WO2010066572A1

WO2010066572A1 - Overrunning clutch for disengageable pulley device

Info

Publication number: WO2010066572A1
Application number: PCT/EP2009/065746
Authority: WO
Inventors: Benoît Arnault; Pierre-Julien Barraud
Original assignee: Aktiebolaget Skf
Priority date: 2008-12-12
Filing date: 2009-11-24
Publication date: 2010-06-17
Also published as: FR2939855A1; FR2939855B1; DE112009004348T5

Abstract

The overrunning clutch for a disengageable device comprises a plurality of wedging elements 19 designed to be mounted between an inner transmission element 3 and a pulley 2 of the device, a cage 22 for the wedging elements, a means 35 for mounting the cage on the inner transmission element, and an elastic coupling means 36 placed between the cage and the mounting means and capable of allowing a circumferential movement of the cage relative to the mounting means.

Description

Overrunning clutch for disengageable pulley device

The present invention relates to the field of overrunning clutches. More particularly, the present invention relates to the field o f disengageable pulleys fitted with overrunning clutches used for example in the pulleys for driving alternators in a motor vehicle.

Such disengageable pulleys are known per se and are increasingly used to remedy the harmful effects of acyclisms or sudden decelerations of the engine which occur in spark-ignition engines, in particular at low revolutions per minute and above all in Diesel engines.

Specifically, a drive belt, which is connected to the engine via a crankshaft pulley, can decelerate suddenly while a driven pulley, for example an alternator pulley, tends, by inertia, to continue rotating at the same speed.

In the case of a rigid coupling between the crankshaft pulley and the alternator shaft, the belt is subjected to very considerable stresses during these instantaneous speed variations. Such variations generate harmful effects such as an abnormal fatigue of the belt with risks of breakage, a slippage of the latter on the pulley, or else a vibration of the belt strands between the pulleys.

In order to attenuate these phenomena, an overrunning clutch has been incorporated, between the driven pulley and the driven shaft, which makes it possible to temporarily decouple the pulley from the shaft in the event of sudden deceleration of the said pulley.

Such a disengageable pulley is known in particular via document JP 2005-282856 and usually comprises two bearings placed on each side of the pulley, and an overrunning clutch mounted between the two bearings and provided with a plurality of wedging cams and a cage comprising a plurality of windows for the housing of the said cams.

In order to limit the wear of these cams, this document makes provision to attach the retention cage to the driven shaft in order to drive the cage and the shaft at the same angular speed. In this manner, when the pulley is in the disengaged position in which it operates in overrun, a slippage occurs only between the cams and a slippage way situated inside the pulley which is correctly lubricated by the centrifugal force which tends to throw the lubricant towards the said slippage way.

However, with such a pulley, the cage has no degree of angular freedom relative to the driven shaft. The Applicant has noticed that this may adversely affect the operational safety of the overrunning clutch particularly by causing risks of interference between the cams and the edges of the windows of the retention cage when the cams tilt.

To remedy this drawback, the Applicant has perfected a disengageable pulley device which has been the subject of a filing of a French patent application published under number 2 914 381. This pulley device comprises a spring wound around the driven shaft, one end of which is attached to the said shaft and the other end to the pulley. The spring can move radially relative to the transmission shaft in order to allow a slight angular movement of the cage relative to the driven shaft if the cams, when they tilt, force against the edge of the windows of the cage.

This arrangement therefore makes it possible to prevent the blocking of the cams by the cage, or else a deterioration of the latter and thereby to promote a correct operation of the overrunning clutch. However, this solution requires providing a blind hole on the outer surface of the driven shaft to allow the mounting of one end o f the spring. In addition, over time, fatigue of the spring may occur that can harm the operating safety of the overrunning clutch.

The object of the present invention is to remedy the aforementioned drawbacks.

The particular object of the present invention is to provide an overrunning clutch for a disengageable pulley which comprises components that are economic to manufacture and assemble.

