Abstract:
A toroidal gearbox in which an annular central disc with a toroidal friction surface and an annular main cylinder of a hydraulic pressure device are located concentrically to a central shaft. A radial partition wall is provided between the central disc and the main cylinder to form two working pressure chambers, the pressurization of which results in axial displacement of the central disc relative to the central shaft to apply contact pressure forces on the friction surface. A pressure piston between the partition wall and the main cylinder having an axial projection effectively bypasses the partition wall and acts on the central disc, in addition to the pressure applied in the pressure chamber between the partition wall and the central disk, thereby achieving an even distribution of the operating force in the circumferential direction, as exerted on the central disc, by the pressure piston.

Description:
[0001]     This application is a national phase application of International application PCT/EP2004/012424 filed Nov. 3, 2004 and claims the priority of German application No. 103 52 174.7, filed Nov. 5, 2003, the disclosure of which are expressly incorporated by reference herein. 
     
    
     BACKGROUND AND SUMMARY OF THE INVENTION  
       [0002]     The present invention relates to a toroidal gearbox comprising a hydraulic pressure device.  
         [0003]     A toroidal gearbox is known from WO 02/053945 A1, in which the main cylinder—which, on its end face facing the central disk is actually open and at its opposite end is closed by a radial end wall—accommodates merely the significant pressure piston and thus has only the associated working pressure chamber. In this known toroidal gearbox, the structurally separate partition wall is supported from the outside in a motionally fixed manner against the open front face of the main cylinder in the axial direction pointing from the central disk to the end wall. This partition wall is inserted in a pressure-resistant and axially displaceable manner, virtually in a configuration as a direct pressure piston, into a central frontal recess in the central disk, which recess in this case forms the other working pressure chamber belonging to this direct pressure piston. The significant pressure piston is provided on its front face facing the partition wall with three axial projections, which are evenly spaced in the peripheral direction and which respectively pass in a positive-locking manner and under a pressure-resistant seal through an associated cylindrical through-hole in the partition wall, such that they are axially displaceable. When the significant pressure piston is pressurized, these projections, which are respectively configured in the style of a pressure pin of solid cross section, bear with their free end faces directly against the radial end wall of that frontal recess in the central disk which forms the cylinder of the direct pressure piston and thereby act mechanically upon the central disk, in addition to the direct hydraulic actuation thereof by the direct pressure piston. This type of force transfer is disadvantageous inasmuch as the transmission of the piston force of the significant pressure piston into the central disk takes place only at discrete locations and therefore, under high loads, a wave-shaped deformation of the central disk occurs. As a result, locally increased stresses upon the central disk are initiated. Furthermore, the time pattern of the transmission, as a result of the ensuing irregularities of the rolling motion of the planet-like, yet non-circling intermediate friction wheels can likewise exhibit an irregularity. The production of the pressure-pin-like projections, especially when configured in one piece with their associated significant pressure piston, is complex. Owing to the function-conditioned sealing of the projections, a high positional accuracy of the same to one another is necessary. Given all this, the production of the projections is expensive.  
         [0004]     The frontal engagement surface on the projection, of coaxial and annular configuration, of the significant pressure piston for the force transmission into the central disk can be configured to be broadly continuous, in particular fully continuous in the peripheral direction, so that an even force distribution in the peripheral direction is achieved. The pressure level which is necessary for a substantially slip -free pressing is low even at high torques, owing to the additional pressing function of the significant pressure piston.  
         [0005]     The production of the significant pressure piston, even when configured in one piece with its frontal projection for the actuation of the central disk, is simplified, inter alia because this projection is configured coaxially to the piston axis. Thus, the production costs of toroidal gearboxes are also kept low.  
         [0006]     In the toroidal gearbox according to an embodiment of the second invention, the drawback of the known toroidal gearbox of the generic type, (according to which the projection of the significant pressure piston is configured as an actuating means and enters into the non-associated working pressure chamber of the direct pressure piston) is avoided, so that the seals which, in the known toroidal gearbox, are necessary for this ventilation are omitted in the toroidal gearbox.  
