Abstract:
What is proposed is a variator disk for a toroidal variator, in particular for a motor vehicle toroidal transmission. The variator disk has a curved running surface which is oriented coaxially with respect to a variator axis and on which rollers of the toroidal variator can roll. The variator disk having furthermore at least two partial disks which are designed as a traction disk, on which the running surface is formed, and as a supporting disk, respectively. The supporting disk is designed for supporting axial forces applied to the running surface. The traction disk is supported on the supporting disk in the radial direction to the variator axis.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of PCT/EP2004/007417, filed on Jul. 7, 2004. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a variator disk for a toroidal variator and to a variator of this type which is suitable for a motor vehicle toroidal transmission. 
   2. Description of the Related Art 
   In the field of transmissions for motor vehicles, there is a trend toward continuously variable transmissions. Continuously variable transmissions make it possible, in general, to operate the series connected internal combustion engine in motor vehicles within a favorable rotational speed range independently of the respective motor vehicle speed. This improves the efficiency of the drive train formed by the internal combustion engine and by the continuously variable transmission. Furthermore, continuously variable transmissions afford a particularly high degree of driving comfort. 
   Among continuously variable transmissions, toroidal transmissions, as they are known, are especially important, specifically, in particular, owing to their higher torque capacity, as compared with belt type continuously variable transmissions (CVTs). 
   Among toroidal transmissions, the Torotrak™ system has particular significance (cf. www.torotrak.com). 
   A typical toroidal transmission of this type has a variator arrangement with two variators. Each variator has two variator disks. The disks have annular traction or running surfaces facing one another which in each case define a toroidal space. The toroidal spaces are arranged coaxially with respect to a variator axis. Within the toroidal spaces, rollers are in each case arranged, which come into engagement with the variator disks in order to transfer a torque from one variator disk to the other variator disk. The rollers are arranged so as to be distributed over the circumference of the toroidal space and can be adjusted spatially within the toroidal space, in order to adjust the transmission ratio of the variator continuously. 
   In the prior art, the variator disks are connected to an assigned variator shaft, as a rule via toothings in the hub region. 
   Furthermore the variator disks known hitherto are supported axially on the variator shaft via a collar. This collar is small in comparison with the diameter of the variator disks. This gives rise to a high bending moment. High stresses are generated within the component as a result of the bending moment. These can be absorbed only by means of a high-mass type of construction. 
   The high-mass type of construction of the variator disks leads to a high weight, to a high mass moment of inertia and to an enlargement of the overall construction length of the transmission. The high mass moment of inertia reduces the dynamics of the vehicle. Due to the high weight, high material costs are incurred, since the disks are produced as a rule, from high-quality material. 
   The high axial pressure forces, particularly also during an adjustment of the rollers, result in a high load on the variator disks in the vicinity of the toothing. This may lead to excessive stresses and consequently cause failure. 
   The manufacture of the toothings is cost-intensive, particularly since the material of the known variator disks is, as a rule, a high-strength rolling bearing steel. 
   So that the high axial forces can be absorbed more effectively, one variator disk may be assigned a supporting disk which is arranged on that side of the variator disk which lies opposite the running surface. By virtue of the supporting disk, it is possible to produce the variator disk with a lower mass and lower weight. Costs are thereby saved. In other words, in this embodiment, the variator disk is formed by at least two partial disks which are designed as a traction disk, on which the running surface is formed, and as a supporting disk, respectively. The supporting disk is designed for supporting axial forces applied to the running surface. 
   Furthermore, as a rule, the supporting disk is connected to the shaft positively in the circumferential direction. This may take place via a toothing. However, the supporting disk may also be produced in one piece with the shaft. 
   Although it is conceivable, even when a supporting disk is used, to connect the traction disk to the shaft via a toothing in the hub region, it is nevertheless preferable to cause the transfer of torque from the traction disk to the shaft to take place via the supporting disk. 
   This may take place in general by means of nonpositive or frictional connection. This is because the high axial pressure forces can be utilized for torque transfer if the axial bearing surfaces on the supporting disk, on the one hand, and on the traction disk, on the other hand, are suitably designed. In this case, the coefficient of friction of steel/steel is utilized in the bearing region. 
