Transmission

Abstract

A transmission comprises a pusher 14, a tine assembly 20, a guide 15 and a gear 16. The pusher rotates about a primary axis 17 and a mechanism (30 figure 9) is configured to controllably adjust a radial position of the pusher relative to the primary axis. The tine assembly is configured such that rotation of the pusher causes movement of the tine assembly. The guide configured to guide movement of the tine assembly. The gear configured to be driven by the tine assembly.

Description

Field The present application relates to a transmission. More particularly, embodiments of the present application relate to a continuously variable transmission. Background A transmission may be used to change the direction and / or speed of rotation in an apparatus. For example, machines such as cars, bicycles and windmills may use a transmission. Such a transmission may have a plurality of possible gear ratios. A multi-ratio transmission may be switchable between a plurality of different gear ratios. The gear ratio may be selected depending on circumstances, for example whether acceleration is desired or to provide a target torque. A continuously variable transmission (CVT) may have a substantially continuous range of gear ratios. This may allow a smoother adjustment of gear ratio. Transmissions, and particularly CVTs, can have a complicated design and / or may be expensive to manufacture. It is desirable to provide a transmission with a simpler design and / or which is less expensive to manufacture. Summary According to an aspect of the present invention, there is provided a transmission. The transmission may comprise a pusher. The pusher may be configured to rotate about a primary axis. The transmission may comprise a mechanism. The mechanism may be configured to controllably adjust a radial position of the pusher relative to the primary axis. The transmission may comprise a tine assembly. The tine assembly may be configured such that rotation of the pusher causes movement of the tine assembly. The transmission may comprise a guide. The guide may be configured to guide movement of the tine assembly. The transmission may comprise a gear. The gear may be configured to be driven by the tine assembly. Optionally, the transmission is configured such that a gear ratio of the transmission decreases as the radial position of the pusher is adjusted radially outwardly. Optionally, the mechanism is configured to apply a force to urge the pusher in a direction that corresponds to a decrease of a gear ratio of the transmission. Optionally, the transmission comprises a controller configured to control the force applied by the mechanism. Optionally, the tine assembly is configured to drive the gear rotationally about the primary axis. Optionally, the transmission is configured such that rotation of the pusher in either rotational direction about the primary axis drives the gear in the same direction. Optionally, the transmission is configured such that rotation of the pusher causes movement of the tine assembly about the primary axis. Optionally, the tine assembly comprises a hub configured such that rotation of the pusher causes movement of the hub. Optionally, the hub is configured to rotate about a hub axis parallel to the primary axis. Optionally, the transmission is configured such that rotation of the pusher in either rotational direction about the primary axis causes the hub to rotate in the same rotational direction about the hub axis. Optionally, the transmission comprises a pusher bearing at an interface between the pusher and the hub, so as to allow relative rotation about the hub axis between the pusher and the hub. Optionally, the tine assembly comprises a plurality of guide tines extending from the hub and configured to engage with the guide such that engagement between the guide tines and the guide guides movement of the tine assembly. Optionally, the guide tines are pivotably secured to the hub. Optionally, the tine assembly comprises a plurality of guide springs configured to bias the respective guide tines into engagement with the guide. Optionally, the guide tines extend in a same sense around the primary axis. Optionally, the tine assembly comprises a plurality of gear tines extending from the hub and configured to engage with the gear so as to drive the gear. Optionally, the gear tines are pivotably secured to the hub. Optionally, the tine assembly comprises a plurality of gear springs configured to bias the respective gear tines into engagement with the gear. Optionally, the gear tines extend in a same sense around the primary axis. Optionally, the guide tines and the gear tines extend in opposite senses around the primary axis. Optionally, the gear comprises an internal gear. Optionally, the gear is centred on the primary axis. Optionally the gear is a guide. Optionally, the guide has a fixed rotational position about the primary axis. Optionally, the guide comprises an internal gear. Optionally, the guide is centred on the primary axis. Optionally the guide is a gear. Optionally, the transmission comprises a driver configured to rotate about the primary axis and engaged with the pusher such that rotation of the driver about the primary axis drives rotation of the pusher about the primary axis. Optionally, the pusher is slidably engaged with the driver such that the pusher slides relative to the driver as the radial position of the pusher is adjusted. Optionally, the transmission comprises a shaft secured to the driver such that the shaft rotates together with the driver. Optionally, the transmission comprises a support structure, wherein the rotation of the driver about the primary axis is relative to the support structure. Optionally, the transmission comprises a drive bearing at an interface between the driver and the support structure, so as to allow the driver to rotate about the primary axis relative to the support structure. Optionally, the guide has a fixed rotational position relative to the support structure. Optionally, the transmission is a continuously variable transmission. Brief Description Of The Drawings The present invention will be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side view of a transmission; Figure 2 is a perspective view of part of the transmission shown in Figure 10; Figure 3 is a perspective view from an underside of the transmission shown in Figure 1; Figure 4 is a plan view of part of the transmission shown in Figure 1; Figure 5 is a plan view of part of the transmission shown in Figure 1; Figure 6 is a schematic diagram of a tine assembly of the transmission shown in Figure 1; Figure 7 is a schematic diagram of a part of the transmission shown in Figure 1; Figure 8 shows a path traced by a point at the edge of the hub during use of the transmission; and Figure 9 is a schematic diagram of a mechanism of the transmission shown in Figure 1. Detailed Description Figure 1 is schematic diagram of a transmission 10. Figure 1 is a side on view of the transmission 10. Figure 2 is a perspective view of part of the transmission 10 shown in Figure 1. In particular, Figure 2 shows the transmission 10 of Figure 1 with the gear 16 and