         [0007]     In the toroidal gearbox according to another embodiment of the invention, a depressurization of the piston rear side of the annular significant pressure piston is facilitated by guiding of the coaxial projection of the piston in a pressure-resistant manner in the central opening in the partition wall, for the separation of atmospheric pressure and working pressure.  
         [0008]     In one embodiment of the toroidal gearbox according to the invention, the axial dimension of the pressure device is kept low by the significant pressure piston having a concentric cylindrical outer face, which is guided in a pressure-resistant and axially displaceable manner in a corresponding cylindrical innerface of the partition wall.  
         [0009]     In further advantageous embodiments of the toroidal gearbox according to the invention, the size of the effective piston cross section of the direct pressure piston can be optimized by a direct pressure piston which actuates the central disk and is guided directly against a corresponding inner shell of the main cylinder, or a direct pressure piston which cooperates via a ring seal in a peripheral groove against a corresponding inner shell, or which cooperates via a ring seal and groove in the corresponding inner shell of the main cylinder.  
         [0010]     In a further advantageous embodiment of the toroidal gearbox according to the invention, the pressure supply to the two working pressure chambers can be simplified with the procurement of an axial annular gap pressure which emerges at one end in the working chamber of the direct pressure piston and at the other end in the working pressure chamber of the significant pressure piston.  
         [0011]     In an advantageous development, the dimension of the effective piston surface of the significant pressure piston can be optimized for pressure-tight, displaceable fit against the cylindrical inner face of the main cylinder.  
         [0012]     In the known toroidal gearbox of the generic type, the central openings in all the annular components of the pressure device, such as main cylinder, significant pressure piston, partition wall with direct pressure piston and central disk with frontal recess as the working pressure chamber of the direct pressure piston, are respectively passed through, in a direct and pressure-resistant manner, by the central shaft, which in this case is the output shaft of the toroidal gearbox. The pressure device of this known toroidal gearbox cannot therefore form a preassemblable gearbox module, owing to the structurally separate assignment of its components to the central shaft.  
         [0013]     In embodiments of the toroidal gearbox according to the invention, the pressure device can be advantageously configured both with respect to its axial dimension and for the purpose of a preassemblable module, by the arrangement of a detachably inserted partition wall which can be axially supported against an axial counter-bearing of the main cylinder.  
         [0014]     As a counter-bearing for its support, in this arrangement of the partition wall, an innerface of the radial end wall of the main cylinder which delimits the working pressure chamber of the significant pressure chamber can be provided.  
         [0015]     In an advantageous alternative embodiment of the toroidal gearbox according to the invention, a hub of the main cylinder having a diameter offset and having a central opening for the main shaft can serve as the counter-bearing for the support of the partition wall detachably inserted in the main cylinder.  
         [0016]     Refinements of the toroidal gearbox according to the invention with respect to the support of the partition wall in the opposite axial direction, pointing from the end wall of the main cylinder to the central disk, against a locking ring inserted in a peripheral groove in the main cylinder and with respect to the guidance of the direct pressure piston, which directly actuates the central disk, with a cylindrical inner shell against a corresponding outer shell of the main cylinder, serve in particular also for the advantageous configuration of the pressure device as a preassemblable gearbox module.  
         [0017]     Further embodiments relate to advantageous features of a depressurization of the rear side of the significant pressure piston, focusing upon the use of a passive pressure chamber, ventilated to the atmosphere, and an advantageous specific development of a ventilation connection, communicating with this pressure chamber, in the toroidal gearbox.  
         [0018]     In the known toroidal gearbox of the generic type, the central disk is connected in a rotationally secure manner to the central shaft directly by corresponding axial drive toothings, the radially outer one of which is incorporated in the central opening in the central disk and the radially inner one of which is incorporated in the cylindrical outer casing of the central shaft. Owing to the, in relation to the external dimensions of the gearbox, very small effective radius on which torque is transferred from the central disk via the drive toothings to the central shaft, the surface pressings against the toothings are high and thereby conditioned consequential damage is considerable.  
         [0019]     In in the toroidal gearbox according to the invention, these aforementioned drawbacks are avoided by virtue of drive toothings which are disposed not in the region of the inner periphery, but in the region of the outer periphery of the central disk.  
