WO2003085810A1

WO2003085810A1 - Linear motor and compressor driven by said motor

Info

Publication number: WO2003085810A1
Application number: PCT/EP2003/002337
Authority: WO
Inventors: Daniele Cossalter; Giovanni Strappazzon; Maurizio Lamantia; Nicola Trivillin; Andrea Contarini; Luca Raviglione; Walter Vignandel
Original assignee: Zanussi Elettromeccanica S.P.A
Priority date: 2002-04-05
Filing date: 2003-03-07
Publication date: 2003-10-16
Also published as: JP2005522175A; ITPN20020022A1; EP1493221A1

Abstract

The present invention refers to a linear motor and a linear compressor driven by such a motor. The linear motor comprises a stator featuring a substantially rectilinear extension according to a longitudinal axis (14), which is constituted by a pair of outer yokes (4, 5) and at least a coil (3). The stator is further constituted by an inner yoke (2) provided with at least a first and a second cavity (19, 20) facing the respective outer yokes (4, 5) and containing the coil (3)-

Description

LINEAR MOTOR AND COMPRESSOR DRIVEN BY SAID

MOTOR

DESCRIPTION

The present invention refers to a linear motor and a linear compressor driven by said motor.

Linear motors are generally constituted by a stator comprising an outer yoke, which has a cross-section in the shape of a C, and an inner yoke, which faces said outer yoke and is arranged at a certain distance, generally known as air gap, therefrom. The legs at the extremities of the C constitute the pole shoes of the magnetic circuit formed by the inner yoke and the outer yoke, whereas a coil of electrically conducting material, such as for instance copper wire, is wound between said pole shoes. In the air gap there is arranged a crosswise magnetized permanent magnet that forms the moving part of the motor. When an electric current is allowed to flow through the coil, a force having a direction which is perpendicular to the direction of magnetization of the permanent magnet acts on said moving part of the motor with an intensity that is in a proportion with the value of said electric current, wherein the coefficient of proportionality depends substantially on the magnet, the air gap and the coil themselves. The form that is currently most used in the art for the outer yoke and the inner yoke of linear motors is the toroidal configuration, i.e. a configuration that may be assumed as being obtained from the rotation of the outer yoke, the permanent magnet and the inner yoke about a vertical axis. Considerable problems and difficulties are anyway encountered in making a linear motor with such a configuration, essentially in connection with the magnetic circuit which must be laminated in view of reducing eddy currents.

A laminated toroidal configuration could theoretically be obtained through the use of laminations of a variable thickness having a cross- section in the shape of a sector of circle ring. However, this solution fails to prove practicable for commercial applications owing to really considerable design and manufacturing complexities that would lead to an extremely high ultimate cost of the motor.

A solution that is currently adopted as a way out of such a problem lies practically in subdividing the magnetic circuit into planar portions which are formed by a plurality of planar laminations and are so arranged close to each other as to form the desired toroidal ring. However, the resulting complexity of such a design is again quite high and, with respect to the solution that may be considered as the ideal one, it certainly entails a worsening from the point of view of both the leakage reactance and the stacking coefficient of the laminations.

In addition, a toroidal structure with the coil wound on the outer portion with respect to the air gap, and therefore with the pole shoes facing the central axis of the torus, further to involving a considerable average length of the coil turns, has a disadvantage in that it does not allow for any adequate packing of the conductors in the respective slots.

The winding of the coil must in fact be carried out on a template or dummy and the portions of the C-shaped magnetic circuit forming the outer yoke are assembled thereupon. Even the permanent magnets, owing to them being difficult to be made in the form of a single toroidal piece, are made in the form of sectors of circle ring. This again involves a poor volume utilization, along with considerable manufacturing difficulties.

