GB2614546A

GB2614546A - Sheave and variable-speed drive system

Info

Publication number: GB2614546A
Application number: GB2200104.4A
Authority: GB
Inventors: John Schrag Stephen
Original assignee: AGCO Corp
Current assignee: AGCO Corp
Priority date: 2022-01-06
Filing date: 2022-01-06
Publication date: 2023-07-12

Abstract

A sheave 100 comprises a first sheave part 101, a second sheave part 107 defining a belt channel 109 for receiving a belt 102. The first sheave part comprises a body 103 and a translation member 105 coupled to the body such that it is movable relative to the body between a retracted configuration and an extended configuration. A biasing arrangement 112 biases the translation member towards its extended configuration. The second sheave part is moveable along the rotation axis towards the first sheave part to drive the translation member towards the body. In use, the translation member can be moved to its retracted configuration when the second sheave part is brought into contact with the first sheave part. This allows for greater axial travel of the second sheave part, thereby increasing the achievable ratio range.

Description

TITLE

SHEAVE AND VARIABLE-SPEED DRIVE SYSTEM

CROSS REFERENCE

[0001] Not applicable.

FIELD

[0002] Embodiments of the present disclosure relate generally to a sheave and a variable-speed belt drive system including the sheave. In particular, embodiments of the present disclosure relate to a sheave for a variable-speed belt drive system wherein use of the sheave can increase the achievable speed ratio range of the variable-speed belt drive system.

BACKGROUND

[0003] Variable-speed belt drive systems generally include two sheaves and a belt arranged to transfer motion from one sheave to the other. One of the sheaves (the "driver" sheave) is mounted on a drive shaft, which is coupled to a motor. The other sheave (the "driven" sheave) is coupled to a driven shaft. When the motor causes the driver sheave to rotate, the belt acts to transfer movement from the driver sheave to the driven sheave. Accordingly, the variable-speed belt drive system includes two pulleys: a driver pulley formed by the belt and the driver sheave, and a driven pulley formed by the belt and the driven sheave. The speed ratio of the drive system is given by the ratio of the effective diameter of the driver pulley and the effective diameter of the driven pulley.

[0004] Each sheave is a wheel-shaped device comprising a channel for receiving the belt that extends around the wheel's circumference. The belt is tapered in cross section (e.g. V-shaped, trapezoidal) and the channel has a correspondingly tapered cross section. Each sheave comprises two sheave parts, which face each other along the rotation axis of the sheave. The channel is defined between the sheave parts, such that changing the axial separation of the sheave part changes the width of the channel.

[0005] To vary the speed of the driven sheave, the speed ratio of the drive system is adjusted. This is achieved by controlling the axial separation of the sheave parts of one of the sheaves (the "control" sheave). When the sheave part of the control sheave are driven together, the belt is forced radially outwardly. Since the belt length and center distance between the shafts is fixed, the narrowing of the belt channel at the control sheave causes the belt to move radially inwardly at the other sheave (the "follower" sheave). Accordingly, the speed ratio is adjusted by adjusting the axial separation of the sheave parts.

[0006] However, the range over which the speed ratio can be adjusted is limited. The sheave part can only be moved closer together until they are brought into contact with one another. This limits the achievable range for the speed ratio of a variable-speed belt drive.

[0007] To address this, additional drives may be used in combination with the variable-speed belt drive to increase overall speed range achievable by the system. For example, a variable-speed belt drive may be used to drive the rotor of a combine harvester. However, since the speed range provided by the variable-speed belt drive alone is insufficient, a two-speed gearbox is also provided.

[0008] It would therefore be desirable to increase the range of speed ratio achievable with a variable-speed belt drive, whilst avoiding the need to provide additional components such as a two-speed gearbox.

BRIEF SUMMARY

[0009] In an aspect of the invention there is provided a sheave for a variable-speed belt drive, the sheave comprising: a first sheave part comprising a body and a translation member coupled to the body such that it is movable relative to the body between a retracted configuration and an extended configuration; a second sheave part arranged to oppose the first sheave part along a rotation axis, wherein the first sheave part and the second sheave part are arranged to define a belt channel for receiving a belt between an inclined inside wall of the first sheave part and an inclined inside wall of the second sheave part; and a biasing arrangement configured to bias the translation member towards its extended configuration; wherein the second sheave part is axially movable relative to the first sheave part to drive the translation member towards the body.