         [0020]     Whereas, in the known toroidal gearbox of the generic type, the direct pressure piston is formed by a specific development of the partition wall, this pressure piston, in the toroidal gearbox according to the invention, can be arranged either structurally alone and motionally fixed relative to the central disk, or structurally integrated by virtue of configuring the direct pressure piston and the central disk in one piece.  
         [0021]     Since, in the known toroidal gearbox of the generic type, which is designed according to the 2-chamber principle, the two input-side central disks situated in the axially central gearbox region are drive-connected by an intervening offset gearbox in the form of a continuously variable transmission having an input shaft disposed parallel to the output shaft, in this gearbox the pressure supply unit for the pressure device, which latter is supplied via an inner, longitudinally running pressure duct of the central shaft, must be housed in a gearbox region situated axially outside the actual gearbox components, whereby the structural length of the total gearbox is naturally enlarged.  
         [0022]     In a toroidal gearbox according to another embodiment of the invention, the structural length of the total gearbox is not enlarged by the arrangement of the pressure supply unit, since the latter is housed in a central housing interior of the gearbox housing, which housing interior adjoins the toroidal friction surface of the central disk, and is connected to the inner pressure duct of the central shaft. This connection point can be configured as a stationary, in particular hydrodynamic shaft bearing for the radial support of the central shaft against the gearbox housing.  
         [0023]     In the toroidal gearbox according to the prior art forming the generic type, axially resilient means are used to generate a basic contact pressure against the toroidal friction surface of the central disk, which is configured in the form of a cup spring which is disposed in the working pressure chamber of the significant pressure piston and is supported directly against the end wall of the main cylinder and acts directly upon the significant pressure piston for the purpose of an actuation of the central disk.  
         [0024]     By contrast, the resilient elements for generating the basic contact pressure in the toroidal gearbox according to a further embodiment of the invention are supported, via the radial partition wall, indirectly against the main cylinder.  
         [0025]     In a development of the foregoing embodiment of the toroidal gearbox, the axial dimension of the pressure device can be shortened, for example, by the fact that the resilient elements for generating the basic contact pressure are inserted in the passive pressure chamber, which is provided between the significant pressure piston and the radial partition wall.  
         [0026]     In a further advantageous embodiment of the toroidal gearbox according to the invention, a particular support of the partition wall against the main cylinder in the axial direction pointing from the end wall of the main cylinder to the central disk can be omitted by virtue of the fact that the resilient elements for generating the basic contact pressure are disposed in the working pressure chamber of the direct pressure piston.  
         [0027]     In the known toroidal gearbox forming the generic type, a possible of an arrangement with resilient elements supported via the radial partition wall, indirectly against the main cylinder, in an embodiment with the resilient elements between the significant pressure piston, and the radial partition wall, would cause the resilient elements for generating the basic contact pressure to be supported, on the one hand, directly against the partition wall used as a direct pressure piston and, on the other hand, to act directly upon the central disk.  
         [0028]     In application of the foregoing resilient element arrangements in a toroidal gearbox according to the invention, the resilient elements for generating the basic contact pressure act upon the central disk indirectly via the direct pressure piston.  
         [0029]     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 for example. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]      FIG. 1  illustrates a partial longitudinal section through a first embodiment of a toroidal gearbox according to the present invention, in which also an embodiment of a pressure supply to the pressure device of the toroidal gearbox is employed,  
         [0031]      FIG. 1   a  illustrates a partial longitudinal section through a second embodiment of a toroidal gearbox according to the present invention, in which also an arrangement of resilient elements for generating a basic contact pressure against a toroidal friction surface of a central disk of the toroidal gearbox is employed, and  
         [0032]      FIG. 2  illustrates a partial longitudinal section through another embodiment of a toroidal gearbox according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0033]     With reference initially to the first embodiment of the first invention in  FIG. 1 , on a central shaft  31  of a toroidal gearbox (which in this embodiment forms the input shaft drivable by a drive unit) there are concentrically disposed an annular main cylinder  4  of U-shaped cross section of a hydraulic pressure device  10 , and an annular central disk  32  having a toroidal friction surface  63 . The main cylinder  4  has, for its mounting on the central shaft  31 , a hub  34  configured in one piece therewith, which hub is connected in a rotationally secure manner to the central shaft  31  by corresponding axial drive toothings  42 ,  43 .  
