The present invention relates to a method of connecting a master brake cylinder to a brake booster, in particular for motor vehicles, in which arrangement the brake booster has a booster casing containing a movable wall dividing the booster casing into a vacuum chamber and a working chamber, a control valve to control the pressure in the working chamber, and a reinforcing tube connecting the transverse end walls of the booster casing, the movable wall being sealed and displaceable with respect to the reinforcing tube, and the assembly resulting from this method.
Brake boosters for motor vehicles are known where an additional force is generated from the pressure difference between a vacuum and the atmospheric pressure.
These brake boosters essentially comprise a booster casing, a movable wall arranged therein, and a control valve. The booster casing features an essentially cylindrical construction, the two transverse end walls serving for attachment. By means of the transverse end wall adjacent the control valve, the brake booster is fastened at the splash wall of a motor vehicle, while the master brake cylinder is attached to the other transverse end wall of the brake booster. The movable wall divides the inside of the booster casing into a vacuum chamber and into a working chamber.
The pressure in the working chamber may reach different values dependent on the position of the brake-pedal-operated control valve. The force which is effective on the movable wall when there is a pressure difference and the pedal force via the control valve are transmitted to the master brake cylinder via a push rod axially arranged in the booster casing.
Usually, the booster casing is of sheet steel. The pressure difference between the atmospheric pressure prevailing outside the booster casing and the vacuum inside will generate forces which will lead to a deformation of the booster casing. In addition to the pressure-difference-originated forces there will be those forces that will be transmitted via the push rod during brake actuation, i.e. the brake pedal force and the boosted force generated by the brake booster. The resultant force will act on the piston of the master brake cylinder, generating a reaction force in the master brake cylinder, the reaction force is opposed to and equal to the total force applied to the push rod.
The pedal-force-originated constituent of the reaction force will proceed from the master cylinder, via the steel parts of the booster casing, to the splash wall where the brake pedal is fastened. The boosting-force-originated constituent of the reaction force will end at the booster casing. The consequence of the reaction force being transmitted to or through the booster casing will be an axial extension of the booster casing upon actuation of the brake. Thus, the master cylinder is displaced which will imply an additional lost travel of the brake pedal. Due to the transmittance ratio of the brake lever, the extension of the booster casing will be transmitted, increased by a multiple amount, on to the brake lever.
In order to prevent a deformation of the booster casing, or at least to reduce the same, upon actuation of the brake, a first copending U.S. patent application of J. Belart and F. Wienecke, Ser. No. 61,113, filed July 26, 1979, assigned to the same assignee as the present application, discloses providing a reinforcing tube in the booster casing, extending axially thereof and connected to both transverse end walls of the booster casing, with the movable wall being sealed with respect to and displaceable on the reinforcing tube. In this brake booster, the reinforcing tube has axial slots through which slots cross members are passed for the mechanical connection of the movable wall to the control valve casing.
Moreover, a second copending U.S. patent application of J. Belart, Ser. No. 141,830, filed April 21, 1980 now U.S. Pat. No. 4,347,779, assigned to the same assignee as the present application, discloses that the axial slots are disposed in that portion of the reinforcing tube which protrudes into the vacuum chamber, that the cross members are disposed on the vacuum side of the movable wall, and that a rolling diaphragm is provided as seal between the movable wall and the reinforcing tube, the rolling diaphragm sealingly covering the axial slots upon a displacement of the movable wall in the direction of the vacuum chamber.
In these suggested brake boosters, the connection of the booster to the master brake cylinder is effected by bolts which are threaded into flange elements provided at the reinforcing tube. Due to these flange elements and because of the imperativeness of a vacuum-tight connection it is necessary to produce a relatively strong reinforcing tube.