WO2011079963A1 - One-way clutch for disengageable pulley device - Google Patents

Abstract

The one-way clutch comprises a plurality of sprags (19), a cage (22) comprising windows (24) for retaining the sprags, and a spring (30) mounted inside said cage and comprising an overlap zone where one end portion of said spring and one opposite end portion are superposed on each other. The spring comprises pockets for the sprags and at least one elastic return element (35) per sprag adapted to urge on the associated sprag in order to exert a tilting torque. The number of elastic return element (35) per sprag in the overlap zone and in the remaining portion of the spring is the same.

Description

One-way clutch for disengageable pulley device.

The present invention relates to the field of one-way clutches or freewheels.

More particularly, the present invention relates to the field o f disengageable pulleys comprising one-way clutches used, for example, in alternator drive pulleys on motor vehicles.

Such disengageable pulleys are known per se and are increasingly used to overcome the harmful effects of acyclisms or sudden decelerations which occur in combustion engines, in particular at low engine speeds and especially in Diesel engines.

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

In the case o f a rigid coupling between the crankshaft pulley and the alternator shaft, the belt is subj ected to very high stresses during these sudden speed variations.

Such variations generate harmful effects such as an abnormal fatigue o f the belt with risks of breakage, a slipping o f the belt on the pulley, or vibration o f the belt strands between the pulleys.

In order to attenuate these phenomena, a one-way clutch has been incorporated between the driven pulley and the driven shaft, allowing the pulley to be uncoupled temporarily from the shaft if said pulley suddenly decelerates.

A disengageable pulley such as this is known, in particular from patent applications US-A1 -2003/00061 14 and US-A1 - 2004/0074730, and comprises two bearings one positioned on each side o f the pulley, and a one-way clutch mounted between the two bearings and provided with a plurality o f lock-up sprags, with a cage comprising windows for the housing o f the said sprags, and with a spring mounted inside the cage. The spring comprises pockets for the sprags and elastic tongues urging each sprag to exert a tilting torque tending to keep said sprags in contact with the sliding tracks o f the shaft and o f the pulley.

In these two documents, in order to obtain a spring having an annular shape with enhanced rigidity, there is formed a partial overlap zone where one end and another end of the spring are superimposed on each other. In the overlap zone, there are two tongues per sprag whereas one tongue press on each of the others sprags in the remaining portion of the spring.

With such a disengageable pulley, when the sprags switch from an overrun or freewheel position to a torque uptake position, and vice- versa, the sprags disposed in the overlap zone may tilt non- synchronously with regards to the others. Such out of phase movements of the sprags would not encourage safe operation o f the pulley.

One aim o f the present invention is to overcome the aforementioned drawback.

It is a particular object of the present invention to provide a one-way clutch in which the sprags may simultaneously switch from a freewheel position to a torque-transmitting position, and vice versa.

A further obj ect of the present invention is to provide a oneway clutch that is extremely dependable and which comprises components that are economical to manufacture and to assemble.

In one embodiment, the one-way clutch is adapted to a disengageable pulley device of the type comprising an inner transmission element and a pulley mounted on said inner element. The one-way clutch comprises a plurality o f sprags designed to be mounted between the inner transmission element and the pulley, a cage comprising windows for retaining the sprags, and a spring mounted inside said cage and comprising and overlap zone where one end portion and one opposite end portion o f the spring are superposed on each other. The spring comprises pockets for the sprags and at least one elastic return element per sprag adapted to urge on the associated sprag in order to exert a tilting torque. The number of elastic return element per sprag in the overlap zone and in the remaining portion o f the spring is the same.

The same number o f elastic return element per sprag is provided in the overlap zone and in the remaining or non-overlap portion of the spring. Thus, each sprag mounted inside the pockets of the spring cooperates with the same number of elastic return element . With a one-way clutch having the same number o f elastic return element acting on each sprag even in the overlap zone, all sprags may tilt simultaneously from an overrun position to a torque uptake position, and vice versa.

Advantageously, elastic return elements of the spring each comprise a tongue projecting into the corresponding pocket.

In one embo diment, the end portions of the spring may be superposed on each other in order that all the elastic return elements are at the same radial position inside the cage. Alternatively, the end portions o f the spring may be superposed in order that the elastic return element(s) of the overlap zone are radially offset inwards with regards to the other elastic return elements .