part of the tine assembly 20 omitted. Figure 2 is a perspective view of the transmission 10 of Figure 1 from generally above and to one side of the transmission 10. Figure 3 is another perspective view of part of the transmission 10 shown in Figure 1. Figure 3 shows the transmission 10 from generally below and to one side of the transmission 10. Figure 3 shows the same parts of the transmission 10 as are shown in Figure 2. In other words, Figure 3 shows the transmission 10 of Figure 1 but with the gear 16 and part of the tine assembly 20 omitted. Figure 4 is a plan view of the transmission 10. In particular, Figure 4 is a plan view of the parts of the transmission 10 that are shown in Figure 2 and Figure 3. Figure 4 is a plan view of the transmission 10 shown in Figure 1 but with the gear 16 and part of the tine assembly 20 omitted. As shown in Figures 2 to 4, optionally the transmission 10 comprises a pusher 14. The pusher 14 may be connected to an input force, for example an input rotation. The pusher 14 may be configured to transfer the input force to other components of the transmission 10, for example so as to drive the gear 16. The gear 16 may be an output gear of the transmission 10. Alternately, the transmission 10 may be driven in reverse. The gear 16 may be an input gear of the transmission 10. The input may cause the pusher 14 to be driven. The movement of the pusher 14 may be the output of the transmission 10, or may be connected to an output of the transmission 10. Optionally, the pusher 14 is configured to rotate about a primary axis 17. The primary axis 17 is shown in Figure 1 and Figure 4. As shown in Figures 2 to 4, optionally the pusher 14 may have a generally circular outer edge. The centre of the circle is offsetable from the primary axis 17. The pusher 14 does not necessarily rotate about its own centre. Optionally, the pusher 14 maintains a constant position along the primary axis 17. The pusher 14 does not move along the primary axis 17. The pusher 14 may be substantially planar. The pusher 14 may be formed from a plate. The pusher 14 may comprise a metal. Figure 7 is a schematic diagram of the pusher 14. Optionally, the centre of the circle defined by the outer edge of the pusher 14 coincides with a hub axis 18. As shown in Figure 7, there may be an offset 19 between the hub axis 18 and the primary axis 17. Figure 7 shows the pusher 14 in a position in which the offset 19 is relatively large. Figure 4, for example, shows the pusher 14 in a position in which the offset between the primary axis 17 and the hub axis 18 is relatively small. Optionally, the pusher 14 is moveable so as to adjust the offset 19 between the primary axis 17 and the hub axis 18. The pusher 14 may be configured to move perpendicularly to the primary axis 17. The pusher 14 may be configured to move parallel to a plane of the pusher 14. The pusher 14 may be configured to move radially with respect to the primary axis 17. The pusher 14 is configured to rotate about the primary axis 17 regardless of the offset 19 between the primary axis 17 and the hub axis 18. As shown in Figure 7, optionally the transmission 10 comprises a mechanism 30. The transmission 10 may be a variable force transmission. For example, the transmission may be a CVT. The mechanism 30 may be configured to adjust the force of the variable force transmission. The mechanism 30 is configured to controllably adjust a radial position of the pusher 14 relative to the primary axis 17. The radial position may correspond to the offset 19 between the primary axis 17 and the hub axis 18. Figure 7 and Figure 4 correspond to different radial positions of the pusher 14 relative to the primary axis 17. Optionally, the mechanism 30 is controllable so as to switch between the plurality of different radial positions of the pusher 14. Optionally, the mechanism 30 is controllable so as to vary the radial position of the pusher 14 within a range. The range may be a substantially continuous range. The radial position of the pusher 14 may be controllable to substantially any radial position within a range, i.e. between a minimum and a maximum. Figure 4 shows the pusher 14 when the radial position of the pusher 14 is close to, but not at, the minimum radial position within the range. The minimum radial position may correspond to the minimum off set 19 between the primary axis 17 and the hub axis 18. Optionally, the minimum offset 19 is substantially zero. Figure 7 shows the pusher 14 with a radial position close to, but not necessarily at, the maximum radial position of the pusher 14. The maximum radial position of the pusher 14 may correspond to the maximum offset 19 between the primary axis 17 and the hub axis 18. Optionally, the maximum offset 19 is equal to or less than half of the diameter of the pusher 14 when viewed in plan view. As shown in Figures 1 to 4, optionally the transmission 10 comprises a tine assembly 20. The tine assembly 20 is configured such that rotation of the pusher 14 causes movement of the tine assembly 20. The pusher 14 may be engaged with the tine assembly 20. For example, as shown in Figures 2 to 4, optionally the pusher 14 is configured to push the tine assembly 20. As the pusher 14 rotates about the primary axis 17, the tine assembly 20 is caused to move. The movement of the tine assembly 20 may be generally about the primary axis 17. Optionally, the tine assembly 20 maintains a constant position along the primary axis 17. The tine assembly 20 does not move along the primary axis 17. The tine assembly 20 may extend further along a plane perpendicular to the primary axis 17 than along the primary axis 17. The tine assembly 20 may comprise a metal. Optionally, the pusher 14 at least partly overlaps the tine assembly 20 along the primary axis 17. Optionally, the pusher 14 is located at the same position along the primary axis 17 as the tine assembly 20. Optionally the tine assembly 20 fully overlaps the pusher 14 along the primary axis 17. Optionally the pusher 14 partly overlaps the tine assembly 20 along the primary axis 17. As shown in Figures 2 to 4, optionally the pusher 14 is substantially concentric with the tine assembly 20. For example, as shown in Figures 2 to 4, the pusher 14 may be located generally radially inwardly of the tine assembly 20. The pusher 14 may be configured to apply a force to a radially inward edge of the tine assembly 20. The pusher 14 may be nested radially inward of the tine assembly 20. The pusher 14 is configured to transmit rotation and / or direction to the tine assembly 20. As shown in Figures 1 to 4 optionally, the transmission 10 comprises a guide 15. The guide 15 is configured to guide movement of the tine assembly 20. As the tine assembly 20 moves, the tine assembly 20 is configured to engage with the guide 15. The engagement between the guide 15 and the tine assembly 20 affects the movement of the tine assembly 20. Optionally, the guide 15 is configured to constrain movement of the tine assembly 20. For example, the guide 15 may prevent tines 22 of the tine assembly 20 from extending radially output beyond the guide 15. Optionally, the guide 15 maintains a constant position