Modular-system-optimized pneumatic brake booster

Abstract

A pneumatic brake booster having a vacuum chamber and a working chamber in a booster housing separated from one another by an elastic diaphragm. The diaphragm bears in regions against a diaphragm plate axially displaceable between a zero position and a maximum stroke. An axial spacing between the zero position and the maximum stroke defines a stroke range of the brake booster. The diaphragm has a rolling fold which, during the displacement of the diaphragm plate, rolls on a rolling region on an inner wall of the booster housing. In order to offer a solution in which it is the intention for a modular system for different stroke ranges to be formed more efficiently and for the efficiency loss to be minimized or avoided, the booster housing has, in the rolling region, a tapered, conical portion with a cone angle 8 and an axial extent >*stroke range.

Claims

1. A pneumatic brake booster having a booster housing, having at least one vacuum chamber and at least one working chamber which are provided in the booster housing and which are pneumatically separated from one another by an elastic diaphragm, wherein the diaphragm bears in regions against a substantially circular diaphragm plate which is axially displaceable in the booster housing between a zero position and a maximum stroke, wherein an axial spacing between the zero position and the maximum stroke defines a stroke range of the brake booster, wherein the diaphragm has a rolling fold which, during the displacement of the diaphragm plate, rolls on a rolling region on an inner wall of the booster housing, wherein the booster housing has, in the rolling region, a tapered, conical portion with a cone angle 8 and an axial extent >*stroke range.

2. The brake booster as claimed in claim 1, wherein a radial spacing (AM) between the diaphragm plate and the rolling region at the maximum stroke is at least a sum of twice a thickness (d) of the diaphragm in the region of the rolling fold with a specific minimum allowable flexing radius (RW) of the diaphragm; AM2d+RW.

3. The brake booster as claimed in claim 2, wherein a radial spacing (AN) between the diaphragm plate and the rolling region at the zero position is at least twice the radial spacing at maximum stroke; AN2*AM.

4. The brake booster as claimed in claim 1, wherein the cone angle is provided in a range between 8 and 10.

5. The brake booster as claimed in claim 4, wherein the cone angle is provided in a range between 8.5 and 9.

6. The brake booster as claimed in claim 1, wherein the booster housing has at least one first housing shell and at least one second housing shell and, between the housing shells, there is formed an annular gap which extends forward in an axial direction and in which a region of the diaphragm is arranged.

7. The brake booster as claimed in claim 6, wherein an axial extent of the annular gap is at least of the same size as its radial gap dimension.

8. The brake booster as claimed in claim 7, wherein the axial extent of the annular gap is at least twice its radial gap dimension.

9. The brake booster as claimed in claim 8, wherein the conical portion extends substantially to the annular gap.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The details and advantages of aspects of the invention will be explained in more detail hereunder by means of descriptions of the figures. In this context, the description of generally known aspects and functions of a brake booster of the generic type will be largely omitted, and only the details which are relevant to aspects of the invention will be discussed.

(2) In detail:

(3) FIG. 1 shows, by way of example, an axial sectional illustration of an embodiment of the brake booster according to an aspect of the invention.

(4) FIG. 2 shows an enlarged illustration of the embodiment of FIG. 1 in the region of the rolling fold with the diaphragm plate in the zero position.

(5) FIG. 3 shows an enlarged illustration of the embodiment of FIG. 1 in the region of the rolling fold with the diaphragm plate at maximum stroke.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) FIG. 1

(7) A pneumatic brake booster 1 is of substantially rotationally symmetrical construction. It has a thin-walled booster housing 2. The booster housing 2 comprises housing shells 10 and 11, which are connected to one another in their radial outer region, and includes a vacuum chamber 3 and a working chamber 4, which are pneumatically separated from one another by an elastomeric diaphragm 5.

(8) The boost force is generated in the pneumatic brake booster 1 by a pressure difference between the vacuum chamber 3 and the working chamber 4 and is introduced into a rigid diaphragm plate 6, which is thereupon moved axially in the booster housing 2 within a structurally provided stroke range H between a zero position N and a maximum stroke M and transmits the boost force to components positioned downstream in terms of action.

(9) Here, the diaphragm 5 is supported in the direction of the vacuum chamber 3 against the diaphragm plate 6, wherein the pneumatically effective area is definable by a projected support area of the diaphragm 5 on the diaphragm plate 6 and thus by the support radius AR. For maximum efficiency, the support radius AR should ideally be equal to the outer radius TR of the diaphragm plate 6 in every operating state and at every stroke position.

