FR2808057A1 - Diaphragm spring for motor vehicle clutch has Belleville washer with radial fingers having mounting openings offset radially to increase internal diameter of washer - Google Patents

Abstract

The diaphragm spring for a motor vehicle clutch has a Belleville washer (34) with radial fingers (36) defined by radial slots (52) and openings (56) for mounting the diaphragm on a support, which are offset radially towards the axis to increase the internal diameter of the washer. The contact zones can be adjacent to the neutral line of the washer.

Description

The invention relates to an annular diaphragm for a clutch mechanism as well as to a friction clutch, in particular for a motor vehicle, comprising this diaphragm.

Conventionally, as described in numerous patents of the applicant, for example in FR-A-2 753 502, a friction clutch for a motor vehicle comprises a disc provided with friction linings on its two faces and intended to be clamped between a reaction plate driven by a motor shaft and a pressure plate forming part of a clutch mechanism.

At its inner periphery, the friction disc is connected in rotation, often by means of a torsion damper, to a driven shaft such as an input shaft of a gearbox.

The clutch mechanism typically comprises a cover fixed on the reaction plate, the aforementioned pressure plate which is integral in rotation with the cover and which is axially movable relative thereto, and clutch means carried by the cover and urging axially the pressure plate towards the reaction plate for the tightening of the friction disc and the transmission by this disc of a torque between the motor shaft and the driven shaft.

Declutching means associated with a declutching stop controlled by a declutching pedal are provided to act on the declutching means and to interrupt the axial thrust which they exert on the pressure plate, in order to interrupt the transmission of the torque between the motor shaft and driven shaft.

Currently, the engagement and disengagement means are very often formed of a single annular metal part called a diaphragm, the radially external part of which forms a Belleville washer mounted to bear on the cover and on the pressure plate and the radially internal part of which comprises slots. radial delimiting between them radial fingers which extend to the internal edge of the diaphragm and on the free ends of which acts the clutch release bearing.

The ends of the radial slots, situated on the side of the Belleville washer, are widened to reduce stresses at the base of the radial fingers and to form orifices for passage of fastening means on the cover, these means being for example the type described in 1e document FR-A-2 753 502 cited above or of another type.

When the force exerted by the clutch release bearing on the ends of the diaphragm fingers for clutch release is sufficient, it causes the diaphragm to tilt around its supports on the cover.

To ensure gradual release (and clutch), the friction linings are fixed elastically on the disc, for example by means of elastically deformable parts in the axial direction or by other equivalent means, having a relatively stiffness. high and limited axial deformation, which are compressed in the engaged position and which relax axially when disengaged by exerting on the pressure plate a force opposite to that exerted by the diaphragm. The force which must be applied to the stop for the declutching is thereby reduced, which reduces the effort on the pedal and is sought after by automobile manufacturers. The general elasticity of the mechanism works in the same direction as the elastic fixing of the friction linings and increases the progressiveness.

The effect of the progressiveness on 1 effort at the stop or at the pedal is all the more important crude curve of the axial load developed by the Belleville washer is more "saddled" (the ensnel being the difference between the maximum and the minimum of the load curve of the Belleville washer as a function of its axial deformation and being all the more important as this difference is large) and we also know that this curve is determined by the geometry of Belleville washer, the sunning being more important when the ratio h / e increases (e being the thickness of the washer and h the height of the cone trunk formed by the washer in the unstressed state). Significant sunning also allows higher torques to be transmitted, the axial load exerted by the diaphragm on the pressure plate in the engaged position being greater. However, if you try to increase the overall height this way, the stresses in the diaphragm become very high and the diaphragm becomes impractical.

The object of the invention is in particular to provide a simple, effective and economical solution to this problem, by reducing the stresses in the diaphragm.

It relates to a diaphragm for the clutch mechanism, having reduced stresses, the axial load curve of which has a very large saddle.

It also relates to a diaphragm of this type, allowing a significant effect of the progressiveness on the force to be applied to the clutch release bearing.

