FR2806457A1 - Hydrokinetic coupling for vehicle has locking clutch with piston which presses against transverse wall of driving case using intermediate friction pad, the friction surfaces being convex and plane - Google Patents

Abstract

The clutch uses a plane friction pad (22) which is fixed to the transverse wall (20) of a motor driven casing. A piston (16) attached to a driven turbine wheel has a convex face (24) adjacent to the friction pad and the radius of curvature of the face increases with the distance from the axis of rotation such that an outer radius (R1) is greater than an inner radius (R2).

Description

The invention relates to a hydrokinetic coupling device, in particular for a motor vehicle, of the type described for example in the patent application FR-A-2,747 filed March 3, 1998.

 In known manner, a hydrokinetic coupling device connects an input element driven by a motor shaft to an output element driving a driven shaft, the input element being a housing which a paddle wheel forming an impeller member integral with the casing and a turbine wheel integral with the driven shaft are mounted face to face, the rotation of the casing and the impeller member causing the circulation of a liquid which rotates the turbine wheel and the driven shaft, with some sliding relative to the rotation of the housing and the impeller member, so by absorbing a portion of the energy transmitted to the motor shaft.

 A locking clutch arranged in the casing makes it possible to secure rotation of the casing and the turbine wheel as soon as the operating conditions allow, in order to reduce to a minimum the energy absorption in the transmission of torque between rotation. motor shaft and the driven shaft. locking clutch comprises a piston movable axially relative to the casing and to the turbine wheel and intended to cooperate friction means with an inner transverse face of the casing, and which is often connected in rotation to the turbine wheel by a torsion damper . According to the embodiments, the friction means comprise one or more friction linings interposed between the piston and the housing.

The axial displacements of the piston between engagement (bridging) and disengaging (disassembly) positions of the locking clutch are driven by variations in hydraulic pressures acting on either side of the piston. It has been found that the variations of the hydraulic pressure on the piston and on the casing during the operation of the device, as well as the variations in the speed of rotation, have the effect of varying the contact areas between the friction surfaces presented by the device. piston, the or lining and housing, resulting in uncontrolled variations in the distribution of contact pressures at the friction interfaces, variations of the contact surfaces with the friction lining or the variations of the transmitted torque. These uncontrolled variations are likely to cause heating, damage and irregular and significant wear of the friction lining or friction, a degradation of the hydraulic fluid used and a phenomenon of interference of the locking clutch.

 It has already been proposed, for example in document FR-A-2 771 790, to limit these drawbacks by providing a possibility of pivoting between the piston and a friction lining support integral rotation of the piston, and giving curved shapes complementary to the friction lining and the internal transverse surface of the housing against which the friction lining is applied, the inner surface of the housing being preferably concave in the contact zone with the friction lining.

This known solution has the disadvantage of a certain complexity, due to the pivoting mounting of the lining support the piston and to the machining of complementary curved surfaces on the different parts, and it is applicable only to a particular type of device. hydrokinetic coupling with locking clutch.

The object of the invention is in particular to avoid these drawbacks of the prior art. It relates to a hydrokinetic coupling device, in particular for a motor vehicle, comprising a housing element <B> dl </ B> and having a transverse internal surface which cooperates via at least one gasket. friction with a piston of a locking clutch for transmitting a torque between the input member and an output member, and means for limiting variations of the contact areas between the friction surfaces of the piston, of the lining and / or the inner face of the housing, characterized in that the areas in contact with said friction surfaces comprise at least one convex curved surface and a flat surface.

With the cooperation of a convex curved surface and a flat surface, the contact areas of the friction surfaces make it possible to control, in a simple and economical manner, the variations of the contact areas between the friction surfaces during operation of the device. This increases the torque transmission capacity of the locking clutch, the durations of the friction lining (s) and the hydraulic fluid used in the hydrokinetic coupling device, reduces clutch chatter and decreases the cost. .

 In addition, this solution is easily applicable to many different configurations of locking clutch and friction means.

According to another characteristic of the invention, the radius of curvature of said convex surface in a plane passing through the axis of rotation is variable with the distance between this surface and the rotation.

 Advantageously, the radius of curvature decreases when distance to the axis of rotation increases.

This allows in particular to reduce the contact area between the friction surfaces when the speed of rotation increases, to maintain a substantially constant maximum contact pressure. According to yet another characteristic of the invention, the friction lining which cooperates with friction with the piston or with the casing during the operation of the device, has a non-uniform stiffness, varies with the distance relative to the axis of rotation.

 In a preferred embodiment of the invention, the packing stiffness decreases between its inner and outer peripheral edges and is minimal on its mean radius.

 In practice, this friction lining may be formed by assembling several annular elements having different stiffnesses and different diameters, which are juxtaposed radially.

