Abstract:
In a hydrodynamic torque converter having a turbine shell and a torsion damper spring carrier jointly mounted to a carrier part by way of rivets extending through aligned openings in the turbine shell and the spring carrier, rivets with rivet shanks and a rivet heads are inserted through the aligned openings and welded to the carrier part by pairs of electrodes by which the rivets are pressed into contact with the carrier part while a welding current is generated from one to the other of the pair of welding electrodes through the respective rivets and the carrier part.

Description:
[0001]    This is a Continuation-In-Part Application of pending International patent application PCT/EP2007/004366 filed May 16, 2007 and claiming the priority of German patent application 10 2006 028 771.1 filed Jun. 23, 2006. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a hydrodynamic torque converter with a turbine shell connected jointly with a torsion damper support structure to a carrier part which is supported rotatably relative to the transmission input shaft hub and to a method for manufacturing such a hydrodynamic torque converter. 
         [0003]    DE 19826351 C2 discloses a hydrodynamic torque converter with a torsion damper connected to a turbine shell. 
         [0004]    Hot-riveting methods using hot rivets having rivet heads for interconnecting a torsion damper to a turbine shell are already known in principle from US 2005/0161442 A1, GB 3 1 528 730 and DE 31 40 368 A1. 
         [0005]    It is the object of the present invention to provide a hydrodynamic torque converter and a method for manufacturing the same which makes it possible to attach the turbine shell of the torque converter after assembly of the torsion damper. 
       SUMMARY OF THE INVENTION 
       [0006]    In a hydrodynamic torque converter having a turbine shell and a torsion damper spring carrier jointly mounted to a carrier part by way of rivets extending through aligned openings in the turbine shell and the spring carrier, rivets with rivet shanks and a rivet heads are inserted through the aligned openings and welded to the carrier part by pairs of electrode by which the rivets are pressed into contact with the carrier part while a welding current flow is established from one to the other of the pair of welding electrodes through the respective rivets and the carrier part. 
         [0007]    It is an important advantage of the invention, that it makes it possible to completely assemble the torsion damper, and optionally to test it for correct operation, and then to connect the turbine of the torque converter non-rotatably to the torsion damper from one side by hot riveting. For this purpose, the head of the hot rivet is provided on the axial side of the turbine whereas the narrow shank of the hot rivet is passed through an opening of the turbine shell and welded to a carrier part of the torsion damper. As a result of this assembly from one side, the turbine can be fastened to the torsion damper after the assembly of the torsion damper. A pre-assembly of turbine and torsion damper can prove complex and costly if the turbine is produced at a different production site from the torsion damper. In that case the turbine and the torsion damper would first have to be brought together at one site for assembly, and possibly then have to be transported to another site for assembly to the housing. This problem is aggravated if the individual components are produced by different manufacturers—in particular OEMs (Original Equipment Manufacturers) and other suppliers. By contrast, delivery of all components to a particular site, where the largest components are produced, provides for the lowest production/assembly cost. 
         [0008]    With hot-riveting, a method as described in DE 102005006253.9-34, which is not a prior publication, is used especially advantageously. In addition to the advantage mentioned in the introduction, a further advantage of this method is that no deposits, which would be in the oil circuit of the hydrodynamic torque converter as soon as it was put into operation, is released. The oil circuit of the transmission, which usually has a common oil circuit with the hydrodynamic torque converter, is therefore kept clean. This is because, with hot-riveting, the deposits—i.e. the weld spatter—can be held back in a special catching area which may be in the form, for example, of an annular pocket or an inner end wall of a rivet hole. 
         [0009]    As compared to the non-rotatable connection using a spline toothing, for example, a connection by hot-riveting has the advantage that it is a rigid connection without tooth flank play, so that noises resulting from resonance oscillations cannot occur. 
         [0010]    The turbine shell can be hot-riveted directly to a sheet metal portion of the torsion damper, so that this sheet metal portion forms the carrier part mentioned. However, for reasons of weight and dynamics, a turbine is made of very thin sheet metal, which in turn makes a connection by the hot-riveting method problematic. For this reason a separate carrier, which may be configured, in particular, as an annular carrier, may be provided. In this case and the hot rivets are welded to the carrier. The sheet metal of the torsion damper and the thin turbine shell are therefore clamped between the carrier and the head of the hot rivet. 