[0010] . In use, the sheave rotates about a rotation axis, causing the belt of the variable-speed belt drive to move over the sheave. The sheave is a variable-diameter sheave. The sheave comprises two sheave parts, which face each other along the rotation axis. A belt channel is defined in the space between the two sheave parts. By moving one sheave part relative to the other sheave part, in the axial direction, the width of the belt channel can be adjusted.

[0011] The position of the belt in the belt channel is adjusted by changing the width of the belt channel. When the distance between the two sheave parts is increased, the belt moves radially inwardly towards the center of the sheave. When the distance between the two sheave parts is reduced, the belt is pushed radially outwardly, away from the center of the sheave.

[0012] One of the sheave parts comprises a body and translation member. The translation member is movable relative to the body in the axial direction between an extended configuration and a retracted configuration. A biasing arrangement biases the translation member towards its extended configuration. In use, the second sheave part is moved axially towards the first sheave part to drive the translation member from its extended configuration towards its retracted configuration. In the retracted configuration, the translation member is moved towards the body, so that the second sheave part can continue to move towards the first sheave part even after the first sheave part and the second sheave part have been brought into contact. Accordingly, providing the translation member allows for greater axial travel of the second sheave part, thereby increasing the achievable ratio range associated with the sheave.

[0013] In the extended configuration, the translation member may co-operate with an inner wall of the body to form the inclined inside wall of the first sheave part. In the retracted configuration the translation member may be axially offset from the inner wall of the body.

[0014] The belt channel may be defined between the inclined inner wall of the second sheave part and the inclined inner wall of the first sheave part. When the translation member is positioned in the extended configuration, an inner surface of the translation member and an inner surface of the body may join to form the inclined inner wall of the first sheave part. When the second sheave part is moved towards the first sheave part, the translation member can move towards its retracted configuration. By driving the translation member away from the inner wall of the body, the second sheave part may continue to move closer to the first sheave part to further narrow the belt channel, driving the belt radially outwardly.

[0015] The body may comprise a cavity for receiving the translation member and movement of the translation member from the extended configuration to the retracted configuration may cause the translation member to move axially away from the inner wall of the body and into the cavity.

[0016] In the extended configuration, the body and the translation member may define a continuous inside wall of the sheave (the first belt channel wall). When the second sheave part is moved towards the first sheave portion to drive the translation member into the retracted configuration, the translation member may move into the cavity. With this arrangement, the first sheave part and the second sheave part can be moved closer together than would otherwise be possible.

[0017] The biasing arrangement may comprise a spring configured to bias the translation member towards the extended configuration. In such embodiments, in order to move the translation member from the extended configuration to the retracted configuration, the second sheave member must exert enough force on the translation member to overcome the biasing force of the spring.

[0018] The second sheave part may comprise a hydraulic actuator configured to move the second sheave part relative to the first sheave part in the axial direction.

[0019] The translation member may be coupled to the body by a splined connection. In this way, torque applied to the translation member by the belt can be transmitted to the shaft via the body.

[0020] The biasing arrangement may comprise a hydraulic actuator. The hydraulic actuator may be operable to move the translation member axially, between its retracted configuration and its extended configuration.

[0021] The sheave may further comprise a sensing arrangement for sensing the axial separation between the first sheave part and the second sheave part. The sensing arrangement may be configured to sense the position of the second sheave part and/or the distance between the first sheave part and the second sheave part.

[0022] The first sheave part and the second sheave part may be coupled to an axial shaft.

[0023] The first sheave part may be fixed to the axial shaft and the second sheave part may be movable along the axial shaft. Providing the translation member in the fixed sheave part, rather than the movable sheave part, may facilitate cost-efficient manufacture. In particular, the movable sheave part may have fewer space constraints as compared to the fixed sheave part. Accordingly, it may be simpler to manufacture the sheave with the fixed sheave part including the translation member.

[0024] In an aspect of the invention there is provided a variable-speed belt drive apparatus comprising; a control sheave coupled to a first axial shaft; a follower sheave coupled to a second axial shaft; and a belt connecting the control sheave and the follower sheave, wherein each of the control sheave and the follower sheave comprises a sheave as described above and the second sheave part of the follower sheave is configured to move with respect to the first sheave part of the follower sheave in response to movement of the second sheave part of the control sheave relative to the first sheave part of the control sheave [0025] The first sheave part of the control sheave may be fixed to the first axial shaft and may comprise a spring configured to bias the translation member towards the extended configuration, and the second sheave part may comprise a hydraulic actuator arranged to cause the second sheave part to move along the first axial shaft.