As a partial solution to the various above-mentioned drawbacks, the US patent no. 6,184,597 Bl describes a linear motor, or a compressor that uses such a motor, in which the stator comprises at least two inner prismatic yokes along with respective outer yokes, both kinds of yokes being made by stacking a plurality of laminations of an essentially rectangular shape. In each one of said outer yokes there are provided, by material-removing machining, at least three pole shoes that form, between two adjacent shoes, slots within which the coil is wound. The result will therefore be that each outer yoke has a coil wound around the central pole expansion along the two slots formed by said central pole expansion with the adjacent pole expansions. Between the inner yokes and the outer yokes there is arranged the moving member which is provided, for each air gap, with a pair of permanent magnets that are spaced from each other and are magnetized with opposite polarities with respect to each other.

Although its construction is surely simplified in some respects, the motor designed and made in accordance with the teaching of the above mentioned patent publication does by no means prove effective in doing away with the afore cited drawbacks and problems to any satisfactory extent, actually. As a matter of fact, although it assures a good stacking coefficient of the laminations for each magnetic circuit taken individually, the stator as a whole fails to make use of the available volume to any efficient extent. On the other hand, the overall structure is not compact at all, or anyway not as compact as desirable, and it involves a rather high number of component parts. In fact, as many as two to four coils are required for the simplest embodiments thereof, along to as many inner yokes and outer yokes. Furthermore, automating the winding operation of the coil inside the slots proves rather difficult from a design point of view and, anyway, it can only be performed at relatively low levels of productivity, owing to the E-shaped cross-section of the outer yokes: such a cross-section, and in particular the presence of the central pole shoe around which the coil is wound, entails the need for a complex movement of the winding needle to be provided for, which actually brings about the afore cited difficulties and limitations. In view of facilitating such a winding operation, the idea is to make the pole shoes separately, for subsequent assembly after that the coil has been wound around the central pole shoe. However, such a solution fails to prove satisfactory, either, since it, further to the above mentioned low-productivity disadvantage, involves an increase in costs due to an increased complexity of the operational sequences in both the manufacturing and assembly steps.

It therefore is a main object of the present invention to do away with all of the afore mentioned drawbacks of prior-art solutions by providing a linear motor that is designed and engineered in an optimum manner in view of ensuring a considerable simplification in both its construction and manufacturing.

A major purpose of the present invention within the above -indicated object thereof is to provide a linear motor in which said simplification in the construction thereof involves both the component parts and the assembly of said component parts with each other.

Another major purpose of the present invention is to provide a linear motor which has a structure that is compact and, at the same time, very efficient, thereby enabling an optimum stacking coefficient to be achieved as far as both the laminations and the winding are concerned, while reducing unused space to a minimum. In particular, a particularly advantageous application of such a motor is the use of it to equip compressors intended for use in refrigeration, air-conditioning and home appliances in general, where space is usually at a premium, i.e. there is generally just a limited space available to accommodate the unit used for the compression of the operating medium or media used therein.

A further major purpose of the present invention is to simplify coil in the slot between two adjacent pole shoes.

Another major purpose yet of the present invention is to simplify the moving member of the motor, and in particular the permanent magnets, in both construction and manufacturing thereof.

A last, although not least purpose of the present invention is to provide an apparatus which is low in cost and capable of being manufactured with the use of readily available machinery and techniques.

According to the present invention, the above indicated aims and advantages, along with further ones that will become apparent from the description given below, are reached in a linear motor incorporating the features and characteristics as recited in the appended claim 1 ; further features and characteristics for the linear motor according to the present invention, and for a linear compressor driven by such a motor, are as recited in the appended sub-claims.

Anyway, features and advantages of the present invention may be more readily understood from the description that is given below of a particular, although not sole embodiment, which is illustrated by way of non-limiting example with reference to the accompanying drawings, in which:

- Figure 1 is a schematic cross-sectional view of the linear motor according to the present invention;

Figure 2 is a top view of the linear motor shown in Figure 1 ;

Figure 3 is a perspective view of a detail of the inner yoke; - Figure 4 is a perspective exploded view of the main component parts of the motor;

- Figure 5 is a similar view as the one appearing in Figure 1 of the motor according to the present invention, illustrating the operation thereof;

- Figure 6 is a perspective view of the assembly of a linear compressor using a motor according to the present invention;

- Figure 7 is a cross-sectional view of the compressor illustrated in Figure 6;

- Figure 8 is a perspective view of a resonance spring for the compressor illustrated in Figure 6.

