Magnetic system for an oscillatory electrodynamic compressor

Abstract

A permanent magnet interconnects inner and outer pole pieces defining a gap in which a moving coil is to oscillate. The pole pieces and the interposed magnet are held together solely by the magnetic field of the permanent magnet. There are no mechanical fastening means.

Description

The invention relates to a magnet system for an oscillatory electrodynamic compressor, e.g. for refrigerators, comprising a permanent magnet, which is connected to an outer pole piece and to an inner pole piece, between which is defined a gap for the formation of a magnetic field and for reception of a moving coil.

Known magnetic systems of this kind are so constructed that the permanent magnet, constructed as a web or block, is centrally arranged on the bottom of the usually pot-like outer pole piece. The magnet carries a cylindrical inner pole piece which forms an annular gap with the outer pole piece. A moving coil may oscillate freely in the axial direction in the annular gap and is connected to a piston which acts in a cylinder unit. Alternatively, the outer pole piece is frequently constructed as a yoke.

In the known arrangements, the outer and inner pole pieces and the permanent magnet, are interconnected by means of bolts, screws, or adhesive.

The present invention is based on the problem of simplifying the structure of a magnet system of this kind.

This is accomplished, in accordance with the invention, in that the inner pole piece, the outer pole piece, and the permanent magnet situated between them, are held together solely by the force of the magnetic field of the permanent magnet, without complementary fastening means.

Accordingly, the invention provides a magnet system for an oscillatory electrodynamic compressor, the magnet system comprising a permanent magnet, an outer pole piece, and an inner pole piece, the pole pieces defining between them a gap for reception of a moving coil, the pole pieces being in contact with the magnet, the pole pieces and the interposed permanent magnet being held together solely by the magnetic field of the permanent magnet.

On the one hand, the invention exploits the physical fact that the magnetic force is effective in the flux direction and that no forces intervene at right angles to the flux direction. On the other hand, the invention is based on the experience gained by tests, to the effect that the magnetic forces available in such magnet systems are, unexpectedly, reliably adequate to interconnect the individual components of a magnet system firmly. Even if considerable tractive forces act on the inner or outer pole piece (the moving coil being kept in periodic oscillatory motion on the inner pole piece by the resonance spring of the oscillating compressor) the cohesion between the components is assured reliably.

In order to insure central positioning of the individual components and to prevent them from slipping relative to one another in conditions of rough usage, the outer pole piece, the inner pole piece, and the permanent magnet, may preferably be secured by mechanical locating means. To this end, it is possible to incorporate as a locating means, in a preferred form of embodiment, a sleeve surrounding the magnet, the sleeve consisting of nonmagnetic but electrically conductive material, which at its opposite end faces has machined recesses which are located with an easy fit on a matching boss on a base portion of the outer pole piece and on a matching boss on the inner pole piece.

The invention will be further described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a cross-section through a known magnet system in an oscillatory compressor;

FIG. 2 is a cross-section through a magnet system according to the invention in an oscillatory compressor;

FIG. 3 shows an embodiment of magnet system corresponding to FIG. 2, on enlarged scale, in cross-section;

FIG. 4 is similar to FIG. 3 and shows another embodiment of a magnet system according to the invention; and

FIG. 5 shows the magnet system of FIG. 4 in end view in the direction of the arrow A in FIG. 4.

A known magnet system incorporated in an oscillatory compressor, will be described briefly in order to delineate the nature of the invention as compared with the prior art. The known compressor shown in FIG. 1 comprises a sealed case 5 wherein an electrodynamic oscillatory drive 7, a cylinder unit 15 containing a piston 11 connected to a moving coil 8, and a pressure pipe 12 are suspended in an axially displaceable manner by means of springs 9 and 10. The oscillatory drive 7 consists of a pot-like outer pole piece 1 whose base 13 has situated on it a block-shaped permanent magnet 2 which on its end face bears a plate-shaped inner pole piece 3. The inner and outer pole pieces 3 and 1 together define an annular gap 4 wherein the moving coil 8 is arranged in a freely displaceable manner. The outer pole piece 1, the inner pole piece 3, and the permanent magnet 2 are held together by means of a bolt 6 of non-magnetic material.

The compressor illustrated in FIGS. 2 and 3, including a magnet system in accordance with the invention comprises a sealed case 63 wherein an electrodynamic oscillatory drive 52, a cylinder unit 17 containing a piston 57 connected to a moving coil 56, and a pressure pipe 47 are suspended in an axially displaceable manner by means of springs 18 and 19. The piston 57 operates within the cylinder unit 17, which has a cylinder compartment 20 separated from a pressure chamber 43 by means of a spring-loaded plate-shaped pressure valve 44.

A resonance spring 64 matched to the weight of the oscillatory drive and to the grid frequency, keeps the system in reciprocating movement corresponding to the grid frequency.

Within the cylinder unit 17 is situated a suction valve 16 at which terminates a pipe 34 whose outer end dips into an oil supply 38 and which makes provision for adequate lubrication of the piston 57 in the cylinder unit 17.