along the primary axis 17. The guide 15 does not move along the primary axis 17. The guide 15 may be substantially planar. The guide 15 may be formed from a plate. The guide 15 may comprise a metal. Optionally, the guide 15 at least partly overlaps the tine assembly 20 along the primary axis 17. Optionally, the guide 15 is located at the same position along the primary axis 17 as the tine assembly 20. Optionally the tine assembly 20 fully overlaps the guide 15 along the primary axis 17. Optionally the guide 15 partly overlaps the tine assembly 20 along the primary axis 17. Optionally, the guide 15 at least partly overlaps the pusher 14 along the primary axis 17. Optionally, the guide 15 is located at the same position along the primary axis 17 as the pusher 14. Optionally the pusher 14 fully overlaps the guide 15 along the primary axis 17. Optionally the guide 15 fully overlaps the pusher 14 along the primary axis 17. As shown in Figure 1, optionally the transmission 10 comprises a gear 16. The gear 16 is configured to be driven by the tine assembly 20. The gear 16 may form an output of the transmission 10. Movement of the pusher 14 may cause the gear 16 to be driven. Direction and / or force may be transmitted from the pusher 14 to the gear 16. Optionally, the gear 16 maintains a constant position along the primary axis 17. The gear 16 does not move along the primary axis 17. The gear 16 may be substantially planar. The gear 16 may be formed from a plate. The gear 16 may comprise a metal. Optionally, the gear 16 at least partly overlaps the tine assembly 20 along the primary axis 17. Optionally, the gear 16 is located at the same position along the primary axis 17 as the tine assembly 20. Optionally the tine assembly 20 fully overlaps the gear 16 along the primary axis 17. Optionally the gear 16 partly overlaps the tine assembly 20 along the primary axis 17. Optionally, the gear 16 is axially distance from the guide 15. Optionally, the gear 16 is axially distance from the pusher 14. During use of the transmission, the guide 15 may be held (e.g. secured to a frame) and the gear 16 may be released (i.e. free to rotate relative to the frame) such that the gear 16 rotates. As mentioned above, the transmission 10 may be driven in reverse. For example, if the gear 16 is held and the guide 15 released the guide 15 will rotate and vice versa. If both the gear 16 and guide 15 are not held the guide 15 or gear 16 with the least resistance will rotate. Optionally the gear 16 and the guide 15 have the same construction. Alternatively, they may have a different construction (e g. different diameters). Optionally the guide 15 is a gear. The guide 15 may be configured to be a guide or gear or both guide and gear configured to guide the movement of the tine assembly 20 and / or to be driven by the tine assembly 20. The gear 16 or guide 15 or both gear 16 and guide 15 may be driven by the tine assembly 20 and / or guide the movement of the tine assembly 20. Optionally the gear 16 is a guide. Optionally the gears are guides. Optionally the guides are gears. Optionally the guides are both gears and guides. Optionally, the transmission 10 is configured such that a gear ratio of the transmission 10 decreases as the radial position of the pusher 14 is adjusted radially outwardly. Figure 2 shows the pusher 14 relatively close to the centre. The offset between the primary axis and the hub axis 18 is relatively small. The pusher 14 is close to its radially inward end of its range of movement. The radial position shown in Figure 2 corresponds to a relatively high gear ratio. In contrast, Figure 7 shows a greater offset 19 between the primary axis and the hub axis 18. The radial position of the pusher 14 has been adjusted (compared to the position shown in Figure 2) radially outwardly. The radial position of the pusher 14 shown in Figure 7 corresponds to a relatively low gear ratio. In general, a low gear ratio may be appropriate when acceleration is desired. A high gear ratio may be appropriate when a greater output torque is desired. The mechanism 30 is configured to controllably adjust the radial position of the pusher 14 relative to the primary axis 17. The mechanism 30 is configure to adjust the gear ratio of the transmission 10. Optionally, a user may control the mechanism 30 so as to set a desired gear ratio for the transmission 10. Alternatively, the mechanism 30 may be configured to adjust the gear ratio of the transmission 10 automatically. Optionally, the mechanism 30 is configured to apply a force to urge the pusher 14 in a direction that corresponds to a decrease of a gear ratio of the transmission 10. For example, as mentioned above, the gear ratio may generally be lower for more radially outward positions of the pusher 14. The mechanism 30 may be configured to apply a force to urge the pusher 14 radially outwardly. During use of the transmission 10, there may be resistance to motion. For example, resistance may be due to friction between a vehicle comprising the transmission 10 and a track (e.g. a road). Resistance may be also due to friction within the transmission 10 itself. Such resistance may generally act to urge the pusher 14 in a direction that corresponds to an increase of the gear ratio of the transmission 10. For example, in the arrangement shown in figures 1 to 4, the resistance may generally act to apply a force to urge the pusher 14 radially inwards. The resistance may generally act to decrease the offset 19 between the primary axis 17 and the hub axis 18. Optionally, the mechanism 30 is configured to apply a force that opposes a force due to resistance. The radial position of the pusher 14 relative to the primary axis 17 may remain relatively stale when the forces from the mechanism 30 and resistance balance each other out. Merely as an example, a bicycle may comprise the transmission 10. A user of the bicycle may push the pedals around. The pushing of the pedals may provide the input power for the transmission 10. The pushing of the pedals round may drive the pusher 14 to rotate, for example about the primary axis 17. Resistance, for example, due to friction between the bicycle and the road, may generally act to urge the pusher 14 radially inwards. The mechanism 30 may act to urge the pusher 14 radially outwards. When the input power by the user and the resistance remain substantially constant, the radial position of the pusher 14 may be stable. When the resistance changes, the radial position of the pusher 14 may change. For example, if the bicycle starts to go uphill then the resistance may increase. As a result, the force urging the pusher 14 radially inwards may increase. This may cause the pusher 14 to move radially inwards. As the pusher 14 moves radially inwards, the gear ratio may increase. The speed of the bicycle may decrease. However, the user may continue to input the same power into pushing the pedals round. Optionally, the mechanism is configured to apply a force to urge the pusher 14, wherein the force is dependent on the radial position of the pusher 14. For example, optionally the force is greater for smaller offsets 19 between the primary axis 17 and the