a part of power train 1 of a motor vehicle is depicted in fig1 . hydrodynamic torque converter 6 is disposed between drive unit 3 , in particular , of an internal combustion engine , from which a crankshaft and transmission 5 protrude . the crankshaft of internal combustion engine 3 , for instance , is non - rotatably connected with housing 10 of torque converter 6 , via a drive plate that is also designated as flex plate . housing 10 of torque converter 6 is rotatable about rotation axis 12 and is equipped with housing wall 14 near the drive and housing wall 15 far from the drive . on housing wall 14 near the drive , starter ring gear 17 is fixed with the help of connection plate 16 that extends radially outwards . housing wall 15 far from the drive is combined in a module with impeller 20 of hydrodynamic torque converter 6 . turbine wheel 21 is interposed between impeller 20 and housing wall 14 near the drive which is fixed on turbine wheel hub 22 with the help of rivet connection elements . turbine wheel hub 22 is rotatably disposed on an output shaft or input shaft 23 of transmission 5 . guide vane 24 is interposed in the usual manner between turbine wheel 21 and impeller 20 . between turbine wheel 21 and housing wall 14 near the drive , torque converter lockup clutch 26 with torsional vibration damper 27 is likewise disposed in the usual manner . torque converter lockup clutch 26 comprises piston 28 which is rotatably supported and is axially displaceable , radially outwardly on turbine wheel hub 22 . piston 28 features a friction surface radially outwards which is facing internal combustion engine 3 and is disposed opposite a further friction surface which is provided on the side facing away from internal combustion engine 3 on housing wall 14 near the drive . friction disk 29 is interposed between the two friction surfaces which are connected non - rotatably with clutch disk 30 . clutch disk 30 is coupled , in the usual manner , with damper flange 35 of torsional vibration damper 27 under interposition of energy storage elements 33 , particularly of bow springs . damper flange 35 is connected with damper hub 38 with the help of welded joint 36 in a form - closed manner . damper hub 38 is again connected radially inside , non - rotatably with one end of input shaft 23 of transmission 5 . to prestress torque converter lockup clutch 26 , piston 28 is coupled with a leaf spring 41 . coupling takes place in a required radial design space or coupling area between friction disk 29 of torque converter lockup clutch 26 and housing wall 14 . leaf spring 41 is attached to housing 10 of torque converter 6 . the effective friction surface of friction disk 29 is also disposed radially within leaf spring 41 or coupling area of leaf spring 41 with piston 28 . fig2 shows a longitudinal section of torque converter 6 according to the invention with coupling spring device 43 . in the following , differences from a known torque converter 6 are explained in accordance with fig1 , wherein same , similar and / or functionally similar components are provided with the same reference signs . piston 28 is connected with housing 10 on converter side , radially outside by means of coupling spring device 43 under axial prestress . housing 10 features drive - side cover 45 and converter - side cover 47 . in contrast to the illustration in accordance with fig1 , piston 28 is essentially disk - shaped and features a rim 49 . first rim 49 of piston 28 features first tooth system 51 . converter - side cover 47 of torque converter 6 is likewise essentially disk - shaped and features second rim 53 with second tooth system 55 . coupling spring device 43 meshes , in a form - closed manner , with first tooth system 51 of first rim 49 and with second tooth system 55 of second rim 53 . as a result , piston 28 is coupled non - rotatably with housing 10 of the torque converter . piston 28 is connected with housing 10 on the converter - side , radially outside by means of coupling spring device 43 under axial prestress . advantageously , friction disk 29 projects into the radial design space still required for coupling , according to the illustration of fig1 ; thus , it is also lengthened nearly up to housing wall 14 , through which a larger effective radius of torque converter lockup clutch 26 is advantageously obtained . the friction linings or friction surfaces of torque converter lockup clutch 26 are disposed adjacently to radial external housing wall 14 . this is possible , since coupling spring device 43 is disposed within the converter - side design space between piston 28 and turbine wheel 21 . fig3 shows a three dimensional exploded view of torque converter 6 depicted in fig2 obliquely from the front . it is apparent that coupling spring device 43 features drive synchronizer spring 57 . drive synchronizer spring 57 features v - shaped spring elements 59 on the opposite side . in the assembled state , spring elements 59 can be brought onto abutments 61 of the corresponding first and second tooth system 51 and 55 , respectively , and thus under prestress . by means of arrow 63 it is hinted that spring elements 59 of drive synchronizer springs 57 keep piston 28 under prestress via abutments 