GB2034430A - Boosters for vehicle brakes - Google Patents

Abstract

In a servo booster assembly for vehicle braking systems a generally cylindrical booster housing comprises two or more identical segments 1 which are connected together along joint faces 2 which extend radially relative to the booster axis and in planes that include the booster axis. The joints may be welded, bolted or banded together. This arrangement not only makes for easier production as the casing segments are identical, but any reaction forces in operation of the booster are transmitted along the casing joint lines and not across them as in known boosters. Thus these forces do not tend to separate or distort the casing segments. The casing segments include a groove 8, for locating a flexible diaphragm (13) dividing the housing into two chambers. <IMAGE>

Description

SPECIFICATION Boosters for vehicle brakes This invention relates to servo booster assemblies for vehicle braking systems of the kind comprising a housing in which is located a movable wall providing two chambers within the housing in which a differential pressure is created for augmenting the force applied by an input member to an axially movable output member. Such booster assemblies will hereinafter be referred to as booster assemblies of the kind set forth.

The housings of such boosters conventionally comprise two dissimilar dished pressed-metal housing shells which are clamped together at their radially outer peripheries which lie in a plane extending normal to the axis of the output member. Often the movable wall comprises a diaphragm, and the radially outer periphery of the diaphragm is held between the clamped outer peripheries of the shells.

It is usual to mount a servo booster assembly in a vehicle by securing one housing shell to the vehicle bulkhead and by securing the other housing shell to the housing of a master cylinder, for example by means of studs attached to the shells. With this arrangement the boosted braking force, from a vacuum or pressure source, applied to the input member of the master cylinder is reacted back from the master cylinder housing through the housing shells to the vehicle bulkhead. Thus, in addition to the differential pressure forces applied to the shells, the shells are subjected to a substantial force acting parallel to the axis of the output member which has to be borne by the joint between the two shells.

Since servo-boosters of this kind generally have a cylindrical form, the central axis of the booster, along which the input and output forces are considered to react, is coincident and co-axial with the axis of the output member.

Furthermore, if the shells are not made of sufficient stiffness the reaction force transmitted by the shells leads to deformation of the shells which can lead to lost brake pedal input motion at high input force levels which has to be compensated for by allowing a greater pedal stroke.

According to the invention in a servo booster assembly of the kind set forth the housing comprises a plurality of segments which are adapted to be connected together along joint lines which extend in planes that include the axis of the output member.

Thus the lines of connection between the housing parts extend generally longitudinally of the booster central axis, with the advantage that the braking reaction forces are not transmitted from one segment to the other across the joints extending along those lines and there is no tendancy for the reaction forces to separate the housing parts.

The segments are preferably provided with ribs or thickened portions where they connect with adjacent segments in order to facilitate sealing of the segments to one another. Such strengthened portions of the segments will also help to resist axial deformation of the housing under the brake reaction force.

The invention has the important advantage that the housing segments may be made identical to one another leading to simplified manufacture and substantial savings in manufacturing costs whereas previously the housing shells had to be of different shapes to accommodate the input and output assemblies respectively. Also, the forces to which the housing segments are subjected in use act in directions parallel to the planes of the joint faces of the segments.

Preferably there are only two housing segments and the two joints between the segments are disposed diametrically opposite to each other with respect to the axis of the output member.

Preferably the housing segments are moulded from plastics material.

The segments may be releasably connected together with resilient seal sandwiched between adjacent edges of the segments, or if desired the segments when made of plastics material may be welded together.

One or more hoops may encircle the segments in planes transverse to the axis of the output member for reinforcement orto hold the segments releasably together. The hoop or hoops may be the sole means of holding the segments together.

It will be appreciated that the segments will be provided with suitable means for providing a fluidtight seal with the movable wall.

A preferred embodiment of the invention will now be further described, by way of example only, with reference to the accompanying drawings in which Figure 1 is a perspective view of one housing segment of a servo booster in accordance with the invention; Figure 2 is cross-section of the segment of Figure 1 taken in a vertical plane after inversion of the segment; Figure 3 is an enlarged cross-sectional view corresponding to the upper part of Figure 2 and showing one method of sealing a flexible diaphragm to the segment; and Figure 4 is a view similar to Figure 3 but of a mod ification.

