Abstract:
A toroidal traction drive has an axial loading system with a primary loading component and a non-linear cam roller loading component.

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to toroidal traction drives and more particularly to axial loading mechanisms for toroidal traction drives. 
     BACKGROUND OF THE INVENTION 
     Toroidal Continuous Variable Transmissions (“CVT”) are used to transmit rotational power from multiple sources, such as jet engines, to an electric generator. Toroidal traction drives use power rollers and toroids to translate rotational motion from the power rollers to a shaft by using the traction between the power rollers and the toroids. In order to generate sufficient traction between the toroids and the power rollers, an axial clamping force is applied to the toroids along an axis defined by the shaft thereby pressing the toroids against the power roller and allowing the power roller to transmit rotational power to the shaft. The input speeds from the multiple power sources generally vary within a certain speed range. 
     As the load on the shaft changes, the amount of axial clamping force required to maintain adequate traction between the power rollers and the toroids, and thereby ensure full power transmission to the shaft also changes. In some systems, the amount of clamping force required to maintain the traction can be predicted, and the clamping force can be gradually increased or decreased to compensate. In other systems, such as electrical generator systems, the load can change suddenly and unpredictably, requiring a fast response to maintain traction. 
     In one example, an axially loaded toroidal drive system uses a spring with a constant stiffness to provide a necessary axial loading force. In another example, an axial loaded toroidal drive system uses linear cam rollers to provide an adjustable axial load. Another example of an axial loading toroidal drive system uses a combination of a linear cam and a fixed spring to provide the axial load. 
     SUMMARY OF THE INVENTION 
     Disclosed is a toroidal traction drive having an axial loading system, where the axial loading system has a primary loading component and a non-linear cam roller loading component. 
     Also disclosed is an integrated drive generator for an aircraft. The integrated drive generator includes a toroidal traction drive generator operable to receive rotational power from at least one source; a shaft operable to output rotational power from the toroidal traction drive to an electrical generator. The toroidal traction drive comprises an axial loading system, where the axial loading system has a primary loading component and a non-linear cam roller loading component. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates an aircraft integrated drive generator system. 
         FIG. 2  schematically illustrates an example toroidal continuously variable transmission. 
         FIG. 2   a  illustrates an alternative example toroidal continually variable transmission. 
         FIG. 3  illustrates an alternate input toroid for a toroidal continuously variable transmission. 
         FIG. 4A  schematically illustrates a first non-linear cam in a minimum cam load position. 
         FIG. 4B  schematically illustrates the first non-linear cam in an intermediate load position. 
         FIG. 4C  schematically illustrates the first non-linear cam in a maximum load position. 
         FIG. 5A  schematically illustrates a second non-linear cam in a minimum cam load position. 
         FIG. 5B  schematically illustrates the second non-linear cam in an intermediate load position. 
         FIG. 5C  schematically illustrates the second non-linear cam in a maximum load position. 
         FIG. 6A  schematically illustrates a third non-linear cam in a minimum cam load position. 
         FIG. 6B  schematically illustrates the third non-linear cam in an intermediate cam load position. 
         FIG. 6C  schematically illustrates the third non-linear cam in a maximum cam load position. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates an aircraft  10  having multiple turbine engines  20 . In the example shown, each turbine engine  20  is mechanically connected to two toroidal traction drives that are substantially similar such as, for example, toroidal traction drive  12 . The toroidal traction drive  12  converts rotation of the turbine engines  20  to rotation of a single shaft within the toroidal traction drive  12 . The shaft further translates its rotation to a generator  14  that generates electrical power, using known generator techniques, for supply to onboard electrical systems  16 . 
       FIG. 2  schematically illustrates the toroidal traction drive  12  of  FIG. 1  in greater detail. The toroidal traction drive  12  includes a center shaft  120  and two pairs of power rollers  110 . Each of the power rollers  110  contacts an input toroid  122  and an output toroid  124 . Each of the toroids  122 ,  124  exerts an axial force F or F′ on the corresponding power roller  110  to prevent the roller  110  from slipping and to ensure full translation of rotation from the power roller to the output toroid  124 , and thus to a gear. The force F is exerted along an axis A defined by the shaft  120 , and is referred to as axially loading the toroidal traction drive  12 . The input toroids  122  are slidably mounted on the shaft  120  using axial ball bearings  138 . 
