Patent Publication Number: US-6991580-B2

Title: Toroidal variable-speed drive unit

Description:
This application claims the priority of German Patent Document No. 102 06 200.5, filed Feb. 15, 2002, the disclosure of which is expressly incorporated by reference herein. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention relates to a toroidal variable-speed drive unit. 
     DE 101 22 176 A1 discloses such a toroidal variable-speed drive unit. This toroidal variable-speed drive unit is arranged within the transmission case of a motor vehicle transmission and has two toroidal chambers, each with two rollers. The torque is transmitted in a continuously variable manner by means of these rollers. Each of the two rollers is 
     fastened to a supporting journal, 
     rotatable about its own axis of rotation, and 
     supported fixedly in terms of rotation with respect to a pivot axis of the supporting journal which is perpendicular to its own axis of rotation. 
     The two supporting journals form, in diagrammatic terms, the two lateral lines of a parallelogram. The upper and the lower line of the parallelogram are formed by two rockers, the central bearing receptacle of which is supported with respect to the transmission case. An axial force can be introduced into the supporting journals by means of actuating members, so that the angles of the parallelogram change. The angular movement of the parallelogram is in this case made technically possible in that the two rockers receive the supporting journals by means of articulated pivot bearings which allow a slight angular movement. 
     DE 199 47 851 A1 also discloses a toroidal variable-speed drive unit. 
     An object of the invention is to provide a cost-effective and nevertheless highly fail-safe toroidal variable-speed drive unit. 
     The high fail-safety is achieved advantageously in that, in addition to the “force synchronization,” typical of toroidal transmissions, which constantly holds all the rollers in the correct pivot-angle position during the operation of the toroidal variable-speed drive unit, “path synchronization” ensures operation. In this “path synchronization,” according to the invention, the supporting journals are received only with one side in a rocker. By contrast, on their other side, the supporting journals are supported with respect to the transmission case or to a component connected firmly to the transmission case. 
     This “rocker-free” support of the supporting journals in a bearing receptacle which is fixed in terms of movement with respect to the transmission case is advantageously particularly cost-effective. Thus, the articulated ends of the supporting journals can be received directly in bearing bores or plain-bearing bushes in the transmission case. This is accompanied by the advantages of a reduction in the diversity of parts. 
     Furthermore, a supporting plate connected fixedly in terms of movement to the transmission case may be provided for receiving the bearing bores or plain-bearing bushes. As a result, in a particularly advantageous way, the transmission case may consist of light, but also soft light metal, whilst the high forces occurring when the toroidal variable high-speed drive unit is in operation are supported in the supporting plate made from steel or cast iron. 
     Additionally, an embodiment of the invention allows an optimum functioning of the toroidal variable high-speed drive unit, in that the friction to be overcome in order to pivot the supporting journal about its own pivot axis is kept low by means of a rolling bearing. In a particularly advantageous way, the coefficient of friction between a convex rolling-bearing outer ring of this rolling bearing and a linear plain bearing may be designed in such a way that, in the case of an unchanged transmission ratio of the toroidal variable high-speed drive unit, the static-friction limit is not exceeded over a period of time, so that there are also no translational axial fluctuations of the supporting journal. By contrast, when a transmission ratio adjustment of the toroidal variable-speed drive unit, that is to say an axial displacement of the supporting journal, is specifically initiated, the static friction is exceeded and, because of the low sliding friction in the linear plain bearing, scarcely any wear occurs. 
     In an embodiment of the invention, in addition to “force synchronization” and to “path synchronization,” what may be referred to as “angle synchronization” ensures to a particular extent that the rollers of the toroidal variable-speed drive unit are in the correct pivot-angle position in relation to one another. This “angle synchronization” ensures the correct pivot-angle position of the rollers in relation to one another even when the toroidal variable-speed drive unit is not in operation and the rollers are nevertheless shaken about. This situation arises, for example, when the motor vehicle is towed away or is transported on a railway wagon. 
     In general, one advantage of power-split motor vehicle transmissions with a toroidal variable-speed drive unit is that, as a result of the use of a power path with a constant step-up, the toroidal variable-speed drive unit is relieved within wide operating ranges. This relief is advantageous particularly in the case of high-torque engines, in which the power take-off torque of the engine is markedly above the maximum permissible input torque of the toroidal variable-speed drive unit and therefore a reduction in the torque of the variable-speed drive unit solely by the preselection of a step-up stage into high speed would not be sufficient. The said high-torque engines are conventionally installed longitudinally in drive trains. 