A further object of the present invention is to provide an overrunning clutch having good operating safety.

In one embodiment, the overrunning clutch for a disengageable pulley device of the type comprising an inner transmission element and a pulley mounted on the said inner element, the overrunning clutch is furnished with a plurality of wedging elements designed to be mounted between the inner transmission element and the pulley, and with a cage for the wedging elements. The overrunning clutch also comprises a means for mounting the cage on the inner transmission element designed to be attached to the said inner element, and an elastic coupling means placed between the cage and the mounting means and capable of allowing a circumferential movement of the cage relative to the mounting means.

Advantageously, the mounting means is made of a rigid material, the coupling means being made of a flexible material. In one embodiment, the coupling means is at least partly placed radially between the mounting means and the cage. The coupling means may be at least partly placed axially between the cage and the mounting means.

Preferably, the cage comprises at least one means for the axial retention of the coupling means.

In one embodiment, the coupling means comprises a body and radial protuberances, each protuberance being housed in the circumferential direction between an abutment portion of the cage and an abutment portion of the mounting means. The body of the coupling means is placed radially between radial portions of the mounting means.

Advantageously, the overrunning clutch comprises a single cage for the wedging elements. The cage may be made in one piece.

The overrunning clutch has no additional cage with a radius different from that of the cage and capable of tilting the cams from the engaged position.

The cage may comprise at least one lug for the axial retention of the mounting means. The lug also forms a means for axial retention of the coupling means. In one embodiment, the coupling means is attached to the cage and to the mounting means, notably by overmoulding.

The invention also relates to a disengageable pulley device comprising an inner transmission element, a pulley mounted on the inner transmission element, and an overrunning clutch provided with a plurality of wedging elements mounted between the inner transmission element and the pulley and with a cage for the wedging elements. The overrunning clutch also comprises a means for mounting the cage on the inner element which is attached to the said inner element, and an elastic coupling means placed between the cage and the mounting means and capable of allowing a circumferential movement of the cage relative to the mounting means and to the inner transmission element.

The disengageable pulley device may be mounted on an alternator shaft for the purpose of driving the said alternator. The pulley may be mounted on a central shaft particularly via an overrunning clutch. The driveshaft may be mounted on or coincide with the alternator shaft. A drive belt driven via the engine may bear on a periphery of the pulley.

By virtue of the overrunning clutch, the pulley drives the central shaft when the engine accelerates or is at a substantially continuous speed or else decelerates very slowly. In the event of sudden slowing of the engine and therefore of the pulley, the central spindle of the disengageable pulley device can continue to rotate more quickly than the pulley itself thanks to the overrunning clutch, thereby sparing the excessive stresses on the drive belt. By virtue of the overrunning clutch, there is a tendency to retain the wedging elements in permanent contact with the slippage ways during an engaged position and during a disengaged position of the overrunning clutch, which in particular makes it possible to switch virtually instantaneously from an overrun position to a torque uptake position and vice versa.

This is particularly advantageous for an application on an alternator in which the acyclisms occur through extremely rapid variations of the rotation speed of the engine, which requires good responsiveness of the device.

In the disengaged position of the overrunning clutch, i.e. when no torque is transmitted between the pulley and the inner transmission element, the mounting means and the coupling means make it possible to drive the overrunning clutch at the same speed as the inner transmission element.

Consequently, the relative slippage between a slippage way arranged on the inner transmission element and the wedging elements is limited. Therefore, the slippage occurs essentially between the wedging elements and a slippage way of the pulley which is perfectly lubricated by centrifuging. The slippages then generate a low drag torque and minimum wear of the wedging elements.

Moreover, the elastic coupling or connection means provided between the cage and the mounting means makes it possible, for example when the wedging elements force against the windows of the cage when they are tilted from the disengaged position to the engaged position or vice versa, to allow a slight angular or circumferential movement of the cage relative to the inner element. This is made possible by the elasticity in the circumferential direction of the coupling means. This prevents the wedging elements being blocked by the cage, or else prevents the latter from damage. This promotes good operation of the overrunning clutch.

