Pumps – Three or more cylinders arranged in parallel – radial – or...
Reexamination Certificate
1999-04-09
2001-06-12
Freay, Charles G. (Department: 3746)
Pumps
Three or more cylinders arranged in parallel, radial, or...
C417S273000
Reexamination Certificate
active
06244832
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a radial piston pump for high-pressure fuel delivery in fuel injection systems of internal combustion engines, in particular in a common rail injection system. A drive shaft that is supported in a pump housing and has an eccentrically embodied shaft segment, on which a ring is slidingly supported that cooperates with preferably a plurality of pistons, which are disposed radially with respect to the drive shaft in a respective cylinder chamber and whose ends oriented toward the drive shaft each have a respective plate.
In this kind of radial piston pump, which is braced on the inside, the plates mounted on the pistons have contact with the ring supported on the drive shaft. Because of the eccentricity of the drive shaft, the pistons are set in succession into a reciprocating motion. The stroke of the pistons is then constant and amounts to twice the eccentricity of the drive shaft.
To improve engine efficiency, it has been proposed that the cylinder chambers be filled with less fuel as the demand drops. In this so-called partial element filling, the components of the radial piston pump are subjected to extreme stress, and both increased wear and damage can occur.
OBJECT AND SUMMARY OF THE INVENTION
It is therefore an object of the invention to enable partial filling of the cylinder chambers of the radial piston pump. In particular, the radial piston pump of the invention should withstand a pumping pressure of up to 2000 bar in the pumping direction, and economical production should be possible.
In a radial piston pump for high-pressure fuel delivery in fuel injection systems of internal combustion engines, in particular in a common rail injection system, having a drive shaft that is supported in a pump housing and has an eccentrically embodied shaft segment, on which a ring is slidingly supported that cooperates with preferably a plurality of pistons. The pistons are disposed radially with respect to the drive shaft in a respective cylinder chamber and whose ends oriented toward the drive shaft each have a respective plate, this object is attained in that all the plates are kept in contact with the ring by a leaf-spring-like device, in particular a single clamp. In conventional radial piston pumps, the intake stroke motion of the piston is attained by a spring, which keeps the plate in contact against the ring. In the context of the present invention, it has been found that the high stresses in conventional radial piston pumps can be ascribed to twisting and tilting of the ring about its own axis. This twisting and tilting is in turn ascribed to the fact that in partial element filling, not all the plates rests permanently on the ring. The leaf-spring-like device assures the intake stroke motion of the pistons, even in a zero-pumping state. It is thus assured that all the plates will contact the ring even when the cylinder chambers are only partly filled with fuel, or are not filled at all. Twisting or tilting of the ring is avoided.
The embodiment according to the invention furthermore offers the advantage that the springs used in conventional radial piston pumps can be dispensed with. In other words, the space needed for the springs in a conventional pump housing is not needed. The machining openings in the pump housing that have to be made to create these spaces, and the associated sealing points, can thus be omitted as well. The pump housing becomes more compact, and its performance is less critical with respect to machining or to a heat treatment. Another advantage is that automatic assembly is made possible.
A particular variant embodiment of the invention is characterized in that the leaf-spring-like device is secured to the ring. This assures that the leaf-spring-like device executes the same motion as the ring. Fastening of the leaf-spring-like device to the ring can be done by an either non positive or positive connection.
Another particular variant embodiment of the invention is characterized in that the leaf-spring-like device is formed by a spring band, which extends in the circumferential direction around the ring and in which one oblong slot for each piston is disposed. The spring band is an economical starting material for the leaf-spring-like device of the invention. One oblong slot each assures that the ring can be displaced, together with the leaf-spring-like device, crosswise to the pistons. In the region of the oblong slots, the contour of the leaf-spring-like device is embodied as a leaf spring, in order to assure the prestressing to the pistons.
Another particular variant embodiment of the invention is characterized in that the leaf-spring-like device includes a plurality of spring wires, which extend in the circumferential direction around the ring. The use of the spring wires offers the advantage that the oblong slots in the variant embodiment described above can be dispensed with. This reduces the cost of producing the leaf-spring-like device of the invention.
Another particular variant embodiment of the invention is characterized in that the leaf-spring-like device is open on one side. The unilateral opening of the leaf-spring-like device can extend either over the entire length of the oblong slot or only in the region of the piston. The assembly of the leaf-spring-like device is made simpler by the unilateral opening.
Another particular variant embodiment of the invention is characterized in that the plate is secured to the piston by a plate holder. This has the advantage that parts of conventional pumps can be used in producing a radial piston pump according to the invention.
Another particular variant embodiment of the invention is characterized in that the plate is rigidly joined to the piston. This has the advantage of preventing twisting and/or tilting of the ring even more effectively than if the plate were movable.
The present invention also relates to a radial piston pump for high-pressure fuel delivery in fuel injection systems of internal combustion engines, in particular in a common rail injection system, having a drive shaft that is supported in a pump housing and has an eccentrically embodied shaft segment, on which a ring is slidingly supported that cooperates with preferably a plurality of pistons. The pistons are disposed radially with respect to the drive shaft in a respective cylinder chamber and whose ends oriented toward the drive shaft each have a respective plate held by a respective plate holder. In such a radial piston pump, the object described above is attained in that the plate holder is secured to the ring. This means that besides its original function, the plate holder also keeps the associated piston in contact with the ring, especially while fuel is being aspirated.
Another particular variant embodiment of the invention is characterized in that the plate holder has at least opposed two claws, whose ends facing one another firmly hold the plate, and at least two opposed claws, whose ends facing one another engage corresponding recesses in the ring. This has the advantage that only the plate holder and the ring need be embodied according to the present invention, in order to gain the advantages described above. For the rest of the pump, recourse can be had to parts for a conventional radial piston pump.
Another particular variant embodiment of the invention is characterized in that one flat face for each piston is provided on the ring. The polygonal design of the ring has the advantage that the course of motion is optimized. However, if a polygonal ring is used, the tilting of the ring about its own axis as described has a disadvantageous effect. The present invention therefore has special significance. By means of the embodiment according to the invention, the motion of the polygonal ring is effectively stabilized even during partial filling of an element.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of a preferred embodiment taken in conjunction with the drawings. Th
Guentert Josef
Simon Hans-Juergen
Streicher Bernd
Freay Charles G.
Greigg Edwin E.
Greigg Ronald E.
Robert & Bosch GmbH
Solak Timothy P.
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