MAGNETIC MOTOR DEVICE OF AN ELECTRODYNAMIC TRANSDUCER

Abstract

A magnetic motor device of an electrodynamic transducer, which includes a bonded annular magnet and a tubular element mounted coaxially relative to the bonded annular magnet. The bonded annular magnet includes a magnetic cylindrical surface, while the tubular element includes a winding extending opposite the magnetic cylindrical surface, the tubular element configured to be driven axially relative to the bonded angular magnet when electric power is supplied to the winding. A metal tubular member includes a metal cylindrical surface, and the metal tubular member is mounted coaxially relative to the tubular element such that the metal cylindrical surface extends opposite the magnetic cylindrical surface relative to the winding.

Claims

1. A magnetic motor device of an electrodynamic transducer, comprising: a bonded annular magnet generating a magnetic field; and a tubular element mounted coaxially relative to the bonded annular magnet; the bonded annular magnet including a magnetic cylindrical surface; the tubular element including a coil extending opposite the magnetic cylindrical surface, the tubular element configured to be driven axially relative to the bonded annular magnet when electrical current is supplied to the coil; and further comprising: a metal tubular member including a metal cylindrical surface, wherein the metal tubular member is mounted coaxially relative to the tubular element such that the metal cylindrical surface extends opposite the magnetic cylindrical surface relative to the coil so as to close the magnetic field.

2. The magnetic motor device as claimed in claim 1, wherein the bonded annular magnet includes a surface opposite the magnetic cylindrical surface, of which an intersection with an axial plane of the bonded annular magnet is a hemi-ellipse.

3. The magnetic motor device as claimed in claim 2, wherein the opposite surface has a truncation forming a truncated cylindrical surface substantially parallel to the magnetic cylindrical surface.

4. The magnetic motor device as claimed in claim 1, wherein the magnetic cylindrical surface of the bonded annular magnet includes two first cylindrical half-surfaces, while the bonded annular magnet generates a magnetic field B, and a ratio of the first cylindrical half-surface to cross section of the metal tubular member, which is a factor of the magnetic field B, is less than a value of magnetic saturation threshold of material of the metal tubular member. Claims. The magnetic motor device as claimed in claim 4, wherein the ratio of the first cylindrical half-surface to the cross section of the metal tubular member, which is a factor of the magnetic field B, is less than 1.5 when the metal tubular member is made of iron.

6. The magnetic motor device as claimed in claim 1, wherein the metal cylindrical surface includes two second cylindrical half-surfaces arranged in an axial extension of one another, and the coil is divided into two windings interspaced axially and configured to extend opposite the second cylindrical half-surfaces respectively.

7. The magnetic motor device as claimed in claim 1, wherein the bonded annular magnet is mounted inside the tubular element, and the metal tubular member extends around the tubular element.

8. The magnetic motor device as claimed in claim 3, wherein the metal tubular member is mounted inside the tubular element, and the bonded annular magnet extends around the tubular element.

Description

[0022] Further features and advantages of the invention will become clear from reading the following description of a specific embodiment of the invention, provided by way of non-limiting example and with reference to the accompanying drawings, in which:

[0023] FIG. 1 is a schematic axial sectional view of a magnetic motor device according to the invention in accordance with one embodiment;

[0024] FIG. 2A is a partial schematic axial sectional view of a detail of FIG. 1;

[0025] FIG. 2B is a graph corresponding to FIG. 2A, illustrating the strength of the local magnetic field; and

[0026] FIG. 3 is a schematic view similar to FIG. 2A, illustrating the dimensional references.

[0027] FIG. 1 illustrates an embodiment of a magnetic motor device of an electrodynamic transducer 10. The magnetic motor device comprises a receiving part 12 connected to a base 14. The receiving part 12 comprises a frustoconical part 16 integral with a tubular part of circular base 18. The frustoconical part 16 carries a membrane 20, while the tubular part 18 includes, coaxially with the axis of the device Z, a tubular element 22 forming a support and integral with the membrane 20, a bonded annular magnet 24 arranged inside the tubular element 22, and a metal tubular member 26 surrounding the tubular element 22. The tubular element 22 is made of card, aluminum, polyimide or glass fibers, or a composite material. Furthermore, the tubular element 22 has a first cylindrical tubular element border 28 close to the attachment to the membrane 20 and a second cylindrical tubular element border 30 spaced from the attachment to the membrane 20. In addition, the tubular element comprises a first winding 32 of a conductor wire made of copper, aluminum or any other alloy of these materials, and even made of silver in some cases, arranged close to the first cylindrical tubular element border 28, and a second winding 34 of said conductor wire in the opposite direction arranged close to the second cylindrical tubular element border 30. The two windings 32, 34 are quite clearly connected by the same conductor wire.

[0028] The bonded annular magnet 24 extends in the tubular part 18 and inside the tubular element 22. The bonded annular magnet has an outer magnetic cylindrical surface 36 which extends opposite and at a distance from the tubular element 22 and opposite (inwardly) an opposed surface 38 having, in the plane of the drawing corresponding to an axial plane of the bonded annular magnet 24, a half-ellipse shape. The bonded annular magnet 24 has a first mid-plane P.sub.M1 perpendicular to the axis Z of the device. The bonded annular magnet 24, in its outer magnetic cylindrical surface 36, also has in its upper part, above the mid plane P.sub.M1, an upper outer cylindrical half-surface 40 extending opposite the first winding 32 of conductor wire, and in its lower part, below the mid-plane P.sub.M1, a lower outer cylindrical half-surface 42 extending opposite the second winding 34 of conductor wire.

