GB2312718A

GB2312718A - Brake booster

Info

Publication number: GB2312718A
Application number: GB9707376A
Authority: GB
Inventors: Philippe Castel
Original assignee: Delphi Automotive Systems France
Current assignee: Delphi Automotive Systems France
Priority date: 1996-05-03
Filing date: 1997-04-11
Publication date: 1997-11-05
Anticipated expiration: 2017-04-11
Also published as: GB2312718B; GB9707376D0

Abstract

A brake booster 10 comprises a housing 12 having front and rear walls 14, 16 and is connected to a vehicle internal wall 34 and a master cylinder 44 by means of at least one tie rod 24. An externally screw-threaded member 46 is releasably secured to the tie rod at 58, and the member and nut 62 secure the tie rod to the front wall 14. Second means 28, 30, 36 secure the tie rod to the rear wall 16. When subject to a sufficient impact (F, Figure 2), the member 46 moves rearwardly relative to the tie rod to provide controlled crushing of the brake booster. Alternatively, the member and nut are associated with the rear wall, and the specification discloses other ways of releasably securing the member 46 to the tie rod.

Description

BRAKE BOOSTER The present invention relates to a brake booster or servomotor for the braking system of a motor vehicle, and in particular to a pneumatic or vacuum brake booster.

WO 95/21083 describes a brake booster comprising a substantially rigid housing divided internally into at least two chambers by a movable diaphragm. At least two tie rods extend through the housing to provide strength to the housing and to provide means for securing the brake booster to an internal wall of the motor vehicle. At least one of the tie rods is compressible, either telescopically or by flexing, such that if a compression force is applied to the brake booster during a frontal impact on the motor vehicle, the brake booster will collapse before the internal wall of the motor vehicle is damaged. These arrangements have disadvantages in terms of difficulties in assembly, and in cost.

It is an object of the present invention to provide a brake booster which overcomes the above mentioned disadvantages.

A brake booster in accordance with the present invention comprises a housing having a front wall and a rear wall; a flexible diaphragm mounted inside the housing to define at least two chambers inside the housing; at least one tie rod extending through the housing from the front wall to the rear wall, the tie rod extending through the rear wall for mounting the brake booster on an internal wall of a motor vehicle; first means for securing the tie rod to the front wall; and second means for securing the tie rod to the rear wall; wherein the first means or the second means comprises an annular part which is secured to the respective wall of the housing, and releasable securing means releasably securing the annular part to the tie rod.

If the brake booster of the present invention is subjected to a compression force at a level which is greater than the force needed to release the releasable securing means securing the annular part to the tie rod, the annular part will slide along the tie rod allowing the housing to collapse. The present invention provides a simplified tie rod arrangement which makes the brake booster easier and cheaper to assemble.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partial cross-sectional view of a first embodiment of brake booster in accordance with the present invention; Figure 2 is a partial cross-sectional view of the brake booster of Figure 1 in a compressed state; Figure 3 is a cross-sectional view on the line III-III of Figure 1 of the anti-rotation feature between the tie rod and the annular part; Figure 4 is an enlarged cross-sectional view of the annular part of the brake booster of Figure 1; Figure 5 is a similar view to Figure 1 of a second embodiment of brake booster in accordance with the present invention; Figure 6 is a similar view to Figure 1 of a third embodiment of brake booster in accordance with the present invention; Figure 7 is a similar view to Figure 1 of a fourth embodiment of brake booster in accordance with the present invention; Figure 8 is a similar view to Figure 1 of a fifth embodiment of brake booster in accordance with the present invention; and Figure 9 is a similar view to Figure 1 of a sixth embodiment of brake booster in accordance with the present invention.

