Power plants – Pressure fluid source and motor – Pulsator
Reexamination Certificate
2001-01-10
2002-10-22
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Pulsator
C060S584000
Reexamination Certificate
active
06467268
ABSTRACT:
This application is based on and claims priority under 35 U.S.C. §119 with respect to Japanese Application No. 2000-006821 filed on Jan. 14, 2000, the entire content of which is incorporated herein by reference.
FIELD OF THE INVENTION
This invention generally relates to vehicle braking. More particularly, the present invention pertains to a brake master cylinder for a braking device of a vehicle.
BACKGROUND OF THE INVENTION
A known brake master cylinder device is described in Japanese Patent Publication 04-27060. The disclosed brake master cylinder includes a cylinder housing including a cap engaged with the opening of a body. A first piston and a second piston penetrate through the cap are slidably disposed via a piston guide in the cylinder housing. A resin made sleeve for determining the position of the first piston is slidably attached to the first piston and is disposed in the cylinder housing.
A first pressure chamber is formed with the first piston, the second piston, and the sleeve. A second pressure chamber is formed with the second piston and the inner wall of the body. The first pressure chamber and the second pressure chamber are provided with a spring mechanism for biasing the first piston and the second piston rearwardly.
In this known brake master cylinder, when the first piston and the second piston are slidably moved into the first pressure chamber and the second pressure chamber respectively by brake pedal depression, the fluid pressure in the respective pressure chambers is increased to convey the pressurized brake fluid from an output port to respective brake systems.
The spring mechanism comprises a return spring, a guide screw, and a spring retainer. The guide screw having a forwardly projecting head portion is engaged with the first piston. The spring retainer slidably moves on the guide screw and contacts the rear side of the head portion of the guide screw. The return spring is provided in a compressed state between the spring retainer and the first piston.
The spring retainer includes a projection protruding in the radially outward direction. The sleeve is provided with an axially extending guide groove for slidable engagement by the projection and a stopper blocking the axial movement of the projection of the spring retainer and restricting the retraction of the projection. This structure makes it possible to reduce the size of the brake master cylinder and to restrict the limitation for the retracted position of the first piston and the second piston.
The air relieving operation for relieving air remaining in the brake fluid is conducted when the brake device is assembled. The air relieving operation includes a so-called pumping operation for releasing bubbled air remaining in the brake fluid from a master cylinder reservoir to the atmosphere by strongly stepping on the brake pedal several times while injecting the brake fluid into the master cylinder reservoir. When air is still remaining in the brake fluid in the master cylinder, the first and the second pistons are rearwardly returned by an unnecessary strong force because the bubbled air compressed by the stepping operation of the brake pedal is expanded simultaneously with releasing of the brake pedal.
However, in this known brake master cylinder in which the position of the second piston is determined by the projection of the spring retainer contacting the stopper of the sleeve, the projection of the spring retainer and the stopper of the sleeve may be deformed or damaged by the severe contact between the projection of the spring retainer and the stopper of the sleeve when the aforementioned air relieving operation is conducted. In addition, because the final retracted position of the second piston when the brake pedal is released is determined based on the position that an opening of the piston port provided on the second piston overlaps with the back side of the cup seal, which is the position when the brake is not applied, bubbled air in the brake fluid may not be completely relieved to the atmosphere through the master cylinder reservoir.
In an electronic control brake system, the flow of brake fluid may be sometimes reversed into each pressure chamber of the master cylinder by a pump connected to a brake piping system. Particularly when the flow of the brake fluid is reversed into the second pressure chamber, the second piston is forced to be further moved in the rearward direction from the retracted position, which may deform and damage the projection of the spring retainer and the stopper of the sleeve.
In light of the foregoing, a need exists for a brake master cylinder which is not as susceptible to the same disadvantages and drawbacks as those discussed above.
A need also exists for a brake master cylinder having a relatively high degree of reliability in which deformation and damage will not occur by contact between a projection of a spring retainer and a stopper of a sleeve when a second piston is suddenly retracted by the operation of a pressure applying device of the brake system or by the air relieving operation.
SUMMARY OF THE INVENTION
The brake master cylinder of the present invention includes a cylinder housing formed by a body having an internal bore open at one end and a cylinder cap assembled to the internal bore at the opening end, a first piston positioned in the cylinder housing and slidably movable in the axial direction, and a second piston positioned forward of the first piston and slidably movable in the axial direction in the cylinder housing, and a sleeve located in the cylinder housing and slidably supporting the first piston and the second piston. The second piston is retractable by a predetermined distance from the non-braking operation position of the second piston.
Because the second piston is retractable by the predetermined distance from the non-braking operation position, any member which moves forward and rearward in one unit with the second piston does not contact the other fixed members under the air relieving operation. This thus prevents the movable and fixed members from deforming and becoming damaged.
A pressure chamber is formed between the second piston and the cylinder housing, a reservoir connecting port is formed in the body for connection to a reservoir, and a generally radially extending reservoir communication conduit is formed in the sleeve, opens to the outer diameter surface of the second piston, and establishes communication between the reservoir connecting port and the pressure chamber. A first cup seal is provided between the second piston and the body at a position forward of the sleeve, a second cup seal is provided between the sleeve and the second piston at a position rearward of the reservoir communication conduit, and a piston port is provided on the second piston at a position rearward of the first cup seal to establish communication between the reservoir communication conduit and the pressure chamber during non-braking operation. The predetermined distance corresponds to the total of the retracting distance of the second piston from the non-braking operation position to the position at which an opening of the piston port and an opening of the reservoir communication conduit overlap and a predetermined additional distance.
Thus, in accordance with the present invention, the second piston is retracted from the non-braking operation position to the position at which the opening of the piston port and the opening of the reservoir communication conduit overlap and is further retractable by the predetermined additional distance. Accordingly, fluid communication between the pressure chamber and the reservoir communication conduit is always ensured to completely relieve the bubbled air in the brake fluid to the atmosphere through the master cylinder reservoir.
The predetermined distance can also be defined by the retracting distance of the second piston from the non-braking operation position to the position at which the opening of the piston port and a lip of the second cylinder cup overlap. The second piston can thus be retracted f
Nakano Toshihiro
Okada Akimoto
Tsubouchi Kaoru
Aisin Seiki Kabushiki Kaisha
Burns Doane , Swecker, Mathis LLP
Lazo Thomas E.
Look Edward K.
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