GB2394519A - A continuously variable transmission device - Google Patents

Abstract

A continuously variable transmission device, for a cycle or ancillary drives, has a plurality of planetary spheres 15 in rolling contact with radially inner and outer races 13, 14 each comprising at least two axially spaced parts 13a-14b. A planet follower carrier 12 engages the planetary spheres 15 and is rotatably mounted with respect to a spindle 18. Axial separation of the outer race parts 14a, 14b is controlled by lever 52 which operates a ball-screw mechanism 17, 28 that moves the race parts 14a, 14b either closer together or further apart, thereby applying a greater or lesser force to the planetary spheres 15. The force applied to the planetary spheres 15 is transferred to the inner race parts 13a, 13b which move, via interengaging parts 30a, 30b, to accommodate the planetary spheres 15 and thereby alter the gear ratio. In one embodiment drive input is via a toothed chain wheel and the planet follower carrier 12 is connected to an output drive. In another embodiment (fig 3) input is to the planet follower carrier 12 via a crankshaft pulley.

Description

239451 9

A CONTINUOUSLY VARIABLE DRIVE TRANSMISSION DEVICE

The present invention relates generally to a continuously variable drive transmission 5 device, and particularly to a drive transmission device in which forces are transmitted by rolling traction.

In patent application no. PCT/GB99/00075 there is described a continuously variable drive transmission for transmitting drive between an input and an output drive 10 member and having radially inner and outer races separated into axially spaced two parts which are relatively axially displaceable and between which are located planetary members the radial position of which is determined by the relative separation of the two parts of one of the races. The other of the races is provided with a mechanism which allows the two parts to move apart or together in order to 15 accommodate changes in the radial position of the planetary members consequent on an adjustment in the axial separation of the two parts of the said one race. This mechanism is effectively torque sensitive in that the forces exchanged between the contacting surfaces of the races and the planetary members is varied in dependence on the torque applied to the said other of the races.

Torque sensitivity is achieved by means of a helical interengagement of the two members of the "other" race in the form of a screw thread. As torque is applied the two parts of the race are caused to tend to turn in relation to one another in a sense such that the screw threaded engagement between them causes relative approach

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thereby increasing the contact forces between the races and the planetary members.

Correspondingly, if the torque is decreased, for a given direction of rotation, the forces on the contacting surfaces between the two parts of the "other" race and the planetary members decreases and this continues to the point where, when there is no 5 torque, the contacting forces fall substantially to zero.

In one arrangement, an epicyclic fixed gear train is connected to the input of the continuously variable transmission device to adapt the transmission for use as a bicycle gear hub transmission. In this arrangement the central shaft of the 10 transmission is a stationary spindle about which the entire device rotates. A radial flange at one end of the central shaft connects the shaft to a fixed outer casing which carries the outer ring of the fixed ratio epicyclic gear. The sun gear of the epicyclic gear is carried by one part of the radially inner or "other" raceway. The carrier of the epicyclic gear train is connected to a radial flange and a cylindrical outer housing 15 from which the bicycle wheel spokes project radially. The carrier of the continuously variable transmission has a cylindrical sleeve which is rotatably mounted on and disposed coaxially and concentrically with respect to the central spindle shaft. At one end the sleeve carries the transmission input drive sprocket.

2 0 In operation, rotation of the input sprocket, for example by means of a chain drive, causes rotation of the planet follower carrier and thus the planetary spheres urged by the roller followers carried by the planet follower carrier. The rotation of the planetary spheres is transmitted to the radially inner races which, carrying the sun gear of the fixed ratio epicyclic gear mechanism, causes the planet gears to rotate which, because

e: c:e:e: : : : they mesh with the stationary ring gear, causes the output housing to turn with a drive transmission ratio and direction of drive dependent on the adjustment of the radial position of the planetary spheres.

5 In a structure in which the transmission loads are high in relation to the overall size of the transmission, as in bicycle hub gears, there is a requirement to increase the load bearing capacity of the inter-engaging parts, such as the ball screw helical inter-

engagement between the two parts of the radially inner race, as in PCT/GB99/00075, without increasing the size of the transmission device.