         [0034]     In the main cylinder  4  there is detachably inserted a radial partition wall  5 , which, in the axial direction pointing from the central disk  32  to the radial end wall  16  of the main cylinder  4 , is supported against the inner face  47  of this end wall  16  and, in the opposite axial direction, is supported against a locking ring  21  inserted in a peripheral groove  20  made in the cylindrical inner shell  44  of the main cylinder  4 .  
         [0035]     On that side of the partition wall  5  facing the central disk  32 , an annular pressure piston  8  is provided, which, with the partition wall  5 , encloses an associated working pressure chamber  6  and is configured in one piece with the central disk  32 —in the axial direction pointing from the end wall  16  to the partition wall  5 , thus directly actuates this central disk  32 , arranged in an axially displaceable manner relative to the central shaft  31 , so that contact pressures can be brought to bear upon the toroidal friction surface  63 . The direct pressure piston  8  is guided with its cylindrical outer shell  35  against the inner shell  44  of the main cylinder  4  and with its cylindrical inner shell  37  against a corresponding outer shell  38  of the hub  34 , respectively in a pressure-resistant and axially displaceable manner.  
         [0036]     On that side of the partition wall  5  facing away from the central disk  32 , a significant annular pressure piston  9  is provided, which, with the end wall  16 , encloses an associated working pressure chamber  7  and, with its cylindrical outer shell  14 , is guided in a pressure-resistant and axially displaceable manner against a corresponding inner shell  15  of the partition wall  5 . On its radially inner peripheral region, the significant pressure piston  9  has a coaxial annular projection  11 , which passes through the central opening  13  in the partition wall  5  and, when pressurized, comes to bear with its free end face against the direct pressure piston  8  and thus additionally actuates the central disk  32 .  
         [0037]     The working pressure chambers  6  and  7  are connected by communicating pressure ducts  45  and  46  in the hub  34  and by radial pressure ducts  48  of the central shaft  31  to a longitudinally running inner pressure duct  25  of the central shaft  31 . The projection  11  of the significant pressure piston  9  can have on its free end face a recess  49  or a few such recesses in order to ensure a constantly open connection between the working pressure chamber  6  and the pressure ducts  45 ,  46 .  
         [0038]     In order to create a passive pressure chamber  22  for the depressurization of the piston rear side of the significant pressure piston  9 , the projection  11  is guided with its cylindrical outer casing  12 , in a pressure-resistant manner, against the corresponding inner casing of the central opening  13 , and the pressure chamber  22  is connected by a ventilation connection  39  to a ventilated region, situated outside the main cylinder  4 , of a housing interior of the gearbox housing. This ventilation connection  39  contains an annular duct  40 , which is created by a bevel on the outer periphery of the partition wall  5  in the region of the end wall  16  and is sealed by ring seals against the working pressure chambers  6  and  7 . The annular duct  40  is connected by a ventilation duct  29  of the partition wall  5  to the pressure chamber  22  and by a ventilation port  23 , provided in the adjacent wall portion  24  of the cylindrical outer wall  19  of the main cylinder  4 , to said ventilated region of a housing interior.  
         [0039]     For the indirect rotationally secure connection to the central shaft  31 , the central disk  32  has on its outer periphery an axial drive toothing  17 , which engages in a rotationally secure manner in a corresponding axial drive toothing  18  on the free end face of the outer wall  19  of the main cylinder  4 .  
         [0040]     Between the central disk  32  and the central shaft  31 , a linear rolling element guide  50  can be inserted, which, in this embodiment, is fixed in the axial direction pointing from the central disk  32  to the end wall  16  by the hub  34  and in the opposite axial direction by a locking ring inserted in an inner peripheral groove in the central disk  32 .  
         [0041]     The main cylinder  4  can be rigidly supported against the central shaft  31 , in the axial direction pointing from the central disk  32  to the end wall  16 , by an axial counter-bearing, in a manner which is not further represented.  
         [0042]     In that region of the housing interior of the gearbox housing which adjoins the toroidal friction surface  63  there is disposed a bearing arm  51 , which is Notionally fixed relative to the gearbox housing and which holds at its one end a bearing sleeve  52 , surrounding the central shaft  31 , of a hydrodynamic bearing, by which the central shaft  31  is radially supported against the gearbox housing.  