   However, the transfer of the torque from the traction disk to the supporting disk may also take place positively. In this case, it is conceivable, in general, to connect the traction disk positively in the hub region of the supporting disk. In order to reduce the circumferential forces, however, it is more beneficial to implement the torque transfer in the region of the outer circumference of the supporting disk or of the traction disk. 
   In this case, it is likewise conceivable, in general, to provide a toothing in the circumferential region. It is considered more favorable, however, to insert positive elements, such as, for example, balls, into corresponding radial recesses of the supporting disk, on the one hand, and of the traction disk, on the other hand. 
   These approaches have in common the fact that excessive stresses due to the notch effect may occur in the region of positive connection of the traction disk and supporting disk. 
   The object of the present invention is to specify an improved variator disk, in particular a variator disk which possesses a low weight and requires a small construction space. 
   SUMMARY OF THE INVENTION 
   This object is achieved with a variator disk for a toroidal variator, in particular for a motor vehicle toroidal transmission, the variator disk having a curved running or traction surface which is oriented coaxially with respect to a variator axis and on which rollers of the toroidal variator can roll, the variator disk having furthermore at least two partial disks which are designed as a traction disk, on which the running surface is formed, and as a supporting disk, respectively, the supporting disk being designed for supporting axial forces applied to the running surface, and, furthermore, the traction disk being supported on the supporting disk in the radial direction to the variator axis. 
   The above object is achieved furthermore by a variator for a toroidal transmission, having two variator disks, between which is arranged a toroidal space in which at least one roller is mounted rotatably, in order to transfer torque from one variator disk to the other with a variable transmission ratio, at least one variator disk being designed in the same way as the above-defined variator disk according to the invention. 
   As a result of the radial support, the variator disk can, overall, be stabilized significantly. A reduction in the variator mass, in the mass moments of inertia and in deformation can be achieved. Furthermore it is possible to reduce the necessary variator disk thickness. This leads to a reduction in the overall length of the variator. 
   It is of particular advantage if the traction disk is supported on a circumferential portion of the supporting disk. 
   It is of particular advantage, in this case, if the running surface defines one side of a toroidal space, the center circle of which possesses a toroidal center radius, and the radius of the circumferential portion of the supporting disk being larger than or equal to the toroidal center radius. 
   As a result of this comparatively large radial bearing diameter, an enlargement of the supporting base is obtained. Furthermore, a reduction in the disk thickness, in the mass moment of inertia and in the weight is achieved. 
   It is of particular advantage if the radius of the circumferential portion of the supporting disk is equal to the toroidal center radius. 
   It was shown that precisely this dimensioning puts the advantages according to the invention to particularly good effect. 
   According to a further preferred embodiment, an axial bearing portion of the supporting disk, said axial bearing portion serving at least for supporting the axial forces introduced into the traction disk, adjoins the circumferential portion via a flattened or rounded annular edge, the annular edge of the supporting disk not touching a corresponding annular edge of the variator disk. 
   Notch stresses in the transitional region of the axial bearing portion and circumferential portion are thereby avoided. 
   According to a further preferred embodiment, the traction disk is centered on the supporting disk. In this embodiment, the traction disk is not centered on the shaft and, as a rule, does not touch the latter. Static overdetermination is thus avoided. 
   In this case, it is of particular advantage if the traction disk is centered on the circumferential portion of the supporting disk. 
   This makes it possible to utilize the circumferential portion twofold, on the one hand, for centering and on the other hand, for the radial support of the bending moment introduced into the outer region of the traction disk. 
   Furthermore, according to a further embodiment, it is advantageous if the traction disk has a central bore for leading through a shaft to which the supporting disk is secured, and if the inner circumference of the central bore is spaced apart, free of touching, from the outer circumference of the shaft. 
   This avoids the situation where static overdetermination occurs particularly when the traction disk is centered on the supporting disk and has radial deformations when the roller runs on the inside diameter. 
   It goes without saying that the shaft is preferably the variator shaft. 
