Abstract:
A pressure applying mechanism for a toric-drive Continuously Variable Transmission (CVT) that comprises two opposed elements each with internal V-shaped ramp surfaces and at least three ball bearings interposed between the elements wherein rotation of one element causes the mechanism to expand in the longitudinal direction and thus generate an appropriate pressure between a drive disk and a driven disk. The invention further includes a pre-load mechanism comprising a washer for adjusting the pre-load on the pressure applying mechanism.

Description:
FIELD 
       [0001]    The present invention generally relates to toric-drive transmissions. More specifically, the present invention is concerned with a pressure applying mechanism for a toric-drive continuously variable transmission. 
       BACKGROUND 
       [0002]    Toric-drive Continuously Variable Transmissions (hereinafter generically referred to as “CVT”) are believed known in the art. The operation of such a CVT will therefore only be briefly discussed herein. 
         [0003]    Generally stated, a toric-drive CVT is provided with a drive disk having a toroidal surface, a driven disk also having a toroidal surface, both disks being linked by rollers in contact with their respective toroidal surfaces. The angle of the rollers with respect to the drive and driven disks dictates the speed ratio between the driven and drive disks. 
         [0004]    Such a toric-drive CVT transmission requires some kind of preloading mechanism to compress the drive and driven disks towards each other to provide a predetermined minimal friction between the disks and the rollers. A pressure applying mechanism is generally also provided to increase the pressure compressing the disks towards each other, therefore increasing the pressure between the disks and the rollers, when the CVT is in use. 
       SUMMARY 
       [0005]    An aspect of the present mechanism includes a pressure applying mechanism for a CVT provided with a longitudinal drive shaft, a drive disk and a driven disk, the pressure applying mechanism comprising: 
         [0006]    a pressure applying element longitudinally movable onto the drive shaft; the pressure applying element having a first surface configured to contact one of the drive and driven disks and an opposite surface including at least three V-shaped double ramps; 
         [0007]    a secondary element so mounted to the longitudinal drive shaft as to be longitudinally fixed thereonto; the secondary element having a surface facing the pressure applying element including at least three V-shaped double ramps; 
         [0008]    at least three ball bearings interposed between the V-shaped ramps of the pressure applying and secondary elements; 
         [0009]    a torque receiving element associated with one of the pressure applying element and the secondary element for rotational movement therewith; the other of the pressure applying element and the secondary element being so mounted to the drive shaft as to be prevented from rotating thereabout; 
         [0010]    whereby, torque applied to the torque receiving element results in a pressure applied to the one of the drive and driven disks via a small circumferential displacement of the at least three bearings in the facing V-shaped double ramps of the pressure applying and secondary elements. 
         [0011]    Another aspect concerns a pressure applying method to apply pressure onto the disks of a CVT provided with a longitudinal drive shaft, a drive disk, a driven disk, a preload mechanism; a pressure applying mechanism provided with a pressure applying element so configured as to apply pressure onto one of the drive and driven disks and a secondary element, the pressure applying method comprising: 
         [0012]    adjusting the preload mechanism so that a predetermined longitudinal gap remains between the pressure applying element and one of the drive and driven disks; 
         [0013]    upon torque detection on one of the pressure applying and secondary elements, applying pressure on one of the drive and driven disks by the pressure applying element. 
         [0014]    Yet another aspect concerns a CVT incorporating a pressure applying mechanism. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    In the appended drawings: 
           [0016]      FIG. 1  is a schematic front elevation view of a dual-cavity toric-drive CVT provided with a pressure applying mechanism according to an illustrative embodiment; 
           [0017]      FIG. 2  is an exploded perspective view of a pressure applying mechanism of the CVT of  FIG. 1 ; 
           [0018]      FIG. 3  is a sectional view of the toric drive CVT of  FIG. 1  showing the CVT in a non-preloaded state; 
           [0019]      FIG. 4  is a sectional view of the toric drive CVT of  FIG. 1  showing the CVT in a preloaded state; 
           [0020]      FIG. 5  is a side elevation transparent view of the pressure applying mechanism of  FIG. 2 ; 
           [0021]      FIG. 6  is a front view of the pressure applying mechanism of  FIG. 2 , shown with the drive gear and the secondary element removed; 
           [0022]      FIG. 7  is an end view of the toric-drive CVT of  FIG. 1 ; 
           [0023]      FIG. 8  is a sectional view taken along line  8 - 8  of  FIG. 7 ; and 
           [0024]      FIG. 9  is a sectional view similar to  FIG. 8  but schematically illustrating the pressure applying mechanism under pressure, when the toric-drive CVT is in use. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one”, but it is also consistent with the meaning of “one or more”, “at least one”, and “one or more than one”. Similarly, the word “another” may mean at least a second or more. 
