Abstract:
A rotary drive transmission having a rotary drive input ( 20 ) and a rotary driven output ( 30 ), the drive transmission being capable of selectively varying the drive ratio between the rotary drive input ( 20 ) and rotary driven output ( 30 ), the drive transmission including a main drive shaft defining the rotary drive input ( 20 ), a differential transmission assembly ( 40 ) having a rotary output member ( 30 ) which defines said rotary driven output ( 30 ), the differential assembly ( 40 ) including a first rotary drive input (I 1 ) and a separate second rotary drive input (I 2 ), the first (I 1 ) and second rotary drive (I 2 ) inputs and said rotary driven output ( 30 ) member being drivingly interconnected with one another such that changes in the relative rotation of the first (I 1 ) and second rotary drive (I 2 ) inputs causes a rotational change in said rotary output member ( 30 ), and selectively operable rotary adjustment means ( 53, 56 ) for adjusting the rotation of the second rotary drive input (I 2 ) for selectively controlling rotation of the rotary output member ( 30 ), the differential assembly ( 40 ) and the adjustment means ( 53, 56 ) each being mounted on the main drive shaft such that said first rotary drive input (I 1 ) and the rotary adjustment means ( 53, 56 ) are directly driven thereby.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an infinitely variable transmission. 
     BACKGROUND 
     Infinitely variable transmissions are known for transmitting rotary motion from a rotary drive source to a rotary driven load such that the speed of rotation of the load may be selectively varied in a continuous and variable manner for a given rotary speed of the rotary drive source. 
     In use, such transmissions have a wide range of applications; for example such transmissions may be used in applications where the rotary drive source delivers a variable rotary drive such as in road vehicles wherein the transmission transmits rotational drive from an engine to the road wheels of the vehicle; alternatively such transmissions may be used in applications where the rotary drive source delivers a constant rotary drive such as in a machine tool lathe application wherein the transmission delivers a constant rotary drive from an electric motor to the chuck of the lathe. 
     Infinitely variable transmissions of the type disclosed in French patent application No. FR 0004842, published as FR2807811 (referred to throughout as such), are known wherein the transmission includes and epicyclic gear assembly having a rotary drive output for connection to a load to be driven and a rotary drive input for connection to a rotary drive source, the rotary drive input being arranged to drive the epicyclic gear assembly via first and second drive inputs driven by said rotary drive input, the first drive input being drivingly connected to said rotary drive input via a variator which is selectively operable to vary the relative rotational speeds of the first and second drive inputs and thereby cause a desired rotational change in said rotary drive outputs. 
     Infinitely variable transmissions of the type disclosed in FR2807811 tend to suffer from certain disadvantages. For example, the transmission is relatively complex and so is relatively expensive to produce. It is also generally bulky and requires a relatively large amount of occupancy space when installed in a drive system. Also the arrangement of components making up the variable transmission makes it difficult to easily change the drive ratios and/or torque transmission capabilities of the variable transmission when tailoring the variable transmission for a particular application. 
     SUMMARY 
     A general aim of the present invention is to provide a variable transmission of the type disclosed in FR2807811 but which is less complex, is more compact and is more versatile to enable drive ratios and/or torque transmission capabilities to be more easily made for tailoring the variable transmission for a particular application. 
     According to one aspect of the present invention there is provided a rotary drive transmission having a rotary drive input and a rotary driven output, the drive transmission being capable of selectively varying the drive ratio between the rotary drive input and rotary driven output, the drive transmission including a main drive shaft defining the rotary drive input, a differential transmission assembly having a rotary output member which defines said rotary driven output, the differential assembly including a first rotary drive input and a separate second rotary drive input drivingly interconnected with the rotary driven output member such that changes in the relative rotation of the first and second rotary drive inputs causes a rotational change in said rotary output member, and selectively operable rotary adjustment means for adjusting the rotation of the second rotary drive input for selectively controlling rotation of the rotary output member, the differential assembly and the adjustment means each being mounted on the main drive shaft such that said first rotary drive input and the rotary adjustment means are directly driven thereby. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of the present invention are hereinafter described with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic axial section through a variable transmission according to a first embodiment of the present invention; 
         FIG. 1 a    is a schematic axial end view of the embodiment of  FIG. 1  as viewed from arrow A; 
         FIG. 2  is a schematic axial section through a variable transmission according to a second embodiment of the present invention; 
         FIG. 2 a    is a schematic axial end view of the embodiment of  FIG. 2  as viewed from arrow A; 
         FIG. 3  is a schematic axial section through a variable transmission according to a third embodiment of the present invention; 
         FIG. 3 a    is a schematic axial end view of the embodiment of  FIG. 3  as viewed from arrow A; 
         FIG. 4  is a schematic axial section through a variable transmission according to a fourth embodiment of the present invention; 
         FIG. 4 a    is a schematic axial end view of the embodiment of  FIG. 4  as viewed from arrow A; 
         FIG. 5  is a schematic axial end view of the variator used in the embodiments of  FIGS. 1 to 4 . 
