GB2085105A

GB2085105A - Brake booster

Info

Publication number: GB2085105A
Application number: GB8129472A
Authority: GB
Original assignee: Aisin Seiki Co Ltd
Current assignee: Aisin Corp
Priority date: 1980-10-01
Filing date: 1981-09-30
Publication date: 1982-04-21
Also published as: DE3139158A1; JPS6021328Y2; GB2085105B; FR2491022A1; FR2491022B1; JPS5763769U

Abstract

A reinforcement member 3 which is spot-welded (at D) to the wall 2a of a booster housing 2 between each two adjacent bolts 4 by which it is connectable to a brake master cylinder is further spot-welded (at E) in the portions radially outwardly of the bolts. Three angularly equispaced bolts 4 are preferably used, with two spot welds between each two adjacent bolts and two spot welds radially outwardly of each bolt. <IMAGE>

Description

SPECIFICATION Brake booster mountings The invention relates to a vehicle brake system having a power multiplying booster device, and more particularly to a reinforcement structure for booster housings in such brake system.

In a vehicle brake system having a power multiplying booster device, the booster device generally has a booster housing which is adapted to be mounted on a master cylinder body. In the booster housing, there is provided a diaphragm or a piston which defines a vacuum or suction pressure chamber at the side adjacent to the master cylinder body and an atmospheric pressure chamber at the other side. The diaphragm or piston is displaced under the pressure difference between the suction pressure chamber and the atmospheric pressure chamber towards the brake master cylinder, and functions to force the master piston in the master cylinder. The booster housing is thus subjected to a suction pressure at the side adjacent to the master cylinder.Further, the booster housing is also subjected to a load which is applied from the brake pedal so that a significant level of stress is produced in the booster housing in the area where the booster housing is attached to the master cylinder.

Conventionally, the booster housing has been provided, at the inner surface of the wall which is attached to the master cylinder body, with a reinforcement plate so that the housing is given with a sufficient strength without using a thicker material. The reinforcement plate is spot welded to the booster housing wall which is attached together with the reinforcement plate to the master cylinder body by bolts. In conventional booster housing structure, three bolts are used for this purpose at circumferentially equi-distant positions and the spot weldings are made between each two adjacent bolts. In this conventional structure, however, problems have been experienced in that stress concentrations are produced in the vicinity of the bolts and result in fatigue failures through prolonged use of the device.

The invention provided a brake force multiplying booster device for mounting on a brake master cylinder body, the device having a housing including an attachment wall the outer surface of which is to abut the brake master cylinder body and the inner surface of which is provided with a reinforcement member, and a plurality of bolts for connecting the attachment wall and the reinforcement member to the master cylinder body, the reinforcement member being spot-welded to the attachment wall between each two adjacent bolts, and further spot welded to the attachment wall at the portions radially outwardly of the bolts.

In the booster device of the invention, since the reinforcement member is spot-welded to the attachment wall of the housing at radially outwarc portions of the installation bolts, it is possible to avoid stress concentrations in the vicinity of the bolts. Thus the life of the booster housing can be increased without increasing the thickness of the housing material.

The invention is illustrated by the drawings, of which: Figure 1 is a view of a reinforcement member attached to a brake booster housing in a conventional manner; Figure 2 is a partially cut-away side view of a brake booster having a housing provided with a reinforcement member attached thereto; Figure 3 is a view similar to Figure 1 but showing the reinforcement member attached in accordance with the invention; and Figure 4 is a chart showing the advantageous results obtainable with the invention.

With reference to Figures 1 and 2 of the drawings, a brake master cylinder 1 of conventional construction has a booster attachment flange 1 a. A brake force multiplying booster B includes a housing 2 having an annular wall 2a, the outer surface of which is attached to the flange 1 a. An annular reinforement member 3 is attached to the inner surface of the wall 2a. The booster housing 2 is installed on the flange 1 a of the brake master cylinder body 1 by three bolts 4.

As shown in Figure 1, the bolts 4 are located at 1 20O angular intervals. Further the bolts 4 have heads 4a secured to the reinforcement member 3 such as by welding and are inserted through the reinforcement member 3 and the annular wall 2a of the housing 2 to project from the housing 2.

The bolts 4 are inserted through the bolt holes in the flange 1 a and engaged with nuts 5. In the housing 2, there is defined a suction pressure chamber C where a suction pressure is introduced in operation.

As shown in Figure 1, the reinforcement member 3 is attached to the wall 2a of the booster housing 2 by spot welds. As shown by reference characters D in Figure 1, such spot-welds are made usually at two points between each two adjacent bolts 4. In the known structure, however, experiences have shown that stress concentrations are produced in the booster housing 2 in the portions radially outwardly of the bolts 4 as shown by reference characters A in Figure 2.

Figure 3 shows an example of the spot-welds in accordance with the invention. It will be noted that the reinforcement member 3 is welded not only between each two adjacent bolts 4 as shown by references D but also in the portions radially outwardly of the bolts 4 as shown by reference characters E. According to this structure, it has been found that stress concentrations in the booster housing 2 in the area shown by the references A in Figure 2 can be significantly decreased. As the result, it is possible to obtain an increased fatigue life.

Figure 4 shows a change of stress level in a conventional structure under various output load of the brake booster as well as that in the embodiment of the invention. As shown in Figure 4, in the conventional structure, the stress level in the'booster housing increased rapidly as the booster output increases beyond a certain value.

However, in the embodiment of the invention, the increase in the stress level stays moderate. With the booster output of 300 kg, the measured stress in the booster housing was 67.2 kg/mm2 in the conventional structure, whereas the comparative stress level was only 29.4 kg/mm2 in the embodiment of the invention.

Claims

1. A brake force multiplying booster device for mounting on a brake master cylinder body, the device having a housing including an attachment wall the outer surface of which is to abut the brake master cylinder body and the inner surface of which is provided with a reinforcement member, and a plurality of bolts for connecting the attachment wall and the reinforcement member to the master cylinder body, the reinforcement member being spot-welded to the attachment wall between each two adjacent bolts, and further stop-welded to the attachment wall at the portions radially outwardly of the bolts.

2. A brake force multiplying booster device according to claim 1 in which the reinforcement member and attachment wall are connected to the brake master cylinder body by three angularly equispaced bolts, spot-welding between the reinforcement member and the attachment wall being made at two places between each two adjacent bolts and at two places radially outwardly of each bolt.

3. A brake force multiplying booster device substantially as described herein with reference to Figure 3 of the drawings.