         [0026]    As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “include” and “includes”) or “containing” (and any form of containing, such as “contain” and “contains”), are inclusive or open-ended and do not exclude additional, unrecited elements or process steps. 
         [0027]    The term “about” is used to indicate that a value includes an inherent variation of error for the device or the method being employed to determine the value. 
         [0028]    Other objects, advantages and features of the pressure applying mechanism for toric-drive transmission will become more apparent upon reading of the following non-restrictive description of illustrative embodiments thereof, given by way of example only with reference to the accompanying drawings. 
         [0029]    It is to be understood that the expression “ball bearings” is to be construed, herein and in the appended claims as either conventional balls or as needle, roller, tapered roller or other types of bearings that can adequately perform the necessary function as will be described hereinbelow. 
         [0030]    Generally stated, an illustrative embodiment of pressure applying mechanism for toric-drive transmission is concerned with a pressure applying mechanism for a toric-drive CVT where the longitudinal movement of the pressure-applying element of the pressure applying mechanism is minimal when the pressure applying mechanism shifts between a preload state and a pressure applying state. 
         [0031]    The preload state occurs when the transmission transfers torque between 0 and a value sufficient to activate the pressure applying state. In the pressure applying state, the pressure in the system is generally the sum of the preload pressure and of the pressure applied by the pressure applying mechanism, which, in turn, is proportional to the torque being transferred by the transmission. 
         [0032]    Since the longitudinal movements are very small between the preload and pressure applying states, the wear of the mechanical parts of the CVT are reduced, at least since the switching delays are minimized by the small movement required. 
         [0033]    Turning now to  FIG. 1  of the appended drawings, a dual-cavity toric-drive CVT  10  including a pressure applying mechanism  12  according to an illustrative embodiment will be described. 
         [0034]    The toric-drive CVT  10  includes a longitudinal shaft  14  (shown in dashed lines) to which are mounted first and second drive disks  16  and  18  for rotation therewith. A driven disk  20  having a toothed outer surface is rotatably mounted to the shaft  14 . Three rollers  22  are provided between the first drive disk  16  and the driven disk  20  while three rollers  24  are provided between the second drive disk  18  and the driven disk  20 . The longitudinal shaft  14  is mounted to a casing (not shown) via bearings  26 . A preload tensioning nut  28  and the pressure applying mechanism  12  are mounted near opposite longitudinal ends of the shaft  14 . 
         [0035]    It will easily be understood by one skilled in the art that the dual cavity toric-drive CVT  10  is only schematically illustrated in  FIG. 1 . Indeed, many subsystems such as, for example, a roller guiding subsystem, are not shown for clarity and since they have no incidence on the structure and operation of the pressure applying mechanism described herein. 
         [0036]    Turning now to the exploded view of  FIG. 2  of the appended drawings, the pressure applying mechanism  12  and the preload mechanism  30  will be described. 
         [0037]    The pressure applying mechanism  12  includes a pressure applying element  32 , a secondary element in the form of a shaft driving element  34 , a plurality of ball bearings  36  mounted in a cage  38  and provided between the pressure applying element  32  and the shaft driving element  34 , a two-part longitudinal stopper  40  configured to be mounted to the shaft  14  and a gear  42  so configured as to be mounted to the pressure applying element  32 . The pressure applying mechanism  12  also includes a friction-reducing disk  44  mounted to the pressure applying element  32  and a wear-preventing sleeve  46  provided between the pressure-applying element  32  and the shaft-driving element  34 . 
         [0038]    Still from  FIG. 2 , the preload mechanism  30  that also includes the preload nut  28  of  FIG. 1  includes a Belleville washer  48 , a Belleville washer centering element  50  a friction reducing disk  53  and a washer  52 . The surfaces of the Belleville washer-centering element  50  and of the washer  52  facing the friction-reducing disk  53  are polished so as to reduce the wear of the friction-reducing disk  53 , which is typically made of brass. 
         [0039]    It is to be noted that the preload nut  28  and two part longitudinal stopper  40  could exchange their respective longitudinal position while performing the same functions. 
         [0040]    A first key  54  collaborates with a keyway (not shown) of the shaft  14  to prevent rotation of the first drive disk  16  with respect to the shaft  14  while a second key  56  collaborates with a keyway (not shown) of the shaft  14  to prevent rotation of the shaft-driving element  34  onto the shaft  14 . 
         [0041]    Turning now to  FIGS. 3 and 4  of the appended drawings, the operation of the preloading mechanism  30  will be described. 
         [0042]      FIG. 3  illustrates the toric-drive CVT  10  when the preload mechanism  30  is not operational, while  FIG. 4  illustrates the preload mechanism  30  applying a preload pressure. 