         [0011]    The carrier can be made sufficiently thick and stiff for it to absorb the forces required for welding and riveting. Furthermore, the carrier may have a centering function for the turbine and/or can function as a spring carrier of the torsion damper. In order to receive deposits, this carrier may include a blind hole. Because the carrier can be produced, in particular, as a turned part, an annular groove may also be provided for the circumferentially distributed hot rivets. The depth of the annular groove advantageously determines the length of the hot rivets. Thus, an especially long rivet may be provided, the shrinkage of which upon cooling is correspondingly high, so that a high tensile stress is also achieved. This high tensile stress provides for an especially good connection. 
         [0012]    Especially advantageously, an embossment may be provided between the sheet metal parts to be connected by means of hot rivets, that is, the sheet metal of the torsion damper and of the turbine shell. Such an embossment forms an element preventing rotation between the sheet metal parts prior to riveting. This embossment may be provided, in particular, in the region of the hot rivets. 
         [0013]    A support of the carrier part on the transmission input shaft hub  4  advantageously ensures proper axial positioning of the torsion damper with respect to the transmission input shaft hub by the carrier part. 
         [0014]    Indirect welding of at least two rivets simultaneously ensures that the main current does not flow via reciprocally movable parts, so that secondary welding and/or surface damage cannot occur on those parts. Welding with at least two welding electrodes distributed uniformly over the circumference provide security against tilting. 
         [0015]    The invention will become more readily apparent from the following description of exemplary embodiments thereof on the basis of the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  shows a hydrodynamic torque converter  1  in a half-section with a torque converter turbine wheel mounted by hot rivets, 
           [0017]      FIG. 2  to  FIG. 4  show, in a detail of the hydrodynamic torque converter according to  FIG. 1 , a production method for the connection by hot riveting of the turbine shell, 
           [0018]      FIG. 5  shows a hot rivet with a conical geometry in an alternative configuration, 
           [0019]      FIG. 6  shows a clamping of a constructional unit of the hydrodynamic torque converter on a hot-riveting machine, and 
           [0020]      FIG. 7  and  FIG. 8  show, analogously to  FIG. 2  to  FIG. 4 , the process steps for hot-riveting such an alternative hot rivet. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0021]      FIG. 1  shows a hydrodynamic torque converter  1  in a half-section. This hydrodynamic torque converter  1  is connected on the input side by a screw connection to a partially flexible drive plate (not shown in detail) and to a crankshaft of a drive engine. Two alternative possibilities for the screw connection are illustrated in the drawing. 
         [0022]    On the output side, the hydrodynamic torque converter  1  is connected via a spline toothing  52  to a coaxially arranged transmission input shaft (not shown in detail) of a transmission. The transmission input shaft, the hydrodynamic torque converter  1  and a crankshaft flange are arranged coaxially with a central axis  25 . 
         [0023]    The hydrodynamic torque converter  1  comprises the housing  50 , a pump shell  35 , a turbine  37  and a stator  38 . The following detailed description of an exemplary embodiment follows the power flow from the crankshaft to the housing  50 . From the housing  50  the power flow passes to the pump shell  35 . With hydrodynamic power transmission the power flow is transmitted from this pump shell  35  to the turbine  37  and, via a torsion damper  17 , to the transmission input shaft mentioned. By contrast, with a lock-up clutch  18  engaged, the power flow is transmitted from the housing  50  via the lock-up clutch  18  to the torsion damper  17  and then to the transmission input shaft. 
         [0024]    The turbine  37  is arranged beside the pump shell  35  on the side of the latter oriented towards the drive engine. The stator  38 , which is supported in the conventional manner on a freewheel  39 , is arranged radially inside and axially between the pump shell  35  and the turbine  37 . 
         [0025]    An inner hub  40  of the freewheel  39  is connected non-rotatably to a stator shaft (not shown in detail) by means of an internal toothing. 
