TECHNICAL FIELD The present disclosure relates to tensioning a belt on a starter generator. In particular, but not exclusively it relates to tensioning a belt on a starter generator of a hybrid vehicle.

Aspects of the invention relate to an apparatus and method for tensioning a belt on a starter generator, and a drive system and vehicle including an apparatus.

BACKGROUND

Hybrid vehicles are known which include a Belt-Driven Integrated Starter Generator (BISG). The BISG is also known as a Belt-Driven Starter Generator (BSG), a Belt-Driven Starter Alternator or Belted Starter Alternator (BSA) and a Motor Generator Unit (MGU). For the purposes of this document, the BISG will be referred to as a "starter generator".

The starter generator has a pulley connected to the crankshaft of the internal combustion engine of the vehicle by a belt. Depending upon whether the starter generator is being driven (in an alternator mode) or whether it is providing a driving force, the belt becomes tight to one side of the starter generator pulley or the other side. To control the tension in the slack side of the belt, tensioning pulleys are provided to increase tension in the slack side.

One such arrangement is shown in Fig. 8. In this example, the belt 801 extends from the crankshaft pulley 802 of the internal combustion engine and around the pulley 803 of the starter generator. The crankshaft pulley 802 and the starter generator pulley 803 are arranged to rotate in the clockwise direction as viewed in the figure.

The belt also passes around a first tensioning pulley 804 on a right side of the starter generator pulley 803 and passes around a second tensioning pulley 805 on the left side of the starter generator pulley 803. In this arrangement, each of the tensioning pulleys 804 and 805 are supported by a respective arm 806 and 807 which is mounted to allow the arm to freely rotate around the starter generator pulley 803. However, the positions of the tensioning pulleys 804 and 805 are limited by the action of the belt 801 on the pulleys and the action of a spring mechanism 808 that connects the two arms 806 and 807. Such a tensioning arrangement where the position of one pulley is determined from the position of the other pulley may be referred to as a decoupling tensioner. The tensioning pulleys 804 and 805 are shown in Fig. 8 in a nominal position that they may take up when the vehicle is switched off. However, when the starter generator is in its drive mode and it is used to create torque, tension in the left side 809 of the belt 801 is increased and the arms 806 and 807 supporting the pulleys 804 and 805 are rotated clockwise around the starter generator pulley 803, as the left side of the belt straightens under tension.

Similarly, when the internal combustion engine is running and the starter generator is in its alternator mode, tension in the right side 810 of the belt 801 is increased, and the arms 806 and 807 supporting the pulleys 804 and 805 are rotated anticlockwise around the starter generator pulley 803, as the right side of the belt straightens under tension. Such hybrid vehicles may also have a conventional starter motor fitted to the internal combustion engine, which is used to initially start the engine. In this case the crankshaft pulley generates a sudden increase in tension in the right side 810 of the belt 801 , causing the right side 810 of the belt 801 to straighten. This situation is shown in Fig. 9, which also illustrates a problem with this arrangement.

The problem is that a larger space than desired must be provided around the starter generator to accommodate the pulleys 804 and 805 in their extreme positions. If sufficient space is not provided, one or both of the pulleys might inadvertently contact another part of the vehicle. In the example of Fig. 9, an insufficient space has not been provided for the pulley 804 and consequently it has come into contact with a vehicle mounted component 901 as indicated at arrow A. In this example, the vehicle mounted component 901 is an air duct.

It is an aim of the present invention to address this problem. SUMMARY OF THE INVENTION

Aspects of the embodiments of the invention provide an apparatus and method for tensioning a belt on a starter generator and a drive system and vehicle including an apparatus as claimed in the appended claims.

