GB1559813A

GB1559813A - Fluid pressure servo motors

Info

Publication number: GB1559813A
Application number: GB3442475A
Authority: GB
Original assignee: Automotive Products PLC
Current assignee: Automotive Products PLC
Priority date: 1976-08-18
Filing date: 1976-08-18
Publication date: 1980-01-30

Description

(54) IMPROVEMENTS IN OR RELATING TO FLUID PRESSURE SERVO MOTORS (71) We, AvToMonw PRODUcrS LIMITED, a British Company of Taohbrook Road, Leamington Spa, Warwickshire, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be partioularly described in and by the following statement: This invention relates to fluid pressure servo motors for providing servo assistance in a liquid pressure control system of a vehicle; the servo motors being of the kind which includes a movable barrier which separates one chamber from another; a driver operable plunger of which a part is engaged within a central bore in a housing which forms part of the barrier; valve means which are arranged to control the pressure differential between the two chambers on opposite sides of the barrier and which are adapted to be moved from one position to another by movement of the plunger in one direction relative to said central bore, said valve means permitting communication between the chambers when in said one position and, when in said other position, blocking communication between the two chamhers and connecting one of the chambers to a source of fluid pressure which so differs from the fluid pressure in the other chamber that the resultant fluid pressure difference across the barrier urges the housing in said one direction so that force generated by the action of fluid pressure on the barrier increases and decreases in proportion to the force that is applied to the driver operable plunger when the servo motor is being used; an output member and a resilient force transmitting element by which forces are transmitted to the output memher from the housing and from the plunger during part of the movement of the plunger in said one direction when the servo motor is being used.

Such a fluid pressure servo motor shall be referred to hereinafter as a "servo motor of the kind referred to".

The best known form of servo motor of the kind referred to is used to provide servo assistance in liquid pressure braking systems for vehicles and is often described as a "brake booster". Usually the output member of a brake booster is arranged to apply thrust to a piston of a liquid pressure master cylinder and the brake booster functions to boost the thrust that is exerted upon the master cylinder piston so that the thrust is greater than the thrust that is imparted by the driver to the driver operable plunger.

The force transmitting means of a brake booster often include a spring, which is known as a "kick-up spring", which acts between the housing and the output member, and which comprises said resilient force transmitting element, and a lever system which is fulcrumed upon the output member, the fulcrum being disposed radially inwards with respect to an outer abutment by which the lever system pivots on the housing and radially outwards with respect to an inner abutment by which the lever system pivots on the driver operable plunger.Such a kick-up spring would be adapted to delay normal operation, of the force transmitting means when the valve means are moved initially from said one position to the other, the kick-up spring transmitting to the output member the initial force that acts to urge the housing in said one direction whilst preventing the levers from exerting a reaction force upon the driver-oper- able plunger. The strength of the kick-up spring would be such that it would collapse and allow the driver operable plunger to act on the levers when the force on the output member reaches that which prevails when the friction material, that is to say the disc brake pads or the brake shoe linings, of the associated brakes have been moved into contact with the co-operating rotary com ponents, that is to say the brake disc or brake drum of those brakes.

An object of this invention is to simplify the construction of a fluid pressure servo motor of the kind referred to which is designed for use as a brake booster.

According to this invention there is provided a fluid pressure servo motor of the kind referred to which is suitable for use as a brake booster, wherein the resilient force transmitting element comprises an annular disc spring which is fulcrum upon the output member and which has outer abutment means which abut the housing radially outwards with respect to the fulcrum, the disc spring having radially inwardly directed spring fingers which project radially inwardly with respect to the fulcrum, the stiffness of the disc spring being sufficient to hold the spring fingers spaced from the driver operable plunger whilst the initial force that acts to urge the housing in said one direction when the driver optrable plunger is moved in said one direction is transmitted to the output member via the disc spring and until the force on the output member reaches a substantial value such as that required when the servo motor is used as a brake booster and the friction material of the asociated brake is first moved into frictional contact with the associated rotary component of that brake whereupon the spring fingers are adapted to be deflected towards the plunger such that the radially inner ends of the spring fingers contact the plunger so that the disc spring transmits to the output member the resultant of the forces applied to it by both the housing and the plunger during further movement of the plunger in said one direction.

Preferably the disc spring has a circumferential array of radially outwardly directed radial projections which each abut the housing and together comprise the outer abutment means. Conveniently parts of the housing in which the central bore is formed cooperate with the disc spring and locate it against angular movement about its centre. The said housing parts may comprise a circumferential array of angularly spaced projections which extend parallel to the axis of said central bore from the end of the housing that is adjacent to the output member, each such projection projecting through a respective aperture in or between an adjacent pair of the outwardly directed radial projections of the disc spring. Alternatively each of the radially-outwardly directed radial projections may be located by engagement within a correspondingly shaped recess in the housing.

It is common practice for the driver operable plunger of a servo motor of the kind referred to to be connected to the respective driver operable pedal by a push rod and for the push rod to be coupled to the plunger by a form of universal joint, such as a ball and socket coupling. Such an arrangement permits angular movement of the push rod relative to the plunger which is desirable both from the viewpoint of ease of assembly within the vehicle and because, if the push rod is connected simply to the respective driver operable pedal, the end of the push rod that is connected to the pedal will swing about the axis of the central bore of the movable wall with swinging movement of the pedal whilst the plunger is constrained for rectilinear sliding movement within the central bore of the movable wall.Connection of the driver operable plunger to the respective driver operable pedal is simplified in a preferred arrangement of servo motor of the kind referred to in which this invention is embodied, wherein the main part of that portion of the plunger that is located within the central bore of the housing during any part of the movement of said part of the plunger within that central bore when the servo motor is in use has a diameter which is less than the diameter of the central bore and the remainder of said plunger portion projects radially from said main part so as to locate the plunger within the bore for angular movement relative to the bore about an axis transverse to the bore and for sliding movement along the bore.