With reference to the above cited and listed Figures, the linear motor, as generally indicated at 1 , comprises a stator that is substantially constituted by an inner yoke 2, at least a coil 3 wound around said inner yoke 2, and a pair of outer yokes 4 and 5 facing laterally said inner yoke 2 and spaced from the latter so as to define a first air gap 6 and a second air gap 7, respectively.

The linear motor further comprises a moving member 8 having an essentially U-shaped cross-section and, therefore, featuring a cross leg 8a that supports a pair of side legs 8b, 8c housed within said first air gap 6 and said second air gap 7, respectively. Said pair of side legs 8b, 8c in turn support a pair of permanent magnets 9 and 10, respectively.

The inner yoke 2 and the outer yokes 4, 5 define the magnetic circuit within which a magnetic flux is generated due to the current circulating in the electric circuit, constituted by the coil 3, and the presence of the permanent magnets 9 and 10. Both the inner yoke 2 and the outer yokes 4, 5 are obtained by stacking upon each other a plurality of laminations which, as indicated at 11, 12 and 13 in Figure 2, respectively, have a high magnetic permeability and are cut to a shape corresponding to the cross-section of each yoke, as this shall be discussed in closer detail further on. The stacking of the laminations 1 1 , 12, 13 is carried out linearly along the longitudinal axis 14, thereby defining a stator with an essentially rectilinear extension. In an advantageous manner, the assembly of the laminations 11, 12, 13 with each other so as to form the inner yoke 2 and the outer yokes 4 and 5, respectively, is obtained by upsetting the individual laminations during the same phase in which they are punched and cut.

The inner yoke 2, and therefore each lamination 1 1 forming the latter, has with respect to the longitudinal axis 14 a cross-section that comprises a central body 15 from which there are extending sideways at least a first and a second pair of pole shoes 16, 16a and 17, 17a arranged in an approximately symmetrical manner with respect to the median vertical plane 18 of the central body 15 itself and facing the outer yokes 4 and 5, respectively; the first pair of pole shoes 16, 16a and the second pair of pole shoes 17, 17a define a first cavity 19 and a second cavity 20, respectively.

The electric circuit is constituted by the coil 3, which is wound peripherally around the central body 15, in correspondence of the first and the second side cavities 19 and 20, along the entire longitudinal extension of the inner yoke 2 as defined by the axis 14.

In an advantageous manner, each pair of pole shoes 16, 16a and 17, 17a is oriented in a direction diverging from the central body 15, in such a manner as to form a cross-section in the shape of essentially a X. In this way, between the legs of such a X there are obtained the afore cited first and second side cavities 19 and 20. which are facing the outer yokes 4 and 5, respectively, a third lower cavity 21, which is facing the cross leg oriented in the opposite direction with respect to said third cavity 21.

The insulation of the electric circuit is obtained by means of two pre- shaped portions 23, 24 that are made of an insulating material and are associated to the inner yoke 2 in correspondence of the central body 15; these pre-shaped portions 23 and 24, which may for instance be moulded, also act as a support for the coil 3 in correspondence of the head-pieces 25, 26. The same pre-shaped portions 23, 24 may as well act as a support means for the electrical connection arrangement used to connect the coil 3 to the power supply wires leading out of the motor (not shown).

The outer yokes 4 and 5, and therefore the respective laminations 12 and 13 that make up said yokes, are substantially rectangular in their cross-section and are so arranged as to face the respective pairs of pole shoes 16, 16a and 17, 17a; as a result, the major side of the rectangle constituting the shape of each lamination 12 extends to substantially cover and include the corresponding pole shoes 16, 16a, in the same way as this occurs in the case of the major side of each lamination 13 as far as the pole shoes 17 and 17a are concerned.

