Pumps – Expansible chamber type – Biasing means effects induction stroke of abutment driven,...
Reexamination Certificate
1999-01-06
2001-04-24
Lopez, F. Daniel (Department: 3745)
Pumps
Expansible chamber type
Biasing means effects induction stroke of abutment driven,...
C417S555100, C417S536000
Reexamination Certificate
active
06220833
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high pressure hydraulic pump, and more particularly to an opposed piston-type pump for use in antilock brake systems (“ABS”) and other brake control systems for vehicles.
BACKGROUND OF THE INVENTION
Typical ABS systems for vehicles include an electric motor driven opposed piston-type pump for supplying pressurized brake fluid to any one of the vehicle brakes on instant, automatically controlled, demand. The electric motor is a part of the ABS unit and includes a drive shaft having an eccentric or cam portion. A pair of pumping pistons are located on opposite sides of the drive shaft within a body of the pump. Respective input and output passageways allow for proper circulation of fluid through the pump. The output associated with each pumping piston provides high pressure brake fluid, approximately 2500 psi, to an associated brake or group of brakes on the vehicle. The ABS system is typically integrated into the vehicle braking system and monitors specific braking parameters such as vehicle acceleration, vehicle speed, the coefficient of friction of the road, and the amount of brake pedal pressure input from a driver. Once minimum threshold values for the ABS characteristics are exceeded, a controller activates the ABS system and the ABS pump provides pressurized brake fluid as needed, instead of pressurization from the brake pedal and master cylinder.
Conventional ABS pumps have complex piston structures including through bores drilled for providing passageways for brake fluid to pass through the piston. To control direction of flow, one-way inlet check valves are provided in the piston fluid passageway between the inlet and the outlet passageways of the pump. The one-way check valves allow fluid from the inlet to pass through the piston to the outlet but prevent flow in the opposite direction. Thus, the piston is able to build up pressure for delivery of pressurized fluid to the output. Conventional pistons have O-rings or D-rings for sealing engagement between the exterior of the piston and the associated housing bore. One-way check valves usually have a ball biased by a spring and require a machined seating surface for the ball to properly seal a desired passage. In addition, sleeves and connectors are utilized for retaining the spring and ball within the piston. The check valve increases the overall length of the piston and thereby requires the pump to be proportionally larger as well. Therefore, the overall weight of the pump is undesirably heavier.
SUMMARY OF THE INVENTION
The present invention is directed to a pump for an antilock brake system having a housing including an inlet and an outlet. A bore located in the housing is in fluid communication with the inlet and the outlet. At least one piston is located in the bore and an eccentric shaft drives the piston in a reciprocating motion to pump brake fluid. A motor is provided for driving the eccentric shaft and a directional seal is connected to the at least one piston and is configured to pressurize fluid on a forward stroke and permit fluid to flow past the seal on a return stroke.
The present invention further provides a pump for a vehicle antilock brake system including a housing having an inlet and an outlet. A bore is located in the housing and is in fluid communication with the inlet and outlet. First and second substantially solid pistons are located in the bore and an eccentric shaft drives the pistons in a reciprocating motion to pump brake fluid. In addition, a motor is provided for driving the eccentric shaft and a directional seal is provided on each piston and is configured to pressurize fluid on a forward stroke and permit fluid to flow past the seal on a return stroke.
Further, the present invention provides a pump for a vehicle antilock brake system having a housing with an inlet and an outlet and a bore located in the housing that is in fluid communication with the inlet and outlet. First and second pistons are located in the bore and are substantially solid and a have circumferential groove. An eccentric shaft is provided for driving the first and second pistons in a reciprocating motion. A motor is utilized for driving the eccentric shaft. In addition, an elastomeric directional seal is located in each of the circumferential grooves of the first and second pistons and includes a main body and an angled lip, wherein the angled lip extends outwardly from the main body to selectively contact the bore of the housing and pressurize fluid on a forward stroke and permit fluid to flow past the seal on a return stroke.
Optionally, a plurality of through bores can be provided in a flange of the piston to increase fluid flow past the seal. Another option for the present invention includes locating a backing ring in the circumferential groove adjacent the seal to increase seal stiffness.
The present invention eliminates the need for a one-way check valve located in the piston. Instead, the present invention provides a directional seal located on the exterior of the piston for selectively sealing a gap between the piston and its associated bore. The directional seal is preferably cup-shaped in cross-section such that the seal lip expands outwardly for engagement with the bore when the piston is driven toward the outlet passageway. However, upon a return stroke toward the inlet passageway, the directional seal lips tend to collapse toward the piston and permit fluid to flow from the inlet toward the outlet and thereby replenish the working fluid in a pumping chamber for the next piston pressure stroke.
Accordingly, the present invention simplifies the overall design and eliminates the need for extra machining steps required for a one-way inlet check valve to be located within a piston. At least approximately six component parts are eliminated by the present invention versus conventional pumps for brake systems. The present pump design further simplifies assembly and thereby reduces manufacturing costs. Further, elimination of a one-way check valve in the piston permits a shorter piston to be used, which translates into a smaller, more compact pump design. In addition, such a compact pump has reduced weight to provide for a lighter, more fuel efficient, vehicle.
REFERENCES:
patent: 1820883 (1931-08-01), Hueber
patent: 2368187 (1945-01-01), Williams
patent: 3092427 (1963-06-01), Sadler et al.
Continental Teves Inc.
Lazo Thomas E.
Lopez F. Daniel
Rader & Fishman & Grauer, PLLC
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