The said remainder of said plunger portion wipes the cylindrical surface of the central bore of the housing as the plunger moves within that central bore and conveniently comprises a piston ring of resilient material, the said main part of that portion of the plunger that is located within that central bore during any part of the movement of said part of the plunger within that central bore having a diameter which is less than the diameter of the central bore.

Hence the driver operable plunger, apart from the piston ring, and the push rod by which it is to be connected to the respective driver operable pedal can be formed as a single one-piece component which can rock angularly about the centre of the piston ring as said part of the plunger slides within the central bore d the movable wall.

The piston ring may comprise an O-ring of elastomeric material which is located within a circumferential groove in the plunger.

Preferably the housing which has a stepped bore, said central bore being the minimum diameter portion of the stepped bore, and said valve means comprise an annular piston which slides within a larger diameter portion of the stepped bore and which is urged in said one direction to seat upon the nearer one of an outer annular valve seat which is formed by a step in the stepped bore and an inner annular valve seat which is formed on the plunger, the annular piston being seated upon the latter when in said one position and upon the former when in said other position. The plunger may have an enlarged end portion at its end remote from the end that is for connection to the respective driver operable pedal, the maximum diameter of the enlarged end portion of the plunger being greater than the diameter of the central bore.The enlarged end portion of the driver operable plunger may be flared outwardly. The driver operable plunger with the inner annular valve seat, the circumferential groove for the 0ring and the enlarged end portion may be a moulding of plastics material.

Embodiments of this invention will be described now by way of example with reference to the accompanying drawings, of which:- Figure 1 is a transverse section of one form of brake booster which embodies this invention; Figure 2 is an end view of a detail of the booster shown in Figure 1; Figure 3 is a view similar to Figure 2 which illustrates a modified form of that detail; Figure 4 is a partly sectioned fragmentary view which illustrates a modification of another detail of the brake booster shown in Figure 1; Figure 5 is a transverse section of the central portion of another form of brake booster which embodies this invention; and Figure 6 is a sectioned fragment showing a modified form of a detail of the brake booster that is illustrated in Figure 5.

Referring to Figures 1 and 2, a fluid pressure servo motor for use as a brake booster comprises an input member 10, an output thrust rod 11 and hollow cylindrical casing 12, the input member 20 and the output thrust rod 11 being connected together end to end within the casing 12. The input member 10 carries at its outer end a conventional stirrup device 13 by which it is adapted to be connected pivotally to a driver operable brake pedal (not shown) in a conventional manner. The output thrust rod 11 is adapted to abut a piston of a liquid pressure master cylinder of a liquid pressure braking system of a vehicle.

The hollow cylindrical casing 12 is formed of two annular sheet metal pressings 14 and 15 which are interlocked at their junction in the cylindrical side wall of the casing 12. The interior of the casing 12 is divided into two chambers 16 and 17 by a barrier which includes a rolling diaphragm 18 of flexible impervious material. The outer periphery 19 of the diaphragm 18 is held in a fluid tight manner between the two annular pressings 14 and 15 at their junction.

The input member 10 extends into the casing 12 through an aperture 21 which is defined by the radially inner periphery of the annular pressing 14. The inner portion of the input member 10 that is within the casing 12 carries a rubber .0ring 22 which is located within a circumferential groove 23 which is formed in, and which is spaced from the inner end of the input member 10. The 0-ring 22 is slidable within the smallest diameter portion 24 of a stepped bore tubular housing 25 which, together with the rolling diaphragm 18, comprises the barrier.Hence the input member 10 is a one-piece component which comprises one part whioh includes the inner portion of the input member and another part which serves as a push rod which extends from said one part to the stirrup device 13, the said one part and the O-ring 22 together comprising a drivertoperable plunger which is engaged in the central bore of the housing 25.

The housing 25 is supported for axial sliding movement through the aperture 21 and an annular seal 26 between the inner periphery of the annular pressing 14 and the tubular housing 25 provides an effective dynamic seal between the interior of the chamber 16 and the space that surrounds the casing 12 of the servo motor. A flexible boot 27 surrounds the outer end of the tubular housing 25, has an outwardly directed radial flange 28 and its end adjacent the annular pressing 14, an inwardly directed radial flange 29 at its outer end and a cylindrical portion 31 which projects outwardly from the radially inner periphery of the inwardly directed radial flange 29.

The annular sheet metal pressing 14 carries bolts 32 by which the casing 12 is secured to a bulkhead when it is installed in a vehicle. Apertures 33 in the inwardly directed radial flange 29 of the boot 27 place the interior of the tubular housing 25 in communication with the space that surrounds the casing 12, the outer end of the tubular housing 25 abutting the inner face of the inwardly directed radial flange 29 of the flexible boot 27. An annular filter 34 is spigotted into the bore of the tubular housing 25 at its outer end and surrounds the input member 10 closely. A circlip 35, which is located within a circumferential groove 36 in the input member 10, locates the annular filter 34 against sliding movement along the input member 10, the outer end of the annular filter 34 being in abutment with the inner face of the inwardly directed radial flange 29 of the boot 27.