[0026] The first sheave part of the follower sheave may comprise a hydraulic actuator configured to move the translation member between the extended configuration and the contracted configuration.

[0027] The apparatus may further comprise a sensing arrangement for detecting an axial separation between the first sheave part and the second sheave part of the follower sheave. The sensing arrangement may be configured to sense the position of the second sheave part and/or the distance between the first sheave part and the second sheave part and/or movement of the second sheave part of the follower sheave. The apparatus may further comprise a controller configured to control the hydraulic actuator of the follower sheave based on the detected axial position of the second sheave part of the follower sheave.

[0028] Within the scope of this application it should be understood that the various aspects, embodiments, examples and alternatives set out herein, and individual features thereof may be taken independently or in any possible and compatible combination. Where features are described with reference to a single aspect or embodiment, it should be understood that such features are applicable to all aspects and embodiments unless otherwise stated or where such features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] One or more embodiments of the invention / disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: [0030] FIG. 1 is a schematic diagram, in a simplified cross sectional side view, illustrating a partial view of a comparative variable-diameter sheave and belt; [0031] FIG. 2 is a cross-sectional side view illustrating a control sheave according to the present disclosure, wherein the translation member is in its extended configuration; [0032] FIG. 3 is a partial, cross-sectional side view of the sheave of FIG. 2, with the translation member in its retracted configuration; [0033] FIG. 4 is a cross-sectional side view illustrating a follower sheave according to the present disclosure, wherein the translation member is in its extended configuration; [0034] FIG.5 is a cross-sectional side view of the sheave of FIG. 4, with the translation member in its retracted configuration; and [0035] FIG. 6 is a schematic diagram illustrating a variable-speed belt drive apparatus according to the present disclosure.

DETAILED DESCRIPTION

[0036] The invention will be described with reference to the Figures.

[0037] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

[0038] This disclosure relates to a sheave for a variable-speed belt-drive apparatus. The sheave is a variable-diameter sheave comprising a belt channel for receiving a belt. The sheave has a first sheave part and a second sheave part arranged to face towards the first sheave part along a rotation axis of the sheave. The belt channel is defined between an inclined inside wall of the first sheave part and an inclined inside wall of the second sheave part. By adjusting the axial separation of the first sheave part and the second sheave part, it is possible to change the radial position of the belt within the sheave. Accordingly, by adjusting the axial separation of the first and second sheave parts, the effective diameter of the pulley formed by the sheave and the belt can be varied.

[0039] FIG. 1 is a schematic, partial view of a comparative variable-diameter sheave pulley 10. The pulley 10 comprises two sheave parts 1, 3 and a belt 2 received between the sheave parts 1, 3. Only the parts of the pulley above the rotation 5 axis of the sheave are illustrated. The possible effective diameter change is physically limited by the geometry of the sheave parts. The sheave parts are designed according to the section geometry of the belt 2. That is, the incline of the inner walls of the sheave parts 1,3 correspond to the incline of the sidewalls 4 of the belt 2. In FIG. 1, the belt 2 is shown at its maximum radial position (as depicted by the position of the sheaves and belt in solid lines) as well as at its minimum radial position (as depicted by the dashed lines) [0040] As an illustrative example, assume the belt has a minimum outer diameter of 280 mm (wherein the minimum outer diameter is determined as a value appropriate for the belt drive in order to maintain an acceptable belt life). The sheave parts have inclined walls, inclined at an angle corresponding to the angle of incline of the sidewal Is of the belt. They are arranged to hold the belt between them, at an axial separation a, when the belt diameter is 280 mm.

[0041] Assuming the maximum belt outer diameter is 503.4 mm, based on the physical limitations of the system, and the pitch diameter is 12 mm less than the outer diameter of the belt the diameter ratio is 1.834. In a variable-speed belt drive, the change in effective diameter happens at both the driver sheave and the driven sheave. Accordingly, the total diameter ratio is 3.364:1.

[0042] This ratio does not provide adequate range to vary speed for a desired rotor range of, for example, 250-1200 RPM. In order to vary the speed of the driven shaft between 250-1200 RPM, a total ratio of 4.8:1 is required (i.e. a ratio of 2.19 at each sheave). To achieve such a ratio with a 280 mm outside belt diameter, a maximum belt diameter of about 599 mm is required.

