GB2066395A - Boosted master cylinder assemblies for vehicle braking systems - Google Patents

Abstract

A master cylinder housing (2, 3, 4) extends integrally through the movable wall (43, 44) of a booster assembly to a master cylinder mounting flange (5) provided with studs (100) for direct connection to a vehicle bulkhead (100'). The master cylinder housing consists of a housing body in which work the master cylinder pistons (22), (34 not shown), a tubular portion (4) to which the movable wall is sealed by an annular seal (48), and a pair of diametrically opposed webs (3) which integrally connect the body and tubular portion. The booster movable wall is connected to the booster output member (22) by a cup-shaped member (65) provided with arms (68) which extend through apertures defined circumferentially between the webs (3). <IMAGE>

Description

SPECIFICATION Boosted master cylinder assemblies for vehicle braking systems This invention relates to boosted master cylinder assemblies for vehicle braking systems of the kind comprising a master cyclinder housing provided with a bore in which works a master cylinder piston, a booster housing, a movable wall dividing the interior of the booster housing into two chambers, a servo valve assembly controlling the pressure differential of the two chambers, and means for conveying force from the movable wall to the master cylinder piston.

For many years it has been conventional practice to provide the booster housing with studs at its rear end for connection to a vehicle bulkhead and with studs at its front end which were connected to a flange provided at the rear end of the master cylinder housing. It was therefore necessary to make the booster housing sufficiently strong to support the master cylinder and to convey braking reaction forces between the master cylinder housing and the vehicle bulkhead.

In the published British Application No. 2009871 A of our subsidiary Girling Limited it has been proposed to provide a booster with a force transmitting means which extends sealably through the movable wall of the booster for conveying braking reaction forces from the master cylinder housing to the vehicle bulkhead, in order to enable the booster housing to be made light in weight.

According to the present invention, in a boosted master cylinder assembly of the kind set forth an integral part of the master cylinder housing extends through said movable wall and is provided at its rear end with fastening means for securing the master cylinder housing to a vehicle bulkhead.

Thus the master cylinder housing is formed integrally with a force transmitting member.

Preferably sealing means is provided to seal the movable wall directly or indirectly to the master cylinder housing, but if desired the movable wall may be sealed to the rear wall of the booster housing.

In published British Application No. 2031086A of Lucas Industries Limited is disclosed a booster provided with a force transmitting means in the form of a tube coaxial with input and output members of the booster. In the particular constructions of booster described in that application the front end of the tube is adapted to be connected by means of studs to the flange provided at the rear end of a master cylinder housing.

The integral force transmitting member of the present invention may comprise one or more tie rods, or a tube, or other suitable member integral with the remainder of the master cylinder housing.

According to a preferable feature of the present invention the master cylinder housing comprises a master cylinder body provided with said bore, and a tubular portion integrally connected to the body by a web, said means for conveying force comprises an arm extending through an aperture defined in the housing adjacent to the web, and the movable wall is sealed directly or indirectly to the tubular portion by an annular seal encircling the tubular portion.

There are preferably two diametrically opposed webs, although three or more might be used.

The annular seal preferably engages directly with the tubular portion.

Preferably the arm comprises a portion of the sidewall of a substantially cylindrical member of which the rear end is adapted to apply in use said force to the master cylinder piston.

The rear end of the cylindrical member may be secured to the valve body, or it may only abut the valve body.

The cylindrical member is preferably substantially cup-shaped, the base of the cup being towards the rear of the assembly.

Preferably the internal diameter of the tubular portion is of greater diameter than the external diameter of the rear end of the master cylinder body, and the sidewall of the cup-shaped member has intermediate diametral dimensions to enable the sidewall to be located substantially within the tubular portion and to move forwards over the rear end of the body.

Preferably the rear end of the master cylinder housing comprises an integral radially extending flange and the fastening means comprises fastening elements connected directly to the flange.

When there is a plurality of webs, a corresponding number of fastening elements is preferably provided, and the fastening elements are arranged in the radial planes of symmetry of the respective webs.

Preferably the rear wall of the booster housing abuts with the rearwardly facing face of the master cylinder flange, and when the fastening elements are studs they preferably pass through the rear wall.

In the description and claims the rear end of the assembly is to be taken to mean that end adjacent to the input member.

A boosted master cylinder assembly in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a partially sectioned side elevation of the assembly, the section being taken in the vertical plane; Figure 2 is a section of a detail on a larger scale than that of Figure 1 and taken on a plane which includes the master cylinder axis but is inclined at 450 to the vertical, the plane being indicated by the chain-dotted line in Figure 4; Figure 3 is a section on the line 3-3 of Figure 1 but with sleeve 49 removed; and Figure 4 is a rear view of the master cylinder housing of the assembly of Figure 1.