The electrodynamic oscillatory drive 52 of the magnet system comprises a pot-like outer soft-iron (ferromagnetically soft) pole-piece 101, a cup-shaped inner soft-iron pole-piece 115, between which a block-like permanent magnet 107 is centrally positioned. The outer pole piece 101 is formed by a base 108 and a sleeve 109 which are rigidly interconnected.

The inner pole piece 115 and the outer pole piece 101 together define an annular gap 104 wherein the moving coil 56 is arranged in a freely displaceable manner.

The inner pole piece 115 has a cavity 135 into which projects the resonance spring 64 which is fastened in a bore 116 of the inner pole piece 115 by means of a bracket 119, a flexible rod 118, and a clamping cylinder 117.

The inner pole piece 115 (with the resonance spring 64 fastened to it) the magnet 107, and the outer pole piece 101, are now held together merely by the force of the magnetic field of the permanent magnet 107, without complementary fastening means. The tractive forces of the resonance spring 64 on the inner pole piece 115, which are occasionally substantial, are insufficient to break this connection.

To secure these components 101, 107, and 115 in their lateral position, the magnet 107 has placed around it a sleeve 111 which, in the example of embodiment of FIG. 2 at one end is brazed to the inner pole piece 115 and at the other end has a recess 112 turned in it, the recess being located with an easy fit and longitudinal play on a boss 114 formed on the base 108 of the outer pole piece 101. The longitudinal play ensures direct contact of the inner pole piece 115 and of the base 108 against the magnet 107. The sleeve 111 consists of a non-magnetic but electrically conductive material, e.g. copper; it serves not only the purpose of locating the components 101, 107, and 115, but simultaneously screens the magnet 107 from the alternating fields engendered by the moving coil, which could result in demagnetization of the magnet 107.

In the example of embodiment illustrated in FIG. 3, the sleeve 111 has recesses 112 turned in both of its extremities, one seating on the boss 114 on the base 108 of the outer pole piece 101, the other seating on a boss 113 on the inner pole piece 115. To prevent possible longitudinal oscillation or end-chatter of the sleeve 111 caused by longitudinal vibrations of the oscillatory drive 52, the sleeve 111 may also be firmly joined to the pole piece 115 in this case, e.g. by means of a brazed joint 102.

Another possibility of securing the components 101, 107 and 115 of the magnet system against lateral sliding motion relative to one another, is depicted in FIGS. 4 and 5.

Within the outer pole piece 101 is again centrally positioned the magnet 107 surrounded by a sleeve 111, which here does not have any recess in its end faces. One end of the sleeve 111 surrounds the boss 113 on the inner pole piece 115, and its other end has three radial projections 125 spaced apart circumferentially at 120.degree. from each other; the external diameter of the three projections 125 matches the internal diameter of the casing 109 of the outer pole piece 101. After assembly, the projections 125, may, as a result of material expansion (for instance by forming a small notch 126) be caused to bear lightly against the casing 109, so that the lateral position of the inner and outer pole pieces as well as the magnet, is secured in this uncomplicated manner.

A tapped bore 131 is incorporated for reception of the resonance spring 64, and tapped holes 132 and set pins 133 are incorporated for direct or indirect fastening of the electrodynamic oscillatory drive 52 to the cylinder unit 17.

Claims

I claim:

1. A magnet system for an oscillatory electro-dynamic compressor, the magnet system comprising a permanent magnet having opposed pole surfaces lying at right angles to its axis, an outer pole piece arranged opposite one pole, and an inner pole piece arranged opposite the other pole, said outer pole piece being cup shaped and having an axially extending wall surrounding said permanent magnet and said inner pole piece, said wall and said inner pole piece defining between them an annular air gap, a hollow cylindrical coil movably located in said air gap, and means for moving said coil axially within said air gap, the pole pieces being in contact with the magnet, the pole pieces and the interposed permanent magnet being held together solely by the magnetic field of the permanent magnet.

2. A magnet system as claimed in claim 1, in which the pole pieces and the permanent magnet are prevented from sliding relative to one another by mechanical locating means.

3. A magnet system as claimed in claim 2, in which the locating means comprises a sleeve of nonmagnetic electrically-conductive material which surrounds the magnet, the ends of the sleeve engaging the respective pole pieces.

4. A magnet system as claimed in claim 3, in which one end of the sleeve is firmly joined to the corresponding pole piece, and the other end of the sleeve fits freely over a locating boss on the other pole piece.

5. A magnet system as claimed in claim 3, in which the sleeve has at least three radial projections spaced around its periphery and in contact with the internal surface of the outer pole piece.

6. A magnet system as claimed in claim 5, in which the radial projections are at the sleeve adjacent a base portion of the outer pole piece, the projections being expanded to bear against the outer pole piece.

7. A magnet system as claimed in claim 1 in which said coil is normally biased by a spring in one axial direction and is connected to a piston actuable to overcome the bias of spring to cause a mechanical oscillation of said coil in a direction of movement at right angles to the pole surfaces of said permanent magnet.