Pumps – Expansible chamber type – Valved piston
Reexamination Certificate
1999-06-01
2001-08-21
Thorpe, Timothy S. (Department: 3746)
Pumps
Expansible chamber type
Valved piston
C417S470000, C092S170100
Reexamination Certificate
active
06276909
ABSTRACT:
PRIOR ART
The invention is based on a piston pump intended in particular for a hydraulic brake system for a vehicle with a slip control system.
One such piston pump is known for instance from German Patent Disclosure DE 41 07 979 A1. This known piston pump has a pump housing with a cylinder bore in which a piston is axially displaceably received. By means of an eccentric drive, the piston can be driven to execute an axially reciprocating stroke motion. The piston of the known piston pump is a workpiece produced by complicated and expensive metal cutting and drilling in graduated form.
ADVANTAGES OF THE INVENTION
The piston of the piston pumps according to the invention the characteristics of claim
1
has a core, for instance of steel, which is provided with a lubricant jacket of plastic on its circumference. A needle of a needle bearing can for instance be used as the core. The lubricant jacket need not cover the axial length of the core; a lubricant jacket in the region of one end of the core suffices, for instance. Two lubricant jackets may also be provided, in the region of both ends of the core. The invention has the advantage that the piston can be produced without metal-cutting machining and thus quickly and inexpensively. By means of the lubricant jacket of plastic, the piston has good sliding properties in the cylinder bore. Post machining of the piston circumference, forming a slide face, for instance by grinding is unnecessary. The core can also be produced by deforming, for instance cold forming, for instance by extrusion, flow turning or upsetting.
Because of the nonmetallic lubricant jacket, an otherwise usual guide ring for guiding the piston can be dispensed with without fear that increased friction or damage to the guide face will occur. By the omission of a guide ring, the expense for assembling the piston pump is advantaceously reduced substantially, and at the same time very good durability and high efficiency of the piston pump are nevertheless assured.
It can be provided that the core rests on an eccentric element. The core, which is of hard material and preferably hardened steel, has the advantage that the drive energy from the eccentric element can thus be transmitted to the piston without functional problems or wear problems.
The core also has the advantage that undesirably great accumulations of material at the lubricant jacket can be avoided.
The piston may be designed such that the piston is not guided at the core, which has the advantage that labor-intensive grinding of the core can be dispensed with. However, the piston can also be designed such that the guidance of the piston is done directly at the core, only in that region of the piston where it is easy to achieve the required surface quality.
If the piston is guided at least in some points directly on the core of the piston, then the requisite surface quality can be produced on the core before the lubricant jacket is applied to the core of the piston. This has the advantage that the requisite surface quality can be produced on the core without a major effort.
It may be provided that the lubricant jacket also serves to provide sealing between the piston and the piston guide. This has the advantage that a sealing ring can be omitted.
With the lubricant jacket, it is advantageously possible at no additional effort to produce a stepped piston, in which one end of the piston has a larger diameter than the other end.
In a preferred feature defined herein; the lubricant jacket is embodied as a sealing element at the same time. As a result, a separate sealing element, such as a sealing ring, is omitted, and it becomes unnecessary to make a groove in the piston or in a wall of the cylinder bore for receiving the sealing element. The step of inserting the sealing element into the groove is also dispensed with in the assembly of the piston pump.
In a refinement of the invention, the plastic lubricant jacket continues past a face end of the core and has a valve chamber into which a check valve is inserted as an inlet or outlet valve of the piston pump of the invention.
The retaining face proposed has the advantage that a durable connection between the core and the lubricant jacket is assured.
The retaining face can be designed in a very simple way such that the lubricant jacket and the core can be put together, and the retaining face advantageously assures a durable connection between the core and the lubricant jacket.
The piston pump of the invention is intended in particular as a pump in a brake system of a vehicle and is used to control the pressure in wheel brake cylinders. Depending on the type of brake system, the abbreviations ABS, ASR, FDR and EHB are used for such brake systems. In the brake system, the pump serves for instance to return brake fluid from a wheel brake cylinder or a plurality of wheel brake cylinders to a master cylinder (ABS) and/or to pump brake fluid out of a supply container into a wheel brake cylinder or a plurality of wheel brake cylinders (ASR or FDR or EHB). The pump is needed in a brake system with wheel slip control (ABS or ASR) and/or a brake system serving as a steering aid (FDR) and/or an electrohydraulic brake system (EHB). With wheel slip control (ABS or ASR), locking of the wheels of the vehicle during a braking event involving strong pressure on the brake pedal (ABS) and/or spinning of the driven wheels of the vehicle in the event of strong pressure on the gas pedal (ASR) can for instance be prevented. In a brake system serving as a steering aid (FER), a brake pressure is built up in one or more wheel brake cylinders independently of an actuation of the brake pedal or gas pedal, for instance to prevent the vehicle from breaking out of the lane desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB), in which the pump pumps the brake fluid into the wheel brake cylinder or wheel brake cylinders if an electric brake pedal sensor detects an actuation of the brake pedal, or in which the pump is used to fill a reservoir of the brake system.
REFERENCES:
patent: 2093062 (1937-09-01), Watson
patent: 4315454 (1982-02-01), Knödel
patent: 4867043 (1989-09-01), Antkowiak
patent: 5746111 (1998-05-01), Mueller et al.
patent: 5823639 (1998-10-01), Zinnkann et al.
patent: 5897303 (1999-04-01), Muller
patent: 6079961 (2000-06-01), Schuller et al.
patent: 6161466 (2000-12-01), Schuller et al.
Ehrlich Joachim
Fluck Tobias
Hellebrandt Michael
Merklein Dieter
Schlitzkus Michael
Greigg Edwin E.
Greigg Ronald E.
Robert & Bosch GmbH
Thorpe Timothy S.
Torrente David J.
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