With reference to Figures 1 and 2 a servo booster housing consists of two identical semi-circular moulded plastics housing segments 1 each of which is provided with a peripheral flange 2 having flat mating faces adapted to lie in face-contact with flat mating faces of the corresponding flange of the other shell segment. A gasket may be sandwiched between the mating faces 2 and the flanges may be provided at spaced points with connecting members, such as screws or bolts. Alternatively, the flanges may be welded together along their entire length. Each housing segment is provided with integral half-cylindrical front and rear portions 3 and 4 respectively extending from front and rear housing walls 5 and 6 in the same direction to receive the output and input assemblies respectively of the booster.The front and rear housing walls 5 and 6 are provided with a respective threaded metal stud 7 for connecting the housing segment to the vehicle bulkhead and the master cylinder (not shown).

A half-annular trough 8 co-axial with the axis X-X of the booster is formed in the inner face of the radially outer portion of each housing segment. The trough 8 is defined by identical opposed annular side walls 9 which are inclined symmetrically with respect to a transerve plane of the housing and such that they approach one another in the radically outward direction, and buy a half-cylindrical base 10 extending between the sidewall 9.

Two identical housing segments as shown in Figures 1 and 2 are assembled for use in a vehicle brake servo booster in which the movable wall comprises a diaphragm assembly. The troughs 8 of each segment when assembled registertoform an annular recess shaped to receive a peripheral bead on the diaphragm of the assembly.

In one arrangement of the movable wall shown in Figure 3 the diaphragm assembly comprises a diaphragm support plate 11 provided with a forwardly extending peripheral flange 12, and a flexible diaphragm 13 provided with an integrally moulded peripheral bead 14 of transverse cross-section complementary to that of the trough 8 and having moulded therein a stiff wire ring 15. The unstressed diameters of the bead 14 and ring 15 are chosen such that when the bead is compressed radially by all three inner faces 9, 10,9 defining the trough so as to effect a seal with the housing around the entire circumference of the movable wall.

The construction of Figure 4 is identical to that of Figure 3 except that the bead 14 has an open channel 16 and is adapted to wrap around a wire ring 15 which is not incorporated into the bead 14 during moulding of the bead but inserted manually during assembly of the booster.

In one modified form of booster housing according to this invention the housing comprises three identical housing segments. The segments are formed as wedge shaped portions of a generally cylindrical booster housing, each segment extending through an angle of 120" with the joint lines lying in planes extending axially of the booster housing and through the axis of the output member. Each segment includes front and rear arcuate portions forming a part of the front and rear cylindrical por tions, similarto portions 3 and 4 of the preferred embodiment. Each of the three segments have corresponding flanges which are welded together dur ing assembly.

It will be appreciated by experts in this art that during operation of boosters made in accordance with either of the above described embodiments, forces produced within the booster upon operation of the brake pedal act on the casing portions in the same direction as the path of the joint faces as opposed to the normal booster housing construction in which the forces induced by the working loads tend to separate the housing parts since they act normally to the joint faces.

Claims (13)

1. A servo booster assembly of the kind set forth in which the housing comprises a plurality of seg ments which are adapted to be connected together along joint lines which extend in planes that include the axis of the output member.

2. A servo booster assembly as claimed in Claim 1 in which the segments are provided with ribs or thickened portions where they connect with adjacent segments.

3. A servo booster assembly as claimed in Claim 1 or Claim 2 in which the segments are identical.

4. A servo booster assembly as claimed in any of the preceding claims in which there are two semicircular housing segments and two joints disposed diametrically opposite to each other with respect to the axis of the output member.

5. A booster assembly as claimed in any preceding claim in which the housing segments are moulded from plastics material.

6. A servo booster assembly as claimed in any preceding claim in which the segments are releasably connected together with a resilient seal interposed between adjacent faces of the segments.

7. A servo booster assembly as claimed in any of Claims 1 to 5 in which the segments are welded together.

8. A servo booster assembly as claimed in Claim 6 in which the segments are held together or reinforced by hoop means encircling the segments.

9. A servo booster assembly as claimed in any preceding claim in which the segments have means for providing a fluid-tight seal with the movable wall.

10. A servo booster assembly as claimed in Claim 9 in which the means comprises a recess in the inner face of each segment wall which together provide an annular recess to receive the bead of the movable wall for sealing location thereof.

11. A servo booster assembly as claimed in Claim 10 in which the movable wall is a diaphragm comprising a bead portion of resilient material having a wire ring moulded therein.

12. Aservo booster assembly as claimed in Claim 10 in which the movable wall comprises a diaphragm having a bead portion of resilient material having an open recess adapted to receive the wire ring.

13. A servo booster assembly of the kind set forth substantially as hereinbefore described with reference to the accompanying drawings.