[0043] FIG. 2 illustrates a partial, cross-sectional side view of a sheave 100, mounted to a shaft 200. This sheave is a "control sheave". The first sheave part 101 comprises a body 103 and a translation member 105 coupled to the body 103. The translation member 105 is coupled to the body such that the translation member 105 is movable relative to the body 103 in the axial direction (i.e. along the rotation axis 118). The translation member 105 is movable between an extended configuration (as shown in FIG. 2) and a retracted configuration (as shown in FIG. 3). A biasing arrangement 115 is configured to bias the translation member 105 towards its extended configuration. In use, the second sheave part 107 is moved towards the first sheave part 101 to bring it into contact with the translation member 105 of the first sheave part 101, and further to drive the translation member 105 away from the second sheave part 107 and towards the body 103.

[0044] The first sheave part 101 and the second sheave part 107 have a substantially frustoconical ring-shape, with inclined inner walls 113, 117 that co-operate to define a tapered belt channel 109.

[0045] The shaft 200 extends through the apertures of the ring-shaped sheave parts, along the rotation axis of the sheave 100. The belt channel 109 tapers radially inwardly, towards the shaft 200. The first sheave part 101 is fixed to the shaft 200; it is configured to remain stationary relative to the shaft 200. The second sheave part 107 is mounted to the shaft 200 and coupled to an actuator 116 arranged to drive the second sheave part 107 along the shaft 200. Accordingly, the axial separation between the first sheave part 101 and the second sheave part 107 can be adjusted by operating the actuator 116 to drive the second sheave part 107 towards the first sheave part 101, or by de-activating the actuator 116 to allow the second sheave part 107 to move away from the first sheave part 101.

[0046] In FIG. 2, the first sheave part 101 is shown with the translation member 105 in its extended configuration. In the extended configuration, the translation member 105 is positioned relative to the body 103 such that an inclined inner wall 108 of the translation member and an inner wall 117 of the body are aligned to form a continuous inclined inside wall 111 of the first sheave part 101. The belt 102 is held between the first sheave part 101 and the second sheave part 107.

[0047] The body 103 comprises a cavity for receiving the translation member 105. The biasing arrangement 115 comprises a plurality of springs 112 arranged inside the cavity, which are configured to drive the translation member 105 inwardly, towards the second sheave part 107.

[0048] When the translation member 105 is driven towards the retracted configuration, by movement of the second sheave part 107 towards the first sheave part 101, the springs 112 are compressed allowing the translation member 105 to move into the cavity.

[0049] The translation member 105 is coupled to the body 103 by a splined connection, so that torque applied to the translation member can be transmitted to the shaft 200 via the body 103. For example, the translation member 105 may be arranged such that a surface of the translation member engages with a cavity wall 119 of the body 103, the splined connection being provided between the cavity wall 119 of the body 103 and the opposing surface of the translation member 105.

[0050] FIG. 3 shows a partial, cross-sectional side view of the sheave 100 of FIG. 2, mounted to the shaft 200, with the translation member 105 in the retracted configuration. In FIG. 3, the second sheave part 107 has been moved, axially, towards the first sheave part 101 to drive the belt 102 radially outwardly to a position at which the pulley formed by the belt 102 and the sheave 100 has a relatively large effective diameter (compared to FIG. 2). Because the translation member 105 is movable towards the body 103, and into the cavity, the second sheave part 107 can be moved closer to the first sheave part 101 than would otherwise be possible. This enables the sheave 100 to drive the belt 102 radially outwardly further than would be possible. In this way, the sheave 100 can be used in a variable-speed belt drive apparatus to achieve a broader range of speed ratios.

[0051] The axial movement of the second sheave part 107 drives the translation member 105 into the cavity of the body 103, compressing the springs 112 of the biasing arrangement 115, so that the inclined inner wall 108 of the translation member 105 is axially offset from the inclined inner wall of the body 103. This movement of the translation member allows the second sheave part 107 to continue to move towards the first sheave part 101, beyond the point at which the inclined inner wall 113 of the second sheave part 107 meets the inclined inner wall of the first sheave 101. Accordingly, the second sheave part 107 can drive the belt 102 radially outwardly beyond the radial positon at which the belt 102 would be moved to if the second sheave part 107 were prevented from moving beyond the point at which the inclined inner wall 113 of the second sheave part 107 meets the inclined inner wall of the first sheave part 101.

[0052] FIG. 4 illustrates another sheave 300 according to the present disclosure. This sheave is a "follower" sheave; it includes a first sheave part 301, a second sheave part 307 and a belt channel 309 defined between the sheave parts for receiving a belt 302. The second sheave part 307 is spring-loaded to bias the sheave part towards the first sheave part 301. That is, the second sheave part 307 is coupled to a spring 313 arranged to bias the second sheave part 307 towards the first sheave part 301.