         [0026]    The turbine  37  has in its radially inner region a plurality of circular openings  5   a,  which can be seen in more detail in  FIG. 2  to  FIG. 4 , distributed evenly on the circumference. Hot rivets  7 , comprising a head  15  and a shank  13 , are inserted in these openings  5   a  from the side of the turbine  37 . The hot rivets  7  clamp a spring carrier  44  against an annular carrier  43 . The establishment of this connection is explained in more detail below in  FIG. 2  to  FIG. 4 . The spring carrier  44  is arranged with limited rotatability against the torsional stiffness of the torsion damper  17  with respect to a sheet metal support  46 . For this purpose, curved coil springs  47 ,  14  of the torsion damper  17  are received in recesses worked into the sheet metal of 
         [0027]    the sheet-metal support  46 , 
         [0028]    the spring carrier  44  and 
         [0029]    a sheet-metal coupling element  53  riveted non-rotatably to the spring carrier  44 . 
         [0030]    The sheet-metal support  46  is provided, radially outside the curved springs  47 ,  14  in the circumferential direction, with curved attachment pieces  49  which guide the bow springs  14 . The sheet-metal support  46  is connected non-rotatably by its radially inner portion to a transmission input shaft hub  51 . This transmission input shaft hub  51  is connected non-rotatably to the transmission input shaft by means of the spline toothing  52  mentioned previously. The carrier  43  is supported radially and axially on the transmission input shaft hub  51  by means of a slide bearing. A lubricant channel  70  is provided for lubricating the axial pairing of slide surfaces. This lubricant channel  70  opens into a lubricant channel  71  which is provided for lubricating the radial pairing of sliding surfaces. At the same time the lubricant channel  70  ensures the lubricant circulation of the converter cooling circuit. The carrier part  43  is supported axially on an axial securing ring  73  via an axial roller bearing  72 . The axial securing ring  73  is in turn supported axially on an outer race  74 —i.e. clamping ring—of the freewheel  39 . 
         [0031]    The sheet-metal coupling element  53  is connected immovably to an inner disk carrier  54 . The inner disk carrier  54  secures inner clutch disks of the lock-up clutch  18  by means of an axial toothing. These clutch disks are displaceable non-rotatably and axially with respect to the inner disk carrier  54 . Likewise, outer clutch disks are secured non-rotatably and axially displaceably to an outer disk carrier  57  rigidly connected to the housing  50 . For this purpose, an axially-oriented internal toothing, in which an external toothing of the outer clutch disks engages, is worked into the outer disk carrier  57 . The outer disk carrier  57  extends coaxially to the housing  50  and is friction-welded immovably thereto. The outer and inner clutch disks engage in one another radially. The inner clutch disks  55  have friction linings which are fastened firmly to a base body on both sides. These friction linings are located on both sides of the outer clutch disks and on one side of the front clutch disk and on a bracing disk  63 . A friction moment is transmitted by the contact surfaces. A piston  64  is provided in order to disengage and engage the lock-up clutch  18 . 
         [0032]    In the production process described below with reference to  FIG. 2  to  FIG. 4 , a pressure is applied to the hot rivet  7  from the side of the transmission—that is, from the right in the drawing plane—in order to weld the hot rivet  7  to the annular carrier  43  and then to upset the hot rivet  7 . For this purpose, as shown in  FIG. 6 , an assembly unit  100  is first assembled, comprising 
         [0033]    the inner disk carrier  54 , 
         [0034]    the torsion damper  17 , 
         [0035]    the annular carrier  43  and 
         [0036]    the transmission input shaft hub  51 . 
         [0037]    The transmission input shaft hub  51  is placed in a receptacle  101  of a machine and the turbine wheel or shell  37  together with the hot rivets  7  is placed in the constructional unit  100 . The hot-riveting process, as illustrated in detail with reference to a single hot rivet in  FIG. 2  to  FIG. 4 , is then carried out by means of at least two electrodes  102   a,    102   b  distributed uniformly on the circumference. The forces for pressing in the hot rivets  7  are taken up by the receptacle  101  via the carrier  43  and the transmission input shaft hub  51 . As indicated by the arrows in  FIG. 9 , welding is carried out indirectly. In this case the welding current flows through one electrode  102   a  into another electrode  102   b.  The main current therefore flows relatively directly via the hot rivets  7 , the carrier  43  and the transmission input shaft hub  51 . This ensures that parts in contact with one another—but movable with respect to one another—are not welded together or do not adhere to one another, and the surfaces of these components are protected. 
         [0038]      FIG. 2  to  FIG. 4  show, in a detail of the hydrodynamic torque converter  1  according to  FIG. 1 , the method for producing the joint in the region of the hot rivet  7 . As compared to  FIG. 1 , the detail is shown rotated through 90°. 