The portion of the input member 10 that extends between the circumferential groove 36 and the inner end is profiled so that the circumferential groove 23 that accommodates the O-ring 22, is disposed substan tially centrally between an axially spaced pair of radially enlarged portions 37 and 38 of the input member 10. The radially enlarged portions 37 and 38 of the input member 10 are spaced apart by a distance that is greater than the axial length of the smallest diameter bore portion 24 of the tubular housing 25, the diameter of that part of the input member 10 that extends between the two radial enlargements 37 and 38 on each side of the circumferential groove 23 being less than the diameter of the smallest diameter bore portion 24 of the tubular housing 25.The enlargement 37 at the inner end of the input member 10 is flared outwardly and arranged to abut that part of tubular housing 25 that surrounds the mouth at the inner end of the smallest diameter bore portion 24 so as to limit movement of the input member 10 away from the output thrust rod 11 and prevent the input member 10 being drawn through the smallest diameter bore portion 24 of the tubular housing 25. The other enlargement 38 of the input member 10 serves as an annular valve seat. The portion of the input member 10 that extends between the circumferential groove 36 and the annular valve seat 38 tapers inwardly from the groove 36 towards the valve seat 38.

The tubular housing 25 has also a medial diameter bore portion 39 and a largest diameter bore portion 41. The inner surface of that part of the tubular housing 25 between the medial diameter bore portion 39 and the largest diameter bore portion 41 is shaped to define a bulbous annulus 42 that serves as an outer annular valve. seat, the diameter of the medial diameter bore portion 39 being greater than the maximum diameter of the enlargement 38 that forms the other, inner annular valve seat.

An annular piston 43 slides within that part of the largest diameter bore portion 41 that extends between the outer annular valve seat 42 and the annular air filter 34 and has an internal diameter which is less than the maximum diameter of the enlargement 38 but which is greater than the diameter of the input member 10 at the junction of enlargement 38 and the inwardly tapered portion of the input member 10 that extends from the groove 36 to the enlargement 38. The annular piston 43 is urged towards the inner and outer valve seats 38 and 42 by a conical coil spring 44 which reacts against the circlip 35. Hence the annular piston 43 seats upon the nearer one of the inner and outer valve seats 38 and 42.Thus the annular piston 43 functions as a valve member which determines whether the annular space that is formed within the medial diameter bore portion 39 of the tubular housing 25 and is in communication with the chamber 16 via a radial passage 45 in the tubular housing 25, is connected to the space that surrounds the casing 22 through the gap that exists between the annular piston 43 and the inner valve seat 38 when the annular piston 43 is seated upon the outer valve seat 42, or is connected to the chamber 17 through a passage 46, which extends through the tubular housing 25 parallel to the axis of the casing, and through the gap that is established between the outer valve seat 42 and the annular piston 43 when the annular piston 43 is seated upon the inner valve seat 38 and is held spaced from the outer valve seat 42.

The radially inner peripheral portion 47 of the diaphragm 18 is enlarged and is held entrapped in a fluid tight manner within an annular groove 48 which is formed in the radially outer surface of the tubular housing 25, the enlarged inner peripheral portion 47 of the diaphragm 18 being retained within the groove 48 by a dished annular retainer plate 49. The diaphragm 18 forms a layer around the outer surface of an annular sheet metal pressing 51 which has a flat radial base which extends radially inwardly from a cylindrical wall.The diameter of the central aperture of the annular member 51 is greater than the diameter of the groove 48 within which the inner peripheral portion 47 of the diaphragm 18 is entrapped and the inner peripheral portion of the annular pressing 51 is trapped between the enlarged inner peripheral portion 47 of the diaphragm 18 and a radially outwardly extending flange 52 which is formed by that part of the tubular housing 25 that is within the chamber 17.

That part of tubular housing 25 that projects from the radial flange 52 towards the sheet metal pressing 15 is castellated comprising a circumferential array of projections 53 which extend parallel to the axis of the casing 12. The projections 53 are surrounded by a flat ring 54 which abuts the flange 52 and serves as part of the housing.

An annular disc spring 55, which is flat in its normal relaxed condition, has a circumferential array of radially outwardly directed projecting portions 56 which extend through a respective space between an adjacent pair of the projections 53 and which comprise outer abutment means which abut the ring 54, and a circumferential array of radially inwardly directed fingers 57 which project into the space that is surrounded by the projections 53. The gap between each adjacent pair of fingers 57 is extended radially outwardly beyond the outer ends of the fingers into the respective outwardly extending radial projection 56 by which that pair of fingers 57 are connected one to the other. Figure 2 shows that each finger 57 is substantially triangu lar when viewed along the axis of the disc spring 55.The outer edge 58 of each spring finger 57 abuts the inner edge of the respective projecting portion 53 of the tubular housing 25 that extends into the space between the adjacent pair of radially outwardly directed projecting portions 56 of the disc spring 55 that are interconnected by that inwardly directed finger 57.

The output thrust rod 11 has a radially outwardly extending annular disc 59 fixed at its inner end. Hence the thrust rod 11 and the disc 59 together comprise an output member. The radially inwardly extending finger portions 57 of the disc spring 55 engage the radial face of the annular disc 59 that is remote from the annular sheet metal pressing 15. The outside diameter of the annular disc 59 is less than the inside diameter of the flat ring 54.

