GB2580613A

GB2580613A - Belt pulley

Info

Publication number: GB2580613A
Application number: GB1900590.9A
Authority: GB
Inventors: Duncombe Andrew
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2019-01-16
Filing date: 2019-01-16
Publication date: 2020-07-29
Anticipated expiration: 2039-01-16
Also published as: GB2580613B; GB201900590D0

Abstract

Aspects of the present invention relate to a belt pulley for an engine-driven component. The belt pulley comprises a central axis about which the belt pulley rotates in use and a shaft slot to receive a shaft upon which the belt pulley is to be mounted. The shaft slot has a length dimension extending radially outwards from the central axis of the belt pulley such that the belt pulley may be mounted on the shaft with an axis of the shaft aligned with the central axis of the belt pulley, or with the shaft axis off-set from the central axis of the belt pulley. A securing slot is provided to receive a securing bolt for securing the belt pulley to the shaft. The securing slot is off-set from the central axis of the belt pulley. Aspects of the present invention also relate to an auxiliary component assembly including such a belt pulley, a vehicle engine including such a belt pulley or auxiliary component assembly, and a vehicle comprising such an engine.

Description

BELT PULLEY

TECHNICAL FIELD

The present disclosure relates to a belt pulley. Aspects of the invention relate to a belt pulley for an engine-driven component, and to a pulley assembly, to a kit of parts, to an engine and to a vehicle including such a belt pulley.

BACKGROUND

It is known to provide engine-driven pulleys for driving engine auxiliary components, such as water pumps and cooling fans. Such pulleys are known to be driven by the engine via a drive wheel and a belt. The belt is conventionally constructed from an elastic material which remains slack during installation of the pulley and is held in tension once the pulley is fully installed. Such pulleys may include a radial slot through which the shaft upon which the pulley is to be mounted extends. During installation, the pulley is first mounted on the shaft with the shaft disposed within the slot off-set from a central axis of the pulley so that the pulley is displaced towards the drive wheel to enable the belt to be in a slack state. A retaining clip is placed on the shaft to retain the pulley on the shaft during the installation process. The belt is then placed over the pulley and the drive wheel. The pulley is then rotated about the offset axis until the belt is tensioned and pulls the pulley in a direction parallel to a longitudinal axis of the slot such that the axis of the shaft aligns with a central axis of the pulley. The pulley is then secured to the shaft and the retaining clip is then removed.

The need to use a retaining clip during the installation process, which is later removed, adds complexity and cost to the assembly process (as the process includes retaining clip fitment and removal steps) and the manufacturing process (as the shaft needs to include formations to receive the clip), and adds additional material and component cost (as retaining clips are required which are not part of the finished assembly).

It is an aim of the present invention to address one or more of the disadvantages associated

with the prior art.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a belt pulley, an auxiliary component assembly, a vehicle engine, and a vehicle as claimed in the appended claims.

According to an aspect of the present invention there is provided a belt pulley for an engine-driven component, the belt pulley comprising a central axis about which the belt pulley rotates in use, a shaft slot to receive a shaft upon which the belt pulley is to be mounted, the shaft slot having a length dimension extending radially outwards from the central axis of the belt pulley such that the belt pulley may be mounted on the shaft with an axis of the shaft aligned with the central axis of the belt pulley, or with the shaft axis off-set from the central axis of the belt pulley, and a securing slot to receive a securing bolt for securing the belt pulley to the shaft, wherein the securing slot is off-set from the central axis of the belt pulley.

The securing slot may have a length dimension extending parallel to the length dimension of the shaft slot.

The belt pulley may comprise a plurality of securing slots, wherein all securing slots extend parallel to each other and to the shaft slot. The belt pulley may comprise three securing slots.

The belt pulley may comprise a securing hole for receiving a securing bolt for securing the belt pulley to a mounting plate attached to the shaft, wherein the securing hole has an axis extending parallel to the central axis of the belt pulley. The securing hole may be circular.

The belt pulley may comprise a tool hole for receiving a rotating tool, the tool hole extending through the pulley in a direction parallel to the central axis of the pulley. The tool hole may be a square hole.

The securing slot may be off-set from the central axis of the belt pulley in line with the length dimension of the shaft slot. Alternatively, the securing slot may be off-set from the central axis of the belt pulley in a radial direction perpendicular to the length dimension of the shaft slot.