The elastic coupling means is distinct from the mounting means and from the cage. The coupling means is situated at a distance from the inner transmission element. There is no contact between the coupling means and the said inner element.

The present invention will be better understood on reading the detailed description of embodiments taken as examples that are in no way limiting and are illustrated by the appended drawings in which: - Figure 1 is a view in axial section of a disengageable pulley device according to a first embodiment;

- Figures 2 and 3 are views in section on H-II and III-III of Figure 1 ;

- Figure 4 is a partial view in section on IV-IV of Figure 3 ; - Figures 5 and 6 are views in perspective of an overrunning clutch of the device of Figures 1 to 4;

- Figure 7 is a view in section of a disengageable pulley device according to a second embodiment; and - Figure 8 is a view in section of a disengageable pulley device according to a third embodiment.

As can be seen in Figures 1 to 3 , the disengageable pulley device 1 comprises a pulley 2, an inner transmission element 3 , for example a hollow shaft, two rolling bearings 4 and 5 and an overrunning clutch 6.

The pulley 2, with an axis 7, has an outer surface provided with a grooved zone 2a with annular grooves and an axial zone 2b formed at an axial end of the grooved zone 2a. The pulley 2 comprises a cylindrical bore 2c extending over the whole length of the pulley 2, except for the bevels (not referenced) placed each at one axial end, and two radial transverse surfaces 2d and 2e.

The inner transmission element 3 , which takes the form of a hollow shaft, has a cylindrical axial outer surface 3a on which is provided, at each of the axial ends, a bevel (not referenced). The inner transmission element 3 also comprises a bore 3b a portion 3c of which comprises a thread for the purpose of attachment to the end of an alternator shaft and for the driving of the said shaft (not shown). Axially opposite to the bore 3b, the inner transmission element 3 comprises internally splines 3d for tightening the said element onto the alternator shaft by means of an appropriate tool interacting with the said splines.

The bearing 4, coaxial with the axis 7, comprises an inner race 8, an outer race 9, between which are housed a row of rolling elements 10 in this instance made in the form of balls, a cage 1 1 for maintaining the circumferential space of the rolling elements 10, and a seal 12.

The inner race 8 comprises a bore 8a of cylindrical shape, fitted onto the outer surface 3a of the inner transmission element 3 , and delimited by two opposite radial lateral surfaces 8b and 8c, and a stepped outer cylindrical surface 8d from which a toroidal circular groove (not referenced) is formed having, in cross section, a concave inner profile capable of forming a raceway for the rolling elements 10, said groove being oriented radially outwards.

The outer race 9 comprises an outer cylindrical surface 9a fitted into the bore 2c of the pulley 2 and delimited by transverse surfaces 9b and 9c, and a stepped bore 9d of cylindrical shape from which a toroidal circular groove (not referenced) is formed having in cross section a concave inner profile capable of forming a raceway for the rolling elements 10 that is oriented radially inwards. The bore 9d in this instance comprises two annular grooves (not referenced) that are symmetrical with one another relative to a plane passing through the centre of the rolling elements 10. Mounted inside the annular groove situated on the outside of the bearing 4 is the seal 12 which rubs against the cylindrical outer surface 8d of the inner race 8 in order to form a seal. The seal 12 is placed radially between the inner race 8 and outer race 9, and is mounted axially between the rolling elements 10 and the radial surfaces 8b and 9b of the races 8 and 9. The said surfaces are axially slightly set back relative to the radial transverse surface 2e of the pulley 2. Similarly, the bearing 5 , coaxial with the axis 7, comprises an inner race 13 fitted to the outer surface 3a of the inner transmission element 3 , an outer race 14 fitted into the bore 2c of the pulley 2, between which a row of rolling elements 15 , made in this instance in the form of balls, is housed, a cage 16 for maintaining the circumferential space of the rolling elements 15 , and a metal seal 17.