hub axis 18. For example, when the resistance increases, the pusher 14 may move radially inwards. As the pusher 14 moves radially inwards, the force applied by the mechanism 30 that opposes the resistance may increase. When the pusher 14 moves radially inwards, a new equilibrium may be found at which the forces urging the pusher radially inwards and radially outwards balance out. Accordingly, a new stable radial position of the pusher 14 may be found. Optionally, the transmission 10 comprises a controller configured to control the force applied by the mechanism 30. In an embodiment, a user may use the controller so as to control the force applied by the mechanism 30. Alternatively, the controller may automatically control the force applied by the mechanism 30. The controller may be configured to control the force applied by the mechanism 30 for a given radial position of the pusher 14. For example, when the transmission 10 is applied to a bicycle the user of the bicycle may use the controller so as to set the force applied by the mechanism 30 for a given radial position of the pusher 14. The user may use the controller so as to set the level of power that they intend to input into the transmission 10 by pushing the pedals round. As the resistance varies, the radial position of the pusher 14 may vary. This adjustment may be automatic. Alternatively, the user may select between a plurality of different gear ratios of the transmission 10. Optionally, the mechanism 30 comprises a resilient member. For example, the resilient member may be a spring. The spring may act to push the pusher 14 away from the centre, i.e. to increase the offset 19. The controller may be configured to controllably adjust a property of the spring. For example, the controller may be configured to adjust a stiffness of the spring and / or a tension in the spring. By adjusting the properties of the spring, the force applied on the pusher 14 for a given radial position of the pusher 14 may be adjusted. Figure 9 is a schematic diagram of the mechanism 30 of the transmission 10. As shown in Figure 9, optionally the mechanism 30 comprises a tether 40. The tether 40 is configured to apply a force to the pusher 14. The tether 40 is configured to apply a force to the pusher 14 so as to move the pusher 14 off-centre. As shown in Figure 7, optionally the pusher 14 comprises an engagement member 39. The engagement member 39 may be configured to engage with the tether 40. The tether 40 may be secured to the pusher 14. For example, the tether 140 may be secured to the engagement member 39. One end of the tether 40 may be secured to the pusher 14. The tether 40 may comprise a chain or a rope, for example. Optionally, the tether 40 is arranged to be in tension during use of the transmission 10. The tether 40 is configured to pull the pusher 14 off-centre. As shown in Figure 9, optionally the mechanism comprises an adjuster 47. The adjuster 47 is configured to adjust the force applied by the tether 40 to the pusher 14. The adjuster 47 may be adjustable so as to control the force applied to the pusher 14. The transmission 10 may comprise a controller configured to control the adjuster 47. In the arrangement shown in Figure 9, the adjuster 47 adjusts the force depending on the position of the adjuster 47. As shown in Figure 9, optionally the mechanism 30 comprises a resilient member 42. The resilient member 42 may be a spring, for example. The resilient member 42 may be in compression during use of the transmission 10. As the position of the adjuster 47 varies, the compression of the resilient member 42 varies correspondingly. The force applied by the compressed resilient member 42 may correspond to the force applied by the tether 40 to the pusher 14. As shown in Figure 9, optionally the mechanism 30 comprises a thread 41. The thread 41 may be secured to one end of the tether 40. The tether 40 may be secured between the pusher 14 and the thread 41. The adjuster 47 is configured to engage with the thread 41. For example, the adjuster 47 may comprise a complementary thread. The adjuster 47 may have an internal thread. The adjuster 47 may be a nut. Rotation of the nut may cause the longitudinal position of the adjuster 47 to vary, thereby compressing the resilient member 42. As shown in Figure 9, optionally the mechanism 30 comprises a washer 46. The washer 46 may be located between the resilient member 42 and the adjuster 47. Due to the compression of the resilient member 42, the resilient member 42 exerts a force on the washer 46, which in turn exerts the force on the adjuster 47. The adjuster 47 is secured to the tether 40 via the thread 41 such that the tether 40 is in tension. The tension depends on the position of the adjuster 47. The washer 46 may be omitted. The resilient member 42 may exert a force directly on the adjuster 47. As shown in Figure 9, optionally the mechanism 30 comprises a housing 43. The housing 43 may be configured to house the resilient member 42. The housing 43 may be configured to at least partly house the tether 40. Optionally the housing 43 is provided by the shaft 11. The tether 40 may extend along the shaft 11. In Figure 9, part of the housing 43 is shown cut away so that the resilient member 42 and tether 40 are visible. In Figure 9, the adjuster 47 and the washer 46 are illustrated disconnected from other parts. However, during use of the transmission 10, the adjuster 47 is connected to the tether 40, for example via the thread 41. The washer 46 is held between the adjuster 47 and the resilient member 42. The tether 40 may extend through a first end 44 of the housing 43. The adjuster 47 may be located at or near a second end 45 of the housing 43. The first end 44 and the second end 45 may be opposite ends of the housing 43. The part of the tether 40 that is exposed from the first end 44 of the housing 43 may be secured to the pusher 14. The tether 40 may be configured to pull the engagement member 39 of the pusher 14 towards the primary axis 17. The engagement member 39 may be located offset from a centre of the pusher 14. By moving the engagement member 39 towards the primary axis 17, the centre of the pusher 14 is moved away from the centre, i.e. increasing the offset 19. It is not essential for the resilient member 42 to be in compression. In an alternative arrangement, the resilient member 42 is in tension. For example, the resilient member 42 may be configured to apply a pulling force so as to pull the pusher 14 off-centre. Alternatively, the resilient member 42 may be replaced by a non-resilient member, i.e. a rigid member. Such a rigid member may be appropriate if the gear ratio is to be fixed, for example. Optionally, as shown in Figures 2 to 4, the transmission 10 is configured such that rotation of the pusher 14 causes movement of the tine assembly 20 about the primary axis 17. As the pusher 14 rotates, the tine assembly 20 is generally urged to move in the same sense about the primary axis 17. As shown in Figure 2 and Figure 4, optionally the transmission 10 comprises a pusher bearing 32. The pusher bearing 32 is located at an interface between the pusher 14 and the tine assembly 20. The