The ball screws are not subject to cyclic fatigue loads and are designed to support static loads. In comparison, in non-cycle applications, the planetary spheres are subject to high fatigue loads and the spheres are designed to provided adequate fatigue life. In pedal cycle applications the spheres have a short fatigue life requirement and therefore the planet diameter can be reduced compared with non-pedal cycle applications. The diameter of the planet spheres in pedal cycle applications usually depends on the bottom gear requirement (ratio and duty) where the planet spheres can be subject to relatively high cyclic loads.

2 o In the context of the present application the term "bicycle" is used interchangeably with the more general term "cycle" and both terms are to be construed in a general sense to include any other pedal powered application.

t' c:.: À..e:.:-: According to an aspect of the invention there is provided a drive transmission comprising a continuously variable drive transmission of the type having a plurality of planetary members in rolling contact with radially inner and outer races each comprising at least two axially spaced parts, with a planet follower carrier engaging 5 the planetary members and rotatably mounted with respect to a spindle, in which the radially inner races are connected to a transmission input drive and the planet follower carrier is connected to a transmission output drive with the outer races held stationary with respect to the spindle and including means for adjusting the axial separation of the outer race parts, whereby to vary the transmission ratio.

The drive transmission according to this aspect of the invention is suitable for use as a bicycle transmission, and particularly for a bicycle gear hub transmission device.

With the input drive being to the inner races, the outer races being held fixed with respect to the stationary spindle and the output drive being taken from the planet 15 follower carrier it is possible to provide a compact, lightweight and mechanically simple continuously variable bicycle hub gear with appropriate gear ratios and force transmission characteristics. In another embodiment, the drive transmission provides a variable speed ancillary drive configured in one arrangement as a crankshaft pulley, that is to say with the input drive being provided by an engine crankshaft, connected 2 o to the inner races by a spline coupling or other means, with the planet follower carrier being connected to an output drive pulley.

Preferably, the transmission device further comprises a first helical inter-engagement means between the radially inner race parts acting to react the forces exerted by the

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transmission of drive forces between the radially inner race and the planet members.

In this arrangement, transmission loads are transferred along the length of the helical inter-engagement. The transmission loads in a bicycle transmission are high relative to the size of the transmission, because the fatigue life requirement is relatively short, 5 and in an arrangement according to this aspect of the invention the loads can be supported over a relatively large length of the helical inter-engagement. Very low gear ratios can be achieved in relatively small bicycle hub transmission arrangements without over-stressing the transmission.

10 In preferred embodiments, the said first helical inter-engagement means comprises a ball screw. This provides an efficient low friction connection between the inner race parts which can readily support the loads of the transmission and readily enable the inner race parts to be moved axially with respect to each other.

15 Preferably, the ball screw comprises a radially inner part and a radially outer part rotatably mounted on the said spindle. This provides for a compact and lightweight mechanical arrangement.

In preferred embodiments, the means for selectively varying the axial separation of 2 0 the two parts of the radially outer race comprises a second helical interengagement means. Preferably, the second helical interengagement means comprises a screw threaded engagement of the outer races themselves, one of the two outer races being rotatable

t.:::: À e. Be: through at least a limited arc of movement about the spindle axis and the said other of the outer races being held rotationally stationary with respect to the spindle. In this way it is possible to adjust the relative axial separation of the outer race parts and thereby the transmission ratio by turning one of the outer race parts with respect to the 5 other outer race part about the spindle axis. The screw thread arrangement provides a relatively simple and robust form of helical interengagement between the outer race parts. Preferably, the said input and output drive members are mounted directly or indirectly 10 on the said spindle for relative rotation about the spindle axis. This further provides for a lightweight simple and mechanically robust transmission arrangement which is suitable for use as a bicycle hub transmission or a variable speed ancillary drive.

The invention also contemplates a variable speed ancillary drive, which may be 15 configured as a crankshaft pulley arrangement, including a transmission device according to the above mentioned aspect of the invention.

According to another aspect of the invention there is provided a continuously variable drive transmission of the type having a plurality of planetary members in rolling 2 0 contact with radially inner and outer races each comprising at least two axially spaced parts, with a planet follower carrier engaging the planetary members and rotatably mounted with respect to a spindle, in which the radially inner races are connected to a first transmission input or output drive and the planet follower carrier is connected to a second transmission input or output drive for drive transmission between the said

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À first and second drives with the outer races held stationary with respect to the spindle and including means for adjusting the axial separation of the outer race parts, whereby to vary the transmission ratio. In this respect the invention also contemplates embodiments where the input and output drives are reversed, that is to say with the 5 inner race being connected to the output drive and the planet follower carrier being connected to the input drive. For example, in applications such as centrifugal air compressors and the like it is necessary for the input shaft speed to be higher than the output speed of conventional prime movers, and this 'reverse' configuration is appropriate for such applications.