 Such a variable rigidity seal allows to maintain a constant distribution of the contact pressure irrespective of the deformation of the element bearing the counter-friction surface. This also makes it possible to better distribute the contact pressures and to reduce their maximum value to increase the service life of the device, in particular that of the friction linings and the hydraulic fluid.

In one embodiment of the invention, the aforementioned convex surface is formed on the face of the piston facing the friction lining.

In this case, the face of the friction lining which cooperates with this convex surface is flat.

As a variant, the aforementioned convex surface is presented by the face of the friction lining which is turned towards the piston, the corresponding surface of the piston then being flat.

According to various embodiments - the friction lining is fixed on the piston or on the aforementioned transverse inner surface of the housing, - the transverse inner surface of the housing is flat or convex, - the friction lining is fixed on an annular element interposed between the piston and the internal transverse surface of the housing, and this annular element is integral in rotation with a component of a torsion damper mounted between the piston and the output element, and carries a second friction lining on its turned side towards the internal transverse surface crankcase.

 In general, the invention provides a simple and economical solution to the problem of controlling variations in the contact area of a friction lining with a counter-friction surface a locking clutch hydrokinetic coupling device. It is also applicable to other types of clutches, in particular dry clutches.

The invention will be better understood and other features, details and advantages thereof will appear more clearly on reading the following description, given by way of example with reference to the accompanying drawings, in which - FIGS. 1 to 8 are schematic views. partial axial section different embodiments of the invention. FIG. 1 diagrammatically shows a device according to the invention, in which a housing 10 has on its outer surface means 12 secured to the end of a drive shaft and contains a turbine wheel 14 which is integral in rotation with a driven shaft and which is inside the housing 10 in front of a paddle wheel 15 forming an impeller integral with the casing 10.

 The locking clutch includes a piston 16 shown here in the bridging position or engagement position the clutch, the piston being movable in translation along the axis of rotation between the bridging position shown in the drawings and a position of disassembly or disengagement of the clutch, in which is spaced from the transverse end wall 20 of the housing 10.

According to the embodiments, the piston 16 is rotatable with respect to the turbine wheel 14 or with respect to the casing 10 with a limited angular displacement, means for connecting the piston 16 in rotation with the turbine wheel 14 or the casing being constituted either by elastically deformable tongues, or by a torsion damper, or other means such as splines, teeth, etc.

The piston 16 is, at its radially outer periphery, integral with an annular element 42 having a radial portion 44 fixed on a piston on the opposite side to the wall 20 of the casing, and lugs 46 parallel to the axis 18 and cooperating circumferentially with elastically deformable members 36 with circumferential action of a torsion damper which connects piston 16 in rotation with the turbine wheel 14. The elastically deformable members 36 are housed in an annular peripheral rim of a guide ring 40 fixed at its periphery internal turbine wheel 14, and are circumferentially supported on the tabs 46 of the element 42 secured to the piston 16.

A radially inner peripheria, the turbine wheel 14 comprises a hub 48 whose inner cylindrical surface is formed with splines 50 for securing in rotation with an output shaft shown in phantom.

The end of the hub facing the wall 20 of the housing 10 comprises sealing means 54 which are housed in a groove of the inner cylindrical surface of the hub 48 and which cooperate with the outer cylindrical surface of the shaft 52 near its end. forming a leaktight separation allowing the bridging between torque converter and lock clutch chambers inside the housing 10. The mounting of the sealing means 54 on the turbine hub 48 reduces the cost this function allows the use economical seals.

 In particular, the sealing means 54 may be an O-ring, a seal with a rectangular section, a segment (open or not), a lobe seal, etc.

The piston 16 is displaceable in translation parallel to the axis of rotation 18 towards the transverse end wall 20 of the housing 10 and in the opposite direction, by variations of the hydraulic pressure on either side of the piston which combine during the operation of the device to centrifugal forces that vary with the speed of rotation, and for the effect of deformation of the entire piston and the housing. The results of these deformations are particularly troublesome at the radially outer portion of the piston 16 and part of the end wall 20 of the housing 10 which cooperates with the outer peripheral portion of the piston 16 in the engagement position of the piston. locking clutch.

 The friction lining 22 which is interposed between the piston 16 and the wall 20 of the casing, thereby undergoes forces whose distribution on its surface varies with operating conditions, these efforts can be concentrated in certain areas of the lining and cause significant deterioration of the filling, heating, chattering phenomenon, etc. as indicated above.

The invention proposes to reduce these disadvantages by cooperation of a convex friction surface and a plane friction surface, as will be indicated in detail below for the various embodiments which have been shown in the drawings. , the convex surface being formed by a curved line, for example by a torus portion, centered on the axis of rotation, the planar surface being in a radial or transverse plane with respect to the axis of rotation.