     Moreover, along with the corresponding design of the motor vehicle transmission, the relief of the toroidal variable-speed drive unit gives rise advantageously to an improvement in the overall efficiency of the motor vehicle transmission in the corresponding driving range, since the power in the power path having a constant step-up can be transmitted with higher efficiency than in that having a continuously variable step-up. 
     A further advantage of the relief of the toroidal variable-speed drive unit is that the pressure forces at the driving/driven discs can thereby be lowered, thus leading to a lowering of the frictional losses. As a result of the reduction in the frictional losses, less heat also has to be discharged. 
     Furthermore, by the toroidal variable-speed drive unit being relieved, its useful life can be increased in an advantageous way. 
     One advantage of apportioning the transmission step-up to at least two driving ranges is that the spread of the motor vehicle transmission is increased. 
     Transmission spreads which are greater than the spread of the toroidal variable-speed drive unit thus become possible. 
     Both driving ranges can advantageously be implemented in the power-split mode, in order to increase the efficiency. 
     By means of a geared-neutral function, there is advantageously no need for a starting element, such as, for example, a hydrodynamic torque converter. The implementation of a geared-neutral mode makes it possible to have operation in which the driving states forward travel, reverse travel and standstill can be achieved solely by the adjustment of the toroidal variable-speed drive unit. Furthermore, there is no need for a reversing unit, such as, for example, a turning set with associated clutches or brakes, which likewise has an advantageous effect on weight, construction space and costs. 
     The motor vehicle transmission is used in a particularly advantageous way in a drive train with a front engine and a rear-axle drive. Furthermore, the motor vehicle transmission is used in a particularly advantageous way in an all-wheel drive which emanates from a modified drive train with a front engine and with a rear-axle drive. Such a drive train is shown in DE 101 33 118.5 which has not already been published. 
     Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a diagrammatic axial section through a motor vehicle transmission which comprises a continuously variable toroidal transmission, an intermediate planetary transmission and a final planetary transmission; 
         FIG. 2  shows a detailed sectional illustration of a detail II of the transmission diagram from  FIG. 1 , this having, inter alia, webs extending outwards in a radiating manner; 
         FIG. 3  shows a section through one of the webs from  FIG. 2  in a detail; 
         FIG. 4  shows a basic diagrammatic section to explain the function of the rollers of the toroidal variable-speed drive unit according to  FIG. 1 ; 
         FIG. 5  shows, in a first alternative embodiment of a roller, the latter and its supporting journal in detail in a sectional illustration; and 
         FIG. 6  shows, in a second alternative embodiment of a roller, the latter and its supporting journal in detail in a sectional illustration. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a diagrammatic axial section through a motor vehicle transmission which comprises a continuously variable toroidal variable-speed drive unit  7 , an intermediate planetary transmission  8  and a final planetary transmission  9 . 
     The motor vehicle transmission is used in a drive train with a front engine and with a rear-axle drive. The motor vehicle transmission is thus arranged in the force flux between the front engine, not illustrated in any more detail, and a rear-axle transmission, by means of which rear drive shafts and consequently driving wheels are driven. The front engine is coupled to an input shaft  5  of the motor vehicle transmission and the rear-axle transmission is connected fixedly in terms of rotation by means of a cardan shaft to an output shaft  6  for the motor vehicle transmission. 
     By means of a friction clutch K 3  arranged at the rear end of the motor vehicle transmission, the input shaft  5  can be coupled frictionally to the output shaft  6 , so that a direct drive-through from the engine to the rear-axle transmission can be effected. 
     The input shaft  5  is mounted at its two end regions, by means of two rolling bearings  135  and  136 , rotatably with respect to a non-rotating case part  26  of the motor vehicle transmission. In this case, the two rolling bearings  135  and  136  are designed as a fixed-bearing/loose-bearing pairing. The input shaft  5  is connected fixedly in terms of movement to an adjacent first toroidal central driving disc  11  of the toroidal variable-speed drive unit  7  and, via the coaxial central input shaft  5 , to a double-web planet carrier  18  of the intermediate transmission  8 . This planet carrier  18  is connected fixedly in terms of rotation to the second central toroidal driving disc  12 , arranged adjacently to the latter, of the toroidal variable-speed drive unit  7 . The two driving discs  11  and  12  are thus connected in parallel in the force flux or fixedly in terms of rotation relative to one another. A concentric intermediate shaft  14  which is arranged coaxially to the input shaft  5  and through which the latter passes with play is constructed fixedly in terms of rotation with an axially central driven disc  10 . This driven disc  10  has worked into it, on its sides facing axially away from one another, the two concave toroidal driven surfaces  16  and  17 . The driven disc  10  is connected fixedly in terms of movement to an inner central wheel  19  of the intermediate transmission  8 . 