The belt pulley may comprise a circular body having a mounting face extending in a plane perpendicular to the central axis of the belt pulley, and a peripheral surface facing radially outwards, a belt lying against the peripheral surface when in use. The mounting surface may be off-set from the peripheral surface in a direction of the central axis of the belt pulley.

According to another aspect of the invention, there is provided an auxiliary component assembly for an engine comprising a rotatable shaft, a mounting plate fixedly associated with the shaft, and a belt pulley as described above, wherein the mounting plate comprises a respective threaded mounting hole aligned with the or each securing slot to receive a securing bolt extending through the or each securing slot.

The mounting plate may comprise a threaded mounting hole aligned with the securing hole to receive a securing bolt extending through the securing hole.

The shaft may include two parallel flat surfaces each located in a different plane parallel to the shaft axis, and the shaft slot may comprise two parallel flat surfaces each located in a different plane parallel to the shaft axis, the parallel flat surfaces of the shaft being spaced apart by a distance less than the spacing between the parallel flat surfaces of the shaft slot such that the parallel flat surfaces of the shaft lie proximate the parallel flat surfaces of the shaft slot to rotationally lock the belt pulley to the shaft.

The auxiliary component assembly may comprise a securing bolt extending through the or each securing slot to retain the belt pulley on the mounting plate but to enable the belt pulley to slide on the mounting plate in a direction parallel to the shaft slot and the mounting slot(s).

The auxiliary component assembly may comprise a mounting bracket for mounting the shaft and belt pulley to a cylinder block of an engine.

The auxiliary component assembly may comprise an auxiliary engine component for attachment to the shaft. The auxiliary engine component may comprise a cooling fan.

According to yet another aspect of the invention there is provided a vehicle engine comprising a belt pulley as described above or an auxiliary component assembly as described above.

According to yet another aspect of the invention there is provided a vehicle comprising a belt pulley as described above or an auxiliary engine component assembly as described above or an engine as described above.

According to yet another aspect of the invention there is provided a method of installing a belt pulley according as described above onto a vehicle engine, the vehicle engine comprising drive wheel, a rotatable shaft for attachment of an auxiliary engine component to the engine, the shaft having a mounting plate fixedly associated with the shaft, the mounting plate comprising a respective threaded mounting hole positioned for alignment with the or each securing slot to receive a securing bolt extending through the or each securing slot, the method comprising fitting the belt pulley to the shaft such that the shaft extends through the shaft slot with the shaft axis off-set from the central axis of the belt pulley, inserting at least one securing bolt through the at least one securing slot and into the respective threaded mounting hole to retain the belt pulley on the shaft, fitting a belt around the belt pulley and the drive wheel, rotating the belt pulley and shaft until the belt tension increases and pulls the belt pulley relative to the shaft and at least one securing bolt in a direction perpendicular to the shaft axis and in a direction of the shaft slot and securing slot(s), until the shaft axis is coaxial with the central axis of the belt pulley, tightening the or each securing bolt to secure the belt pulley in coaxial position on the shaft.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a perspective view of a belt pulley of an embodiment of the invention; Figure 2 shows a perspective view of the belt pulley of Figure 1 as part of a component assembly of an embodiment of the invention fitted to a vehicle engine in an initial installation position; Figure 3 shows a perspective view of the belt pulley of Figure 1 as part of a component assembly of an embodiment of the invention fitted to a vehicle engine in an intermediate installation position; Figure 4 shows a perspective view of the belt pulley of Figure 1 as part of a component assembly of an embodiment of the invention fitted to a vehicle engine in a final installed position; Figure 5A shows a cross-sectional view of a portion of the component assembly of an embodiment of the invention shown in Figures 2 to 4; Figure 5B shows a cross-sectional view similar to that of Figure 5A but illustrating the belt pulley in a displacement orientation; Figure 6 shows an exploded view of parts of the component assembly of Figures 2 to 4, including the belt pulley of Figure 1; Figure 7 shows a front view of vehicle in accordance with an embodiment of the invention, comprising the engine with fitted belt pulley of Figure 4, with parts of the vehicle exterior omitted from view for ease of illustration; and Figure 8 shows a perspective view of a belt pulley of an alternative embodiment of the invention.