     In order to ensure a correct axial load is applied, and thereby prevent slipping of the power rollers  110  regardless of the load on the shaft  120 , a hydraulic axial loading system and a roller cam axial loading system are incorporated in at least one of the input toroids  122 , and apply the axial load to the input and output toroids  122 ,  124 . A constant spring  126  on a second end of the shaft  120  applies a counter-force F′ to the input and output toroids  122 ,  124 . The counter-force F′ is dependent on the particular spring  126  utilized and the axial loading force F, and can be determined by one skilled in the art in light of the present disclosure. 
     The input toroid  122  on the end of the shaft  120  axially opposite the spring  126  includes multiple cam rollers  130  (the roller cam loading system) and multiple hydraulic pistons  132  (the hydraulic loading system) that are capable of controlling the axial load on the input and output toroids  122 ,  124 . A hydraulic input port  134  provides hydraulic fluid through hydraulic passages  136  to the hydraulic pistons  132 , thereby allowing for control of the hydraulic pistons  132  by an outside controller. The hydraulic pistons  132  increase or decrease an axially aligned roller gap  340 ,  440  (illustrated in  FIGS. 4A-4C  and  5 A- 5 C respectively) in the cam rollers  130  and thereby increase or decrease the axial loading, and control the traction between the power rollers  110  and the input and output toroids  122 ,  124 . Similarly, the cam rollers  130  can rotate to increase or decrease the axial load provided by the cam rollers  130  by increasing the roller gap  340 ,  440  according to known cam roller principles. 
       FIG. 3  illustrates an alternate input toroid  222  including an alternate axial loading system similar to the system illustrated in  FIG. 2 . In the example illustrated in  FIG. 3 , the hydraulic pistons  132  of  FIG. 2  are omitted and the cam rollers  230  are sealed using an inner diameter seal  238  and an outer diameter seal  240 . Hydraulic fluid is pumped into or out of the roller gap  340 ,  440  within the sealed cam rollers  230 , through a fluid input  234  on hydraulic passage  236 , thereby directly altering the roller gap  340 ,  440 . Increasing the roller gap  340 ,  440  increases the axial loading and decreasing the roller gap  340 ,  440  decreases the axial loading. As with the example of  FIG. 2 , the input toroid  222  in the example of  FIG. 3  is mounted to the shaft via axial ball bearings  250   
     In alternate embodiments, non-hydraulic pistons such as piezo-electric pistons can be utilized in place of the hydraulic pistons  132  to affect the roller gap in the cam rollers  130 ,  230 .  FIG. 2   a  illustrates the example system using a piezo-electric piston  132   a  in place of the hydraulic piston  132  shown in  FIG. 2 . 
       FIGS. 4A-4C  partially schematically illustrate a cam roller  130 ,  230 , using linear cam roller disks  310 ,  320  and a non-linear (ovoid) bearing  330  to create a non-linear cam roller  130 ,  230 . The non-linear nature of the illustrated cam roller  130 ,  230  causes the force required to rotate the cam roller  130 ,  230  to increase in an non-linear fashion as the cam roller  130  is rotated, thereby causing the rotational force on the cam roller  130 ,  230  required to achieve a set axial load to increase in a non-linear fashion.  FIG. 4A  illustrates the cam roller  130 ,  230 , in a minimum cam load position. The ovoid cam follower  330  contacts the top roller disk  310  and the bottom roller disk  320  at the lowest diameter  350  of the ovoid cam follower  330 , and the cam roller gap  340  is minimized. In the minimum axial load position, the rotational force required to increase the axial load is also minimized. 