     A driving disc  11  or  12  is in frictional contact with its associated driven surface  16  or  17  via two planets, which are known as rollers  13   a ,  13   b  or  15   a ,  15   b . In each case two rollers  13   a ,  13   b  or  15   a ,  15   b  are assigned to one of two toroidal chambers  93 ,  94 . As explained in more detail further below with regard to  FIG. 4 , the rollers  13   a ,  13   b  or  15   a ,  15   b  are in each case both rotatable about their own axis of rotation  95   a ,  95   b  or  96   a ,  96   b  and pivotable about a pivot axis perpendicular to their own axis of rotation  95   a ,  95   b.    
     The inner central wheel  19  of the intermediate transmission  8  has a drive connection  20  to an inner central wheel  21  as a first transmission member of the final transmission  9 . 
     This drive connection  20  contains main planets  46  mounted on one web of the planet carrier  18  of the intermediate transmission  8  and having toothed rims  43   a ,  43   b  which are arranged on both sides of a radial drive web of the planet carrier  18  and of which one toothed rim  43   a  meshes with the inner central wheel  19  connected to the concentric intermediate shaft  14  and the other toothed rim  43   b  meshes with a second inner central wheel  48  which is arranged axially on the other side of the radial drive web and which finally, in turn, has a drive connection  51 , containing an engageable and disengageable clutch K 2 , to the inner central wheel  21  forming the first transmission member of the final transmission  9 . 
     The toothed rim  43   a  of the main planet  46 , the said toothed rim meshing with the one inner central wheel  19  of the intermediate transmission  8 , is additionally in meshing engagement with a secondary planet  63  which is mounted on the second web of the planet carrier  18  and, in turn, meshes with an outer central wheel  22  which is connected fixedly in terms of rotation via a pot-shaped drive connection  23  to one clutch half of an engageable and disengageable friction clutch K 1 . A second clutch half of this friction clutch K 1  is connected fixedly in terms of rotation to an outer central wheel  24  forming a second transmission member of the final transmission  9 . 
     The final transmission  9  has a third transmission member in the form of a planet carrier  25  which is connected fixedly in terms of rotation to the non-rotating case part  26  of the motor vehicle transmission by means of a radial supporting web  36  and which supports planet wheels  34   a ,  34   b  with two toothed rims  37   a ,  37   b  having the same number of teeth, which are arranged on both sides of the supporting web  36  and of which one toothed rim  37   a  adjacent to the intermediate transmission  8  meshes both with the inner and with the outer gearwheel  21  and  24 . 
     The final transmission  9  has a fourth transmission member in the form of a second outer central wheel  27  which meshes with the other toothed rim  37   b  of the planet wheels  34   b  and which has a drive connection  28  to the output shaft  6 . 
     A parking-lock wheel  33  is arranged concentrically and fixedly in terms of movement on the outer circumference of the outer central wheel  27 . 
     In the lower driving range, in forward travel the clutch K 1  is engaged and the clutch K 2  disengaged, so that the power is split at the intermediate transmission  8 , a first part of the power flowing to the power take-off shaft  6  and a second part of the power flowing via the toroidal variable-speed drive unit  7  into the drive shaft  5 . 
       FIG. 2  shows a detailed sectional illustration of a detail II of the transmission diagram from  FIG. 1 , although the rollers  13   b ,  15   b  from  FIG. 1  are not illustrated. 
     The input shaft  5  has a first axial region  54 , in which the toroidal variable-speed drive unit  7  or the driving and driven discs  10 ,  11 ,  12  are also located. This first axial region  54  is designed as a solid shaft, with the result that its diameter is very small. This first axial region  54  is followed by a second axial region  34 , in which a first wheel-set plane of the intermediate transmission  8  also lies, the said wheel-set plane comprising, inter alia, 
     the inner central wheel  19 , 
     the toothed rim  43   a , and 
     the secondary planet  63 . 
