Torque transmission assembly for a motor vehicle

A torque transmission assembly including a hydrodynamic torque convener able to be coupled to a crankshaft on the one hand, and able to be coupled to a gearbox input shaft on the other, the torque converter including a primary element and a secondary element which are rotationally mobile about an axis of rotation, and damping means including a transmission member and a bearing element, the transmission member including an elastic leaf rotating as one with the primary element or with the secondary element, and the bearing element being home by the secondary element or by the primary element respectively, the elastic leaf being capable of flexing and of transmitting a rotational torque between the primary element and the secondary clement, the flexing of the elastic leaf being accompanied by a relative rotation between the primary and secondary elements.

The present invention relates to a torque transmission assembly for a motor vehicle.

A transmission assembly comprises a known hydrodynamic torque converter. An example of such a torque converter is illustrated schematically and partially inFIG. 1and makes it possible to transmit a torque from an output shaft of an internal combustion engine of a motor vehicle, such as for example a crankshaft1, to an input shaft2of a gearbox.

The torque converter classically comprises an impeller wheel3, able to involve hydrokinetically a turbine wheel4, through an engine5.

The impeller wheel3is coupled to the crankshaft1and to the turbine wheel4is coupled to the guide rings6.

A first group of compression spring-type elastic members7a,7bis amounted between the guide rings6and a central hub8coupled to the input shaft2of the gearbox. The elastic members7a,7bof the first group are arranged in a series through a phasing member9, so that the said elastic members7a,7bbecome deformed in phase with each other, the phasing member9being mobile relative to the guide rings6and relative to the hub8.

A second group of elastic members7cis assembled with play between the guide rings6and the central hub8, parallel with the first group of elastic members7a,7b,the said elastic members7cbeing designed to be active over a limited angular range, in particular as angular end-of-stroke of the guide rings6relative to the central hub8. The angular stroke, or the angular shift marked α, of the guide rings6relative to hub8, is defined relative to a rest position (α=0) in which no torque is transmitted through the damping means formed by the aforesaid elastic members7a,7b.

The torque converter also comprises clutch means10making it possible to transmit a torque from the crankshaft1to the guide rings6, in a determined operating phase, without utilizing the impeller wheel3or the turbine wheel4.

The second group of elastic members7cmakes it possible to increase the rigidity of the damping means as angular end-of-stroke, i.e. for a large angular shift a of the guide rings6relative to the hub8(or conversely).

It is noted that the representation of the function M=f (α) defining the torque M transmitted through the device according to the angular shift α, comprises a first linear portion of slope Ka (for low values of angular shift α) and a second linear portion of larger slope Kb (for high values of angular shift α). Ka and Kb are the angular rigidities of the device, respectively at the start and at the end of the angular stroke. If one defines K1to mean the accumulated rigidities of the first springs of each pair of the first group, K2to mean the accumulated rigidities of the second springs of each pair of the first group and K3to mean the accumulated rigidities of the springs of the second group, then Ka=(K1.K2)/(K1+K2) and Kb=Ka+K3.

The change in slope between the first and second portions of the curve can generate vibrations and a major hysteresis during the operation of the torque converter, affecting the quality of filtration obtained using the damping means.

The purpose of the invention is particularly to provide a simple, effective and economic solution to this problem.

To that end, it proposes a torque transmission assembly for a motor vehicle, the said unit comprisinga hydrodynamic torque converter able to be coupled to a crankshaft on the one hand, and able to be coupled to a gearbox input shaft on the other hand,a primary element and a secondary element which are rotationally mobile relative to each other around an axis of rotation X, anddamping means, characterized in that the said damping means comprise a transmission member and a bearing element, the transmission member comprising an elastic leaf rotating as one with the primary element or secondary element and the bearing element being the secondary element or the primary element respectively, the elastic leaf being able to bend and transmit a torque between the primary element and the secondary element, the flexion of the elastic leaf being accompanied by a relative rotation between the primary and secondary elements, according to the axis of rotation (X), to damp the acyclisms of rotation between the primary element and the secondary element.

Such damping means offer a progressive characteristic curve, with no change in slope. The invention thus makes it possible to reduce the vibrations generated in operation and ensures a good quality of filtration.

