Brake booster with a stress-optimized mounting point

Abstract

Pneumatic brake booster (1) comprising a booster housing (2) with a booster housing interior (7) and with at least one housing shell (3), wherein the housing shell (3) is formed from a sheet metal in a substantially axially symmetrical manner about a central axis (Z) and has a substantially planar contact flange (4) for contact with a further component (8) outside the booster housing (2), wherein at least one fastening point (5) for fixing the brake booster (1) to the further component is provided and the fastening point (5) is arranged at a distance from the central axis (Z) in a common surface (10) with the contact flange (4), characterized in that the surface of the housing shell (3) is locally enlarged within a surface area bounded by a closed contour (15), wherein the surface area with the enlarged surface is defined as an axially driven surface towards the booster housing interior (7).a substantially arc-shaped bead (6) is formed, which is arranged adjacent to the attachment point (5) and surrounds it radially on the outside, wherein the bead (6) is curved about a central axis (M) of the attachment point (5) or about the central axis (Z) and both the attachment point (5) and the contour (15) are arranged within an imaginary circular sector (14) with a center on the central axis (Z) and a circular angle (µ) of at most 45°.

Description

[0001] The invention relates to a pneumatic brake booster, in particular for a hydraulic motor vehicle braking system, with features according to the preamble of claim 1.

[0002] Brake boosters of this type are widespread and well-known. The booster housing of such a brake booster is usually made of thin-walled sheet metal using forming techniques. A flat mounting flange is typically formed on one or more housing halves. In the assembled state, depending on the application, a master cylinder attached to the brake booster or a body panel to which the brake booster itself is mounted rests against this mounting flange. Mounting points are arranged in the surface of the mounting flange, which are used to attach the brake booster to the body or a master cylinder to the brake booster.

[0003] Due to its design, the amplifier housing must withstand considerable forces, for which thick walls would be advantageous. At the same time, however, there is always a requirement for weight reduction, which could be achieved by using increasingly thinner walls. To prevent undesirable deformation of the amplifier housing, it is therefore known to stiffen thin-walled housing shells using beads and indentations.

[0004] For example, from DE 10 2015 209 785 A1 it is known to stiffen the mounting flange by providing it with long, transversely drawn beads arranged radially between the fastening points.

[0005] From DE 10 2015 209 788 A1 another brake booster is known, the rear housing shell of which, in its conical section, is provided with particularly deep indentations running concentrically to the central axis in order to reduce the dead volume, which also have a stiffening effect on the booster housing.

[0006] From DE 10 2010 001 812 A1 a brake booster is known which is equipped with straight beads for the general stiffening of the housing half shells, which, extending radially outwards from the central axis almost over the entire housing half shell, are either formed individually or are connected in pairs at their base by a transverse leg.

[0007] During operation, significant static and dynamic forces are introduced into the amplifier housing via the mounting points. Particularly high stresses develop in the housing wall around these mounting points, which, in extreme cases, can lead to material fatigue, cracking, and impaired function of the brake booster over time. The designs mentioned above do not solve this specific problem and, because they allow for particularly rigid and thin-walled amplifier housings, can even exacerbate it.

[0008] The task, therefore, is to offer an improved brake booster that reduces the risk of damage in the area of ​​the mounting points and improves durability.

[0009] The problem is solved according to the invention by a brake booster with the combination of features according to claim 1. Dependent claims, together with figures and descriptions, specify further embodiments and advantageous developments according to the invention.

[0010] By locally increasing the surface area of ​​the housing shell in the form of relatively short, circumferentially elongated arc-shaped beads in a particularly stressed area radially adjacent to the mounting point, the forces introduced from the mounting point into the housing shell are distributed over a larger area, reducing the proportion of tensile stresses and thus weakening or preventing stress peaks. The stiffness of the housing shell is not affected and can even be increased, allowing the use of thinner sheet metal and saving weight and manufacturing costs.

[0011] The details and advantages of the invention are explained in more detail below with reference to the figures. Descriptions of generally known aspects and functions of a brake booster of this type are largely omitted, and only the details relevant to the invention are discussed.