     Two oil ducts  56   a ,  56   b  are drilled obliquely into the solid shaft in this second axial region  34 . These oil ducts  56   a ,  56   b  issue, on the one hand, into an annular space  58  and, on the other hand, into a central bore  57  of the input shaft  5 , the said central bore lying essentially in a third axial region  55 . The two oil ducts  56   a ,  56   b  thus make a flow connection between the central bore  57  which is under oil pressure and the annular space  58  which lies essentially in the first axial region  54 . Whilst the radially inner wall of the annular space  58  is formed by the input shaft  5 , the radially outer delimitation of the annular space  58  is formed by the concentric intermediate shaft  14  designed as a hollow shaft. Orifices for the outflow of lubricating oil from the annular space  58  lie at bearing points which are designed as the following rolling bearings:
     a) a first needle bearing  50  for the rotatable support of the driven disc  10  with respect to the input shaft  5 ,   b) a single-row grooved ball bearing  60  for the axial and radial mounting of the intermediate shaft  14  with respect to a case part  62  of the motor vehicle transmission,   c) a second needle bearing  61  for the rotatable support of the second central toroidal driving disc  12  with respect to the intermediate shaft  14 , and   d) a third needle bearing  85  for the radial support of the central wheel  19  with respect to the input shaft  5  in the second region  34 .   

     a) to c) are explained in more detail below. 
     a) The first needle bearing  50  comprises rolling bodies which are arranged within a cage  64  and roll on the input shaft  5  in a region in which the latter is designed as a solid shaft. The cage  64  is inserted into a central bore of the driven disc  10  and bears axially, on the one hand, against an end face  65  of one end  70  of the intermediate shaft  14 . On the other hand, the cage  64  bears axially against an axial securing ring  66  which is inserted into an inner groove at one axial end of the driven disc  10 . At the other axial end of the driven disc  10 , the latter is screwed to an externally threaded sleeve  68 , of which the radially outward-projecting end collar bears axially against an end face of the driven disc  10 . Axially between the first needle bearing  50  and the externally threaded sleeve  68 , the driven disc  10  is connected fixedly in terms of rotation to the intermediate shaft  14  by means of a splined-shaft toothing  67 . In this case, a slight axial play is allowed between the cage  64  and the end face  65  or between the externally threaded sleeve  68  and an external toothing  69 , associated with the splined-shaft toothing  67 , of the input shaft  5 . 
     The lubrication of the large needle bearing  50  takes place by means of lubricating oil which emerges, past a sealing ring  190  functioning as a virtual throttle, from the annular space  58  at the end  70  of the intermediate shaft  14 . 
     b) The grooved ball bearing  60  has a bearing outer ring which is secured in the axial direction with respect to the case part  62 , on the one hand, at a step  71  and, on the other hand, at an axial securing ring  72  which is inserted into an inner groove of the case part  62 . 
     In a similar way, a bearing inner ring of the grooved ball bearing  60  is secured in the axial direction with respect to the intermediate shaft  14 , on the one hand, at a step  73  and, on the other hand, at an axial securing ring  74  which is inserted into a circumferential groove of the intermediate shaft  14 . 
     The lubrication of the grooved ball bearing  60  takes place by means of lubricating oil which emerges from the annular space  58  through an oblique bore  75  in the intermediate shaft  14 . This bore  75  is arranged axially next to the grooved ball bearing  60  and is directed towards the rolling body of the latter. 
     c) The second needle bearing  61  comprising rolling bodies which are arranged within a cage  76  and roll on the intermediate shaft  14 . The cage  76  is pressed into a central bore of the driven disc  12  and bears axially against an end face  77  of a bore bottom of this central bore. 
     An oblique bore  79 , which supplies the second needle bearing  61  with lubricating oil, is drilled into the intermediate shaft  14  radially within the driven disc  12  and axially next to the second needle bearing  61 . 
     As a consequence of the system, the driven disc  12  is fixed in terms of rotation and axially prestressed with respect to a planet-carrier bolt receptacle  80  of the planet carrier  18  by means of an axial toothing  82  and a cup spring  81 . 
