Hitachi Automotive Systems, Ltd.

Tokico, Ltd.

Kabushiki Kaisha Hitachi Seisakusho

Hitachi, Ltd.

Shuzo Watanabe

Mitsuhiro Endo

Toshio Takayama

Hiromi Ando

Tadaaki Nakamura

Tetsuya Takahashi

A pneumatic booster capable of suppressing braking force from becoming excessive relative to an input force applied to a brake pedal. A valve mechanism () includes a poppet valve () movably attached to a small-diameter cylindrical portion of a valve body (), an annular abutment portion formed on a plunger body of a plunger () to bring a variable-pressure chamber B into and out of communication with the atmosphere by unseating from and seating on the poppet valve, respectively, a movable seat member () movably guided by the valve body to bring a negative-pressure chamber A and the variable-pressure chamber B into and out of communication with each other, and a transmitting member () having one end abutting against the movable seat member and the other end disposed to surround a stepped piston of the plunger so as to be abuttable against a reaction disk ().

Pneumatic booster

A pneumatic booster () disposed between a brake pedal () and a master cylinder () includes a cylindrical member () provided on an outer circumferential side of an output rod (). A seal member () seals between an outer circumferential side of the cylindrical member and a cylindrical portion of a front shell, and an O-ring seals between the cylindrical member and the output rod. The cylindrical member causes a differential pressure between a negative pressure chamber (A) and an atmosphere chamber (C) to be applied to a valve body (). One axial side of the cylindrical member is configured to cause an atmosphere pressure to be applied to the valve body by abutting against a cylindrical protruding portion of the valve body, thereby pushing the valve body with the aid of the differential pressure in the direction as a biasing direction of a return spring.

Pneumatic booster and brake system

In a pneumatic booster, a front shell and a rear shell are connected by means of a rod. A stud bolt on one end of the rod extends through the front shell to the outside, and a support plate fitted around the stud bolt is engaged with the rod and abutted against an inner surface of the front shell. A seal member is provided in an annular groove formed in the support plate. A projection is formed in the support plate. When the support plate is reversely mounted on the stud bolt, the projection is abutted against the front shell, and the seal member is unable to provide a seal between the stud bolt and the front shell. In a leak inspection, air is flowed into a constant-pressure chamber through a cut portion formed in a distal end of the projection, to thereby detect reverse mounting of the support plate.

An elastic member is interposed between a reaction disk and a plunger. By moving the plunger to open a poppet seal such that atmospheric air is introduced into the variable pressure chambers, a pressure differential is created between the variable pressure chambers and constant pressure chambers (negative pressure). As a result, servo power is applied to an output rod, and a resulting reaction force is partly transmitted back to an input rod through the reaction disk. During a rapid braking operation, a piston is caused to retract by a pin, thus pushing the elastic member into an outer peripheral groove formed on the piston so that the elastic member is axially compressed. As a result, the movement amount of the plunger can be increased without receiving a reaction force, enabling the rapid development of servo power.

A valve bodyis connected to a power piston, which divides a housing into a constant pressure chamber (negative pressure) and a variable pressure chamber. In the valve bodythere is provided a brake assisting mechanismbetween a reaction diskand a plungerA poppet sealis opened by movement of the plungerto thereby introduce atmospheric air into the variable pressure chamber and generate a thrust force in the power piston. During rapid braking, a plunger rodadvances relative to a sleeveand ballsshift outward and the plunger roddirectly abuts against a reaction rodresulting in contraction of the brake assisting mechanismTherefore, the amount of movement of the plungercan be increased without being affected by a reaction force from the reaction diskthus enabling rapid development of servo power.

A tandem pneumatic booster includes a front shell having a relatively long cylindrical portion and a rear shell having a relatively short cylindrical portion. The cylindrical portions of the front and rear shells are joined together to form a shell body. An opening edge of a cylindrical portion of a center shell is disposed in the joint between the front and rear shells, together with an outer peripheral bead of a diaphragm of a rear power piston. The cylindrical portion of each of the front, rear and center shells has a frusto-conical shape gradually increasing in diameter toward the opening edge thereof. Thus, when front shells, rear shells and center shells are stacked on one another, respectively, as constituent parts before assembly, the depth of fitting between each pair of adjacent shell elements is increased sufficiently to stably maintain the stacked conditions of the shell elements.

A tandem pneumatic booster having a shell body, the inside of which is divided into two, front and rear, chambers by a center shell. Each chamber includes a negative pressure chamber and a working pressure chamber. A valve body is slidably fitted in the shell body and the center shell with seal members therebetween. The valve body is provided with an air passage for communication between the front and rear working pressure chambers. A valve mechanism is actuated in association with an input shaft to introduce atmospheric air into the front and rear working pressure chambers through the air passage so as to apply thrust to front and rear power pistons. The diaphragm of the front power piston has a bead on an inner periphery thereof. The valve body has a groove on an outer periphery thereof. A portion of the air passage which leads to the front working pressure chamber has a main passage portion extending axially in the valve body, and a bypass extending radially outward from the main passage portion. A communicating port leading to the front working pressure chamber extends axially from the bypass. The bypass opens into the groove, and the radially outer end of the bypass is sealed with the bead.

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Yamanashi, Japan

Shuzo Watanabe