Nippondenso Co., Ltd.

Nippon Soken, Inc.

Kazuo Sunami

Mitsuo Inagaki

Kenji Takeda

Hiroyuki Shinkai

A housing of a brake booster 100 includes a pair of shells 1 and 5 and a ring 3 interposed therebetween which cooperatively define an interior space for accommodating a power piston 13. The interior space is divided into a front chamber 15 and a rear chamber 16 partitioned by the power piston 13. The power piston 13 has a diaphragm 2 interposed between the front chamber 15 and the rear chamber 16. The diaphragm 2 is shiftable in an axial direction thereof in response to pressure imbalance between the front chamber 15 and the rear chamber 16. A convolution chamber 2d is provided between an inner side of the housing and an outer peripheral edge of the diaphragm 2. The convolution chamber 2d is defined by a resilient annular member flattened in the axial direction and isolated from both the front chamber 15 and the rear chamber 16. The annular member elastically rolls along the inner side of the housing in response to pressure imbalance between the convolution chamber 2d and one of the front 15 and rear chambers 16. And, a port 28 is formed in the ring 3 to supply constant pressure into the convolution chamber 2b.

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Nishio, Japan

Kazuo Sunami