     The annular space  58  is sealed off, on its side facing the intermediate transmission  8 , by means of a sealing ring  83  which is inserted into a concentric bore of the central wheel  19  produced in one part with the intermediate shaft  14  and which functions as a virtual throttle in that the sealing ring  83  allows a defined leakage. The sealing ring  83  is secured by means of a cage  84  of the third needle bearing  85 . The sealing ring  83  bears with its inside against the input shaft  5  axially next to the two oil ducts  56   a ,  56   b  and allows the defined leakage throughflow for the supply of lubricant to the third needle bearing  85 , whilst maintaining a lubricant pressure in the annular space  58 . 
     A planet-carrier arm  86  extends radially outwards in the third region  55  axially next to the central wheel  19 . This planet-carrier arm  86  has webs  87  which extend outwards in a radiating manner and which are interrupted circumferentially by recesses  88 . The main planets  46  pass through these recesses  88 , so that the toothed rims  43   a ,  43   b  are adjacent to the planet-carrier arm  86  on both sides. 
       FIG. 3  shows, in a detail, a section through one of the webs  87  extending outwards in a radiating manner. The webs  87  are designed identically, and therefore only one of the three webs  87  distributed uniformly on the circumference is explained below. 
     The web  87  has, radially on the outside, a bore  89  which is oriented parallel to a central axis  52 , also evident in  FIG. 1  and  FIG. 2 , of the motor vehicle transmission and into which a planet-carrier bolt  90  of the secondary planet  63  is inserted with a press fit. This press fit is located centrally on the planet-carrier bolt  90 , so that the latter projects axially with an end region  91  facing the toroidal variable-speed drive unit  7  and with an end region  92  facing away from the latter. The planet-carrier bolt  90  has on the end region  92  facing away, radially on the inside, a long hole which issues into a central concentric blind-hole bore. This blind-hole bore is closed at its access orifice by means of a ball. At the bottom of the blind-hole bore, the said bottom being located in the other end region  91 , there is, in the planet-carrier bolt  90 , a transverse bore which makes a flow connection from the blind-hole bore to a needle mounting of the secondary planet  63 . 
     Arranged radially inwards from the planet-carrier bolt  90  is the second inner central wheel  48  which meshes with the toothed rim  43   b  not evident in the drawing plane of  FIG. 3 . This central wheel  48 , which rotates during driving, throws radially outwards, as a result of the centrifugal force, lubricating oil of which a fraction passes through 
     the long hole, 
     the blind-hole bore and 
     the transverse bore 
     to the needle mounting of the secondary planet  63 , so that the said needle mounting is always lubricated and cooled in a low-friction and fail-safe manner. 
       FIG. 4  shows a basic diagrammatic section through the rollers  13   a ,  13   b  of the first toroidal chamber  93  and the rollers  15   a ,  15   b  of the second toroidal chamber  94  of the toroidal variable-speed drive unit  7  according to  FIG. 1 . For the sake of greater clarity, the driving discs and driven disc are not illustrated. The basic diagrammatic section is illustrated in the actual installation position of the motor vehicle transmission, so that components lying below in the installation position are designated hereafter as being arranged “below” and components lying above in the installation position are designated hereafter as being arranged “above.” 
     Since the four rollers  13   a ,  13   b ,  15   a ,  15   b  of the two toroidal chambers  93 ,  94  are designed essentially identically and have identical functioning, the common features are first explained hereafter with reference to the rollers  13   a ,  13   b  of one toroidal chamber  93 . 
     The two rollers  13   a ,  13   b  are both rotatable about their own axis of rotation  95   a ,  95   b  and pivotable about a pivot axis  97   a ,  97   b  perpendicular to their own axis of rotation  95   a ,  95   b . For this purpose, each of the rollers  13   a ,  13   b  is mounted rotatably about its own axis of rotation  95   a ,  95   b  by means of two bearings  98   a  or  98   b  and  99   a  or  99   b  on an eccentric journal  100   a  or  100   b  which is arranged by means of a thrust-type needle bearing  101   a  or  101   b  so as to be slightly pivotable about a further pivot axis  102   a  or  102   b  arranged, offset, parallel to the axis of rotation  95   a  or  95   b . In this case, the eccentric journal  100   a  or  100   b  is received, mounted by rolling bearings, pivotably about this further pivot axis  102   a  or  102   b  in a supporting journal  103   a  or  103   b . This supporting journal  103   a  or  103   b  extends perpendicularly to the axis of rotation  95   a ,  95   b  or to the further pivot axis  102   a  or  102   b  and at its two ends  104   a ,  105   a  or  104   b ,  105   b  has rolling bearings with crowned bearing outer rings. These bearing outer rings or ends  104   a ,  105   a  or  104   b ,  105   b  are received, on the one hand, in bores  107   a  or  107   b  of a steel supporting plate  106  and, on the other hand, in bores  108   a  or  108   b  of a rocker  109 . Both the supporting plate  106  and a central rocker bearing  110  of the rocker  109  are connected fixedly in terms of movement to a light-metal transmission case  111  of the motor vehicle transmission. 
