The present invention relates to the field of toroidal variators .

A toroidal variator may be used for instance in a supercharger for a combustion engine, in an air conditioning system, in an alternator, in a cooling fan or in a main transmi ssion of a motor vehicle.

A toroidal variator i s generally provided with an input di sc and an output disc facing each other and delimiting a toroidal space, and with a plurality of rollers positioned within the toroidal space and coming into engagement contact with raceway s of the input and output di scs to transfer a torque from one di sc to the other. The rollers are arranged so as to be di stributed over the circumference of the toroidal space and can be adj usted spatially within said space in order to adjust the transmi ssion ratio of the variator continuously . Each roller of the toroidal variator is supported by a carriage connected to a control mechani sm allowing said roller to be steered across the raceways of the di scs.

The rotational speeds of the input and output discs determine the operating ratio of the variator, whi ch ratio i s by definition the output speed divided by the input speed. Each change of the rollers angular position results in a change of the variator ratio .

The manufacture of the di scs and rollers is cost-intensive since the material s used are high- strength steel s. Otherwi se, the contact stresses on the di scs and the rollers may limit the lifetime of the toroidal variator.

One aim of the present invention i s to overcome these drawbacks.

It is a particular obj ect of the present invention to provide a torque transmi ssion assembly for a toroidal variator which i s simple to manufacture and economic, while guaranteeing an improved lifetime.

In one embodiment, the torque transmi ssion assembly for a toroidal variator compri ses at least one input di sc and one output di sc each comprising a guiding portion delimiting a raceway, and a plurality of rollers mounted rotatably between the input and output di scs and coming into engagement with said di scs in order to transfer a torque . Each roller compri ses an outer portion delimiting a rolling surface in contact with the raceways . The guiding portion of each di sc has fibre flows extending sub stantially parallel to the associ ated raceway. Alternatively or in combination, the outer portion of each roller has fibre flows extending sub stantially parallel to the associated rolling surface.

Advantageously, the guiding portion of each di sc delimits a toroidal raceway .

In one emb odiment, each roller compri ses a radial portion extended at a large-diameter edge by a curved portion forming the outer portion.

In one embodiment, there are respectively two, three or four rollers.

In one preferred embodiment, the input and output di scs are identical.

In one embodiment, the input and output discs and/or the rollers are made of a metal sheet.

In another aspect, the invention provides a method of manufacturing a torque transmi ssion assembly for a toroidal variator compri sing at least an input di sc and an output di sc each compri sing a gui ding portion delimiting a raceway, and a plurality of rollers mounted rotatably between the input and output di scs and coming into engagement with said di scs in order to transfer a torque. Each roller compri ses an outer portion delimiting a rolling surface in contact with the raceways. Said method compri ses the step of forming the guiding portion of each di sc so that the fibre flows of said guiding portion extend sub stantially parallel to the associated raceway . Alternatively or in combination, said method compri ses the step of forming the outer portion of each roller so that the fibre flows of said outer portion extend sub stantially parall el to the associated rolling surface. Advantageously, the method compri ses the step of forming each di sc and/or each roller by cutting and stamping a metal sheet. Preferably, the metal sheet has before and after the step of forming fibre flows extending sub stantially parallel to its maj or faces . Thi s may be the case for instance when the metal sheet is obtained from the rolling of a bloom.

In another aspect, the invention provides a di sc for a torque transmi ssion assembly whi ch compri ses a guiding portion delimiting a raceway adapted to cooperate with a plurality of rollers of the torque transmi ssion assembly. The guiding portion of the di sc has fibre flows extending sub stantially parallel to the associated raceway.

In another aspect, the invention provi des a roller for a torque transmi ssion assembly which compri ses an outer portion delimiting a rolling surface adapted to cooperate with di scs of the torque transmi ssion assembly . The outer portion of each roller has fibre flows extending sub stantially parallel to the associated rolling surface.

The present invention and its advantages will b e better understood by studying the detailed description of a specifi c embodiment given by way of a non-limiting example and illustrated by the appended drawings on which :

- Figure 1 i s a section of a torque transmi ssion assembly for a toroidal variator according to an example of the invention,

- Figures 2a to 2c are steps of a method of manufacturing a di sc of the assembly of Figure 1 , and

- Figures 3 a to 3 d are steps of a method of manufacturing a roller of the assembly of Figure 1 .

As illustrated on Figure 1 , which illustrates an embodiment of a torque transmi ssion assembly according to the invention, said assembly comprises an input di sc 1 mounted on an input shaft 2 and an output di sc 3 mounted on an output shaft 4. The shafts 2, 4 extend along a common axi s 5. The input and output discs 1 , 2 are identical to one another and each compri se a toroidal portion 6, 7 formed around the axi s 5 and delimiting a concave toroidal raceway 6a, 7a. The input and output di scs 1 , 2 axially face each other and a toroidal space 8 i s axially defined between the facing raceways 6a, 7a. Each disc 1, 2 comprises an axial bore 9, 10 into which is mounted the associated shaft 2, 4.