According to an aspect of the invention there is provided an apparatus for tensioning a belt on a starter generator, the apparatus comprising: support means for supporting a first pulley and a second pulley, the support means being mounted adjacent to a starter generator; and a first pulley for providing tension in a belt of the starter generator, the first pulley being supported by the support means and mounted to rotate about its axis of rotation with respect to the support means; wherein the support means is configured to enable rotational movement of the axis of rotation of the first pulley about the axis of the starter generator, and the apparatus comprises a stop means arranged to limit the movement of the axis of rotation of the first pulley about the axis of the starter generator.

This provides the advantage that a reduced space may be provided for the accommodation of the first pulley. In an embodiment of the invention the support means is mounted on the starter generator, and the first pulley is suitable for providing tension in a belt at a first side of the starter generator and the apparatus comprises a second pulley supported by the support means for providing tension in the belt at a second side of the starter generator. In an embodiment the support means comprises a first part supporting the first pulley and a second part supporting the second pulley and a separating means connecting the first and second parts of the support means, the separating means being configured to limit positioning of the first pulley in dependence upon position of the second pulley. In one such embodiment, the separating means comprises a spring means connecting the first and second parts of the support means, and the spring means may comprise a spring extending around the outside of a pulley of the starter generator.

In an embodiment, the stop means comprises at least one first stopping element fixed to the support means and at least one second stopping element fixed with respect to the starter generator. In such embodiments the stop means may comprise a plurality of first stopping elements spaced about the axis of the integrated starter generator and a plurality of second stopping elements which are correspondingly spaced. In such embodiments the stop means may comprise at least three first stopping elements and a corresponding number of second stopping elements. In some such embodiments, the at least one second stopping element is mounted on the starter generator. In some such embodiments, the at least one second stopping element is fixed to the support means. In some such embodiments, the at least one first stopping element and/or the at least one second stopping element comprises a resilient deformable member, and the resilient deformable member may be formed of rubber or a synthetic polymer.

This provides the advantage that the resilient deformable member reduces noise and peak forces that may occur during operation of the apparatus. In an embodiment, the stop means is configured to limit the movement of the axis of rotation of the first pulley about the axis of the starter generator in both clockwise and anticlockwise directions.

This provides the advantage that the space required to accommodate the first and second pulleys is reduced.

According to another aspect of the invention there is provided a drive system for a vehicle as claimed in claim 14. According to a further aspect of the invention there is provided a vehicle as claimed in claim 15.

According to a still further aspect of the invention there is provided a method of providing tensioning in a belt on a starter generator the method comprising: supporting a first pulley and a second pulley adjacent to a starter generator to enable the first pulley to rotate about its axis of rotation and to enable rotational movement of the axis of rotation about the axis of the starter generator and limiting the movement of the axis of rotation of the first pulley about the axis of the starter generator In an embodiment of the method, the first pulley and the second pulley are supported by support structure and the method comprises mounting the support structure on the starter generator In an embodiment, the method comprising fitting a belt around the first pulley the second pulley and a pulley of the starter generator so that the first pulley is located on the belt at a first side of the starter generator and the second pulley is located on the belt at a second side of the pulley of the starter generator. In an embodiment of the method, the process of supporting a first pulley and a second pulley comprises supporting the first pulley on a first part and supporting the second pulley on a second part and a separating means is configured to limit positioning of the second pulley in dependence upon position of the first pulley The separating means may comprise a spring means connecting the first part and second part The spring means may comprise a spring extending around the outside of a pulley of the starter generator