DETAILED DESCRIPTION

A belt pulley 10 for an engine-driven component in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figures 1 to 6.

With reference to Figure 1, the belt pulley 10 comprises a circular body with a circular face 11 and a circumferential edge surface 12 depending from a peripheral edge of the circular face 11. The circumferential edge surface 12 includes upstanding radial walls 13 extending radially outwardly from the edges of the circumferential edge surface 12. In use, a belt 14 (see Figures 2 to 4) is tensioned over the circumferential edge surface 12. The circumferential edge surface 12 includes formations 15 configured to engage with corresponding formations (not shown) on the belt 14 to help locate and retain the belt 14 in place on the belt pulley 10. The radial walls 13 also help locate and retain the belt 14 in place on the belt pulley 10.

The belt pulley 10 includes a central axis X-X which extends through a centre point C in the centre of the circular face 11 and circular body of the belt pulley 10.

A shaft slot 16 is formed in the circular face 11 of the belt pulley 10. The shaft slot 16 has a length dimension which extends from the centre point C of the belt pulley radially outwards. A centre line S of the shaft slot 16 extends through the centre point C of the belt pulley 10 and through an off-set point 0 which is radially off-set from the centre point C. An off-set axis Y-Y extends through the off-set point 0 and parallel to the central axis X-X.

The belt pulley 10 includes three securing slots 17 and one securing hole 18 disposed adjacent to the shaft slot 16. The securing slots 17 each have a length dimension L which extends parallel to the length dimension S of the shaft slot. Each securing slot 17 is off-set from the central axis X-X of the belt pulley 10. Two securing slots 17 are disposed on one side of the shaft slot 16, and one securing slot 17 is disposed on the opposite side of the shaft slot 16 to the other securing slots 17. The securing hole 18 is disposed on the same side of the shaft slot 16 as the single securing slot 17, and is aligned with the length dimension L of that securing slot 17.

In use, the belt pulley 10 is mounted to a shaft 19, to which is mounted an auxiliary engine component 20 (see Figure 5A -shown here spaced apart from the shaft 19 but would be mounted to the shaft 19 in use), such as an engine cooling fan, but may include any other rotationally-driven component such as an oil pump, fuel pump, alternator, etc. Thereby, rotation of the belt pulley 10 rotates the shaft 19 and thereby the auxiliary engine component 20.

The belt pulley 10 and shaft 19 are part of an auxiliary component assembly which also includes a mounting plate 21 fixedly associated with the shaft 19. In the embodiment shown in Figures 2 to 6, the auxiliary component assembly also includes an engine cooling fan as the auxiliary engine component 20, and a mounting bracket 22 for rotatably supporting the shaft 19 and mounting the auxiliary component assembly to a cylinder block 101 of a vehicle engine 100. In the embodiment shown, the mounting plate 21 is formed integrally with the shaft 19, although the mounting plate may alternatively be a separate component secured to the shaft 19.

The mounting plate includes a plurality of threaded mounting holes 23 (see Figure 6). The threaded mounting holes 23 are positioned on the mounting plate 21 so as to align with the securing slots 17 and securing hole 18 of the belt pulley 10 when the belt pulley is fitted to the shaft 19.

The shaft 19 includes a central axis Z-Z (see Figure 5A). The shaft 19 includes two opposing parallel flat surfaces 24 which lie in respective planes which are parallel to the shaft axis Z-Z. The shaft slot 16 includes parallel flat surfaces 25. The distance between the parallel flat surfaces 24 of the shaft 19 is slightly less than the distance between the parallel flat surfaces of the shaft slot 16 such that when the belt pulley 10 is fitted to the shaft 19, each parallel flat surface 24 of the shaft 19 lies closely adjacent or in light contact with the respective parallel flat surface 25 of the shaft slot 16. Thereby, once so fitted, the belt pulley 10 cannot rotate relative to the shaft 19.

The belt pulley 10 includes a tool hole 26 extending through the circular face 11. In the embodiments shown, the tool 26 is square, but other non-circular shapes may be provided.

The tool hole 26 is configured to receive a projection of a pulley-rotating tool (not shown), the tool comprising a spanner or other lever with a projection at one end for insertion into the tool hole 26 to enable the belt pulley 10 to be rotated, as described in more detail below.