61 which act on friction surface 65 of drive - side cover 45 . fig4 shows a longitudinal section of a detail of torque converter 6 with a further coupling spring device 43 which features drive - side diaphragm spring 67 as well as converter - side diaphragm spring 69 . drive - side diaphragm spring 67 meshes with first tooth system 51 of first rim 49 . converter - side diaphragm spring 69 meshes with second tooth system 55 of second rim 53 of converter - side cover 47 . for non - rotatable coupling of piston 28 with housing 10 , diaphragm springs 67 and 69 moreover feature tooth system 71 respectively , through which diaphragm springs 67 and 69 can be coupled mutually non - rotatably . the torque flow occurs also , starting from second rim 53 via tooth systems 55 , 71 and 51 and finally to first rim 49 of piston 28 . fig5 shows a detail view of a further torque converter 6 with diaphragm spring ring 73 . diaphragm spring ring 73 features annular spring leaf 75 . spring leaf 75 of diaphragm spring rings 73 features bent sections 77 which realize tooth system 79 . for non - rotatable coupling of piston 28 with second rim 53 of converter - side cover 47 , tooth system 79 meshes with first tooth system 51 of first rim 49 of piston 28 . on the opposite side , spring leaf 75 features tooth system 81 which meshes with second tooth system 55 of converter - side cover 47 . thus , via a single component , namely diaphragm spring ring 73 , its spring leaf 75 and tooth systems 79 and 81 , non - rotatable coupling and prestress of piston 28 as well can occur advantageously . fig6 shows a further longitudinal section of a detail view of torque converter 6 with leaf spring 83 and disk - shaped catch 85 . disk - shaped catch 85 meshes with second tooth system 55 of the converter - side cover of housing 10 . catch 85 is non - rotatably attached to leaf spring 83 , wherein the attachment occurs via rivet 87 . leaf spring 83 is attached to piston 28 under prestress . fig7 shows a partially broken illustration , viewed in the alignment of fig6 , from the top with a partial auxiliary section and a partial section of carrier 85 of leaf spring 83 and of piston 28 as well . through the auxiliary section , rivet 87 is visible . the attachment of leaf spring 83 to piston 28 takes place likewise via rivet 89 . arrow 63 hints at the direction of force of leaf spring 83 necessary to prestress piston 28 . fig8 shows a further sectional illustration of a detail of torque converter 6 with leaf spring 83 . in contrast to the illustration according to fig6 and 7 , no catch 85 is provided according to fig8 . instead of carrier 85 , leaf spring 83 features bent fixing plate 91 . leaf spring 83 can be attached directly on drive - side cover 45 by means of fixing plate 91 and rivet 87 . fig9 shows a sectional illustration of leaf spring 83 , viewed in the alignment direction of fig8 , from the bottom onto fixing plate 91 , wherein the cutting plane runs through rivet 89 of leaf spring 83 with piston 28 . in fig9 , drive - side cover 45 and rivet 87 are not depicted . fixing plate 91 features two bores 93 , in which two rivets 87 can be fixed . fig1 shows a further longitudinal section of a detail view of torque converter 6 with diaphragm spring ring 95 and disk carrier 97 as well . fig1 and 12 show a plan view of diaphragm spring ring 95 and disk carrier 97 as well viewed from the direction of arrow a from fig1 . fig1 shows the diaphragm spring ring in the applied state within disk carrier 97 . fig1 shows diaphragm spring ring 95 after a partial rotary motion which is hinted by arrow 99 . in fig1 it is apparent that diaphragm spring ring 95 can be held analogously to the functioning manner of a bayonet closure , in a form - closed manner , within recess 101 of the disk carrier . to execute a rotation , as hinted by arrow 99 , the diaphragm spring ring must first be brought under prestress in the drawing plane of fig1 and 12 so that teeth 103 of tooth system 105 of diaphragm spring ring 95 can slide through recess 101 of disk carrier 97 . recess 101 is formed by cutouts 107 located opposite of disk carrier 97 . furthermore , a tooth system of disk carrier 97 is realized by cutouts 107 . tooth system 109 of disk carrier 97 serves on the one hand for bayonet - closure type of fixation of diaphragm spring ring 95 , as already described , and on the other hand for non - rotatable coupling of piston 28 with drive - side cover 45 of housing 10 . here , for instance , disk carrier 97 is non - rotatably attached to drive - side cover 45 by means of weld 111 . for axially relocatable , non - rotatable coupling of piston 28 , tooth system 109 of disk carrier 97 moreover meshes with tooth system 113 of piston 28 . for assembly , first piston 28 can be inserted inside drive - side cover 45 . afterwards , diaphragm spring ring 95 , as described above , can be mounted like a bayonet closure , so that it interlocks in disk carrier 97 . the diaphragm spring ring can rest on disk carrier 97 in order to generate the required prestress and at the same time it is secured against rotation . the direction of prestress force which acts through piston 28 corresponds to the direction of view as hinted by arrow a .