Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
2000-05-30
2001-10-16
Ryznic, John E. (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
Reexamination Certificate
active
06302011
ABSTRACT:
This invention relates to a retainer for holding a return spring and output push rod in an axial bore of a hub of a movable wall in a vacuum brake booster.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,233,911 discloses a typical tandem brake booster through which a force is developed to effect a brake application. In such a brake booster, corresponding first and second walls divide the interior into first and second front chambers and first and second rear chambers. The first front chamber is externally connected to a first source of fluid pressure by a conduit and internally directly connected to the second front chamber and to the first and second rear chambers by various passageways in a hub associated with the first and second walls. A control valve located in the hub is positioned such that the first fluid pressure is communicated in the first and second rear chambers through the passageways to define a rest or ready position. In responsive to an input force, the control valve is positioned such that a second fluid pressure is presented through a passageway to the first and second rear chambers to create a pressure differential across the first and second walls. This pressure differential acts on the first and second walls to develop an output force, which is provided to a master cylinder to assist in effecting a brake application. On termination of the input force, a return spring positions the control valve to a rest or ready location to define a first mode of operation where the second fluid is evacuated from the first and second rear chambers to provide for equalization of the first fluid pressure in the first and second rear chambers. This type vacuum brake booster functions in an adequate manner to provide an assist in effecting a brake application.
U.S. Pat. Nos. 4,409,885; 4,942,738; 5,313,796; 5,329,769 and 5,802,852 disclose brake booster and master cylinder arrangements wherein at least a portion of the master cylinder housing is positioned within the interior of the booster housing to define an integrated brake assembly. Such brake boosters operate in a satisfactory manner but because of their overall size occupies considerable under the hood space when installed in a vehicle. In this arrangement it is common for the brake boosters and master cylinders to manufactured in different locations and assembled as a central location. Unfortunately, the output push rod, which is considered to be part of the brake booster, must be separately shipped to the assembly location, as it is not fixed to the movable wall. U.S. Pat. Nos. 4,892,027 and 4,898,073 disclose structure, which is designed to retain an output push rod within a brake booster. However, when a housing of a master cylinder is recessed into a brake booster if the return spring is located between the shell housing and movable wall external to the hub, there is a possibility of interference between the housing of the master cylinder housing and moveable wall of the brake booster.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide structure for retaining both an output push rod and a return spring within an axial bore of a hub member associated with a movable wall of a brake booster assembly.
The brake booster has housing with an interior divided by a movable wall assembly into at least a first front chamber and at least a first rear chamber. The wall assembly has a hub with a cylindrical projection, which extends through the housing into the surrounding environment. A control valve located in an axial bore formed in the hub has a first mode of operation wherein the front chamber which is permanently connected to a first source of pressure (vacuum) is in communication with the rear chamber to provide for equal pressures therein and a second mode of operation wherein the second chamber is in communication with a surrounding environment (atmospheric pressure) to create a pressure differential across the movable wall assembly. An operational force created by a pressure differential acting on the wall assembly is communicated through a reaction member into an output push rod. After the operational force overcomes a return spring, the output push rod moves pistons in a master cylinder to pressurize fluid therein. This pressurized fluid is supplied to wheel brakes to effect a brake application. The brake booster is characterized by a retainer having a base with an axial opening and a plurality of axial legs, which extend from the base. The base is located in the axial bore with a shaft of the output push rod passing through the axial opening while the plurality of axial legs are located in corresponding a plurality of arcuate and axial slots located on the peripheral surface of the axial bore in the cylindrical body of the hub. The plurality of axial legs frictionally engage the hub to position the base in the axial bore such that a head of the output push rod is located adjacent the reaction member and the shaft and return spring are concentrically located along the axis of the axial bore.
An advantage of the brake booster resides in a retainer, which holds a return spring and output push rod in a concentric position within an axial bore of a hub connected to a movable wall.
A further advantage of resides in the manufacture of a brake booster where a return spring means and output push rod are held in an axial bore of a hub by a retainer prior to being connected to a housing of a master cylinder.
REFERENCES:
patent: 3357317 (1967-12-01), Hager
patent: 4069742 (1978-01-01), Gephart et al.
patent: 4665802 (1987-05-01), Barker et al.
patent: 4766804 (1988-08-01), Barker
patent: 4882980 (1989-11-01), Arino et al.
patent: 5002169 (1991-03-01), Barker
patent: 5249505 (1993-10-01), Hewitt
Comstock Warren
McCormick Jr. Leo H
Robert Bosch Corporation
Ryznic John E.
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