Traction roller transmission
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to fixed-ratio traction roller transmissions in which the contact forces applied to the traction surfaces, which are in contact with one another for the transmission of movement, are dependent on the torque transmitted through the transmission. 
     2. Description of the Prior Art 
     Traction roller transmissions require large contact forces for the frictional engagement of their motion transmitting rollers in order to prevent slippage. However, the required contact forces vary with the amount of torque transmitted through the transmission. In the &#34;Mechanical Design And Systems&#34; handbook, pages 14-8 and 14-9, McGraw-Hill, New York, 1964, a planetary type traction roller transmission is described in which, in the simple arrangement of FIGS. 14.6 and 14.7, the outer ring surrounding the sun and the planetary rollers is slightly undersized so as to compress and force the traction rollers and the sun into frictional engagement with each other. With this arrangement however, the pressure on the traction surfaces is always the same, that is, it is always high independently of the torque transmitted through the transmission. 
     There are also traction roller transmissions in which the contact forces applied to the traction rollers are variable and depend on the torque transmitted through the transmission. Applicants earlier, U.S. Pat. No. 4,052,915, for example, has a number of traction rollers disposed in an annular space formed between a sun roller and slightly conical traction rings so mounted in the transmission housing that a torque transmitted through the transmission forces the traction rings toward each other for engagement of the traction rollers with the ring and the sun roller. 
     In all these arrangements however, the sun roller and the ring rotate in opposite directions relative to the movement of the planetary roller axes and, accordingly, special provisions are required to maintain the planetary roller axes in exact parallel alignment with the axes of the traction rings and of the sun roller. Furthermore, as the traction ring will always rotate in a direction opposite to the direction of rotation of the sun roller assuming that the &#34;planetary&#34; rollers are only permitted to rotate about their own axes, an output shaft connected to the traction rings will always rotate in a direction opposite to that of an input shaft connected to the sun roller. Rotation of the input and output shafts in opposite directions however, is sometimes undesirable and the transmission support structure requires heavy mounts capable of assuming the full reaction torque of the output shaft. 
     SUMMARY OF THE INVENTION 
     In a fixed ratio traction roller transmission a power transmitting traction roller structure is disposed in the annular space between a traction ring and a sun roller disposed centrally within the traction ring. The traction roller structure consists of a number of roller casters each having two rollers disposed adjacent each other, one in engagement with the sun roller and the other in engagement with the traction ring. The combined diameter of the two rollers in each caster is slightly larger than the gap between the sun roller and the traction ring and the casters are pivotally supported by a pivotal support structure such that a torque transmitted through the transmission rollers forces the casters into a more upright position with respect to the surfaces of the sun roller and the traction ring and into firm frictional engagement with each other and with the traction ring and the sun roller. 
     The casters are also tiltably supported by the pivotal support structure which is arranged, with respect to the direction of rotation of the sun roller and the traction ring, in front of the roller casters such that the roller casters are trailing the pivotal support structure and align themselves with the axis of the traction ring and the sun roller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will become more readily apparent from the following description of preferred embodiments thereof shown, by way of example only, in the accompanying drawings, in which: 
     FIG. 1 is a cross-sectional view of the traction roller transmission showing the general arrangement of its elements; 
     FIG. 2 is a cross-sectional view along lines II--II of FIG. 1 showing the arrangement of the roller blocks without the housing; 
     FIG. 3 shows a more elaborate support structure for the roller block; and 
     FIG. 4 is a cross-sectional view along lines IV--IV of FIG. 3. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 1, the traction roller transmission comprises a housing 10 having a main part 11 and a cover 12 mounted on the housing part 11 by bolts 13. Coaxial input and output shafts 14 and 15 are rotatably supported in the housing cover 12 and the main housing part 11 by bearings 16 and 17. The input shaft 14 extends into a bore 18 in the output shaft 15 and is supported therein by a roller bearing 19. The input shaft 14 carries a sun roller 20 and the output shaft 15 has a traction ring 21 connected thereto by a bell structure 221. The traction ring 21 is concentric with the sun roller 20 with its inner traction surface 22 being radially spaced from the traction surface 23 of the sun roller 20 and a number of roller casters 24 are arranged in the annular space 251 (FIG. 2) between the sun roller 20 and the traction ring 21. Each roller caster 24 consists of a caster frame 25 supporting two parallel and adjacent transmission rollers 26 and 27 which are in engagement with each other and of which one (26) is in engagement with the sun roller 20 and the other (27) is in engagement with the traction ring 21. 