As far as the moving part of the motor is concerned, each one of the permanent magnets 9, 10, which are supported by the moving member 8 and accommodated inside the first and the second air gap 6 and 7, respectively, is advantageously made in a single-piece construction that is magnetized crosswise and along a single direction with respect to the respective air gap. The moving member 8 supporting the permanent magnets 9, 10 also works in the sense of transmitting to an operating machine, such as for instance a compressor as discussed in greater detail further on, the motion generated by the interaction of the electric current with the magnetic flux. Such a motion transmission occurs with the aid of generally known driving means, such as for instance a shaft (not shown in the Figures 1 to 5) associated to the moving member 8 and passing through the aperture 27 provided in the inner yoke 2.

The operation of the above-described apparatus is as follows: when an electric current is supplied to the coil 3, polarities of opposite sign are produced on the pole shoes 16, 16a and 17, 17a and these polarities, jointly with the outer yokes 4, 5 for re-closing the magnetic circuit, generate a magnetic flux in a transversal direction with respect to said first and said second air gap 6 and 7, as indicated by the arrows A, B, A', B' in Figure 5. As a result, the permanent magnets 9, 10 are attracted, with a force F of a value that is proportional to the electric current, by the respective pole shoe of opposite sign. By energizing the coil 3 with an alternating current, a reciprocating and synchronous motion of the moving member 8 is in this way obtained. The magnetic flux A, B, A', B' follows paths that run parallel to the rolling plane of the laminations 1 1 , 12, 13 (corresponding to the plane of the sheet in Figure 5) and offer just a low reluctance. The so obtained reciprocating motion is transmitted by the moving member 8, via appropriate motion transmission or driving means, to an operating machine.

From the description given above it can therefore be readily appreciated that the linear motor according to the present invention is actually capable of reaching all of the afore indicated aims and advantages: in fact, the structure of the motor developing in a linear manner and the extremely simple shapes of the laminations 11, 12, 13 are such as to enable a considerable simplification in the overall construction of the motor to be achieved, to such an extent as to ideally allow for a fully automated production under clear advantages in terms of costs. Such a simplification comes about both in the phase in which the individual component parts of the motor are manufactured and in the phase in which the component parts themselves are then assembled into the final product: in this case, in fact, the inner yoke and the outer yokes can be obtained directly during the phase in which the laminations are punched off the electric steel strip by means of an upsetting operation followed by the stacking of the same laminations; even the aperture 27 for the motion transmission means to pass therethrough is obtained in the same punching operation.

The configuration of the side cavities 19, 20, which have quite a large cross-section area and are arranged externally with respect to the inner yoke 2, allows for the coil 3 to be most conveniently wound directly in the same cavities without any further and/or more complex operations, such as for instance a pre-assembled coil having to be inserted in the cavity, complex routes to be travelled several times, yokes to be manufactured in a number of separate portions for subsequent assembly, and the like, being necessary, actually.

The linear motor having a structure as described above is furthermore very compact in its overall size; at the same time, it is very efficient thanks to a very high value of the ratio of available space, or active space, to total occupied or used space. This depends on a number of factors, i.e.: the configuration of the side cavities which, by making it much easier for the coil 3 to be wound, i.e. facilitating coil winding, enables not only the same coil to be packed with an optimum filling coefficient in the same side cavities, but also the resistance of the coil to be reduced; the linear extension of both the inner yoke and the outer yokes with an optimum stacking coefficient of the laminations; the configuration of the inner yoke, in particular the X- shaped configuration thereof, which enables component parts of the operating machine associated to the motor to be accommodated in the lower cavity 21 and upper cavity 22 thereof.

It will of course be appreciated that the present invention may be subject to a number of modifications and variants, and may be used in conjunction with a number of different applications, without departing from the scope of the present invention.

Figures 6 through to 9 can be noticed to illustrate the application of the linear motor according to the present invention to a compressor; same reference numerals are used in these Figures to indicate same component parts of the motor that have already been described with reference to the previous Figures. The motor illustrated in the now considered Figures can therefore be noticed to include a stator comprising an inner yoke 2, a coil 3 wound around said inner yoke 2 in correspondence of the side cavities 19, 20, and a pair of outer yokes 4 and 5 facing said inner yoke 2. The moving member 8 supports a pair of permanent magnets 9, 10 in correspondence of the side legs 8b, 8c housed in the air gaps comprised between the inner yoke 2 and the outer yokes 4, 5; in correspondence of the cross leg 8a there are associated means for transmitting the reciprocating motion that is imparted to the moving member 8 when the motor is being supplied with an alternating current. These means are constituted by a shaft 28 passing through the aperture 27 provided centrally in the inner yoke 2; the shaft 28 has an enlarged head-piece at its upper end portion, which forms the piston 29 of the compressor.