The bearing 5 is identical to the bearing 4 and is placed symmetrically relative to the latter with respect to a radial plane passing through the centre of the pulley 2. The bearing 5 is axially slightly set back relative to the radial transverse surface 2d of the pulley 2. The bearings 4 and 5 are therefore placed at each axial end o f the pulley 2, the overrunning clutch 6 being mounted axially between them. The overrunning clutch 6 therefore benefits from protection against the intrusion of foreign bodies via the bearings 4 and 5 , and in particular the seals 12 and 17. The overrunning clutch 6 comprises a plurality of wedging elements or cams 19 placed between two slippage ways 20 and 21 , axi- symmetric in shape. The cams 19 are of the "engaging" type, that is to say having a tendency, under the effect of the centrifugal forces during the rotation of the overrunning clutch, to tilt in the direction promoting their locking between the two slippage ways 20 and 21 for the purpose of facilitating a virtually instantaneous transition from overrun operation to torque take-up operation.

The slippage way 20 is formed directly by the bore 2c of the pulley 2. The slippage way 21 is formed directly by the axial outer surface 3a of the shaft 3 or the inner transmission element.

In other words, the pulley 2 can be manufactured with an inner surface with a particularly simple shape that is entirely axial with the exception of the end bevels. The pulley 2 can therefore be obtained at low cost. This inner surface forms an outer bearing surface or a surface of large diameter for the cams 19.

On the opposite side, the slippage way 21 is formed on the outer surface 3a of the shaft 3. The outer profile of revolution of the shaft 3 has the same diameter over the whole of its length. Finishing can be carried out in a single operation on a resurfacing machine and makes it possible to obtain, in a long run and at low cost, the small- diameter, or inner bearing surface, slippage way 21 for the cams 19 of the overrunning clutch 6.

The overrunning clutch 6 also comprises a generally annular- shaped cage 22 for retaining the cams 19. It is formed from a thin metal sheet blank by folding, cutting and stamping.

The cage 22 comprises an annular axial portion 23 furnished with a plurality of windows 24 forming housings for the cams 19. The windows 24 are evenly spaced relative to one another in the circumferential direction. The cage 22 allows evenly-spaced circumferential retention of the cams 19.

The cage 22 also comprises an annular radial portion 25 which extends radially outwards an axial end of the axial portion 23 situated in the vicinity of the bearing 4. The free end of the radial portion 25 remains at a distance from the bore 2c.

As illustrated more clearly in Figure 6, axially on the side opposite to the radial portion 25 , the cage 22 comprises radial portions 26 extending radially outwards an axial end of the axial portion 23 situated on the side of the bearing 5 (Figure 1 ) and remaining at a distance from the bore 2c of the pulley 2. The radial portions 26 are identical, situated in one and the same radial plane and each extending over a limited angular sector. In this instance they are three in number, only two being visible in Figure 6, and spaced from one another in the circumferential direction. The circumferential dimension of the radial portions 26 is substantially equal to the circumferential dimension separating two successive windows 24.

Each radial portion 26 is extended axially, at its circumferential ends, by a short axial portion 27, 28 extending axially in the direction of the windows 24 and of the cams 19 and being connected to the axial portion 23. The axial portion 27 of a radial portion 26 is connected to the axial portion 28 of the immediately adjacent radial portion 26 by means of a radial portion 29 connected to the axial portion 23. The cage 22 therefore comprises three radial portions 29 axially offset towards the cams 19 relative to the radial portions 26, and offset in the circumferential direction relative to the radial portions 26. The radial portions 29 are situated in one and the same radial plane and each extend over a limited angular sector. The large-diameter edges of the radial portions 29 are extended axially outwards by axial portions 30 connecting in the circumferential direction to the large-diameter edges of the radial portions 26.