In an embodiment of the method, the first pulley and the second pulley are supported on a support structure which also supports at least one first stopping element and said limiting the movement of the axis of rotation comprises fixing at least one second stopping element with respect to the starter generator A plurality of first stopping elements may be spaced about the axis of the starter generator and the method may comprise fixing a plurality of correspondingly spaced second stopping elements The method may comprise fixing the at least one second stopping element to the starter generator. According to another aspect of the invention there is provided an apparatus for tensioning a belt on a starter generator, the apparatus comprising: a support structure supporting a first pulley and a second pulley, the support structure being configured to be mounted adjacent to a starter generator; and a first pulley providing tension in a belt of the starter generator, the first pulley being supported by the support structure and mounted to rotate about its axis of rotation with respect to the support structure; wherein the support structure is configured to enable rotational movement of the axis of rotation of the first pulley about the axis of the starter generator, and the apparatus comprises stopping elements arranged to limit the movement of the axis of rotation of the first pulley about the axis of the starter generator. According to a further aspect of the invention there is provided an apparatus tensioning a drive belt, the apparatus comprising: a support structure for supporting a first pulley; and a first pulley providing tension in a belt, the first pulley being supported by the support structure and mounted to rotate about its axis of rotation with respect to the support structure; wherein the support structure is configured to enable rotational movement of the axis of rotation of the first pulley about a second axis, and the apparatus comprises stopping elements arranged to limit the movement of the axis of rotation of the first pulley about the second axis. 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: Fig. 1 shows a front view of an example apparatus 101 for tensioning a belt 102, which is mounted on a starter generator 103;

Fig. 2A and Fig. 2B show respectively arear perspective view and a front perspective view of the apparatus 101 , separate from the starter generator 103;

Fig. 3 shows schematically the apparatus 101 adjacent to a starter generator 103 located within a vehicle 301 ;

Fig. 4 shows a front view of the apparatus 101 adjacent to the starter generator 103 which is located adjacent to the internal combustion engine 303;

Fig. 5 shows the apparatus 101 with the first stopping elements 1 19 abutting the second stopping elements 120 after rotation from the configuration shown in Fig. 4; Fig. 6 shows an alternative apparatus 101 B

Fig. 7 shows a method 700 of providing tensioning in a belt on a starter generator;

Fig. 8 shows a known arrangement for providing tension in a belt of a starter generator; and Fig. 9 shows the arrangement of Fig. 8 during operation when the starter generator is in its alternator mode.

DETAILED DESCRIPTION

The Figures illustrate an apparatus 101 for tensioning a belt 102 on a starter generator 103, the apparatus 101 comprising: support means 104 for supporting a first pulley 105 and a second pulley 106, the support means 104 being mounted adjacent to a starter generator 103; and a first pulley 105 for providing tension in a belt 102 of the starter generator 103, the first pulley 105 being supported by the support means 104 and mounted to rotate about its axis of rotation 109 with respect to the support means 104; wherein the support means 104 is configured to enable rotational movement of the axis of rotation 109 of the first pulley 105 about the axis 108 of the starter generator 103, and the apparatus 101 comprises a stop means 1 10 arranged to limit the movement of the axis of rotation 109 of the first pulley 105 about the axis 108 of the starter generator 103.

Fig. 1 shows a front view of an example apparatus 101 for tensioning a belt 102, which is mounted on a starter generator 103. The apparatus 101 comprises a supporting structure 104 providing the supporting means 104 for supporting a first pulley 105 and a second pulley 106. The supporting structure 104 is mounted adjacent to the starter generator 103, and extends around the pulley 107 of the starter generator 103. The pulley 107 of the starter generator 103 is operatively connected to the rotor (not shown) of the starter generator so that it in operation it rotates about its axis 108. (Axis 108 extends into the page in Fig. 1 .)

The apparatus 101 also comprises a first pulley 105 for providing tension in the belt 102 of the starter generator 103. The first pulley 105 is supported by the supporting structure 104 and mounted so that it is able to rotate about its axis of rotation 109 with respect to the supporting structure 104. (The axis of rotation 109 of the pulley 105 also extends into the page in Fig. 1 and it is therefore parallel to the axis 108 of the starter generator 103.) The supporting structure 104 is configured to enable rotational movement of the axis of rotation 109 of the first pulley 105 about the axis 108 of the starter generator 103. The apparatus 101 also comprises a stop means 1 10 arranged to limit the movement of the axis of rotation 109 of the first pulley 105 about the axis 108 of the starter generator 103.