(10) To compensate for the movement of the diaphragm 5, the latter has a roll fold 7 which, during the displacement of the diaphragm plate 6 between the zero position N and the maximum stroke M, rolls on a rolling region 8 on the inner wall of the booster housing 2.

(11) At the radial outer edge of the diaphragm 5, there is integrally formed a circumferential sealing bead 13 which is clamped between the housing shells 10 and 11 in a separately formed annular cavity in pneumatically sealed fashion.

(12) FIG. 2

(13) The booster housing 2 according to an aspect of the invention has, in the rolling region 8, a conical portion 9 whose axial extent A is at least one third and preferably half of the stroke range H and whose cone angle lies in a range between 8 and 10, preferably between 8.5 and 9 and is ideally 8.8.

(14) FIG. 3

(15) To ensure a permanent function with optimized efficiency and reduced material expenditure, the components of the brake booster 1 according to an aspect of the invention are designed such that a radial spacing AM between the diaphragm plate 6 and the rolling region 8 on the booster housing 2 at maximum stroke M seeks to assume a value which is the sum of twice the thickness d of the diaphragm 5 in the region of the rolling fold 7 and a specific minimum admissible flexing radius RW of the diaphragm 5, but does not fall below this. AM2d+RW; AM.fwdarw.2d+RW applies.

(16) Here, the flexing radius RW is a minimum admissible bending radius of the diaphragm 5 in the case of which, taking into consideration the specific material properties and the thickness d, cracking owing to stress-induced overloading in the boundary layers is avoided over the entire intended operating duration of the brake booster 1. For example, for a diaphragm 5 made of EPDM material with a thickness d1 mm, the flexing radius RW1.5 mm is preferably defined.

(17) The requirements for the minimum admissible radial spacing AM at maximum stroke M imperatively apply for the structural design of the long-stroke embodiment. In the case of a short-stroke embodiment, it is for example possible within an aspect of the invention for the cone angle a to be increased in relation to the long-stroke design in order to permit the same radial spacing AM, or the cone angle a may remain the same, whereby the radial spacing AM is slightly increased.

(18) The stroke range H for a long-stroke embodiment of the brake booster 1 according to an aspect of the invention could for example lie in a range between 40 mm and 50 mm and preferably be 46 mm.

(19) For a short-stroke embodiment of the brake booster 1 according to an aspect of the invention, the stroke range H could for example lie in a range between 30 mm and 40 mm and preferably be 36 mm. A resulting stroke difference between the short-stroke and long-stroke embodiments of 10 to 20 mm can be easily realized without efficiency loss with a single standardized embodiment of the diaphragm 5.

(20) The booster housing 2 of the illustrated embodiment of the brake booster 1 according to an aspect of the invention is designed such that the radial spacing AN between the diaphragm plate 6 and the rolling region 8 at zero position N is approximately and at least twice the radial spacing AM at maximum stroke M. Taking into consideration the design principles for the spacing AN as disclosed above, the losses owing to the flexing work in the rolling fold 7 and the extent of the bladder formation thereof can thus be brought into an optimum relationship, and the efficiency loss can thus be minimized.

(21) In order to improve the guidance of the rolling fold 7, avoid damage at the transition thereof to the sealing bead 13 and prevent the sealing bead 13 from slipping out or disengaging into the interior space of the booster housing 2, the two housing shells 10 and 11 are formed such that an axially forwardly extending annular gap 12 is formed in between. Here, the diaphragm 5 or the rolling fold 7 runs through the annular gap 12.

(22) Here, the radial gap dimension b of the annular gap 12 is configured to be substantially smaller than the thickness of the sealing bead 13 and only insignificantly wider than the thickness d of the membrane 5. Here, the axial extent a of the annular gap 12 should be configured to be at least equal to and preferably at least twice the radial gap dimension b thereof.

(23) In the illustrated preferred embodiment of the brake booster 1 according to an aspect of the invention, the conical portion 9 extends directly to the annular gap 12.

LIST OF REFERENCE DESIGNATIONS

(24) 1 Brake booster 2 Booster housing 3 Vacuum chamber 4 Working chamber 5 Diaphragm 6 Diaphragm plate 7 Rolling fold 8 Rolling region 9 Conical portion 10 Housing shell 11 Housing shell 12 Annular gap 13 Sealing bead a Cone angle a Axial extent A Axial extent b Radial gap dimension d Thickness of the diaphragm H Stroke range M Maximum stroke N Zero position AM Radial spacing at maximum stroke AN Radial spacing at zero position AR Support radius RW Specific minimum admissible flexing radius TR Diaphragm plate radius