Tensioner assembly

Abstract

A tensioner assembly 60 for a drive belt 50, comprising a pair of pivot arms 70A, 70B locatable within an area enclosed by the drive belt. A pair of belt tensioners 110A, 110B is each received by one

Description

FIELD OF THE INVENTION The present invention relates to a tensioner assembly for a drive. BACKGROUND Tensioner assemblies for drive using, for example, drive belts are known. Such tensioner assemblies seek to apply appropriate tension to the drive belt to ensure correct operation. Although such tensioner assemblies exist, they each have their own shortcomings. Accordingly, it is desired to provide an improved tensioner assembly. SUMMARY According to a first aspect, there is provided a tensioner assembly for a drive belt, comprising: a pair of pivot arms locatable within an area enclosed by the drive belt; a pair of belt tensioners, each received by one of the pair of pivot arms; and a biasing device configured to urge the pair of pivot arms apart to displace the pair of belt tensioners apart to apply a tension on a contacting surface of the drive belt. The first aspect recognizes that a problem with existing tensioner assemblies is that they can be complex, heavy and occupy more space than may be available in some belt drive applications. Accordingly, a tensioner assembly is provided. The tensioner assembly may be for a drive belt, such as, for example, a bidirectional drive belt. The tensioner assembly may comprise a pair or two pivoting or rotatable arms. The arms may be located or positioned within an area or volume enclosed, bounded, surrounded or defined by the drive belt. The tensioner assembly may comprise a pair of (two) belt tensioners. Each of the belt tensioners may be received by a respective one of the pair of arms. The tensioner assembly may comprise a biasing device. The biasing device may be configured or arranged to urge or apply pressure to displace or move the pair of arms apart or away from each other. The urging of the arms apart may displace or move the pair of belt tensioners apart. Movement of the pair of belt tensioners apart may apply a tension, pressure or force on a contacting, interacting or facing surface of the drive belt. In this way, a low-complexity, light and compact belt tensioner is provided. The drive belt may be a loop, hoop or continuous band. The drive belt may have a radially inner or inwardly-facing surface. The drive belt may have a radially outer or outwardly-facing surface. The contacting surface may comprise the radially inner surface. The pair of pivot arms may be configured to support displacement of the pair of belt tensioners within the area enclosed by the drive belt. Hence, movement of the belt tensioners may be contained within the envelope of the drive belt. The biasing device may engage with the pair of pivot arms to displace the pair of pivot arms apart to displace the pair of belt tensioners apart to apply the tension on the contacting surface of the drive belt. The pair of pivot arms may have a pivot or axle and the biasing device may be configured to displace the pair of belt tensioners apart to apply the tension on the contacting surface of the drive belt. The pair of pivoting arms may each have a pivoting end providing the pivot and a free end distal from the pivot. Hence, each pivot arm may pivot about a single point towards one end of the arm. The tensioner assembly may comprise a pivot mechanism and the pair of pivoting arms may be pivotally received on the pivot mechanism to provide for pivoting of one pivoting arm with respect to another, the pivot mechanism providing for pivoting both of the pair of pivot arms together. Hence, the pivot arms may pivot both with respect to each other and around the pivot or axle to apply tension to the drive belt. The biasing device may engage with the pair of pivot arms towards each free end and each one of the pair of belt tensioners may be interposed between the free end and the pivot. Placing the biasing device towards the free end provides for a lever advantage in the force applied by the belt tensioners. Each one of the pair of belt tensioners may be located towards each free end and the biasing device may engage with the pair of pivot arms between the free end and the pivot. The pair of pivot arms may be arcuate. This helps to provide for increased displacement than would otherwise be possible if the arms were straight, since the free ends of the arms may contact the drive belt with the housing when trying to provide for the same amount of displacement of the belt tensioners. The biasing device may comprise a spring configured to displace the pair of belt tensioners towards the contacting surface of the drive belt. The belt tensioners may comprise pulley wheels. The assembly may comprise at least one stop positioned to limit movement of the belt tensioners towards drive belt. The assembly may comprise at least one stop positioned to limit movement of each of the pivot arms to limit movement of the belt tensioners towards drive belt. The at least one stop may be positioned to limit movement of the drive belt towards the support. The assembly may comprise the drive belt retained by a pair of drive pulleys. The assembly may comprise the pair of drive pulleys. The pivot arms may be positioned between the pair of drive pulleys. A first of the pair of drive pulleys may be driven by a drive and a second of the pair of drive pulleys may be driven by the drive belt and the pivot arms may be positioned towards the second of the pair of drive pulleys. The assembly may comprise a housing configured to receive the support, the pair of belt tensioners, the biasing device, the pair of drive pulleys and the drive belt. According to a second aspect, there is provide a wheelchair comprising: a drive; a drive shaft coupled with the drive; a driven shaft coupled with driven wheels; a belt assembly having a drive belt coupling the drive shaft with the driven shaft; and the tensioner assembly of the first aspect. The tensioner assembly may have the features set out above. Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims. Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which: FIG. 1 illustrates a bidirectional belt drive according to one embodiment; FIG. 2 shows the bidirectional belt drive with a portion of the housing removed; FIG. 3 shows the operation of the tensioner assembly in more detail when the drive belt is being driven in one direction; and FIG. 4 shows the operation of the tensioner assembly in more detail when the drive belt is being driven in an opposing direction. DESCRIPTION OF THE EMBODIMENTS Before discussing embodiments in any more detail, first an overview will be provided. Some embodiments provide an arrangement that provides for tensioning of a typically bidirectional drive. When using a bidirectional drive, different portions of the belt displace at different times due to the belt changing from being in tension to being in slight compression. Maintaining all portions of the belt at an appropriate tension is important for the correct and reliable operation of the drive. Accordingly, some embodiments provide for a compact tensioner for such a drive. The tensioner is typically positioned and operates within the space enclosed or bounded by the belt being tensioned, which provides for a particularly compact arrangement. Typically, the tensioner has a pair of pivoting arms or carriers which carry tensioners which are urged by a biasing device towards an inner surface of the belt in order to apply appropriate tension in all operating conditions. This provides for a low complexity and low weight arrangement. FIG. 1 illustrates a bidirectional belt drive 10, according to one embodiment. The bidirectional belt drive 10 comprises a housing 20. The housing retains a first drive shaft 30 and a second drive shaft 40. The first drive shaft 30 and the second drive shaft 40 are bidirectional, meaning that they are operable to be driven to rotate in either a clockwise or an anticlockwise direction. In this arrangement, the first drive shaft 30 is driven typically by a motor (not shown) and the second drive shaft 40 provides for a power take-off to drive, for example, wheels of a wheel chair. FIG. 2 shows the bidirectional belt drive 10 with a portion of the housing 20 removed. A drive belt 50 is provided which is received by a first pulley 35 connected with the first drive shaft 30 and by a second pulley 45 connected with the second drive shaft 40. The drive belt 50 is driven in the direction A when the first drive shaft 30 is driven in an anticlockwise direction which rotates the first pulley 35 in the anticlockwise direction, moving the drive belt 50 in the direction A, which rotates the second pulley in the anticlockwise direction and rotates the second drive shaft 40 in the anticlockwise direction. Likewise, when the first drive shaft 30 is driven in the clockwise direction, this rotates the second pulley 35 in the clockwise direction and drives the drive belt 50 in the direction B, which rotates the second pulley 45 in the clockwise direction which rotates the second drive shaft 40 in the clockwise direction. In this arrangement, the drive belt is driven by the first drive shaft 30, in order to drive the second drive shaft 40. Located between the first drive shaft 30 and the second drive shaft 40 and enclosed within the housing 20 is provided a tensioner assembly 60. The housing 20 defines a recess 25 which accommodates at least some of the structure of the tensioner assembly 60. The tensioner assembly 60 operates to tension the drive belt 50 when operating in either direction. As will be explained in more detail below, that portion of the drive belt 50 extending between the first pulley 35 and the second pulley 45 is either under tension or slight compression (causing slack), depending on the direction of rotation of the drive belt 50. The tensioner assembly 60 operates to apply appropriate tension to the drive belt 50 and take up slack when being driven in either direction. Although the tensioner assembly 60 could be located anywhere between the first pulley 35 and the second pulley 45, it is typically located towards the second pulley 45 where the displacement of the drive belt 50, due to it being either in tension or slack, is greatest. The tensioner assembly 60 is located within the space bounded by the drive belt 50. That is to say, the tensioner assembly 60 is located within an area defined by the path of the drive belt 50. This provides for a compact arrangement in which the tensioner assembly 60 applies tension to the radially inner surface of the drive belt 50. In other words, the tensioner assembly 60 urges or displaces radially outwards to tension the drive belt 50. The tensioner assembly 60 has a pair of pivot arms 70A, 70B. In this example, the pivot arms 70A, 70B are arcuate and curve so that the radially inner surfaces of each arm 70A, 70B face each other. The pivot arms 70A, 70B have a pivot end 80A, 80B, each of which is pivotally received by a common pivot 90. The common pivot 90 typically also pivots about itself. Each pivot arm 70A, 70B has a free end 100A, 100B located at an opposite end of the pivot arms 70A, 70B from the pivot end 80A, 80B. Each pivot arm 70A, 70B carries a belt tensioner 110A, 110B. The belt tensioners 110A, 110B are mounted for rotation on the associated pivot arm 70A, 70B. In this example, the belt tensioners 110A, 110B are a cog, which would be suitable for contacting with a drive belt 50 in the form of a notched or ridged drive belt or a chain. However, it will be appreciated that different shaped belt tensioners 110A, 110B can be provided to suit the shape of the drive belt, such as providing a complementarily shaped pulley. Each belt tensioner 110A, 110B is located approximately midway between the pivot end 80A, 80B and the free