Patent Publication Number: US-2017363194-A1

Title: Torque transmission device, more particularly for a motor vehicle

Description:
FIELD OF THE INVENTION 
     The present invention relates to a torque transmitting device and a hydrokinetic torque coupling device for a motor vehicle, such as a torque converter, for instance. 
     BACKGROUND OF THE INVENTION 
     A known hydrodynamic torque converter is schematically and partially illustrated in  FIG. 1  and makes it possible to transmit a torque from the output shaft of an internal combustion engine in a motor vehicle, such as for instance a crankshaft  1 , to a transmission input shaft  2 . 
     The torque converter conventionally comprises an impeller wheel  3 , able to hydrokinetically drive a turbine wheel  4  through a reactor  5 . 
     The impeller wheel  3  is coupled to the crankshaft  1  and the turbine wheel  4  is coupled to guiding washers  6 . 
     A first group of elastic members  7   a ,  7   b  of the compression spring type is mounted between the guiding washers  6  and a central hub  8  is coupled to the transmission input shaft  2 . The elastic members  7   a ,  7   b  of the first group are arranged in series through a phasing member  9 , so that the elastic members  7   a ,  7   b  are deformed in phase with each other, with the phasing member  9  being movable relative to the guiding washers  6  and relative to the hub  8 . 
     A second group of elastic members  7   c  is mounted with some clearance between the guiding washers  6  and the central hub  8  in parallel with the first group of elastic members  7   a ,  7   b , with the elastic members  7   c  being adapted to be active on a limited angular range, more particularly at the end of the angular travel of the guiding washers  6  relative to the central hub  8 . The angular travel, or the angular shift noted a, of the guiding washers  6  relative to the hub  8 , is defined relative to a rest position (α=0) wherein no torque is transmitted through the damping assembly formed by the above-mentioned elastic members  7   a ,  7   b.    
     The torque converter further comprises a clutch  10  making it possible to transmit a torque from the crankshaft  1  to the guiding washers  6  in a determined operation phase, without any action from the impeller wheel  3  and the turbine wheel  4 . 
     The second group of elastic members  7   c  makes it possible to increase the stiffness of the damping assembly at the end of the angular travel, i.e. for a significant a angular offset of the guiding washers  6  relative to the hub  8  (or vice versa). 
     It can be seen that the representation of function M=f(α) which defines the M torque transmitted though the device according to the α angular shift, comprises a first linear portion of slope Ka (for the low values of the α angular shift) and a second, more important, linear portion of slope Kb (for the high value of the α angular shift). Ka and Kb are the angular stiffness of the device, at the beginning and at the end of the angular travel respectively. If K 1  defines the cumulated stiffness of the first springs of each pair of the first group, and K 2  defines the cumulated stiffness of the second springs of each pair of the first group, and K 3  defines the cumulated stiffness of the springs of the second group, then Ka=(K 1 ·K 2 )/(K 1 +K 2 ) and Kb=Ka+K 3 . 
     The break of slope between the first and second portions of the curve may generate vibrations and a significant hysteresis upon operation of the torque converter which might affect the quality of filtration obtained using the damping assembly. 
     Using a damping assembly using elastic members instead of springs, for other applications, and specifically in a dual flywheel, is known. Using elastic leaves makes it possible to obtain a gradual characteristic curve, with no break of slope, so as to improve the filtration quality. 
     Document FR 3 008 152 can be mentioned, which discloses a dual flywheel comprising a primary flywheel intended to be rotationally coupled to a crankshaft, forming a torque input element and bearing supporting members, a secondary flywheel rotationally mobile relative to the primary flywheel, forming a torque output element and bearing elastic leaves, with the leaves being elastically held and radially resting on the supporting members so as to bend upon rotation of the primary flywheel relative to the secondary flywheel. 
     Each leaf more particularly comprises a radially internal strand attached to the secondary wheel and a radially external strand resting against the matching supporting member, with the strands being connected together through a curved or bent area. 
     Such damping assemblies only allow a limited angular displacement of the primary wheel relative to the secondary wheel. As a matter of fact, the structure of the leaves requires to limit the displacement so as to limit the mechanical stress in the leaves to an admissible value. 