pusher bearing 32 may be configured to support relative movement between the pusher 14 and the tine assembly 20. For example, the pusher bearing 32 may be configured to allow the tine assembly 20 to rotate relative to the pusher 14. Optionally, the tine assembly 20 is configured to be centred on the hub axis 18. The pusher bearing 32 may be configured to allow relative rotation between the pusher 14 and the tine assembly 20 about the hub axis 18. The pusher 14 is not rotationally fixed to the tine assembly 20. Optionally, the orientation of the pusher 14 is fixed by its rotation position about the primary axis 17. The pusher 14 may be configured to move in either rotational direction around the primary axis 17. Optionally, the pusher 14 is configured to move in two degrees of freedom. One degree of freedom is rotation about the primary axis 17. The other degree of freedom is its radial position relative to the primary axis 17. As shown in Figures 2 to 4, optionally the tine assembly 20 comprises a hub 21. The hub 21 is configured such that rotation of the pusher 14 causes movement of the hub 21. Optionally, the hub 21 of the tine assembly 20 is configured to move in three degrees of freedom. Two degrees of freedom correspond to the two degrees of freedom of the pusher 14. In particular, one degree of freedom corresponds to the radial position of the pusher 14. The radial position of the pusher 14 may correspond to a corresponding radial position of the hub 21. Another degree of freedom of the hub 21 corresponds to the rotational position about the primary axis 17. The rotation of the pusher 14 about the primary axis 17 may dictate the rotational position of the hub 21 about the primary axis 17. The hub 21 may have an additional degree of freedom compared to the pusher 14. The additional degree of freedom may be rotation of the hub 21 about the hub axis 18. The pusher bearing 32 may allow the hub 21 to rotate about the hub axis 18 relative to the pusher 14. As the pusher 14 pushes the tine assembly 20 about the primary axis 17. The hub 21 may rotate about the hub axis 18 relative to the pusher 14. The hub axis 18 may be parallel to the primary axis 17. As shown in Figures 2 to 4, optionally the tine assembly 20 comprises a plurality of guide tines 22 (which may be referred to as pawls). The guide tines 22 extend from the hub 21. For example, the guide tines 22 may extend generally radially outwardly from the hub 21. The guide tines 22 are configured to engage with the guide 15. The guide tines 22 may be configured to engage with the guide 15 such that engagement between the guide tines 22 and the guide 15 guides movement of the tine assembly 22. For example, the engagement between the guide tines 22 and the guide 15 may affect the rotation of the hub 21 relative to the pusher 14 about the hub axis 18. As shown in Figures 2 to 4, optionally the guide 15 comprises engagement feature for engaging with the guide tines 22. For example, the guide 15 may comprise a plurality of teeth configured to engage with the guide tines 22. The guide tines 22 may comprise a base that is secured to the hub 21. The guide tines 22 may comprise a tip that is configured to come into contact with the guide 15. The tips of the guide tines 22 may abut against the teeth. The guide 15 may comprise an engagement surface 35. The engagement surface 35 may comprise the engagement features such as the teeth. As shown in Figures 2 to 4, optionally the guide 15 comprises an internal gear. The engagement surface 35 of the guide 15 may be an inner surface of the guide 15. The tine assembly 20 may be located generally radially inward of the guide 15. The tine assembly 20 may be nested within the guide 15. The guide 15 may surround the tine assembly 20 when viewed along the primary axis 17. As shown in Figures 2 to 4, optionally the guide tines 22 extend in the same sense around the primary axis 17. The guide tines 22 may be generally elongate. The guide tines 22 may have a length that is less than a maximum distance between the hub 21 and the guide 15. The transmission 10 may be arranged such that the guide tines 22 remain substantially continuously in contact with the guide 15. The guide tines 22 are generally longer than the distance between the hub 21 of the tine assembly 20 and the guide 15. The guide tines are angled elative to a radial direction extending directly radially outwards from the hub axis 18. As shown in Figures 2 to 4, the guide tines 22 may be generally angled in the same rotational direction as each other. For example, as shown in Figures 2 to 4, the guide tines 22 may be angled generally anticlockwise relative to the radial direction from the hub axis 18. As shown in Figures 2 to 4, optionally the guide tines 22 are curved. As shown in Figures 2 to 4, optionally the guide tines 22 are curved generally around the hub axis 18. Optionally, the transmission 10 is configured such that rotation of the pusher 14 in either rotational direction about the primary axis 17 drives the gear 16 in the same direction. The input can be turned both clockwise or anticlockwise the output will rotate in the same direction. For example, the transmission 10 may be configured such that clockwise rotation of the pusher 14 results in a clockwise rotation of the gear 16, while an anticlockwise rotation of the pusher 14 corresponds to a clockwise rotation of the gear 16. Alternatively, the transmission 10 may be configured such that a clockwise rotation of the pusher 14 drives an anti-clockwise rotation of the gear 16, while anti-clockwise rotation of the pusher 14 drives an anti-clockwise rotation of the gear 16. The rotational direction of the input for the transmission 10 may be varied. For example, the transmission 10 may be used in a machine in which the direction of input rotation switched between clockwise and anti-clockwise. The transmission 10 may be configured to provide a consistent output rotational direction. The direction of rotation may be controlled by the engagement between the tine assembly 20 and the guide 15, as well as the engagement between the tine assembly 20 and the gear 16. For example, the shape and positioning of the guide tines 22 may be selected so as to provide the desired direction of output. Optionally, the transmission 10 is configured such that rotation of the pusher 14 in either rotational direction about the primary axis 17 causes the hub 21 to rotate in the same rotational direction about the hub axis 18. For example, the direction in which the guide tines 20 extend, the shape of the guide tines 20 and the shape of the engagement features that at the engagement surface 35 of the guide 15 may be selected so as to control the direction of rotation of the hub 21 of the tine assembly 20. During use of the transmission 10, the movement of the hub 21 of the tine assembly 20 may be a combination of rotational movement about the primary axis 17 (dictated by the rotation of the pusher 14) and rotation of the hub 21 about the hub axis 18 (affected by engagement between the guide tines 22 and the guide 15). Each point on the hub 21 may trace a geometrical pattern as the tine assembly 20 moves during