GB2166840A

GB2166840A - A diaphragm disc for a vacuum brake power amplifier

Info

Publication number: GB2166840A
Application number: GB08526713A
Authority: GB
Inventors: Rudiger Eckhart
Original assignee: FAG Kugelfischer Georg Schaefer KGaA; Kugelfischer Georg Schaefer and Co
Current assignee: IHO Holding GmbH and Co KG
Priority date: 1984-10-31
Filing date: 1985-10-30
Publication date: 1986-05-14
Also published as: DE3439734A1; GB8526713D0; FR2572346A1

Abstract

The disc has a cylindrical centring portion (9) and, extending outwardly therefrom, an angularly bent collar (13 or 13a). The collar (13 or 13a) has an inner cone section (10 or 10a) and an outer cone section (11 or 11a) which are 12 mutually axially oppositely directed. The imaginary apex (AA) of the inner cone section (10a) may be disposed, when the disc is in place in an amplifier, on the amplifier's side (I) which is subject to a relatively low pressure, or the imaginary apex (AA) may be disposed on the side which is subject to a relatively high pressure. The shape of the disc is to obtain, with a reduced use of material, high strength factors. <IMAGE>

Description

SPECIFICATION A diaphragm disc for a vacuum brake power amplifier This invention relates to a diaphragm disc for a vacuum brake power amplifier, for example a brake power amplifier of the kind used in a hydraulic brake of a motor vehicle.

Differently shaped diaphragm discs for vacuum brake power amplifiers are described, for example, in German Patent Applications Nos. OS 30 31 206 and OS 31 08 291. The portions of the discs which are subject to the highest stress-that is to say the areas of transition from a cylindrical centring portion to a pressure surface of the disc which is generally perpendicular to the centring portion-have hitherto been curvedly constructed so as to ensure sufficiently high fatigue strength of the diaphragm disc, the curves having more or less large radii capable of suitably resisting the bending stress which occurs under load application. Thus, it has been necessary, owing to the bending moment incurred, to construct the diaphragm discs of a thicker and hence heavier material than that called for by the prevailing primary tensile stresses.

It is an aim of the invention to provide a diaphragm disc of low weight yet capable of meeting all requirements of static and dynamic strength.

With this aim in view, the present invention is directed, according to one of its aspects, to a diaphragm disc for a vacuum brake power amplifier, having a cylindrical centring portion and, extending outwardly therefrom, an angularly bent collar, in which the collar has an inner cone section and an outer cone section which are mutually axially oppositely directed and which are constructed so that the imaginary apex of the inner cone section is disposed, when the disc is in place in an amplifier, on the amplifier's side which is subject to a relatively high pressure, and the imaginary apex of the outer cone section is disposed on the side which is subject to a relatively low pressure.

According to a second aspect of the present invention, there is provided a diaphragm disc for a vacuum brake power amplifier, having a cylindrical centring portion and, extending inwardly therefrom, an angularly bent collar, in which the collar has an inner cone section and an outer cone section which are mutually axially oppositely directed and which are constructed so that the imaginary apex of the inner cone section is disposed, when the disc is in place in an amplifier, on the ampiifier's side which is subject to a relatively low pressure, and the imaginary apex of the outer cone section is disposed on the side which is subject to a relative high pressure.

In one preferred embodiment of the present invention, the crest of the angularly bent collar protrudes, in an axial direction towards what, in the assembled amplifier, is the chamber of relatively low pressure, beyond a flanged edge portion of the disc.

In another preferred embodiment of the present invention a flanged edge portion of the disc is positioned beyond the crest of the angularly bent collar in an axial direction towards what, in the assembled amplifier, is the chamber of relatively low pressure.

Examples of diaphragm discs made in accordance with the present invention are illustrated in the accompanying drawings, in which: Figure 1 is a diagrammatic half-axial sectional view of a vacuum brake power amplifier; Figure 2 is an axial sectional view of a diaphragm disc of the vacuum brake power amplifier shown in Fig. 1; and Figure 3 is an axial sectional view of a modified form of diaphragm disc.

With reference to Fig. 1, a diaphragm disc 1 is slidingly arranged in a casing made up of two sealingly joined casing dishes 2 and 3.