     A need exists to increase the angular displacement between the torque input element and the torque output element so as to still improve the filtration quality, while generating acceptable mechanical stress in operation. 
     SUMMARY OF THE INVENTION 
     The invention more particularly aims at providing a simple, efficient and cost-effective solution to this problem. 
     For this purpose, it provides for a torque transmitting device, specifically for a motor vehicle, comprising a torque input element and a torque output element able to pivot about an axis with respect to one another, at least one elastic leaf, rotationally coupled to the torque output element or to the torque input element respectively, with the elastic leaf being able to be elastically and radially held by a supporting member carried by the torque input element or the torque output element respectively, with the elastic leaf being able to bend upon rotation of the torque input element with respect to the torque output element. 
     The elastic leaf comprises a radially external strand comprising a radially external surface forming a raceway supported by the rolling body, a radially internal strand rotationally coupled with the torque output element or torque input element respectively, a radially median strand radially located between the radially internal and external strands, with the median strand comprising a first circumferential end connected with the internal strand by a first curved or bent area, with the median strand comprising a second circumferential end connected with the external strand by a second curved or bent area. 
     Such a structure of the leaf makes it possible to reduce the constraints within the leaf, and thus enables a larger displacement of the torque input element with respect to the torque output element, as compared to the prior art, for the same level of allowable constraints. 
     The median strand and/or the first curved or bent area may comprise at least one area having a smaller section than the external strand and/or than the second curved or bent area. 
     Such a characteristic enables a better distribution of mechanical stresses within the leaf. 
     More particularly, the thickness, i.e. the axial dimension, of the elastic leaf, is substantially constant, with the variation in section being obtained by varying the width, i.e. by varying the radial dimension of the leaf section. 
     The raceway along which the rolling body is able to roll in operation comprises a bearing area at rest forming the bearing area of the rolling body in the position of rest of the device, i.e. when no torque is transmitted through the device, with a forward or drive bearing area forming the bearing area of the rolling body when the torque input element pivots with respect to the torque output element in a first so-called forward or drive direction of rotation, with the drive bearing area being located opposite the second curved or bent portion with respect to the bearing area at rest, and a backward or coast bearing area forming the bearing area of the rolling body when the torque input element pivots with respect to the torque output element in a second so-called backward or coast direction of rotation, with the coast bearing area being located on the second curved or bent portion side with respect to the bearing area at rest, with the drive bearing area angularly extending over a range from 10 to 100°, for example of the order of 90°, with the coast bearing area angularly extending over a range from 10 to 30°, for example of the order of 25°. 
     The external strand may angularly extend over a range from 80 to 180°, for example of the order of 150°. 
     The raceway thus angularly extends over only a portion of the external strand, preferably over the portion of the strand positioned opposite the second curved area, so as to limit mechanical stresses. 
     The median strand may angularly extend over a range from 80 to 165°, for example of the order of 130°. 
     The median strand may comprise a portion substantially extending along an arc of circle. 
     More particularly, the semi-circular portion of the median strand may be substantially concentric with the internal strand, in order to lower the stress. 
     The drive bearing area comprises a straight or concave portion, located close to the bearing area at rest, with the rest of the raceway being domed or convex. 
     The supporting member may comprise a rolling body so mounted as to pivot about a shaft, with said shaft being attached to the torque input element, respectively the torque output element. 
     In such case, the rolling body of the supporting member may consist of a roller so mounted as to pivot about a shaft, for instance through a rolling bearing, such as a needle bearing, for instance. 
     The elastic leaf may be so designed that, in a relative angular position between the torque input element and the torque output element different from a rest position, the supporting member exerts a bending stress on the elastic leaf causing a cross reaction force of the elastic leaf on the supporting member, with such reaction force having a circumferential component which tends to move back the torque input element and the torque output element toward said relative rest position. 
     The elastic leaf may be so designed that, in a relative angular position between the torque input element and the torque output element different from a rest position, the supporting member exerts a bending stress on the elastic leaf causing a cross reaction force of the elastic leaf on the supporting member, with such reaction force having a radial component which tends to hold the elastic leaf in contact with the supporting member. 