It also relates to a diaphragm of this type allowing a transmission of high torques, with a reduction in the effort to apply the clutch release bearing for the clutch.

It also relates to a friction clutch, in particular for a motor vehicle, comprising a diaphragm of the type indicated above.

It proposes, for this purpose, an annular diaphragm for a clutch mechanism, comprising a radially external annular part forming a Belleville washer with high saddle, a radially internal annular part comprising radial slots delimiting between them radial fingers extending towards the interior, and orifices for passage of means for attaching the diaphragm to a support, attachment means bearing at one end on the Belleville washer, characterized in that the bearing zones of the attachment means on the washer Belleville are closer to the center line or neutral line of the Belleville washer than its internal circumference.

This configuration results in the articulation zone of the Belleville washer on its support being offset radially outwards, with a reduction of the stresses in the Belleville washer.

In a preferred embodiment of the invention, the hooking means are C-shaped hooks and comprise an elongated radial arm which extends along the Belleville washer between an aforementioned passage orifice and the area of abovementioned support on the Belleville washer, the length of this arm being determined by the distance between said passage orifice and the support area in the vicinity of the neutral line of the Belleville washer.

This results in several advantages - the elongation of the hook arm increases the elasticity of the hook and reduces the influence of wear phenomena on the elastic force which it applies to the diaphragm, - this elongation makes it possible to offset radially towards the axis the orifices for passage of the attachment means, without modifying the diameter of the diaphragm articulation on its support, and to reduce the internal diameter of the Belleville washer, which results in a greater sinking of the diaphragm. As indicated above, the increase in sunshine, combined with the progressiveness due to the elastic fixing of the linings and the general elasticity of the mechanism, has the effect of reducing the pedal force when disengaging.

The ratio of Belleville washer internal external diameters can thus be greater than or equal to approximately 1.45, preferably approximately 1.

These characteristics, which allow the diaphragm to increase in size without excessively increasing the stresses in the diaphragm, also have the effect of increasing the rigidity of the diaphragm fingers and therefore of reducing the delay in lifting the pressure plate associated with the diaphragm.

In a first embodiment, the aforementioned passage orifices are formed outside the Belleville washer, in the vicinity of its internal circumference.

In an alternative embodiment, the aforementioned passage orifices are formed in the Belleville washer, in particular on or in the vicinity of the neutral line, this washer.

This makes it possible to combine the advantages due to a large Belleville washer, with the diaphragm attachment on its support at a sufficient distance from the axis of rotation so as not to interfere with the torsional damper.

This also makes it possible to mount the diaphragm according to the invention on a clutch cover of the standard type.

In a first embodiment of the invention, said radial slots extend between the internal circumference of the Belleville washer and internal edge of the diaphragm.

In this embodiment, the radial fingers of the diaphragm delimited by the radial slots are shorter in the prior art and are more rigid, which is an advantage in terms of the clutch control.

In another embodiment, the length of said radial slots is substantially equal to or slightly less than the radial distance between the internal edges of the diaphragm and the abovementioned orifices.

In this the radial slots each extend substantially between two consecutive holes, for example in the middle between these holes.

In another embodiment, the radial slots have different lengths, some are aligned with the aforementioned holes and extend 'to these holes and others extend between the above holes and have a length less than the radial distance between the internal edge of the diaphragm and the aforementioned holes. advantageously, one radial slot in two extends from the internal edge of the diaphragm to the abovementioned orifice, which forms the end of the slot.

According to the embodiments, the number of radial fingers of the diaphragm can be equal to the number of aforementioned orifices or double this number.

The invention also provides a friction clutch in particular for a motor vehicle comprising a cover integral in rotation with a pressure plate and a reaction plate between which a friction disc is mounted, and an annular diaphragm mounted on the cover to urge axially the pressure plate towards the reaction plate, this clutch being characterized in that the diaphragm is of the type described above.