As will be described in further detail below, limiting the movement of the axis of rotation of the first pulley 105 in this way results in the apparatus 101 requiring less space for its accommodation.

In the example of Fig. 1 , the apparatus 101 also comprises a second pulley 106, supported by the supporting structure 104, for providing tension in the belt 102 of the starter generator 103. In the arrangement of Fig. 1 , the first pulley 105 is arranged to provide tension in the belt 102 at a first side 102A of the starter generator 103 and the second pulley 106 is arranged to provide tension in the belt 102 at a second side 102B of the starter generator 103. The second pulley 106 is also mounted such that it is able to rotate about its axis of rotation 1 1 1 with respect to the supporting structure 104, and the supporting structure is configured to enable the axis of rotation 1 1 1 of the pulley 106 to rotate about the axis 108 of the starter generator 103. The supporting structure 104 of the apparatus 101 is mounted on the starter generator 103 in Fig. 1 . However, it will be appreciated that the supporting structure 104 may be mounted on a different part of a vehicle in which the starter generator is mounted, provided it is mounted adjacent to the pulley 107 of the starter generator. For example, in an alternative arrangement the supporting structure 104 may be supported from the engine block.

The supporting structure 104 includes a fixed part 1 12 comprising several (in this case three) lugs 1 13 which define holes (201 in Fig.2A) for receiving bolts 1 14 to enable the supporting structure 104 to be bolted to the starter generator 103. The supporting structure 104 includes a first part 1 15 on which is mounted the first pulley 105 so that it is able to rotate about its axis of rotation 109 with respect to the first part 1 15. The first part 1 15 is itself mounted to rotate with respect to the fixed part 1 12 such that, when the fixed part 1 12 is rigidly fixed to a starter generator, the axis of rotation 109 of the pulley 105 is able to rotate about the axis 108 of the starter generator. The supporting structure 104 includes a second part 1 16 on which is mounted the second pulley 106 so that it is able to rotate about its axis of rotation 1 1 1 with respect to the second part 1 16. The second part 1 16 is itself mounted to rotate with respect to the fixed part 1 12 such that, when the fixed part 1 12 is rigidly fixed to a starter generator, the axis of rotation 1 1 1 of the pulley 106 is able to rotate about the axis 108 of the starter generator.

A rear perspective view of the apparatus 101 , separate from the starter generator 103 is shown in Fig. 2A. This view of the apparatus 101 shows the fixed part 1 12, which has the three lugs 1 13 defining the bolt holes 201 . A front perspective view of the apparatus 101 , separate from the starter generator 103 is shown in Fig. 2B.

The fixed part 1 12 comprises a central portion 202, a rear portion 203 and a front portion 204. The central portion 202 has a cylindrical inner face and the rear portion 203 and front portion 204 extend radially outwards from the rear and front ends respectively of the central portion 202. The first part 1 15 and the second part 1 16 are mounted on bearings around the central portion 202 between the front portion 204 and rear portion 203 and to enable each of the first part and the second part to independently rotate about the central portion 202. By this mechanism, the axes 109, 1 1 1 of the first and second pulleys 105 and 106 are able to rotate about the axis of the starter generator (103 in Fig. 1 ).

The support structure 104 also comprises a separating means 207 connecting the first and second parts 1 15 and 1 16 of the support structure 104. The separating means 207 is configured to limit positioning of the first pulley 105 in dependence upon position of the second pulley 106. In the present example, the separating means 207 comprises a spring means connecting the first and second parts 1 15, 1 16 of the support structure 104, so that in use the spring means may be strained to cause the pulleys 105 and 106 to apply tensioning forces to the belt 102. In the present example, the spring means comprises a spring 207 that extends around the fixed part 1 12. The spring 207 has a first end 1 17 attached to the first part 1 15 and a second end 1 18 attached to the second part 1 16. In the absence of a belt, as shown in Fig. 2, the first part 1 15 and the second part 1 16 are free to rotate about the fixed part 1 12 but the angular spacing of the first pulley 105 and the second pulley 106 is approximately maintained by the spring 207. (The angular spacing may be varied to a degree due to the flexibility of the spring 207.) In the present example, the spring means 207 is a single arch-shaped spring. However, other spring means may be used as are known in the art. For example, the first and second parts may be provided with arms that are spaced separately from the first and second pulleys, and a helical spring may be connected between the arms to maintain the relative angular positioning of the first and second pulleys.