In the context of the present invention the term "spindle" refers to any axle like component suitable for a continuously variable drive transmission of the aforementioned type.

15 Various embodiments of the invention will now be more particularly described, by way of example, with reference to the accompanying drawings in which: Figure l is an axial cross-section view of an embodiment of the present invention in a configuration resulting in a high transmission ratio superimposed with a configuration resulting in a low transmission ratio; 2 0 Figure 2 is a sectional view taken on the line I-I of Figure l; and, Figure 3 is an axial cross-section view similar to that of Figure l but showing a drive transmission according to another embodiment of the present invention.

Referring now to the drawings of Figures l and 2, a drive transmission device

# r, ',, t I c, À generally indicated 10, which in this embodiment constitutes a bicycle hub gear, comprises an outer cylindrical casing 12 housing a continuously variable rolling traction drive transmission. The rolling traction drive transmission comprises radially inner and outer races 13, 14 axially separated into two parts 13a, 13b and 14a, 14b.

5 Between the races 13, 14 are located planet balls 15 between which are located respective planet follower rollers 16 mounted on a follower cage 17 or carrier which is connected to the cylindrical casing 12 for rotation therewith. The cylindrical casing 12 constitutes the output drive member of the transmission device and includes radial flange portions 32a, 32b at opposite axial ends thereof for receiving wheel spokes or 1 0 the like of a bicycle wheel (not shown). The cylindrical casing is rotatably mounted on a central spindle shaft 18 which is provided with threaded end portions 19a, 19b at opposite ends thereof for fixing the hub transmission device between two support stays (not shown) of a bicycle frame so that the central spindle 18 is held stationary with respect to the bicycle frame for torque reaction in use. The outer casing 12 is 15 borne on the spindle 18 by a bearing 20a located on an increased diameter portion of the spindle at one end of and by a bearing 20b at the other axial end thereof. The bearing 20b is borne on an input shaft 21 which constitutes the input drive member of the transmission device which is itself borne on a bearing 22 on the spindle at the opposite end of the spindle to the bearing 20a. The input drive shaft 21 carries an 20 input drive sprocket 31 for engagement with a bicycle chain for driving the transmission. The planets and/or the races may be made of any material capable of supporting the loads exerted on them in use, and in particular may comprise a ceramic material

l le,:e t.' tte:' which has the benefit of having a high modulus of elasticity which gives it a high rigidity. The contact patches of the planets and races are therefore small and efficiency is high.

5 The two axially separated parts 13a, 13b of the radially inner race 13 are provided with axially extending coaxial shaft portions 30a and 30b each having a set of overlapping helical grooves 23 on the respective radially inner and outer sides thereof.

The helical grooves 23 house balls 24 which run in the helical grooves 23. The helical grooves 23 and balls 24 constitute a helical interengagement or threaded 10 coupling between the two parts 13a, 13ballowing the twoparts 13a, 13btorotatewith respect to one another with low friction provided by the balls 24, and at the same time vary their relative axial positions. The balls 24 are prevented from escaping from the helical grooves by simple stops (not shown) mounted in the outer grooves near their respective ends. A light torsion spring 26 pre-loads the two parts 13a, 13b of the 15 inner race 13 towards one another to maintain initial contact. As an alternative, where heavy loads are involved, the balls 24 may be replaced by rollers, with corresponding changes being made to the shape of the grooves.

The inner race part 13a is connected to the input shaft 21 by a spline coupling 40 for 2 0 rotation therewith and is rotatably mounted on the spindle by means of the bearing 22 and a bearing 25 at the opposite end of the inner race part 13a.

The two parts 14a, 14b of the radially outer race 14 are interengaged by a helical interengagement or threaded coupling comprising helical grooves 27 in the first part

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14a of the outer race and corresponding helical grooves 28 in the second part 14b. The helical grooves 27 and 28 constitute a threaded interengagement between the two parts 14a, 14b which enables the axial separation of the two parts to be altered by relative rotation of the outer race parts 1 4a, 14b.