         FIGS. 6 and 7  are schematic axial sections of transmissions that have a planetary carrier.  FIGS. 6 a  and 7 a    are schematic axial end views of the embodiments of  FIGS. 6 and 7 . 
         FIG. 8  is a schematic view of a wheel assembly. 
     
    
    
     DETAILED DESCRIPTION 
     The first embodiment  10  illustrated in  FIGS. 1 and 1   a  includes a rotary drive input  20  and a rotary driven output  30  which is driven by the rotary drive input  20  via an epicyclic gear assembly  40  and variator  50 . In use, the rotary drive input  20  is drivingly connected to a rotary drive source (not shown) such as an electric or fluid motor or an engine and the rotary driven output  30  is drivingly connected to a load which is to be rotationally driven. For example in a road vehicle application, the rotary drive source would be an internal combustion engine and the load would be one or more of the vehicle&#39;s road wheels. 
     The variator  50  includes a pair of axially opposed housing discs  51 ,  52 . The axially opposed sides of the housing discs  51 ,  52  each include an annular channel  53  which in the illustrated embodiment is semi-circular in cross-section. The annular channels  53  have a common radial centre R and together define an annular chamber  54 . Housed within the annular chamber  54  are a plurality of wheels  56  which are preferably rotatably mounted on a common frame  55  ( FIG. 5 ). Each wheel  56  rotatably engages both opposed channels  53  and has an axis of rotation A R  which is angularly adjustable about the radial centre R whilst being constrained to move within a plane containing the axis of rotation of the housing discs  51 ,  52 . As illustrated in  FIG. 5 , three wheels  56  may be provided. Each wheel  56  rotates about an axle  59  mounted on a bracket  150 . Each bracket  150  has co-axial shaft extensions  151  rotatably mounted on the frame  55  so that the bracket  150  is rotatable about an axis of rotation passing through centre point R. The shaft extensions  151  of each bracket  150  are each provided with meshing bevel gears  154  such that all brackets  150  rotate in unison about the axis of rotation of their shaft extensions in order to adjust the angular position of the wheels  56 . One of the shaft extensions  151  is connected to a rotary drive means (not shown) via a stub shaft  156  to enable variable angular adjustment of the brackets  150  and wheels  56  carried thereby. Preferably a resilient torque adjuster  351  is provided which maintains a predetermined amount of torque for rotatably driving shafts  151  to thereby eliminate back lash between the bevel gears  154 . Torque adjuster  351  maybe a coiled spring. 
     Preferably the frame  55  is fixed to a surrounding housing (not shown) to maintain it static. Preferably the frame  55  carries a bearing or bush sleeve  155  which rotatably supports shaft  25 . 
     Housing disc  51  is drivingly connected to a drive source (not shown) which may for example be the flywheel of an internal combustion engine. The drive connection may be achieved by a plurality of dowels  57 . In  FIG. 1 , housing disc  51  constitutes the rotary drive input  20 . A main drive shaft  25  co-axially extends from the housing disc  51 . The shaft  25  has an enlarged section  25     a    having splines interengaged with splines in the disc  51 . Accordingly, disc  51  and shaft  25  rotate in unison. 
     The housing disc  52  is rotatably mounted on the shaft  25  by a thrust bearing  26 . 
     Accordingly rotation of housing disc  51  in a given direction causes wheels  56  to rotate and in turn cause the housing disc  52  to rotate in the opposite direction to that of disc  51 . The relative speed of rotation of discs  51 ,  52  is dependent upon the angular position of the axis of rotation of the wheels  56  about radial centre R. For example each wheel  56  may be angularly adjusted to provide a variable change in ratio between a maximum step-up in ratio (as indicated by position M SU ) and a maximum step-down in ratio (as indicated by position M SD ). 