     The damping assembly may comprise at least two elastic leaves, with each elastic leaf rotating together with the torque output element, or the torque input element respectively, with each leaf being associated with a supporting element rotationally linked with the torque input element, or the torque output element respectively, with each leaf being elastically maintained supported by said matching supporting element, with each elastic leaf being adapted to bend upon rotation of the torque input element relative to the torque output element. 
     Both leaves may then have the same structure and be mutually symmetrical, with the axis of symmetry being the axis of rotation of the torque input element relative to the torque output element. 
     Both leaves may be integral, with the radially internal strands of the leaves being formed in the same annular portion. 
     The invention also provides for a hydrokinetic torque coupling device for a motor vehicle, comprising:
         a cover intended to be rotationally coupled to a crankshaft,   an impeller wheel rotationally coupled to the cover,   a turbine wheel able to be hydrokinetically driven into rotation by the impeller wheel,   a hub coupled to the turbine wheel and able to be rotationally coupled to a transmission input shaft,   a clutch movable from an engaged position in which the cover and the hub are coupled together through a torque transmission device of the above-mentioned type, with the torque input element of the device being connected to or consisting of the clutch, with the torque output element being connected to or consisting of the hub, and a disengaged position in which the cover and the hub are coupled together through the hydrokinetic coupling assembly consisting of the impeller wheel and the turbine wheel.       

     The clutch may comprise a piston able to rest on a portion of the cover in the engaged position, so as to provide a rotational coupling of the cover and the piston, and able to be spaced from the cover in the disengaged position, so as to rotationally uncouple the cover and the piston. 
     The supporting members may be mounted onto the annular flange rotationally coupled to the piston. 
     It should be noted that a hydrokinetic torque coupling device may be a torque converter when the hydrokinetic torque coupling assembly comprises an impeller wheel, a turbine wheel and a reactor, or may be a coupler when the hydrokinetic torque coupling assembly has no reactor. 
     The cover may, at least partially, accommodate the impeller wheel, the turbine wheel and/or the torque transmitting device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood, and other details, characteristics and advantages of the invention will appear upon reading the following description given by way of a non restrictive example while referring to the appended drawings wherein: 
         FIG. 1  is a schematic representation of a torque converter of the prior art; 
         FIG. 2  is a sectional view of a part of a hydrokinetic torque coupling device according to one embodiment of the invention; 
         FIG. 3  is an exploded perspective view of a part of the hydrokinetic torque coupling device; 
         FIG. 4  is a sectional view along the Iv-Iv plane in  FIG. 2 ; 
         FIG. 5  is a half-view, from the front, showing a leaf which is provided on the hydrokinetic torque coupling device; 
         FIG. 6  is a half-view, in perspective, showing said leaf; 
         FIG. 7  is a diagram showing the characteristic curves of the hydrokinetic torque coupling device according to the invention and according to the prior art; 
         FIG. 8  is a diagram showing the variation in the mechanical stresses exerted in the leaf according to the displacement of the torque input element relative to the torque output element, within an elastic leaf according to the invention and within an elastic leaf according to the prior art. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
       FIGS. 2 to 6  illustrate a hydrokinetic torque coupling device for a motor vehicle, according to one embodiment of the invention. The hydrokinetic torque coupling device is more particularly a hydrodynamic torque converter. Such device makes it possible to transmit a torque from the output shaft of an internal combustion engine in a motor vehicle, such as for instance a crankshaft  1 , to a transmission input shaft  2 . The axis of the torque converter bears reference X. 
     In the following, the words “axial”, “radial” and “circumferential” are defined relative to the X axis. 
     The torque converter conventionally comprises an impeller bladed wheel  3 , able to hydrokinetically drive a turbine bladed wheel  4  through a reactor  5 . 
     The impeller wheel  3  is attached to a cover (not shown) which defines an internal volume accommodating the impeller wheel  3 , the turbine wheel  4  and the reactor  5 . Said cover comprises attaching means making it possible to rotationally couple the cover to the crankshaft  1 . 
     The torque converter further comprises a central hub  8 , the radially internal periphery of which is ribbed, with an X axis and accommodated in the internal volume of the cover. The central hub  8  comprises an annular rim  9  which radially extends outwards, and a cylindrical part  10  wherein an annular groove is formed and used for mounting an O-ring  11 . 
