GB2332489A

GB2332489A - A brake booster

Info

Publication number: GB2332489A
Application number: GB9726818A
Authority: GB
Inventors: Philippe G Castel; Russell Lascelles; Michel J Vermoesen
Original assignee: Delphi Automotive Systems France; Motors Liquidation Co
Current assignee: Delphi Automotive Systems France; Motors Liquidation Co
Priority date: 1997-12-20
Filing date: 1997-12-20
Publication date: 1999-06-23
Anticipated expiration: 2017-12-20
Also published as: FR2772708B1; DE19857054A1; FR2772708A1; GB9726818D0; GB2332489B; DE19857054C2

Abstract

A brake booster 10 comprises a front wall 14 and a rear wall 16, a diaphragm 18 defining first and second chambers 20, 22, a piston assembly 24 sealably slidably mounted in the rear wall, and at least one tie rod 30 extending between the front and rear walls. The tie rod is secured at one end 38 to the rear wall and at the other end 40 to the front wall by a nut 42. The nut has a main body 52, which abuts the inside of the front wall around the edge 50 of aperture 34, and an annular ridge 44 which extends through the aperture and is bent over, e.g.by a tool (46, Fig.2), to crimp the edge of the aperture between the main body and the bent over ridge.

Description

H- 199924

Technical Field

2332489 A BRAKE BOOSTER The present invention relates to a brake booster or servomotor of the braking system of a motor vehicle.

Background of the Inventio

A known brake booster includes a housing having a front wall and a rear wall, a diaphragm secured inside the housing to define a pair of chambers inside the housing, and one or more tie rods extending between the front and rear walls. Each tie rod is normally crimped at one end to one of the walls, and secured at the other end to the other wall by a nut threaded on the tie rod with a flat annular or other seal between the nut and the wall. Such an arrangement risks leakage around the seal until the booster is installed in a motor vehicle, needs testing and a special nut design to ensure that a seal is actually present, and requires the two walls of the housing to be crimped together.

Summary of the Inventio

It is an object of the present invention to overcome one or more of the above mentioned problems.

A brake booster in accordance with the present invention comprises a housing having a front wall and a rear wall; a diaphragm mounted inside the housing to defme first and second chambers within the housing; a piston assembly sealably slidably mounted in the rear wall. and at least one tie rod extending between the front wall and the rear wall and through apertures in the front and rear walls; wherein the tie rod is secured at one end to one of the walls of the housing, and wherein the tie rod is secured at the other end to the other wall by a nut, the nut having a main body which abuts the other wall inside the housing around the edge of the respective 2 aperture, and an annular ridge which extends through the aperture and is bent over to crimp the edge of the aperture between the main body and the bent over ridge.

In the present invention, the crimping of the nut of the tie rod to the other wall of the housing removes the need for an additional seal, removes the need to crimp together the walls of the housing, and reduces the risk of leakage prior to installation of the brake booster in a motor vehicle.

Brief Description of the Drawings

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a cross-sectional view of a brake booster in accordance with the present invention; Figure 2 is a cross-sectional view of a nut, tie rod and the front wall of the housing of the brake booster of Figure 1 prior to crimping of the nut to the front wall; and Figure 3 is a similar view to that of Figure 2 after crimping of the nut to the front wall.

Description of the Preferred Embodiment

Referring to Figure 1, the brake booster 10 in accordance with the present invention comprises a housing 12 comprising a front wall 14 and a rear wall 16. A diaphragm 18 is positioned inside the housing 12 to define a front chamber 20 and a rear chamber 22 inside the housing. The front chamber 20 is connectable to a vacuum source (not shown) and the rear chamber 212 is connectable to air at atmospheric pressure or above. A piston assembly 24 is slidably sealably mounted in the rear wall 16. A push rod 26 is connected to the piston assembly 24 and is connectable to the brake pedal (not shown) of a motor vehicle. An actuating rod 28 is connected to the 3 piston assembly 24 and is connectable with a piston (not shown) of a master cylinder of the braking system of the motor vehicle.

