GB2036220A - Servo boosters for vehicle braking systems - Google Patents

Abstract

It is common practice in servo boosters to employ a poppet valve provided with a skirt which is sealingly secured at its free end to the valve body in which it is housed. A valve assembly is described in which a poppet valve member (29) is secured to a sleeve (34) which is slidable in the valve body (3) and is connected by a part-spherical thrust coupling (41), centred at the ball 13, with the input rod (12). The sleeve and input rod are biassed rearwardly by a single spring (46), and in the construction described in the resilient valve member is provided with a sealing lip (39) to effect a sliding seal between the sleeve and the valve body. <IMAGE>

Description

SPECIFICATION Servo boosters for vehicle braking systems This invention relates to servo boosters for vehicle braking of the kind in which a movable wall is subjected to a differential pressure controlled by valve means.

Servo boosters of the kind set forth often employ an annular resilient valve member provided with a sealing portion adapted to engage alternatively with coaxial valve seats arranged respectively on a valve control member and on the valve body, and with a flexible rearwardly extending skirt. The rear end of the skirt is secured in position in the bore of the valve body to form a seal therewith. Two coupled compression springs are generally employed, one to bias to a retracted position an input rod extending through the valve member and engaging with the valve control member, and the other to urge forwardly the valve seat portion of the valve member relative to the valve body.

According to the invention in a servo booster of the kind set forth the valve means comprises a valve body connected to the movable wall and provided with an axial bore in which works a valve control member, the valve body and valve control member being provided with co-axial rearwardly facing valve seats, an annular resilient valve member carried by a sleeve slidable in the bore and located rearwardly of the control member, the valve member comprising a sealing portion at its front end adapted to engage with the valve seats and connected by an axially compressible portion to a rear portion secured to the sleeve, means sealing the sleeve to the wall of the bore rearwardly of the sealing portion of the valve member, resilient means biassing the sleeve rearwardly relative to the valve body, a pedal-operated input rod extending through the sleeve and valve member to engage with the valve control member, and means connecting the sleeve to the input rod.

The terms 'front' and 'rear' will be used in the following description and claims in the sense that the rear of the booster is that end through which the input rod extends.

Preferably the axially compressible portion of the valve member is arranged such that its resilience is sufficient not to require the incorporation of a spring biassing the sealing portion of the valve member forwards relative to the rear portion, but if desired a spring may be incorporated.

Preferably the sealing means between the sleeve and said bore comprises said rear portion of the valve member which is arranged to effect a sliding seal with the bore wall.

The resilient means conveniently comprises a spring, either in the form of a coiled compression spring or a spring washer mounted on the sleeve and acting between the rear end of the valve body and a radially outwardly directed flange on the sleeve.

The connection between the sleeve and the input rod preferably comprises a part-spherical or part-cylindrical thrust coupling to enable pivotal movement of the input rod about its connection with the valve control member.

The valve assembly of a servo booster in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawing which is a longitudinal cross-section of the rear end of the booster, the valve body and input rod being shown in their retracted positions.

As is conventional, the rear housing wall 1 of the booster is provided with a rearwardly extending tubular extension 2, and a generally cylindrical valve body 3 comprises a head 4 and a rearwardly extending portion 5 of smaller diameter which is slidably sealed in tubular extension 2 by an annular seal assembly 6.

Valve body 3 is provided with a stepped through bore 7 comprising front and rear bore portion 8 and 9 connected by an intermediate bore portion 10 of reduced diameter in which is slidably located a valve control member 11.

An axially extending pedal-operated input rod 1 2 is provided with a ball 1 3 and its front end which is retained in a blind bore in the rear end of vale control member 11 by a dimple 14.

An output rod 1 5 for engagement with a master cylinder piston, not shown, is threadedly secured at its rear end to a thrust disc 1 6 which is backed by an elastomeric reaction disc 1 7 located in bore portion 8. An annular ring 1 8 slidably receives the front end of valve control member 11 and reduces, in well known manner, the effective diameter of the rear end of reaction disc 1 7. Brake engineers will be very familiar with the function of reaction disc 17.

The radially inner margin of a diaphragm support plate 23 is secured to the head by a novel arrangement, which forms no part of the present invention but which is fully described in our copending patent Application No. of even date. Briefly, the valve body 3 is provided with a portion 1 9 of generally square transverse cross-section, and the central aperture in support plate 23 is of compementary shape to enable the plate 23 during assembly to be passed forwardly over the portion 1 9 and then to be turned through 45 to bring the plate 23 to the position shown.

An elongate key plate 20 is received in an inclined, generally transversely extending bore 21 in valve body 3, and has a bifurcated inner end 22 which is located in position by a step 23 formed in the rear end of ring 1 8.

The bifurcated end 22 embraces a reduced diameter portion 24 of the valve control member 11 and determines the retracted position of valve control member 24 by engagement with a head 25 of the valve control member 11. The radially outer end 26 of the key plate 20 is received withing a recess defined in the inner margin of plate 23 so as to lock the plate 23 against rotation relative to the valve body 11.