     The lower ends  108   a  and  108   b  of the supporting journals  103   a ,  103   b  are supported axially against pistons of hydraulic axial actuating members  112   a ,  112   b  which are arranged below the supporting journal  103   a ,  103   b . The cylinders of the hydraulic axial actuating members  112   a ,  112   b  are supported axially with respect to the said light-metal transmission case  111  in a way not illustrated in any more detail. Below the hydraulic axial actuating members  112   a ,  112   b  is arranged an electrohydraulic control plate, not illustrated in any more detail, of the motor vehicle transmission. This control plate has solenoid valves and control slides for controlling or regulating the clutches K 1 , K 2 , K 3  and the axial actuating members  112   a ,  112   b.    
     The torque transmission of the toroidal variable-speed drive unit  7  takes place by the rotation of the rollers  13   a ,  13   b  about their own axis of rotation  95   a ,  95   b . By contrast, the transmission ratio of the toroidal variable-speed drive unit  7  is adjusted by pivoting about the pivot axis  97   a ,  97   b.    
     Reference is made below, once again, to the two toroidal chambers  93  and  94 . 
     To initiate the abovementioned pivoting about the pivot axes  97   a ,  97   b ,  113   a ,  113   b , the axial actuating members  112   a  and  114   a  or  112   b  and  114   b  are acted upon by hydraulic pressure. At the same time, in each case, the pistons located on the same side are acted upon by pressure. During this action of pressure, all four rollers  13   a ,  15   a ,  13   b ,  15   b  pivot about their pivot axes  97   a ,  97   b  as a result of the forces acting at the rolling points between the rollers  13   a  and  15   a  or  13   b  and  15   b  and the driving/driven disc  10 ,  11 ,  12  of the toroidal variable-speed drive unit  7 , until a force equilibrium has been established again at the rollers  13   a ,  15   a ,  13   b ,  15   b  and axial actuating members  112   a ,  114   a ,  112   b ,  114   b . Thus, by means of the new pivot-angle position about the pivot axes  97   a ,  97   b ,  113   a ,  113   b , a new transmission ratio of the toroidal variable-speed drive unit  7  is set continuously and without any interruption in traction. 
     As a result of the identical hydraulic supporting forces and similar frictional forces and therefore similar forces in rolling contact, all four rollers  13   a ,  13   b ,  15   a ,  15   b  assume the same pivot-angle position in terms of amount with regard to their four pivot axes  97   a ,  97   b ,  113   a ,  113   b , their arrangement being symmetrical to one another. This orientation of the pivot-angle position of the rollers in relation to one another, which is achieved in this way, is designated as what may be referred to as “force synchronization.” 
     In the event of the abovementioned hydraulic pressure change at the two axial actuating members  112   a ,  114   a  or  112   b ,  114   b  of one side, the rocker  109  pivots, since the two supporting journals  103   a ,  116   a  or  103   b ,  116   b  are displaced axially with respect to their pivot axes  97   a ,  113   a  or  97   b ,  113   b , and, between their lower bearing outer rings and the rocker  109 , friction occurs in the region of their bores  108   a ,  118   a  or  108   b ,  118   b . As a result of the articulated crowned receptacle, the angle between the rocker  109  and the supporting journals  103   a ,  103   b ,  116   a ,  116   b  changes. Owing to these changed geometric conditions, all four rollers  13   a ,  13   b ,  15   a ,  15   b  have forced upon them a path leading to a pivot-angle position in which the rollers  13   a ,  13   b ,  15   a ,  15   b  are arranged symmetrically to one another. This second synchronization ensuring safety in addition to the “force synchronization” is designated as what may be referred to as “path synchronization.” 