With reference to Figures 1 and 2 the boosted master cylinder assembly comprises an alloy, cast and machined master cylinder housing 1 comprising a body 2 integrally connected by a pair of diametrically opposed webs 3 to a coaxial tubular portion 4 provided at its rear end with a radially extending mounting flange 5, and front and rear booster housing shells 6 and 7 constituting a booster housing which is partitioned into annular front and rear booster chambers 8 and 9 by an annular movable wall 10.The front booster housing shell 6 is provided at its radially inner extremity with a forwardly directed flange 11 which is sealed to the external surface of the master cylinder body 2 by an annular resilient seal 12 located in an external annular recess 13 in the edge of a radial flange 14 provided on the body 2 rearwardly of an enlargement 15 provided with two identical, axially spaced sockets 1 6 and 1 7 which are adapted in known manner to receive respective connections from the outlets of a tandem fluid reservoir, not shown.

Master cylinder body 2 is provided with a stepped bore 18 comprising a portion 19 of smallest diameter connected by a portion 20 of intermediate diameter to a largest diameter portion 21 adjacent to the rear end of the body 2.

A primary piston 22 projects rearwardly from the body 2 in its retracted position, as shown in Figure 1, and is sealed to the wails of bore portions 20 and 21 respectively by an annular seal 23 carried by the piston and by a fixed annular seal 24 held against a washer 25 located at the step between bore portion 20 and 21 by an annular spacer 26 retained by a circlip 27 fitted in a internal annular recess formed in body 2. The seal 23 is backed by an apertured radial flange 28 on the primary piston which abuts with the washer 25 to determine the retracted position of the primary piston. The step against which the washer 25 abuts is provided with radially directed grooves to provide fluid communication between the annular space 29 defined in front of seal 24 and a substantially axially extending passage 30 which communicates at its front end with socket 17.A recuperation port 31 for primary pressure space 32 of the master cylinder is provided by a radial drilling which intersects passage 30 and is closed off at its outer end by a ball 33.

Primary piston 22 is connected in known manner to a secondary piston 34 by a lost-motion connection 35, and the secondary piston 24 is sealed to the wall of bore portion 19 by three axially spaced seals 36, 37 and 38 carried by the piston. A recuperation port 39 for the secondary pressure space 40 defined in front of seal 36 is provided by a radial drilling from the base of front socket 16. Lost motion connection 35 is biassed to its fully extended condition by a relatively strong coiled compression spring 41 acting between the pistons 22 and 34, and the pistons are biassed to their retracted positions by a less strong spring 42 acting rearwardly on secondary piston 34.

The booster movable wall 10 comprises a diaphragm support plate assembly 43 which supports an elastomeric diaphragm 44 provided at its radially outer periphery with an annular bead 45 clamped between the radially outer peripheries 46 and 47 of the shells 6 and 7 respectively, and at its radially inner periphery with an annular bead 48 received in an external annular recess in tubular portion 4. Diaphragm support plate assembly 43 comprises two identical moulded plastics segments which abut each other on a plane which includes the axis of the master cylinder and is indicated as the line A-A in Figure 3. If desired, the diaphragm support plate assembly 43 could be formed from two or more segments of different sizes. The segments are held in the assembled condition by ultrasonic welding and by a metal sleeve 49.Alternatively, the segments may be adhesively connected together, or they may be connected by a snap engagement with one another. In another embodiment the assembly 43 is a single moulding. The metal sleeve 49 is provided at its rear end with a radially outwardly directed flange 50 which forms an abutment for the rear end of a coiled compression spring 51 biassing the movable wall to a retracted position in which circumferentially spaced projections 52 on the rear of the diaphragm 44 engage with the rear booster housing shell 7.

Sleeve 49 fits over a forwardly projecting tubular part 53 of the diaphragm support assembly 43 which is coaxial with and spaced radially outwardly from the outer surface of the tubular portion 4, and a rolling diaphragm portion 54 of the diaphragm 44 rolls from the internal surface of the tubular part 53 to the external surface of the tubular portion 4 on forward movement of the movable wall 10.

The diaphragm support assembly 43 comprises a frusto-conical rear wall 55 which is connected to the tubular part 53 by twelve equally spaced radial fins 56 which are interconnected by integral coaxial reinforcing sleeves 57 and 58.

Rear booster housing shell 7 is provided with a rearwardly directed tubular extension 59 in which is retained an annular seal assembly 60 which effects a sliding seal with a cylindrical valve body 61 which houses a substantially conventional poppet valve assembly 62 controlled by a pedal opsrated input rod 63. At its front end the valve body 61 has a threaded connection 67 with the smallest diameter portion 64 of a pressed metal cup-member 65, which comprises a body portion 66 of substantially the same length as the smallest diameter portion 64 and a pair of forwardly extending part-cylindrical side walls 68 of which the edges are defined by diametrically opposed longitudinal slots 69 which are open at their front ends.

A valve control member 70 passes through a central aperture defined by the edge of an inwardly directed radial flange 71 of portion 64 and is held captive thereto by a circlip 72. An elastomeric reaction disc 73 is arranged in wellknown manner within the bore of portion 64, sandwiched between an output washer 74 and a collar 75 surrounding the front end of valve control member 70, and output washer 74 engages with the headed rear end of a booster output rod 76 which is carried substantially within a tapered axial bore 77 in the rear of piston 22.