         [0043]     Integrated in the bearing arm  51  is a pressure line  26 , which, in dependence on a connected pressure control unit of the toroidal gearbox, can be subjected to an, in particular, torque-dependent and transmission-dependent working pressure. By means of the bearing sleeve  52 , the line end  27  of the pressure line  26  is brought into overlap with a peripheral groove  53  in the central shaft  31 , which, for its part, is connected by at least one radial connecting bore  54  to the pressure duct  25  of the central shaft  31 , so that the working pressure chambers  6  and  7  are connected to the pressure line  26 .  
         [0044]     In the toroidal gearbox in the second embodiment of the invention in figure la, on a central shaft  31   a  of a toroidal gearbox (which in this embodiment, too, forms the input shaft drivable by a drive unit) there are concentrically disposed an annular main cylinder  4   a  of U-shaped cross section of a hydraulic pressure device, and an annular central disk  32   a  having a toroidal friction surface  63   a . The main cylinder  4   a  has, for its mounting on the central shaft  31   a , a hub  34   a  configured in one piece therewith, which hub is connected in a motionally fixed manner to the central shaft  31   a.    
         [0045]     In the main cylinder  4   a  there is detachably inserted a radial partition wall  5   a , which, in the axial direction pointing from the central disk  32   a  to the radial end wall  16   a  of the main cylinder  4   a , is supported against the inner face  47   a  of this end wall  16   a.    
         [0046]     On that side of the partition wall  5   a  facing the central disk  32   a , an annular pressure piston  8   a  is provided, which, with the partition wall  5   a , encloses an associated working pressure chamber  6   a  and is configured in one piece with the central disk  32   a —in the axial direction pointing from the end wall  16   a  to the partition wall  5   a , thus directly actuates this central disk  32   a , arranged in an axially displaceable manner relative to the central shaft  31   a , so that contact pressures can be brought to bear upon the toroidal friction surface  63   a . The direct pressure piston  8   a  is guided with its cylindrical outer shell  35   a  against the inner shell  44   a  of the main cylinder  4   a  and with its cylindrical inner shell  37   a  against a corresponding outer shell  38   a  of the hub  34   a , respectively in a pressure-resistant and axially displaceable manner.  
         [0047]     On that side of the partition wall  5   a  facing away from the central disk  32   a , a significant annular pressure piston  9   a  is provided, which, with the end wall  16   a , encloses an associated working pressure chamber  7   a  and, with its cylindrical outer shell  14   a , is guided in a pressure-resistant and axially displaceable manner against a corresponding inner shell  15   a  of the partition wall  5   a . On its radially inner peripheral region, the significant pressure piston  9   a  has a coaxial annular projection  11   a , which passes through the central opening  13   a  in the partition wall  5   a  and, when pressurized, comes to bear with its free end face against the direct pressure piston  8   a  and thus additionally actuates the central disk  32   a.    
         [0048]     The working pressure chambers  6   a  and  7   a  are connected one to another by an open axial annular gap between the projection  11   a  and the hub  34   a  and to a longitudinally running inner pressure duct  25   a  of the central shaft  31   a  by radial pressure ducts  46   a  in the hub  34   a , and by communicating radial pressure ducts  48   a  of the central shaft  31   a.    
         [0049]     The projection  11   a  of the significant pressure piston  9   a  can have on its free end face a recess or a few such recesses in order to ensure a constantly open connection between the working pressure chamber  6   a  and the pressure ducts  46   a.    
         [0050]     In order to create a passive pressure chamber  22   a  for the depressurization of the piston rear side of the significant pressure piston  9   a , the projection  11   a  is guided with its cylindrical outer casing, in a pressure-resistant manner, against the corresponding inner casing of the central opening  13   a , and the pressure chamber  22   a  is connected by a ventilation connection  39   a  to a ventilated region, situated outside the main cylinder  4   a , of a housing interior of the gearbox housing. This ventilation connection  39   a  contains an annular duct  40   a , which is created by a narrowed offset on the outer periphery of the partition wall  5   a  in the region of the end wall  16   a  and is sealed by ring seals against the working pressure chambers  6   a  and  7   a . The annular duct  40   a  is connected by a ventilation duct  29   a  of the partition wall  5   a  to the pressure chamber  22   a  and by a ventilation port  23   a , provided in the adjacent wall portion  24   a  of the cylindrical outer wall  19   a  of the main cylinder  4   a , to said ventilated region of a housing interior.  