Advantageously, this clutch comprises an automatic device for compensating for the wear of the friction linings carried by the disc and of the corresponding friction surfaces of the pressure and reaction plates.

Thanks to this automatic wear adjustment device, the position of the diaphragm in the engaged state and load applied by the diaphragm to the pressure plate remain essentially the same throughout the clutch's service life, so that the position of the clutch release bearing in the engaged state also remains the same and that the force to be applied on the clutch release bearing (therefore on the clutch clutch pedal) for the clutch release does not increase over time.

In general, the invention makes it possible, with simple and economical means, to produce clutch mechanisms capable of transmitting high torques while reducing the force at the clutch release bearing. The invention will be better understood and other characteristics, details and advantages thereof will appear more clearly on reading the description which follows, given by way of example with reference to the accompanying drawings in which - Figure 1 is a schematic view in axial section of a friction clutch of a conventional type; - Figure 2 is a half front view of a diaphragm according to the invention; - Figure 3 is a schematic half-sectional view of the diaphragm of Figure 2; - Figure 4 shows a detail of the realization of this diaphragm; - Figure 5 is a schematic front view of a variant of the diaphragm according to the invention - Figures 6, 7 and 8 are views similar to Figure 5 and show other alternative embodiments of the diaphragm according to the invention; - Figure 9 is a graph showing the curve of variation of the axial load exerted on a pressure plate by a diaphragm according to 1 invention and the progressiveness, as a function of the travel of the clutch release bearing; - Figure 10 is a graph showing the curve of variation of the force applied to the clutch release bearing as a function of the stroke of this stop.

The clutch shown diagrammatically in FIG. 1 essentially comprises an engine flywheel 10 fixed by screws on the end of an engine shaft 12 such as the crankshaft of an internal combustion engine of a motor vehicle, the flywheel 10 forming a plate of reaction of a clutch mechanism 14 which comprises a cover 16 coaxial with the flywheel 10 and fixed thereto by screws, a pressure plate 18 coaxial with the flywheel 10 and mounted inside the cover 16 being integral in rotation with this cover and axially movable relative to the latter, and an annular diaphragm 20 carried by the cover 16 and axially urging the pressure plate 18 towards the reaction plate formed by the flywheel 10.

A friction disc 22 coaxial with the flywheel 10 and the pressure plate 18 is mounted between them and is connected, by means of a torsion damper 24, to a cylindrical hub 26 integral in rotation with a driven shaft 28 , as the input shaft of a gearbox 30.

The friction disc 22 carries on two faces, at its radially external peripheral part, friction linings 32 which are elastically deformable mounted in the axial direction on discs 22, for example by means of cambered blades forming part of this disc .

The diaphragm 20 which biases the pressure plate 18 axially towards the flywheel 10 for the tightening of the friction disc 22 between them and the transmission of a torque between the motor shaft and the driven shaft 28, comprises a Belleville washer 34 which acts on the pressure plate 18, and radial fingers 36 extending towards the rotation to cooperate with a declutching stop 38 movable in translation on the axis of rotation by a control comprising a declutching fork 40 which is actuated by a declutching pedal 42 via suitable connecting means 44. Of course, other known means can be used to move the declutching stop in translation on the axis of rotation.

In FIG. 1, the declutching pedal 42, declutching fork 40, the declutching stop, the diaphragm 20 and the pressure plate 18 are shown in the disengaged position, in which friction disc 22 is not clamped between pressure plate 18 and the flywheel 10 and where no torque is transmitted between the engine shafts 12 and the driven 28.