[0053] The sheave 300 is mounted to an axial shaft 200. In FIG. 4, the first sheave part 301 is fixed to the shaft 200 and the axial position of the second sheave part 307 can be adjusted to change the axial separation between the first and second sheave parts 301, 307 and thereby adjust the effective diameter of the pulley.

[0054] In the embodiment illustrated in FIG. 4, the first sheave part 301 comprises a translation member 305. The translation member 305 is arranged within a cavity of the body 303 of the first sheave part 301 and is coupled to a hydraulic actuator configured to control the axial position of the translation member 305. The translation member 305 is accordingly configured to move between its extended configuration (as shown in FIG. 4) and its retracted configuration (as shown in FIG. 5).

[0055] The translation member 305 is coupled to the shaft 200 so that it is slidable along the shaft 200, whilst also transmitting torque. For example, the translation member 305 can be coupled to the shaft 200 by a pinned connection (not shown) to a sleeve 306 which is coupled to the shaft by a splined connection. This allows the translation member 305 to both slide along the shaft 200 and transmit torque to the shaft 200. The body 303 can be pinned to the translation member 305 by pins 304.

[0056] In the extended configuration, the translation member 305 co-operates with the body 303 to define an inclined inside wall 311 of the first sheave part 301. That is, an inclined inner wall 315 of the translation member 305 and an inner wall 317 of the body 303 are aligned to form a continuous inclined inside wall 311 of the first sheave part 301. The first and second sheave parts 301, 307 are initially arranged with an axial separation corresponding to the minimum belt diameter. The second sheave part 307 is moved towards the first sheave part 301, to drive the belt 302 radially outwardly. As the second sheave part 307 moves towards the first sheave part 301 the hydraulic actuator coupled to the translation member 305 is controlled to allow the translation member 305 to move into the cavity, away from the second sheave part 307. This movement of the translation member 305 is only initiated once the belt 302 is at a large enough diameter that it is no longer engaged with the translation member 305. This movement of the translation member 305 makes it possible for the second sheave part 307 to continue to move towards the first sheave part 301, driving the belt 302 radially outwardly, beyond the position of the belt 302 when the inclined walls of the first sheave part 301 and the second sheave part 307 meet.

[0057] When the hydraulic actuator is activated, the translation member 305 is maintained in its extended configuration. The hydraulic actuator is relieved, via release valves, to move the translation member 305 to its retracted configuration. Accordingly, in use, the hydraulic actuator can be released to allow the second sheave part 307 to drive the translation member 305 into the cavity.

[0058] In order to ensure that movement of the translation member 305 is only initiated once the belt 302 is at a large enough diameter that it is no longer engaged with the translation member 305, the sheave may comprise a sensing arrangement. The hydraulic actuator may be activated and relieved based on data sensed by the sensing arrangement. The sensing arrangement may be configured to sense the axial position of the second sheave part 307. For example the sensing arrangement may comprise a sensor for sensing the axial position of the second sheave part. Alternatively, the sensor may be configured to sense the position of the second sheave part 307 relative to the first sheave part 301.

[0059] In some embodiments, the sensing arrangement may be configured to control the hydraulic actuator based on a different part of the belt drive system to the sheave. For example, the sensing arrangement may be configured to control the hydraulic actuator of the first sheave part 301 of the follower sheave 300 based on the configuration of the control sheave. For example, the sensing arrangement may sense an increase/decrease in pressure at the hydraulic actuator coupled to the second sheave part of the control sheave resulting from compression/release of the spring of the biasing arrangement of the control sheave.

[0060] FIG. 5 illustrates the follower sheave 300 with the translation member 305 in the retracted configuration. In this configuration, the translation member 305 has been driven into the cavity of the body 303 of the first sheave part 301, allowing the second sheave part 307 to move axially closer to the first sheave part 301, and thereby increasing the amount by which the belt 302 is driven radially outwardly.

[0061] FIG. 6 is a schematic diagram illustrating a variable-speed belt drive apparatus 600. The apparatus includes a control sheave 601 coupled to a first axial shaft 602, a follower sheave 603 coupled to a second axial shaft 604, and a belt 605 connecting the control sheave 601 and the follower sheave 603. The control sheave 601 is a sheave having the structure described in relation to FIGS. 2 and 3 (control sheave 100). The follower sheave 603 is a sheave having the structure described in relation to FIGS. 4 and 5 (follower sheave 300).