     The turbine wheel  4  is fastened to the annular rim  9  of the central hub  8 , for instance by rivets  12  or by welding. 
     The torque converter further comprises a piston  13  comprising a radially internal cylindrical part  14 , mounted around the cylindrical part  10  of the hub  8 , around the O-ring, from which a radial part  15  extends. The radially external periphery of the radial part  15  of the piston  13  comprises a clutch lining  16 , intended to rest onto a radial surface of the cover. 
     The piston  13  is rotationally coupled to a radially extending annular flange  17 . The piston  13  and the flange  17  are mounted so as to pivot about the hub  8 . 
     Two supporting members or rolling bodies  18  shaped as rollers or cylindrical rollers, are fastened on the radially external periphery of the flange  17 . The rolling bodies  18  are positioned so as to be diametrically opposed. The rolling bodies  18  are more specifically mounted about axially extending shafts  19 , with said shafts  19  being mounted on the flange using rivets  20 , screws or bolts, for instance. The rolling bodies  18  are mounted on the shafts  19  through rolling bearings  21 , such as needle bearings, for instance. 
     The torque converter further comprises two diametrally opposed elastic leaves  22 , formed here in one piece and assembled together with an annular central part  23  fixed to the hub  8  by screws  24  for instance. The two leaves  22  may, of course, consist of two separate parts. 
     In any case, the elastic leaves  22  are preferably regularly distributed around the X axis and are symmetrical relative to the X axis so as to ensure the balance of the torque converter. 
     Each leaf  22  comprises a radially external strand  25  comprising a radially external surface  26 , a radially internal strand  27  formed by a portion of the annular central part  23 , and a radially median strand  28  radially positioned between the radially internal  27  and external  25  strands. The median strand  28  comprises a first circumferential end linked to the internal strand  27  through a first curved or bent area  29 , with the median strand  28  comprising a second circumferential end linked to the external strand  25  through a second curved or bent area  30 . 
     Each external strand  25  develops on the circumference with an angle ranging from 120° to 180°. The radially external surface  25  forms a raceway supported by the corresponding rolling body  18 , with said rolling body  18  being positioned radially outside the external strand  25 . Each raceway  26  has a globally convex shape. The raceway  29  may directly consist of a zone of the external strand  25  or of a part which is added onto said external strand  25 . 
     Each median strand  28  develops on the circumference with an angle ranging from 80° to 165°. 
     The external  25  and median  28  strands, as well as the curved or bent areas  29 ,  30  are elastically deformable. Each curved area  29 ,  30  forms an angle of about 180°. 
     The raceways  26  have profiles so arranged that, when the transmitted torque increases, the rolling bodies  18  each exert a bending stress on the matching elastic leaf  22 , which causes the free distal end  31  of the elastic leaves  22  to move towards the X axis and a relative rotation between the cover and the hub  8  such that the later move away from their relative rest positions illustrated in  FIG. 4 . Rest position means the relative position of the cover with respect to the hub  8 , in which no torque is transmitted between the latter. 
     The profiles of the raceways  26  are thus such that the rolling bodies  18  exert bending stresses having radial components and circumferential components onto the elastic leaves  22 . 
     The elastic leaves  22  exert, onto the rolling bodies  18 , a back moving force having a circumferential component which tends to rotate the rolling bodies  18  in a reverse direction of rotation and thus to move back the turbine wheel  4  and the hub  8  towards their relative rest positions, and a radial component directed outwards which tends to maintain the raceways  26  supported by the matching rolling body  18 . 
     When the cover and the hub  8  are in their rest position, each elastic leaf  22  is preferably radially pre-stressed toward the X axis so as to exert a reaction force directed radially outwards, so as to maintain each leaf  22  supported by the matching rolling body  18 . 
     The profiles of the raceways  26  may equally be so arranged that the characteristic transmission curve of the torque according to the angular displacement α is symmetrical or not relative to the rest position. According to one embodiment shown here in the figures, the angular displacement α may be more important in a so-called forward or drive direction of rotation than in an opposite, so-called backward or coast direction of rotation. 
     The torque converter may also comprise friction element so arranged as to exert a resisting torque between the cover and the hub  8  during the relative displacement thereof so as to dissipate the energy stored in the elastic leaves. 