   According to a further embodiment which is preferred overall, an axial bearing portion of the supporting disk and an axial force transfer portion of the traction disk are coordinated with one another in terms of form, material and surface quality, in such a way that a torque transfer by means of these portions can take place by nonpositive or frictional connection. The coefficient of friction of roller with respect to toroidal disk is in this case as a rule, very much lower than the coefficient of friction of toroidal disk with respect to supporting disk. 
   It is thereby possible to carry out the torque transfer solely on the basis of a nonpositive or frictional connection. 
   In this embodiment, therefore, it is preferable if the traction disk and the supporting disk are not connected positively to one another in the circumferential direction. 
   Since a positive connection, in particular a toothing or a connection by means of balls and recesses, is dispensed with, on the one hand, a cost saving is obtained. However, an improvement in terms of load-bearing capacity is also achieved since there are no notching points in the region of the positive connection. The variator disk may in this case be designed overall, to be narrower or thinner in the axial direction. 
   It is of particular advantage, furthermore, if the traction disk and the supporting disk are produced from the same basic material. 
   This makes it possible, overall, to have a more cost-effective manufacture. The different intended uses can be taken into account in that, for example, the case-hardness depths are defined according to the different loads (rolling load, bending load, etc.). 
   It is, of course, also possible, alternatively, to produce the two partial disks from different materials. 
   However, insofar as the two partial disks are produced from the same basic material, it is advantageous if the traction disk and the supporting disk are produced from steel. 
   It is thereby possible, overall, for a cost-effective variator disk to be produced. Steel can be optimized sufficiently well for various intended uses. 
   It is of particular advantage overall if at least the supporting disk is produced from case-hardened steel. 
   This leads to a cost-effective type of construction of the variator disk, since case-hardened steel, as a rule, is more cost-effective than ceramic materials or metal matrix composite materials. 
   According to a further embodiment which is preferred overall, a back surface of the traction disk, said back surface lying axially opposite the running surface, is oriented essentially flush with a back surface of the supporting disk. 
   This ensures that the bending moments introduced into the traction disk can be supported essentially completely on the circumferential portion inwardly in the radial direction. 
   According to a further preferred embodiment, the traction disk is supported on a circumferential portion of the supporting disk, wherein, furthermore, a back surface of the traction disk follows, essentially free of steps, the contour of the opposite running surface radially outwardly, starting from the circumferential portion of the supporting disk. 
   This avoids the situation where notching points occur at such steps in the traction disk. It can also be ensured that the bending moments can be introduced optimally into the supporting disk. Stated in simplified form, the bending moments lead to stresses inside the traction disk which, directed approximately parallel to the running surface, are capable of being supported on the circumferential portion of the supporting disk. 
   According to a further preferred embodiment, the back surface of the variator disk has no horizontal portion. 
   This likewise leads to an optimization of the introduction of the forces arising from bending moments into the supporting disk. 
   It is advantageous, overall, if the back surface of the variator disk is designed in the form of an annular cup. 
   This affords a structure by means of which the introduction of stresses into the supporting disk can be further optimized. 
   According to a further embodiment which is preferred overall, the supporting disk has an axial portion, the inner circumference of which is connected to a variator shaft positively in the direction of rotation, the axial portion extending through a central bore of the traction disk. 
   As a result, overall, an axially compact type of construction is achieved. 
   It goes without saying that the features mentioned above and those yet to be explained below, can be used not only in the combination specified in each case, but also in other combinations or alone, without departing from the scope of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are illustrated in the drawing and are explained in more detail in the following description. In the drawing: 
       FIG. 1  shows a diagrammatic illustration of a toroidal transmission which has two variators according to the invention; 
       FIG. 2  shows the upper part of a longitudinal section through a first embodiment of a variator disk according to the invention; and 
       FIG. 3  shows a view, similar to  FIG. 2 , of an alternative embodiment to the variator disk according to the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In  FIG. 1 , a diagrammatically illustrated toroidal transmission is generally designated by  10 . 
   The toroidal transmission  10  has a transmission input shaft  12 , a countershaft  14  and a transmission output shaft  16 . 
   A variator arrangement in the toroidal transmission  10  is shown at  20 . The variator arrangement  20  has a variator main shaft  22  and a variator secondary shaft  24 . Furthermore the variator arrangement  20  contains two variators  26 A,  26 B. 