The outer race part 1 4a is connected to and held stationary with respect to the spindle shaft 18 by a radial flange 29 which extends between the increased diameter portion of the spindle and the axial threaded part of the outer part 14a.

10 A radially extending control lever 51 extends within the casing and a peg 55 secured to the radially outer raceway part 14b runs in a slot 56 in the lever S l. The other end of the lever S 1 is connected to a shaft part SO which passes through a slotted aperture in the increased diameter portion of the spindle to connect the internal lever S 1 to an external radially extending lever 52. Movement of the control lever 52 about the axis 15 of the shaft SO causes the lever S 1 to turn correspondingly through a small angle and thus cause the raceway part 14b to turn about the axis of the spindle, with respect to the fixed radially outer raceway part 14a. This movement is converted by the helical interengagement constituted by the helical threaded channels 27 and 28 into axial approach or separation of the two radially outer raceway parts 14a, 1 4b depending on 2 0 the direction of rotation of the lever 52.

Rotation of the drive shaft 21 thus causes the radially inner race parts 1 3a and 1 3b to rotate with the shaft 21 and carrying with it, by rolling contact, the planetary spheres 1S which roll also over the curved surfaces ofthe radially outer race parts 14a, 14b.

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. À I. Is: The planetary balls 1 S are constrained only by their contact with the curved surfaces of the radially inner and radially outer races 13, 14 but each pair of planet balls 15 has a roller follower 16 intercalated circurnferentially therebetween so that the planetary motion of the balls 15 is conveyed to these rollers and to the planet cage or carrier 17 5 which, is connected to the output drive. Variation in the relative approach or separation of the radially outer race parts 14a, 14b caused by turning the control lever 52 in one direction or the other, causes a greater or lesser force to be applied to the planetary balls 15 urging them radially inwardly to contact with the radially inner race parts 13a, lab. As the two radially outer parts 14a, 14b are brought together the 10 forces exerted on the planetary balls 15 increases and the radially inner force applied to the radially inner races 13a, 13b urging these apart is accommodated by relative rotation of the race part 13b with respect to the race part 13a on the helical interengagement of the shaft parts 30a, 30b.

15 The hand and lead of the outer helical thread are determined according to the forces applied to the outer raceway parts 1 4a and 1 4b. The hand and lead of the thread are chosen so that the tendency of the outer raceway parts to separate due to the normal contact forces applied by the planets is balanced by the tendency of the raceway parts to close together due to the tractive forces applied by the planets. By so doing, the 2 o force required to change the gear ratio is relatively small, even under the application of large drive torques. In practice, the actual force required to change ratio under load, and whether a force is required to prevent the transmission from self-shifting, depends to a large extent on the friction characteristics of the outer helical thread interengagement 27, 28. In general a ballscrew keeps shift forces low, but additional

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i means are required to stop the transmission from self shifting, for example, a shift motor with high 'cogging' torque, while a helical screw, as shown in Figure l requires higher shift forces but will hold the ratio selected. In this arrangement, shift torque can be reduced by reducing pedal torque during gear shifts.

Referring now to Figure 2, at their radially outermost position (shown by the broken lines 60 in Figure 2) the planetary spheres 15 engage and become supported in cradles 62 which are part of the carrier 17 such that drive torque is transmitted directly from the input drive member 21, to the inner race parts 13a, 13b through the planetary 10 spheres 15, to the output drive member, via the cradles 62 and carrier 17. In this radially outermost position further axial separation of the outer raceway parts disengages the planetary spheres from the outer raceway parts. In this way, there is a direct drive between the input drive member and the output drive member in, for example, a top gear configuration where the planetary spheres do not engage the outer 15 raceway parts. In this top gear configuration the rolling contact friction of the planetary spheres is reduced and this improves the efficiency of the transmission.