The leaf and the bearing element respectively form a cam follower and a cam surface arranged to cooperate with the cam follower.

The primary element can form a torque input element of the torque converter intended to be coupled to the crankshaft and the secondary element can form a torque output element of the torque converter intended to be coupled to the input shaft of the gearbox, the damping means being arranged between the torque input element and the torque output element while being designed to act in opposition to the rotation of the torque input element relative to the torque output element.

Preferably, the torque output element comprises a central hub.

The radially internal periphery of the central hub can comprise grooves able to cooperate with complementary grooves of an input shaft of a gearbox.

Preferably, the bearing element comprises at least one rolling member. The rolling member can be mounted rotating as one with the torque input element or the torque output element. Or the rolling member can be mounted floating relative to the torque input element or the torque output element.

In a first embodiment of the invention, the torque input element is formed by a turbine wheel, which is itself connected hydrokinetically to an impeller wheel, the impeller wheel being intended to be coupled to the crankshaft.

In this case, the turbine wheel, or respectively the torque output element, can be coupled to at least one annular flange surrounding the central hub, the radially internal periphery of the said flange being coupled rotationally to the said turbine wheel, or respectively to the said central hub.

The bearing element can be mounted on the radially external periphery of the flange.

The turbine wheel, or respectively the torque output element, can comprise two flanges axially delimiting between them an internal space serving as housing, at least partly, of the elastic leaf and/or the bearing element.

The impeller wheel can be is coupled rotationally to the cap in such manner as to house, at least partly, the impeller wheel, the turbine wheel, and/or the damping means.

The torque converter can comprise clutch means able to couple together rotationally the cap and the turbine wheel, in a clutched position, and able to release the cap of the turbine wheel in an unclutched position.

The clutch means can comprise an annular piston whose radially external periphery is coupled rotationally the turbine wheel, the piston being able to be coupled by friction to the cap in clutched position.

The piston can comprise a support zone, located for example radially outside, able to come to rest against the cap in clutched position, so as to effectuate a coupling rotationally by friction of the cap and the piston.

The elastic leaf can be designed so that, in a relative angular position between the turbine wheel relative to the torque output element different from a rest position, the bearing element exerts a flexion stress on the elastic leaf producing a contrary reaction force of the elastic leaf on the bearing element, that reaction force having a circumferential component tending to retract the turbine wheel and the torque output element towards the said relative rest position.

The elastic leaf can be designed so that, in a relative angular position between the turbine wheel relative to the torque output element different from a rest position, the bearing element exerts a flexion stress on the elastic leaf producing a contrary reaction force of the elastic leaf on the bearing element, that reaction force having a radial component tending to keep the elastic leaf in contact with the bearing element.

In one example, the angular displacement of the turbine wheel relative to the torque output element can be greater than 20°, preferably greater than 40°.

The elastic leaf comprises a portion of anchoring as one with the torque output element, or respectively the turbine wheel, and an elastic portion comprising a radially internal strand, a radially external strand and an arched or bent portion connecting the internal strand and the external strand.

The damping means can comprise at least two elastic leafs, each elastic leaf being as one with the torque output element, or respectively the turbine wheel, each leaf being associated with a bearing element linked to the turbine wheel, or respectively to the torque output element, each leaf being maintained elastically at rest against the said corresponding bearing element, each elastic leaf being able to bend during the rotation of the turbine wheel relative to the torque output element.

In another embodiment, the primary element can be formed by clutch means and by a cap, the clutch means being able to couple together rotationally the cap and the torque output element, in a clutched position, and able to release the cap of the torque output element in an unclutched position, the damping means being located between the clutch means and the torque output element.

The clutch means can comprise an annular piston which is coupled rotationally to the hub, the piston being able to be coupled by friction to the cap in clutched position.

As for the other embodiment, the piston can comprise a support zone, located for example radially outside, able to come to rest against the cap in clutched position, so as to effectuate a coupling rotationally by friction of the cap and the piston. Or in a second embodiment of the invention, the torque input element can be formed by clutch means. The damping means are located between the clutch means and the torque output element. These clutch means are able to couple rotationally the cap and the torque output element, in a clutched position, and able to release the cap of the torque output element in an unclutched position. The damping means are similar to those described for the first embodiment of the invention. Therefore, the torque transits from the cap towards the hub passing through the damping means.