         [0043]    From  FIG. 3 , it is clear that the Belleville washer  48  is in an uncompressed state. It is also clear that the Belleville washer  48  is positioned between the Belleville centering element  50  and the pressure-applying element  32 . By rotating the nut  28  (see arrow  60 ), the drive disk  18  is longitudinally moved onto the shaft  14  (see arrow  62 ), moving the rollers  24 , the driven disk  20 , the rollers  22  and the drive disk  16  to compress the Belleville washer  48  since the disk driving element  34  is prevented from moving longitudinally by the stopper  40 . 
         [0044]    Turning now to  FIG. 4  of the appended drawings, the nut  28  is rotated until the distance “A”, which is the gap between the friction-reducing disk  44  and the outer surface  63  of the drive disk  16  is adjusted to a predetermined value. It has been found that a distance “A” of about 0.001 inch is an adequate distance for a typical toric-drive CVT application. It is interesting to keep the gap “A” as small as possible to thereby minimize the movement required when the pressure applying mechanism engages. 
         [0045]    One skilled in the art will be in a position to select an adequate Belleville washer so that an appropriate preload pressure is applied when a small distance “A” is achieved. 
         [0046]    Of course, other adjustment elements could be used to replace the nut  28  to adjust the gap “A” to the predetermined value. For example, the disk  18  could be mounted to the shaft  14  so as to be controllably moved longitudinally and thereafter prevented from moving longitudinally to therefore adequately preload the CVT  10 . 
         [0047]    When the toric-drive CVT is in the preloaded configuration shown in  FIG. 4 , it is ready to be used. More specifically, when the CVT  10  is in the preloaded configuration shown in  FIG. 4 , torque can be applied to the gear  42  from an external power source such as a prime mover (not shown) and transferred to the driven disk  20  via the shaft  14 , pressure applying mechanism  12 , the drive disks  16 ,  18  and the rollers  22  and  24 . 
         [0048]    The pressure applying mechanism  12  will now be described in greater detail with reference to  FIGS. 5 to 9 . 
         [0049]      FIG. 8  illustrates a portion of the pressure applying mechanism  12  when it is in a preload configuration. When this is the case, no torque is applied to the toothed gear  42 . As can be seen from  FIG. 8 , the surface of the pressure applying element  32  facing the shaft driving element  34  includes, for each bearing  36 , a ball bearing receiving V-shaped double ramp  70 . Similarly, the surface of the shaft driving element  34  facing the pressure applying element  32  includes, for each bearing  36 , a ball bearing receiving V-shaped double ramp  72 . 
         [0050]      FIG. 8  shows the ball bearings  36  is a resting state, i.e. that they are positioned resting in the “bottom” of the V-shaped double ramps  70  and  72 . Accordingly, the distance “B” is as small as possible. 
         [0051]      FIG. 9  shows a portion of the pressure applying mechanism  12  when a torque is applied to the toothed gear  42 , i.e. when the CVT  10  is in use. When this is the case, the torque is transferred to the pressure-applying element  32  via its connection to the gear  42 . This torque is represented by arrow  74  in  FIG. 9 . The torque detected by and applied to the pressure applying element  32  forces the element  32  to rotate. This rotation angularly moves the pressure-applying element  32  with respect to the shaft-driving element  34  since the shaft-driving element  34  is prevented from rotating by the key  56  (see  FIG. 2 ). Accordingly, the ball bearings  36  do not stay in the bottom of the V-shaped double ramps  70  and  72  but are moved along one side of the ramps  70  and  72  until the outer surface of the friction-reducing element  44  is in contact with the disk  16 . In other words, the ball bearings  36  are moved until distance “C” generally equals distance “B” ( FIG. 8 ) plus distance “A” ( FIG. 4 ). 
         [0052]    One skilled in the art will understand that since the gap “A” is adjustable via the setting of the preload mechanism  30  as described hereinabove, one can therefore adjust the amount of longitudinal movement of the pressure applying element  32  and thus the amount of longitudinal movement of the various CVT elements. 
         [0053]    When the outer surface of the friction-reducing element  44  is in contact with the outer surface  63  of the drive disk  16 , and while a torque is still applied to the toothed gear  42 , this torque is transferred from the gear  42  to the shaft-driving element  34  via the ball bearings  36 . At the mean time this torque transferred from the ramps  72  to the balls  36  and to the other ramps  72  generate a pressure force due to the wedging effect of the ball bearings  36  in the V-shaped double ramps  70  and  72 . This pressure is applied to the disk  16  (see arrow  76 ) by the pressure-applying element  32 . 