Referring to the embodiment shown in Figure 3, in this arrangement the transmission device 100 constitutes a variable speed ancillary drive which is configured as a 20 crankshaft pulley. The transmission of Figure 3 comprises all the same basic elements as the drive transmission of Figures 1 and 2 and where appropriate the same or similar parts are indicated by the same reference numerals. In the embodiment of Figure 3 the input shaft 21, which constitutes one end of a crankshaft, comprises the input drive member of the transmission. The input shaft 21 is connected to the shaft

. Be. -+ i. À À À;: I..:..DTD: portion 30b of the radially inner race part 1 3b by means of a spline coupling 40. The input shaft 21 is mounted directly on the spindle l 8 for relative rotation with respect thereto by means of the bearing 25 and a further bearing 41 positioned at one end of the spindle. In this arrangement the spindle 18 has a shorter axial length than the 5 spindle in the arrangement of Figures I and 2 and extends axially within the casing 12 from one side of the planetary spheres adjacent the end of the input shaft where it is supported in the bearing 4 l, to the other side thereof where it is supported at a mid point along its length in the bearing 25. The other end of the spindle extends outwards of the casing where it is connected to a torque reaction member 70 which 10 is fixed with respect to the spindle to prevent relative rotation of the spindle and reaction member. The torque reaction member 70 replaces the stays of the bicycle frame to which the spindle in the transmission of Figures 1 and 2 is connected to by means of the threaded parts 1 9a, 1 9b at the opposite axial ends of the spindle.

15 The input drive shaft 21 is mounted for rotation with respect to the carrier by means of a rolling element bearing 71 located between a stepped diameter end portion 21a of the input shaft and a radially inner surface of a first cylindrical part 12a of the casing 12. The casing part 12a which is connected to the carrier 17 comprises a pair of coaxial concentric inner and outer cylinders. The outer cylinder 72 which 2 o constitutes an output drive member includes a plurality of V-shaped grooves 73 in its radially outer surface. The output drive member 72 is in the form of a so-called "poly-V" type pulley which engages a similarly grooved drive belt (not shown) for transmission of the drive from the input shaft 21 through the continuously variable drive transmission to the output drive member 72 and drive belt. The cylindrical

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he À c; casing 12 further comprises a second part 12b axially adjacent and connected to the part 12a and cylinder 72. The part 12b comprises a stepped diameter cylinder having a plurality of radially extending air cooling fins 73 on a radially outer surface of a greater diameter part with an adjacent smaller diameter part including a radial lip 73 5 at the axial end thereof for retaining an oil ring seal 74 in the region between the smaller diameter portion and a ratio changer shaft 75 rotatably mounted on the outer surface of the spindle 18 coaxial and concentric with the spindle, the said smaller diameter part and the torque reaction member 70. A further oil seal ring 76 is provided at the other end of the transmission device between the outer surface of the 1 0 input shaft 21 and the inner surface of the casing part 12a at the axial end thereof furthest from the casing part 12b. The oil seal ring 76 is fixed with respect to the cylindrical part 12a such that the input shaft 21 rotates within the seal 76. The other oil seal ring 74 is similarly fixed in relation to the cylindrical casing part 12b such that the ratio changer shaft 75 is rotatable with respect to the seal. A further oil seal in the 1 5 form of an o-ring seal 79 is located between the outer surface of the spindle shaft 18 and the inner surface of the shaft 75. The o-ring 79 is preferably located in aligned circumferential grooves in the shafts 18 and 75.

In this embodiment the ratio changer shaft 75 is mounted coaxially on the spindle 2 0 such that rotation of the shaft 75 about the spindle axis by rotation of a radially extending ratio change lever 77 causes a radial flange part 78 of the shaft 75 to rotate the outer race part 14a, to which it is connected, about the spindle axis with respect to the outer race part 14b which is rotationally fixed with respect to the spindle 18.

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. i a;. ,i It will be understood that the variable speed ancillary drive embodiment of the continuously variable transmission described with reference to the arrangement shown in Figure 3 functions in a broadly similar manner to the continuously variable bicycle transmission shown in the arrangements of Figures l and 2. In the embodiment of 5 Figure 3 however, the transmission is configured to transmit up to lOkW of power, for example, with a cooling capacity provided by the fins of about l kW. Thus, while the bicycle transmission can be lubricated with traction grease, the ancillary drive arrangement of Figure 3 requires a traction oil splash system, for example, and an oil to air heat exchanger which in the present arrangement is provided by the cooling fins 10 73.