use of the transmission 10. Merely as one example, Figure 8 schematically shows the traced path 38 traced by one point at a radially outward surface of the hub 21 of the tine assembly 20 during use of the transmission 10. The geometrical pattern shown in Figure 8 is produced when the input power and resistance are constant, i.e. during a steady state of use of the transmission 10. Figure 6 schematically depicts a tine assembly of the transmission 10 shown in Figure 1. As shown in Figure 6, optionally the tine assembly 20 comprises a plurality of gear tines 23 (which may be referred to as pawls). The gear tines 23 extend from the hub 21. The gear tines 23 are configured to engage with the gear 16. The gear tines 23 may be configured to engage with the gear 16 so as to drive the gear 16. Figure 6 is a view of the tine assembly 20 from above the transmission 10 (in the orientation shown in Figure 1). The gear tines 23 may be located above the guide tines 22. The guide tines 23 are located at a different axial position from the guide tines 22. The gear tines 23 are axially spaced from the guide tines 22. The axial position of the guide tines 22 may correspond to the axial position of the guide 15, shown in Figure 1. The axial position of the gear tines 23 may correspond to the axial position of the gear 16, shown in Figure 1. Figure 6 shows the tine assembly 20 without the guide 15 or the gear 16. The guide tines 22 and the gear tines 23 of the tine assembly 20 shown in Figure 6 are relatively unconstrained. They are secured via their basis at one end to the hub 21. However, the tips of the gear tines 23 and the guide tines 22 are not in engagement with the guide 15 or the gear 16. During use of the transmission 20, the guide tines 22 engage with the guide and the gear tines 23 engage with the gear 16. As shown in Figure 6, optionally the guide tines 22 are pivotably secured to the hub 21. Optionally, the gear tines 23 are pivotably secured to the hub 21. For example, as shown in Figure 6, the gear tines 23 are secured to the hub 21 via respective pivot points 26. The pivot points 26 may comprise pivot pins. The pivot pins may extend axially through at least part of the hub 21 and at least part of the gear tine 23. Similarly, the guide tines 22 may be pivotably secured to the hub 21 via corresponding pivot points. The pivot points may comprise pivot pins that extend at least partly through the hub 21 and at least partly through the guide tines 22. As shown in Figure 6, optionally the tine assembly 20 comprises a plurality of guide springs 29. The guide springs 29 are configured to bias the respective guide tines 22 into engagement with the guide 15. For example, the guide springs 29 shown in Figure 6 may act to generally push the guide tines 22 radially outward so as to come into contact with the engagement surface 35 of the guide 15. Alternatively, the guide springs 29 may be configured to pull the guide tines 22 into engagement with the guide 15. Although not shown in Figure 6, optionally the tine assembly comprises a plurality of gear springs configured to bias the respective gear tines 23 into engagement with the gear 16. The guide tines 22 may be substantially the same as the gear tines 23. The guide springs 29 may be substantially the same as the gear springs. The pivot points 26 for the gear tines 23 may be substantially the same as the pivot points for the guide tines 22. This may help to reduce the cost of manufacture by reducing the number of different parts that are required to be made. As shown in Figure 6, for example, optionally the gear tines 23 extend in the same sense that as primary axis 17. The engagement between the gear tines 23 and the gear 16 may dictate movement of the gear 16 caused by the movement of the tine assembly 20. As shown in Figure 6, optionally the hub 21 of the tine assembly 20 comprises a hub plate 25. The hub plate 25 may be connected to the gear tines 23 via the pivot points 26. Optionally, a further hub plate is provided for securing the guide tines 22 to the hub 21 via respective pivot points. The two hub plates maybe provided at opposite axial ends of the hub 21. Optionally, the guide tines 22 are located between the hub 21 and the guide 15. Optionally, the gear tines 23 are located between the hub 21 and the gear 16. As shown in Figure 4, for example, optionally the hub 21 comprises a first hub member 24. The first hub member 24 may be located at the same axial position as the guide tines 22 and the guide 15. The first hub member 24 may be formed as an annulus. The first hub member may surround the pusher 14. The first hub member 24 may interface with the pusher 14 via the pusher bearing 32. As shown in Figure 6, optionally the hub plate 25 is secured to the first hub member 24 via one or more fixing members 27. For example, the fixing members 27 may be bolts. The bolts may extend axially through the hub plate 25 and the first hub member 24. Figure 5 schematically depicts part of the transmission 10 shown in Figure 1. Figure 5 shows the transmission 10 from generally above, but with the guide tines 23 of the tine assembly 20 omitted. As shown in Figure 5, optionally the tine assembly 20 is configured to drive the gear 16 rotationally about the primary axis 17. The gear 16 may be centred on the primary axis 17. As shown in Figure 5, optionally the gear 16 comprises an internal gear. For example, the guide 16 may comprise an engagement surface 36. The engagement surface 36 may comprise engagement features. The engagement features may be configured to engage with the gear tines of the tine assembly 20. The engagement features may be teeth, for example. As shown in Figure 5, the engagement surface 36 may be an internal surface, i.e. a radially inward surface of the fear 16. The gear 16 may be located to surround the tine assembly 20 when viewed along the primary axis 17. The tips of the gear tines 23 engage with the engagement surface 36 of the gear 16. As shown in Figure 5, optionally the hub 21 of the tine assembly 20 comprises a second hub member 35. The second hub member 35 may be at the same axial position as the gear tines 23. The second hub member 35 may have the same features as the first hub member 24. The second hub member 35 may be secured to the first hub member 24. Alternatively, the second hub member 35 may be formed integrally with the first hub member 24. The second hub member 35 may be fixed to the first hub member 24 such that movement of the first hub member 24 corresponds to the same movement of the second hub member 35. The hub 21 of the tine assembly 20 may have no moving parts. As the tine assembly 20 is driven in movement by the pusher 14, the gear tines 23 cause the gear 16 to rotate. The input for moving the pusher 14 may transmit through to rotation of the gear 16. The gear 16 may be an output of the transmission 10. The gear 16 may be coupled with another gear so as to change the gear ration of the transmission 10. The tips of the gear tines 23 may engage with the teeth at the engagement surface of the gear 16 so as to drive the gear 16. Optionally, the guide 15 has a fixed rotational position about the primary axis 