A torque transmission assembly comprising a hydrodynamic torque converter according to one embodiment of the invention is represented onFIGS. 2 to 4. This makes it possible to transmit a torque from an output shaft of an internal combustion engine of a motor vehicle, such as for example a crankshaft1, to an input shaft2of a gearbox. The axis of the torque converter bears the reference X.

The torque converter comprises a paddle impeller wheel3, able hydrokinetically to drive a paddle turbine wheel4. In this example, the hydrokinetic drive is effectuated through a reactor5.

The impeller wheel3is anchored to a bell-shaped cap11by welding one to the other and delimiting an internal volume12housing the impeller wheel3, the turbine wheel4and the reactor5. The said cap11comprises anchoring means13making it possible to couple rotationally the cap11to the crankshaft1.

The torque converter further comprises a central hub8whose radially internal periphery is grooved, on the X axis and placed in the internal volume12of the cap11. The central hub8comprises an annular rim14extending radially outward.

Two annular flanges are mounted in the said internal volume12, the two flanges being anchored by their radially internal periphery to the rim14of the hub8, through rivets or by welding, for example. The flanges extend radially and are arranged axially on both sides of the rim14. In particular, each flange15comprises a radially internal portion15aand a radially external portion15b.The radially internal portions15aof the two flanges15are axially closer to each other than the radially external portions15bof the two flanges15.

Two auxiliary annular flanges17also are mounted in the internal volume12of the cap11, around the central hub8and are arranged axially on both sides of the flanges15. The auxiliary flanges17extend radially and are anchored to each other at their radially external periphery through rivets18.

One of the auxiliary flanges17is anchored through rivets19to the turbine wheel4.

Two support members or rolling members20, being in the form of cylindrical rollers or wheels, are anchored on the radially external periphery of the auxiliary flanges17. The rolling members20are located in a manner diametrically opposed to each other. In particular, the rolling members20are mounted around axes21extending axially between the two auxiliary flanges17, the said axes21being riveted at their ends to the auxiliary flanges17.

Two elastic leafs22are mounted between the auxiliary flanges17. Particularly, as is better visible onFIG. 4, each elastic leaf22comprises an anchoring portion23mounted between the two flanges and anchored to the latter through the rivets24, of which there are three here, and an elastic portion comprising a radially internal strand25, a radially external strand26and an arched or bent portion27connecting the internal strand25and the external strand26. The arched or bent portion27has an angle of approximately 180°. In other words, the elastically deformable portion of the elastic leaf22comprises two areas radially shifted from each other and separated by a radial space.

The internal strand25develops circumferentially around the rim14of the central hub8. The external strand26develops circumferentially on an angle ranging between 120° and 180°.

The radially external strand26comprises a radially external surface28forming a rolling track coming to rest against the corresponding rolling member20, the said rolling member20being located radially outside the external strand26of the elastic leaf22. The rolling track28has an overall convex shape. The rolling track28can be formed directly by a zone of the external strand26or by a part which is retracted onto the said external strand26.

Between each elastic leaf22and the corresponding rolling member20, the torque transmitted between the turbine wheel4and the central hub8breaks down into radial stresses and circumferential stresses. The radial stresses make it possible to bend the corresponding leaf22and the circumferential stresses allow the corresponding rolling member20to move on the rolling track28of the leaf22and to transmit the torque.

When the torque transmitted between the turbine wheel4and the hub8varies, the radial stresses being exerted between the elastic leaf22and the rolling member20vary and the flexion of the elastic leaf22is modified. The modification of the flexion of the leaf22is accompanied by a displacement of the rolling member20along the corresponding rolling track28due to circumferential stresses.

The rolling tracks28have profiles arranged so that, when the transmitted torque increases, the rolling members20each exert a flexion stress on the corresponding elastic leaf22causing a closening of the free distal end29of the elastic leaf22in the direction of the X axis and a relative rotation between the turbine wheel4and the hub8such that they deviate from their relative rest position. Rest position is defined as the relative position of the turbine wheel4relative to the hub8in which no torque is transmitted between them.