In one embodiment, one of the end portions of the spring has no elastic return elements.

The end portions of the spring may each comprise one pocket, or at least two pockets spaced relative to one another in the circumferential direction.

Advantageously, the spring comprises annular portions partly delimiting the pockets, said annular portions having wave-form deformations to position the end portions of the spring by abutment.

Advantageously, the spring is made of metal plate by stamping.

In one embo diment, all the elastic return elements are identical.

The invention also relates to a disengageable pulley device comprising an inner transmission element, a pulley mounted on said inner element and at least a one-way clutch as previously defined.

The disengageable pulley device may be mounted on an alternator shaft for its driving. The pulley may be mounted on a central shaft particularly via the one-way clutch. The drive shaft may be mounted on or coincide with the alternator shaft. A drive belt driven off the engine may bear against a periphery of the pulley.

By virtue of the one-way clutch, the pulley drives the central shaft when the engine accelerates, or is at a substantially constant engine speed, or alternatively decelerates very slowly. In the event of sudden slowing of the engine and therefore of the pulley, the central shaft may continue to rotate more quickly than the pulley itself thanks to the one-way clutch, thus safeguarding the drive belt against excessive stresses.

With a one-way clutch having exactly the same number o f elastic return element acting on each sprag even in the overlapping zone o f the spring, the sprags may tilt simultaneously from an overrun or freewheel position to a torque uptake position, and vice versa.

Illustrative and non-limiting embodiments of the present invention will be described below in detail with reference to the appended drawings, in which:

- Figure 1 is a view in axial section of a disengageable pulley device according to a first embodiment of the invention,

- Figure 2 is a view in axial section o f a one-way clutch of the device o f Figure 1 ,

- Figure 3 is a view in perspective o f a spring of the one-way clutch o f Figure 2,

- Figure 4 is a view o f the spring of Figure 3 before mounting, - Figure 5 is a view in axial section o f the spring on V-V o f

Figure 3 ,

- Figure 6 is a view in axial section o f a spring according to a second embodiment of the invention,

- Figure 7 is a view in axial section o f a spring according to a third embodiment of the invention, and

- Figure 8 is a view o f the spring of Figure 7 before mounting. As shown by Figure 1 , the disengageable pulley device 1 comprises a pulley 2, an inner transmission element 3 , for example a ho llow shaft, two rolling bearings 4, 5 and an overrunning or one-way clutch 6.

The pulley 2, with an axis 7, comprises an outer surface provided with a grooved zone 2a with annular grooves and an axial zone 2b formed at an axial end o f 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) positioned one at each axial end, and two radial transverse surfaces 2d and 2e.

The inner transmission element 3 , which takes the form of a ho llow shaft, comprises a cylindrical axial outer surface 3 a and a bore 3b, a portion 3 c o f which comprising a screw thread so that an alternator shaft (not shown) may be fixed and driven. Axially opposite to the bore 3b, the inner transmission element 3 comprises internally splines 3 d 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 ring 8 , an outer ring 9, between which are housed a row of rolling elements 10, which in this case are balls, a cage 1 1 for maintaining the circumferential spacing o f the rolling elements 10, and a seal 12.

The inner ring 8 comprises a cylindrical bore 8a fitted onto the outer surface 3 a 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 is formed and having, in cross section, a concave inner profile capable o f forming a raceway for the rolling elements 10, said groove being oriented radially outwards .

The outer ring 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 is formed and having in cross section a concave inner pro file capable o f 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 axially on the outside of the bearing 4 is the seal 12 which rubs against the cylindrical outer surface 8d of the inner ring 8 in order to form a seal. The seal 12 is placed radially between the inner ring 8 and outer ring 9, and is mounted axially between the rolling elements 10 and the radial surfaces 8b and 9b of the rings 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 ring 13 fitted to the outer surface 3 a of the inner transmission element 3 , an outer ring 14 fitted into the bore 2c of the pulley 2 , between which are housed a row of rolling elements 15 , which in this case are balls, a cage 16 for maintaining the circumferential space o f the rolling elements 15 , and a seal 17. The bearing 5 is axially set back relative to the radial transverse surface 2d of the pulley 2. 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 one-way clutch 6. The one-way clutch 6 is mounted axially between them. The one-way clutch 6 thus enjoys protection against the intrusion of foreign bodies from the bearings 4 and 5 , and in particular from the seals 12 and 17.