The output thrust rod 11 extends through the central aperture 61 of an annular member 62 which is fixed to the ends of the projections 53 remote from the remainder of the tubular housing 25. Each projection 53 projects into a correspondingly-shaped recess 63 in the outer periphery of the annular member 62. The annular member 62 is fixed to the projections 53 by a circlip 64 which is fitted into an aligned series of grooves 65, which are formed in the outer surfaces of the projections 53, and which rests upon shoulders 66 that are formed in those parts of the annular member 62 that extend into the spaces between adnular member 62 has a circumferential jacent projections 53, the shoulders 66 being aligned with the grooves 65.The anarray of projections 67 that project from its periphery towards the annular pressing 15, each projection 67 having a shoulder 68 formed in its outer surface. A conical compression spring 69 has its smaller diameter end seated in the circumferential array of shoulders 68, and reacts at its larger diameter end against the inner surface of the sheet metal pressing 15 to urge the assembly of the tubular housing 25 and the annular member 62 away from the sheet metal pressing 15. The face of the annular member 62 remote from the sheet metal pressing 15 is rebated to define a cylindrical recess 71 which accommodates the annular disc 59 that is fixed to the output thrust rod 11.

The inner end of the output thrust rod 11 projects into a cavity 72 that is formed in the opposed end face of the input member 10, the diameter of the cavity 72 being greater than the diameter of that part of the output thrust rod 11 which projects into it so that there is a substantial clearance between the wall of the cavity 72 and that part of the output thrust rod 11 which projects into it. A light coil spring 73 has one end seated upon a shoulder formed in the base of the cavity 72 and reacts at its other end against a radial flange 74 which is formed upon the output thrust rod 11. The light coil spring 73 urges the enlarged end 37 of the input member 10 into abutment with the periphery of the adjacent mouth of the smallest diameter bore portion 24 of the tubular housing 25.

The inner ends of the inwardly directed spring fingers 57 form arcuate dimples which have their concave surfaces facing the annular disc 59 and their convex surfaces facing the end surface of the input member 10 which surrounds the mouth of the cavity 72, that end surface also being domed to present a convex annular surface to the disc spring 55. The end face of the tubular housing 25 that faces the disc spring 55 has a portion which is tapered inwardly at a shallow angle towards the periphery of the mouth of the smaller diameter bore portion 24 that is formed in that end face. The outside diameter of the shallow tapered end surface portion of the tubular housing 25 is less than the inside diameter of the flat ring 54.The shallow tapered portion of the end face of the tubular housing 25 that faces the disc spring 55 provides the clearance necessary to allow the fingers 57 of the disc spring 55 and the convex annular surface at the adjacent end of the input member 10 to be moved into mutual abutment with one another when the spring fingers 57 are deflected from' the natural flat condition that is shown in Figure 1. Figure 1 also shows that the input member 10 is spaced from the radially inner ends of the fingers 57 of the disc spring 55 when the enlarged end portion 37 of the input member 10 is seated in the mouth that is formed at the end of the smallest diameter bore portion 24 of the tubular housing 25 that is adjacent the annular member 62 and the disc spring 55.

The output thrust rod 11 extends through the central aperture 75 of the annular sheet metal pressing 15 and slides within the bore of an annular grommet 76 which is fitted into the central aperture 75 of the annular sheet metal pressing 15. An annular recess 77 is formed in the bore of the annular grommet 76 between its ends. The surface of the recess 77 is arcuate in cross section and the recess 77 extends substantially equally to each side of the aperture 75 in the annular sheet metal pressing 15. The aperture 75 is formed in the base of a substantially cupshaped portion of the annular sheet metal pressing which extends into the chamber 17 at the centre of the annular sheet metal pressing 15.The annular sheet metal pressing 15 carries a union 78 which is adapted to receive one end of a pipe which has its other end connected to the intake manifold of the engine of the vehicle. The union defines -a passage 79 through the annular pressing 15 and carries a non-return valve in that passage 79.

In use of the brake booster shown in Figures 1 and 2, the casing 22 is bolted to a bulkhead of the vehicle by the bolts 32 so that the outwardly directed radial flange 28 at the inner end of the boot 27 is trapped between the annular sheet metal pressing 14 and the bulkhead. The bulkhead has an aperture through which the input member 10 and that part of the tubular housing 25 that is enclosed by the boot 27 projects, the input member 10 being pivotally connected to the driver operable brake pedal of the vehicle in the conventional manner by way of the stirrup device 13.The body of the associated liquid pressure master cylinder is received within the recess that is formed in the outer surface of the annular sheet metal pressing 15 by the cupshaped portion that is formed at the centre of that pressing 15, the output thrust rod 11 projecting into the bore of the master cylinder so that its end abuts a piston of the master cylinder.

The chamber 17 is placed in communication with the intake manifold of the engine of the vehicle through the union 78. The non-return valve that is carried by the union 78 allows air to flow from the chamber 17 to the intake manifold of the engine and prevents air flow in the reverse direction.

The moveable components of the servo motor device will be positioned as shown in Figure 1 of the drawings when the brakes of the vehicle are released. In this condition the input member 10 is at the end of its stroke furthest from the sheet metal pressing 15, the enlarged end portion 37 being seated in the mouth that is formed at the end of the smallest diameter bore portion 24 that is nearer the sheet metal pressing 15. Also the annular piston 43 is seated upon the inner valve seat 38 and is held displaced from the outer valve seat 42.

When the engine of the vehicle is running, air is withdrawn from the chamber 17 and the chamber 16 via the non-return valve is the passage 79, the chamber 16 being in communication with the chamber 17 via the radial passage 45 and the passage 46 that extends parallel to the axis of the casing 12. Hence the pressure on both sides of the barrier that comprises the rolling diaphragm 18 and the tubular housing 25 is balanced because the two chambers I6 and 17 are in communication. The stiffness of the disc spring 55 is such that the annular disc 59 that is fixed to the inner end of the output thrust rod 11 is held by the inwardly directed fingers 57 of the disc spring 55 so that it is seated within the cylindrical recess 71 that is formed in the annular member 62, the disc spring 55 being in its natural condition.The output thrust rod 11 is held at the end of its stroke furthest from the associated master cylinder by the action d the conical spring 69 upon the assembly of the annular member 62 and the tubular housing 25, the annular disc 59 at the inner end of the output thrust rod 11 being engaged within the cylinderical recess 71 that is formed in the annular member 62.