Each axial portion 30 is extended by an axial lug 31 extending axially towards the outside of the cage 22, i.e. on the side of the bearing 5. The lugs 3 1 have a smaller circumferential dimension than that of the axial portions 30.

Again with reference to Figures 1 to 3 , the overrunning clutch 6 also comprises a spring 32 that is made in the form of an annular metal strip wound on itself and connected end-to-end or with partial overlap. The spring 32 is mounted inside the cage 22, and more particularly placed radially between the outer surface 3a of the transmission element 3 and the axial portion 23 of the cage 22. The spring 32 is situated axially between the radial portions 25 and 29 o f the cage 22. The spring 32 also comprises cavities or windows 33 which correspond to those of the cage 22 in order to be able to mount the cams 19. Therefore, the windows 33 are evenly spaced circumferentially.

The spring 32 is again provided with at least one elastic return element 34 per cam 19 made in the shape of a tongue originating from the edge of a window and designed to press on a surface arranged for this purpose on the associated cam 19 in order to exert a tilting torque tending to keep the cams 19 in contact with the slippage ways 20 and 21. In a static position, the return elements 34 exert a force directed towards the pulley 2.

As a variant, it would be possible to provide an individual return element associated with each cam in order to exert a force tending to maintain a permanent contact with the slippage ways 20 and 21. It would, for example, be possible to mount, for each of the cams 19, an elastic return spring placed between the cam 19 and the cage

22.

In order to connect the inner transmission element 3 and the cage 22, the overrunning clutch comprises an end-plate 35 attached to the inner transmission element 3 axially between the bearing 5 and the spring 32, and an elastic coupling means 36 placed between the said end-plate and the cage 22. The end-plate 35 allows the mounting of the cage 22 onto the inner transmission element 3 , the coupling means 36 for its part providing an elastic connection in the circumferential direction of the cage 22 with the said inner transmission element 3 as will be described in greater detail below.

The end-plate 35 may be made economically from a metal sheet blank by folding, cutting and stamping or else by moulding of a synthetic material. As illustrated more clearly in Figure 6, the end- plate 35 comprises an axial centring portion 37 of generally annular shape coming into contact against the outer surface 3a of the inner transmission element 3 (Figure 1 ) in order to allow the end-plate 35 to be centred on the latter. The axial portion 37 is attached to the inner transmission element 3 by any appropriate means, for example by tight fitting onto the outer surface 3a. The axial portion 37 is situated axially between the inner race 13 of the bearing 5 and the spring 32 while remaining at a distance from these two elements.

The axial end of the axial portion 37 situated on the side of the bearing 5 is extended radially outwards by an annular radial portion 38, itself extended towards the outside of the radial portions 39 extending in the direction of the bore 2c of the pulley 2 while nevertheless remaining at a distance from the said bore. The radial portions 39 are identical, situated in one and the same radial plane and each extending over a limited sector. In this instance they are three in number and spaced apart from one another in the circumferential direction.

Each radial portion 39 is extended axially, at its circumferential ends, by a short axial portion 40, 41 extending axially on the side of the axial portion 37, i.e. in the direction of the cage 22. The axial dimension of the axial portions 40, 41 is substantially equal to that of the axial portions 27, 28 of the cage 22. The axial portion 40 of a radial portion 39 is connected to the axial portion 41 of the immediately adjacent radial portion 39 by means of a radial portion 42. The end-plate 35 therefore comprises three radial portions 42 axially offset towards the cage 22 relative to the radial portions 39, and offset in the circumferential direction relative to the said radial portions 39. The radial portions 42 are situated in one and the same radial plane and each extend over a limited angular sector. The circumferential dimension of the radial portions 42 is smaller than the circumferential dimension of the radial portions 29 of the cage 22.