     In the illustrated embodiment, the cross-sectional shape of each channel  53  is semi-circular. Accordingly, the surface to surface loading between each wheel  56  and the surfaces of the opposed channels  53  with which the wheel engages is the same throughout the range of angular adjustment of the wheel  56  about centre point R. It is appreciated that the amount of load which the wheel  56  needs to transmit will vary depending upon its angular position about centre point R viz. for a given rotational speed of housing disc  51  each wheel will need to transmit a maximum load when the wheel is at its limits M SU , M SD  of angular adjustment and a minimum load when at a central point between these limits. Accordingly it is envisaged that the cross-sectional shape of one or both of the opposed channels  53  may be hyperbolic or parabolic such that the contact pressure between the engaged surface of each wheel  56  and the opposed channels  53  increases as the wheel  56  is angularly adjusted to move towards its M SU  or M SD  limit from a central point between these limits. 
     The epicyclic gear assembly  40  comprises a first drive input I 1  defined by a first sun gear  42 , a driven output defined by a second sun gear  44  and at least one planetary gear  45  in mesh with both the first and second sun gears  42 ,  44  respectively. The planetary gear(s)  45  is(are) rotatably mounted on a planetary carrier defined by the driven housing disc  52  of the variator  50 . The disc  52  defines a second drive input I 2  for the epicyclic gear assembly  40 . 
     The second sun gear  44  is drivingly coupled with the rotary driven output  30 . For example, as shown in  FIG. 1 , the rotary drive output  30  is defined by a sleeve  32  on which gear teeth are formed for defining the second sun gear  44 . Preferably, a bearing  141  is provided for providing rotational support for the sleeve  32 . 
     As indicated above, the epicyclic gear assembly  40  is rotatably driven by two drive inputs I 1 , I 2  and the assembly acts to differentially combine the two drive inputs in order to rotatably drive the driven output  30 . 
     In the embodiment of  FIG. 1 , the first drive input I 1  is defined by the sun gear  42  and the second drive input I 2  is defined by the driven housing disc  52  of the variator  50 . 
     The sun gear  42  which defines the first drive input I 1 , is directly mounted on a main drive shaft  25  so as to rotate in unison therewith. 
     The sun gear  42  is mounted on splines (not shown) formed on the main drive shaft  25  and is axially displaceable relative to the drive shaft  25 . 
     The enlarged section  25   a  of main drive shaft  25  defines an axial abutment stop  24  which abuttingly engages the housing disc  51 . The abutment stop  24  is urged into axial abutment with the housing disc  51  by a shaft adjustment means  80 , preferably in the form of a threaded nut  81  screw threadedly received on a screw thread  82  formed at one end of the main shaft  25 . 
     Located between nut  81  and sun gear  42  is a thrust bearing  90  and washer  91 . Accordingly, tightening of the nut  81  causes the housing discs  51 ,  52  to be urged axially toward one another via a compressive force applied via, on the one hand, thrust bearings  26 ,  90  and sun gear  42  and via, on the other hand, axial abutment stop  24 . 
     This enables a predetermined amount of compressive force to be applied by the discs  51 ,  52  onto wheels  56  in order to ensure transmission of rotary power or torque without slippage. Application of the predetermined compressive force is conveniently achieved by manipulation of the nut  81  at one end of the shaft  25  and does not affect the epicyclic gear assembly since sun gear  42  is axially displaceable on shaft  25 . 
     It will be appreciated that removal of nut  81  enables the sun gear  44  to be axially withdrawn, the thrust bearing  90  to be withdrawn, the planetary gear(s)  45  to be withdrawn and sun gear  42  to be withdrawn. In other words, the gear components of the epicyclic gear assembly  40  can be easily removed and replaced by gears of different diametric sizes in order to change the gearing ratio of the epicyclic gear assembly. It also enables disc  52  to be removed to permit easy removal of the frame  55  and wheel  56  assembly. 
     Instead of using a nut  81  to apply a compressive force, it is envisaged that alternative means may be used, for example a hydraulic piston which would enable a variable compressive force to be applied during operation of the transmission. 
     This enables the variable drive transmission shown in  FIG. 1  to be easily tailored to suit a particular application. 
     It will be appreciated that since the second drive input I 2  to the epicyclic gear assembly is defined by the housing disc  52  of the variator  50 , the variable drive transmission of  FIG. 1  is relatively compact compared to variable transmissions of the type disclosed in FR2807811. 
     In the embodiment of  FIG. 1 , the planetary gears  45  are rotatably received on stub shafts  49  projecting from the outer axial face  60  of the housing disc  52 . Thus housing disc  52  defines the planetary carrier for planetary gear  45 . 
     Preferably the planetary gears  45  are stepped gears as this provides for a greater choice in gear ratios. 