[0062] In the arrangement shown in FIG. 6, the spring of biasing arrangement of the translation member of the control sheave 601 is stiffer than the spring coupled to the second sheave part of the follower sheave. This ensures that the belt tension does not compress the spring of the translation member of the control sheave 601.

[0063] A sensing arrangement 609 is arranged to sense the axial position of the second sheave part of the follower sheave 603 and to communicate the sensed data to a controller 611. The controller 611 is configured to receive data from the sensing arrangement to determine the position of the second sheave part and to control the hydraulic actuator coupled to the translation member of the follower sheave 603 based on the position of the second sheave part of the follower sheave 603.

[0064] In alternative embodiments, the sensing arrangement 609 may be configured to sense an increase/decrease in pressure at the hydraulic actuator coupled to the second sheave part of the control sheave resulting from compression/release of the spring of the biasing arrangement of the control sheave.

[0065] It will be appreciated that variations can be made to the above-described embodiments without departing from the scope of the claims.

[0066] It will be appreciated that while the biasing arrangement of the translation member of the control sheave is described as including a spring, an alternative means could be provided to bias the translation member towards its extended configuration. While the biasing arrangement of the control sheave is described as including a plurality of springs, only a single spring may be required.

[0067] Although the sheaves are described as having a substantially frustoconical ring-shape, the sheaves may have an alternative shape.

[0068] Although the translation member of the follower sheave is described as being connected to the shaft by a sleeve and pinned connection, it will be appreciated that other types of connection could be provided, so long as the translation member can slide along the shaft whilst also transmitting torque.

Claims

CLAIMSWhat is claimed is: 1. A sheave for a variable-speed belt drive, the sheave comprising: a first sheave part comprising a body and a translation member coupled to the body such that it is movable relative to the body between a retracted configuration and an extended configuration; a second sheave part arranged to oppose the first sheave part along a rotation axis, wherein the first sheave part and the second sheave part are arranged to define a belt channel for receiving a belt between an inclined inside wall of the first sheave part and an inclined inside wall of the second sheave part; and a biasing arrangement configured to bias the translation member towards its extended configuration; wherein the second sheave part is axially movable relative to the first sheave part to drive the translation member towards the body.
2. The sheave of claim 1 wherein in the extended configuration, the translation member co-operates with an inner wall of the body to form the inclined inside wall of the first sheave part and in the retracted configuration the translation member is axially offset from the inner wall of the body.
3. The sheave of claim 2 wherein the body comprises a cavity for receiving the translation member and movement of the translation member from the extended configuration to the retracted configuration causes the translation member to move axially away from the inner wall of the body and into the cavity.
4. The sheave of any preceding claim wherein the biasing arrangement comprises a spring configured to bias the translation member towards the extended configuration.
5. The sheave of any preceding claim wherein the second sheave part comprises a hydraulic actuator configured to move the second sheave part relative to the first sheave part in the axial direction.7. The sheave of any preceding claim wherein the translation member is coupled to the body by a splined connection.8. The sheave of claims 1 to 3 wherein the biasing arrangement comprises a hydraulic actuator.9. The sheave of claim 8, further comprising a sensing arrangement for sensing the axial separation between the first sheave part and the second sheave part.10. The sheave of any preceding claim wherein the first sheave part and the second sheave part are coupled to an axial shaft.11. The sheave of any preceding claim wherein the first sheave part is fixed to the axial shaft and the second sheave part is movable along the axial shaft.12. A variable-speed belt drive apparatus comprising; a control sheave coupled to a first axial shaft; a follower sheave coupled to a second axial shaft; and a belt connecting the control sheave and the follower sheave, wherein each of the control sheave and the follower sheave comprises a sheave according to claim 1 and the second sheave part of the follower sheave is configured to move with respect to the first sheave part of the follower sheave in response to movement of the second sheave part of the control sheave relative to the first sheave part of the control sheave.13. The apparatus of claim 12 wherein the first sheave part of the control sheave is fixed to the first axial shaft and comprises a spring configured to bias the translation member towards the extended configuration, and the second sheave part comprises a hydraulic actuator operable to cause the second sheave part to move along the first axial shaft.14. The apparatus of claim 11 or claim 12 wherein the first sheave part of the follower sheave comprises a hydraulic actuator configured to move the translation member between the extended configuration and the contracted configuration.15. The apparatus of claim 14 further comprising: a sensing arrangement for detecting an axial position of the second sheave part of the follower sheave; and a controller configured to control the hydraulic actuator of the follower sheave based on the detected axial position the second sheave part of the follower sheave.