The end-plate 35 again comprises axial portions 43 extending axially from a large-diameter edge of the radial portion 38 and connecting axially with the radial portions 42 and circumferentially with the axial portions 40, 41. The axial portions 43 are coaxial with the axial portion 37 and delimit radially between them a radial space for the mounting of the coupling means 36.

The coupling means 36 is made in a single piece and can advantageously be obtained by moulding a synthetic material, for example made of nitrile or of elastomer. As illustrated in Figures 3 and 6, it comprises an annular body 45 mounted between the axial portions 37, 43 of the end-plate 35 while leaving a slight radial clearance with the latter, and radial tabs or protuberances 46 to 51 locally extending the body 45 outwards. These protuberances are delimited in the circumferential direction by flat axial surfaces and have an axial dimension that is equal to that of the body 45. These protuberances 46 to 51 are six in number, identical with one another and extend over a limited angular sector, for example of the order of 5 to 10° . The protuberances 46, 47 and 48 , 49 and 50, 51 are spaced in twos in the circumferential direction at a constant spacing. The protuberances 47, 48 and 49, 50 and 51 , 47 are spaced in twos at an increased circumferential spacing. Each protuberance 46, 48 and 50 is housed in the circumferential direction between the axial portion 28 o f the cage 22 and the axial portion 41 of the end-plate 35 while coming into contact against the said portions. Each protuberance 47, 49 and 5 1 is, for its part, housed in the circumferential direction between the axial portion 27 of the cage 22 and the axial portion 40 of the end- plate 35 while coming into contact against the axial portion 27. A slight space is provided between each of these protuberances 47, 49 and 51 and the corresponding axial portion 40 of the end-plate 35. The axial portions 27, 28 of the cage 22 and the axial portions 40, 41 o f the end-plate 35 therefore form abutments for the protuberances 46 to 51 and delimit between them housings for the said protuberances. Between the axial portions 27, 28 connecting one of the portions 29 o f the cage 22 are placed, in the circumferential direction, two of the protuberances 46 to 51 and two of the axial portions 40, 41 of the end- plate 35. The pairs of protuberances 47, 48 and 49, 50 and 51 , 47 are each surrounded radially by one of the axial portions 30 of the cage 22, a slight radial space being provided between these elements. The protuberances 46 to 51 are placed axially between the radial portions 29 of the cage 22 and the radial portions 39 of the end-plate 35 and come to bear against the radial portions 29.

In order to assemble the cage 22, the end-plate 35 and the coupling means 36, the coupling means 36 is first assembled to the end-plate 35 , and then the end-plate 35 is pushed axially until the coupling means 36 comes to bear against the radial portions 29 of the cage 22.

Then, in order to obtain a unitary assembly consisting of these three elements that can be handled, transported and installed without risk of coming apart, the lugs 31 are deformed, as illustrated in Figures 4 and 5 , in order to curve and press against the radial portions 42 of the end-plate 35. The deformation can be carried out by crimping in a particularly economical manner, for example with a crimping tool furnished with appropriate teeth. Specifically, the cage 22 is made o f thin metal sheet, which makes for easy local plastic deformation.

The cage 22 and the end-plate 35 are axially attached, the coupling means 36 being placed axially between these two elements. In this position, there is a slight axial space between the radial portions 42 of the end-plate 35 and the radial portions 29 of the cage

22. The radial portions 38 , 39 protrude slightly axially relative to the free ends of the axial portions 30. The lugs 31 form means for axially retaining the coupling means 36 and the end-plate 35.

The overrunning clutch 6 is lubricated by means of a lubricant, such as grease, placed inside the pulley 2 between the two bearings 4 and 5.

The operating mode of the overrunning clutch 6 is as follows. During a steady speed or during an acceleration of the pulley 2, the cams 19 have a tendency, under the effect of the centrifugal forces and by contact with the slippage ways 20 and 21 , to tilt in a first direction which makes it possible to obtain, by buttressing, a locking between the two slippage ways 20 and 21 of the pulley 2 and of the inner element 3. The overrunning clutch 6 operates in torque uptake or engagement and transmits a drive torque between the pulley 2 and the inner element 3. In these conditions, there is no relative angular movement of the inner transmission element 3 and the pulley 2.