     As illustrated in  FIG. 1 a   , the driven sun gear  44  is driven by the planetary gear(s)  45 . The planetary gear(s)  45  is rotatably driven about stub shaft  49  by the drive sun gear  42 . 
     In  FIG. 1 a   , sun gear  42  is illustrated as rotating in a clockwise direction. Accordingly, the sun gear  42  acts to rotate the planetary gear  45  in an anti-clockwise direction at a speed of rotation (speed A) dependent upon the gear ratio between sun gear  42  and the planetary gear  45 . 
     The planetary gear  45  is also driven by the planetary carrier (disc  52 ) in an anti-clockwise direction due to it being caused to orbit the sun gear  42  in an anti-clockwise direction. This has the effect of increasing the speed of rotation of the planetary gear  45  by an additional speed (speed B) such that the resultant speed of rotation of the planetary gear is a combination of speed A+speed B. 
     The orbital movement of planetary gear  45  in the anti-clockwise direction acts to impart an anti-clockwise rotation on the sun gear  44  at a speed (speed C) which is dependent upon the orbital speed of planetary gear  42  (i.e. speed of rotation of housing disc  52 ). 
     This is contrary to the direction of rotation which the rotational movement of planetary gear  42  attempts to rotate the sun gear  44 , i.e. the planetary gear  42  attempts to rotate the sun gear in the clockwise direction. 
     Accordingly, if the combined rotational speed (speed A+speed B) of the planetary gear  42  exceeds the orbit speed (speed C), the sun gear  44  will be caused to rotate in a clockwise direction at a speed which is proportional to the difference between the rotational speed of the planetary gear  42  and its orbital speed. 
     Conversely, if the orbital speed (speed C) exceeds the combined rotational speed (speed A+speed B) then the sun gear  44  will be caused to rotate in an anti-clockwise direction at a speed which is proportional to the difference between the planetary gears&#39; rotational and orbital speeds. If the orbital speed and rotational speed of the planetary gear  42  are equal, then the sun gear  44  will not be rotationally driven and will remain static, i.e. a neutral condition will prevail. 
     Accordingly, it will be appreciated that the planetary gear  45  rotatably drives the sun gear  44  in either an anti-clockwise or clockwise direction or does not impart a rotatable drive to the sun gear  44  (neutral condition) in dependence upon the relative speed of rotation of the sun gear  42  and disc  52 . 
     It is envisaged that the construction of the epicyclic gear assembly  40  may be varied in order to provide different drive transmission paths through the epicyclic gear assembly  40  and so provide different drive/torque transmission characteristics for driving the load. 
     Examples of different epicyclic gear assembly constructions are illustrated in  FIGS. 2 to 4  wherein components similar to those in the gear assembly  40  of  FIG. 1  are designated by the same reference numerals. 
     In the embodiment  100  illustrated in  FIG. 2 , the rotary drive output  30  is defined by a sleeve  32  having a radial flange  132  on which is mounted an internally toothed ring gear  135 . 
     In embodiment  100  each planetary gear  45  is carried by the housing disc  52  via a stub shaft  49  and is in driving connection with the ring gear  135  via an idler planetary gear  145 . Each idler gear  145  is rotatably mounted on the housing disc  52  via a stub shaft  146 . 
     The embodiment  100  of  FIG. 2  functions in a similar manner to embodiment  10  in that the direction of rotation of the ring gear  135  is dictated by the difference between the peripheral speed (speed C) which the orbital motion of the idler gear  145  imparts onto ring gear  135  and the peripheral speed (speed A+speed B) which the rotational motion of the idler gear  145  imparts onto ring gear  135 . 
     In the embodiment  200  illustrated in  FIG. 3  the radial flange  132  of the rotary drive output  30  defines a planetary carrier upon which the planetary gear(s)  45  are rotatably mounted via stub shaft(s)  49 . 
     An internally toothed ring gear  152  is mounted on the housing disc  52  and is arranged to mesh with the or each planetary gear  45 . The or each planetary gear  45  is, in turn, in mesh with the sun gear  42 . 
     Accordingly, as illustrated in  FIG. 3 a   , the anti-clockwise rotating ring gear  152  (I 2 ) acts to rotate each planetary gear  45  in an anti-clockwise direction and the clockwise rotating sun gear  42  (I 1 ) also acts to rotate each planetary gear  45  in an anti-clockwise direction. If the peripheral speed at the interface between, on the one hand, the ring gear  152  and planetary gear  45  exactly matches, on the other hand, the peripheral speed at the interface between the planetary gear  45  and sun gear  42  then the stub shaft  49  will remain stationary and a ‘neutral’ drive condition will prevail, i.e. the drive output  30  will remain stationary. 