Referring to Figures 1 to 4 of the drawings, the brake booster 10 (which is a pneumatic or vacuum brake booster) in accordance with the present invention comprises a housing 12 having a front wall 14 and a rear wall 16. A flexible diaphragm 18 divides the internal space of the housing to form a front chamber 20 and a rear chamber 22. A pair of tie rods 24 extend through the housing 12 between the front wall 14 and the rear wall 16. At one end 26, the tie rods 24 have a screw-threaded portion 28 which extends through the rear wall 16. A first nut 30 is screw threaded on each portion 28 in the rear chamber 22 of the brake booster 10. The screw-threaded portions 28 pass through apertures 32 in an internal wall 34 (typically the firewall separating the engine compartment from the passenger compartment) of a motor vehicle, and a second nut 36 is screw threaded on to each portion 28. With this arrangement, the tie rods 24 are secured to the rear wall 16 of the brake booster 10 and the brake booster is secured to the internal wall 34. At the other end 38, the tie rods 24 pass through the front wall 14 of the housing 12 and through apertures 40 in a housing 42 of a brake master cylinder 44 to secure the tie rods to the front wall 14 and to secure the master cylinder 44 to the brake booster 10. The arrangement thus far described, and the operation of the brake booster 10, is well known to those skilled in the art and will not be described in further detail.

The means for securing each tie rod 24 to the front wall 14 (and the brake booster 10 to the master cylinder 44) comprises an annular part 46 (Figure 4) which includes an enlarged head 48 which engages the front wall 14 inside the front chamber 20 of the brake booster 10; a through bore 50 through which the tie rod extends; and a screw threaded portion 52 which extends through the front wall 14 of the housing 12 and the aperture 40 in the master cylinder housing 42. The threaded portion 52 of the annular part 46 abuts a head portion 54 at said other end 38 of the tie rod 24. The through bore 50 of the annular part 46 has a first portion 56 which makes a tight sliding fit on the tie rod 24 and which frictionally grips a roughened surface portion 58 on the tie rod, and a second portion 60 which loosely slides on the tie rod and across the roughened surface portion 58. A nut 62 is screw threaded on the screw threaded portion 52 of the annular part 46 to secure each tie rod 24 to the front wall 14 and to secure the master cylinder 44 to the brake booster 10. The roughened surface portion 58 is preferably formed by knurling or any other suitable process. The annular part 46 is preferably formed from steel.

The annular part 46 (Figure 3) preferably has a longitudinally extending slot 66 in the second portion 60 of the through bore 50, and each tie rod 24 preferably has a corresponding rib 68 adjacent the head portion 54 which locates in the slot. This arrangement prevents relative rotation between the tie rod 24 and the annular part 46 during tightening of the nuts 36,62. Any other suitable arrangement may be used to prevent such relative rotation.

During a collision, the brake booster 10 may be subjected to an impact force F on the front wall 14 of the housing 12. For an impact force F which is less than the frictional gripping force between the first portion 56 of the through bore 50 of each annular part 46 and the roughened surface portion 58 of each tie rod 24, the brake booster 10 will remain undamaged. However, if the impact force F exceeds the frictional gripping force, each annular part 46 will be pushed along each tie rod 24 towards the rear wall 16 of the housing 12 (as shown in Figure 2), and the housing will be damaged. In a collision, such an arrangement will substantially ensure that the brake booster 10 is damaged before any damage occurs to the internal wall 34 of the motor vehicle. In a preferred arrangement, the frictional gripping force between each annular part 46 and each tie rod 24 is in the range between 3000 and 5000 N.

The second embodiment of brake booster 100 shown in Figure 5 is substantially the same as the brake booster 10 shown in Figures 1 to 4, and like parts have been given the same reference number. In this second embodiment, the securing arrangements for the tie rods 24' are reversed. The nuts 30',36' secure one end 26' of each tie rod 24' to the front wall 14 of the housing 12 and secure the master cylinder 44 to the brake booster 100. The annular part 46' and the nut 62' secure the other end 38' of each tie rod 24' to the rear wall 16 of the housing 12 and secure the brake booster 100 to the internal wall 34. With this arrangement, in a frontal impact, the tie rods 24' are pushed through the apertures 32 in the internal wall 34 as the housing 12 collapses.