In contrast, during a rapid deceleration of the pulley 2, the cams 19 tend to tilt in a second direction opposite to the first, which causes the unlocking or freeing of the cams 19 which nevertheless remain in contact with the slippage ways 20 and 21. The overrunning clutch 6 then no longer transmits torque and temporarily allows a relative rotary movement of the pulley 2 relative to the inner transmission element 3. The overrunning clutch 6 therefore provides a one-way coupling between the pulley 2 and the transmission element

3.

In the disengaged position, the end-plate 35 and the coupling means 36 make it possible to obtain the rotational driving of the cage 22, and more generally of the overrunning clutch 6. The inner transmission element 3 and the cage 22 are secured in rotation, which removes or restricts the relative slippage in the circumferential direction between the slippage way 21 arranged on the inner transmission element 3 and the cams 19. The slippage occurs mainly at the slippage way 20 of the pulley 2. Because of the centrifuging of the lubricant due to the rotation of the device, the slippage way 20 of the pulley 2 is perfectly lubricated and accordingly the slippage of the cams 19 on the said way can occur with an extremely reduced wear and without generating considerable friction torque.

Moreover, the coupling means 36 can allow the cage 22 to rotate slightly relative to the inner transmission element 3 , for example if the cams 19 were to be forced against the edges of the windows 24, when they were to tilt during the transition from the disengaged position to the engaged position or vice versa.

Specifically, if the cams 19 are forced against the edge of the windows 24 of the cage 22, a slight angular or circumferential movement of the cage 22 relative to the inner transmission element 3 and relative to the end-plate 35 is possible because the protuberances 46 to 51 can deform by compression in the circumferential direction. Therefore, by deformation of the protuberances 46 to 51 of the coupling means 36, damage to the cage 22 is prevented. Once the stress exerted by the cams 19 against the edges of the windows 24 ceases, the cage 22, via the axial portions 27 or 28, no longer exerts force in the circumferential direction on the protuberances 46 to 51 , the latter tending to resume their shape by elasticity. The cage 22 then resumes its initial position relative to the inner transmission element 3 and to the end-plate 35.

Naturally, it can be conceived that the deformation of the protuberances 46 to 51 and the movement in the circumferential direction of the cage 22 depends on the nature of the material used for the coupling means 36 and on the circumferential dimension of the protuberances 46 to 51. These features can easily be modified according to the circumferential or angular movement that it is desired to allow for the cage 22 relative to the inner transmission element 3 and the end-plate 35.

The embodiment illustrated in Figure 7 in which the identical elements bear the same reference numbers differs in particular in that the cage 22 is, in cross section, generally L-shaped and comprises an axial portion 23 with increased axial dimension. To connect the cage 22 and the inner transmission element 3 , the overrunning clutch 6 comprises an annular bush or sleeve 61 attached to the outer surface 3a of the inner transmission element 3 , for example by tight fitting, and a coupling means 62 placed between the sleeve 61 and the axial portion 23 of the cage 22. The coupling means 62 is made in the form of an annular body made of synthetic material, for example of nitrile or of elastomer, and is overmoulded on the free end of the axial portion 23 of the cage 22 and on the outer surface of the sleeve 61. Alternatively, the coupling means 62 could comprise recesses spaced from one another in the circumferential direction so as to promote its deformation in this direction.

The embodiment illustrated in Figure 8 in which the identical elements bear the same references differs from the embodiment previously described in that the axial portion 23 of the cage 22 is extended, axially on the side opposite to the radial portion 25 , by a radial portion 63 extending radially inwards. This radial portion 63 makes it possible to promote the grip of the coupling means 62 when it is overmoulded onto the cage 22.