When the clutch pedal 42 is released, it returns to the position shown in dotted lines, the clutch release bearing 38 is moved to the right in the drawing and ceases to stress axially towards the motor shaft 12 the radial fingers 36 of the diaphragm 20 which returns , by tilting on its supports of the cover 16, in the engaged position where the Belleville washer 34 forming its radially external part axially biases the pressure plate 18 towards the flywheel 10 for the tightening of the pressure disc on the flywheel 10 and transmission of 'a torque between the drive shaft 12 and the driven shaft 28.

elastically deformable mounting of the friction linings 32 on the disc 22 allows progressive engagement and disengagement over a stroke of a few tenths of a millimeter.

in the engaged state, the elastically deformable means for mounting the friction linings on the disc are axially compressed. They exert on the pressure plate 18 an axial force opposite to that which is applied to it by the Belleville washer 34 of the diaphragm 20. To pass from the engaged state to the disengaged state, it is necessary to apply to the clutch release bearing 38 an axial force directed towards the motor shaft 12 and having a sufficient amplitude to tilt the diaphragm 20 around its supports on the cover 16.

In known manner, the geometry of the Belleville washer 34 can be determined so that the axial load which it exerts on the pressure plate 38 decreases during the stroke of the stopper 38 towards the declutching position. This characteristic, associated with the progressiveness of the clutch due to the elastic mounting of the friction linings 32 makes it possible to reduce the force which must be applied to the stop 38 for disengaging.

The significant overall variation curve of the axial load exerted by the diaphragm 20 on the pressure plate 18 as a function of the travel of the declutching stop 38 further reduces the force to be applied to the stop 38 for declutching, as will see it in more detail below.

However, it was found that it was not possible to increase the overall surface of this curve sufficiently by increasing the h / e ratio of the Belleville washer (h being the height of the truncated cone formed by the Belleville washer at the unconstrained state and e being its thickness). The invention provides a simple and effective solution to this problem, consisting of a new configuration of the diaphragm 20 which will now be described with reference to Figures 2 and following.

In these figures, the Belleville washer 34 of the diaphragm 20 is delimited by an external circumference 46 which is that of the diaphragm 20 and by an internal circumference 48 shown in phantom lines which passes through the closed ends of the radial slots 52 which extend up to at the internal circular edge 54 of the diaphragm and which delimit between them the radial fingers 36 of this diaphragm.

The width or radial dimension of the Belleville washer 34 is greater than in the diaphragms of the prior art, the ratio of the external and internal diameters of the washer 34 being greater than or equal to about 1.45 preferably greater than or equal to 1, 5 approximately in the embodiments of FIGS. 5 to 8, whereas in the prior art in general between 1.2 and 13.

This increase in the width of the Belleville washer 34 of the diaphragm 20 greatly increases the overall length of the variation curve of the axial load, as will be described in more detail with reference to FIGS. 9 and 10.

In the embodiment of FIGS. 4, the orifices 56 formed in the diaphragm for its mounting on the cover 16, consist of the enlarged end parts of a radial slot 52 in two, these enlarged end parts being elongated in the radial direction for mounting C-shaped hooks 58, a small radial branch 60 of which is fixed to the cover 16 by a rivet or the like, and a longer radial branch 62 of which extends along the Belleville washer 34 and rests at its free end on this washer in the vicinity of its center line, on the side opposite to the cover 16. The greater length of the branch 62 gives the hook 58 greater elasticity (a lower stiffness) which makes it less sensitive to axial shifts due to wear phenomena.

This also makes it possible to offset radially towards the axis the internal circumference of the Belleville washer and the orifices 56 for passage of the hooks while retaining the radial position of the diaphragm joint on the cover. This increases the radial width of Belleville washer and its saddle and reduces the length of the radial fingers 36, which increases their rigidity.

As shown, this rigidity can also be increased by forming ribs 64 these fingers over most of their length, for example ribs with a circumferential V section.

In the alternative embodiment of Figure 5, the 'fices 56 which are formed in the diaphragm 20 for mounting on the cover 16, are more constituted by enlarged ends radial slots 52 but are formed inside the Belleville washer 34, in the vicinity of its internal circumference 48 and at a distance from the axis which is substantially unchanged from the prior art, so that the diaphragm 20 according to the invention can be mounted on a cover 16 in the same way as a diaphragm of the prior art.

arrangement of the orifices 56 in the Belleville washer 34 also has the advantage of not bringing the attachment or articulation means of the diaphragm on the cover too close to the axis and therefore of avoiding any risk of interference with the damper torsional 24.