 In the simplified and enlarged view of FIG. 2, which corresponds to the embodiment of FIG. 1, the friction lining is flat and is fixed on a radial flat portion of the inner surface of the end transverse wall 20 of the casing. 10. The face 24 of the piston 16 which faces the seal 22, is of convex shape, over a radial extent substantially corresponding to the radial extent of the seal. This convexity of the contact surface of the piston 16 with the gasket 22 makes it possible to keep the area of the contact surface between the face 24 of the piston 16 and the gasket 22 substantially constant regardless of the deformation of the piston. The radius of curvature of the face 24 of the piston, in a plane passing through the axis of rotation 18, is determined so that the contact pressure of the piston on the lining is less than the maximum allowable stress by the lining. To reduce this stress, the radius of curvature will be as large as possible, without however exceeding a maximum value above which the contact face 24 of the piston with the liner 22 would be substantially equivalent to a flat surface.

 Advantageously, the radius of curvature of the face 24 can vary according to the distance to the axis of rotation, this radius gradually decreasing from the radially inner end to the radially outer end of the face 24 as shown schematically in FIG. radius of curvature R2 is less than the radius of curvature This gradual decrease in the radius of curvature makes it possible to reduce the surface area of contact with the lining when the speed of rotation increases. Indeed, when increasing the speed of rotation, resulting stress on the piston decreases. This reduction can be compensated by an increase in the mean radius (relative to the rotation axis) of the contact zone and by a decrease in the radius of curvature of the surface 24 of the piston, this reduction of the curvature being able to be determined the maximum contact pressure applied to the liner remains substantially constant during variations in the operating conditions of the device.

 In the variant embodiment shown in FIG. 3, the annular friction lining 22 is flat and is fixed on a planar radial face 26 of the piston 16, facing a curved annular surface of the transverse wall 20 of the casing 10, this surface annular 28 having a convexity facing the liner 22 and the flat face 26 of the piston.

 As already described for the embodiment of FIGS. 1 and 2, the surface convexity 28 makes it possible to keep the area of the contact surface with the lining 22 substantially constant regardless of the deformation of the piston and / or the wall 20 of housing 10.

The radius of curvature of the convex surface 28 in a plane passing through the axis of rotation can gradually decrease when the distance to the axis of rotation increases, with the same effects as those described above.

 In the variant embodiment of FIG. 4, the lining 22 is of convex shape on the side of the planar facing surface 26 of the piston 16 and is fixed on the convex curved surface 28 of the internal face of the transverse wall 20 of the casing 10. this convex surface 28 corresponding to that shown in FIG.

 The same advantages are thus obtained as with the embodiments of FIGS. 1 to 3, the radius of curvature of the convex face of the liner 22 in a plane passing through the axis of rotation that can be constant or decrease progressively when the distance to the axis of rotation increases.

 In the variant embodiments of FIGS. 5 to 8, two friction linings are fixed to an annular element 30 comprising a radial portion 32 interposed between the piston 16 and the transverse wall 20 of the casing 10, parts 34 extending parallel to the casing. 'axis of rotation and cooperating with the members 36, such as circumferential action coil springs, the torsion damper which connects the rotation piston 16 and the turbine wheel 14. As in the example of Figure 1, the elastically deformable members 36 are housed in an annular peripheral flange 38 of a guide washer 40 fixed at its inner periphery to the turbine wheel 14 and are circumferentially supported on the axial portions 34 of the annular element 30 to transmit a pair of rotation to the turbine wheel 14 with damping of vibrations and irregularities of torque, when the locking clutch is engaged.

Unlike the embodiment of FIG. 1, the sealing means 54 which cooperate with the output shaft 52 are carried by a centering member 56 integral with the inner periphery of the transverse wall 20 of the casing 10 and play the same role as in FIG. 1 by offering the same advantages, these means 54 being for example a lip seal as shown, or an O-ring, an anointed rectangular section, a segment, a lobed seal, etc.

 In an embodiment of FIGS. 6, the two friction linings 22, 42 fixed on the two faces of the radial portion 32 of the annular element 30 are flat and each cooperate with a convex surface, formed on the face face 24 of the piston 16 as already described with reference to Figure 2 and on the inner face 28 of the transverse wall 20 of the housing 10, as already described with reference to Figure 3.

The radii of curvature in a plane passing through the axis of rotation, convex surfaces 24 and 28 above can be constant, although gradually decrease when the distance to the axis of rotation increases, as already described.