As is conventional, the rear end of the valve control member 11 is formed with a first annular valve seat 27, and a co-axial second annular valve seat 28 is formed on valve body 3 at the step between bore portions 9 and 10.

A poppet valve member 29 comprises an annular valve head 30 for engagement with seats 27 and 28 and connected by an axially flexible portion 31 to a skirt 32, but, as compared with conventional arrangements, the skirt 32 is not secured against movement with respect to the valve body 3 but instead is secured by means of an integral radially inwardly directed bead 33 to the front end of a sleeve 34 which is axially slidable in bore portion 9 of the valve body portion 5. Bead 33 is received within an annular trough 35 defined at the front end of sleeve 34 by radially inwardly and outwardly directed portions 36 and 39 respectively integrally connected by a cylindrical portion 38 of reduced diameter compared with the main part of sleeve 34.

In order to seal skirt 32 of the poppet valve member 29 to the valve body 3, bead 33 is provided with an integral rearwardly and radially outwardly extending sealing lip 39 in sliding sealing engagement with bore portion 9. Portion 31 of the poppet valve member 29 has sufficient inherent axial resilience that an auxiliary spring is not required to biass the valve head 30 forwardly. Valve head 30 is reinforced by a metal washer 40.

Input rod 1 2 is connected to sleeve 34 by means of a part-spherical thrust coupling 41 to permit some pivotal movement of rod 1 2 about the centre of ball 13, the thrust coupling 41 comprising a domed thrust washer 42 abutting against the rear of sleeve portion 36 and a substantially cylindrical block 43 mounted on the input rod 1 2 and backed by a circlip 44 secured in an annular recess 45 in rod 12, the mutually engaging surfaces of the washer 42 and block 43 being partspherical and having the centre of ball 1 3 as their centre of curvature.An axially resilient spring washer 46 acts between the rear end of valve body 3 and a radially outwardly directed flange 47 adjacent to the rear end of sleeve 34 to bias rearwardly both the sleeve 34 and thus the input rod 12, together with the valve control member 11. A coiled compression spring may be used instead of the washer 46.

The usual air filter assembly 48 is mounted in the rear end of the sleeve 34.

Valve body 3 is formed with an inclined passage 49 which, in the retracted position of the input rod shown, provides fluid communication between the front and rear chambers 50 and 51 respectively of the booster housing, by way of valve seat 28 which is spaced from valve head 30. Front chamber 50 is permanently connected to a vacuum source.

In the retracted position of the input rod the valve seat 27 is held firmly in engagement with valve head 30 by the action of spring 46 on the input rod 1 2 and valve control member 11. On initial forward movement of the input rod 1 2 from its retracted position sleeve 34, valve head 30 and valve control member 11 move forwards together, until the valve head 30 engages with valve seat 28 to cut off communication between chambers 50 and 51. On further forward movement of input rod 1 2 and sleeve 34, valve seat 27 is parted from valve head 30 which has been arrested by valve seat 28, and portion 31 becomes axially compressed. The opening of valve seat 27 allows atmospheric air to enter the rear chamber 51 through the bore of sleeve 34 to provide the necessary pressure differential between chambers 50 and 51 to boost the force applied to the output rod 15.

Although the valve assembly has been described with reference to a vacuum-servo booster, it will be appreciated that the valve assembly, and the sealing lip 39 in particular, may be modified for use in a booster operated by compressed air rather than a vacuum source.

Claims (6)

1. A servo booster of the kind set forth in which the valve means comprises a valve body connected to the movable wall and provided with an axial bore in which works a valve control member, the valve body and valve control member being provided with coaxial rearwardly facing valve seats, an annular resilient valve member carried by a sleeve slidable in the bore and located rearwardly of the control member, the valve member comprising a sealing portion at its front end adapted to engage with the valve seats and connected by an axially compressible portion to a rear portion secured to the sleeve, means sealing the sleeve to the wall of the bore rearwardly of the sealing portion of the valve member, resilient means biassing the sleeve rearwardly relative to the valve body, a pedaloperated input rod extending through the sleeve and valve member to engage with the valve control member, and means connecting the sleeve to the input rod.

2. A servo booster as claimed in Claim 1 in which the axially compressible portion of the valve member is arranged such that its resilience is sufficient not to require the incorporation of a spring biassing the sealing portion of the valve member forwards relative to the rear portion.

3. A servo booster as claimed in claim 1 or claim 2 in which the sealing means between the sleeve and said bore comprises said rear portion of the valve member which is arranged to effect a sliding seal with the bore wall.

4. A servo booster as claimed in any of the preceding claims in which the resilient means comprises a spring mounted on the sleeve and acting between the rear end of the valve body and a radially outwardly directed flange on the sleeve.

5. A servo booster as claimed in any of the preceding claims in which the connection between the sleeve and the input rod comprises a part-spherical or part-cylindrical thrust coupling to enable pivotal movement of the input rod about its connection with the valve control member.

6. A servo booster substantially as described with reference to the accompanying drawings.