US 4,399,735 AGranted

Brake booster

AssigneesToyota Jidosha Kogyo Kabushiki Kaisha, Aisin Seiki Kabushiki Kaisha

InventorsMasayoshi Katagiri, Osamu Ogura, Takashi Fujii

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Abstract

A brake booster of stroke-enlarging type which includes a casing, a power piston so disposed as to divide the interior of the casing into two chambers for being actuated by the difference of pressure in the two chambers, a control piston, containing therein a valve mechanism for controlling the difference of pressure in the two chambers and a transmission mechanism for transmitting an input of an input member to an output member, being coaxially fitted into a central bore of the power piston relatively movably thereto and a reaction lever, which is abutted at an output portion in the middle thereof by the output member, receiving output of the transmission mechanism and output of the power piston respectively as an input at a first input portion and a second input portion thereof located on either side of said output portion in the middle, whereby a greater stroke can be obtained at the output member than a stroke input at the input member. Between the control piston and the power piston a locking mechanism including a ball and a ball retainer is disposed. The ball retainer is for transmitting an output of the power piston to the reaction lever via the ball, through abutment on a first input portion of the reaction lever. After the ball has been locked between the power piston and the control piston a reactionary force which comes from the reaction lever back to the ball retainer is mostly transmitted from the ball to the control piston, not to the power piston. Therefore the power piston is not pushed back even after the peak of the assisting force given to the power piston by the pressure difference.

Claims12

Dependent claims

In a brake booster in which an output stroke of an output member is greater than an input stroke of an input member and which comprises (a) a casing, (b) a power piston axially movably disposed in said casing between said input and output members to divide an interior space of said casing into two pressure chambers, said power piston being actuated by a pressure difference between said two pressure chambers and having an internal surface defining an axially formed central bore, (c) a control piston having an external peripheral surface, and containing therein a control valve mechanism for controlling said pressure difference and further having a first transmission mechanism for transmitting an input force from said input member toward said output member, said control piston being coaxially received in said central bore and axially movable relative to said power piston, and (d) a reaction lever having an intermediate output portion, and first and second input portions located on opposite sides of said output portion, said first and second input portions receiving output forces of said first transmission mechanism and said power piston, respectively, said output portion abutting on said output member, an improvement comprising:

a second transmission mechanism including at least one ball associated with the external peripheral surface of said control piston and the internal peripheral surface of said power piston defining said central bore, and a ball retainer axially movably disposed and loosely retaining said at least one ball, said ball retainer abutting, on said second input portion of said reaction lever, said external peripheral surface having a recess whose depth increases progressively in the direction of advanvement of said power piston toward said output member, said internal peripheral surface including a ball driving surface and further including a ball locking surface, said at least one ball engaging said driving and locking surfaces such that said driving surface drives said at least one ball together with said power piston while said power piston is advanced relative to said control piston and such that said locking surface prevents said at least one ball from radially outwardly moving off the bottom surface of said recess after said power piston is advanced through a predetermined distance, whereby, in an initial operating stage of said booster, the output force of said power piston is transmitted to said reaction lever via said at least one ball and said ball retainer, and after the predetermined distance of advancement of said power piston and the resultant locking of said at least one ball between said locking surface and the bottom surface defining the part of said recess, a reactionary force from said output member is transmitted to said control piston but not to said power piston.

A brake booster comprising:

a casing;
an axially movable input member for receiving an input force;
an axially movable output member for providing a boosted output force;
a power piston axially movably disposed in said casing between said input and output members to divide an interior space of said casing into two pressure chambers, said power piston having an internal peripheral surface, and being spring-biased toward a retracted position thereof, and moved against the biasing force to an advanced position thereof in response to pressure difference between said two pressure chambers, said power piston having an axially formed central bore;
a control piston coaxially received in said central bore and spring-biased toward a retracted position thereof, said control piston having an external peripheral surface and being axially movable over a predetermined distance relative to said power piston, and being fixed to said power piston after said predetermined distance of relative movement thereof is achieved through the advancement of said power piston to said advanced position;
a control valve disposed in association with said input member and said control piston, and actuated by relative movement between said input member and said control piston for controlling said pressure difference;
a first transmission mechanism disposed within said control piston for transmitting forces from said input member and said control piston toward said output member;
a reaction lever having an intermediate output portion, and first and second input portions on opposite sides of said output portion, said output portion abutting on said output member, and said first input portion abutting on an output portion of said first transmission mechanism;
and
a second transmission mechanism including a ball retainer axially movably disposed between said power piston and said control piston and abutting at its axially forward end, on said second input portion of said reaction lever, said second transmission mechanism further including at least one ball loosely retained in said ball retainer and associated with the external peripheral surface of said control piston and the internal peripheral surface of said power piston defining said central bore, said external peripheral surface having a recess whose depth increases progressively in the direction of advancement of said power piston, said internal peripheral surface including a ball driving surface for advancing said ball together with said power piston while said power piston is moved to said advanced position, and further including a ball locking surface for preventing said ball from moving radially outward off the bottom surface of said recess after said power piston is located at said advanced position.

7 more elements

Dependencies are inferred from the claim text.