GB2091828A - Brake booster - Google Patents

Abstract

A brake booster for an automotive vehicle has a low-pressure casing (1) formed by two sheet-metal casing shells (18, 19) provided with reinforcing plates (14, 15) retained axially by reinforcing depressions (20, 21 and 22, 23), or the edge (37) of shell portion (13). One shell (19) has an integrally-formed peripheral bead (24) adjoining an integrally- formed cylindrical portion (25). The latter also has reinforcing axial depressions (26) and is joined to the periphery of the other shell (18) so as to trap between them the beaded rim (30) of the rolling diaphragm (6). <IMAGE>

Description

SPECIFICATION Brake booster This invention relates to brake boosters and in particular to a low-pressure casing for a brake booster for an automotive vehicle, of the kind comprising two sheet-metal casing shells which are sealingly interconnected and which each include a casing end wall having an abutting reinforcement plate at its inner side.

In low-pressure brake boosters for automotive vehicles, the master brake cylinder is customarily fitted to one casing end wall of the low-pressure casing, while the other casing end wall is fastened to the automotive vehicle, preferably to the splashboard or bulkhead. The brake forces which are transmitted onto the actuating pistons of the master brake cylinder when braking will have to be retransmitted as reaction forces from the master brake cyclinder onto the point where the brake booster is fastened to the automotive vehicle. Taking into consideration that these comparatively high tension forces are transmitted via the low-pressure casing, the low-pressure casing has so far been designed with comparatively thick walls, although this is in antipathy to a generally desired reduction of the brake booster's weight.

A substantial reduction in weight by a thinwalled low-pressure casing design may be achieved in that the tension forces are transmitted via separate tie elements, for instance, tie bolts (German printed and published patent application DE-OS 28 45 794) or via a central reinforcement tube which interconnects the two casing end walls (German printed and published patent application DE-OS 28 37 911). In either case, the sealing of the axially movable wall, the points where these tie elements extend through, necessitates additional structural arrangements and represents a possible source of failure.

To avoid taking up the usable casing interior by force-transmitting elements, such as tie bolts or a central reinforcement tube, and yet to provide a thin-walled and therefore light-weight design of the casing, it has already been proposed (patent application P 30 31 206.2) to arrange at the inner sides of each of the two casing end walls a central ring flange serving as a reinforcement plate, which ring flange is connected to the master brake cylinder or to the automotive vehicle, with at least that portion of each casing end wall which lies radially outside the reinforcement plate being shaped as a truncated cone and with a reinforcing ring being inserted in each case at the circumferential edge of the casing at the transition to a cylindrical casing section. The reinforcing ring is a component which has to be fitted separately.

It is, therefore, an object of the present invention to improve a low-pressure casing of the kind initially referred to in such a manner that, beside a thinwalled, and for this reason light-weight, design of the low-pressure casing, there is ensured a sufficient amount of rigidity to transmit the forces occurring, while it is desired to transmit not only tension forces, but also pressure forces via the thin-walled lowpressure casing and onto the reinforcement plates.

According to the invention in its broadest aspect, a low-pressure casing for a brake booster for an automotive vehicle is characterised in that reinforcement depressions are arranged in the area of the casing shell lying outside the reinforcement plate, which depressions at least partly bear axially against the outer edge of the reinforcement plate. These depressions not only provide the low-pressure casing of thin-walled design with sufficient rigidity to transmit the tension forces occurring, but also to transmit the pressure force acting in an axial direction, this pressure force resulting from the low pressure taking effect in the casing interior.

It is provided in an advantageous embodiment of the idea of the present invention, that that portion of the casing sheel which lies radially outside the reinforcement plate is of truncated-cone-shaped design and includes depressions extending in the direction of the cone's surface line, that a substantially cylindrical circumferential section of the casing is adjacent to the truncated-cone-shaped casing shell portion and that the sheet metal of the casing shell is folded to form a circumferential doubled sheet-metal bead at the transition from the truncated-cone-shaped casing shell portion to the cylindrical circumferential section of the casing. At the transition from the section of the casing.At the transition from the truncated-cone-shaped portion into the cylindrical circumferential section of the casing, this sheet-metal bead forms a circumferential supporting rib which latter renders it possible without the employment of an additional reinforcing ring or the like to direct forces occurring in the neighbouring casing shell portions, in particular tension forces and pressure forces, in each case into the adjacent casing sheel portion. Also in this arrangement, the forces which are transmitted by the depressions will be transmitted into the circumferential sheet-metal bead. Manufacture is compara tivelysimple, in particular when using thin sheetmetal, because only drawing or folding processes will then take place.

To increase the strength of the sheet-metal bead, in particular for the transmission of tension forces which try to unfold the sheet-metal bead, the edges of the circumferential, doubled sheet-metal bead may be welded together. Suitably, the circumferential sheet-metal bead is formed integrally with the casing shell and folded. However, it is also possible for the circumferential sheet-metal bead to include two flanges of the truncated-cone-shaped casing sheel portion and of the cylindrical circumferential section, which flanges abut each other and are connected to each other. When the casing shell is of this bipartite design, a reduced deformation of the two parts will be required.

