LINEAR DRIVE DEVICE PROVIDED WITH AN ARMATURE BODY HAVING A MAGNET CARRIER
A linear drive device includes an excitation winding producing a variable magnetic field and including an associated magnetic-flux-carrying yoke body having pole surfaces, and an armature body including a magnet carrier having at least two permanent magnet parts and an axial oscillation movement being transferable to the at least two permanent magnet parts by the variable magnetic field of the excitation winding. The magnet carrier includes an electrically insulating material at least partially extending into the magnetic field area defined by the pole surfaces of the yoke body and the excitation winding.
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This application is a Divisional, under 35 U.S.C. §121, of U.S. application Ser. No. 10/591,082, filed Aug. 29, 2006, which is a U.S. national stage application of PCT/EP2005/050956 filed Mar. 3, 2005, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German patent application No. 10 2004 010 404.2 filed Mar. 3, 2004; the prior applications are herewith incorporated by reference in their entirety.
BACKGROUND OF THE INVENTIONThe invention relates to a linear drive device including at least one excitation winding for producing a variable magnetic field and provided with at least one associated magnetic-flux-carrying yoke body as well as an armature body which includes a magnet carrier provided with at least two permanent magnet parts and to which an axial oscillation movement can be transferred by the magnetic field of the excitation winding. A corresponding drive device is deduced from U.S. Pat. No. 5,559,378 A.
Corresponding linear drives are used in particular to set pump plungers of compressors in linear oscillating vibration. The system comprising such a compressor and a linear drive device is therefore also designated as a linear compressor (see, for example, JP 2002-031054 A). In corresponding known linear compressors, the armature body capable of oscillating, forms a spring-mass system designed for a certain oscillation frequency.
The known drive device comprises at least one excitation winding in a laminated iron yoke core in an E-shape. Its magnetic field exerts a force which depends on the direction of the current on two alternately polarised plate-shaped permanent magnets or on a linearly movable magnet carrier of an armature body, which can be used to drive, for example, a pump plunger of a compressor.
The air gap between the pole surfaces of such a yoke body and the surface of the permanent magnets represents an additional resistance in the magnet circuit which reduces the magnetic field strength produced by the excitation winding in the air gap and thus correspondingly reduces the driving force.
During the oscillating movement of the armature body, lateral parts of its magnet carrier dip into the air gap field at the pole surfaces of the yoke carrier, inducing eddy currents, losses and a corresponding braking force in electrically conductive materials. A corresponding effect can be observed in known drive units whose magnet carrier is generally made of highly conducting aluminium, and the permanent magnets provided with thin glass-fibre reinforced plastic covers can be stuck in recesses of the support.
BRIEF SUMMARY OF THE INVENTIONIt is thus an object of the present invention to construct the linear drive device provided with the features specified initially such that the aforementioned induced braking force is reduced.
The advantages associated with this configuration of the drive device can be seen in particular in that as a result of using insulating material for the magnet carrier, no eddy currents are induced therein under the pole surfaces. Thus, no additional braking force is induced by this region of the magnet carrier.
The following features can be additionally provided for the drive device:
The magnet carrier can consist entirely of an insulating material. Instead, it is also possible that this consists of metal and the parts of the magnet carrier which dip into the magnetic field area of the yoke body and/or the excitation winding are constructed of an insulating material. Consequently, no eddy currents are induced in these insulating material parts under the pole surfaces.
It is particularly advantageous if each magnet part with respect to the associated yoke body and/or the excitation winding are covered by a magnet cover made of a ferromagnetic sheet or a corresponding layer, the magnet covers being spaced axially apart by means of a spacing joint. These ferromagnetic covers are used firstly for secure fixing of the magnet parts in or on the magnetic carrier. Secondly, they reduce the effective magnetic air gap, increase the field of the excitation winding(s) and thus the driving force.
In this case, the ferromagnetic magnet covers can advantageously be spaced apart from one another by a distance a>2 s, where s is the distance from the surface to the pole surfaces of the yoke body. A magnetic short circuit can thus be avoided between the neighbouring magnet parts.
Each of the ferromagnetic magnet covers advantageously covers a larger area than the respectively associated magnet part.
An Fe-Si alloy is preferably used as the material for the ferromagnetic magnet covers.
The thickness of the ferromagnetic covers is advantageously selected between 0.2 mm and 1.5 mm, preferably between 0.35 and 1 mm.
The magnet parts are appropriately embodied as plate- or sheet-shaped.
The armature body constructed according to the invention is preferably rigidly connected to a pump plunger of a compressor.
The invention is explained in detail hereinafter using preferred exemplary embodiments with reference to the drawings. In the figures:
In the linear drive device according to an exemplary embodiment of the invention shown in
As can be further deduced from
The ferromagnetic covers 16a, 16b, 17a and 17b can in particular be embodied in the form of a metal sheet or a corresponding layer. Preferably provided for this purpose are ferromagnetic sheets of relatively low electrical conductivity (below that of the known aluminium), in particular so-called electric sheet made of an Fe-Si alloy, the thickness d of this sheet metal generally being between 0.2 mm and 1.5 mm, preferably between 0.35 mm and 1 mm. It is also advantageous if these sheets project somewhat over the associated magnet parts on three sides, they at least partly cover the edge of the recesses in the frame portion 13 in which the magnet parts 9a and 9b are to be fitted and are fixed to the magnet parts in the carrier frame, for example, are glued therein. The associated ferromagnetic sheets 16a and 16b or 17a and 17b are mutually spaced in the area of the centre at a joint 18 between the two oppositely magnetised permanent-magnet parts 9a and 9b to thus prevent a magnetic short circuit. The axial extension a of a corresponding spacing joint 19 should preferably be selected so that this is twice the spacing s from the surface to the pole surface Fp of the corresponding yoke body 5a or 5b.
Claims
1. A linear drive device comprising:
- an excitation winding producing a variable magnetic field and including an associated magnetic-flux-carrying yoke body having pole surfaces; and
- an armature body including a magnet carrier having at least two permanent magnet parts and an axial oscillation movement being transferable to the at least two permanent magnet parts by the variable magnetic field of the excitation winding, the magnet carrier including an electrically insulating material at least partially extending into the magnetic field area defined by the pole surfaces of the yoke body and the excitation winding.
2. The device of claim 1, wherein the magnet carrier consists entirely of an insulating material.
3. A linear drive device comprising:
- an excitation winding producing a variable magnetic field having a longitudinal extent along a longitudinal axis, the excitation winding including an associated magnetic-flux-carrying yoke body having a pair of pole surfaces axially spaced from one another relative to the longitudinal axis; and
- an armature body including a magnet carrier having a plurality of permanent magnet parts and a pair of electrically insulating portions, the armature body being movable in an axial oscillation movement that is transferable to the at least two permanent magnet parts by the variable magnetic field of the excitation winding, the pair of electrically insulating portions being axially spaced from one another relative to the longitudinal axis and at least one of the plurality of permanent parts is disposed axially intermediate the pair of electrically insulating portions, and each one of the pair of electrically insulating portions is disposed to at least partially extend into a respective magnetic field area defined by a respective one of the pair of pole surfaces of the yoke body and the excitation winding.
4. The device of claim 3, wherein the magnet carrier consists entirely of an insulating material.
Type: Application
Filed: Nov 24, 2009
Publication Date: Mar 18, 2010
Applicant: BSH BOSCH UND SIEMENS HAUSGERATE GMBH (Munich)
Inventor: Günter Ries (Erlangen)
Application Number: 12/624,536