     The toroidal variable-speed drive unit  7  has, in addition to these two synchronizations, a third synchronization which, even with the input shaft  5  at a standstill, ensures the abovementioned symmetrical arrangement of all the supporting journals  103   a ,  103   b ,  116   a ,  116   b  of the rollers  13   a ,  13   b ,  15   a ,  15   b  to one another. This synchronization, designated as what may be referred to as “angle synchronization,” takes place by means of four belts  119 ,  120 ,  121 ,  122  which connect to one another, on the one hand, the two supporting journals  103   a  and  103   b  or  116   a  and  116   b  belonging to a toroidal chamber  93  or  94  and, on the other hand, the two supporting journals  103   a  and  116   a  or  103   b  and  116   b  arranged on the respective side, that is to say on the right or on the left. The four belts  119 ,  120 ,  121 ,  122  are in this case each simply looped crosswise, in order to bring about a reversal of direction of rotation during the pivoting of the supporting journals  103   a ,  103   b ,  116   a ,  116   b . The four supporting journals  103   a ,  103   b ,  116   a ,  116   b  have, between their upper ends and their middle region in which the rollers  13   a ,  13   b ,  15   a ,  15   b  are arranged, two take-up discs  123 ,  124 ,  125 ,  126 ,  127 ,  128 ,  129 ,  130  arranged axially adjacently with respect to the pivot axes  97   a ,  97   b ,  113   a ,  113   b . The four belts  119 ,  120 ,  121 ,  122  are looped in each case around two of these take-up discs, the two belts  119 ,  120  associated with the individual toroidal chambers  93  and  94  being arranged in a lower plane, and the two belts  121 ,  122  connecting the supporting journals  103   a ,  103   b ,  116   a ,  116   b  of the two toroidal chambers  93  and  94  being arranged in an upper plane. 
       FIG. 5 , in a first alternative embodiment of a roller  1013   a , shows the latter in detail in a sectional illustration. 
     The roller  1013   a  is both rotatable about its own axis of rotation  1095   a  and pivotable about a pivot axis  1097   a  perpendicular to its own axis of rotation  1095   a . For this purpose, the roller  1013   a  is mounted by means of two bearings  1098   a  and  1099   a  rotatably about its own axis of rotation  1095   a  on an eccentric journal  1100   a  which, by means of a thrust-type needle bearing  1101   a , is arranged so as to be slightly pivotable about a further pivot axis  1102   a  arranged, offset, parallel to the axis of rotation  1095   a . In this case, the eccentric journal  1100   a  is received, mounted by rolling bearings, pivotably about this further pivot axis  1102   a  in a supporting journal  1103   a . This supporting journal  1103   a  is bulged out in a middle region. The roller  1013   a  is arranged in this middle region. The supporting journal  1103   a  extends essentially perpendicularly to the axis of rotation  1095   a  or to the further pivot axis  1102   a  and at its two ends  1104   a ,  1105   a  has needle bearings with bearing outer rings  1140 ,  1141  designed to be crowned on the outside. The upper bearing outer ring  1140  is received in a bore  1107   a  of a steel supporting plate  1106  and the lower bearing outer ring  1141  is received in a bore  1108   a  of a rocker  1109 . Both the supporting plate  1106  and a bearing receptacle, not illustrated in any more detail, of the rocker  1109  are connected fixedly in terms of movement to a light-metal transmission case, not illustrated in any more detail, of the motor vehicle transmission. 
     The supporting journal  1103   a  is provided, above the upper needle bearing, with a journal  1150  which is designed coaxially with the pivot axis  1097   a  and which is connected fixedly in terms of rotation and axially non-displaceably to a take-up disc  1151  by means of a splined-shaft toothing and a shaft securing ring. Looped around this take-up disc  1151  is a toothed belt  1153  which connects the supporting journal  1103   a  illustrated to a supporting journal, not evident in  FIG. 5 , of the same toroidal chamber. The belt  1153  is in this case simply looped crosswise, so that the supporting journal, not evident, of the same toroidal chamber always rotates in the opposite direction. 
     Between the lower needle bearing and the roller  1013   a , the supporting journal  1103   a  is produced in one part with a take-up disc  1154 . A belt  1155  is simply looped crosswise around this take-up disc  1154  and connects the supporting journal  1103   a  illustrated to a supporting journal, not evident in  FIG. 5 , of a second toroidal chamber, in such a way that the supporting journal of the second toroidal chamber always rotates in the opposite direction. 
