Motors: expansible chamber type – Three or more cylinders arranged in parallel radial or... – Radially disposed cylinders
Reexamination Certificate
2000-11-20
2002-12-17
Walberg, Teresa (Department: 3742)
Motors: expansible chamber type
Three or more cylinders arranged in parallel radial or...
Radially disposed cylinders
C091S498000, C417S273000
Reexamination Certificate
active
06494127
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radial piston engine with roller guides for axial guidance of the rollers, via which the pistons are braced against the cam ring.
2. Discussion of the Background
From British Patent GB B 2238086 there is known a radial piston engine corresponding to the preamble of claim
1
, wherein the object was to reduce the manufacturing complexity previously associated with axial positioning of the rollers and thus to lower the manufacturing and assembly costs. This object was supposedly achieved in that, in each of the spaces between the roller end faces and the cylindrical inside face as the roller guide, there is disposed a wedge piece, whose cross section viewed in piston displacement direction is a circular segment, and which positions the roller axially in the cylinder relative to the cam. ring. The wedge pieces disclosed in the cited patent can be divided substantially into three different designs.
In a first design, each wedge piece has on the side facing the roller a plane surface which bears on the end face of the roller and on the side facing away from the roller a cylindrical surface which is in contact with the inside face of the cylinder. In addition, this wedge piece is accommodated in the space between roller, piston and cylindrical inside face, without being rigidly connected to any of these components. By virtue of the fact that the wedge piece is freely movable in piston displacement direction relative to the roller, the piston urges the wedge pieces toward the cam ring during a load stroke. In the process, the wedge pieces do not yet come into contact with the cams formed on the cam ring. In the ensuing idle stroke of the piston, however, the wedge pieces strike the cams formed on the cam ring. This recurring striking contact between the cams and the wedge pieces as well as the friction occurring therebetween can lead to severe wear of the wedge pieces. A further disadvantage of this design is that the width of the cam ring must be at least sufficiently large that the cam ring in addition to the roller also provides a contact face for the two laterally disposed wedge pieces. Aside from large total weight of the radial piston engine, a broad cam ring results in high manufacturing costs due to the greater manufacturing complexity associated with precision machining of the cam ring.
In a second design, each of the two wedge pieces has on the side facing the roller a driver-like projection, which extends toward the other wedge piece in an opening provided in the piston between piston and roller. Since in this case the wedge pieces are driven back into the cylinder by the roller during an idle stroke of the piston, striking contact between the wedge pieces and the cams basically cannot occur. Due to the high relative velocity between the roller and the driver-like projections of the wedge pieces in contact with the outside circumference of the roller, however, severe abrasion can take place on the driver-like projections. With increasing abrasion of the driver-like projections, the space available for play of the wedge pieces in piston displacement direction could ultimately increase to the point that striking contact could occur between the wedge pieces and the cams. A further disadvantage of this design is that driver-like projections must be formed on the roller guides and recesses must be formed on the piston, thus increasing the manufacturing complexity and thus the manufacturing costs.
In addition, the friction between the roller and the wedge pieces in the two foregoing designs occurs over the entire end face of the roller. This relatively large-area frictional contact necessitates precision machining of the friction faces of both components, once again resulting in high manufacturing costs.
At that time a further assumption was that, by virtue of the recurring contact of the rollers with the cam ring, the rollers and thus the respective piston automatically assume a particular angular position in the cylinder or relative to the cam ring, which is critical for reliable operation of the radial piston engine. In certain cases, however, for example during initial operation of the radial piston engine, when hydraulic fluid is fed to the cylinders for the first time, it is conceivable that the pistons and thus the rollers may be inserted so far into the respective piston that contact between roller and curved path does not yet occur. To ensure the necessary angular position of the piston in the cylinder in those cases, one of the two wedge pieces has, in a third design, on the side facing the cylindrical inside face, an elongated slot, into which a bolt, clamp or the like extending through the cylinder wall engages and in this way prevents turning of the piston in the cylinder and thus of the roller relative to the cam ring. The presence of the slot leads to weakening of the wedge piece in question, however, and thus to shortening of the useful life of the wedge piece, which is subjected to severe stresses and strains during operation of the radial piston engine. In addition, sliding contact takes place between the wedge piece and the bolt or clamp, which appears disadvantageous as regards good roller guidance. Furthermore, such a structural feature means high manufacturing complexity.
BRIEF SUMMARY OF THE INVENTION
In view of the disadvantages encountered in conventional radial piston engines, the object of the present invention is therefore to provide an optimally engineered radial piston engine, which is characterized by greater manufacturing simplicity and at the same time functionally reliable operation.
This object is achieved by the inventive subject matter according to the features of claim
1
, which is characterized in particular in that the roller guides disposed on the front sides of the rollers are rigidly connected to the respective roller with respect to sliding in piston displacement direction.
Since the respective roller urges the roller guides in piston displacement direction, in other words both during the load stroke and during the idle stroke, the roller guides can be dimensioned such that they do not project beyond the outside circumference of the respective roller, thus ensuring that striking contact does not take place between the roller guides and the cam ring. This ultimately leads to longer useful life of the roller guides and thus to functionally reliable operation of the radial piston engine on the whole. In addition, material economies are achieved in the manufacture of the roller guides.
If the roller guides do not come into contact with the cam ring, the width of the cam ring can be further reduced to a width which corresponds at most to the width of the rollers. In this way, not only is the total weight of the radial piston engine lessened, but also manufacturing complexity and thus the manufacturing costs are considerably reduced with regard to precision machining of the curved paths of the cam ring.
By suitable structural measures, such as by formation of a cylindrical projection on the roller guide, which projection is inserted in a corresponding recess on the front side of the roller, the relative velocities at the friction faces of roller and roller guides and thus the wear of the two components can also be reduced. Because of the reduced wear, the play developed between roller and roller guides is kept to a minimum, even after prolonged operating time. This contributes to functionally reliable and dependable operation of the radial piston engine on the whole.
Further advantageous features of the inventive radial piston engine are subject matter of the dependent claims.
The roller and roller guides can be rigidly connected with respect to sliding in displacement direction by simple manufacturing techniques. For example, the roller guides can be provided on the side facing the end face of the roller with a cylindrical projection, which is insertable into a central cylindrical recess formed on the end face of the roller. Likewise, it would natural
Mannesmann Rexroth AG
Van Quang
Walberg Teresa
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