As it can be seen in the drawings of Figures l to 3, in both arrangements the radially inner races are connected to the transmission input drive and the carrier is connected to the transmission output drive, the arrangements differing only with respect to the 15 specific design features of the input and output drive means.

Although aspects of the invention have been described with reference to the embodiments shown in the accompanying drawings it is to be understood that the invention is not limited to those precise embodiments and various changes and 20 modifications may be effected without exercise of further inventive skill. For example, the freewheel function normally provided in a cycle transmission may be included within the function of the transmission. Provided the preload between the inner race halves is small, that is spring 26 is weak, in the absence of input torque, as when freewheeling, the planet balls are in only light contact with the races and the

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i À; amount of drag torque thereby generated is negligible. In the ancillary drive arrangement it will be understood that the functions of the torque reaction member 70 and ratio changer 77 may be interchanged, the only requirement being that relative rotation of one with respect to the other causes relative axial movement of the two 5 outer parts 14a, 14b. If the torque reaction member 70 and ratio changer 77 are interengaged, the hand of the outer helical interconnection is also changed so that substantially all torque reaction is provided by the now torque reaction member 77, with the ratio changer 70 being only lightly loaded, even under full load shifting (ratio change) conditions.

The ancillary drive embodiment of Figure 3 has been described with reference to a crankshaft pulley arrangement. It will be understood, however, that the present invention contemplates further ancillary drive configurations including other pulley arrangements where the ancillary drive is configured to be driven by a drive belt 15 pulley connected to the inner race shaft part 30b with the planet follower carrier being connected to a drive shaft to provide an output drive to the ancillary device, for example an alternator, that is to say in a reverse configuration to that shown in Figure

Claims (13)

: les - i À e le À: CLAIMS

1. A continuously variable drive transmission of the type having a plurality of planetary members in rolling contact with radially inner and outer races each 5 comprising at least two axially spaced parts, with a planet follower carrier engaging the planetary members and rotatably mounted with respect to a spindle, in which the radially inner races are connected to a transmission input drive and the planet follower carrier is connected to a transmission output drive with the outer races held stationary with respect to the spindle and including means for adjusting the axial separation of 10 the outer race parts, whereby to vary the transmission ratio.

2. A transmission device as claimed in Claim 1, further comprising a first helical

interengagement means between the radially inner race parts acting to react the forces exerted by the transmission of drive forces between the radially inner race and the 15 planet members.

3. A transmission device according to Claim I or Claim 2, wherein the said first helical interengagement means comprises a ball screw.

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4. A transmission device according to Claim 3, wherein the ball screw comprises a radially inner part and a radially outer part rotatably mounted on the said spindle.

5. A transmission device as claimed in any preceding claim wherein the means for selectively varying the axial separation of the two parts of the radially outer race j

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comprises a second helical interengagement means.

6. A transmission device as claimed in Claim 6, wherein the second helical interengagement means comprises a screw threaded engagement of the outer races 5 themselves, one of the two outer races being turnable through at least a limited arc of movement about the spindle axis and the said other of the outer races being held stationary with respect to the spindle.

7. A transmission device as claimed in any preceding claim, wherein the said l o input and output drive members are mounted on the said spindle for relative rotation about the spindle axis.

8. A transmission device as claimed in any preceding claim wherein the said output drive comprises a poly-V grooved cylinder.

9. A transmission device as claimed in any preceding claim wherein the said output drive is provided with means for engaging a drive belt or chain.

10. A transmission device as claimed in a Claim 9 wherein the said means for 20 engaging a drive belt comprises a poly-V belt, V belt, toothed belt or flat belt engagement means.

l 1. A transmission device as claimed in any preceding claim wherein the said output drive is rotatable with at least one air cooling means.

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12. A continuously variable drive transmission of the type having a plurality of planetary members in rolling contact with radially inner and outer races each comprising at least two axially spaced parts, with a planet follower carrier engaging 5 the planetary members and rotatably mounted with respect to a spindle, in which the radially inner races are connected to a first transmission input or output drive and the planet follower carrier is connected to a second transmission input or output drive for drive transmission between the said first and second drives with the outer races held stationary with respect to the spindle and including means for adjusting the axial 10 separation of the outer race parts, whereby to vary the transmission ratio.

13. A continuously variable drive transmission substantially as hereinbefore described with reference to the accompanying drawings.