Pumps – Three or more cylinders arranged in parallel – radial – or...
Patent
1996-12-23
1998-06-09
Freay, Charles G.
Pumps
Three or more cylinders arranged in parallel, radial, or...
91499, 92 71, F04B 120
Patent
active
057624771
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a piston/slide shoe arrangement of a hydraulic piston machine having a slide shoe, which is in articulated connection with a piston, with a friction-reducing plastics material therebetween, wherein the plastics material, forming a channel, extends into a through-opening in the slide shoe in a direction towards a sliding contact surface of the slide shoe which in operation lies against a swash plate.
Such an arrangement is known from the non-prior-published German patent application 43 01 123.
Normally, the piston is joined to the slide shoe by way of a ball-and-socket joint. In the case of an axial piston machine, the slide shoe lies against a swash plate so that, as a cylinder drum receiving the piston rotates with respect to the swash plate (or vice versa), a back and forth movement of the piston is produced. During this movement, the slide shoe is pivoted in relation to the piston.
In operation, friction occurs firstly between the slide shoe and the swash plate and secondly between the slide shoe and the piston. This is not critical provided that a natural or synthetic oil having satisfactory lubricating properties is used as hydraulic fluid. In that case, lubrication is ensured by this oil, so that wear and tear is kept within limits. If the hydraulic fluid does not have the required lubricating properties, however, as is the case, for example, with water as hydraulic fluid, measures must be taken not only to keep the wear and tear within limits, but actually to allow operation of the machine in the first place. Without such measures, the parts moving against one another would sooner or later wear away and permanently damage the machines.
In the prior application, the task of reducing friction is therefore assumed by the plastics material which is arranged between the piston and the slide shoe. Occasionally, however, the plastics material on the slide shoe has become displaced under adverse conditions. This displacement can even extend to the plastics material working its way out of the region between the ball-and-socket joint of the piston and the slide shoe. In that case, the piston will rub directly against the slide shoe, which will sooner or later lead to the two parts wearing each other away. Indeed, this relative movement between the piston and the slide shoe is made somewhat more difficult by that part of the plastics material which extends through the through-opening in the slide shoe in the direction towards the sliding contact surface. As this plastics material, however, has to form a channel in order to allow passage of hydraulic fluid to the sliding contact surface, and this channel widens out towards the piston to provide a reliable fluid connection to a supply channel in the piston even with an obliquely positioned slide shoe, the resulting holding force effected is sometimes insufficient to accommodate the shear forces that occur. These shear forces occur in particular when the machine is put into operation every now and then after intervals of non-use.
The invention is based on the problem of improving the piston/slide shoe arrangement in such a manner that it has a relatively long service life even under adverse operating conditions.
In an arrangement of the kind mentioned in the introduction, this problem is solved in that the slide shoe and the plastics material have outside the through-opening at least one connecting element which takes up shear forces between slide shoe and plastics material.
With a construction of that kind, on the one hand the plastics material continues to be retained as the friction-reducing element between the slide shoe and the piston. On the other hand, however, the plastics material is safeguarded against being displaced from the region between the piston and the slide shoe by shear forces, that is, forces which arise as a result of piston and slide shoe moving against one another.
The connecting element preferably surrounds an axis of the slide shoe substantially point-symmetrically, or several connecting elements are provided whi
REFERENCES:
patent: 3183848 (1965-05-01), Raymond
patent: 3958901 (1976-05-01), Drevet
patent: 5601009 (1997-02-01), Jepsen et al.
patent: 5685215 (1997-11-01), Jepsen et al.
Jepsen Hardy Peter
Kristensen Egon
Martensen Lars
Danfoss A/S
Freay Charles G.
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