprises structure defining ; an annular cup-shaped reaction member having a bottom wall formed with a central hole and a peripheral flange normal thereto; an annular shoulder defining the periphery of said thrust-applying surface on the end wall of said valve housing, and adapted to project through the last-defined hole to slidably support said reaction member thereon ; four equally-spaced cutouts in said last-defined flange with a like-plurality of pressure flanges projecting into said cutouts, respectively, from the periphery of said annular bottom wallnormal to the last-defined peripheral flange ;a pressure-distributing member formed as a rectangular fulcrum plate defining a pair of spaced fulcrum edges, and provided with a pair of parallelly spaced flanges having terminal fulcrum edges, respectively, said fulcrum plate being coaxially seated on said output element to move as a unit therewith and axially spaced from the thrust-applying surface on the valve housing end wall; two pairs of radially disposed levers normally perpendicular to the axis of said output element with the inner end portions of one pair offset from the corresponding straight portions of the other pair of levers and provided with arcuate cutouts, respectively, adapted to straddle-mount substantially half of the diameter of the aforesaid output element; a centrally apertured thrust element movably carried by said output elements; fulcrum plate, inner end portions of said levers, said thrust element and said thrust-applying surface being arranged in series in that order in surface engagement to releasably stabilize said levers in said non-reaction transmitting position normal to the exis of said output Element due to lever-action being negated by such surface engagement of said levers, initial movement of said pedal-operated input element from normal position being effective to move said reaction mechanism with its levers in said normal position and said output element as a unit to effect slack take-up until the output element encounters a resistance of sufficient magnitude to arrest such unitary movement, said levers requiring movement concurrently with or prior to operative energization of the servomotor, to an angulated (tilted) position with respect to the axis aforesaid under the pedal-operated input element to convert such surface engagement of said levers into pressure line-contacts (fulcrums) for the lever inner extremes and intermediate points thereon enabling lever-action for transmission of proportional reaction from said output element to said input element during servo-assist; whereupon, additional manual force exerted on said input element is effective to move said reaction member and outer extremes of said levers relatively thereto to dispose the latter in said angulated disposition with respect to the axis aforesaid accompanied by additional spatial separation of said fulcrum plate and said thrust-applying surface on the exterior of the end wall of said valve housing causing the surface engagement aforesaid of said levers to be interrupted and simultaneous conversion of said fulcrum edges into line-contacts with intermediate points on said levers, and the inner extremes of each pair of levers in line-contact with said thrust element and surface, respectively, aforesaid, and thereby producing operative mechanical connections for three radially spaced points on each of said levers to rock to impart lever-action; a mechanical connection between said reaction member and said outer valve sleeve enabling unitary movement thereof; and a normally compressed spring continuously reacting between the end wall of the cup-shaped metallic shell of greater depth and said levers to bias them, said reaction member into contact with the closed end of said valve housing and connected outer valve sleeve toward ''''unapplied'''' position of said control valve device corresponding to ''''power-off'''' disposition of said piston assembly.

Claim 14

The servomotor as claimed in claim 12 in which an annular shoulder is provided on said output element by diminishing the normal diameter thereof for the distributing member plate to seat against, and projecting from said last-defined shoulder is a reduced integral extension which projects through a central hole in said distributing member plate, arcuate cutouts provided in the inner end portions of said reaction levers, coaxial holes through said annular thrust elements, respectively, and through the central opening aforesaid in the end wall of said valve housing, to slidably support the inner valve sleeve aforesaid.

Claim 15

The servomotor as claimed in claim 13 in which said mechanical connecting means comprises structure defining an elongated truncated thrust member defined by a hollow conical wall closed at one end and open at the other and adapted to project into said tubular extension with said last-defined closed end predeterminately spaced normally from the end of the reduced extension aforesaid on said output element to accommodate actuation of said control valve device toward ''''applied'''' position, and engageable with the end of said reduced extension to actuate said output element directly in the event of power-runout or malfunction otherwise of said servo-motor, the open end of said truncated member being defined by an annular outstanding flange adapted to abut the confronting rear end of said tubular extension whereby the latter and said truncated member are actuatable as a unit to control said control valve device toward ''''applied'''' and ''''unapplied'''' positions under the pedal-operated input element operably projecting into the hollow of said truncated member in engagement with the closed end thereof; and a port tHrough the wall of said truncated member for maintaining communication between said source of atmospheric pressure and the interior of said tubular extension.