The third embodiment of brake booster 200 shown in Figure 6 is substantially the same as the brake booster 10 shown in Figures 1 to 4, and like parts have been given the same reference number. In this third embodiment, the means for securing each tie rod 24 to the front wall 14 (and the brake booster 200 to the master cylinder 44) comprises an annular part 246 which includes an enlarged head 248 which engages the front wall 14 inside the front chamber 20 of the brake booster 200; a through bore 250 through which the tie rod extends; and a screw threaded portion 252 which extends through the front wall 14 of the housing 12 and the aperture 40 in the master cylinder housing 42. The threaded portion 252 of the annular part 246 abuts a head portion 254 at the other end 38 of the tie rod 24. The through bore 250 of the annular part 246 makes a tight sliding fit on the tie rod 24. Seals (not shown) may be positioned in the through bore 250 in contact with the tie rod 24. A nut 62 is screw threaded on the screw threaded portion 252 of the annular part 246 to secure each tie rod 24 to the front wall 14 and to secure the master cylinder 44 to the brake booster 200. The other end 38 of the tie rod 24 has a groove 256 formed in its outer surface, and a portion 258 of the threaded portion 252 of the annular part 246 is deformed into the groove, after the nut 62 is screw threaded into position, to releasably secure the annular part to the tie rod. During a collision, the brake booster 200 may be subjected to an impact force on the front wall 14 of the housing 12. If the impact force exceeds the force required to pull the portion 258 of each annular part 246 out of the groove 256 in each tie rod 24, each annular part 246 will be pushed along each tie rod 24 towards the rear wall 16 of the housing 12 (in a similar manner to that shown in Figure 2), and the housing will be damaged.

The fourth embodiment of brake booster 300 shown in Figure 7 is substantially the same as the brake booster 10 shown in Figures 1 to 4, and like parts have been given the same reference number. In this fourth embodiment, the means for securing each tie rod 24 to the front wall 14 (and the brake booster 300 to the master cylinder 44) comprises an annular part 346 which includes an enlarged head 348 which engages the front wall 14 inside the front chamber 20 of the brake booster 300; a through bore 350 through which the tie rod extends; and a screw threaded portion 352 which extends through the front wall 14 of the housing 12 and the aperture 40 in the master cylinder housing 42. The threaded portion 352 of the annular part 346 abuts a head portion 354 at the other end 38 of the tie rod 24. The through bore 350 of the annular part 346 makes a tight sliding fit on the tie rod 24. Seals (not shown) may be positioned in the through bore 350 in contact with the tie rod 24. A nut 62 is screw threaded on the screw threaded portion 352 of the annular part 346 to secure each tie rod 24 to the front wall 14 and to secure the master cylinder 44 to the brake booster 300. Alignable, diametrically extending holes 356,358 are formed in the other end 38 of the tie rod 24 and in the threaded portion 352 of the annular part 346, respectively, and a breakable pin 360 is positioned in the holes 356,358 after the nut 62 is screw threaded into position, to releasably secure the annular part to the tie rod. During a collision, the brake booster 300 may be subjected to an impact force on the front wall 14 of the housing 12. If the impact force exceeds the force required to break the pins 360, each annular part 346 will be pushed along each tie rod 24 towards the rear wall 16 of the housing 12 (in a similar manner to that shown in Figure 2), and the housing will be damaged. As an alternative to a breakable pin, a breakable circlip may be position in alignable grooves in each annular part and each tie rod.

The fifth embodiment of brake booster 400 shown in Figure 8 is substantially the same as the brake booster 10 shown in Figures 1 to 4, and like parts have been given the same reference number. In this fifth embodiment, the means for securing each tie rod 24 to the front wall 14 (and the brake booster 400 to the master cylinder 44) comprises an annular part 446 which includes an enlarged head 448 which engages the front wall 14 inside the front chamber 20 of the brake booster 400; a through bore 450 through which the tie rod extends; and a screw threaded portion 452 which extends through the front wall 14 of the housing 12 and the aperture 40 in the master cylinder housing 42. The threaded portion 452 of the annular part 446 abuts a head portion 454 at the other end 38 of the tie rod 24. The through bore 450 of the annular part 446 makes a tight sliding fit on the tie rod 24. Seals (not shown) may be positioned in the through bore 450 in contact with the tie rod 24. A nut 62 is screw threaded on the screw threaded portion 452 of the annular part 446 to secure each tie rod 24 to the front wall 14 and to secure the master cylinder 44 to the brake booster 400. After the nut 62 is screw threaded into position, a portion 456 of the tie rod 24 is deformed outwardly to engage the enlarged head 448 of the annular part 446 to releasably secure the annular part to the tie rod. During a collision, the brake booster 400 may be subjected to an impact force on the front wall 14 of the housing 12. If the impact force exceeds the force required to break off or flatten the portion 456 of each tie rod 24, each annular part 446 will be pushed along each tie rod 24 towards the rear wall 16 of the housing 12 (in a similar manner to that shown in Figure 2), and the housing will be damaged.