In use, when the belt pulley 10 is fitted to a vehicle engine 100 as part of an auxiliary component assembly, the belt pulley 10 is rotatably driven by the vehicle engine via the belt 14 that extends around the belt pulley 10 and around a drive wheel 102 which is connected to the drive shaft of the vehicle engine 100. In the operative configuration, the belt 14 needs to be in sufficient tension between the belt pulley10 and the drive wheel 102 to frictionally engage both to transfer rotation movement of the drive wheel 102 to the belt pulley 10 without slipping.

The method of installing the belt pulley 10 of an embodiment of the invention is described below.

The belt pulley 10 is fitted to the shaft 19 in an initial installation position as shown in Figure 2. The flat surfaces 24 of the shaft 19 are aligned and in contact with the respective parallel flat surface 25 of the shaft slot 16 so that the belt pulley 10 cannot rotate relative to the shaft 19. However, the belt pulley 10 is not centrally positioned on the shaft 19, but instead central axis Z-Z of the shaft 19 is co-axial with off-set axis Y-Y of the belt pulley 10 such that the belt pulley is positioned closer to the drive wheel 102 than it would be if the belt pulley 10 was centrally positioned on the shaft 19. Three securing bolts 27 are then fitted through the three securing slots 17 and into the respective threaded mounting holes 23 in the mounting plate 21. The securing bolts 27 are fitted sufficiently far into the mounting holes 23 to retain the belt pulley 10 on the shaft 19, but to still allow the belt pulley 10 to slide on the shaft 19 with the shaft 19 travelling along the shaft slot 16 and the securing bolts 27 sliding along the securing slots 17.

The belt 14 is then fitted around the belt pulley 10 and drive wheel 102. Since, in this initial installation position, the distance between the belt pulley 10 and the drive wheel 102 is less than if the belt pulley 10 was centrally positioned on the shaft 19, the belt 14 is slack, as can be seen in Figure 2.

A rotating tool (not shown) is then used to rotate the belt pulley 10 from the initial installation position to an intermediate position (shown in Figure 3) and finally to a final installed position (shown in Figure 4). The projection of the rotating tool is inserted into the tool hole 26. For the embodiment shown, the projection of the rotating tool would be square to closely fit within the square tool hole 26. The lever of the rotating tool is then rotated, to rotate the belt pulley 10.

As the belt pulley 10 is rotated, the off-set positioning of the belt pulley 10 on the shaft 19 (i.e. with the central axis Z-Z of the shaft 19 co-axial with off-set axis Y-Y of the belt pulley 10) means that the belt 14 is tensioned between the belt pulley 10 and the drive wheel 102.

When the belt pulley nears being rotated through 180 degrees from the initial installation position, the tension in the belt 14 pulls the belt pulley towards the drive wheel 102 such that the shaft 19 slides within the shaft slot 16 (and the securing bolts 27 slide within the securing slots 17) until the belt pulley 10 is centrally position on the shaft 19 such that central axis Z-Z of the shaft 19 is co-axial with central axis X-X of the belt pulley 10. Once in this position, shown in Figure 4, the three securing bolts 27 extending through the securing slots 17 are tightened to clamp the belt pulley 10 to the mounting plate 21. In addition, a fourth securing bolt 27 is fitted through the securing hole 18 and into the respective mounting hole 23 in the mounting plate 21, and is similarly tightened to clamp the belt pulley 10 to the mounting plate 21. In this installed position, the securing force provided by the securing bolts 27 is via the bolt heads compressing the belt pulley 10 onto the mounting plate 21, such that excessive load is not taken by the shafts of the securing bolts 27 in use of the belt pulley 10/auxiliary component assembly.

It will be appreciated that the above-described configuration of belt pulley 10, and method of installation with belt 14 as part of an auxiliary component assembly, avoids the need for auxiliary, cumbersome and expensive belt-tensioning tools to stretch the belt over belt pulley. Instead, the belt pulley 10 and belt 14 can be simply fitted in slack position, tensioned and secured with a small, cheap, simple rotating tool. This makes assembly quicker, easier and requires less expensive tooling, all of which makes the assembly process more efficient and cost-effective.