     If the peripheral speed of the planetary gear  45  exceeds that of the sun gear  42  (as brought about by the ring gear  152  (I 2 )) then the stub shaft  49  will be caused to orbit the sun gear  42  in an anti-clockwise direction and so cause the rotary output  30  to rotate in an anti-clockwise direction and at a speed which is proportional to the difference in peripheral speeds between the sun gear  42  and planetary gear  45 . Conversely, if the peripheral speed of the planetary gear  45  is greater than that of the ring gear  152  (as brought about by a decrease in the speed of rotation of the ring gear  152  (I 2 )), then the stub shaft  49  will be caused to orbit the sun gear  42  in a clockwise direction and so cause the rotary output  30  to rotate in a clockwise direction and at a speed which is proportional to the difference in peripheral speeds between the ring gear  152  and planetary gear  45 . 
     The embodiment  300  illustrated in  FIG. 4  is similar to embodiment  200  in that the radial flange  132  defines a planetary carrier. In embodiment  300 , an externally toothed ring gear  160  is mounted on the housing disc  52  and meshes with each planetary gear  45 . Each planetary gear  45  drivingly meshes with sun gear  42  via an idler planetary gear  145 . 
     Operation of embodiment  300  is the same as that of embodiment  200  in that the rotary output  30  will be caused to rotate in the anti-clockwise direction in the event that the peripheral speed of the idler planetary gear  145  is greater than the peripheral speed of sun gear  42  and is rotated in the clockwise direction in the event that the peripheral speed of the planetary gear  45  is greater than the peripheral speed of the ring gear  160 . 
     In the above embodiments of  FIGS. 1 to 4 , the first input drive I 1  is defined by a sun gear  42 . However, as illustrated by way of example in the embodiments shown in  FIGS. 6 and 7 , it is envisaged that the first input drive I 1  may instead by defined by a planetary carrier  432 . 
     In the fifth embodiment  400 , parts similar to those in the previous embodiments have been designated by the same reference numerals. The epicyclic gear assembly  40  includes a planetary carrier  432  which carries at least one pair of planetary gears  45 ,  145 . The planetary carrier  432  is mounted on shaft  25  so as to be rotatable in unison therewith but is preferably axially movable thereon to thereby enable an axial loading to be applied by the shaft adjustment means  80  onto discs  51 ,  52 . 
     Planetary gear  45  of each pair of planetary gears is in mesh with ring gear  152  mounted on disc  52  and planetary gear  145  is in mesh with sun gear  44  on sleeve  32 . 
     The embodiment  500  shown in  FIG. 7  differs from embodiment  400  in that in embodiment  500 , planetary gear  45  is in mesh with an externally toothed ring gear  160  and also with the sun gear  44  i.e. intermediate planetary gear  145  has been omitted. 
     Operation of embodiments  400  and  500  is similar to that for the previous embodiments illustrated in  FIGS. 1 to 4 . In summary, as illustrated in  FIGS. 6 a  and 7 a   , the planetary gear  45  is caused to undergo rotation about its axis caused by the combination of two drive sources, viz. a rotary speed A caused by rotation of the planetary carrier and rotary speed B caused by rotation of the ring gear  152  or  160 . These rotary speeds A, B act in the same direction to drive the sun gear  44  in an anti-clockwise direction (when shaft  25  is rotating in a clockwise direction). 
     The planetary carrier  432  rotates in a clockwise direction and so moves the planetary gears  45 ,  145  in a clockwise orbit around the sun gear  44  and so attempts to drive the sun gear  44  in the clockwise direction at a speed C. 
     As in the earlier embodiments of  FIGS. 1 and 2 , it will be seen therefrom that the direction of rotation and speed of rotation of the output  30  will be dependent upon the difference between the combined speeds (A+B) and that of speed C. 
     In the embodiments described with reference to  FIGS. 1 to 4 , the channels  53  of the variator  50  are shown as being semi-circular in circumferential extent. It is envisaged that channels  53  may instead have a shorter circumferential extent, such as for example a quarter of a circle. This is illustrated, by way of example, in the embodiments  400 ,  500  of  FIGS. 6 and 7  respectively. 
     A modified wheel assembly WA for transmitting drive between the discs  51 ,  52  is illustrated in  FIG. 8 . Parts similar to those illustrated in the earlier drawings are designated by the same reference numerals.