   Each variator has a driving disk  28 A,  28 B and a driven disk  30 A,  30 B. 
   The driving disks  28 A,  28 B enclose, together with the respective driven disks  30 A,  30 B, in each case a toroidal space  32 A,  32 B. 
   A plurality of rollers  34 , as a rule in each case three rollers  34 , are arranged in the toroidal spaces  32 A,  32 B in each case so as to be distributed circumferentially over the toroidal space. 
   The rollers  34  can be adjusted spatially within the toroidal space  32  by means of an actuator mechanism, not illustrated in any more detail, as shown diagrammatically at  36 , in order to vary the transmission ratio of the variator arrangement  20 . In this case, it goes without saying that all the rollers  34  of the variators  26 A,  26 B are adjusted codirectionally so that the reaction forces occurring can be absorbed uniformly over the circumference of the variator arrangement  20 . 
   At  38 , a wheel set is shown, which connects the countershaft  14  in the manner of a constant to the variator secondary shaft  24  to which the driving disks  28 A,  28 B are secured. The driven disks  30 A,  30 B are secured to the variator main shaft  22  which is connected to a summing transmission  40 . 
   The summing transmission  40  has a planetary wheel set  42 . The variator main shaft  22  is connected to the sun wheel of the planetary wheel set  42 . The countershaft  14  is connected to the planet carriers of the planetary wheel set  42  via a further wheel set (not designated). 
   The sun wheel can be connected to the transmission output shaft  16  via a high-regime clutch  44 . The ring wheel of the planet wheel set  42  can be connected to the transmission output shaft  16  via a low-regime clutch  46 . 
   The functioning of the toroidal transmission  10  is generally known and is not described here in detail for the sake of concise illustration. 
     FIG. 2  shows a detail of a variator  26  of the toroidal transmission  10  and, in particular, shows an upper half of a longitudinal section of a variator disk  50 . 
   The variator disk  50  may form any one of the variator disks  28 ,  30  in the toroidal transmission  10 . 
   The variator disk  50  is mounted on a variator shaft  52 . The variator shaft  52  may be the variator main shaft  22  or the variator secondary shaft  24 . 
   The variator shaft  52  has an outer circumference, shown at  53 , and defines a variator axis  54 . 
   The variator disk  50  has a traction disk  58  and a supporting disk  60 . 
   The supporting disk  60  is mounted on the outer circumference  53  of the variator shaft  52  via a toothing  62 . The supporting disk  60  is thus connected fixedly in terms of rotation to the variator shaft  52  positively in the circumferential direction. 
   The variator shaft  52  has a stop  64 , on which the supporting disk  60  is supported in the axial direction. 
   The supporting disk  60  is approximately L-shaped in the longitudinal section, with an axial portion  66  extending axially and with a radial portion  68  extending radially from the latter. 
   The toothing  62  is formed on the inner circumference of the axial portion  66 . 
   Formed on the radial portion  68 , on the side pointing toward the traction disk  58 , is an axial bearing portion  70 . The latter extends essentially perpendicularly with respect to the variator axis  54 . 
   On the outer circumference of the radial portion  68 , a circumferential portion  72  is provided, which extends approximately parallel with respect to the variator axis  54 . The circumferential portion  72  has a radius  73 . 
   The axial bearing portion  70  and the circumferential portion  72  are connected by means of an annular edge  74  which in the present case has a rounded design. 
   At  76 , a back surface is shown, which is formed on the radial portion  68  and which lies opposite the axial bearing portion  70 . The back surface  76  generally points away from the traction disk  58 . 
   The traction disk  58  has a curved annularly peripheral running surface  80 . The running surface  80  defines, with a corresponding running surface of a counterdisk (not illustrated), a toroidal space  32 . 
   The toroidal space  32  defines a toroidal center circle. The distance from the toroidal center circle to the opposite running surfaces of the variator disks is essentially constant. This distance is illustrated in  FIG. 2  by a roller radius  81 . This distance corresponds to the radius of a roller  34  which is arranged in the toroidal space  32  and is indicated only partially in  FIG. 2  (for the sake of clear illustration). 