Although the embodiment of belt pulley 10 described above comprises three securing slots 17 and one securing hole 18, the invention is not intended to be limited to such a configuration of belt pulley 10. It is intended that the belt pulley 10 may comprise just one securing slot and one securing hole, or more than one securing slot 17 and more than one securing hole 18.

Operation of such alternative embodiments would be the same as described above, with only the securing bolt(s) 27 in the securing slot(s) 17 loosely fitted in the initial installation position, and those securing bolt(s) 27 tightened, and additional securing bolt(s) 27 fitted and tightened through the securing hole(s) once the belt pulley is rotated into the final installed position.

An advantage of including a plurality of securing slots 17 is that in engine configurations in which the belt 14 is under higher levels of tension in the final installed position, any off-set tensile force exerted on the belt pulley 10 by the belt 14, particularly during the installation process as the belt pulley 10 is rotated from the initial installation position to the final installed position, before the securing bolts 27 are fully tightened, is distributed over more than one securing bolt 27. This can help to prevent binding of the belt pulley 10 to the securing bolts 27 during the installation process. Such off-set force is explained by reference to Figures 5A and 5B, in which is can be seen in Figure 5A that the belt 14 tension force will be acting in a direction shown by arrow B, but the point at which the securing bolts 27 hold the belt pulley 10 in position against the mounting plate 21 is off-set in a direction of the shaft axis Z-Z by a distance shown by dimension D. In the absence of the lower securing bolt 27 shown in Figure 5A, the belt tension force B acting on the belt pulley 10 would pull the belt pulley 10 out of its position in which the central axis X-X of the belt pulley 10 is coaxial with the central shaft axis Z-Z. This would result in a tilted orientation of the belt pulley 10 as shown in Figure 5B in which a gap (shown by arrow E in Figure 5B) is formed between the face of the mounting plate 21 and the adjacent circular face 11 of the belt pulley 10. This tilting action could cause the belt pulley 10 to bind on the securing bolt 27 at the point indicated P1 in Figure 5B, and to bind on the edge of the mounting plate 21 at the point indicated P2 in Figure 5B. Even if the belt pulley 10 did not fixedly bind on the securing bolt 27 or mounting plate 21 at points P1 and P2, there could be deformation or wear at these points which could eventually lead to weakness or failure in one or more of the above-mentioned components. It is therefore advantageous to include a lower securing bolt 27 as shown in Figure 5A to hold the belt pulley 10 square and coaxial with the shaft 19 in the position shown in Figure 5A.

Figure 7 shows a vehicle 1000 including an engine 100 which comprises a belt pulley 10 and auxiliary component assembly of embodiments of the invention.

Figure 8 shows a belt pulley 10 of another embodiment of the invention. Like features in common with the belt pulley 10 of the previously-described embodiment retain the same reference numerals and detailed description thereof will not be repeated. A difference with the belt pulley 10 in Figure 8 is the configuration of securing slots 17. In this embodiment one of the securing slots 17 is in line with the shaft slot 16, and in the embodiment shown, is a continuation of the shaft slot 16. The function and operation in use of the alternative configuration of belt pulley 10 would be as described with the previous embodiment. The configuration of securing slot 17 being continuous with the shaft slot 16 may make manufacture of the belt pulley 10 simpler, quicker and cheaper. This may particularly be the case if only one securing slot 17 is provided, being continuous with the shaft slot 16. Although in the alternative embodiment of belt pulley 10 shown, there are two securing slots 17 and two securing holes 18, as mentioned above, it is intended within the scope of the invention that there may be only one securing slot 17 and/or only one securing hole 18, or more than two securing slots 17 and/or more than two securing holes 18.

In the embodiments shown and described, one single tool hole 26 is provided. However, in alternative embodiments of the invention, the belt pulley 10 may include a plurality of tool holes 26. If a plurality of tool holes 26 are provided, the holes may be of any shape, including circular, since if a plurality of tool holes 26 are provided, the pulley rotating tool would include a corresponding plurality of projections to be received in the tool holes and so would be able to rotate the belt pulley 10 even with circular tool holes 26.