Cup member 65 is sealed to the front face of valve body 61 by an annular seal 78 which is sandwiched between the valve body 61 and a step 79 of cup member 65 connecting body portion 66 and portion 64, and is slidably sealed to the inner surface of tubular portion 4 by an annular seal 80 held against an abutment ring 81 by a sprung retaining ring 82, the abutment ring 81 engaging with a small step 83 formed in body portion 66 of cup member 65.

Valve body 61 is formed internally with a rearwardly facing valve seat 84, and the space 85 within the seat is connected permanently to the rear booster chamber 9 by a forwardly extending passage 86 in valve body 61, an annular space 87 defined within rear shell 7 axially between the rear of flange 5 and tubular extension 59, and a pair of diametrically opposed, radially extending recesses 88, shown in Figure 4, provided in the rear face of flange 5. Valve body 61 is provided with a further forwardly extending passage 89 which communicates at its rear end with an annular space 90 defined outwardly of valve seat 84, and at its front end with front booster chamber 8 by way of registering holes 97 provided in step 79 and washer 78, and the interior of cup body portion 66.

The manner in which the movable wall 10 is connected to the cup member 65 will now be described. At its front end tubular part 53 of the diaphragm support plate assembly 43 is provided with a substantial radially inwardly directed flange 91 which, as shown in Figure 3, is provided with two diametrically opposed cut-outs 92 each of which is defined by a pair of opposed parallel sides 93 connected by an arcuate side 94 extending circumferentially about the axis of the diaphragm support plate assembly 43. As shown in Figure 3, the transverse cross-sectional shape of the webs 3 interconnecting master cylinder body 2 and tubular portion 4 are of substantially complementary shape, aliowing for clearance, to that of the cut-outs 92.Side walls 68 of cup member 65 are received at their front ends within a bore 95 defined by the radially inner edge of flange 91 and are each provided with an arcuate, radially outwardly directed flange 96 which is received within an annular recess defined in the front face of flange 91 and is overlapped by radially inwardly directed lugs 103 depending from a flange 104 of sleeve 49, to effect a thrust connection between flange 91 and cup member 65, and thereby provide a thrust connection between movable wall 10 and valve body 61.

The mounting flange 5 provided at the rear end of the master cylinder housing comprises an annular central portion 98 from which depend diametrically opposed ears 99 through which pass studs 100 for direct connection to a vehicle bulkhead 100'. Respective annular seals 101 located in annular recesses 102 in ears 99 are provided to seal the studs 100 to the rear booster wall 7. As shown in Figure 2, the axes of the studs 7 lie in the same plane, indicated by the chaindotted line in Figure 4 and the line A-A in Figure 3, that contains the axis of the assembly and extends symmetrically through the webs 3. Thus webs 3 are in line with the studs 100 and provide a direct path for brake reaction force to be transmitted from the master cylinder body 2 to the vehicle bulkhead 100'.

In a modification, not shown the sliding seal 80 is replaced by a rolling diaphragm connected between the body 66 of cup member 65 and the rear end of tubular portion 4.

It will be appreciated that more than two webs 3 may be provided if desired.

Claims (11)

1. A boosted master cylinder assembly of the kind set forth in which an integral part of the master cylinder housing extends through the movable wall and is provided at its rear and with fastening means for securing the master cylinder housing to a vehicle bulkhead.

2. An assembly as claimed in claim 1 in which the master cylinder housing comprises a master cylinder body provided with said bore, and a tubular portion integrally connected to the body by a web, said means for conveying force comprises an arm extending through an aperture defined in the housing adjacent to the web, and the movable wall is sealed directly or indirectly to the tubular portion by an annular seal encircling the tubular portion.

3. An assembly as claimed in claim 2 in which the arm comprises a portion of the sidewall of a substantially cylindrical member of which the rear end is adapted to apply in use a force to a booster output member engageable with the master cylinder piston.

4. An assembly as claimed in claim 3 in which the cylindrical member is substantially cupshaped, the base of the cup being towards the rear of the assembly.

5. An assembly as claimed in claim 3 or claim 4 in which the rear end of the cylindrical member is secured to the valve body of the servo valve assembly, the valve body extending sealably through the rear end of the booster housing.

6. An assembly as claimed in any of claims 3 to 5 in which the internal diameter of the tubular portion is of greater diameter than the external diameter of the rear end of the master cylinder body, and the sidewall of the cylindrical member has intermediate diametral dimensions to enable the sidewall to be located substantially within the tubular portion and to move forwards at least partially over the rear end of the body.

7. An assembly as claimed in any of the preceding claims in which the rear end of the master cylinder housing comprises an integral radially extending flange, and the fastening means comprises fastening elements connected directly to the flange.

8. An assembly as claimed in claim 2, or any one of claims 3 to 7 each as appended to claim 2, in which there is a plurality of circumferentially spaced webs and a corresponding number of fastening elements which are arranged in the radial planes of symmetry of the respective webs.

9. An assembly as claimed in claim 7 or claim 8 in which the rear wall of the booster housing abuts the rearwardly facing face of the master cylinder flange.

10. As assembly as claimed in claim 9 in which the fastening elements are studs which pass through the rear wall.

11. A boosted master cylinder assembly substantially as described with reference to the accompanying drawings.