17. The guide 15 may be centred on the primary axis 17. As shown in Figure 1, optionally the transmission 10 comprises a driver 12. The driver 12 is configured to rotate about the primary axis 17. The driver 12 may be engaged with the pusher 14 such that rotation of the driver 12 about the primary axis 17 drives rotation of the pusher 14 about the primary axis 17. The driver 12 may be seen more clearly in Figure 3, which shows a perspective view of the transmission 10 from below. The driver 12 may be centred on the primary axis 17. The driver 12 may have an external (radially outward surface) that is substantially circular. The driver 12 may be rotated so as to provide an input power for the transmission 10. The driver 12 is configured to engage with the pusher 14. For example, as shown in Figure 2 optionally the driver 12 comprises one or more protrusions 33. The protrusions 33 are configured to protrude from the main body of the driver 12 in an axial direction. The main body of the driver 12 may be substantially planar. For example, the driver 12 may be generally disc-shaped. Optionally, the driver 12 maintains a constant position along the primary axis 17. The driver 12 does not move along the primary axis 17. The driver 12 may be substantially planar. The driver 12 may be formed from a plate. The driver 12 may comprise a metal. Optionally, the driver 12 at least partly overlaps the tine assembly 20 along the primary axis 17. primary axis 17. primary axis 17. Optionally the tine assembly 20 partly overlaps the driver 12 along the Optionally the driver 12 partly overlaps the tine assembly 20 along the Optionally, the driver 12 at least partly overlaps the pusher 14 along the primary axis 17. Optionally the pusher 14 partly overlaps the driver 12 along the primary axis 17. Optionally the driver 12 fully overlaps the pusher 14 along the primary axis 17. Optionally, the driver 12 is axially distanced from the gear 16. As shown in Figure 2, optionally the pusher 14 defines one or more apertures 34 (which may be referred to as slits). The apertures 34 are configured to accommodate the protrusions 33 of the driver 12. As shown in Figure 2, optionally the driver 12 comprises a plurality of protrusions 33. Two protrusions 33 are shown in Figure 2. However, the number of protrusions 33 may be one, three or more than three. Optionally, the pusher 14 define a plurality of apertures 34 for accommodating respective protrusions 33. Alternatively, the pusher 14 may define one aperture 34, three apertures 34 or more than three apertures 34. Optionally, the protrusions 33 are slidably engaged within the respective apertures 34. The pusher 14 may be slidably engaged with the driver 12 such that the pusher 14 slides relative to the driver 12 as the radial position of the pusher 14 is adjusted. For example, when the resistance forced and the force applied by the mechanism 30 do not balance each other, the radial position of the pusher 14 may change. As the radial position changes, the pusher 14 might slide across the driver 12 in a direction perpendicular to the primary axis 17. The protrusions 33 slide relative to the edges that define the apertures 34. As shown in Figure 2, the apertures 34 may be longitudinal. The protrusions 33 are free to slide within the slits. The apertures 34 are longer than the protrusions 33 in a distance perpendicular to the primary axis 17. The apertures 34 are substantially the same size as the protrusions 33 in a circumferential direction around the primary axis 17. There may be a relatively snug fit between the protrusions 33 and the edges that define the apertures 34 in the pusher 14. Desirably there is little or no clearance between edges of the protrusions 33 and edges that define the apertures 34. This helps to increase the accuracy with which the rotation of the pusher 14 is driven by the rotation of the driver 12. As shown in Figures 1 to 5, optionally the transmission 10 comprises a shaft 11. The shaft 11 may be secured to the driver 12 such that the shaft 11 rotates together with the driver 12. The shaft 11 may be rotated so as to provide the input for the transmission 10. As shown in Figure 1, optionally the transmission 10 comprises a support structure 13. The rotation of the driver 12 about the primary axis 17 may be relative to the support structure 13. As shown in Figure 3, optionally the transmission 10 comprises a drive bearing 31. The drive bearing 31 may be located at an interface between the driver 12 and the support structure 13. The drive bearing 31 may be configured to allow the driver 12 to rotate about the primary axis 17 relative to the support structure 13. The support structure 13 may have a fixed rotational position about the primary axis 17. The support structure may have a fixed rotational position relative to the guide 15. Optionally, the support structure 13 maintains a constant position along the primary axis 17. The support structure 13 does not move along the primary axis 17. The support structure 13 may be substantially planar. The support structure 13 may be formed from a plate. The support structure 13 may comprise a metal. Optionally, the support structure 13 at least partly overlaps the driver 12 along the primary axis 17. Optionally the support structure 13 partly overlaps the driver 12 along the primary axis 17. Optionally the driver 12 fully overlaps the support structure 13 along the primary axis 17. Optionally, the support structure 13 is axially distanced from the gear 16. Optionally, the support structure 13 is axially distanced from the guide 15. Optionally, the support structure 13 is axially distanced from the tine assembly 20. Optionally, the guide 15 is located axially between the gear 16 and the support structure 13. Optionally, the tine assembly 20 is located axially between the gear 16 and the support structure 13. An apparatus may comprise the transmission 10. The apparatus may be a vehicle such as a bicycle, a motorbike, a car, a van or a lorry, for example. The apparatus may be stationary. For example, the apparatus may be a windmill or a blind or an architectural covering or a lifting device or a winch or a break. It will be appreciated that there may be many other variations of the abovedescribed examples. For example, an apparatus may comprise a plurality of the transmission 10. The transmissions 10 may be arranged in series so as to provide a target gear ratio. It is not essential for the pusher 14 to be generally annular. In an alternative embodiment, the pusher 14 has a linear shape. The pusher 14 interfaces with the tine assembly 20 so as to cause rotation of the tine assembly. List of reference numerals 10 transmission 11 shaft 12 driver 13 support structure 14 pusher 15 guide 16 gear 17 primary axis 18 hub axis 19 offset 20 tine assembly 21 hub 22 guide tines 23 gear tines 24 first hub member 25 hub plate 26 pivot point 27 fixing member 29 guide spring 30 mechanism 31 drive bearing 32 pusher bearing 33 protrusion 34 aperture 35 second hub member 36 engagement surface 38 traced path 39 engagement member 40 tether 41 thread 42 resilient member 43 housing 44 first end 45 second end 46 washer 47 adjuster