The one-way clutch 6 comprises a plurality o f wedging cams or sprags 19 placed between two sliding ways 20 and 21 , and which are axisymmetric in shape . The sprags 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 one-way clutch, to tilt or pivot in the direction promoting their locking between the two sliding ways 20, 2 1 for the purpose of facilitating the transition from overrun operation to torque take-up operation.

The sliding way 20 is formed directly by the bore 2c of the pulley 2. The sliding way 21 is formed directly by the axial outer surface 3 a of the shaft 3 or the inner transmission element. In other words, the pulley 2 may be manufactured with an inner surface with a particularly simple shape that is entirely axial with the exception o f the end bevels. The pulley 2 may therefore be obtained at low cost. This inner surface forms an outer bearing surface or a surface of large diameter for the sprags 19.

On the opposite side, the sliding way 2 1 is formed on the outer surface 3 a of the shaft 3. The outer profile of revolution of the shaft 3 has the same diameter over the whole of its length. Finishing may 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, sliding way 21 for the sprags 19.

The one-way clutch 6 also comprises an annular cage 22 for retaining the sprags 19. The cage 22 of annular overall shape is advantageously formed from a thin metal sheet blank by folding, cutting and stamping, or alternatively from a synthetic material such as a po lyamide.

The cage 22 comprises an annular axial portion 23 provided with a plurality o f pockets or windows 24 forming housings for the sprags 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 sprags 19. The cage 22 also comprises an annular radial portion 25 which extends radially outwards an axial end o f the axial portion 23 situated in the vicinity o f the bearing 4. The free end o f the radial portion 25 remains at a distance from the bore 2c of the pulley 2.

Axially on the side opposite to the radial portion 25 , the cage 22 also comprises an annular radial portion 26 extending radially outwards an axial end of the axial portion 23 and remaining at a distance from the bore 2c of the pulley 2. A large-diameter edge of the radial portion 26 is extended axially by a short axial portion 27 extending in the direction of the bearing 5.

The one-way clutch 6 further comprises a spring 30 mounted inside the cage 22, and disposed radially between the outer surface 3 a of the transmission element 3 and the axial portion 23 of said cage. The spring 30 is situated axially between the radial portions 25 , 26 o f the cage 22. In its mounted position, the spring 30 has an annular shape.

As shown on Figures 3 to 5 , the spring 30 is made in the form of an annular strip wound on itself and connected with partial overlap . The spring 30 may be formed from a thin metal sheet blank by fo lding, cutting and stamping, or else by moulding a synthetic material such as polyamide.

The spring 30 comprises two annular portions 3 1 , 32 formed on opposite sides, coupling portions 33 formed at uniform intervals in a circumferential direction between said annular portions. The annular portions 3 1 , 32 and the coupling portions 33 are mounted into contact with the bore of the axial portion 23 of the cage. Windows or pockets

34 are defined between the annular portions 3 1 , 32 and coupling portions 33. The pockets 34 are uniformly circumferentially spaced relative to one another and face to the windows 24 of the cage 22 in order to be able to mount the sprags 19.

The spring 30 also comprises elastic return tongues 35 , each tongue proj ecting circumferentially from the corresponding coupling portion 33 into the associated pocket 34 for urging the sprag 1 9. In other words, each tongue 35 originates from the edge of a pocket 34 and is designed to press against a purpose-made surface of the associated sprag 19 so as to exert a tilting torque that tends to keep the sprags 19 in contact with the sliding ways 20, 21 . The tongues 35 are disposed between the cage 22 and the sprags 19. In a static position, the tongues 35 exert a force directed towards the pulley 2. The tongues

35 are identical each other.

Each tongue 35 comprises a rounded portion 36 formed on its exterior side and extending radially outwards in order to have highter rigidity and strength. The rounded portions 36 extend inside the windows 24 of the cage. The end of each tongue 35 is slightly rounded radially inwards and radially disposed inside the bore o f the axial portion 23 of said cage. When the sprags 19 are disposed in the respective pockets 34 o f the spring 30 and in the windows 24 of the cage 22, the ends of the tongues 35 are brought into contact with smooth recessed portions formed on said sprags 1 9 thereby forcing the sprags towards a direction in which they are locked between the pulley 2 and the shaft 3.