When the driver operable pedal is depressed to apply the brakes, the input member 10 is moved towards the annular sheet metal pressing 15. The input member 10 is free to rock about the centre of the O-ring 22 as it is moved towards the annular pressing 15 because the O-ring 22 is the only part of the input member 10 that is in sliding contact with the bore of the tubular housing 25, the form of the inner valve seat 38 allowing the necessary relative movement between that valve seat 38 and the annular piston 43 that accompanies such rocking movement of the input member 10 without the annular piston 43 being unseated from the inner valve seat 38 to allow air flow between the annular valve member 43 and the inner valve seat 38.Hence the outer end of the input member 10 that comprises the push rod that is connected to the driver operable pedal via the stirrup device 13 is free to follow the swinging movement of the driver operable pedal without disturbing the functioning of those parts of the input member 10 that functions as the plunger and the valve seat for the valve means of the servo motor.

Initially that part of the input member 10 which is within the smallest diameter bore portion 24 of the tubular housing 25 moves relative to the tubular housing 25 along that smallest diameter bore portion 24 and towards the output thrust rod 11.

The light coil spring 73 collapses without any significant thrust being transmitted througll it to the output thrust rod 11. The annular valve member 43 follows such movement of the input member 10 towards the annular sheet metal pressing 15, due to the action of the coil spring 44 that holds it seated upon the inner valve seat 38, until it is moved into engagement with the bulbous annulus 42 that forms the outer valve seat, whereupon the inner annular valve seat 38 moves away from the annular valve member 43 so as to allow atmospheric air to enter the annular space that is formed between the input member 10 and the medial diameter bore portion 39 of the tubular housing 25, the atmospheric air flowing into the chamber 16 through the radial passage 45.

Thus a pressure differential is created across the barrier between the chambers 16 and 17 and the resultant thrust acts on the barrier to urge it towards the annular sheet metal pressing 15 against the action of the conical coil spring 69. Initially the output member moves with such movement of the barrier towards the annular sheet metal pressing 15 so that thrust is imparted to the associated master cylinder piston which is moved to displace liquid from the associated master cylinder and initiate application of the associated brakes.Initially the resistance to such movement of the output member with movement of the barrier towards the annular sheet metal pressing 15 is negligible and is insufficient to deflect the inwardly directed spring fingers 57 of the disc spring 55 so that the annular disc 59 that is fixed to the inner end of the output thrust rod 11 is held seated within the cylindrical recess 71 by the diaphragm spring fingers 57, the disc spring 55 remaining in its natural flat condition with the inner ends of its fingers 57 being advanced with such movement of the tubular housing 25 towards the annular sheet metal pressing 15 so that they remain spaced from the opposed end face of the input member 10.

When the associated master cylinder piston has been moved sufficiently to displace sufficient liquid from the master cylinder bore to effect engagement of the brake pads or brake shoe linings of the associated brakes with the respective brake disc or brake drum, the resistance to further movement of the master cylinder piston, and thus to further movement of the output member with further movement of the barrier towards the annular sheet metal pressing 15, increases substantially and by an amount sufficient to deflect the inwardly directed spring fingers 57 of the disc spring 55. Hence the input member 10 and the barrier move together towards the annular sheet metal pressing 15 relative to the output thrust rod 11 and the annular disc 59 which are stationary.Such movement of the barrier relative to the output member causes deflection of the inwardly directed spring fingers 57 about the outer periphery of the annular disc 59, which functions as a fulcrum for the disc spring 55, so that the arcuate inner ends of the radially inwardly directed spring fingers 57 of the disc spring 55 and the opposed end face of the inner portion of the input member 10 are moved into mutual abutment. It will be appreciated that the fulcrum for the disc spring 55 is located radially inwardly with respect to the abutment means of the disc spring 55, namely the radially outwardly projecting portions 56, and that the spring fingers 57 project radially inwardly with respect to the fulcrum.

-Once the input member 10 is in contact with the inner ends of the radially inwardly directed spring fingers 57 of the disc spring 55, further thrust that is applied to the input member 10 via the driver operable brake pedal and which urges the input member 10 towards the annular sheet metal pressing 15 is applied to the inner ends of the; radially inwardly directed spring fingers 57 of the disc spring 55. Also the thrust due to the pressure differential on the barrier is applied to the abutment means of the disc spring 55 through the flat ring 54.Thus the disc spring 55 functions as a lever system and the resultant of the thrusts that act upon the inner and outer peripheries of the disc spring 55 is applied to the output thrust rod 11, via the disc 59, and acts through the output member to urge the master cylinder piston of the associated liquid pressure master cylinder in the brake applying direction.

Hence the thrust that is applied to the associated master cylinder piston through the output member after initial application of the brake pad or brake linings to the brake is greater than the thrust that is applied to the input member 10 because, due to the lever action of the disc spring 55, it is the resultant oif the thrust that is imparted to the input member 10 and the thrust due to the pressure differential on the barrier. Also the thrust due to the action of the pressure differential on the barier increases and decreases in proportion to increases and decreases in the thrust that is applied to the input member 10.