It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

CLAIMS1. A belt pulley for an engine-driven component, the belt pulley comprising: a central axis about which the belt pulley rotates in use; a shaft slot to receive a shaft upon which the belt pulley is to be mounted, the shaft slot having a length dimension extending radially outwards from the central axis of the belt pulley such that the belt pulley may be mounted on the shaft with an axis of the shaft aligned with the central axis of the belt pulley, or with the shaft axis off-set from the central axis of the belt pulley; a securing slot to receive a securing bolt for securing the belt pulley to the shaft, wherein the securing slot is off-set from the central axis of the belt pulley.
2. A belt pulley according to claim 1 wherein the securing slot has a length dimension extending parallel to the length dimension of the shaft slot.
3. A belt pulley according to claim 1 or claim 2 comprising a plurality of securing slots, wherein all securing slots extend parallel to each other and to the shaft slot.
4. A belt pulley according to claim 3 comprising three securing slots.
5. A belt pulley according to any preceding claim comprising a securing hole for receiving a securing bolt for securing the belt pulley to a mounting plate attached to the shaft, wherein the securing hole has an axis extending parallel to the central axis of the belt pulley.
6. A belt pulley according to claim 5 wherein the securing hole is circular.
7. A belt pulley according to any preceding claim, comprising a tool hole for receiving a rotating tool, the tool hole extending through the belt pulley in a direction parallel to the central axis of the belt pulley.
8. A belt pulley according to claim 7 wherein the tool hole is a square hole.
9. An auxiliary component assembly for an engine comprising: a rotatable shaft; a mounting plate fixedly associated with the shaft; and belt pulley according to any preceding claim; wherein the mounting plate comprises a respective threaded mounting hole aligned with the or each securing slot to receive a securing bolt extending through the or each securing slot.
10. An auxiliary component assembly according to claim 9 when dependent on claim 5, wherein the mounting plate comprises a threaded mounting hole aligned with the securing hole to receive a securing bolt extending through the securing hole.
11. An auxiliary component assembly according to claim 9 or claim 10 wherein the shaft includes two parallel flat surfaces each located in a different plane parallel to the shaft axis, and the shaft slot comprises two parallel flat surfaces each located in a different plane parallel to the shaft axis, the parallel flat surfaces of the shaft being spaced apart by a distance less than the spacing between the parallel flat surfaces of the shaft slot such that the parallel flat surfaces of the shaft lie proximate the parallel flat surfaces of the shaft slot to rotationally lock the belt pulley to the shaft.
12. An auxiliary component assembly according to claim 11 comprising a securing bolt extending through the or each securing slot to retain the belt pulley on the mounting plate but to enable the belt pulley to slide on the mounting plate in a direction parallel to the shaft slot and the securing slot(s).
13. An auxiliary component assembly according to any of claims 9 to 12 comprising a mounting bracket for mounting the shaft and belt pulley to a cylinder block of an engine.
14. An auxiliary component assembly according to any of claims 9 to 13 comprising an auxiliary engine component for attachment to the shaft.
15. An auxiliary component assembly according to claim 14 wherein the auxiliary engine component comprises a cooling fan.
16. A vehicle engine comprising a belt pulley according to any of claims 1 to 8 or an auxiliary component assembly according to any of claims 9 to 15.
17. A vehicle comprising a belt pulley according to any of claims 1 to 8 or an auxiliary engine component assembly according to any of claims 9 to 15 or an engine according to claim 16.
18. A method of installing a belt pulley according to any of claims 1 to 8 onto a vehicle engine, the vehicle engine comprising drive wheel, a rotatable shaft for attachment of an auxiliary engine component to the engine, the shaft having a mounting plate fixedly associated with the shaft, the mounting plate comprising a respective threaded mounting hole positioned for alignment with the or each securing slot to receive a securing bolt extending through the or each securing slot, the method comprising: fitting the belt pulley to the shaft such that the shaft extends through the shaft slot with the shaft axis off-set from the central axis of the belt pulley; inserting at least one securing bolt through the at least one securing slot and into the respective threaded mounting hole to retain the belt pulley on the shaft; fitting a belt around the belt pulley and the drive wheel; rotating the belt pulley and shaft until the belt tension increases and pulls the belt pulley relative to the shaft and at least one securing bolt in a direction perpendicular to the shaft axis and in a direction of the shaft slot and securing slot(s), until the shaft axis is coaxial with the central axis of the belt pulley; tightening the or each securing bolt to secure the belt pulley in coaxial position on the shaft.