   The toroidal center circle has a toroidal center radius which is shown at  82  in  FIG. 2 . 
   The running surface  80  is provided on the traction disk  58  on the side which faces away from the supporting disk  60 . On the side facing the supporting disk  60 , an axial force transfer portion  84  is formed on the traction disk  58 . The axial force transfer portion  84  corresponds in form and orientation to the axial bearing portion  70  of the supporting disk  60  and bears against said axial bearing portion during operation. 
   Furthermore, the traction disk  58  has a circumferential portion  86  which engages over the supporting disk  60  and which is assigned to the circumferential portion  72  of the supporting disk  60 . Furthermore, the traction disk  58  has a back surface  88  on its side lying opposite the running surface  80 . The back surface  88 , where it runs further on, is oriented flush with the back surface  76  of the supporting disk  60 . 
   The traction disk  58  has, furthermore, a central bore  90 . The central bore  90  is dimensioned such that the axial portion  66  of the supporting disk  60  can extend through here. A clearance is arranged between the outer circumference of the axial portion  66  and the inner circumference of the central bore  90  so that the traction disk  58  and the supporting disk  60  do not touch one another in this region. 
   Furthermore, between the axial force transfer portion  84  and the central bore  90 , there is a beveled portion which is spaced apart by a gap  92  from a correspondingly beveled portion of the supporting disk  60 . 
   The relative dimensions of the traction disk  58  and supporting disk  60  are, overall, such that these do not touch one another in a region radially within the axial bearing portion  70 . 
   In the longitudinal sectional view of  FIG. 2 , it can be seen that the traction disk  58  and supporting disk  60  fit one into the other in such a way that their form corresponds essentially to the form of a one-part variator disk. In other words, the radial portion  68  of the supporting disk  60  is received into an axial recess on the rear side  88  of the traction disk  58  in such a way that the back surfaces  76 ,  88  merge flush one into the other. 
   The traction disk  58  is in this case supported in the axial direction with its axial force transfer portion  84  on the axial bearing portion  70  of the supporting disk  60 . When a roller  34  is in the position illustrated in  FIG. 2 , a force which is not only axial, but generates a bending moment, is exerted on the traction disk  58 . The radial forces which occur as a result of the bending moment and are thus introduced into the traction disk  58  can be supported on the supporting disk  60  via the circumferential portions  86 ,  72 . 
   The traction disk  58  in this case has a high-mass design above the circumferential portion  86 , so that the radial forces can be introduced reliably into the supporting disk  60 . The traction disk  58  is centered via its circumferential portion  86  on the supporting disk  60  (and consequently also with respect to the variator shaft  52 ). However, on account of the high-mass type of construction, the design of the traction disk  58  above the circumferential portion  86  is suitable for introducing radial forces into the supporting disk  60 , specifically via its circumferential portion  72 . In other words, that part of the traction disk  58  which engages over the circumferential portion  72  is not designed merely as a centering collar. On the contrary, this portion is an integral component of the traction disk  58  absorbing the variator forces. 
   The back surface  76 ,  88  of the variator disk  50  is designed in the manner of an annular cup. Below the toroidal center radius  82 , the thickness of the variator disk  50  becomes, overall, thicker radially inwardly toward the variator axis  54 . Above the toroidal center ranges  82 , the thickness of the variator disk  50  (or of the traction disk  58 ) decreases radially outwardly to an increasing extent. In this case, because of the cup form, the back surface  88  of the traction disk  58  follows approximately the profile of the running surface  80  above the toroidal center radius  82 . 
   The radius  73  of the circumferential portion  72  is approximately equal to the toroidal center radius  82 . 
   The impression of an annular cup is obtained, that is to say a form as though the two-part variator disk  50  surrounds the toroidal space  32  in the manner of an annular cup. 
   Owing to the gradual increase in thickness of the two-part variator disk  50  from the radially outermost portion towards the axial bearing portion  70 , an approximately frustoconical form is obtained in the longitudinal section. 
   The back surface  76 ,  88  of the variator disk  50  has essentially no horizontal portion. Instead, the profile of the back surface  76 ,  88  is approximately arcuate, with a markedly larger radius than the roller radius  81 . 