         [0051]     For the indirect rotationally secure connection to the central shaft  31   a , the central disk  32   a  has on its outer periphery an axial drive toothing  17   a , which engages in a rotationally secure manner in a corresponding axial drive toothing  18   a  on the free end face of the outer wall  19   a  of the main cylinder  4   a.    
         [0052]     As in the first embodiment of  FIG. 1 , a linear rolling element guide (not represented here) can be inserted between the central disk  32   a  and the central shaft  31   a.    
         [0053]     The main cylinder  4   a  can be rigidly supported against the central shaft  31   a , in the axial direction pointing from the central disk  32   a  to the end wall  16   a , by an axial counter-bearing, in a manner which is likewise not further represented.  
         [0054]     Provided in the working pressure chamber  6   a  is a cup spring  61   a  for generating a basic contact pressure against the toroidal friction surface  63   a , which, in the axial direction pointing from the central disk  32   a  to the end wall  16   a , is supported with its radially inner marginal region against the partition wall  5   a  and, in the opposite direction, acts with its radially outer marginal region, via the direct pressure piston  8   a , upon the central disk  32   a.    
         [0055]     In this way, the advantage is additionally achieved that the partition wall  5   a  does not continue to have to be separately supported against the main cylinder  4   a —for example by means of a locking ring—in the axial direction pointing from the end wall  16   a  to the central disk  32   a.    
         [0056]     The omission of an inner peripheral groove in the main cylinder for a locking ring allows the external diameter of the significant pressure piston  9   a , and thus the effective pressure surface thereof, to be enlarged compared to the first embodiment of  FIG. 1 .  
         [0057]     This is also abetted by the radially outward shifted arrangement of the seal acting between the corresponding cylindrical surfaces  35   a  and  44   a  of the direct pressure piston  8   a  and the main cylinder  4   a , which seal is inserted in an inner peripheral groove in the outer wall  19   a.    
         [0058]     Since the working pressure chambers  6   a  and  7   a  are openly connected to each other by the axial annular gap between the projection  11   a  and the hub  34   a , it is sufficient for the supply of pressure, for example in the manner envisaged in the first embodiment of  FIG. 1  via a pressure line  26  connected to the central pressure duct  25   a  of the central shaft  31   a , to connect only one of these two working pressure chambers—via radial bores  46   a  in the hub  34   a —to the pressure duct  25   a . Hence, a special seal between the projection  11   a  of the significant pressure piston  9   a  and the hub  34   a  of the main cylinder  4   a  is unnecessary.  
         [0059]     With reference now to a further embodiment of the toroidal gear according to the invention, in  FIG. 2  on a central shaft  31   b  of the toroidal gearbox (which constitutes the input shaft) there are once again concentrically disposed an annular main cylinder  4   b  of U-shaped cross section of a hydraulic pressure device  10   b , and an annular central disk  32   b  having a toroidal friction surface  63   b.    
         [0060]     The main cylinder  4   b  can be rigidly supported against the central shaft  31   b , in the axial direction pointing from the central disk  32   b  to the radial end wall  16   b  of the main cylinder  4   b , by a locking ring  56  inserted in a peripheral groove  55   b  in the central shaft  31   b.    
         [0061]     The main cylinder  4   b  is connected to the central shaft  31   b  in a rotationally secure manner, via its radially inner hub  34   b  the central opening  33   b  of which is passed through in a positive-locking manner by the central shaft  31   b , by corresponding axial drive toothings  42   b ,  43   b.    
         [0062]     For the indirect rotationally secure connection to the central shaft  31   b , the central disk  32   b  has on its outer periphery an axial drive toothing  17   b , which engages in a rotationally secure manner in a corresponding drive toothing  18   b  in the cylindrical outer wall  19   b  of the main cylinder  4   b.    