Claim 16

The servomotor as claimed in claim 12 including a mechanical connection between said reaction member and the outer valve sleeve aforesaid comprising structure defining: a plurality of thrust pins operably projecting through the coaxial openings aforesaid in the closed ends of said seal chambers in the end wall of said valve housing and sealing elements in said cylindrical chambers aforesaid to engage the bottom wall of said movable reaction member to enable unitary movement of the latter and said last-defined valve sleeve.

Claim 17

The servomotor as claimed in claim 15 in which said thrust pins are shortened to introduce a predetermined lost-motion movement between said outer valve sleeve and said movable reaction member whereby the latter portion of movement of the latter valve sleeve is effective to move said reaction member as a unit, to place said reaction levers in said angulated (tilted) position effective to transmit reaction from said output element to said manual input element upon activation of said control valve device to ''''applied'''' position to operatively energize said servomotor.

Claim 18

The servomotor as claimed in claim 14 in which the aforesaid means for sealing and slidably supporting said tubular extension comprise structure defining: an elongated flexible tubular member having a pair of parallel overlapping cylindrical walls connected at one end to induce relative rolling-action therebetween and an open end defining a pair of annular beads, respectively, said tubular extension operably projects through said inner wall in contact therewith, an annular channel formed by a lip-flange defining the opening in said metallic shell of lesser depth, and an annular groove formed in the exterior surface of said tubular extension and adapted to receive said annular beads, respectively, under tension in airtight sealed relationship whereby the inner wall elongates according to movement of said tubular extension in an applying-direction of said control valve device, and the outer wall correspondingly shortens during such relative movement of the inner wall, the latter being in sealing engagement with the opening aforesaid in said metallic shell of lesser depth and at the same time accommodating sliding movement relative thereto thus enabling exclusion of foreign matter from the working parts of the servomotor and isolation of the variable pressure chamber in the matter from atmospheric pressure.

Claim 19

The servomotor as claimed in claim 17 including structure defining an annular air-filtering element composed of porus material and contained in a complemental embossment defining the closed rear end of a cylindrical casing adapted to receive the outer wall aforesaid in close adjacency with the forward end thereof in compressive overlying engagement with the outer surface of the annular bead defining the open end of said outer wall, and thereby stabilizing the open end of the latter in said annular channel formed by said lip-flange projecting from the opening of the metallic shell of lesser depth aforesaid, said manual input element being adapted to project through a central hole provided in said embossment into the hollow of said truncated member into engagement with the closed end of the latter to actuate said tubular extension and connected outer valve sleeve toward ''''applied'''' position of said control valve device under operator force applied to said pedal adapted to operate said input element.

Claim 20

The servomotor as claimed in claim 1 in which the work-load (resistance) aforesaid is produced by pressurization of fluid by a master brake cylinder adapted to actuate a vehicular brake system under a pressure differential effective on said piston assembly and operator force applied via the pedal aforesaid to said input element, jointly acting on said output element operatively connected to a piston slidably disposed in said master cylinder.

Claim 21

The servomotor as claimed in claim 12 in which each of the pair of parellelly spaced flanges associated with said distributing member, is provided with a pair of spaced extensions in the same plane therewith for reception of the inner end portions of one pair of diametrically-opposed reaction levers with their inner extremities contiguous to said output element, said last-defined flanges and pairs of extensions being effective in cooperation with the outer end portions of said reaction levers projecting through their respective cutouts aforesaid formed in the peripheral flange of said reaction member aforesaid, to stabilize said reaction levers in operating positions.

Claim 22

The servomotor as claimed in claim 12 in which the rectangular plate aforesaid of the distributing member, is provided with an additional pair of parallelly spaced flanges in spaced relation to the first-defined pair of flanges, with the space between each pair of flanges and the spaces between said pairs of flanges being adapted to receive the inner end portions, respectively, of said four reaction levers to stabilize the same in part in operating positions as a function of their inner extremities being contiguous to said output element, and wherein said offset pair of reaction levers is formed straight to lie in the same plane with the other pair of straight levers, the inner end surface portions thereof being contiguous to said rectangular plate and the thrust element engaging said thrust surface, to fully occupy the space normally obtaining between said rectangular plate and said last-defined thrust element, and a lever-retaining clip fast on each of said pressure flanges aforesaid is adapted to overlie the outer extremity of each of said levers to stabilize the same against fortuitous radially outward displacement.

