Airvalve assembly for a brake booster

#This invention relates to brake boosters for use in a braking system, and more particularly to an airvalve assembly for a brake booster.

#The use of a brake booster in a braking system is well known. The brake booster typically comprises front and rear housing parts which are joined around their outer peripheral edge, a flexible diaphragm secured inside the housing to define front and rear chambers within the housing, and an input member which allows relatively high pressure fluid to enter one of the chambers and boost the output braking force.

#In general, such designs provide a constant boost ratio throughout their operating range. However, systems have also been proposed to obtain more than one ratio. U.S. Pat. No. 5,699,713, for example, shows a brake booster having a spring arranged to yield under a predetermined force to change the ratio of operative surface areas and thereby increase the boost ratio. U.S. Pat. No. 5,884,548 teaches a brake booster in which an adjusting mechanism is compressible so as to develop a greater degree of pressure differential when a force applied by an input rod exceeds a predetermined level. U.S. Pat. No. 5,893,316 discloses a brake booster that includes a spring that is compressed when a brake reaction exceeds a preset load, and a servo ratio can be established by the choice of areas of contact between a reaction disc and other components.

#FIG. 1 is a schematic cross-sectional view of an airvalve assembly according to the present invention for a brake booster of a motor vehicle;

#FIG. 2 is a perspective view of a clip for use in the airvalve assembly;

#FIG. 3 is a graph of output obtained by the present invention as a function of the input; and

#FIG. 1 shows an airvalve assembly 10 according to the present invention for a vacuum brake booster of a motor vehicle. As is conventional, the airvalve assembly 10 comprises a first member or plunger 12 and a second member or airvalve 14. The plunger 12 and the airvalve 14 are movable relative to each other to allow the passage of a fluid such as air into a boost assist chamber. A pressure differential is thereby established in the brake booster in order to magnify the force available to brake the vehicle, as is well known.

#A spring clip 16, preferably formed as a unitary piece, is shown separately in FIG. 2. The clip 16 includes a base 18 and one or more cantilevered arms 20. The base 18 of the spring clip can be mounted to a housing 24 of the airvalve assembly, and is laterally translatable therein for a short distance as the brake pedal of the vehicle is initially depressed. The clip 16 also includes a cutout region 26 that surrounds a notched portion of the plunger 12 to locate the plunger within the housing. The arms 20 extend inwardly toward the cutout region 26, and their distal ends engage the airvalve 14 to normally position the plunger and the airvalve relative to each other. It should be appreciated, of course, that the orientation of the spring clip 16 could be reversed such that the arms 20 instead engage the plunger 12.

#When the operator of the motor vehicle depresses the brake pedal, an input shaft 28 moves to the left as shown in FIG. 1 and likewise forces second member 14 toward the left. At forces below a certain magnitude, the spring arms 20 can be essentially immovable relative to the clip base 18. At such low braking levels, the plunger 12 therefore simply translates to the left for a distance equivalent to the distance traveled by the airvalve 14, and into engagement with a reaction disk. The brake booster thus obtains a first ratio when the application of force is below the certain magnitude. When the input braking force exceeds that magnitude, equal to the preload of the spring arms 20, the arms can collapse. As is known in the art, a second ratio can then be obtained.