[0029] The bonded annular magnet 2.4 is quite clearly fixed in position relative to the tubular part 18, for example via the base 14.

[0030] The metal tubular member 26, for example formed on the basis of iron, is also fixed in position inside the tubular part 18 and extends coaxially around and at a distance from the tubular element 22. The metal tubular member has a second mid-plane P.sub.M2, coinciding in FIG. 1 with the first mid-plane P.sub.M1 of the bonded annular magnet 24. As will be explained in greater detail hereinafter, the tubular element 22 is free relative to the bonded annular magnet 24 and the metal tubular member 26 and is axially movable relative thereto.

[0031] The metal tubular member 26 has an inner cylindrical surface 45 divided into two inner cylindrical half-surfaces mutually opposed relative to the second mid-plane P.sub.M2: an upper inner cylindrical half-surface 44, which extends opposite the first winding 32 of conductor wire, and, opposite relative to the second mid-plane P.sub.M2, a lower inner cylindrical half-surface 46, which extends opposite the second winding 34 of conductor wire.

[0032] The coiled tubular element 22 is thus assembled freely in an annular chamber 47, or gap, which extends between the metal tubular member 26 and the bonded annular magnet 24. It is movable axially about a rest position in order to entrain the membrane 20.

[0033] Reference is made to FIG. 3 in order to define the dimensions and relative positions of the bonded annular magnet 24 and of the metal tubular member 26. FIG. 3 is a detailed view illustrating a hemi-section of the bonded annular magnet 24 and of the metal tubular member 26.

[0034] The bonded annular magnet 24 thus has a radius R and a height H from the mid-plane P.sub.M1 corresponding to the height of the upper outer cylindrical half-surface 40, while the metal tubular member 26 has a thickness E and an inner radius R2. This thickness E is determined relative to the maximum field density before saturation of the material, and in this case of the iron. The ratio between the outer cylindrical half-surface of the bonded annular magnet 24, in the gap 47, to the cross section of the metal tubular member 26 along the mid-plane P.sub.M2, this being a factor of the magnetic field imparted by the bonded annular magnet 24, must therefore be less than the value of the magnetic saturation threshold of the material used, for example 1.5 for iron.

[0035] Also, by selecting for the bonded annular magnet 24 a radius R of 10 mm and a height H of 6 mm, corresponding to a total half-height of the bonded annular magnet 24, for a magnetic field of 0.4 T (tesla) imparted by a neodymium charge of the bonded annular magnet, and by selecting for the metal tubular member 26 an inner radius R2 of 11 mm thus defining a gap 47 of 1 mm, and a thickness of the metal tubular member 26 E of 2 mm, a field density in the metal tubular member 26 close to 1.0 I is obtained. This value is less than 1.5 T.

[0036] Reference is now made to FIG. 2A, showing the magnetic field lines 48 which extend between the bonded annular magnet 24 and the metal tubular member 26, in order to describe the advantages of the magnetic motor device according to the invention. In FIG. 2A, the tubular element 22 is also shown in part, equipped with its two windings, that is to say the first winding 32 and the second winding 34.

[0037] The curved magnetic field lines 48 thus extend inside the bonded annular magnet 24, along an axial section, substantially parallel to the opposite surface 38 of the outer cylindrical magnetic surface 36 so as to lead perpendicularly into the two half-surfaces 40, 42 respectively. These magnetic field lines 48 are oriented here, in FIG. 2A, in a clockwise direction. Also, the magnetic field is oriented in the gap 47 from the upper outer half-surface 40 of the bonded annular magnet 24 toward the upper inner cylindrical half-surface 44 of the metal tubular member 26. It is then guided axially in the metal tubular member 26 toward the lower inner cylindrical half-surface 46 and passes in the opposite direction through the gap 47 toward the lower outer cylindrical half-surface 42 so as to rejoin the bonded annular magnet 24. FIG. 2B correspondingly shows the variations of the magnetic field in the gap 47, said magnetic field reversing in the lower part compared to the upper part, as has just been explained above.

[0038] The linearity of the magnetic field usable in the gap 47 is therefore no longer linked to the outer elements, but to the single metal tubular member 46. The sound quality of a loudspeaker produced with the magnetic motor device according to the invention is thus increased. Furthermore, and as has been explained above, the geometry of the metal tubular member 46 can be perfectly determined, and in particular its thickness, as a function of the maximum field density of the material used, that is to say 1.5 T in the case of iron.

[0039] Furthermore, the tubular element 22 having the two windings 32, 34 is entirely adjusted in the magnetic field, which makes it possible to achieve increased linearities and to improve yet further the output sound quality.

[0040] In accordance with the present embodiment, the metal tubular member 26 is arranged around the tubular element 22, while the bonded annular magnet 24 is arranged inside the tubular element. Insofar as the space around the metal tubular member 26 is relatively free, the thermal dissipation is thus large. The elements used made of plastic material, in particular in order to guide the tubular element 22, are thus protected from heat.

[0041] However, another embodiment in Which the metal tubular member 26 and the bonded annular magnet 24 are exchanged, in another, reverse arrangement, is envisaged. The metal tubular member 26 thus evacuates the thermal energy axially.

[0042] In accordance with vet a further embodiment, illustrated in FIG. 1 by dashed lines 50, 52 parallel to the axis of the device Z, the opposed surface 38 of the bonded annular magnet 24 has a truncation thus forming a truncated cylindrical surface 54 parallel to and coaxial with the magnetic cylindrical surface 36. The annular magnet 24 is thus made lighter.