The assembly also comprises a plurality of identical rollers 11 positioned within the toroidal space 8 and rolling into contact with both of raceways 6a, 7a. The rollers 11 transmit drive between the raceways 6a, 7a with reversal of direction so that the direction of rotation of shaft 4 is opposite to that of shaft 2. The rollers 11 are arranged so as to be distributed over the circumference of the toroidal space 8. There are three rollers 11. Each roller 11 rotates around an axis 12 and is supported by a carriage (not shown). When the roller 11 and the associated carriage tilt, the ratio transmitted from the input disc 1 to the output disc 3 varies. When the rollers 11 contact the output disc 3 at a greater radius than that at which it contacts the input disc 1, the output disc rotates slower than the input disc. Conversely, when the corresponding radius at which the rollers 11 contact the input disc 1 is the greater, the output disc 3 rotates faster than the input disc.

With respect to the axis 12, each roller 11 comprises an annular radial portion 11a having an axial bore lib into which is mounted a shaft (not shown) supported by the carriage and extending along the axis 12. Each roller 11 is also provided with a frustoconical portion 11c extending radially outwards from the radial portion 11a and which is extended at a large-diameter edge by an annular radial portion lid, and with an annular curved portion lie extending axially from a large- diameter edge of said radial portion lid. The outer surface of the curved portion lie delimits an annular rolling surface llf in contact with the toroidal raceways 6a, 7a of the input and output shafts. The width of the rolling surface llf can be chosen independently on the roller body wall thickness. Particularly it is possible to keep a wide rolling surface llf while using a small roller thickness. This allows to reduce the weight and the manufacturing time, and also to provide some elastic behaviour of the roller in order to avoid hard points and early failures. The ratio between the diameter of the disc and the diameter of the roller is comprised between 1 and 3, and preferably between 1.5 and 2.

The method of manufacturing such discs and rollers will now be described on the basis of Figures 2a to 2c and Figures 3a to 3d. In the method of manufacturing the input disc, a piece of metal sheet 14 obtained by a rolling process, and having fibre flows 15 extending parallel to its major planar faces, is used to obtain a blank as shown on Figure 2a. The fibre flows 15 are flows of material which are induced during formation of the metal sheet 14. Firstly, the metal sheet 14 is cut in a shape of a disc and then the bore 9 is formed as shown on Figure 2b. Secondly, the annular disc obtained is pressed by a pressing tool (not shown) so as to form the annular toroidal portion 6 delimiting the raceway 6a and to obtain the final shape of the input disc 1 as shown on Figure 2c. After the steps of cutting and stamping, the fibre flows 15 of the toroidal portion 6 remain parallel to the toroidal outer surface of the disc which forms the raceway 6a. The input disc 1 may then be hardened by heat treatment and the raceway 6a may then be finished (for instance by grinding or hard turning) and superfinished (for instance by lapping or honing or vibrofinishing) in order to obtain its geometric characteristics and its definitive surface finish. The output disc 3 is also formed according to this method.

For manufacturing a roller 11, a metal sheet 16 obtained by a rolling process, and having fibre flows 17 extending parallel to its major planar faces, is used to obtain a blank as shown on Figure 3a. In a first step, the metal sheet 16 is cut in a shape of a disc and the bore lib is formed as shown on Figure 3b. Then, the annular disc obtained is pressed by a pressing tool (not shown) so as to form the frustoconical portion 11c, the radial portion lid and an annular outer portion extending axially as shown on Figure 3c. In a third step, the annular outer portion is slightly curved radially inwards so as to form the annular curved portion lie as shown on Figure 3d. After the steps of cutting and stamping, the fibre flows 17 of the curved portion lie remain substantially parallel to the rolling surface llf. The roller 11 may then be hardened by heat treatment and the rolling surface llf may then be fini shed (for instance by grinding or hard turning) and superfini shed (for instance by lapping or honing or vibrofini shing) in order to obtain its geometric characteri stics and its definitive surface fini sh.

For the input and output discs 1 , 3 , with such an orientation of the fibre flows of the toroidal portion relative to the associated raceway, the di scs have a high fatigue resi stance and an increased lifetime. For a conventional input or output disc, a machining operation i s foreseen to form the toroidal raceway. As a result, many of the fibre flows of the material of the di scs are interrupted by the machining. With such a conventional di sc having fibre flows which are broken at the raceway, the fatigue resi stance of the raceway drops, thus shortening the lifetime. Similarly, with the orientation of the fibre flows 17 of the curved portion l i e relative to the rolling surface l l f, each roller 1 1 has a high fatigue resi stance and an increased lifetime.

In the di sclo sed method of manufacturing, the di scs 1 , 3 and the rollers 1 1 are formed with a stamping step . Alternatively, it could al so be possible to foresee another metal working step, for instance a spinning step or a forging step, for respectively manufacturing the di scs and the rollers with fibre flows extending sub stantially parallel to the associated raceway and to the associated rolling surface.

Although the present invention has been illustrated on the basi s of a torque transmi ssion assembly having a single space or cavity within which the rollers are positioned, it shoul d be understood that the invention can al so be applied to a torque transmi ssion assembly having two cavities or even more.