The present invention relates to the field of ball and ramp devices for 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 power 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 cavity or space, and with a plurality of rollers positioned within the toroidal space and coming into engagement contact with raceways 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, which ratio i s by definition the input speed divided by the output speed. Each change of the rollers angular position results in a change of the variator ratio .

Patent application GB-A-2 43 8 412 (Torotrak) di sclo ses a toroidal variator compri sing an input di sc, an output di sc, rollers mounted rotatably between the input an output di scs and coming into engagement with raceways provided on said di scs, and a ball and ramp device to generate an axial force proportional to the torque applied to the input di sc. Said device i s formed by a plate, the rear face of the input di sc and a set of b all s axially interposed between ramp s provi ded on said rear face and the plate.

The manufacture of the massive input di sc i s cost-intensive since the material used i s high- strength steel. Besides, the forming of the toroidal raceway and the ramp s on such a di sc requires long machining operations.

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 ball and ramp device for a toroidal variator which i s simple to manufacture and economic.

In one embodiment, the ball and ramp device for a toroidal variator compri ses first and second di scs, and a plurality of rolling elements di sposed between ramps provi ded on the first and second di scs and extending along the circumferential direction. One of said di scs compri ses a plate having the ramp s, a ring delimiting an outer toroidal raceway and an intermediate supporting part axially interposed between said ring and the plate.

The plate may compri se a radial portion having the ramps. The intermediate supporting part may be axially di sposed between the radi al portion and the ring.

Preferably, the pl ate compri ses an inner axial portion and an outer axial portion radially surrounding said inner axial portion. The intermediate supporting part may be radially located between the inner and outer axial portions of the plate. In one embodiment, said inner and outer axial portions extend from the radial portion.

In one embodiment, the plate further compri ses outer axial lugs extending from the outer axial portion and located into recesses formed on the ring. Alternatively, the intermediate supporting part compri ses outer axial lugs extending into recesses formed on the ring.

Advantageously, the outer lugs may further extend into recesses formed on the plate.

The intermediate supporting part is advantageously made from thermopl astic. The supporting part may be overmoulded onto the plate and the ring.

Preferably, the other di sc compri ses a radi al portion having the ramp s and axially facing the radi al portion of the plate. The ring may be made from a metal sheet. Further, the ring may have in cross- section a toroidal shape.

In one embodiment, the rolling elements comprise ball s or rollers which may be tapered or not.

The present invention and its advantages will b e better understood by studying the detail ed description of specifi c embodiments given by way of non-limiting examples and illustrated by the appended drawings on which :

- Figure 1 i s a section of a ball and ramp device for a toroidal variator according to a first embodiment of the invention,

- Figure 2 i s a perspective view of the device of Figure 1 ,

- Figure 3 i s an exploded perspective view of the device of Figure 1 ,

- Figure 4 i s a section of a ball and ramp devi ce for a toroidal variator according to a second embodiment of the invention,

- Figure 5 i s an exploded perspective view of the device of Figure 4,

- Figure 6 i s a section of a ball and ramp devi ce for a toroidal variator according to a third embodiment of the invention, and

- Figure 7 i s an exploded perspective view of the device of

Figure 6.

As illustrated on Figures 1 to 3 , which illustrates an example of a ball and ramp device 1 0 for a toroidal variator according to the invention, said device 1 0, with an axi s 12, comprises a first di sc 1 4 and a second di sc 16 axially facing each other, and a plurality of ball s 1 8 axially di sposed between said di scs.

The first di sc 14 i s advantageously formed from a metal sheet by folding, cutting and stamping. The di sc 14 is annular, coaxial with the axis 12 and compri ses an inner axial portion 14a having an axi al bore into which i s mounted a shaft (not shown), a radial portion 14b extending radially outwards from the axial portion 14a, and an outer axial portion 14c extending axially from a large-diameter edge of the radial portion 14b and radially surrounding the inner axial portion 14a. The radi al portion 14b compri ses, on its internal front surface which axi ally faces the second di sc 16, a plurality of recesses extending in the circumferential direction and forming ramps 20. The ramps 20 are obtained by local deformations of the radi al portion 14b . In the illustrated embodiment, the ramp s 20 are three in number and regularly spaced from one another in the circumferential direction. The ramps 20 are identical to one another and formed on the radial portion 14b, at a common radius with respect to the axi s 12. The ramps 20 have in cross section a concave profile adapted to the ball s 1 8 and forming a raceway for said ball s. Each ramp 20 has a depth which gradually varies in the circumferential direction.

The second di sc 16, coaxial with the axi s 12, compri ses a plate 22, a ring 24 and an intermediate supporting part 26 axially interposed therebetween. The plate 22 is advantageously formed from a metal sheet by folding, cutting and stamping. The plate 22 i s annular and compri ses an inner axial portion 22a having an axial bore of same diameter as the bore of the axial portion 14a of the di sc. The plate 22 al so compri ses a radial portion 22b extending radially outwards from the axial portion 22a and an outer axial portion 22c extending axially from a large-diameter edge of the radi al portion 22b and radially surrounding the inner axial portion 22a. The radial portion 22b axially faces the radial portion 14b of the di sc 14. An axial gap i s formed between said radial portions 14b, 22b . The axial portions 22a, 22c and the radial portion 22b of the plate are respectively symmetrical with the axial portions 14a, 14c and the radi al portion 14b of the di sc relative to a transverse radial pl ane passing through said axial gap .