For each pocket 34 defined between two coupling portions 33 , on the annular portions 3 1 , 32 are respectively formed opposite corrugated deformations 37, 38 having a wave-form extending radially inwards. The deformations 37 axially face the deformations 38 in circumferential direction and are uniformly spaced relative to one another.

As above-mentioned, the spring 30 is made in the form o f an annular strip wound with a partial overlap zone 40. In this zone, a first end portion 41 of the spring and a second circumferentially opposite end portion 42 are superimposed on each other. In this case, the end portions 41 , 42 each comprise two pockets 34. The end portion 42 has no tongue 35 extending into the corresponding pockets 34. The other pockets 34 of the spring each comprise a tongue 35.

When the two end portions 41 , 42 are overlapped on each other to form the annular spring 30, the pockets 34 of the end portion 42 having no tongue 35 are overlapped on the pockets 34 of the end portion 41 each comprising a tongue 35. Thus, in the overlap zone 40 , there is only one tongue 35 for each sprag 19 housed in the pockets 34 of the end portions 41 , 42. The number of tongue 35 acting on each sprag 19 in the overlap zone 40 where there is a double structure and in the remaining portion of the spring 30 where there is a single structure is the same.

The overlap zone 40 of the spring 30 is locked by abutting the edge o f the end portion 41 against the corrugated deformations 37, 38 provided around the pocket 34 which is directly adj acent to the end portion 42. The corrugated deformations 37, 38 of the end portion 42 radially surround and come into contact with the corrugated deformations 37, 38 of the end portion 41 . More precisely, the corrugated deformations 37, 38 of the end portion 42 are housed into those of the end portion 4 1 . The corrugated deformations 37, 38 form self-retention means for the spring 30. Besides, the spring has a small degree of freedom in the circumferential direction with respect to the cage by virtue of the corrugated deformations made in the form o f waves. In this mounted position, the superposed corrugated deformations 37, 38 could also be welded together in another embodiment. Alternatively, it could also be possible, in replacement o f corrugated deformations 37 and 38 , to foresee any other appropriate means in order to obtain the circumferential maintain o f the end portions 41 , 42 in the mounted position of the spring 30.

The operating mode o f the one-way clutch 6 is as fo llows . During a steady speed or during an acceleration of the pulley 2 , the sprags 19 have a tendency, under the effect of the centrifugal forces and by contact with the sliding ways 20 and 21 , to pivot or tilt in a first direction which allow them, by buttressing between the two sliding ways 20 and 21 , to become locked together with the sliding way belonging to the pulley 2 and to the inner element 3. The one-way clutch 6 operates in torque uptake or coupled mode and transmits a driving 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.

With the disposition of the tongues 35 in order that each sprag

19 cooperate with the same number of tongue even in the overlap zone 40, all the sprags 19 are equally energized and behave in the same way in order to operate synchronously when said sprags tilt from the position of idle rotation to the engaged position.

During a rapid deceleration o f the pulley 2, the sprags 19 tend to tilt in a second direction opposite to the first, which causes the unlocking or freeing of the sprags 19 which nevertheless remain in contact with the sliding ways 20, 21 . The one-way clutch 6 then no longer transmits any torque and temporarily allows a relative rotary movement of the pulley 2 relative to the inner transmission element 3.

In this embodiment, the first end portion 41 having the tongues 35 is wounded radially below the end portion 42 having no tongues. In this way, the tongues 35 in the overlap zone 40 are slightly radially offset inwards with regards to the other tongues of the remaining portion o f the spring. Alternatively, as shown in Figure 6, the spring 30 may be wound on itself in order that, in the overlap zone 40, the end portion 41 having the tongues 35 be overlapped on the end portion 42. In this embo diment, all the tongues 35 are approximatively disposed at the same radial position inside the cage 22.