The stop means 1 10 comprises at least one first stopping element 1 19 fixed to the supporting structure 104 and at least one second stopping element 120 which may be fixed with respect to the starter generator 103. The first stopping elements 1 19 may be fixed to the first part 1 15 of the support structure 104 and the second stopping elements 120 may be fixed to the fixed part 1 12 of the support structure 104. In the present example the second stopping elements are fixed to the front portion 204 of the fixed part 1 12. In an alternative embodiment, second stopping elements may be provided that are configured to be mounted directly on the starter generator.

In the present example, the stop means 1 10 comprises a plurality of first stopping elements 1 19 angularly spaced about the axis 108 of the integrated starter generator 103 and a plurality of second stopping elements 120 which are correspondingly spaced. Consequently, during operation, each of the first stopping elements 1 19 are arranged to contact a corresponding second stopping element 120 at substantially the same time as the other first stopping elements 1 19.

In the present example the stop means 1 10 comprises three first stopping elements and a corresponding number of second stopping elements. However, other embodiments are envisaged having more than three first stopping elements and a corresponding number of second stopping elements, while other embodiments are envisaged having fewer than three first stopping elements and a corresponding number of second stopping elements. The first stopping elements 1 19 may be evenly angularly spaced about the axis 108 of the starter generator 103. In this way, undesirable forces that may tend to distort the support structure 104 are minimised. The first stopping elements 1 19 and/or the second stopping elements 120 may comprise a resilient deformable member. For example, at least a portion of the first stopping elements 1 19 and/or the second stopping elements 120 may comprise a resilient deformable member formed of rubber or a synthetic polymer that is resiliently deformable like rubber. In the present example, the second stopping elements 120 have been provided with a resilient deformable member 121 .

During operation, a movement (anticlockwise in Fig. 1 ) of the first stopping elements 1 19, repeatedly brings the first stopping elements into contact with the second stopping elements 120, which stops further movement in that direction. By having a resilient deformable member 121 positioned at the point of contact, the impact of the first stopping elements 1 19 on the second stopping elements 120 is cushioned, so that noise resulting from the impact is reduced, and peak forces caused by the impact may also be reduced. The apparatus 101 is shown schematically in Fig. 3 adjacent to a starter generator 103 located within a vehicle 301 . The vehicle 301 has a drive system 302 comprising an internal combustion engine 303, the starter generator 103, the belt 102 and the apparatus 101 which is arranged to provide tension in the belt 102. During operation of the vehicle, the internal combustion engine 303 is used to provide torque required to power movement of the vehicle 301 but, as is known in hybrid vehicles, some of the power produced by the engine 303 may be used to provide power to the starter generator 103, which in its generator mode generates electricity. The generated electricity is stored within one or more batteries 304.

A portion of the power generated by the engine 303 may also be used to provide power to other accessories, such as an air-conditioner compressor 305.

In a driving mode, the starter generator 103 may be used to start movement of the vehicle 301 and provide a power boost to assist the engine 303 when required.

The vehicle 301 may also comprise a separate starter motor 306 used to start the engine 303 when the vehicle is initially started. The apparatus 101 is shown in Fig. 4 adjacent to the starter generator 103 which is located adjacent to the internal combustion engine 303. The engine 303 has a crankshaft, on which is mounted a crankshaft pulley 401 , and a water pump having a water pump pulley 402. In the present example, the vehicle also comprises an air conditioner compressor 305 having an air-conditioner pulley 403.