     The raceway  26  of each leaf  22  comprises a bearing area at rest  32  forming the bearing area of the rolling body  18  in the position of rest of the torque converter, with a forward or drive bearing area  33  forming the bearing area of the rolling body  18  when the cover pivots with respect to the hub  8  in a forward direction of rotation, with said drive bearing area  33  being located opposite the second curved or bent portion  30  with respect to the bearing area at rest  32 , and a backward or coast bearing area  34  forming the bearing area of the rolling body  18  when the cover pivots with respect to the hub  8  in a second so-called backward or coast direction of rotation, with said backward bearing area  34  being located on the second curved or bent portion  30  side with respect to the bearing area at rest  32 . 
     The drive bearing area  33  angularly extends over a range from 10 to 100° for example of the order of 90°, from the area  32 . The coast bearing area  34  angularly extends over a range from 10 to 30° for example of the order of 25°, from the area  32 . 
     The median strand  28  comprises a portion  35  which substantially extends along an arc of circle (defined by the dotted lines in  FIG. 5 ). More particularly, the semi-circular portion  35  of the median strand  28  is substantially concentric with the semi-circular trajectory of the point of contact between the supporting member  18  and the raceway  26  of the external strand  25 . 
     The median strand  28  and/or the first curved or bent area  29  comprise at least an area having a smaller section than the external strand  25  and/or than the second curved or bent area  30 . 
     More particularly, the thickness, i.e. the axial dimension, of the elastic leaf  22 , is substantially constant, with the variation in section being obtained by varying the width L ( FIG. 5 ), i.e. by varying the radial dimension of the leaf  22  section. 
     The forward bearing area  33  comprises a straight or flat or still concave portion  36  (defined by dotted lines in  FIG. 5 ), located close to, or extending from the bearing area at rest  32 , with the rest of the raceway  26  being domed or convex. 
       FIG. 7  shows the characteristic curve of a torque transmitting device, i.e. the evolution of the torque M transmitted through the device, according to the angular shift or displacement α of the torque input element, as compared to the torque output element, in the forward direction, respectively:
         for a torque transmitting device of the prior art according to the one shown in  FIG. 1  and provided with two spring stages (curve C 1 ),   for a torque transmitting device similar to the one disclosed in the document FR 3 008 152 wherein each leaf only comprises an external strand forming the raceway and an internal strand (curve C 2 ),   for a torque transmitting device according to the invention, provided with a leaf comprising an external strand, a median strand, and an internal strand (curve C 2 ),       

     The α=0 position defines the rest position of the device. 
     It may be noted that the curve C 1  comprises a first linear portion  37  having a slope Ka (for the low values of the angular displacement C) and a second linear portion  38  having a higher slope Kb (for the high values of the angular shift a). Ka and Kb are the angular stiffness of the device, at the beginning and at the end of the angular travel respectively. As mentioned above, the break of slope between the first and second portions  36 ,  37  of the curve C 1  may generate vibrations and a significant hysteresis upon operation of the torque converter which might affect the quality of filtration obtained using the damping means. 
     It may also be noted that the curve C 2  is more gradual and shows no break of slope, with the torque quickly increasing, however, with the angular displacement α, which may affect the quality of the filtration obtained. 
     It may eventually be noted that the curve C 3  comprises an area  39  having a low, or even no, slope, with the torque increasing again with the angular displacement α in the area bearing reference number  40 . Such area  39  could be used in cylinder deactivation applications, for example. 
     Such area extends from a displacement α 1  ranging from 10 to 45°, for example of the order of 30°, and a displacement α 2  ranging from 30 to 65°, for example of the order of 50°. 
       FIG. 8  shows the evolution of maximum mechanical stresses σmax, typically tension stress, within each leaf  22 , in the case of a device of the prior art, according to the one disclosed in document FR 3 008 152 (curve C 4 ), and in the case of a device according to the invention (curve C 5 ). 
     It may be noted that the leaves  22  of the device according to the invention are subject to smaller stresses than in the case of the prior art, for the same angular displacement α, which makes it possible to increase the total displacement of the device while remaining within the limit of permissible constraints. 
     The filtration quality is thus substantially increased as compared to the devices of the prior art.