The stator is contained within an upper flange 30 and a lower flange 31; on the upper flange 30 there is provided the cylinder 32, within which there is slidably housed the piston 29, and a pair of receptacles 33, 34 adapted to slidably accommodate the respective legs 8b, 8c during the operation of the motor and, therefore, during the reciprocating motion of the moving member 8. On the lower flange 31 there is provided an aperture 35 for the shaft 28 to pass therethrough, as well as a pair of apertures 36, 37 for the legs 8b, 8c of the moving member 8 to pass therethrough. The lower flange 31 is further provided with a support 38 for elastically deformable means 39, which shall be explained in greater detail further on and which are connected to the support 38 on the lower side and the moving member 8 on the upper side.

The resulting assembly is closed on top by a head piece 40 provided with the apertures 41 and 42 for the passage of the delivery and suction ducts, respectively. n In the case that the inner yoke 2 has a configuration with a cross- section in the shape of essentially a X, then upper flange 30 and the cylinder 32 are able to extend into the fourth cavity 22 that is provided on the upper side of the inner yoke 2; the portion 43 of the piston 29 that is oriented towards the inner yoke 2 will then be able to be given a cylindrical configuration with two levelled faces 48, 49 that are substantially so shaped as to counter-fit the shape of the fourth cavity 22 itself, in such a manner that, upon reaching the bottom dead centre during its stroke within the cylinder 32, the piston 29 can be received into said fourth cavity 22; this expedient enables the structure of the assembly to be made extremely compact by making use in an optimum manner of the volume defined by the motor to accommodate the mechanical parts of the compressor therein, as this has already been hinted at earlier in this description. Similarly, the lower flange 31 will be able to extend substantially into the third lower cavity 21. In an advantageous manner, the outer yokes 4, 5 and the inner yoke 2 may be provided with projections 50, 51, 52, 53, 54, 55, 56, 57 cooperating with respective receptacles provided in the upper flange 30 and lower flange 31 , in order to facilitate centering these flanges during assembly.

From Figure 6, which illustrates the overall assembly without the head 40, the overall compactness of the structure of the compressor made in accordance with the above description can be clearly inferred.

The elastically deformable means 39, which are generally referred to as resonance springs in this specific industry sector, may be constituted by one or more torsion springs of any per se known type, which however would prove scarcely satisfactory to the purpose of reducing bulkiness in the height dimension of the structure.

A possible solution in this connection is given by the flat spring described in the US patent publication no. 6, 184, 597 B l with particular reference to Figure 32. However, this solution, although ensuring a reduced vertical size, would introduce a rotary motion of the moving member 8 about the vertical axis 18 as a result of the reciprocating motion of the moving member itself, thereby ultimately determining an undesired helical motion that could lead to the moving member 8 being brought into colliding with the stator.

A particularly advantageous solution in this sense is therefore represented by the resonance spring 39 that is illustrated in Figure 8. This spring 39 consists of at least two elastically deformable members 44, 45 having an arcuate shape, each one of said members being constituted by one or more elastic leaves and featuring three or more arms 46, 47, wherein these arms are in the number of four for each member in the embodiment illustrated in Figure 8. These elastically deformable members 44, 45 are arranged upon each other, in such a manner as to ensure that the respective concavities thereof come to face each other, and are joined to each other in correspondence of the end portions of said arms 46, 47: when a load is applied perpendicularly with respect to the extension of the arms 46, 47, the elastically deformable members 44, 45 undergo flexural stress, i.e. are caused to bend.