The belt 102 extends around the crankshaft pulley 401 , the water pump pulley 402, the air- conditioner pulley 403, the first pulley 105 of the apparatus 101 , the starter generator pulley 107, the second pulley 106 of the apparatus 101 and an idler pulley 404, back to the crankshaft pulley 401 .

The apparatus 101 is shown in Fig. 4 in an orientation that it may assume when the vehicle is not operational. Tension may be produced in the belt 102 due to the action of the pulleys 105 and 106 which are urged against the belt by the action of the spring 207. When the engine 303 and the starter generator 103 are not providing power, tension in the first side 102A of the belt 102 and the second side 102B of the belt 102 may be equal resulting in the configuration of Fig. 4.

During operation of the engine 303 or the starter motor 306 (shown in Fig. 3) the crankshaft is rotated clockwise as viewed in Fig. 4 and tension in the first side 102A of the belt 102 is increased while tension in the second side 102B of the belt is reduced. Consequently, the tension in the first side of the belt 102A provides a resultant force to the first pulley 105 that pushes the axis 109 of the first pulley around the axis 108 of the starter generator (in an anticlockwise direction in Fig. 4), and the first side 102A of the belt 102 tends to become straighter. That is, the first side 102A of the belt 102 wraps around the first pulley through a smaller angle. Therefore, this movement causes the resultant force applied by the belt 102 to the first pulley 105 to be reduced.

The first part 1 15 of the support structure 104, on which the first pulley 105 is mounted, is connected to the second part 1 16, on which the second pulley 106 is mounted, by the spring 207. Consequently, this movement (anticlockwise around the starter generator axis 108) of the first pulley 105 also causes a similar movement of the second pulley 106. This movement of the second pulley 106 causes the second side 102B of the belt 102 to become wrapped through a larger angle around the second pulley 106, and the resultant force applied by the second pulley 105 to the belt 102 is increased.

In the absence of the stop means 1 10, the rotation of the pulleys 105 and 106 around the axis 108 of the starter generator 103 would continue until the resultant forces applied by first side 102A and the second side 102B of the belt 102 to the pulleys 105 and 106 are equalised. However, in the present case, the stop means 1 10 is configured to limit the movement of the axis of rotation 109 of the first pulley 105 about the axis 108 of the starter generator 103 in the anticlockwise direction. Thus, the first pulley 105 is able to rotate about the axis 108 of the starter generator until the first stopping elements 1 19 abut the second stopping elements 120.

The apparatus 101 is shown in Fig. 5 with the first stopping elements 1 19 abutting the second stopping elements 120 after such a rotation. The stopping elements 1 19 and 120 have limited the anticlockwise movement of the first pulley 105 to its position shown in Fig. 5. In the present example, this has enabled a relatively large gap, A (of greater than 20mm), to exist between the first pulley 105 and an air duct 501 that is also present in the engine compartment of the vehicle. An alternative apparatus 101 B is shown in Fig. 6. The apparatus 101 B may be identical to the apparatus 101 of Fig. 1 , except that it is provided with third stopping elements 1 19B in addition to the previously described first stopping elements 1 19 and second stopping elements 120. The third stopping elements 1 19B are fixed to the second part 1 16 of the supporting structure 104, which supports the second pulley 106. As shown in Fig. 6, a third stopping element 1 19B is arranged between each of the first stopping elements 1 19 and the nearest second stopping element 120 in the clockwise direction.

When the starter generator 103 is in its alternator mode, the first stopping elements 1 19 and second stopping elements 120 of apparatus 101 B operate to limit movement of the axis 109 of the first pulley 105 in the same manner as for apparatus 101 .