   Furthermore, the back surface  76 ,  88  of the variator disk  50  is designed to be essentially free of steps. 
   The measure whereby the axial portion  66  passes through the central bore  90  results, overall, in a compact construction in the axial direction. 
   The traction disk  58  and the supporting disk  60  are not connected positively to one another in the circumferential direction. Torque transfer takes place solely by virtue of a nonpositive or frictional connection at those surfaces of the axial bearing portion  70  and axial force transfer portion  84  which lie opposite one another. This is because the high axial impingement forces occurring in the case of a variator  26  of this type can thereby be utilized for the transfer of torque. 
   The traction disk  58  and the supporting disk  60  are preferably both produced from steel. The traction disk  58  may be produced, for example, from rolling bearing steel. By contrast the supporting disk  60  may be produced from normal case-hardened steel. 
   Alternatively, it is also possible to produce both disks from case-hardened steel, the case-hardness depths being defined according to the different loads (rolling load, in the case of the traction disk  58  and bending load, in the case of the supporting disk  60 ). 
   Since a positive connection is dispensed with, on the one hand, cost savings are obtained. On the other hand, points at which excessive notch stresses may occur are avoided. The variator disk can consequently be designed, overall, to be narrower or thinner in the axial direction. 
   The circumferential portions  72 ,  86  consequently serve for centering and for the support of bending moments. The surfaces of the axial bearing portion  70  and axial force transfer portion  84  serve for axial support and for torque transfer. 
   The functioning of the variator disk  50  is as follows: 
   During operation, a high pressure force is exerted on the running surface  80  of the traction disk  58  by the roller  34 . The axial forces occurring in this case are absorbed via the axial bearing portion  70  of the supporting disk  60 . The bending moments occurring and the radial forces directed inwardly toward the variator axis  54 , which are induced as a result, are absorbed via the circumferential portion  72  of the supporting disk. As a result of the rotation of the roller  34 , a torque about the variator axis  54  is exerted on the traction disk  58 . Owing to the high axial pressure forces in the surfaces of the axial bearing portion  70  and axial force transfer portion  84 , the supporting disk  60  is in this case made following in the circumferential direction. Due to the positive connection between the supporting disk  60  and the variator shaft  52  in the circumferential direction, the variator shaft  52  is consequently likewise made following in the circumferential direction. 
   The variator disk  50  may be a driving disk  28  or a driven disk  30 . 
   In  FIG. 3 , an alternative embodiment to a variator disk according to the invention is designated in general by  50 ′. 
   The variator disk  50 ′ corresponds in form and functioning, in general, to the variator disk  50  of  FIG. 2 . Only the differences are therefore dealt with below. 
   On the one hand, it can be seen that the traction disk  58 ′ has a flattening  96  in its radially outer portion. The traction disk  58  thereby tapers to a sharper point in its radially outer portion. 
   The thickness of the variator disk  50 ′ is shown diagrammatically at  98 . This continuously increases radially inwardly from a radially outer portion of the variator disk  50 ′. 
   The supporting disk  60 ′ has only one radial portion which is fitted into a rear-side recess of the traction disk  58 ′. The toothing between the supporting disk  60 ′ and variator shaft  52 ′ consequently lies behind the traction disk  58 ′. 
   A peripheral annular gap is arranged between the inner circumference of the central bore  90 ′ of the traction disk  58 ′ and the outer circumference of the variator shaft  52 . 
   In this embodiment, the annular edge  74 ′ is not rounded. It may, however, be rounded, in order to avoid notch stresses in this region. 
     FIG. 3  contains, furthermore, the illustration of forces which occur. This illustration can apply in the same way to the variator disk  50  of  FIG. 2 . 
   A roller force  100  is thus exerted on the traction disk  58 ′ by a roller  34 ′. Since these forces can also act above the toroidal center circle  73 , a bending moment  102  may arise in this situation. The stresses occurring in this case are absorbed radially by the circumferential portion  72 ′, as shown at  106 . 
   The axial forces occurring are absorbed via the axial bearing portion  70 ′ as shown diagrammatically at  104 .