Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
2000-07-31
2001-12-11
Look, Edward K. (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
Reexamination Certificate
active
06327958
ABSTRACT:
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 part of the brake booster, must be separately shipped to the assembly location, as it is not always fixed to the movable wall.
In the vacuum brake boosters in the patents identified above a resulting output force produce in response to an output force follows a linear curve. In some applications it is desirable to modify the output force of a vacuum brake booster in a manner defined by the structure disclosure in U.S. Pat. No. 5,893,316 through a force transmitting assembly which includes a spring pack located between a reaction disc and plunger connected to an input push rod. In this vacuum brake booster, both the spring pack and push rod are separate items and separately installation in the vacuum brake booster before assembly on a vehicle. 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.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide structure for aligning an output push rod with a holder of a spring pack in a bore of a valve body and thereby retaining an output push rod within a vacuum brake booster.
In the instant brake booster, a housing formed by joining a front shell with a rear shell has an interior divided by a movable wall assembly into at least a first front chamber and at least a first rear chamber. The movable wall assembly has a valve body with a cylindrical projection, which extends through the rear shell into the surrounding environment. A control valve which is located in an axial bore of the valve body has a first mode of operation wherein the front chamber which is permanently connected to a first source of pressure (vacuum) and is in communication with the rear chamber to provide for equal pressures in the front and rear chambers and a second mode of operation wherein the rear chamber is in selective communication with the surrounding environment (atmospheric pressure) to create a pressure differential across the movable wall assembly. An operational force created by a pressure differential which acts 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 for holding the output push rod within the vacuum booster. The retainer has a base with an axial opening, a first plurality of axial legs with hooks on the end thereof which extend in a first direction from the base and a second plurality of legs that extend in a second direction from the base that are connected to a support ring. A return spring acts on and holds the support ring against a shoulder on the valve body to locate the base of the retainer adjacent the holder such that tabs which form the axial opening in the retainer urge the reaction disc against the holder. At the same time the tabs hold the output push rod within the valve body such that a head of the output push rod is located adjacent the reaction member with the shaft of the output push rod located along the axis of the axial bore of the valve body and the return spring concentrically positioned with respect to the axial bore.
An advantage of the brake booster of the instant invention 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 the present invention resides in ease of the manufacturing a brake booster whereby return spring means acts on a retainer to position and hold an output push rod and reaction disc against a holder of a spring pack prior to being assembled to a housing of a master cylinder.
REFERENCES:
patent: 4898073 (1990-02-01), Seip et al.
Hewitt Wayne Allen
Horner Charles Byron
Comstock Warren
Leslie Michael
Look Edward K.
McCormick Jr. Leo H.
Robert Bosch Corporation
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