Claim 23

The servomotor as claimed in claim 21 in which the pair of reaction levers which projects through the spaces, respectively, between the two pairs of flanges is substantially the same width as the diameter of said output element, and the inner end portions thereof project between spaced overextending end portions of the other pair of reaction levers which is wider than the diameter of said output element, whereby the inner extremities of all four reaction levers cluster around said output element in contiguous relationship thereto.

Claim 24

For use as a brake booster, a pressure differential operated servomotor comprising structure defining: a housing having an apertured end wall, a wall movable in said housing from normal position, a low-pressure servo chamber one one side of the movable wall in continuous communication with a source of pressure different from atmosphere, a variable-pressure servo chamber on the other side of said movable wall selectively communicable with said low-pressure servo chamber and a source of high pressure, an output element operably associated with said movable wall, and a manual input element: a cylindrically walled valve housing fast on and concentrically disposed with respect to said movable wall, and provided with a walled closed end and an open end closed by a detachable ported and centrally apertured plate; a follow-up poppet-type control valve device for controlling fluid communication to establish equivalent pressures in said servo chambers corresponding to ''''unapplied'''' position of said valve device to inactivate said movable wall, and for controlling fluid communication between said high pressure source and said variable-pressure servo chamber to establish said differential pressure corresponding to ''''applied'''' position of said valve device to activate said movable wall, said valve device including an outer valve sleeve having a circularly apertured wall intermediate thereof which projects radially inwardly with an extension thereof projecting through the aperture in said plate and the aperture in the end wall of the servo housing in sealed relationship with respect to the latter apeRture, and an inner valve sleeve which slidably projects through the aperture in the intermediate wall of said outer valve sleeve in sealed relationship thereto; an elongated cylindrical extension coaxially projects from the interior of the closed end of said valve housing to slidably support the inner valve sleeve in sealed relationship, the outer valve sleeve being radially spaced from the interior of the cylindrical wall of said valve housing to produce therewith an annular variable-pressure valve chamber; a first annular valve seat carried by the closed end wall of said valve housing; a second annular valve seat formed on one side of the intermediate wall of said outer valve sleeve; spaced first and second outstanding annular flanges defining annular valve faces at opposite ends, respectively, of said inner valve sleeve with one of said flanges detachably mounted thereon; fluid passage means incorporated in said outer valve sleeve and adapted to establish continuous fluid communication between said valve chamber and said second valve seat; another fluid passage means through the closed end wall of said valve housing and normally connecting said servo chambers via the port aforesaid in the closure plate when said first valve seat and face are normally disengaged (unseated), and said second valve seat and face normally engaged (seated) to isolate said high pressure source from said valve chamber; spring means including a normally compressed spring for biasing said valve sleeves relatively to releasably engage (seat) said second valve seat and face and disengage (unseat) said first valve seat and face corresponding to said ''''unapplied'''' position of said valve device, said outer valve sleeve being movable under manual force exerted on said input element from ''''unapplied'''' position relatively to the inner valve sleeve and to said valve housing to effect engagement (seating) of said first valve seat and face and disengagement (unseating) of said second valve seat and face corresponding to ''''applied'''' position of said valve device, such relative movement of said valve sleeves being accommodated by yielding of said spring means accompanied by augmented compressive status thereof, thus raising the pressure in said variable-pressure servo chamber while maintaining the pressure in the low-pressure servo chamber substantially constant, to produce said differential pressure in said servo chambers effective to move said movable wall and output element in a work-performing direction in cooperation with additional manual force exerted on said input element to jointly perform such work; a first normally compressed spring adapted to operably react continuously on said outer valve sleeve in opposition to manual force exerted thereon via said input element; and a pair of normally engaged abutment portions on said outer valve sleeve and said closure plate, respectively, effective when engaged to define the ''''unapplied'''' position aforesaid of said valve device.