In the two previous embodiments, each of the pockets 34 of the end portion 41 comprises a tongue 35 and the pockets 34 of the end portion 42 have no tongue. Alternatively, it could also be possible to foresee an end portion 41 having a pocket with one tongue 35 and another pocket without tongue, and an adapted corresponding end portion 42 having a pocket in which a tongue 35 projects into and another pocket having no tongue in order that, in the overlap zone 40, the two sprags 19 each cooperates with one tongue as in the remaining portion of the spring.

In the two previous embo diments, the end portions 41 , 42 each comprise two pockets 34 spaced relative to one another in the circumferential direction. The overlapping of two pockets 34 permits to have a good circularity o f the spring 30 after mounting. Alternatively, as shown in Figure 7, in which identical parts are given identical references, the spring 30 comprises an end portion 41 having one pocket 34 with one tongue and an opposite end portion 42 having one pocket 34 without tongue. In the overlap zone 40, only two pockets 34 are superposed on each other. In this embodiment, the end portion 41 is overlapping on the end portion 42.

It should be noted that the embodiments illustrated and described were given merely by way of non-limitating indicative examples and that modifications and variations are possible within the scope of the invention. For instance, in the described embodiments, the spring is adapted in order that one tongue be associated with each sprag even in its overlap zone. It is easily understood that it could also be possible to foresee a different number of tongue, for example two, for each sprag so long as the same number of elastic tongue per sprag is provided in the overlap zone and in the remaining portion of the spring. In an application to an alternator drive pulley for a motor vehicle, thanks to the one-way clutch, the pulley drives the central shaft when the engine accelerates, or is at a substantially constant speed, or alternatively decelerates very slowly. In the event of a sudden slowing down o f the engine and therefore of the pulley, the central shaft o f the disengageable pulley device may continue to rotate more quickly than the pulley itself thanks to the one-way clutch, thereby preventing excessive stresses on the drive belt. Moreover, the one-way clutch allows a practically instantaneous switch from freewheel operation to torque-transmitting operation in torque uptake, and is very reliable over time.

The one-way clutch according to the invention can be used in any system where a torque is to be transmitted between a drive element and driven element, for instance an automatic gearbox or a clutch mechanism.

Claims

1 . One-way clutch suitable 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 one-way clutch comprising a plurality o f sprags ( 19) designed to be mounted between the inner transmission element and the pulley, a cage (22) comprising windows (24) for retaining the sprags, and a spring (30) mounted inside said cage and comprising an overlap zone (40) where one end portion (4 1 ) and one opposite end portion (42) o f the spring are superposed on each other, the spring comprising pockets (34) for the sprags and at least one elastic return element (35) per sprag adapted to urge on the associated sprag in order to exert a tilting torque, characterized in that the number of elastic return element (35) per sprag in the overlap zone (40) and in the remaining portion of the spring is the same.

2. One-way clutch according to claim 1 , wherein elastic return elements o f the spring each comprise a tongue (35) projecting into the corresponding pocket (34) .

3. One-way clutch according to claims 1 or 2, wherein the end portions (41 , 42) of the spring are superposed on each other in order that all the elastic return elements (35) are at the same radial position inside the cage.

4. One-way clutch according to claims 1 or 2, wherein the end portions (41 , 42) of the spring are superposed on each other in order that the elastic return element(s) o f the overlap zone (40) are radially offset inwards with regards to the other elastic return elements.

5. One-way clutch according to any of the preceding claims, wherein one of the end portions (41 , 42) of the spring has no elastic return element (35) .

6. One-way clutch according to any of the preceding claims, wherein the end portions (41 , 42) of the spring each comprise one pocket (34) .

7. One-way clutch according to any of the preceding claims 1 to 5 , wherein the end portions (4 1 , 42) of the spring each comprise at least two pockets (34) spaced relative to one another in the circumferential direction.

8. One-way clutch according to any of the preceding claims, wherein the spring (30) comprises annular portions (3 1 , 32) partly delimiting the pockets (34), said annular portions having wave-form deformations (37 , 38) to position the end portions (41 , 42) o f the spring by abutment.

9. One-way clutch according to any of the preceding claims, wherein all the elastic return elements (35) are identical.

10. Disengageable pulley device comprising an inner transmission element (3 ), a pulley (2) mounted on the said inner element and at least a one-way clutch (6) according to any one o f the preceding claims.

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