In the foregoing description the projections 53 of the castellated end portion of the tubular housing 25 are described as extending between adjacent pairs of the radially outwardly extending projecting portions 56 of the disc spring 55 by which the inwardly directed spring fingers 57 are connected together. Various other arrangements are possible. For example each such projecting portion 53 of the castellated end portion of the tubular housing 25 may project through a respective one of the radial slots which separate the inwardly directed spring fingers 57 of the disc spring 55. Figure 3 shows another configuration of disc spring that may be employed in place of the disc spring 55 that has been described above with reference to Figure 2.The inner end of each of the inwardly directed spring fingers 57A of this modified form of disc spring 55A is enlarged and is substantially diamond shaped. The slots that separate each adjacent pair of such inwardly directed spring fingers 57A are branched at their outer ends so that they are substantially Y-shaped, one branch of each substantially Y-shaped slot together with the adjacent branch of the substantially Y-shaped slot on the opposite side of the inwardly directed finger 57A that is bounded by the said one branch of the first-mentioned Y-shaped slot projecting into a radially outwardly extended projecting portion 56A of the disc spring, each radially inwardly directed spring finger 57A projecting inwardly from the centre of such a radially outwardly directed portion 56A.The portions 56A of the disc spring serve as the abutment means of that disc spring. It will be appreciated that the fulcrum for the disc spring 55A again comprises the adjacent peripheral edge of the disc 59 and is located radially inwardly with respect to the abutment means and that the inwardly directed spring fingers project radially inwardly with respect to that fulcrum.

Figure 4 shows an alternative arrangement for connecting the input member 10 to the driver operable pedal. The driver operable pedal includes an angle bracket 81. A portion 82 of one of the flat sides of the angle bracket 81 is deformed from the remainder of that flat side so as to define an apperture 83 between itself and the remainder 84 of that flat side. The outer end 85 of the input member 10 is domed instead of being fixed to the stirrup device 13, the stirrup device 13 being omitted. A diametral hole 86 is formed adjacent that outer end 85. A spring clip 87, which has a straight portion which extends through the diametral hole 86 and an outer portion which embraces the outer surface of the input member 10 is fitted to the input member 10.The domed end 85 of the input member 20 is engaged with the concave surface of the deformed portion 82 of the angle bracket 81 and those parts of the spring clip 87 which project to each side of the input member 10 extend through the aperture 83 on each side of the deformed portion 82 so that the input member 10 is retained coupled to the angle bracket 81 with the domed end 85 engaged with the concave surface of the deformed portion 82.

The ring 22 may be omitted if the design of the brake booster is such that it is not necessary to ensure a fluid tight seal between the drivereperable plunger portion of the one-piece input member and the smallest diameter bore of the tubular housing because other sealing means are provided to complete the barrier between the two chambers. In such an arrangement it is sufficient for that part of the input member within the smallest diameter bore to comprise radially-projecting locating means which locate it for angular movement relative to the smallest diameter bore about an axis transverse to that bore and for sliding movement along that bore.

Figure 5 shows another arrangement for transmitting thrust with servo asistance from an input member to an output member via an annular disc spring in a brake booster.

The general construction of the brake booster that includes the arrangement shown in Figure 5 is similar to that which has just been described with reference to Figure 1 and will not be described again in detail.

The following description will concentrate upon the features of the brake booster that includes the arrangement shown in Figure 5 that differ from corresponding features of the brake booster described above with reference to Figure 1. Those parts of the brake booster that include the arrangement shown in Figure 5 that are similar to corresponding parts of the brake booster that has been described above with reference to Figure 1 will be identified in the following description by the same references that were used in the foregoing description of the brake booster shown in Figure 1.

The input member comprises a push rod 110 which has a ball 111 formed at one end and which is adapted to be connected pivotally to a driver operable pedal at its other end. The ball 111 is received within a socket which is formed in a plunger 112 so that the push rod 110 is free for limited angular movement relative to the plunger 112.

The plunger 112 is operable by the driver for sliding movement within the smallest diameter portion 24 of a stepped bore tubular housing 125 which, together with a rolling diaphragm 118, forms the barrier. The diaphragm 218 and the tubular housing 125 are connected together as is described and claimed in the Complete Specification of our co-pending Patent Application No.

49839/74 (Serial No. 1,486,609).

In addition to the smallest diameter bore portion 24, the stepped bore of the tubular housing 125 has two intermediate diameter portions 139 and 140 and a largest diameter portion 141. The smaller diameter intermediate bore portion 139 corresponds to the medial diameter bore portion 39 of the brake booster described above with reference to Figure 1. The larger diameter in termediate diameter bore portion 140 is that part of the stepped bore in which the annular piston 43 slides and is between the largest diameter bore portion 141 and the smaller diameter intermediate bore portion 139.

The inner annular valve seat 138 comprises an annulus which is formed at the end of the plunger 112 that surrounds the push rod 120.

The conical coil spring 44 that urges the annular piston 43 towards the inner and outer valve seats 138 and 42 reacts against the base of a tophat section annular sheet metal component 142. A second conical coil spring 143 reacts against a flanged annular spring retainer 144, which abuts the shoulder between the larger intermediate diameter bore portion 140 and the largest diameter bore portion 141, and urges the tOphat section component 142 against a circlip 135 which is fitted into a circumferential groove 136 is the push rod 110, the smaller diameter end of the second coil spring 143 being in contact with the outer flange of the tophat section component 142.

The air filter (not shown), which is not spigotted into the largest diameter bore portion 141, would be carried by the servo motor casing (not shown) at a suitable point adjacent the flexible boot (not shown) that connects the push rod 112 to the sheet metal parts of that casing.