In an alternative embodiment shown in FIG. 7, the aforementioned convex surface 24 of the piston cooperates with a plane friction lining 22 fixed on one face of the radial portion 32 of the aforementioned annular element 30, and the other friction lining 42 fixed. on the other side of the radial portion 32 is abutting against an annular portion 44 of the transverse wall 20 of the casing 10, this annular portion 44 being flat and extending in a radial plane relative to the axis of rotation .

In addition, the rigidity of the friction lining 22 cooperating with the convex surface 24 of the piston varies radially with the distance 'of the axis of rotation, the rigidity being greater in the radially inner and radially outer portions of the lining and more weak in the middle part of the filling.

This lining, in combination with the convex surface 24 of the piston, makes it possible to keep the distribution of the contact pressure on the lining 22 constant substantially constant regardless of the deformation of the piston 16. In addition, the contact pressure on the lining 22 is distributed. on a larger surface so that the maximum contact pressure is less important. This makes it possible to increase the lifetime of the lining and that of the other components of the device.

 a particular embodiment, the liner 22 may be formed of different materials for example by assembling or juxtaposition in the radial direction of elements having different rigidities, a median element being surrounded by elements with greater rigidity.

 In the variant embodiment shown in FIG. 8, the face 26 of the piston which bears on the lining 22 is flat and extends in a radial plane with respect to the axis of rotation, and this is the surface of the lining 22 intended to cooperate with the flat face 26 of the piston which is convex.

 For the rest, the embodiment of FIG. 8 is identical to that of FIG.

 In alternative embodiments not shown, the variable stiffness friction lining could be on the side of the transverse wall 20 of the housing 10 and have a flat face cooperating with a convex surface of the transverse wall 20 of the housing 10 or have a convex surface cooperating with a flat surface of the transverse wall 20 of the housing 10.

 As already described for the other embodiments, the radii of curvature of the convex surfaces in the embodiments of FIGS. 7 and 8 and in their aforementioned embodiments may be uniform or may gradually decrease when the distance to the axis of rotation increases.

Claims (1)

 1 - Hydrokinetic coupling device, in particular a motor vehicle, comprising an inlet element (10) forming a housing and having a transverse inner surface which cooperates via at least one friction lining with a piston (16). ) a locking clutch for transmitting a rotational torque between the input member (10) an output member (14, 48, 52), and means for limiting the variations of the contact areas between the piston friction surfaces (16), the lining (22) and / or the inner face of the casing characterized in that the areas in contact with said friction surfaces comprise at least one convex curved surface (28) and a flat surface ( 26). 2 - Device according to claim 1, characterized in that said convex curved surface is centered on the axis of rotation (18) and the flat surface is in a radial plane or transverse to the axis of rotation (18). 3 - Device according to claim 1 or 2, characterized in that the radius of curvature of said convex surface (24, 28) in a plane passing through the axis of rotation (18) is variable with distance between this surface and the axis of rotation. 4 - Device according to claim 3, characterized in that said radius of curvature decreases when the distance to the axis of rotation increases. 5 - Device according to one of the preceding claims characterized in that the friction lining (22) which engages friction with the piston (16) or with the housing (10) during operation of the device, has a non-uniform stiffness, which varies in a radial direction with the distance to the rotation. 6 - Device according to claim 5, characterized in that the rigidity of the seal (22) decreases between its inner and outer peripheral parts and is lower in its middle part. - Device according to claim 5 or 6, characterized in that the friction lining (22) is formed by assembling or juxtaposition in the radial direction of annular elements having different stiffnesses and diameters. 8 - Device according to one of the preceding claims, characterized in that said convex surface is formed on the face (24) of the piston facing the friction lining (22). 9 - Device according to one of claims 1 to 7, characterized in that said convex surface above is formed by the face of the friction lining (22) which faces the piston (16). 10 - Device according to one of the preceding claims, characterized in that the transverse inner surface of the housing (10) cooperating with the friction lining is flat. - Device according to claim 9 or 10, characterized in that said transverse inner surface of the housing (10) is convex. 12 - Device according to one of the preceding claims, characterized in that said friction lining (22) is fixed on said transverse inner surface of the housing (10). 13 - Device according to one of claims 1 to 11, characterized in that said friction lining (22) is fixed on an annular element) interposed between the piston (16) and said transverse inner surface of the housing (10) and this annular element (30) is rotatably connected to a component (36) of a torsion damper mounted between the piston (16) and the output element (14) and carries a second friction lining (42) on its face facing said transverse inner surface of the housing (10). 14 - Device according to one of the preceding claims, characterized in that its output element comprises an output shaft (52) secured in rotation with a turbine hub (48) and cooperating with sealing means (54) which are carried either by the turbine hub (48) or by a centering member (56) integral with the housing (10), sealing means (54) separating converter chambers and locking clutch in the housing (10). ) for bridging said clutch.