         [0039]      FIG. 2  shows the turbine wheel  37  and the spring carrier  44  which are to be fastened to the annular carrier  43  (not shown in  FIG. 2 ). The turbine wheel  37  and the spring carrier  44  have circular through-openings  5   a,    5   b.  The hot rivet  7  with the shank  13  and the head  15  is also shown. The openings  5   a,    5   b  have a larger diameter than the shank  13 , so that in the assembly position the hot rivet  7  has play with respect to the openings  5   a,    5   b.  In this exemplary embodiment the end face  9  of the hot rivet  7  oriented away from the head  15  is configured with a tip  16 . The hot rivet  7  consists, for example, of a steel with a low carbon content, in order to ensure high toughness. The opening  5   b  in the spring carrier  44  is provided on the side thereof oriented away from the head  15  with a step which enlarges the opening  5   b  on this side in the catching area  23 . The function of this catching area  23  is described below. In this exemplary embodiment the catching area  23  is cylindrical and can be described as an annular pocket. However, the catching area  23  may also have a different geometry. 
         [0040]      FIG. 3  shows additionally the annular carrier  43  to which the turbine  37  and the spring carrier  44  are to be fastened non-detachably by means of the hot rivet  7 . For this purpose, the hot rivet is first inserted in the openings  5   a,    5   b  with the aid of a welding electrode (not shown here), to which the head  15  of the hot rivet  7  is connected firmly but detachably. This connection of the head  15  to the welding electrode is produced, for example, by a vacuum. Alternatively, the head  15  may be connected to the welding electrode by mechanical clamping. Alternatively, the hot rivet may already be fitted in the opening  5   a  or  5   b,  so that the position of turbine  37  with respect to spring carrier  44  is defined. 
         [0041]    The end face  9  of the hot rivet  7  is then welded to the surface  10  of the carrier  43 . This is done here by a resistance welding process, for example. All electric welding methods are, however, suitable. As the resistance welding process, a projection welding process, in particular, is used here. For this purpose the end face  9  of the hot rivet  7  is formed appropriately as the tip  16 . The welding is effected by an electrical welding pulse. In this exemplary embodiment the pulse has a length in the order of magnitude of 30-60 milliseconds, a usual value when resistance-welding the end faces of hot rivets  7 .  FIG. 3  also shows the welding zone  30  now produced. An arc stud welding process, for example, is an alternative to electric resistance welding. It is, however, less suitable here, since the arc would jump to the other side with this method, which is undesirable. 
         [0042]      FIG. 4  shows the non-detachable connection of the carrier  43  to the turbine  37  and the spring carrier  44  after the next and last process step has been carried out. In this step the hot rivet  7  is deformed plastically. This plastic deformation is produced by applying a second electrical pulse which follows the first welding pulse after a short time interval. This second pulse has a lower current strength and is significantly longer than the first welding pulse. It may last, for example, 1000 milliseconds. The hot rivet  7  is heated and softened by the second pulse. 
         [0043]    At the same time a force which leads to a plastic deformation in the form of an upsetting of the shank  13  of the hot rivet  7  is exerted in the longitudinal direction  8  of the hot rivet  7 . The upsetting force may have the same value as the welding force, or may be lower or higher than the welding force. This upsetting movement is carried out until at least a portion of the underside  12  of the head  15  of the hot rivet  7  rests against the surface  11  of the turbine  37 . The material of the shank  13  forced to the sides during upsetting now completely fills the openings  5   a,    5   b  zonally in the circumferential direction. The weld spatter produced during welding of the end face  9  of the hot rivet  7  to the surface  10  of the carrier part  43 , as well as material displaced in this catching area during upsetting, is received in the catching area  23  of the opening  5   b,  so that a clean, smooth contact surface is present both 
         [0044]    between the carrier  43  and the spring carrier  44 , and 
         [0045]    between the spring carrier  44  and the turbine  37 . 
         [0000]    The weld spatter cannot therefore enter the oil circuit of the hydrodynamic torque converter, or possibly of the transmission, as scale loss. 
         [0046]    An electric welding circuit is established via two rivets as shown in  FIG. 6  by the two electrodes ( 102   a,    102   b ) so that welding current flows via one electrode ( 102   a ) through one rivet into the carrier  43  and through the carrier  43  and the other rivet to the other electrode ( 102   b ). 