The bore of the tubular housing 125 is rebated at the end of its smallest diameter portion 24 that is further from the largest diameter bore portion 141 so as to form an inner annular shoulder 145. A second, outer, annular shoulder 146 is also formed axially in the tubular housing 125 and is connected to the inner annular shoulder 145 by a frusto-conical surface portion 147 which tapers towards the smallest diameter bore portion 24.

The plunger 112 carries a circlip 148 which co-operates with the inner annular shoulder 145 to limit movement of the plunger 112 towards the annular piston 43.

The ring 54 is seated within the outer annular shoulder 146 and the outwardlydirected radial portions 56 of the disc spring 55, which comprise the abutment means of the disc spring 55, are seated upon the ring 54, the tubular housing 125 having a circumferential array of six arcuate recesses 149 which each receives the outer peripheral portion of a respective one of the outwardlydirected portions 56 of the disc spring 55.

The inner ends of the fingers 57 of the disc spring 55 are flat, not dimpled as shown in Figures 1 and 2. The inner end of the fingers 57 abut an annulus 137 when they are deflected from the flat condition shown in Figure 5. The annulus 137 is formed at the end of the plunger 112 remote from the push rod 110.

The output member that comprises the output thrust rod 11 and the disc 59, is connected to the tubular housing 125 by a retainer plate 162 which is engaged in the manner of a bayonet connection with a cooperating circumferential array of lobes 163 that are formed on the tubular housing 125.

The inner peripheral portion of the retainer Dlate 162 abuts the disc 59 and forms a tubular portion into which the output thrust rod 111 is spigotted. The smaller diameter end of the coil spring 69 (not shown) is seated within the annular shoulder formed by the tubular portion and the remainder of the retainer plate 162. The arrangement of the abutment means, the fulcrum of the fingers of the disc spring 55 are as described above with reference to Figures 1 and 2.

Figure 6 shows a modification of the brake booster described above with reference to Figure 5. For convenience of illustration, the driver operable plunger has been removed from the smallest diameter bore portion 24 of the stepped bore tubular housing 125A. The disc-spring 55A, which is shown in Figure 3, is shown seated upon the ring 54 in the outer annular shoulder 146, the radially-outwardly projecting portions 56A of that spring 55A each being received within a correspondingly-shaped recess (not shown) which is formed in the outer cylindrical wall of the outer annular shoulder 146.

The output thrust rod 111 is connected to the tubular housing 125A by a modified retainer plate 162A which, in addition to the tubular portion into which the output thrust rod 111 is spigotted, comprises an annular disc portion which is slid into the cylindrical recess that is formed by the outer annular shoulder 146 and which has an outwardly-directed radial spoke 165 which projects into an aperture 164 in the cylindrical wall of the outer annular shoulder 146. The radial spoke 165 is U-shaped in cross-section, the depth of each sidewall 166 diminishing radially-outwardly so that the spoke 165 can be hooked into the aperture 164 during assembly of the booster. The arrangement of the abutment means, the fulcrum and the fingers of the disc spring 55A are as is described above with reference to Figure 3.

WHAT WE CLAIM IS:- 1. A fluid pressure servo motor of the kind referred to which is suitable for use as a brake booster, wherein the resilient force transmitting element comprises an annular disc spring which is fulcrumed upon the output member and which has outer abutment means which abut the housing radially outwards with respect to the fulcrum, the disc spring having radially inwardly directed spring fingers which project radially inwardly with respect to the fulcrum, the stiffness of the disc spring being sufficient to hold the spring fingers spaced from the driver operable plunger whilst the initial force that acts to urge the housing in said one direction when the driver operable plunger is moved in said one direction is transmitted to the output member via the disc spring and until the force on the output member reaches a substantial value such as that required when the servo motor is used as a brake booster and the friction material of the associated brake is first moved into frictional contact with the associated rotary component of that brake whereupon the spring fingers are adapted to be deflected towards the plunger such that the radially inner ends of the spring fingers contact the plunger so that the disc spring transmits to

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. tOphat section component 142 against a circlip 135 which is fitted into a circumferential groove 136 is the push rod 110, the smaller diameter end of the second coil spring 143 being in contact with the outer flange of the tophat section component 142. The air filter (not shown), which is not spigotted into the largest diameter bore portion 141, would be carried by the servo motor casing (not shown) at a suitable point adjacent the flexible boot (not shown) that connects the push rod 112 to the sheet metal parts of that casing. The bore of the tubular housing 125 is rebated at the end of its smallest diameter portion 24 that is further from the largest diameter bore portion 141 so as to form an inner annular shoulder 145. A second, outer, annular shoulder 146 is also formed axially in the tubular housing 125 and is connected to the inner annular shoulder 145 by a frusto-conical surface portion 147 which tapers towards the smallest diameter bore portion 24. The plunger 112 carries a circlip 148 which co-operates with the inner annular shoulder 145 to limit movement of the plunger 112 towards the annular piston 43. The ring 54 is seated within the outer annular shoulder 146 and the outwardlydirected radial portions 56 of the disc spring 55, which comprise the abutment means of the disc spring 55, are seated upon the ring 54, the tubular housing 125 having a circumferential array of six arcuate recesses 149 which each receives the outer peripheral portion of a respective one of the outwardlydirected portions 56 of the disc spring 55. The inner ends of the fingers 57 of the disc spring 55 are flat, not dimpled as shown in Figures 1 and 2. The inner end of the fingers 57 abut an annulus 137 when they are deflected from the flat condition shown in Figure 5. The annulus 137 is formed at the end of the plunger 112 remote from the push rod 110. The output member that comprises the output thrust rod 11 and the disc 59, is connected to the tubular housing 125 by a retainer plate 162 which is engaged in the manner of a bayonet connection with a cooperating circumferential array of lobes 163 that are formed on the tubular housing 125. The inner peripheral portion of the retainer Dlate 162 abuts the disc 59 and forms a tubular portion into which the output thrust rod 111 is spigotted. The smaller diameter end of the coil spring 69 (not shown) is seated within the annular shoulder formed by the tubular portion and the remainder of the retainer plate 162. The arrangement of the abutment means, the fulcrum of the fingers of the disc spring 55 are as described above with reference to Figures 1 and 2. Figure 6 shows a modification of the brake booster described above with reference to Figure 5. For convenience of illustration, the driver operable plunger has been removed from the smallest diameter bore portion 24 of the stepped bore tubular housing 125A. The disc-spring 55A, which is shown in Figure 3, is shown seated upon the ring 54 in the outer annular shoulder 146, the radially-outwardly projecting portions 56A of that spring 55A each being received within a correspondingly-shaped recess (not shown) which is formed in the outer cylindrical wall of the outer annular shoulder 146. The output thrust rod 111 is connected to the tubular housing 125A by a modified retainer plate 162A which, in addition to the tubular portion into which the output thrust rod 111 is spigotted, comprises an annular disc portion which is slid into the cylindrical recess that is formed by the outer annular shoulder 146 and which has an outwardly-directed radial spoke 165 which projects into an aperture 164 in the cylindrical wall of the outer annular shoulder 146. The radial spoke 165 is U-shaped in cross-section, the depth of each sidewall 166 diminishing radially-outwardly so that the spoke 165 can be hooked into the aperture 164 during assembly of the booster. The arrangement of the abutment means, the fulcrum and the fingers of the disc spring 55A are as is described above with reference to Figure 3. WHAT WE CLAIM IS:-