With reference to Figure 7 the spring 39 is fixed on its upper side, and therefore in correspondence of the elastically deformable member 44, to the cross leg 8a of the moving member 8, coaxially with the shaft 28, and on its lower side, i.e. in correspondence of the elastically deformable member 45, to the support 38 that is a part of the lower flange 31. Such an attachment of the spring is carried out with the aid of such known fastening means as for instance screws, bolts and the like. In a preferred manner, the spring itself is so designed as to ensure the greatest possible extent of evenness in the distribution of the applied stresses.

From the description given above it can be readily appreciated how the advantages that have been pointed out for a linear motor made in accordance with the present invention are actually capable of being extended to the application of such a motor to a compressor of the afore described kind. In fact, a great deal of the volume occupied by the component parts making up the mechanical part of the compressor can actually be accommodated , i.e. contained within the afore cited lower cavity 21 and upper cavity 22 of the motor itself.

Furthermore, the use of the above-described resonance spring 39 enables the encumbrance of the assembly in the height dimension thereof to be further reduced, thereby making the overall structure of the compressor still more compact, without introducing any problem connected with a rotary movement imparted to the moving member 8. In addition to all that, the compression stroke of the spring is increased with respect to other prior-art solutions, since the elastically deformable members 44, 45 can be brought so far as to almost contact each other, thereby creating the possibility for the useful stroke of the piston 29 to be increased and, as a result, the efficiency of the compressor to be ultimately enhanced.

It should be noticed that the materials used to implement the present invention, as well as the shapes and the size of the individual component parts, may each time be selected so as to most appropriately fit any particular need or comply with any application-related requirement, without this implying any departure from the scope of the present invention.

Claims

1. Linear motor comprising a stator having a substantially rectilinear extension along a longitudinal axis (14) and being constituted by a pair of outer yokes (4, 5) and at least a coil (3), characterized in that said stator is further constituted by an inner yoke (2) provided with at least a first and a second cavity (19, 20) facing the respective outer yokes (4, 5), said at least a coil (3) being contained within said first and said second cavity ( 19, 20).

2. Linear motor according to claim 1, characterized in that said inner yoke (2) has a cross-section comprising a central body (15) from which there extend a first and a second pair of pole shoes (16, 16a, 17, 17a) arranged in an approximately symmetrical manner with respect to said central body (15) and adjacent to said first cavity (19) and said second cavity (20), respectively.

3. Linear motor according to claim 2, characterized in that said coil (3) is wound peripherally around said central body (15) in correspondence of said first and said second cavity (19, 20)

4. Linear motor according to claim 2, characterized in that said inner yoke (2) is obtained by stacking a plurality of laminations (11) upon each other, said laminations having a high magnetic permeability and being cut to a shape corresponding to the cross-section of said inner yoke (2).

5. Linear motor according to claim 2, characterized in that said first and said second pair of pole shoes (16, 16a, 17, 17a) are symmetrical with respect to the vertical median plane (18) of said central body (15).

6. Linear motor according to claim 5, characterized in that said first and second cavities (19, 20) are defined by said first pair of pole shoes (16, 16a) and said second pair of pole shoes (17, 17a), respectively.

7. Linear motor according to claim 2, characterized in that said outer yokes (4, 5) are substantially rectangular in their cross-section and are arranged so as to face said first pair and said second pair of pole shoes (16, 16a, 17, 17a), respectively.

8. Linear motor according to claim 7, characterized in that said outer yokes (4, 5) are obtained by stacking a plurality of laminations (11) upon each other, said laminations having a high magnetic permeability and being cut to a shape corresponding to the cross-section of said outer yokes (4, 5).

9. Linear motor according to claim 7, characterized in that said outer yokes (4, 5) are spaced from the respective first and second pairs of pole shoes (16, 16a, 17, 17a) so as to define a first and a second air gap (6, 7), respectively.

10. Linear motor according to claim 9, characterized in that it further comprises a moving member (8) provided with a cross leg (8a) supporting a pair of side legs (8b, 8c) that are housed within said first and said second air gap (6, 7), respectively, in which each one of said side legs (8b, 8c) in turn supports a permanent magnet (9, 10).

11. Linear motor according to claim 10, characterized in that each one of said permanent magnets (9, 10) are made in a single-piece construction that is magnetized crosswise along a single direction.