A pair of tie rods 30 extend between the front and rear walls 14,16 of the housing 12 to strengthen the housing. Each tie rod 30 has a threaded portion 32 at each end which extends through an aperture 34,36 in the front and rear wall 14,16 respectively. The threaded portions 32 which extend through the rear wall 16 can be used to mount the brake booster 10 in the motor vehicle. The threaded portions 32 which extend through the front wall 14 can be used to mount the master cylinder on the brake booster 10. A flange 39 is formed at one end 38 of each tie rod 30. The flange 39 is located inside the housing 12 against one of walls (which in this example, is the rear wall 16) and the tie rod 30 is crimped or secured in place by upsetting a portion 41 of the tie rod against the outer surface of the rear wall 16. Other suitable arrangements for securing the one end 38 of the tie rods 30 may be used. The arrangement as thus far described is known to those skilled in the art and will not be described in more detail.

In accordance with the present invention, the other end 40 of each tie rod 30 is secured to the adjacent (front) wall 14 by a nut 42. The nut 42 is threaded on the threaded portion 32 of the tie rod inside the housing 12 and abuts the front wall 14 (Figures 2 and 3). The nut 42 has an upstanding annular ridge 44 which extends through the aperture 34 on the front wall 14.

During assembly, a tool 46 is threaded on to the threaded end 32 of the tie rod to bring the tool into abutment with the nut 42. The tool 46 has a shaped end face 48 which projects inside the ridge 44 on the nut 42. Further threading of the tool 46 up to a predetermined torque causes the shaped end face 48 to distort and bend the ridge 44 around the edge 50 of the aperture 34 in the front wall 14 to crimp the edge of the aperture between the bent over ridge 44 and the main body 52 of the nut 42. Adjacent the ridge 44, and radially outward thereof, an annular groove 54 is preferably formed in the 4 main body 52 of the nut 42. The edge 50 of the aperture 34 in the front wall 14 is preferably bent into the groove 54 during bending of the ridge 44.

Means may be provided for resisting rotation of each nut 42 once each nut engages the front wall 14 of the housing 12. For example, the aperture 34 in the front wall 14 may be hexagonal or other non-circular shape and the radially outward shape of the ridge 44 (which projects through the aperture) may be similarly shaped. Alternatively, the surface of the nut 42 engaging the front wall 14, or the surface of the groove 54, where present, may be knurled or formed with splines to grip the front wall.

With this arrangement, the tie rods 30 can be secured and sealed at both ends to the walls 14,16 of the housing 12. There is no requirement for an additional seal, and no requirement to crimp together the walls 14,16 of the housing 12. By permanently securing the tie rods 30 at each end, the booster 10 is sealed prior to installation in the motor vehicle.

Although the above described embodiment shows the nuts 42 adjacent the front wall 14 of the housing 12, it will be appreciated that the nuts may alternatively or additionally be used at the rear wall 16 of the housing. Also, the crimping of the nuts 42 against the front or rear wall 14.,16 may be achieved by other means besides the tool 46 threaded on the threaded end 32 of the tie rods 30. For example, the ridge 44 may be bent by simply pushing the nut under load.

Claims

1. A brake booster comprising a housing having a front wall and a rear wall; a diaphragm mounted inside the housing to define first and second chambers within the housing; a piston assembly sealably slidably mounted in the rear wall; and at least one tie rod extending between the front wall and the rear wall and through apertures in the front and rear walls.. wherein the tie rod is secured at one end to one of the walls of the housing. and wherein the tie rod is secured at the other end to the other wall by a nut, the nut having a main body which abuts the other wall inside the housing around the edge of the respective aperture, and an annular ridge which extends through the aperture and is bent over to crimp the edge of the aperture between the main body and the bent over ridge.

2. A brake booster as claimed in Claim 1, wherein an annular groove is formed in the main body of the nut adjacent to, and radially outward of, the annular ridge, the edge of the aperture in the other wall being bent into the groove.

3. A brake booster as claimed in Claim 1 or Claim 2, further comprising means on the other wall and/or the nut for resisting rotation of the nut relative to the tie rod.

4. A brake booster as claimed in any one of Claims 1 to 3, wherein the brake booster comprises two tie rods, each having a nut crimped to the other wall of the housing.

5. A brake booster as claimed in any one of Claims 1 to 4, wherein the other wall is the front wall of the housing.

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