         [0054]    It is to be noted that the friction between the pressure applying element  32  and the disk  16  is reduced by the friction reducing elements  44 , typically made of Teflon or other friction reducing materials. Similarly, the friction between the pressure applying element  32  and the disk-driving element  34  is reduced by the sleeve  46 , typically made of brass or other friction reducing materials. 
         [0055]    It is also to be noted that the ball bearing receiving V-shape double ramps  70  and  72  are schematically illustrated in the appended figures. Indeed, the angles of the ramps have been exaggerated for illustration purpose. 
         [0056]    One skilled in the art will understand that since the gap “A” separating the pressure applying element  32  from the disk  16  in the CVT preload state, i.e. when no torque is applied, is very small, the pressure applying mechanism  12  can react quickly and apply pressure onto the toric-drive CVT  10  to thereby reduce premature wear of the mechanical components thereof. The gap “A” being minimal it also means that the rotation movement seen from  FIGS. 8 to 9  is going to be kept minimal thus reducing wear in the pressure applying mechanism. 
         [0057]    It is to be noted that while the above disclosure describes a pressure applying mechanism where the toothed gear  42  is mounted to the pressure applying element  32  and where the secondary element, i.e. the shaft driving element  34 , is keyed to the shaft  14 , other configuration of these elements may be used. As a non-limiting example, the toothed gear  42  could be associated with the secondary element  34  which would not be keyed to the shaft  14  while the pressure-applying element  32  would be so keyed to the shaft  14  to allow longitudinal movement therebetween while preventing rotation thereabout. In this illustrative embodiment, the element  32  would simultaneously apply pressure onto the drive disk  16  and drive the shaft  14 . 
         [0058]    It is also to be noted that while the pressure applying element  32  is shown separate from the drive disk  16 , it would be within the skills of one skilled in the art to integrate these two parts into an integrated element (not shown). Of course, should this be the case, the torque receiving gear  34  would be mounted to the secondary element  34  which would be free to rotate about the shaft. Furthermore, the preloading assembly  30  including the Belleville washer  48  would be provided between the secondary element  34  and the two-part stopper  40  which could be made more substantial. 
         [0059]    It is also to be noted that while the disks  16  and  18  have been described herein as drive disks and the disk  20  has been described herein as a driven disk, these functions could be reversed. 
         [0060]    Furthermore, the cam system could also be installed into the disk  20 . That would require splitting the disk  20  in two disks and placing the cam, having the same ball-ramp configuration as shown herein, between the split disks. The torque applied to, or coming from, the split disk  20  would then flow through a pressure applying element  32  with similar ball ramp configuration and controlled distance A resulting once again in the generation of a longitudinal force related to the torque applied on the pressure applying element  32   
         [0061]    It will be noted that while a dual-cavity toric-drive CVT has been described and illustrated herein, the basic principles of the pressure applying mechanism and method described herein could be applied to a single cavity toric-drive CVT. 
         [0062]    Similarly, while a full toric-drive transmission has been shown herein, the basic principles of the pressure applying mechanism and method described herein could be applied to half toric-drive transmissions (not shown). 
         [0063]    Also, while ball bearings have been illustrated herein mounted between the elements  32  and  34 , needles, rollers or tapered rollers (not shown) could be used. 
         [0064]    The double ramps  70  and  72  are qualified herein as being V-shaped. One skilled in the art will understand that other shapes could be used. 
         [0065]    While the torque-receiving element has been illustrated and described as being a gear  42 , other mechanical elements could be used, such as, for example a pulley, a sprocket or a direct hollowed shaft connection. 
         [0066]    It is to be noted that the CVT described above has a pressure applying mechanism and a preload mechanism that work in parallel. More specifically, when the pressure applying mechanism is operational, the contact between the pressure applying element  32  and the disk  16  adds magnitude to the longitudinal force initially applied by the preload mechanism. Accordingly, variations in torque loads applied to the gear  42  does not cause movements of the CVT elements and therefore do not induce wear of these elements or wear of the pressure applying mechanism. It is also to be noted that since the torque must be applied to the pressure applying element before going into the CVT, the proper amount of longitudinal force to insure traction in the CVT is always present in both toroidal cavities thus insuring traction and preventing gross slip at all times. 
         [0067]    It is to be understood that the pressure applying mechanism for toric-drive transmission is not limited in its application to the details of construction and parts illustrated in the accompanying drawings and described hereinabove. The pressure applying mechanism for toric-drive transmission is capable of other embodiments and of being practiced in various ways. It is also to be understood that the phraseology or terminology used herein is for the purpose of description and not limitation. Hence, although the pressure applying mechanism for toric-drive transmission has been described hereinabove by way of illustrative embodiments thereof, it can be modified, without departing from the spirit, scope and nature thereof.