An embodiment has proved to be particularly favourable with respect to the transmission of forces, wherein the reinforcement depression of the truncated-cone-shaped casing shell portion and/or of the cylindrical circumferential section of the casing extend into the circumferential sheet-metal bead.

If the reinforcement depressions are placed at the casing's exterior, the casing interior will remain completely unimpaired; in this case, there will be provided at least one depression projecting from the casing's inner side and are directly supported on the edge of the reinforcement plate in order to retain the reinforcement plate in the casing shell and to transmit pressure forces occurring. However, if the reinforcement depressions are disposed at the casing's inner side, there is no need for this additional, inwardly projecting depression; the reinforcement depressions will then be directly supported on the edge of the reinforcement plate.

The reinforcement plate may extend up to the cylindrical circumferential section of the casing and a reinforcement depression which projects inwardly from the cylindrical circumferential section will then bear axially against the edge of the reinforcement plate. A direct transmission of the pressure forces will thereby be obtained, without burdening the thin-walled casing shell. The tension forces occurring will be transmitted directly from the edge of the reinforcement plate into the cylindrical circumferential section of the casing, which latter does not permit of any appreciable amount of expansion, not even in the case of a very thin-walled design.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a partial longitudinal sectional view of a low-pressure casing of a brake booster and Figure 2 to 9 are partial sectional views of varied embodiments of the low-pressure casing.

The brake booster shown in Figure 1 includes a low-pressure casing 1 which is subdivided into a working chamber 3 and a low-pressure chamber 4 by an axially movable wall 2. The axially movable wall 2 is composed of a sheet-metal deep-drawn diaphragm plate 5 and a flexible diaphragm 6 abutting thereon and forming a rolling diaphragm 7 as a seal between the outer circumference of the diaphragm plate 5 and the low-pressure casing 1.

A control valve 9 which is actuatable by a piston rod 8 and is arranged concealed in the low-pressure casing 1 in Figure 1 communicates with the diaphragm plate 5 and transmits, when actuated, the boosting force generated by the diaphragm plate 5 via a push rod 10 onto a master brake cylinder (not shown) fitted to the low-pressure casing 1. A com pression spring 11 maintains the diaphragm plate 5 in its initial position.

The low-pressure casing 1 comprises two casing shells 12, 13 deep-drawn from comparatively thin sheet metal and each having a circle-shaped reinforcement plate 14 or 15 abutting at their inner side.

The reinforcement plate 14 is fastened to the splash board or bulkhead (not shown) of the automotive vehicle through fastening screws 16. The opposite reinforcement plate 15 is fastened to the master brake cylinder through fastening screws 17.

In the embodiment shown in Figure 1,there is placed radially outside the reinforcement plate 14,15 a truncated-cone-shaped casing shell portion 18, 19 which has at its outer side reinforcement depress ions 20, 21 extending in the direction of the cone's surface lines.

Inwardly projecting depressions 22, 23 which are either of circumferential design or subdivided into sections placed between the depressions 20, 21 bear axially and radially against the edge of the reinforcement plates 14, 15.

In the case of the one casing shell 13, the truncated-cone-shaped casing shell portion 19 runs into a circumferential sheet-metal bead 24 which is formed as a doubled sheet-metal fold, and the sheet-metal parts which lie on one another may be interconnected by spot welding or roller welding.

Subsequent to the sheet-metal bead 24 is formed integrally therewith a substantially cylindrical circumferential section of the casing 25 which has at its outer side several paraxial reinforcement depressions 26 and which merges into a flange ring 27. The flange ring 27 is part of a curl-up orfolding engagement 28 which is established at the edge of the other casing shell 12. Provided in the area ofthis engagement is a circumferential groove 29 in which is inserted a beaded rim 30 of the rolling diaphragm.

The reinforcement plates 14, 15 consist, for example, of steel or of light metal.

The embodiment shown in Figure 2 differs from the embodiment according to Figure 1 only in that, also at the casing shell 12, close to the pedal, there is provided a cylindrical circumferential section of the casing 31 with paraxially extending outward reinforcement depressions 32, the casing section 31 corresponding basically to the cylindrical circumferential section of the casing 25 of the other casing shell 13 with its depressions 26. In this arrangement, likewise the casing shell 12 includes at the transition from the truncated-cone-shaped portion 18 to the cylindrical circumferential section 31 a circumferential doubled sheet-metal bead 33. Moreover, in this figure as well as in the following figures, like parts have been assigned like reference numerals as in Figure 1.

In contrast to the embodiments according to Figure 1 and 2, in the case of the embodiment according to Figure 3, the depressions 21 and 26 are arranged at the casing's inner side. There is no need for a separate, inwardly projecting depression which would correspond to the depression 23; the depressions 21 of the truncated-cone-shaped casing shell portion 19 bear at their inner end against the edge of the reinforcement plate 15.