[0012] In detail, the Fig. 1 a known generic brake booster in axial section (a) and spatial representation (b). Fig. 2 Spatial interior view (a) and detailed section (b) of a housing shell according to a first embodiment according to the invention. Fig. 3 Spatial external view (a) and detailed section (b) of a housing shell according to a second embodiment according to the invention. Fig. 4 Spatial external view of a housing shell according to a third embodiment according to the invention. Fig. 5 Spatial external view of a housing shell according to a further embodiment according to the invention. Fig. 1

[0013] A pneumatic brake booster 1 is usually essentially at least axially symmetrical and, as in the illustrated embodiment, rotationally symmetrical about the central axis Z. It has a thin-walled booster housing 2 with vacuum and working chambers arranged in an interior space 7 of the booster housing. A housing shell 3, 3' of the booster housing 2 is usually manufactured from a sheet metal part by deep drawing and, in addition to a conical shell section 13, 13', has a substantially planar mounting flange 4, 4'. The planar mounting flange 4, 4' is delimited from the non-planar area of ​​the housing shell 3, 3' surrounding it radially by an outer contour 9 and serves to contact the brake booster 1 with another component 8, 8' in order to fix them together. This could be, for example, a vehicle body or a master brake cylinder.

[0014] The four mounting points 5, 5', 5'', 5''' shown in view b serve to connect the brake booster 1 to component 8 and are arranged, spaced apart from the central axis Z, in a surface 10 common with the mounting flange 4. One mounting point 5 has an opening 11 through the housing shell 3 and a fastening element 12 projecting outwards through the opening 11 and is surrounded on all sides by the surface 10. The fastening element 12 is usually a separate threaded bolt or screw and, in assembly, is pressed against the inside of the housing shell 3 or connected to it by a form-fit or material-fit connection.

[0015] The housing shell 3 is also shaped such that the surface 10 of the mounting flange 4 transitions directly into the conical shell section 13 of the housing shell 3 via a radius R1. A portion of the operating forces is introduced from the area of ​​the mounting point 5 into the shell section 13 via the radius R1; particularly high local stresses arise in this area during vehicle operation. Fig. 2

[0016] The Fig. Figure 2 shows a first embodiment according to the invention of an improved housing shell 3.

[0017] The mounting flange 4, as in the known embodiment described above, is essentially ring-shaped and bounded by the outer contour 9 of the conical shell section 13. The four mounting points 5, 5', 5'', 5''' are also arranged in pairs axially symmetrical to the central axis Z. In contrast to the known embodiment, the surface area of ​​the housing shell 3 is locally enlarged near the mounting point 5 (the same applies analogously to the other mounting points 5', 5'', 5'''). The enlarged surface area is bounded by a closed contour 15 and is formed as a groove 6 driven towards the interior of the amplifier housing. The groove 6 is essentially arc-shaped and curved around the central axis Z, and the mounting point 5 is formed radially around its outer edge.This distributes the forces introduced from the area of ​​the mounting point 5 into the conical shell section 13 over a larger area, thereby reducing local stresses and optimizing the force flow. To optimally reduce stresses without impairing the stiffness of the housing shell 3, the groove is limited in the circumferential direction. Both the mounting point 5 and the contour 15 are thus arranged within a circular angle µ of an imaginary circular sector 14 extending orthogonally outwards from the central axis Z. In the illustrated embodiment, the circular angle µ is on the order of approximately 30°, although other values ​​are possible within the scope of the invention, depending on the embodiment. For optimal function, however, the circular angle µ should preferably not exceed 45°.

