Expansible chamber devices – Relatively movable working members – Interconnected with common rotatable shaft
Patent
1996-08-12
1997-11-11
Denion, Thomas E.
Expansible chamber devices
Relatively movable working members
Interconnected with common rotatable shaft
92 72, 92153, 92154, 91491, 91499, 417269, 74 60, F01B 300
Patent
active
056852150
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a hydraulic piston engine for operation with a lubricant-free, water-based pressure fluid, with a rotatable shaft, which is coupled to work pistons and journalled in a housing with at least one radial journal bearing, in which a first sliding surface of metal turns faces a second sliding surface of plastic material.
From EP 0 512 138 a hydraulic piston pump is known of the type mentioned in the introduction, where the drive shaft is made of metal, and the bearing liners of the radial journal bearings are made of a highly stable plastic material on polyetheretherketone basis. The piston pump further comprises pistons of metal, which are supported in cylinder bushings of the plastic material mentioned, with an intermediary, well-defined annular gap, which ensures a passing flow of cooling water in operation. Further, the pump shaft comprises cooling bores for admission of water to the radial journal bearings. However, the publication supplies no directions towards solving the problems concerning the radial journal bearings, which have proved to appear in practice when the pump must be operated at high pressures and/or high rotational speeds.
In practice is has not yet proved possible to achieve operational reliability with known, hydraulic piston engines which are driven by a lubricant-free, water-based pressure fluid. Especially during start and at high bearing loads have the motors been subject to failure. The development effort has mainly been concentrated on choice of materials for the facing sliding surfaces of the radial journal bearings with a view to reducing the friction between them.
The hydraulic piston engine according to the present invention is characterised in that in the journal bearing in a load area, which by the influence of the work pistons during operation is continuously loaded with a radial force, at least one recess has been made in one of the sliding surfaces, which recess is supplied with pressure fluid during operation for at least partial absorption of the radial force, and that the areal centre of gravity of this recess has been angularly displaced in the direction against the direction of rotation of the shaft in relation to a certain position determined by the geometry of the engine, which position indicates the areal centre of gravity for an area where the radial load from the work pistons would exist on the sliding surface in question, if the journal bearing was without friction and without recess. In this manner a hydraulic piston motor is obtained, which is driven by a lubricant-free, water-based pressure fluid, and which appears particularly reliable in operation, particularly during start and at high bearing loads.
For hydraulic piston engines it is known that a permanent high-load area exists at one of the facing sliding surfaces of the radial journal bearing as a consequence of the stationary, static load condition of drive shaft or bearing liner during operation of the piston engine in question, not considering a frictionally conditioned stress by direct contact between the bearing surfaces. The high-load area comprises geometric, radial extreme points for the transmission of the piston forces to the bearing surface via the drive shaft at the smallest, respectively the highest number of pressure-activated pistons for the motor in question. In the case of an axial piston motor, the high-load area is situated on the sliding surface of the bearing liner, and in the case of a radial piston motor, the high-load area is situated on the sliding surface of the drive shaft.
The design according to the present invention reduces the frictional load, and thereby the mechanical wear in the journal bearing. Therefore a water-driven hydraulic piston engine according to the invention can achieve a considerably longer life that the design known from EP 0 512 138. This applies in particular to intermittent duty, where the engine is frequently started and stopped.
It must be assumed that among other things the longer life is c
REFERENCES:
patent: 3838942 (1974-10-01), Pokorny
patent: 3872775 (1975-03-01), Clerk
patent: 3964323 (1976-06-01), Seibert
patent: 5055004 (1991-10-01), Ebbing et al.
patent: 5450823 (1995-09-01), Istomin
Jepsen Hardy Peter
Klynder Flemming
Danfoss A/S
Denion Thomas E.
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