In the embodiments according to Figures 4 and 5, the reinforcement plate 15 extends in each case up to the cylindrical circumferential section 25. As shown in Figure 4, this cylindrical circumferential section 25 may include separate indentations or a circumferential depression 34 by which the edge of the reinforcement plate 15 is held. Instead of this, it is also possible to support the inwardly disposed, paraxial depressions 26 of the cylindrical circumferential section 25 axially at the edge of the reinforcement plate 15, as shown in Figure 5.

In the embodiments according to Figure 6 to 9, the casing shell 13 is of bipartite design. The other casing shell 12 (not shown in these drawings) may be designed accordingly. In all the embodiments shown, the casing shell 13 comprises a casing end wall 35 and a circumferential wall of the casing 36 which forms the cylindrical circumferential section of the casing 25. The reinforcement plate 15 extends to the casing periphery in Figure 6 and 7. A marginal flange 37 connected to the casing end wall 35 extends over the edge of the reinforcement plate 15 there. In the embodiment according to Figure 6, the marginal flange 37 is connected to a flange 38 of the circumferential wall of the casing 36 by virtue of a folded edge 39. Awelding connection is established between the marginal flange 37 and the flange 38 of the circumferential wall 36 in the embodiment according to Figure 7. In both cases, the inward depression 26 of the circumferential wall of the casing 36 bears agaist the flange 38.

The fixing of the edge of the reinforcement plate 15 by virtue of an inwardly projecting depression 23 in the embodiments according to Figures 8 and 9 corresponds to the design according to Figures 1 and 2, and the same applies to the arrangement of an outward depression 21 at the truncated-cone- shaped casing shell portion 19. The end wall has an outwardly projecting marginal flange 40 in this arrangement which is connected to a likewise outwardly-protruding flange 41 of the circumferential wall 36, that is to say, either by welding (Figure 8) or by folding of a flanged edge 42 (Figure 9).

Claims (10)

1. A low-pressure casing for a brake booster for an automotive vehicle, of the kind comprising two sheet-metal casing shells which are sealingly interconnected, which each include a casing end wall having an abutting reinforcement plate at its inner side, characterised in that reinforcement depressions (20,21,22,23,26) are arranged in the area of the casing shell (12, 13) lying outside the reinforcement plate (14, 15), which depressions at least partly bear axially against the outer edge of the reinforcement plate (14,15).

2. A low-pressure casing as claimed in claim 1, characterised in that the portion (18, 19) of the casing shell (12,13) lying radially outside the reinforcement plate (14,15) is of truncated-cone-shaped design and includes depressions (20, 21) extending in the direction of the cone's surface lines, in that a substantially cylindrical circumferential section of the casing (25, 31) is adjacent to the truncated-cone-shaped casing shell portion (18, 19) and in that the sheet metal of the casing shell (12,13) is folded to form a circumferential, doubled sheet-metal bead (24, 33, 37, 38, 40, 41) at the transition from the truncated-coneshaped casing shell portion (18, 19) to the cylindrical circumferential section of the casing (25,31).

3. A low-pressure casing as claimed in claim 2, characterised in that the edges of the circumferential, doubled sheet-metal bead (24, 33, 37, 38,40, 41) are welded together.

4. A low-pressure casing as claimed in claim 2, characterised in that the circumferential sheet-metal bead (24, 33) is formed integrally with the casing shell and folded.

5. A low-pressure casing as claimed in claim 2, characterised in that the circumferential sheet-metal bead includes two flanges (37, 38,40, 41) of the truncated-cone-shaped casing shell portion (18, 19) and of the cylindrical circumferential section of the casing (25) which flanges abut each other and are connected to each other.

6. A low-pressure casing as claimed in claim 2, characterised in that the reinforcement depressions (20,21,26,32) of the truncated-cone-shaped casing shell portion (18, 19) and/or of the cylindrical circumferential section of the casing (25) extend into the circumferential sheet-metal bead (24, 33).

7. A low-pressure casing as claimed in claim 1, characterised in that the reinforcement depressions (20, 21) are placed at the casing's exterior and in that at least one depression (22, 23, 34) projecting from the casing's inner side takes support on the edge of the reinforcement plate (14, 15).

8. A low-pressure casing as claimed in claim 1, characterised in that the reinforcement depressions (21,26) are disposed at the casing's inner side and are directly supported on the edge of the reinforcement plate (14,15).

9. A low-pressure casing as claimed in claim 1, characterised in that the reinforcement plate (14, 15) extends up to the cylindrical circumferential section of the casing (25) and in that a reinforcement depression (26, 34) which projects inwardly from the cylindrical circumferential section of the casing (25) bears axially against the edge of the reinforcement plate (14,15).

10. A low-pressure casing for a brake booster for an automotive vehicle substantially as described with reference to the accompanying drawings.