[0018] The corresponding cross-sectional profile in view b further illustrates that the surface 10, in which the fastening point 5 and the mounting flange 4 are located, transitions into the groove 6 via a sequence of two directly intersecting radii R1 and R2. Exceeding the yield strength of the sheet metal material used is thus prevented by introducing elastic bending components in the radii R1 and R2. Fig. 3

[0019] The Fig. Figure 3 shows a second embodiment of an improved housing shell according to the invention. In contrast to the embodiment according to Fig. 2 the fastening points 5,... are designed to be offset outwards in some areas with respect to the radial outer contour 9 of the mounting flange and the surface 10 is arranged axially offset from the conical shell area 13, whereby it transitions in cross-section into the groove 6 via a sequence of three radii R1, R2, R3 that immediately merge into each other. Fig. 4

[0020] The Fig. Figure 4 shows a third embodiment of the housing shell 3 according to the invention. The mounting flange (4) is essentially diamond-shaped, although other angular and, in particular, square contours are also permissible within the scope of the invention. The housing shell 3 has two mounting points (5, 5') at opposite corners of the diamond. The arcuate grooves (6 and 6') are curved about the central axes (M, M') of the respective mounting points (5, 5'). Fig. 5

[0021] Another embodiment of the housing shell 3 according to the invention in the Fig. 5 represents a kind of combination of the explanations according to Fig. 3 and Fig. 4. The mounting flange 4 is as shown in the Fig. 3 essentially ring-shaped with fastening points 5 and 5' arranged axially symmetrically to the central axis Z and partially offset to the outside. As in the embodiment according to Fig. In 4, there are only two fastening points 5 and 5', and the two arc-shaped beads 6 and 6' are each curved around the central axes M, M'. In contrast to the design according to Fig. In section 4, however, the beads 6 and 6' are additionally rotated about the central axes M, M' and thus arranged asymmetrically with respect to the central axis Z. Such a design can be particularly advantageous for asymmetrical load profiles. Reference symbol list 1 brake booster 2 amplifier housings 3 Housing shell 4. Mounting flange 5 Mounting point 6 groove 7 Amplifier housing interior 8 components 9 Outer contour 10 area 11 Breakthrough 12 Fastening element 13 Shell section 14 Circle sector 15 contour µ circular angle R radius M Central axis Z central axis

Claims

[1] Pneumatic brake booster (1) comprising a booster housing (2) with a booster housing interior (7) and with at least one housing shell (3), wherein the housing shell (3) is formed from a sheet metal in a substantially axially symmetrical manner about a central axis (Z) and has a substantially planar contact flange (4) for contact with a further component (8) outside the booster housing (2), wherein at least one fastening point (5) for fixing the brake booster (1) to the further component is provided and the fastening point (5) is arranged at a distance from the central axis (Z) in a common surface (10) with the contact flange (4). characterized by, that the surface of the housing shell (3) is locally enlarged within a surface area bounded by a closed contour (15), wherein the surface area with the enlarged surface is formed as an axially driven, substantially arc-shaped bead (6) directed towards the amplifier housing interior (7), which is arranged adjacent to the mounting point (5) and surrounds it radially outside, wherein the bead (6) is curved about a central axis (M) of the mounting point (5) or about the central axis (Z) and both the mounting point (5) and the contour (15) are arranged within an imaginary circular sector (14) with a center on the central axis (Z) and a circular angle (µ) of at most 45°. [2] Brake booster (1) according to claim 1, characterized by , that the mounting flange (4) is essentially ring-shaped, with at least two fastening points (5, 5') being provided axially symmetric to the central axis (Z). [3] Brake booster (1) according to claim 1, characterized by , that the mounting flange (4) is essentially rectangular and that at least two fastening points (5, 5') are provided at opposite corners. [4] Brake booster (1) according to one of claims 2 or 3, characterized by , that the fastening points (5, 5') are arranged offset outwards in some areas with respect to a radial outer contour (9) of the mounting flange. [5] Brake booster (1) according to at least one of the preceding claims, characterized by , that the common surface (10) of the fastening point (5) and the mounting flange (4) transitions into the groove (6) in a cross-sectional profile via a sequence of radii (R1, R2,...) that immediately merge into one another. [6] Brake booster (1) according to at least one of the preceding claims, characterized by, that the fastening point (5) includes a penetration (11) and / or an outwardly projecting fastening element (12) which is surrounded on all sides by the surface (10).

Images