The casing is constructed to maintain a subatmospheric pressure within its interior when the amplifier is in use. A diaphragm 4 conforms to and is in sealing engagement with the diaphragm disc 1, thereby dividing the casing into a sub-atmospheric-pressure chamber I and a working chamber 11. A plunger 5 of the amplifier is connected to a control piston 6 against which the diaphragm disc and diaphragm are held by the pressure in the chamber II. A brake pedal 14 is in turn connected to the plunger 5 so that depression of that pedal moves the plunger 5, and hence the piston 6, in an inward direction relative to the power amplifier.As this happens, outside air streams into the working chamber Il so that, owing to the pressure difference between the chamber I in which a vacuum prevails and the working chamber II, the diaphragm disc 1 is slidingly moved against the bias of a spring 7 towards the base of the chamber and actuates, via a piston rod 8, the piston or pistons of the main brake cylinder (not illustrated).

Fig. 2 illustrates the diaphragm disc on its own. It has a cylindrical centring portion 9, and extending outwardly therefrom, a first cone section 10 extending axially in one direction, and a second cone section 11 extending axially in the opposite direction. This construction is such that the point of intersection C where the conic sections meet projects in an axial direction beyond a flanged edge portion D of the disc into the sub-atmospheric-pressure chamber I. It will be seen that the imaginary apex A of the inner cone section 10 lies on the working chamber side of the disc, and the imaginary apex B of the outer cone section 11 lies on the vacuum chamber side.

The various transitions from one section of the disc to another are by way of curved por tions having deliberately small radii 12. The purpose of the small radii is, in addition to reducing the tension of the material in comparison to what it would be with larger radii, resulting from the enlargement of the surface, to avoid or at least reduce bending stresses or moments which shorten the disc's working life and which occur in the area of the smallest force-transmitting section, that is to say the area adjacent to the axis. Owing to the almost sharp-edged angles, little or no detrimental bending stresses will occur in this danger area. It may, substantially exclusively, be subject to comparatively harmless tensile stresses which, however, permit a reduction of the thickness of the material by more than a third yet which at the same time extend its working life. This has been ascertained by a number of experiments.

Fig. 3 illustrates a modified construction of diaphragm disc. The same physical features are present and the same benefits are obtained, but in this instance the collar 13a projects away from the vacuum chamber I, so that the collar 13a has an inverse arrangement. In this modification, it will be seen that the imaginary apex AA of the inner cone section 10a lies on the vacuum chamber side of the disc and the imaginary apex BB of the outer cone section BB lies on the working chamber side. Also, the flanged edge portion D is positioned beyond the crest of the angularly bent collar 13a in a direction towards the vacuum chamber side.

Claims

1. A diaphragm disc for a vacuum brake power amplifier, having a cylindrical centring portion and, extending outwardly therefrom, an angularly bent collar in which the collar has an inner cone section and an outer cone section which are mutually axially oppositely directed and which are constructed so that the imaginary apex of the inner cone section is disposed, when the disc is in place in an amplifier, on the amplifier's side which is subject to a relatively high pressure, and the imaginary apex of the outer cone section is disposed on the side which is subject to a relatively low pressure.

2. A diaphragm disc for a vaccum brake power amplifier, having a cylindrical centring portion and, extending inwardly therefrom, an angularly bent collar in which the collar has an inner cone section and an outer cone section which are mutually axially oppositely directed and which are constructed so that the imaginary apex of the inner cone section is disposed, when the disc is in place in an amplifier, on the amplifier's side which is subject to a relatively low pressure, and the imaginary apex of the outer cone section is disposed on the side which is subject to a relatively high pressure.

3. A diaphragm disc for a vacuum brake power amplifier according to claim 1 or claim 2, in which the crest of the angularly bent collar protrudes, in an axial direction towards what, in the assembled amplifier, is the chamber of relatively low pressure, beyond a flanged edge portion of the disc.

4. A diaphragm disc for a vacuum brake power amplifier according to claim 1 or claim 2, in which a flanged edge portion of the disc is positioned beyond the crest of the angularly bent collar in an axial direction towards what, in the assembled amplifier, is the chamber of relatively low pressure.

5. A diaphragm disc for a vacuum brake power amplifier, substantially as described herein with reference to Fig. 2 or Fig. 3 of the accompanying drawings.

6. A vacuum brake power amplifier having a diaphragm disc as claimed in any preceding claim.

7. A vacuum brake power amplifier substantially as described herein with reference to Figs. 1 and 2 of the accompanying drawings, with or without the modification shown in Fig.