Expansible chamber devices – Relatively movable working members – Interconnected with common rotatable shaft
Reexamination Certificate
1999-06-23
2001-05-29
Ryznic, John E. (Department: 3745)
Expansible chamber devices
Relatively movable working members
Interconnected with common rotatable shaft
C092S129000
Reexamination Certificate
active
06237465
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an axial piston machine with a plurality of reciprocating pistons, each of which is located so that it can move longitudinally in a cylinder bore and is supported on a bearing surface of a drive plate, whereby the drive plate is oriented at an angle with respect to a transverse plane that is a perpendicular to the axis of rotation of the axial piston machine, thereby forming a tilt angle.
2. Background Information
The prior art includes axial piston machines in a variety of configurations. There are essentially two main groups of axial piston machines: wobble plate construction and swash plate construction. In the axial piston machines that utilize the wobble plate construction, the drive plate rotates, while the cylinder bores in which the respective longitudinally movable reciprocating pistons are located and fixed stationary in relation to the housing. In axial piston machines that utilize the swash plate construction, the drive plate does not rotate in the housing of the axial piston machine, while the cylinder bores of the reciprocating pistons are located in a rotating cylinder drum. Both groups of axial piston machines exist both with a variable and with a constant tilt angle of the drive plate. Theoretically, both groups of axial piston machines can be used as a pump or as a motor.
The size of the stroke of the reciprocating pistons is the determining factor for the volume flow of the axial piston machines, and thus for their performance. The stroke is a function of the tilt angle of the drive plate and increases as the tilt angle increases.
The level of the acceptable stresses in t material (surface pressure, piston deflection) represents the limiting factor for the maximum allowable transverse force on the piston. The maximum transverse force on the piston occurs when the force is split on the drive plate between a longitudinal and transverse force on the piston at the acceptable maximum tilt angle of the drive plate at a specific maximum operating pressure of the axial piston machine. The decisive factor is thereby always the reciprocating cylinder that is extended farthest from its cylinder hole and is exposed to the maximum operating pressure. In particular, high stresses can occur on the edges of the cylinder bore and the reciprocating piston.
To increase the delivery of the axial piston machine, the simplest approach would be to increase the tilt angle of the drive plate. Such an increase, however, would have a disproportional effect on the load on the reciprocating piston because, not only is the transverse force on the piston increased as a function of the tilt angle, but also as a result of the fact that the reciprocating piston is extended farther out of the cylinder bore, a correspondingly increased tilting moment is applied to the extended lever arm.
On the axial piston machines of the prior art, the tilt angle is, therefore, not more than 18 degrees to 20 degrees.
SUMMARY OF THE INVENTION
The object of the present invention is to make available an axial piston machine of the type described above that combines compact size with a high delivery capacity.
The present invention provides an axial piston machine with a bearing surface having a concave curvature when viewed in the direction of the longitudinal center plane of the axial piston machine, at least in the vicinity of the reciprocating piston that is extended farthest out of the cylinder bores.
The concave bearing surface means that the transverse force that is exerted on the reciprocating piston that extends the farthest out of its cylinder bore and is under operating pressure, and which results from the splitting of the forces at the point of support of the reciprocating piston on the bearing surface of the drive plate, is determined not only by the tilt angle of the drive plate, but also by the curvature of the bearing surface. Therefore, as a result of the inclusion of the curvature of the bearing surface, the support angle of the reciprocating piston on the bearing surface of the drive plate is smaller than the tilt angle of the drive plate.
Consequently, at the same tilt angle of the drive plate, the transverse force exerted on the reciprocating piston that is extended farthest out of its cylinder bore is reduced. Conversely, the present invention teaches that this fact can be taken advantage of so that with the same maximum possible transverse force on the piston, i.e., with the utilization of the maximum allowable material loads, the tilt angle of the drive plate can be increased, and thus the delivery of the axial piston machine of the present invention can be significantly increased.
In one embodiment of the present invention, the curvature of the bearing surface is designed so that the surface pressures of the reciprocating pistons in the cylinder bores and/or the deflections of the reciprocating pistons that occur during operation differ from each other by not more than 20%, and in particular by not more than 10%. In this manner, there is a uniform load on all the reciprocating pistons and cylinder bores.
The axial piston machine of one embodiment of the present invention includes the tilt angle of the drive plate between 20 degrees and 30 degrees. This axial piston machine has small outside dimensions and a large geometric volume flow, and thus a high delivery capacity. As a result of the curvature of the bearing surface, the loads on the reciprocating pistons and cylinder bores are lower than in propulsion systems of the prior art.
The invention can be applied to different type of axial piston machines, theoretically regardless of how the reciprocating piston is supported on the bearing surface of the drive plate. For example, the reciprocating piston can be supported on the bearing surface by spherical heads or slippers. In one embodiment of the present invention, the reciprocating pistons are supported on the bearing surface of the drive plate by slippers, whereby the slide face of the piston facing the drive plate has a convex curvature in particular a spherical curvature. The radius of curvature of the convex slide face is essentially equal to the radius of curvature of the concave bearing surface of the drive plate. This slipper design can absorb high loads and, therefore, makes possible a high operating pressure, which in turn results in a high delivery capacity of the axial piston machine of the present invention. The slipper can be appropriately pressed toward the bearing surface of the drive plate by a hold-down plate. The end surface of the hold-down plate that faces the slippers has a convex curvature, in particular a spherical curvature.
Additional advantages and details of the present invention are explained in greater detail below with reference to the exemplary embodiment illustrated in the accompanying schematic drawing.
REFERENCES:
patent: 1882632 (1932-10-01), Jaworowski
patent: 2374595 (1945-04-01), Franz
patent: 3233550 (1966-02-01), Smith
patent: 4741251 (1988-05-01), Hayashi et al.
patent: 5554009 (1996-09-01), Ohta et al.
patent: 6092457 (2000-07-01), Inoue et al.
Forster Franz
Sprenger Karl
Linde Aktiengesellschaft
Ryznic John E.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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