The sixth embodiment of brake booster 500 shown in Figure 9 is substantially the same as the brake booster 10 shown in Figures 1 to 4, and like parts have been given the same reference number. In this sixth embodiment, the means for securing each tie rod 24 to the front wall 14 (and the brake booster 500 to the master cylinder 44) comprises an annular part 546 which includes an enlarged head 548 which engages the front wall 14 inside the front chamber 20 of the brake booster 500; a through bore 550 through which the tie rod extends; and a screw threaded portion 552 which extends through the front wall 14 of the housing 12 and the aperture 40 in the master cylinder housing 42. The threaded portion 552 of the annular part 546 abuts a head portion 554 at the other end 38 of the tie rod 24. The through bore 550 of the annular part 546 makes a tight sliding fit on the tie rod 24. Seals (not shown) may be positioned in the through bore 550 in contact with the tie rod 24. A nut 62 is screw threaded on the screw threaded portion 552 of the annular part 546 to secure each tie rod 24 to the front wall 14 and to secure the master cylinder 44 to the brake booster 500. The tie rod 24 has an annular tapered or chamfered shoulder 556 which engages a corresponding annular tapered or chamfered surface 558 at the opening to the through bore 550 in the enlarged head 548 of the annular part 546 to releasably secure the annular part to the tie rod. During a collision, the brake booster 500 may be subjected to an impact force on the front wall 14 of the housing 12. If the impact force exceeds the force required to push the surface 558 on each annular part 546 passed! the shoulder 556 on each tie rod 24, each annular part 446 will be pushed along each tie rod 24 towards the rear wall 16 of the housing 12 (in a similar manner to that shown in Figure 2), and the housing will be damaged.

The present invention may be used on a brake booster having any number of tie rods, and the releasable securing means between an annular part and an associated tie rod may be used on one or more of the tie rods. It will also be appreciated that the releasable securing means may be used at both ends of a tie rod.

Claims

Claims:

1. A brake booster comprising a housing having a front wall and a rear wall; a flexible diaphragm mounted inside the housing to define at least two chambers inside the housing; at least one tie rod extending through the housing from the front wall to the rear wall, the tie rod extending through the rear wall for mounting the brake booster on an internal wall of a motor vehicle; first means for securing the tie rod to the front wall; and second means for securing the tie rod to the rear wall; wherein the first means or the second means comprises an annular part which is secured to the respective wall of the housing, and releasable securing means releasably securing the annular part to the tie rod.

2. A brake booster as claimed in Claim 1, wherein the releasable securing means comprises a frictional grip between the annular part and the tie rod.

3. A brake booster as claimed in Claim 2, wherein the annular part has a through bore which has a portion which makes a tight sliding fit on the tie rod and which frictionally grips a roughened surface portion on the tie rod.

4. A brake booster as claimed in Claim 3, wherein the roughened surface portion has been formed by knurling.

5. A brake booster as claimed in Claim 3 or Claim 4, wherein the through bore has a longitudinally extending slot therein and the tie rod has a corresponding rib which locates in the slot to prevent relative rotation between the tie rod and the annular part.

6. A brake booster as claimed in Claim 1, wherein the releasable securing means comprises a groove in the tie rod into which a portion of the annular part is deformed.

7. A brake booster as claimed in Claim 1, wherein the releasable securing means comprises a breakable pin or circlip securing the annular part to the tie rod.

8. A brake booster as claimed in Claim 1, wherein the releasable securing means comprises a deformed portion of the tie rod which engages the annular part.

9. A brake booster as claimed in Claim 1, wherein the releasable securing means comprises a tapered shoulder on the tie rod which engages a corresponding tapered surface on the annular part.

10. A brake booster as claimed in any one of Claims 1 to 9, wherein the annular part has an enlarged head which engages the respective wall of the housing internally.

11. A brake booster as claimed in any one of Claims 1 to 10, wherein the annular part has a screwthreaded portion extending through the respective wall of the housing on which a nut is screw threaded to secure the tie rod to the respective wall of the housing.

12. A brake booster substantially as herein described with reference to, and as shown in, the accompanying drawings.