In this embodiment, the sleeve 62 comprises a radial portion 64 extending radially outwards the axial end of the sleeve situated on the side of the bearing 5. This radial portion 64 makes it possible to prevent a deformation in the axial direction of the coupling means 62. The coupling means 62 is also overmoulded onto this radial portion 64 and its outer surface is flush with the end of the said radial portion 64. In a manner similar to the first embodiment described, in these second and third embodiments, if the cams 19 are forced against the edges of the windows 24 of the cage 22, a movement in the circumferential direction of the latter relative to the sleeve 61 and to the inner transmission element 3 is possible by deformation in the circumferential direction of the coupling means 62.

In these latter two embodiments, the cage 22 can be formed from a thin metal sheet blank by folding, cutting and stamping, or else by moulding a synthetic material such as polyamide. The coupling means 62 is in this instance overmoulded onto the sleeve 61. Alternatively, it could be attached by any other appropriate means, for example by bonding.

In an application on a drive pulley of an alternator for a motor vehicle, by virtue of the overrunning clutch, the pulley drives the central shaft when the engine accelerates or is at a substantially steady speed or else decelerates very slowly. In the event of a sudden slowing of the engine and therefore of the pulley, the central spindle of the disengageable pulley device can continue to rotate faster than the pulley itself thanks to the overrunning clutch, thereby preventing excessive stresses on the drive belt. Moreover, the overrunning clutch allows a virtually instantaneous transition from operation as an overrunning clutch to operation in torque uptake, and has good reliability over time by virtue, in particular, of very low wear of the cams on the slippage ways.

Claims

1. Overrunning clutch for a disengageable pulley device of the type comprising an inner transmission element (3) and a pulley (2) mounted on the said inner element, the overrunning clutch comprising a plurality of wedging elements ( 19) designed to be mounted between the inner transmission element and the pulley, and a cage (22) for the wedging elements, characterized in that it also comprises a means (35 ; 61 ) for mounting the cage on the inner transmission element designed to be attached to the said inner element, and an elastic coupling means (36; 62) placed between the cage and the mounting means and capable of allowing a circumferential movement of the cage relative to the mounting means.

2. Overrunning clutch according to Claim 1 , in which the mounting means (35 ; 61 ) is made of a rigid material, the coupling means (36; 62) being made of a flexible material.

3. Overrunning clutch according to Claim 1 or 2, in which the coupling means (36; 62) is at least partly placed radially between the mounting means (35 ; 61 ) and the cage (22).

4. Overrunning clutch according to any one of the preceding claims, in which the cage (22) comprises at least one means (31 ; 23) for the axial retention of the coupling means.

5. Overrunning clutch according to any one of the preceding claims, in which the coupling means (36; 62) is at least partly placed axially between the cage (22) and the mounting means (35 ; 61 ).

6. Overrunning clutch according to any one of the preceding claims, in which the coupling means (36) comprises a body (45) and radial protuberances (46 to 51 ), each protuberance being housed in the circumferential direction between an abutment portion of the cage and an abutment portion of the mounting means.

7. Overrunning clutch according to Claim 6, in which the body

(45) of the coupling means is placed radially between radial portions (37, 43) of the mounting means.

8. Overrunning clutch according to any one of the preceding claims, in which the cage (22) comprises at least one lug (31 ) for the axial retention of the mounting means.

9. Overrunning clutch according to any one of Claims 1 to 4, in which the coupling means (62) is attached to the cage (22) and to the mounting means (61 ), notably by overmoulding.

10. Disengageable pulley device comprising an inner transmission element (3), a pulley (2) mounted on the said inner element and an overrunning clutch (6) according to any one of the preceding claims designed to provide a one-way clutch between the pulley (2) and the inner transmission element (3).

1 1. Alternator comprising a shaft and a disengageable pulley device according to Claim 10, mounted on the said shaft.