         [0063]     In the main cylinder  4   b  there is inserted a radial partition wall  5   b , which, in the axial direction pointing from the central disk  32   b  to the radial end wall  16   b  of the main cylinder  4   b , is supported against an axial counter-bearing in the form of a diameter offset  47   b  of the hub  34   b  of the main cylinder  4   b . The partition wall  5   b  is supported, in the opposite axial direction, against a locking ring  21   b  inserted in a peripheral groove  20   b  in the hub  34   b.    
         [0064]     The central disk  32   b  is configured in one piece with a direct pressure piston  8   b , which is thus situated on that side of the partition wall  5   b  facing the central disk  32   b  and acts directly upon the central disk  32   b.    
         [0065]     The partition wall  5   b , which is sealed in a pressure-resistant manner against the hub  34   b , has on its radially outer region a cylinder  30   b , which, together with the hub  34   b  and the direct pressure piston  8   b , encloses a working pressure chamber  6   b  belonging to the latter. In this case, the direct pressure piston  8   b  is guided with an outer cylindrical piston surface  35   b  against the corresponding inner face  36   b  of the cylinder  30   b  and with an inner cylindrical piston surface  37   b  against a corresponding outer narrow hub surface  38   b  of the hub  34   b , respectively in a pressure-resistant and axially displaceable manner.  
         [0066]     The main cylinder  4   b  has an annular significant pressure piston  9   b  disposed between its end wall  16   b  and the partition wall  5   b , which with its outer cylindrical piston surface  57   b  is guided against the corresponding inner face  44   b  of the main cylinder  4   b  and with its inner cylindrical piston surface  58   b  is guided against the corresponding outer wide hub surface  59   b  of the hub  34   b , respectively in a pressure-resistant and axially displaceable manner.  
         [0067]     In this way, the significant pressure piston  9   b  and the end wall  16   b  of the main cylinder  4   b  enclose a working pressure chamber  7   b  belonging to this pressure piston.  
         [0068]     The working pressure chambers  6   b  and  7   b  are connected by a respective pressure duct  46   b  and  45   b , and herewith communicating further pressure ducts in the hub  34   b  of the main cylinder  4   b , to a peripheral groove  60   b  in the central shaft  31   b , which communicates by at least one radial bore  48   b  with a longitudinally running inner pressure duct  25   b  of the central shaft  31   b . The pressure duct  25   b  can be subjected, for example in the manner described in connection with the toroidal gearbox of  FIG. 1 , to an, in particular, torque-dependent and transmission-dependent working pressure.  
         [0069]     On its front face facing the partition wall  5   b , the significant pressure piston  9   b  has a coaxial annular projection  11   b , which is configured for the actuation of the central disk  32   b  and is disposed in the annular space  40   b  enclosed by the cylindrical wall  19   b  of the main cylinder  4   b  and the cylinder  30   b  of the partition wall  5   b  and which, when pressurized, comes to bear with its free end face against the central disk  32   b.    
         [0070]     In order to relieve the piston rear side of the pressure piston  9   b , this pressure piston and the partition wall  5   b  enclose a passive pressure chamber  22   b , which is connected by a ventilation connection  39   b  to a ventilated region of a housing interior of the gearbox housing.  
         [0071]     The ventilation connection  39   b  contains a ventilation duct in the form of a longitudinal groove  29   b  in the outer casing  41   b  of the cylinder  30   b , which longitudinal groove, on the one hand, emerges in the pressure chamber  22   b  and, on the other hand, communicates via a ventilation passage  28   b  in the projection  11   b  of the significant pressure piston  9   b  with a ventilation connection  23   b , which is provided in that wall portion  24   b  of the cylinder wall  19   b  enclosing the annular space  40   b  and which is openly connected to the ventilated region of the housing interior.  
         [0072]     In place of the longitudinal groove  29   b , an axial bore may also be provided in the wall portion  30   b.    
         [0073]     Finally, in this toroidal gearbox also, between the central shaft  31   b  and the central shaft  32   b  it is possible to insert a linear rolling element guide  50   b , which, in this embodiment, is fixed in the axial direction pointing from the central disk  32   b  to the end wall  16   b  by the hub  34   b  and in the opposite axial direction by a locking ring inserted in an inner peripheral groove in the central shaft  31   b.    
         [0074]     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.