     The supporting journal  1103   a  is provided, below the lower needle bearing, with a journal  1152  which is designed coaxially to the pivot axis  1097   a  and which is supported axially on a hydraulic axial actuating member not illustrated in any more detail. Below this hydraulic axial actuating member is arranged an electrohydraulic control plate, not illustrated in any more detail, for the control of the axial actuating member, of further axial actuating members and of clutches according to  FIG. 1 . 
       FIG. 6 , in a second alternative embodiment of a roller, shows the latter in detail in a sectional illustration. 
     The roller  2013   a  and the supporting journal  2103   a  are designed in broad parts in a similar way to the roller of the first alternative embodiment, and therefore only the essential differences are dealt with below. 
     Instead of a take-up disc arranged above an upper needle bearing, the supporting journal  2103   a  is produced, in a region between the upper needle bearing and the roller  2013   a , in one part with a take-up disc  2151 . Looped around this take-up disc  2151  is a belt  2153  which connects the supporting journal  2103   a  illustrated to a supporting journal, not evident in  FIG. 6 , of the same toroidal chamber. The belt  2153  is in this case simply looped crosswise, so that the supporting journal, not evident, of the same toroidal chamber always rotates in the opposite direction. 
     The bearings for mounting the supporting journal may also be designed as barrel-shaped bearings, in which case a crowned bearing outer ring is dispensed with and the barrel-shaped rolling bodies are arranged directly in the bores of the rocker and the bores of the supporting plate. 
     Furthermore, instead of the bores for receiving the bearing outer rings, linear bearings may be provided both in the supporting plate and in the rocker. 
     The take-up discs or the belts which connect the supporting journals to one another perform the function of an axial offset transmission. Consequently, for codirectional torque transmission with a transmission ratio of 1:1, the supporting journals may also be connected via an odd number of gearwheels, by means of toothed belts, by means of linkages or else by means of slotted guides. 
     Instead of the two oil ducts, any number of oil ducts offset circumferentially, at an angle or radially may be drilled into the solid shaft. If appropriate, a single oil duct may be sufficient. 
     Instead of the oblique bore, illustrated in  FIG. 1 , in the intermediate shaft for the supply of lubricating oil to the grooved ball bearing, a bore may also be provided which is oriented transversely to the central axis and which is directed towards an oil baffle of the grooved ball bearing. 
     Instead of the two sealing rings, illustrated in  FIG. 2 , which function as a virtual throttle, the intermediate shaft designed as a hollow shaft and the input shaft arranged within the latter may be provided with a fit. Then, instead of the sealing rings, the fit functions as a virtual throttle. 
     The illustrated clutches for selecting the driving range may be designed as a friction clutch, as a positive clutch, such as, for example, a claw clutch, or as a combined friction and positive clutch, such as, for example, a synchronizing device. 
     In particular, the clutch arranged at the rear end of the motor vehicle transmission may be designed, for the purpose of direct drive-through, as a friction clutch or as a positive clutch or, alternatively, as a combined positive and friction clutch. 
     The illustrated coaxial motor vehicle transmission with a continuously variable toroidal variable-speed drive unit and with a geared-neutral function is appropriate, furthermore, for all-wheel drive, such as is illustrated in DE 101 33 118.5. In this case, the transmission take-off shaft may be followed by a power divider for all-wheel drive. 
     Depending on the construction space available in the axial direction of the drive train, the motor vehicle transmission may have any number of driving ranges. In this case, one driving range may be designed as a direct gear, in which the engine rotational speed is conducted directly to the transmission take-off shaft, without any meshing engagement of gearwheels, so that particularly high efficiency is achieved. In particular, such a direct gear is appropriate in vehicles with a consumption characteristic diagram having a flat profile, that is to say with low consumption over a wide rotational speed range. 
     Further power-split driving ranges which have additional planet sets and clutches are appropriate. 
     The motor vehicle transmission may have an input step-up stage which, however, makes it possible to have selectively a step-up to high speed or to a low speed. 
     The parking-lock wheel shown in  FIG. 1  may be arranged in alternative embodiments at any desired point on the output shaft. 
     The embodiments described are merely exemplary embodiments. A combination of the features described for different embodiments is likewise possible. Further, in particular undescribed features of the device parts belonging to the invention may be gathered from the geometries, illustrated in the drawings, of the device parts. 
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.