The radial slots 52, which extend between the internal periphery 48 of the Belleville washer 34 and the internal circular edge 54 of the diaphragm 20, are angularly offset relative to the orifices, so that the ends 50 of the radial slots 52, which are widened to reduce stresses at the bases of the radial fingers 36, are sufficiently spaced from the orifices 56 so as not to weaken the diaphragm.

In the embodiment of Figure 5, the number of radial slots 52 is twice the number of holes 56 and two radial slots extend between two consecutive holes 56.

In the variant embodiment of the figure, the configuration of the Belleville washer 34 and that of the radial slots 52 are the same as in the embodiment of FIG. 5, but the diaphragm 20 of FIG. 3 has two times less radial slots 52 than that of Figure 5, so that the number of radial slots 52 is equal to the number of holes 56, and the radial slots 52 each extend in the middle between two consecutive holes.

In the variant embodiment of the figure, the width or radial dimension of the Belleville washer 34 has been increased compared to those in FIGS. 5 and 6, and the radial slots 52 are shorter. Their number is equal to the double number of the orifices 56, which are formed at the same distance from the axis as in the embodiments of FIGS. 5 and 6, the radial slots 52 being one in two angularly aligned with the orifices 56 and a on two extending in the middle between two consecutive orifices 56.

In the embodiment of FIG. 7, the ratio of the external and internal diameters of the Belleville washer 34 is approximately 1.8, while that of approximately 1.5 in the embodiments of FIGS. 5 and 6 .

The variant embodiment shown in the figure differs from that of FIG. 7 in that the radial slots 52 aligned with the orifices 56 in the embodiment of FIG. 7, have been extended up to these orifices in the embodiment of FIG. 8. The radial slots 52 therefore have different lengths, one in two extending to an orifice 56 which then forms the enlarged end of the corresponding radial slot 52 and one in two being shorter and extending in the middle between two radial slots 52 ending in orifices 56.

In FIG. 9, curve A represents the variation of an axial load due to the elastic fixing of the friction linings and to the elasticity of the mechanism during disengagement, between the rest position of the stop corresponding to the engaged state ( position 0 on the graph in Figure 6) and the end position of the stop corresponding to the disengaged state (+ 6 mm in the example shown).

The dotted curve B represents the variation of the axial load developed by the annular diaphragm according to the invention as a function of its axial deformation.

Curve A ′ represents the variation of the aforementioned axial load of the curve during declutching when the wear of the friction linings is significant and substantially reaches its maximum value, which has the effect of shifting to the right in the drawing of 1a Figure 1 the positions of the clutch release bearing in the engaged state and in the disengaged state, and which has a consequence the maximum value of the axial load exerted by the diaphragm on the pressure plate. FIG. 10 represents the load variations relative to the clutch release bearing as a function of the stroke of this stop when the ratio of the diaphragm lever arms is close to 4, curve C representing the difference in curves and A and corresponding to l 'force applied to the stop for disengagement, and the curve B1 representing variation in axial load developed by the diaphragm and reported at the stop.

clearly sees in Figures 9 and 10 the overall curves B and B1 which corresponds to the difference between the maximum and the minimum of the axial load developed by the diaphragm.

Thanks to this saddle and to the progressiveness of the clutch, the value of the force applied to the curved abutment C) varies little over about two-thirds of the declutching stroke and remains less than 100 daN in this embodiment.

note also on the graph in FIG. 10 that in the event of wear of the friction linings, the curve C would be shifted to the left at 'and that it would be necessary to exert a greater force on the clutch release bearing to move it from its position corresponding to the engaged state for disengaging.

It is therefore advantageous to provide in the clutch an automatic device for adjusting the wear of the friction linings and the wear of the corresponding friction surfaces of the pressure plate 18 and of the reaction plate, which makes it possible to maintain the stroke. of disengagement of the stop 38 between the values 0 and +6 mm from the abscissa axis in FIG. 10 and therefore to keep a reduced value of the force to be applied to this stop for the disengagement, throughout the lifetime of the 'clutch.

