FR2612015A1 - Torque transfer device of dynamo-electric type - Google Patents

Abstract

Torque transfer device characterised in that it includes a driving piece 1 of multipole cylindrical shape with permanent magnets 3 which cooperates with a concentric driven piece 2 consisting of a set of short-circuited axial conducting bars 4 embedded in a shell 5 of a soft magnetic material, so that the transferred torque changes substantially linearly with the difference in speeds between the driving piece 1 and the driven piece 2 up to a maximum, then vanishes.

Description

The present invention relates to a torque transfer device which applies in particular to motor vehicles.

There are known mechanical torque transfer devices which use viscous coupling systems. These systems have the disadvantage of requiring a complex structure with a relatively large number of parts. In addition, the use of these sets results in viscous friction.

The object of the present invention is to provide a torque transfer device which avoids any mechanical friction.

To this end, the torque transfer device according to the invention comprises a driving part of cylindrical multipolar shape with permanent magnets, which cooperates with a concentric driven part consisting of a set of shorted conductive axial bars and embedded in a carcass. in soft magnetic material, so that the transferred torque evolves in a substantially linear manner with the difference in speeds between the driving part and the driven part up to a maximum and then cancel each other out.

According to one embodiment of the invention, the number of bars of the driven part is an odd number which is not a multiple of the number of poles of the driving part.

According to one embodiment of the invention, the permanent magnets are made of hard ferrite.

According to one embodiment of the invention, the permanent magnets are made of rare earth.

The torque transfer device according to the invention thus has the advantage of having no mechanical friction, while having a solely mechanical structure which is very reliable and very robust.

Other characteristics and advantages of the present invention will emerge from the description which follows the embodiment given by way of examples with reference to the appended drawings in which - Figure 1 is a perspective view of the torque transfer device according to the invention, - Figure 2 is a section along the plane II-II of Figure 1, - Figure 3 is a section similar to Figure 2 of another embodiment of the invention.

The torque transfer device according to the invention comprises a driving part 1 of cylindrical shape, which cooperates with a driven part 2 concentric. A frame, not shown in the figures, is a fixed part which has a role of mechanical support for the two moving parts, that are the driving part 1 and the driven part 2.

The driving part 1 of cylindrical shape is constituted by permanent magnets 3 made of hard ferrite or rare earth and blades 7 made of solid soft magnetic material. This structure makes it possible to create, at the periphery of the driving part 1, a radial and alternating magnetic field along its perimeter.

The driven part 2 is of hollow cylindrical shape in which is housed freely the driving part 1. The driven part 2 is constituted by a carcass 5 of annular shape which has notches in the internal face so as to be able to receive bars 4 in conductive material such as copper, in the axial grooves thus formed. The carcass 5 is constituted by a stack of sheets of soft magnetic material.

The bars 4 are electrically connected by two short-circuit flanges 6, which are housed at each end of the bars 4.

In the case of FIG. 2, the number of permanent magnets 3 of the driving part 1 is the same as the number of bars 4 of the driven part 2. In the case of FIG. 3, the number of bars 4 of the driven part 2 is an odd number which is not a multiple of the number of poles 7 of the driving part, that is to say of the number of permanent magnets 3.

The driving part 1 (entry of the movement), due to its structure, creates a multipolar radial field which closes through the carcass 5 of the driven part 2 and, consequently, crosses all of the 4-conductor bars. When there is a speed difference between the driven part 2 and the driving part 1, the magnetic flux passing through the bars 4 becomes variable and it therefore creates a voltage which results in the appearance of an induced current. in the bars 4 short-circuited by the flanges 6.

The interaction of the induced currents and the inductive magnetic flux causes the appearance of a tangential Laplace force and therefore of a torque tending to reduce the slip.

When the two driving parts 1 and driven 2 rotate at different speeds, the induced circuits, constituted by the bars 4 short-circuited by the flanges 6, are crossed by the inductive magnetic field which happens to be alternating in this case . An electromotive force is therefore created in the bars 4 and, consequently, a so-called induced current.

The induced currents cutting the inductive flow cause a tangential force, that is to say a torque going in the direction of reduction of the slip, that is to say of a speed differential.

We thus obtain a variation of the torque as a function of the speed differential, which is first of all appreciably linear and then bends towards a maximum and finally cancels out.

The torque transfer device according to the invention thus has the additional advantage of having a very short response time, without requiring piloting. In addition, it is insensitive to temperature; indeed, if the operating characteristics are degraded during a rise in temperature, the phenomenon is reversible and the device is not damaged.

Claims (4)

1 - Torque transfer device characterized in that it comprises a driving part (1) of cylindrical multipolar shape with permanent magnets (3) which cooperates with a concentric driven part (2) consisting of a set of bars (4) axial conductors short-circuited and embedded in a carcass (5) of soft magnetic material, so that the transferred torque evolves in a substantially linear manner with the difference in speeds between the driving part (1) and the driven part (2) up to a maximum and then cancel. 2 - Torque transfer device according to claim 1 characterized in that the number of bars (4) of the driven part (2) is an odd number and that it is not a multiple of the number of blades (7) of the piecemenante (1). 3 - Torque transfer device according to claim 1 characterized in that the permanent magnets (3) are made of hard ferrite. 4 - Torque transfer device according to claim 1 characterized in that the permanent magnets (3) are made of rare earth.