Therefore, the profiles of the bearing tracks28are such that the rolling members20exert flexion stresses on the elastic leafs22having radial components and circumferential components.

The elastic leafs22exert a retraction force on the rolling members20having a circumferential component which tends to make the rolling members20turn in an opposite rotation direction and therefore to retract the turbine wheel4and the hub8towards their relative rest position, and a radial component directed outward tending to keep the rolling track28at rest against the corresponding rolling member20.

Preferably, when the turbine wheel4and the hub8are in their rest position, illustrated in particular inFIG. 4, the elastic leafs22are prestressed radially towards the X axis so as to exert a reaction force, directed radially outward, in order to keep the blades22at rest against the rolling members20.

The profiles of the rolling tracks28can be arranged interchangeably so that the characteristic curve of transmission of the torque according to the angular displacement will be symmetrical or not relative to the rest position. According to one advantageous embodiment, the angular displacement can be larger in one rotation direction known as direct, than in an opposite rotation direction, called retro direction.

The angular displacement of the turbine wheel4relative to the hub8can be greater than 20°, preferably greater than 40°.

The elastic leafs22are regularly distributed around the X axis and are symmetrical relative to the X axis so as to guarantee the balance of the torque converter.

The torque converter can also comprise friction means arranged to exert a resistive torque between the turbine wheel4and the hub8at the time of their relative displacement so as to dissipate the energy accumulated in the elastic leafs22.

The torque converter also comprises clutch means10able to couple together rotationally the cap11and the hub8, in a clutched position, and able to release the cap11from the hub8in an unclutched position.

The clutch means10comprise an annular piston30extending radially, housed in the internal space12of the cap10, whose radially external periphery has teeth31in the shape of cylindrical sectors, engaged in notches32with shapes complementary to the flanges17. Therefore, the piston30is coupled rotationally to the flanges17and to the turbine wheel4and is free to move axially relative to the flanges17, to a certain extent.

The radially external periphery of the piston30also comprises a support zone with friction fittings33and able to come to rest against part11bof the cap11in clutched position so as to effectuate a coupling rotationally of the cap11and the piston30.

The piston is thus movable along the X axis, between its clutched and unclutched positions, the displacement of the piston30being controlled by pressure chambers located on both sides of the piston30.

Such clutch means10make it possible to transmit a torque from the crankshaft1to the input shaft2of the gearbox, in a determined operating phase, without involving the impeller wheel3or the turbine wheel4. In this case, the torque is transmitted from the crankshaft1, through the cap11, the piston30, the auxiliary flanges17, the rolling members20, the elastic leafs22, the flanges15, and the hub8.

In the example as illustrated inFIGS. 2 and 3, the damping means are arranged relative to the turbine wheel4in such manner that the passage of torque is effectuated through the said damping means in “hydrokinetic” mode as well as in “clutch” mode. “Hydrokinetic” mode means the mode in which the torque is transmitted from the cap11to the hub8through the turbine wheel4. “Clutch” mode means the mode in which the torque is transmitted from the cap11to the hub8through the piston30. In the example, whether it be in “hydrokinetic” mode or in “clutch” mode, the torque always transits through the damping means20,22. Indeed, the damping means20,22are coupled permanently to the turbine wheel4and in unclutchable fashion to the cap11through the piston30.

Other embodiments not shown can be possible. In particular, the rolling members20can be carried by the flanges15while the elastic leafs can be carried by the auxiliary flanges17.

In another example not shown, it could be devised that the damping means are arranged so that in “hydrokinetic” mode, the torque transits directly from the turbine wheel4towards the hub8without passing through the damping means, and that in “clutch” mode, the torque transits from the cap11, towards the hub8passing through the piston30and the damping means. In this case, the turbine wheel is connected directly to the central hub8by a riveted connection, for example.

In another exampleFIG. 5, instead of being interposed between the turbine wheel4and the hub8, the damping means could be placed inside a chamber36, between a piston37and a cap38.

Or elseFIG. 6illustrates another torque converter35in which the damping means are located in a volume39located outside a space delimited by a cap41of the converter35.