Claim 25

For use as a brake booster, a pressure differential operated servomotor comprising structure defining: a housing having an apertured end wall, a wall movable in said housing from normal position, a low-pressure servo chamber one one side of the movable wall in continuous communication with a source of pressure different from atmosphere, a variable-pressure servo chamber on the other side of said movable wall selectively communicable with said low-pressure servo chamber and a source of high pressure, an output element operably associated with said movable wall, and a manual input element: a cylindrically walled valve housing fast on and concentrically disposed with respect to said movable wall, and provided with a walled closed end and an open end closed by a detachable ported and centrally apertured plate; a follow-up poppet-type control valve device for controlling fluid communication to establish equivalent pressures in said servo chambers corresponding to ''''unapplied'''' position of said valve device to inactivate said movable wall, and for controlling fluid communication between said high pressure source and said variable-pressure servo chamber to establish said differential pressure corresponding to ''''applied'''' position of said valve device to activate said movable wall, said valve device including an outer valve sleeve having a circularly apertured wall intermediate thereof which projects radially inwardly with an extension thereof projecting through the aperture in said plate and the aperture in the end wall of the servo housing in sealed relationship with respect to the latter apeRture, and an inner valve sleeve which slidably projects through the aperture in the intermediate wall of said outer valve sleeve in sealed relationship thereto; an elongated cylindrical extension coaxially projects from the interior of the closed end of said valve housing to slidably support the inner valve sleeve in sealed relationship, the outer valve sleeve being radially spaced from the interior of the cylindrical wall of said valve housing to produce therewith an annular variable-pressure valve chamber; a first annular valve seat carried by the closed end wall of said valve housing; a second annular valve seat formed on one side of the intermediate wall of said outer valve sleeve; spaced first and second outstanding annular flanges defining annular valve faces at opposite ends, respectively, of said inner valve sleeve with one of said flanges detachably mounted thereon; fluid passage means incorporated in said outer valve sleeve and adapted to establish continuous fluid communication between said valve chamber and said second valve seat; another fluid passage means through the closed end wall of said valve housing and normally connecting said servo chambers via the port aforesaid in the closure plate when said first valve seat and face are normally disengaged (unseated), and said second valve seat and face normally engaged (seated) to isolate said high pressure source from said valve chamber; spring means including a normally compressed spring for biasing said valve sleeves relatively to releasably engage (seat) said second valve seat and face and disengage (unseat) said first valve seat and face corresponding to said ''''unapplied'''' position of said valve device, said outer valve sleeve being movable under manual force exerted on said input element from ''''unapplied'''' position relatively to the inner valve sleeve and to said valve housing to effect engagement (seating) of said first valve seat and face and disengagement (unseating) of said second valve seat and face corresponding to ''''applied'''' position of said valve device, such relative movement of said valve sleeves being accommodated by yielding of said spring means accompanied by augmented compressive status thereof, thus raising the pressure in said variable-pressure servo chamber while maintaining the pressure in the low-pressure servo chamber substantially constant, to produce said differential pressure in said servo chambers effective to move said movable wall and output element in a work-performing direction in cooperation with additional manual force exerted on said input element to jointly perform such work; a first normally compressed spring adapted to operably react continuously on said outer valve sleeve in opposition to manual force exerted thereon via said input element; and a pair of normally engaged abutment portions on said outer valve sleeve and said closure plate, respectively, effective when engaged to define the ''''unapplied'''' position aforesaid of said valve device.

Claim 26

The servomotor as claimed in claim 23 in which said first spring is backed by a portion of said servo housing, and effective via said outer valve sleeve on said movable wall upon engagement of the pair of abutment portions, to bias the latter wall toward normal position in unison with said outer valve sleeve toward ''''unapplied'''' position of said valve device.

Claim 27

The servomotor as claimed in claim 23 in which said first spring is backed by the closed end wall of said valve housing.

Claim 28

The servomotor as claimed in claim 25 plus a second normally compressed spring operably disposed in said low-pressure servo chamber to continuously react between a portion of said servo housing and said movable wall to bias the latter toward normal position.

Claim 29

The servomotor as claimed in claim 23 in which said elongated cylindrical extension is a portion of said output element.

Claim 30

The servomotor as claimed in claim 23 in which said first and second valve seats comprise structure defining a pair of resiLient O-rings detachably carried in annular surface grooves formed in said closed end wall of said valve housing and intermediate wall of said outer valve sleeve, respectively.

Claim 31

The servomotor as claimed in claim 23 in which said first and second valve faces comprise structure defining a pair of annular resilient elements detachably carried by the peripheral margins of said annular outstanding flanges, respectively, at opposite ends of said inner valve sleeve.