     For supporting the roller casters 24, the housing 10, that is housing cover 12, has support blocks 28 mounted thereon by bolts 29 and projecting into the spaces between the roller casters 24. Each support block 28 is provided at one side with a ball pivot structure 30 for abutment by the adjacent roller caster and, at the opposite side, means 31 are provided adjacent the radially outer end of the support block for tilting the roller caster adjacent the opposite side about its pivot structure 30. The sum of the diameters of the two rollers 26 and 27 in each roller caster 24 is slightly larger than the radial dimension of the space between the sun roller&#39;s traction surface 23 and the traction ring&#39;s inner surface 22 and the roller casters 24 are all slightly tilted such that a plane receiving the axes of the rollers 26 and 27 of a caster 24 intersects a plane receiving the axes of the sun roller 20 and the adjacent roller 26 of a roller caster 24 at an angle α. Tilting the casters 24 in such a way that the angle α becomes smaller forces the caster rollers 26 and 27 into frictional engagement with each other and with the traction surfaces 22 and 23 of the traction ring 21 and the sun roller 20 for the transmission of motion between the sun roller 20 and the traction ring 21. 
     The means 31 for tilting the roller caster 24 is shown schematically in FIG. 2 as being a coil spring. Preferably, however, as shown in FIG. 3, the tilting means 31 consists of a piston 32 disposed in a cylinder 33 formed in the support block 28. The piston 32 and cylinder 33 are preferably of relatively large diameter in order to avoid the need for a high pressure fluid source for operating the piston 32 so as to obtain the desired tilting forces. 
     The pivot structure 30, which is also only schematically shown in FIG. 2 as being a rolling ball, consists preferably of a universal joint 34 and a lateral bearing structure 35, the arrangement being shown more clearly in FIG. 4. The universal joint 34 has a housing portion 36 associated with the adjacent roller caster 24 and a housing portion 37 slidably supported by the adjacent support block 28 with a joint member disposed between the two housing portions 36 and 37. The lateral bearing structure 35 may consist of needle rollers, or it may be a friction-type bearing or it may be a hydraulic bearing. The support block 28 and the housing portion 37 are V-shaped so as to cause self-centering of the pivot structure 30 on the support block 28. The roller caster 25 has preferably a housing having front and rear wall sections 38 and 39 and side walls 40, with the transmission rollers 26 and 27 mounted within the housing. Preferably the sun roller 20 is wider than the traction ring 21 so as to provide essentially the same specific contact pressures at the sun roller&#39;s traction surface 23 and the traction ring&#39;s inner surface 22. Also, the radially inner roller 26 may be wider than the outer roller 27. To adapt for any greater width of the inner roller 26, the caster housing 25 has a projection 41 adjacent the inner roller 26. The transmission rollers 26 and 27 also have circumferential grooves 42 and 43 adapted to receive lubricant squeezed from the contact areas of the rollers 26, 27 with the traction surfaces 22 and 23 during operation of the transmission. 
     OPERATION OF THE TRACTION ROLLER TRANSMISSION 
     Rotation of the input shaft 14 and the sun roller 20 in a direction as indicated by arrow 50 (FIGS. 2, 3) applies a force F1 (FIG. 3) to the roller 26 whenever a torque is transmitted. Roller 26 rotating in the direction of arrow 51 drives roller 27 to rotate in the direction of arrow 52 and roller 27 drives the traction ring 21 in the direction of arrow 53 while a reaction force F2 is applied by the traction ring 21 to the outer roller 27. The two spaced forces F1 and F2 which are essentially oppositely directed and of the same size generate a torque tending to tilt the transmission roller casters about their pivot structure 30 so as to reduce the size of the angle α which action forces the transmission rollers into firm frictional engagement with each other and with the sun roller 20 and the traction ring 21. The greater the torque transmitted through the transmission, the greater are the forces F1 and F2 and the greater is the frictional engagement of the transmission rollers with the sun roller and the traction ring. 
     Both, the sun roller 20 and the traction ring 21, are rotating in the same direction and, with respect to the movement of their traction surfaces 23 and 22, the pivot structures 30 are disposed in front of the roller casters 24 so that the roller casters 24 are trailing their pivot support with regard to the movement of the sun roller surface 23 as well as the traction ring&#39;s surface 22. The transmission rollers 26 and 27 will, therefore, automatically align themselves perfectly with the axes of the sun roller and the traction ring thereby avoiding spin and wear in the contact areas of the transmission rollers 26 and 27 with the sun roller 20 and the traction ring 21. 
     The arrangement described permits the transmission of large forces in a relatively small housing with the output shaft rotating in the same direction as the input shaft. 
     A particular transmission designed for the jet drives of a surface effect ship has, for example, the capability to transmit 11520 hp. with a traction ring diameter of 42 inches and a sun roller diameter of 22 inches at a traction ring speed of 975 rpm and a sun roller speed about twice the traction ring speed. 
     The invention is, of course, not limited to the embodiments described herein. The inner and outer traction rollers may, for example, be of different diameters, i.e. the outer traction roller 27 might have a smaller diameter than the inner traction roller 26. Also, as presented in the description the transmission is a speed reduction transmission. The transmission may however, just as well be a speed-up transmission wherein the shaft associated with the traction ring is the input shaft and the shaft associated with the sun roller is the output shaft. Both, sun roller and traction ring would then have to rotate in a direction opposite to that indicated by the arrows 50 and 53.