       FIG. 4B  illustrates the cam roller  130 ,  230  in an intermediate axial cam load position. Relative to the minimum axial cam load position ( FIG. 4A ), the top cam roller disk  310  and the bottom cam roller disk  320  are rotated in opposite directions (counter-rotated). In an alternate example, only a single disk, either the first cam roller disk  310  or the second roller disk  320 , is rotated and the other cam roller disk  310 ,  320 , is held stationary. The rotation of the roller disks  310 ,  320  causes the non-linear bearing  330  to rotate to a position where an intermediate diameter  352  is contacting each roller disk  310 ,  320 . As the diameter of the roller bearing  330  contacting the roller disks  310 ,  320  increases, the rotational force required to further rotate the cam roller  130 ,  230  increases. Similarly, as the cam follower approaches the peaks  312 ,  322  in the roller disks  310 ,  320 , the roller gap  340  is increased, thereby increasing the axial load on the input toroid. 
       FIG. 4C  illustrates the cam roller  130 ,  230  in a maximum cam load position. The top cam roller disk  310  and the bottom cam roller disk  320  have been further counter-rotated, and the largest diameter  354  of the cam roller bearing  330  is contacting each roller disk wall  310 ,  320 . In the maximum load position, the cam roller  130 ,  230  cannot rotate or increase the axial load, and all increased axial loading must be provided by the hydraulic loading system. 
       FIGS. 5A-5C  illustrate another example non-linear cam roller bearing that can be used in the example toroidal traction drives  12  of  FIGS. 1-3 . The example cam roller  130 ,  230  of  FIGS. 5A-5C  uses a spherical cam follower  430 , and non-linear cam roller disks  410 ,  420 . As with the example of  FIGS. 4A-4C , counter-rotation of the top cam roller disk  410  and the bottom cam roller disk  420  causes the cam follower  430  to roll relative to the cam roller disks  410 ,  420 , and thereby increase the cam roller gap  440  and the axial loading provided by the cam. The curved shape of the roller disks  410 ,  420  in the example of  FIG. 5  serves a similar function to the ovoid cam follower shape in the example illustrated in  FIG. 4 , and causes the force required to rotate the roller disks  410 ,  420  to increase as the bearing approaches the peaks  412 ,  422  of the roller disks  410 ,  420 . 
     By combining non-linear cam rollers  130 ,  230  with a hydraulic loading system, the non-linear cam roller  130 ,  230  reacts to load changes immediately, thereby providing a fast reaction time. However, due to the non-linear nature of the cam roller  130 ,  230 , the cam roller  130 ,  230  only reacts alone until the force required to further rotate the cam roller  130 ,  230  is equalized with the hydraulic loading, at which point both axial loading systems (the cam roller  130 ,  230  and the hydraulic loading) begin working together. Thus, the toroidal drive can achieve the reaction time benefit of a cam roller system, the resilience benefit of a hydraulic loading system, and both systems can work with repeated, unanticipated load changes. 
       FIGS. 6A-6C  illustrate another example non-linear cam roller that can be used in the example toroidal traction drives  12  of  FIGS. 1-3 . The example cam roller  130 ,  230  of  FIGS. 6A-6C  uses cylindrical cam followers  530  having an ovoid cross section. The cylindrical cam follower  530  includes a plurality of gear teeth  532  on an outer circumference  534  of the cylindrical bearing  530 . The cam roller walls  510 ,  520  likewise include a gearing portion  512 ,  522  that interfaces with the teeth  532  on the cylindrical bearing  530  to prevent the cylindrical bearing  530  from slipping as force is applied to it. 
     A diameter  550 ,  552 ,  554  of the cam follower  530  is not constant, resulting in an oval shaped cam follower  530 , and gives rise to the non-linear behavior of the cam follower. In practice the cylindrical cam follower  530  of  FIGS. 6A-6C  and the ovoid shaped cam followers of  FIGS. 4A-4C  function similarly and provide the least axial loading force when the shortest diameter  550  of the cylindrical cam follower  530  is contacting the cam roller walls  510 ,  520 , providing an intermediate axial loading when an intermediate diameter  552  is contacting the cam roller walls  510 ,  520 , and providing a maximum loading when the largest diameter  554  is contacting the cam roller walls  510 ,  520 . 
     Although example embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. A worker of skill in the art would also recognize that the above examples can be implemented alone or in any combination. For that reason, the following claims should be studied to determine the true scope and content of this invention.