Claims

1. A transmission comprising:a pusher configured to rotate about a primary axis;a mechanism configured to controllably adjust a radial position of the pusher relative to the primary axis;a tine assembly configured such that rotation of the pusher causes movement of the tine assembly;a guide configured to guide movement of the tine assembly; and a gear configured to be driven by the tine assembly.

2. The transmission of claim 1, configured such that a gear ratio of the transmission decreases as the radial position of the pusher is adjusted radially outwardly.

3. The transmission of claim 1 or 2, wherein the mechanism is configured to apply a force to urge the pusher in a direction that corresponds to a decrease of a gear ratio of the transmission.

4. The transmission of claim 3 comprising:a controller configured to control the force applied by the mechanism.

5. The transmission of any preceding claim, wherein the tine assembly is configured to drive the gear rotationally about the primary axis.

6. The transmission according to any preceding claim, configured such that rotation of the pusher in either rotational direction about the primary axis drives the gear in the same direction.

7. The transmission according to any preceding claim, configured such that rotation of the pusher causes movement of the tine assembly about the primary axis.

8. The transmission of any preceding claim, wherein the tine assembly comprises a hub configured such that rotation of the pusher causes movement of the hub.

9. The transmission of claim 8, wherein the hub is configured to rotate about a hub axis parallel to the primary axis.

10. The transmission according to claim 9, configured such that rotation of the pusher in either rotational direction about the primary axis causes the hub to rotate in the same rotational direction about the hub axis.

11. The transmission of claim 9 or 10 comprising:a pusher bearing at an interface between the pusher and the hub, so as to allow relative rotation about the hub axis between the pusher and the hub.

12. The transmission of any of claims 8-11, wherein the tine assembly comprises a plurality of guide tines extending from the hub and configured to engage with the guide such that engagement between the guide tines and the guide guides movement of the tine assembly.

13. The transmission of claim 12, wherein the guide tines are pivotably secured to the hub.

14. The transmission of claim 13, wherein the tine assembly comprises a plurality of guide springs configured to bias the respective guide tines into engagement with the guide.

15. The transmission of any of claims 12-14, wherein the guide tines extend in a same sense around the primary axis.

16. The transmission of any of claims 12-15, wherein the tine assembly comprises a plurality of gear tines extending from the hub and configured to engage with the gear so as to drive the gear.

17. The transmission of claim 16, wherein the gear tines are pivotably secured to the hub.

18. The transmission of claim 17, wherein the tine assembly comprises a plurality of gear springs configured to bias the respective gear tines into engagement with the gear.

19. The transmission of any of claims 16-18, wherein the gear tines extend in a same sense around the primary axis.

20. The transmission of claim 19, wherein the guide tines and the gear tines extend in opposite senses around the primary axis.

21. The transmission of any preceding claim, wherein the gear comprises an internal gear.

22. The transmission of any preceding claim, wherein the gear is centred on the primary axis.

23. The transmission of any preceding claim, wherein the guide has a fixed rotational position about the primary axis.

24. The transmission of any preceding claim, wherein the guide comprises an internal gear.

25. The transmission of any preceding claim, wherein the guide is centred on the primary axis.

26. The transmission of any preceding claim comprising:a driver configured to rotate about the primary axis and engaged with the pusher such that rotation of the driver about the primary axis drives rotation of the pusher about the primary axis.

27. The transmission of claim 26, wherein the pusher is slidably engaged with the driver such that the pusher slides relative to the driver as the radial position of the pusher is adjusted.

28. The transmission of claim 26 or 27 comprising:a shaft secured to the driver such that the shaft rotates together with the driver.

29. The transmission of any of claims 26-28 comprising:a support structure, wherein the rotation of the driver about the primary axis is relative to the support structure.

30. The transmission of claim 29 comprising:a drive bearing at an interface between the driver and the support structure, so as to allow the driver to rotate about the primary axis relative to the support structure.

31. The transmission of claim 30, wherein the guide has a fixed rotational position relative to the support structure.

32. The transmission of any preceding claim, wherein the transmission is a continuously variable transmission.

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