Power plants – Pressure fluid source and motor – Pulsator
Reexamination Certificate
2000-01-14
2001-08-21
Ryznic, John E. (Department: 3745)
Power plants
Pressure fluid source and motor
Pulsator
C060S454000
Reexamination Certificate
active
06276137
ABSTRACT:
TECHNICAL FIELD
The technical field of this invention is vehicle brake master cylinders.
BACKGROUND OF THE INVENTION
A vehicle brake master cylinder provides control and routing of brake fluid flow to the individual wheel brakes. The master cylinder is typically provided with primary and secondary pistons, each providing brake fluid at an operator determined pressure from a separate portion of a brake fluid reservoir to a separate pair of brake mechanisms.
A particular function performed by the master cylinder is the control of fluid as required between each portion of the brake fluid reservoir and its assigned wheel brakes. This is accomplished with the assistance of bypass and compensation openings through the walls of the master cylinder housing between the brake fluid reservoir and the primary and secondary pressure chambers of the master cylinder. Bypass openings are located immediately in front of the primary seals on the primary and secondary pistons so that they are open to the appropriate wheel brakes with the pistons in their deactivated positions; and each thus permits replenishment of fluid in the brake lines in front of its associated piston to fill the volume between the piston and brake apply mechanisms in preparation for the next braking activation. Each bypass opening is passed by its associated primary seal almost immediately with activation of the piston to trap fluid in the brake lines and thus permit increase of braking pressure with further advance of the piston. A compensation opening is located behind the primary seal of each piston, even in the deactivated position of the piston, and maintains fluid volume behind the primary seal to prevent air from being pulled across the seal into the pressure chamber.
Such master cylinders may be used on vehicles provided with traction control or other systems capable of activating wheel brakes independently of the master cylinder and having a pump with an inlet open to the brake lines downstream of the master cylinder to provide brake fluid to the wheel brakes at the required pressure. In some modes of operation, such a pump can temporarily remove fluid from the brake lines at a rate which is greater than the flow capacity of the bypass opening, and/or the compensation opening across the seal, to replenish the fluid. In such vehicles, improved ability to flow fluid from the reservoir, through the master cylinder, to the traction control pump would help provide improved traction control response time. But it is not desirable to enlarge the bypass openings to provide the desired improved fluid flow, because a larger opening has a greater tendency to wear out or damage the seal that repeatedly slides over it. In addition, the seal construction tends to require a compromise between wear life and the ability to pass fluid downstream past the seal when required as described above; and a change in seal construction to permit greater fluid flow from the compensation opening past the seal into the brake lines may also cause a reduction in seal wear life.
SUMMARY OF THE INVENTION
The master cylinder of this invention provides separate flow paths through the secondary piston of an otherwise standard master cylinder to provide greater fluid flow capacity from the reservoir to both the primary and secondary pressure chambers in response to the removal of brake fluid from the brake lines fed by the primary and secondary pressure chambers by a pump providing brake pressure for activation of one or more wheel brakes independent of the master cylinder. The secondary piston is provided with an axial fluid flow passage having a primary check valve permitting fluid flow only out of the axial fluid flow passage into the primary pressure chamber and a secondary check valve permitting fluid flow only out of the axial fluid flow passage into the secondary pressure chamber. A cross flow passage is provided in the secondary piston intersecting the axial fluid flow passage between the primary and secondary check valves to communicate the axial fluid flow passage with the intermediate chamber and thus with the reservoir through the secondary compensation opening.
The first advantage of the master cylinder of this invention is improved reaction time for a traction control system, especially as applied to both the primary and secondary pressure chambers of a master cylinder, with changes only to the secondary piston of the master cylinder. An additional advantage is the ability to change the primary seals of both master cylinder pistons to emphasize resistance to wear, since these seals no longer have to fold down to allow compensation of brake fluid into the pressure chambers.
In a preferred embodiment, the axial fluid flow passage may be provided completely through the secondary piston, with an enlarged portion at each axial end receiving the check valve directed for outward flow only. At least one cross passage may extend radially through the piston from its outer surface to intersect the axial fluid flow passage. The additional operations on the secondary piston required to provide such construction comprise standard drilling and pressing operations, and the check valves may be off-the-shelf parts and/or self-contained assemblies for minimal cost.
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Hageman John Benjamin
Hous Kenneth Richard
Kottmyer Daniel Lee
Delphi Technologies Inc.
Ryznic John E.
Sigler Robert M.
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