When the starter generator 103 is in a drive mode, for example when providing torque to start movement of the vehicle, tension is increased in the second side 102B of the belt 102 and reduced in the first side 102A of the belt 102. The increased tension in the second side 102B of the belt produces a larger resultant force on the second pulley 106 when compared to the resultant force provided by the first side 102A of the belt 102 on the first pulley 105. Consequently, the second pulley 106 is pushed around the axis 108 of the starter generator 103 in the clockwise direction, and due to the spring 207 connecting the second part 1 16 to the first part 1 15 of the supporting structure 104, the first pulley 105 is also pushed around in the clockwise direction. In the absence of the third stopping elements 1 19B this motion would continue until the resultant forces on the first and second pulleys 105 and 106 is again equalised. However, in the present case, this movement is limited by the third stopping elements 1 19B abutting the second stopping elements 120.

In the present example, the second stopping elements 120 are provided with a resilient portion 601 A, 601 B on each of their two sides. When the first and second pulleys 105 and 106 are rotated anticlockwise around the axis 108 of the starter generator 103, the first stopping elements 1 19 abut a resilient portion 601 A on one side of the second stopping elements 120, and when the first and second pulleys 105 and 106 are rotated clockwise around the axis 108 of the starter generator 103 the second stopping elements 1 19B abut a resilient portion 601 B on the opposite side of the second stopping elements 120.

In an alternative arrangement to that of Fig. 6, the position of the second pulley 106 may be limited in both the clockwise and anticlockwise directions by limiting the positioning of the first pulley 105. For example, the third set of stopping elements 1 19B, like the first set of stopping elements 1 19, may be fixed to the first part 1 15, which supports the first pulley 105. Alternatively, the stopping elements 1 19 may be made sufficiently broad so that they each provide the function of the first and third stopping elements.

A method 700 of providing tensioning in a belt on a starter generator is shown in Fig. 7. The method comprises, at block 701 , providing a support means for a first pulley and a second pulley adjacent to a starter generator. For example, block 701 may comprise providing the supporting structure 104 as described above with regard to Fig. 1 , which enables the first pulley 105 to rotate about its axis of rotation 109 and enables rotational movement of the axis of rotation 109 about the axis 108 of the starter generator 103. This process may comprise mounting the first and second pulleys on bearing on the first and second parts 1 15 and 1 16 respectively of the support structure 104, and mounting the first and second parts 1 15 and 1 16 on bearings on the fixed part 1 12 of the support structure. The spring 207 may then be attached at each of its ends to the first and second parts 1 15 and 1 16.

At block 702 of the method, a stop means is provided for limiting the movement of the axis of rotation 109 of the first pulley 105 about the axis 108 of a starter generator 103, adjacent to which the support means may be located. The stop means may be attached to the support structure 104, for example, by fixing first stopping elements 1 19 to the first part 1 15 and fixing second stropping elements 120 to the fixed part 1 12, for example by welding. The method may comprise mounting the support means on the starter generator, so that the first and second pulleys are arranged adjacent to a pulley of the starter generator. A belt may then be fitted around the first pulley, the second pulley and the starter generator, so that the first pulley is located on the belt at a first side of the starter generator and the second pulley is located on the belt at a second side of the starter generator.

In an embodiment, the support means comprises a first part supporting the first pulley and a second part supporting the second pulley and a separating means connecting the first and second parts of the support means, the separating means being configured to limit positioning of the first pulley in dependence upon position of the second pulley. The separating means may comprise a spring means connecting the first and second parts of the support means, and the spring means may comprise a spring such as spring 207 which extends around the outside of a pulley of the starter generator.

In an embodiment, the stop means comprises at least one first stopping element (such as stopping elements 1 19) fixed to the support means (such as the first part 1 15 of the supporting structure 104). The method then comprises fixing at least one second stopping element (such as stopping elements 120) with respect to the starter generator. This may be achieved by locating the second stopping elements on a fixed part (such as fixed part 1 13) of a support structure that is then fixed to the starter generator by bolts (1 14). Alternatively, the at least one second stopping element may be fixed directly to the starter generator.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.