end 100A, 100B. However, this need not be the case and the belt tensioners 110A, 110B may be located at any suitable position on the pivot arms 70A, 70B. A spring 120 is provided which engages towards the free ends 100A, 100B. The spring 120 operates to urge the free ends 100A, 100B apart by pivoting the pivot arms 70A, 70B about its pivot end 80A, 80B. Urging of the free ends 100A, 100B causes movement of the belt tensioners 110A, 11 OB apart and towards the radially inner surface of the drive belt 50. Although in this arrangement the spring 120 is located towards the free ends 100A, 100B, it will be appreciated that this need not be the case and the spring 120 may be located anywhere along the pivot arms 70A, 70B. Indeed, the positions of the belt tensioners 110A, 110B and the spring 120 could be swapped. Locating the spring 120 at a different location to the belt tensioners 110A, 110B helps to maximize the size of the spring 120 and the belt tensioners 110A, 110B while still providing for a compact tensioner assembly 60. A pair of stops 130A are provided. The stops 130A, 130B limit the extent of pivoting of the pivot arms 70A, 70B. This, in turn, limits the movement of the belt tensioners 110A, 110B and helps to ensure that the drive belt 50 cannot be pushed against the inner surface of the housing 20. FIG. 3 shows the operation of the tensioner assembly 60 in more detail when the drive belt 50 is being driven in the direction A. When being driven in the direction A, an upper portion 50A of the drive belt 50 will be in tension, while a lower portion 50B of the drive belt 50 will be in slight compression, leading to slack (a slight displacement of the drive belt 50 radially outwards) that needs to be taken up by applying tension to that portion of the drive belt 50. Accordingly, the tension in the upper portion 50A causes the belt 50A to displace slightly in the direction D1 compared to the resting state of the drive belt 50 when not being driven. This, in turn, causes the belt tensioner 110A to displace, which causes the pivot arm 70A to pivot in the direction D2. The presence of the spring 120 causes the pivot arm 70B to pivot in the direction D3. This causes the belt tensioner 110B to be urged against the radially inner surface of the lower portion 50B to take up slack by the belt tensioner 110B applying a pressure against the radially inner surface of the lower portion 50B. To prevent the lower portion 50B being pressed by the belt tensioner 110B against the inner surface of the housing 20, movement of the pivot arm 70B towards the lower portion 50B is limited by the stop 130B. However, slack in the drive belt 50 is still taken up when movement of the pivot arm 70B is limited by the stop 130B since, when the pivot arm 70B is against the stop 130B, the spring 120 will apply a force to the pivot arm 70A to slightly displace the pivot arm 70A in a direction opposite to direction D2 in order that the belt tensioner 110A displaces towards the inner surface of the upper portion 50A in order to retain tension on the drive belt 50. FIG. 4 shows the operation of the tensioner assembly 60 in more detail when the drive belt 50 is being driven in the direction B. When being driven in the direction B, the lower portion 50B of the drive belt 50 will be in tension, while the upper portion 50A of the drive belt 50 will be in slight compression, leading to slack (a slight displacement of the drive belt 50 radially outwards) that needs to be taken up by applying tension to that portion of the drive belt 50. Accordingly, the tension in the lower portion 50B causes the belt 50 to displace slightly in the direction D4 compared to the resting state of the drive belt 50 when not being driven. This, in turn, causes the belt tensioner 110B to displace, which causes the pivot arm 70B to pivot in the direction D5. The presence of the spring 120 causes the pivot arm 70A to pivot in the direction D6. This causes the belt tensioner 110A to be urged against the radially inner surface of the upper portion 50A to take up slack by the belt tensioner 110A applying a pressure against the radially inner surface of the upper portion 50A. To prevent the upper portion 50A being pressed by the belt tensioner 110A against the inner surface of the housing 20, movement of the pivot arm 70A towards the upper portion 50A is limited by the stop 130A. However, slack in the drive belt 50 is still taken up when movement of the pivot arm 70A is limited by the stop 130A since, when the pivot arm 70A is against the stop 130A, the spring 120 will apply a force to the pivot arm 70B to slightly displace the pivot arm 70B in a direction opposite to direction D5 in order that the belt tensioner 11 OB displaces towards the inner surface of the lower portion 50B in order to retain tension on the drive belt 50. The bidirectional belt drive 10 is typically provided as part of a driven wheelchair. A drive such as an electric motor couples with the first drive shaft 30. Drive wheels couple with the second drive shaft 40. Driving the drive in a first direction causes movement of the drive belt in direction A. Driving the drive in a second direction opposing the first direction causes movement of the drive belt in direction B. This provides for bidirectional rotation of the drive wheels of the wheelchair. Hence, some embodiments provide an arrangement where, as belt tension increases or decreases in the upper or lower section of the belt, depending on direction of travel, tension is maintained. The free-running tensioner wheels apply pressure in opposing directions to the drive belt. The arms rotate around the axle (pivot) and the spring ensures that tension is provided evenly across the driven belt This arrangement is particularly use in a belt driven wheelchair where wind-up would cause an issue. Tension is maintained in both directions to ensure belt does not slip. Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

