Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
2000-05-30
2001-10-02
Ryznic, John E. (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
Reexamination Certificate
active
06295916
ABSTRACT:
BACKGROUND OF THE INVENTION
U.S. Pat. 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. Pats. 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. Pats. 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 concentric return springs located in an axial bore of a hub member and compressed on securing a housing of a master cylinder with a front shell of a brake booster.
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 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 return spring arrangement that has a first coil of a first spring connected to a base of a retainer and a second coil connected to an end cap to hold a second concentric spring between the base and end cap. The first and second spring are oppositely wound spirals such that the coils do not mesh which could cause interference in the smooth movement of the wall assembly during the creation of an operational force. The retainer member is frictionally retained in the hub to locate the return springs within the stepped axial bore and compressed by engagement of a housing of a master cylinder from a solid height to position the movable wall in a rest position within the housing of the brake booster. The length of the first and second spring can vary in order for a smaller installation force is required bring the first and second return springs into a installation height within the stepped axial bore to a position.
An advantage of the brake booster resides in a return spring arrangement wherein concentric springs are utilized to position a movable wall in a rest position.
A further advantage of the brake booster resides in the use of multiple return springs to reduce the diameter and length as compared with a single spring for performing a similar function.
A still further advantage of the brake booster resides in the use of oppositely wound spiral springs to avoid a possible interference by coils being compresses during the transfer of an operational force from a movable wall to an output push rod.
A still further advantages of the brake booster resides in locating a return spring arrangement within a stepped axial bore of a hub and relying on the engagement with a housing of the a master cylinder to set an installation height to define a rest position for a movable wall.
REFERENCES:
patent: 4105088 (1978-08-01), Levijoki
patent: 4535679 (1985-08-01), Kytta
patent: 5228377 (1993-07-01), Watanabe
patent: 5249505 (1993-10-01), Hewitt
patent: 5272958 (1993-12-01), Moinard et al.
patent: 5333534 (1994-08-01), Uyama
patent: 6003426 (1999-12-01), Kobayashi et al.
Comstock Warren
McCormick Jr. Leo H.
Robert Bosch Corporation
Ryznic John E.
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