1. A fluid pressure servo motor of the kind referred to which is suitable for use as a brake booster, wherein the resilient force transmitting element comprises an annular disc spring which is fulcrumed upon the output member and which has outer abutment means which abut the housing radially outwards with respect to the fulcrum, the disc spring having radially inwardly directed spring fingers which project radially inwardly with respect to the fulcrum, the stiffness of the disc spring being sufficient to hold the spring fingers spaced from the driver operable plunger whilst the initial force that acts to urge the housing in said one direction when the driver operable plunger is moved in said one direction is transmitted to the output member via the disc spring and until the force on the output member reaches a substantial value such as that required when the servo motor is used as a brake booster and the friction material of the associated brake is first moved into frictional contact with the associated rotary component of that brake whereupon the spring fingers are adapted to be deflected towards the plunger such that the radially inner ends of the spring fingers contact the plunger so that the disc spring transmits to

the output member the resultant of the forces applied to it by both the housing and the plunger during further movement of the plunger in said one direction.

2. A servo motor according to Claim 1, wherein the dise spring has a circumferential array of radially outwardly directed radial projections which each abut the housing and together comprise the outer abutment means.

3. A servo motor according to Claim 1 or Claim 2, wherein parts of the housing in which the central bore is formed cooperate with the disc spring and locate it against angular movement about its centre.

4. A servo motor according to Claim 3, wherein said housing parts comprise a circumferential array of angularly spaced projections which extend parallel to the axis of said central bore from the end of the housing that is adjacent to the output member, each such projection projecting through a respective aperture in or between an adjacent pair of the outwardly directed radial projections of the disc spring.

5. A servo motor according to Claim 3, wherein each of the radially-outwardly directed radial projections is located by engagement within a correspondingly-shaped recess in the housing.

6. A servo motor according to any one of Claims 1 to 5, wherein the main part of that portion of the plunger that is located within the central bore of the housing during any part of the movement of said part of the plunger within that centraF bore when the servo motor is in use has a diameter which is less than the diameter of the central bore and the remainder of said plunger portion projects radially from said main part so as to locate the plunger within the bore for angular movement relative to the bore about an axis transverse to the bore and for sliding movement along the bore.

7. A servo motor according to Claim 6, wherein said radially projecting remainder extends continuously around the circumference of the plunger.

8. A servo motor according to Claim 7, wherein said radially projecting remainder comprises a piston ring of resilient material which wipes the cylindrical surface of the central bore as the plunger moves within that central bore.

9. A servo motor according to Claim 8, wherein the driver operable plunger apart from said piston ring is part of a one piece component which also comprises a push rod which is for connection to the respective driver operable pedal.

10. A servo motor according to Claim 9, wherein the piston ring comprises an Oring of elastomeric material which is located within a circumferential groove in the plunger.

11. A servo motor according to any one of Claims 1 to 10, wherein the housing which has a stepped bore, said central bore being the minimum diameter portion of the stepped bore, and said valve means comprise an annular piston which slides within a larger diameter portion of the stepped bore and which is urged in said one direction to seat upon the nearer one of an outer annular valve seat which is formed by a step in the stepped bore and an inner annular valve seat which is formed on the plunger, the annular piston being seated upon the latter when in said one position and upon the former when in said other position.

12. A servo motor according to Claim 11 when appended to Claim 9, wherein the plunger has an enlarged end portion at its end remote from the end of the one piece component that is for connection to the respective driver operable pedal, the maximum diameter of the enlarged end portion of the plunger being greater than the diameter of the central bore.

13. A servo motor according to Claim 12, wherein the enlarged end portion of the driver operable plunger is flared outwardly.

14. A brake booster substantially as described hereinbefore with reference to and as illustrated in Figures 1 and 2, or substantially as described hereinbefore with reference to and as illustrated in Figures 1 and 2 and modified substantially as described hereinbefore with reference to and as illustrated in Figure 3, Figure 4, Figure 5 or Figure 6.