Pumps – Motor driven – Fluid motor
Patent
1991-10-04
1992-12-22
Smith, Leonard E.
Pumps
Motor driven
Fluid motor
91313, F04B 912
Patent
active
051730367
DESCRIPTION:
BRIEF SUMMARY
present invention relates to an arrangement for the control of a fluid driven linear motor comprising a cylinder and a piston in which the two opposite sides of the piston are alternately supplied with fluid from a slide valve device.
Such linear motors may be used for driving for instance pumps for high pressure washing machines, water jet cutting, injection and dosage of chemicals, hydraulic systems, or for pumping most types of liquids and gases.
In a previously known linear motor of the type mentioned above, the turning of the piston takes place when a spring-loaded mechanical device pushes the slide to its opposite position for the purpose of reversing the movement of the piston. This mechanical device also comprises a spring-loaded toggle mechanism which is necessary in order to retain the slide at each terminal position. The structure of the previously known linear motor is very complicated because of its many moving parts, and therefore correspondingly costly to manufacture, and besides, the rate of the stroke of the motor is restricted because of the comparatively large mass of the piston system. The piston system further contains parts which can move axially among themselves, partly because of play and partly from the effect of springs, and this also gives rise to additional vibrations and accompanying noise.
From German Patent Specifiction 875 179 a linear motor is known where the slide has an axially extending chamber wherein a pilot device is movable between two terminal positions in time with the movements of the piston. The pilot device also has an axially extending cavity and both the slide and the pilot device have radial ports so that driving fluid can be conveyed through some of these radial ports and the axial cavity of the pilot device to one or the other of the end surfaces of the slide depending upon the relative positions of the slide and the pilot device. In order to move the slide from one of its terminal positions to the other, it is first necessary to shift the pilot device inside the slide. This is done by means of separate end bolts protruding externally of the valve housing and being activated through some mechanism by the piston. Due to unavoidable clearance between the various parts in the pilot device activating mechanism and the fact that the pilot device must be shifted against the full driving fluid pressure, the stroke rate or speed of the motor is severely restricted, the noise level and wear rate is high, while the efficiency is not at an optimum.
The aim of the present invention is to provide an arrangement of the type mentioned initially which makes it possible to achieve a quicker stroke rate in the linear motor and at the same time makes its structure simpler, less costly and more reliable.
This is achieved according to the invention by an arrangement in a fluid driven linear motor, for instance for operating a high pressure pump, comprising a cylinder and a piston. The two opposite sides of the piston are supplied with driving fluid from a slide valve device. The slide valve device has a slide which is moved between its terminal positions under the effect of a pilot device which is moved synchronously with the movements of the piston. The slide has an axially continuous cavity in which the pilot device is slidingly received and arranged to alternately bring the cavity into fluid communication with the ends of the slide when the piston is at its terminal positions. The slide further has means for supplying driving fluid to the cavity. The cavity of the slide at its axially separated ends is provided with inwardly protruding seals which interact with the pilot device. The pilot device has a first section of reduced cross section which opens the cavity towards the ends of the slide when it is in a position opposite one or the other of the seals.
By arranging the slide and pilot device in this manner, rapid and reliable shifting of the position of the slide is achieved without the need to use appreciable force or a complicated, noisy and costly mechanism which could
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Ingerman Jeffrey H.
Smith Leonard E.
Speeder, A.S.
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