12. Linear motor according to claim 10, characterized in that said moving member (8) is adapted to transmit, via appropriate motion- transmission means, the motion generated by said motor to an operating machine, such as a compressor.

13. Linear motor according to any of the preceding claims, individually or in any combination thereof, characterized in that said first and said second pairs of pole shoes (16, 16a, 17, 17a) are oriented in a direction diverging from the central body (15), so that said cross-section of said inner yoke (2) is assigned a configuration in the shape of essentially a X.

14. Linear motor according to claim 13, characterized in that the contiguous legs of said X-shaped cross-section define said first and said second cavity (19, 20) facing said outer yokes (4, 5), as well as a third cavity (21) facing said cross leg (8a) and a fourth cavity (22) oriented in the opposite direction with respect to said third cavity (21).

15. Linear motor according to any of the preceding claims, individually or in any combination thereof, characterized in that the insulation of said coil (3) is obtained by means of at least two pre-shaped portions (23, 24) made of an insulating material and associated to said inner yoke (2) in correspondence of said central body (15).

16. Linear motor according to claim 15, characterized in that said pre-shaped portions (23, 24) are adapted to support said coil (3) in correspondence of the head pieces (25, 26) of said inner yoke (2).

17. Linear motor according to claim 16, characterized in that said pre-shaped portions (23, 24) are adapted to support the electrical connection arrangement used to connect the coil (3) to the power supply wires leading out of the motor.

18. Linear motor according to any of the preceding claims, individually or in any combination thereof, characterized in that the assembly of said laminations (1 1, 12, 13) with each other so as to form the inner yoke (2) and the outer yokes (4, 5), respectively, is obtained by an upsetting operation carried out on each single lamination (11 , 12, 13) during the same phase in which such laminations are punched and cut.

19. Compressor driven by a linear motor according to any of the preceding claims, individually or in any combination thereof.

20. Compressor according to claim 19, characterized in that said motion-transmission means according to claim 12 are constituted by a shaft (28) extending through an aperture (27) appropriately provided in said inner yoke (2).

21. Compressor according to claim 20, characterized in that said shaft (28) has an enlarged head-piece at its upper end portion, which forms the piston (29) for said compressor.

22. Compressor according to claim 19, characterized in that said stator is contained within an upper flange (30) and a lower flange (31).

23. Compressor according to claim 22, characterized in that said lower flange (31)and said upper flange (30) extend into said third cavity

(21) and said fourth cavity (22), respectively.

24. Compressor according to claims 21 and 22, characterized in that in said upper flange (30) there is formed a cylinder (32) within which said piston (29) is housed slidably.

25. Compressor according to claim 24 driven by a linear motor according to claim 14, characterized in that the portion (43) of said piston which is oriented towards said inner yoke (2) has a cylindrical configuration with two levelled faces (48, 49) that are substantially so shaped as to counter- fit the shape of said fourth cavity (22), in such a manner that, upon reaching the bottom dead centre during its stroke within said cylinder (32), said piston (29) can be received into said fourth cavity (22).

26. Compressor according to claim 22, characterized in that said lower flange (31) is provided with an aperture (35) for said shaft (28) to pass therethrough, as well as a support (38) for elastically deformable means (39) that are connected to said support (38) on the lower side and to said moving member (8) on the upper side.

27. Compressor according to claim 26, characterized in that said elastically deformable means are constituted by a resonance spring (39) provided with at least two elastically deformable members (44, 45) having a pre-defined curvature, in which each said elastically deformable member is constituted by one or more elastic leaves featuring three or more arms (46, 47) each.

28. Compressor according to claim 27, characterized in that said elastically deformable members (44, 45) are arranged upon each other, in such a manner that the respective concavities thereof come to face each other, said elastically deformable members (44, 45) being joined to each other in correspondence of the end portions of said arms (46, 47).

29. Compressor according to claim 28, characterized in that said arms (46, 47) are in the number of four for each of said elastically deformable members (44, 45).

30. Linear motor and compressor driven by said motor, characterized by what has been described and illustrated with reference to the accompanying drawings.