The plate 22 further compri ses a plurality of circumferenti al recesses forming ramps 28 provided on the internal front surface of the radial portion 22b facing the first di sc 14. The ramps 20, 28 axially face each other in an inverted position. The plate 22 al so compri ses identical axial lugs 22d extending from the outer axial portion 22c axially on the opposite side of the di sc 14. In the illustrated embodiment, the outer lugs 22d are eight in number and regularly spaced from one another in the circumferential direction. In the di sclosed embodiment, the ring 24 has in cross-section a toroidal shape. The ring 24 i s annular and compri ses a toroidal portion 24a having an axial bore of same diameter as the bore of the plate 22. The external front surface of the toroidal portion 24a delimits a concave toroidal raceway 24b adapted to be into contact with rollers (not shown) of the associated toroidal variator. Such rollers transmit drive between the toroidal raceway 24b and a facing toroidal raceway of the toroidal variator. The raceway 24b may 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 characteristics and its definitive surface fini sh. The outer axial surface of the ring 24 compri ses a plurality of recesses 30 regularly spaced from one another in the circumferential direction. Each lug 22d of the plate 22 axially extends into one of these recesses 30 of complementary shape. Collaboration between the lugs 22d and the recesses 30 provides an angular connection between the plate 22 and the ring 24.

The intermediate supporting part 26 is di sposed axially between a convex internal surface 24c of the toroidal portion 24a of the ring which i s axially opposite to the concave raceway 24b and the external front surface of the radial portion 22b of the plate. The supporting part 26 i s in axial contact against the ring 24 on one side and in axial contact with the plate 22 on the other side . The supporting part 26 i s di sposed radially between the outer axial portion 22c and the bore of the inner axial portion 22a of the plate.

The supporting part 26 i s annular and compri ses a radial portion 26a having a concave external surface in axial contact with the convex surface 24c of the ring of complementary shape, and an opposite internal radial surface in axial contact with the radial portion 22b of the plate of complementary shape. The outer axial surface of the radi al portion 26a i s in radial contact with the outer axial portion 22c of the plate. The bore of said radial portion 26a recovers the inner axial portion 22a of the plate. The supporting part 26 al so compri ses an inner annular skirt 26b extending radially inwards an axial end of the bore of the radial portion 26a. The radial skirt 26b has a bore of same diameter as the b ore of the plate 22 and is axially located between the inner axial portion 22a of said plate and the ring 24. The supporting part 26 further compri ses a plurality of rib s 26c extending radially outwards the outer axial surface of the radial portion 26a and regularly spaced from one another in the circumferential direction. Each rib 26c is located axially between the outer axi al portion 22c of the plate and the ring 24, and circumferentially between two successive lugs 22d of said plate. Each lug 22d extends axially across the space delimited between two successive rib s 26c.

The supporting part 26 al so compri ses axial pins 26d extending from the internal front surface of the radial portion 26a and protruding into corresponding holes 32 formed in the radial portion 22b of the plate. The supporting part 26 is made in one part by overmoulding a thermoplastic materi al, for instance such as a polyamide, onto the plate 22 and the ring 24. This results in an excellent cohesion between these parts, in particular at the holes 32 which the melted plastic material penetrates to form the pins 26d by matching shape. The production of the supporting part 26 by moulding makes it possible to give it shapes with a large degree of lightness and a low manufacturing cost. Alternatively, the supporting part 26 could however be made of another material, for instance metal, and/or be fixed onto the pl ate 22 and the ring 24 by any other appropriate means, for example by gluing.

The embodiment shown on Figures 4 and 5 , in which identical parts are given identical references, differs from the previous emb odiment in that a plurality of rollers 40 are axially di sposed between the di sc 14 and the plate 22. Associated ramp s 42, 44 are respectively formed on the radi al portion 14b of the di sc and the radial portion 22b of the plate in a similar way to the ramps of the previous embodiment. The ramps 42, 44 each have in cross section a U- shaped profile adapted to the rollers 40 and form raceways for said rollers. In the illustrated embodiment, the rolling surfaces of the rollers 40 have a cylindrical profile. Alternatively, the rolling surfaces may have a tapered profile. The embodiment shown on Figures 6 and 7, in which identical parts are given identical references, differs from the first embodiment in that the intermediate supporting part 26 compri ses a plurality of outer axial lugs 26e extending axially the outer axial surface of the radial portion 26a on the opposite si de of the di sc 14, while being regularly spaced from one another in the circumferential direction. Each lug 26e extends axially from the internal front surface of the radial portion 26 and protrudes axially both into the space delimited between two successive rib s 26c and one recess 30 of the ring 24. Axially on the opposite si de of the ring 24, each lug 26e i s located into one of the recesses 50 of compl ementary shape formed on the radial portion 22c of the plate. With such an embodiment, a torque applied to the plate 22 i s transmitted to the ring 24 by the lugs 26e of the supporting part 26.

In the di sclo sed embodiment, the rolling el ements are ball s.

Alternatively, the rolling elements may be cylindrical or taper rollers. In another variant, it could al so be possible, for each di sclo sed embodiment, to foresee a cage axially di sposed between the di scs 14, 16 for maintaining the rolling elements circumferentially spaced apart.

The interposition of a supporting part axially between the plate having the ramps and the ring having the toroidal raceway permits to obtain a robust and low cost ball and ramp device adapted to a toroidal variator. With such a device having a di sc made as an assembly of di stinct components, the plate and the ring may be made from different metal, each selected in order to b est address the mechanical requirements, and manufactured by using any forming process, for instance forging. For instance, the supporting part may be made from a lower quality material, for instance a thermopl astic such as PA6.6, whereas the ring i s made from a bearing steel and the plate is made from a medium/high carbon steel, such as C55 , or a construction steel such as E24.