Hydraulic radial piston machines

Details Hydraulic radial piston machines Hydraulic radial piston machines

1996-12-05

2000-01-04

Freay, Charles G.

Pumps

Condition responsive control of drive transmission or pump...

Adjustable cam or linkage

417273, 91498, F04B 106

Patent

active

060103116

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to positive displacement reciprocating piston machines of the type where the displacement of a piston within a cylinder causes fluid to be displaced within that cylinder.
For purposes of definition, a radial piston hydraulic machine of the high-speed variable-displacement kind can either be of the type where a rotary cylinder-barrel is mounted for rotation on a ported pintle-valve or where the cylinder-barrel is mounted for rotation on a shaft. In the second type, a stationary axial distributor-valve is fluidly connected to the cylinder-barrel to act as the means for porting the individual cylinders.
Radial piston machines have a number of advantages over other type of hydrostatic machines such as improved self-priming, particularly important in open-circuit pump systems, as the centrifugal effect tends to throw the pistons from their cylinders, especially when the cylinder-barrel is travelling at high rotational speed. Furthermore, the response time in changing the rate of fluid output is exceedingly fast, principally due to the use of low stroke/bore ratio's.
In the type of radial piston machine employing a pintle-valve, a cylinder-barrel mounted for rotation about its longitudinal axis, and where the cylinder-barrel is provided with a series of generally radial cylinder-bores. Each cylinder-bore contains a piston and each piston is operatively connected to the surrounding annular track-ring. The annular track-ring may be set into an eccentric positional relationship with respect to the rotating axis of the machine to determine the amount of piston stroke. The arcuate-slots in the pintle-valve are arranged to communicate with fluid inlet and outlet conduits attached to the exterior of the machine, and thus rotary movement of the cylinder-barrel is accompanied by radial displacement of the pistons and corresponding displacement of fluid through these conduits. The control-system of the machine operates in determining the required degree of eccentricity required between the track-ring and the pintle-valve for the piston stroke, so that the demands of a hydraulic system or circuit can be satisfied. The control-system thereby acts to regulate the supply of hydraulic fluid output from the hydrostatic machine to meet the varying fluid demands of the hydraulic system or circuit.
Variable-delivery radial piston machines have displaceable track-rings which can vary the stroke of the pistons on an imaginary line projecting generally parallel to the longitudinal axis of the arcuate-slots provided on the pintle-valve, or the banana-shaped slots in the case of an axial distributor-valve. All the piston reaction load acting on the track-ring have to be transmitted in some manner into the body of the housing. Based on geometric and kinematic considerations, prior art track-rings have been purposely constrained so that movement can only take place in accordance with one of the six possible degrees of freedom, this being achieved in either of following manners:
(i) In this type the track-ring is positioned in the housing so as to be able to be guided to slide in a straight-line fashion along a surface track or tracks. Typically two hydraulic-rams operate the track-ring to cause it to move along the surface track or tracks in order to change or adjust its eccentric position relative to the rotating axis of the machine. Examples of which are shown Great Britain Patent No. 1,302,084 and U.S. Pat. Nos. 1,656,544 and 2,807,140. Track-rings of this type are subjected to severe forces, from both the piston forces acting on the inner diameter as well as the hydraulic-ram forces acting on the outer diameter, these forces acting transversely to each other such that they cannot cancel each other out. Consequently, the track-ring must be of sufficient bulk and material strength to resist such adverse forces, in particular, those forces generated by the two opposing hydraulic-rams which in effect, act to trying to collapse the track-ring. The track-ring must be designed to resist deforma

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