         [0047]    Because, according to this method, a welded connection is produced only between the hot rivet  7  and the carrier  43 , it is possible to fasten the spring carrier  44  and the turbine  37 , which do not need to be weldable, to the carrier  43 . For example, the spring carrier  44  and the turbine  37  may be components made of aluminum, surface-coated steel—in particular nitrated steel—ceramics or plastics, in particular fiber-reinforced plastics—as well as composites of such components. Only the hot rivet  7  and the carrier part  43  must be made of a weldable material. 
         [0048]    Furthermore, by virtue of the fact that the hot rivet  7  has clearance with respect to the bore  5  prior to the implementation of the method, the end face  9  of the hot rivet  7  can be welded to the carrier  43  without a short circuit even when connecting electrically conductive materials for the carrier  43 , since the welding current is conducted only through the hot rivet  7  itself. In all cases the high electrical resistance needed for welding occurs between the end face  9  of the hot rivet  7  and the surface  10  of the carrier  43 . 
         [0049]    After implementation of the method, the hot rivet  7  shrinks because of the preceding thermal reshaping. In this way, additional clamping of the joint is obtained, resulting in high strength of the connection. 
         [0050]    Furthermore, the welding and subsequent plastic deformation take place in one work cycle on a standard welding press, without the requirement for additional retooling or resetting. 
         [0051]    Hardening of the weld zone  30  possibly occurring after the welding is reduced by the subsequent heating in connection with the plastic deformation. 
         [0052]    Apart from the cylindrical geometry of the opening  5   b  described above, it is possible to provide a conical geometry, as represented in  FIG. 5 . A conical opening is simpler to produce than a cylindrical one when using a casting as the spring carrier  44  or the turbine  37 , for example. The diameter of the opening increases with increasing distance from the carrier  43 . The cone angle α may vary; in this example it is approximately α=25°. It can be seen that the material displaced during upsetting of the shank  13  presses against the wall of the openings in the spring carrier  44  and thus fills these openings almost completely. In addition, in this exemplary embodiment a peripheral sealing ring  27  is formed integrally on the underside  98  of the head  15  of the hot rivet  7 . After the upsetting process, the sealing ring  27  bears against the surface  11  of the spring carrier  44  and additionally seals the joint. Alternatively, a similar peripheral sealing ring which performs the same function may be provided on the surface  11  of the spring carrier  44 . 
         [0053]    For installation, the rivet is preferably attached to the welding electrode ( 102   a,    102   b ) for example, by vacuum. However, the rivet may also be attached to the welding electrode magnetically or mechanically. 
         [0054]    The openings in the turbine shell  37  may be punched or drilled. 
         [0055]    In  FIG. 2  to  FIG. 4  the openings  5   a,    5   b  are shown with an exaggerated diameter for greater clarity. In practice, the stud  13  has a very small clearance in the openings  5   a,    5   b,  so that centering for the subsequent welding is achieved. Given this small clearance, in order to create a receptacle for the material discharged between head and turbine during the riveting process, a configuration as shown in  FIG. 7  and  FIG. 8  may be provided. 
         [0056]      FIG. 7  and  FIG. 8  show a rivet  113  with an annular groove ( 105   a,    105   b ) on the underside of the head  107  in two process steps. This annular groove receives material discharged during riveting of the turbine  37 . With this configuration in conjunction with small radial play, a very high radial bracing force is produced between the stud  113  and the turbine  37  and the spring carrier  44 . It is noted that, in addition to providing a force-locking connection, shear forces can also be transmitted by the rivet  107 . 
         [0057]    The catching area  123  for receiving the weld spatter is configured differently in this case than as shown in  FIG. 2  to  FIG. 4 . Thus, the catching area  123  according to  FIG. 7  and  FIG. 8  is a depression in the annular carrier  143 . This depression may be in the form of a shallow blind hole. Because the carrier  143  is a turned part, however, the depression may also be in the form of an annular groove which is produced in one work cycle when turning the carrier  143 . 
         [0058]    The embodiments described are only exemplary configurations. A combination of the features described for different embodiments is also possible. Further features of the device parts, which form part of the invention, are apparent from the geometries of the device parts shown in the drawings.