Claims

1. A tensioner assembly for a drive belt, comprising:a pair of pivot arms locatable within an area enclosed by said drive belt;a pair of belt tensioners, each received by one of said pair of pivot arms; anda biasing device configured to urge said pair of pivot arms apart to displace said pair of belt tensioners apart to apply a tension on a contacting surface of said drive belt.

2. The tensioner assembly of claim 1, wherein said drive belt is a loop comprising a radially inner surface and a radially outer surface and said contacting surface comprises said radially inner surface.

3. The tensioner assembly of claim 1 or 2, wherein said pivot arms are configured to support displacement of said pair of belt tensioners within said area enclosed by said drive belt.

4. The tensioner assembly of any preceding claim, wherein said biasing device engages with said pair of pivot arms to displace said pair of pivot arms apart to displace said pair of belt tensioners apart to apply said tension on said contacting surface of said drive belt.

5. The tensioner assembly of any preceding claim, wherein said pair of pivot arms have a pivot and said biasing device is configured to displace said pair of pivot arms apart about said pivot to displace said pair of belt tensioners apart to apply said tension on said contacting surface of said drive belt.

6. The tensioner assembly of claim 5, wherein said pair of pivot arms each have a pivoting end providing said pivot and a free end distal from said pivot.

7. The tensioner assembly of any preceding claim, comprising a pivot mechanism and wherein said pair of pivot arms are pivotally received on said pivot mechanism to provide for pivoting of one pivoting arm with respect to another, said pivot mechanism providing for pivoting both of said pair of pivot arms together.

8. The tensioner assembly of claim 6 or 7, wherein said biasing device engages with said pair of pivot arms towards each free end and each one of said pair of belt tensioners is interposed between said free end and said pivot.

9. The tensioner assembly of any one of claims 6 to 8, wherein each one of said pair of belt tensioners is located towards each free end and said biasing device engages with said pair of pivot arms between said free end and said pivot.

10. The tensioner assembly of any preceding claim, wherein said pair of pivot arms are arcuate.

11. The tensioner assembly of any preceding claim, where said biasing device comprises a spring configured to displace said pair of belt tensioners towards said contacting surface of said drive belt.

12. The tensioner assembly of any preceding claim, wherein said belt tensioners comprise pulley wheels.

13. The tensioner assembly of any preceding claim, comprising at least one stop positioned to limit movement of said belt tensioners towards drive belt.

14. The tensioner assembly of any preceding claim, comprising at least one stop positioned to limit movement of each of said pivot arms to limit movement of said belt tensioners towards drive belt.

15. The tensioner assembly preceding claim 13 or 14, wherein said at least one stop is positioned to limit movement of said drive belt towards said support.

16. The tensioner assembly of any preceding claim, comprising said drive belt retained by a pair of drive pulleys.

17. The tensioner assembly of claim 16, wherein said pivot arms are positioned between said pair of drive pulleys.

18. The tensioner assembly of claim 16 or 17, wherein a first of said pair of drive pulleys is driven by a drive and a second of said pair of drive pulleys is driven by saiddrive belt and said pivot arms are positioned towards said second of said pair of drive pulleys.

19. The tensioner assembly of any one of claims 16 to 18, comprising a housing 5 configured to receive said support, said pair of belt tensioners, said biasing device, said pair of drive pulleys and said drive belt.

20. A wheelchair comprising:a drive;io a drive shaft coupled with the drive;a driven shaft coupled with driven wheels;a belt assembly having a drive belt coupling the drive shaft with the driven shaft; andthe tensioner assembly of any preceding claim.12

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