Claims (1)

CLAIMS 1 - Annular diaphragm for a clutch mechanism, comprising a radially external annular part forming a Bellevi washer (34) 1 strongly encased, a radially internal annular part comprising radial slots (52) delimiting between them radial fingers () s extending inwards, and orifices (56) for passage of the diaphragm attachment means on a support, these attachment means bearing at one end on the Belleville washer, characterized in that the support zones hooking means on the Belleville washer (34) are closer to the center line or neutral line of the Belleville washer than to its internal circumference (48). 2 - Diaphragm according to claim 1, characterized in that said support zones are in the vicinity of the neutral line or center line of Belleville washer (34). 3 - Diaphragm according to claim 1 or, characterized in that the aforementioned passage orifices (56) are formed outside the Belleville washer and in that each attachment means comprises an elongated radial arm (62) extending to distance along the diaphragm between an orifice (56) above and aforesaid support area. 4 diaphragm according to one of claims 1 to 3, characterized in that the hooking means are elongated hooks (58) in the form of C. 5 - diaphragm according to one of claims 1 to 4, characterized in that the ratio of the external and internal diameters of the Belleville washer (34) is greater than or equal to about 1.45. 6 - Diaphragm according to one of claims 1 to 5 characterized in that the aforementioned ratio of the diameters of the Belleville washer (34) is greater than or equal to about 1.5. 7 - A diaphragm according to claim 1 or 2, characterized in that the aforesaid orifices (56) are formed between the external (46) and internal (48) circumferences of the Belleville washer (34). 8 - Diaphragm according to claim, characterized in that the aforesaid orifices (56) are formed on or in the vicinity of the neutral line of Belleville washer (34). 9 - Diaphragm according to one of the preceding claims, characterized in that said radial slots (52) extend between the internal circumference (48) of the Belleville washer (34) and internal edge (54) of the diaphragm. 10 - Diaphragm according to one of the preceding claims, characterized in that the number of radial slots (52) is equal to twice the number of orifices (56). 11 - Diaphragm according to one of claims 1 to 8 characterized in that said radial slots (52 each extend substantially in the middle between two consecutive orifices (56). 12 - Diaphragm according to claim 11, characterized in that the length of said radial slots (52) is substantially equal to or slightly less than the radial distance between the internal edge (54) of the diaphragm and the aforementioned 'slots (56). 13 - Diaphragm according to one of the preceding claims, characterized in that said radial slots (52) are all substantially the same length 14 - diaphragm according to one of claims 1 to 12, characterized in that said radial slots (52) have different lengths 15 - diaphragm according to claim 14, characterized in that some of said radial slots (52) are aligned with the aforesaid 'slots (56) and extend to these holes which form enlarged ends desd 16 - A diaphragm according to claim 14 or 15, characterized in that certain radial slots (52) extend between the aforesaid orifices (56) and have a length less than the radial distance between the internal edge of the diaphragm (54 ) and orifices (56). 17 - Diaphragm according to all of claims 14 to 16, characterized in that one radial slot in two extends from the internal edge of the diaphragm (54) to an orifice (56) specified ". 18 - Diaphragm according to one of preceding claims, characterized in that the radial fingers (36) are formed with stiffening ribs 19 - Friction clutch, in particular for a motor vehicle, comprising a cover (16) integral in rotation with a pressure plate (18) and a reaction plate (10) between which is mounted a friction disc (22), and an annular diaphragm (20) mounted on the cover for axially urging the pressure plate () towards the reaction plate (10), characterized in that the diaphragm (20) is of the type described in one of the preceding claims 20 - Clutch according to claim 19, characterized in that it comprises an automatic device for taking up the wear of the friction linings ( 3 2) carried by the friction disc (22) and corresponding friction surfaces of the pressure and reaction plates.