CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63/424,631 filed November 11 , 2022, the contents of which are incorporated herein in their entirety.

FIELD

[0002] This disclosure relates generally to the field of tensioners for an endless drive system, and more particularly to an endless drive arrangement for a vehicle that includes an engine and a secondary drive device such as a motorgenerator unit (MGU).

BACKGROUND

[0003] An ever-increasing number of engines having a motor-generator unit (MGU) have been developed since the 1990s in order to improve fuel mileage. In such engines, the combustion process is stopped when the vehicle comes to rest, for example, at a stoplight. In this condition the MGU is operated as a starter motor to restart the engine. Once the engine is started, the MGU can be selectively operated as a generator to recharge the batteries. In some vehicles, the MGU can also be used as a booster to help drive the crankshaft at the same time that the engine drives the crankshaft (i.e. while the vehicle is operating), so as to supplement power when needed.

[0004] The MGU is mechanically connected to the engine via an endless drive member such as a belt (i.e. an accessory drive belt). The endless drive member is kept in tension, but the tension varies along the length of the endless drive member. A span of the endless drive member that approaches a rotating pulley that is adding power will be at higher tension (and is sometimes referred to as the ‘tight side’), whereas a span of the endless drive member that leaves a rotating pulley that has added power will be at lower tension (and is sometimes referred to as the ‘slack side’).

[0005] Additionally, the endless drive member is subject to tension fluctuations during operation, particularly as the MGU shifts its function between starter or booster, and generator, in which case the tight side and slack side of the endless drive member reverses (referring to the spans on either side of the MGU pulley).

[0006] Most vehicles employ a tensioner to maintain tension on the endless drive member. In order to accommodate changes in which span of the endless drive member is the tight side and which is the slack side, some tensioners employ two tensioner arms each with a pulley that is driven into the endless drive member in order to keep both spans of the endless drive member in tension regardless of which is the tight side and which is the slack side. These may be referred to as dual arm tensioners. Various dual arm tensioners are known in the art, examples of which are found in publication numbers DE10253450 A1 ; EP 1 464 871 A1 ; US2004/0171448A1 ; EP1122464 A1 ; and DE4243451 A1. Some dual arm tensioners are V-tensioners. In some instances the V-tensioners are positioned inside the area enclosed by the endless drive member, which results in a compact arrangement for the endless drive arrangement. However, such tensioners typically have relatively large hub loads, which are the forces that act on the pulleys on the tensioner arms, arising from tension in the endless drive member. It would be advantageous to provide a solution that has reduced hub loads as compared to the hub loads on some other dual arm tensioners, or to provide a tensioner that resolves other issues relating to at least some other dual arm tensioners.

SUMMARY

[0007] In an aspect, an endless drive arrangement is provided for a vehicle with an engine and a secondary drive device. The endless drive arrangement includes a crankshaft pulley mounted to a crankshaft of the engine, a secondary drive device pulley mounted on a shaft of the secondary drive device, an endless drive member and a tensioner. The endless drive member connects the crankshaft pulley and the secondary drive device pulley, such that the endless drive member encloses an internal area. A first span of the endless drive member, in use, is driven towards the secondary drive device pulley and engages a first side of the secondary drive device pulley. A second span of the endless drive member, in use, is driven away from the secondary drive device pulley and engages a second side of the secondary drive device pulley. The tensioner includes a base that is mountable to a stationary structure. The base defines a tensioner arm pivot axis. The tensioner further includes a first tensioner arm that has a first tensioner pulley rotatably mounted thereto. The first tensioner pulley is engaged with the first span of the endless drive member. The first tensioner arm is pivotably mounted to the base for pivoting about the tensioner arm pivot axis. The tensioner further includes a second tensioner arm that has a second tensioner pulley rotatably mounted thereto. The second tensioner pulley is engaged with the second span of the endless drive member. The second tensioner arm is pivotably mounted to the base for pivoting about the tensioner arm pivot axis. The tensioner further includes a tensioner arm biasing member that has a first end that is engaged with the first tensioner arm and a second end that is engaged with the second tensioner arm so as to bias the first and second tensioner arms in first and second free arm directions, thereby urging the first and second spans of the endless drive member towards each other. The endless drive arrangement is operable in a first mode in which the crankshaft pulley drives travel of the endless drive member and the secondary drive device pulley is driven by the endless drive member, and in a second mode in which the secondary drive device pulley drives travel of the endless drive member. The first and second tensioner arms and the base are positioned such that the tensioner arm pivot axis is positioned outside of the internal area, and on one of the first and second sides of the secondary drive device pulley. A first centerline extends from the tensioner arm pivot axis to the first tensioner pulley rotation axis, and a second centerline extends from the tensioner arm pivot axis to the second tensioner pulley rotation axis. One of the first and second centerlines extends without crossing any of the first and second spans of the endless drive member, and the other of the first and second centerlines extends across both of the first and second spans of the endless drive member.

BRIEF DESCRIPTION OF DRAWINGS

[0008] The foregoing and other aspects will be more readily appreciated having regard to the accompanying drawings, wherein:

[0009] Figure 1 is a schematic view of the tensioner shown in Figure 1 in an endless drive arrangement on an engine of a vehicle;

[0010] Figure 2 is a perspective view of an embodiment of a tensioner having first and second tensioner arms;

[0011] Figure 3 is a first exploded perspective view of the tensioner shown in Figure 2;

[0012] Figure 4 is a second exploded perspective view of the tensioner shown in Figure 2; and

[0013] Figure 5 is a partially sectional side view of the tensioner shown in Figure 2 illustrating forces acting on the first and second tensioner arms.

DETAILED DESCRIPTION OF EMBODIMENTS

[0014] For simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiment or embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. It should be understood at the outset that, although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below.

[0015] Various terms used throughout the present description may be read and understood as follows, unless the context indicates otherwise: “or” as used throughout is inclusive, as though written “and/or”; singular articles and pronouns as used throughout include their plural forms, and vice versa; similarly, gendered pronouns include their counterpart pronouns so that pronouns should not be understood as limiting anything described herein to use, implementation, performance, etc. by a single gender; “exemplary” should be understood as “illustrative” or “exemplifying” and not necessarily as “preferred” over other embodiments. Further definitions for terms may be set out herein; these may apply to prior and subsequent instances of those terms, as will be understood from a reading of the present description.

[0016] Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the disclosure. For example, the components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, “each” refers to each member of a set or each member of a subset of a set. [0017] The indefinite article “a” is not intended to be limited to mean “one” of an element. It is intended to mean “one or more” of an element, where applicable, (i.e. unless in the context it would be obvious that only one of the element would be suitable).

[0018] Any reference to upper, lower, top, bottom or the like are intended to refer to an orientation of a particular element during use of the claimed subject matter and not necessarily to its orientation during shipping or manufacture. The upper surface of an element, for example, can still be considered its upper surface even when the element is lying on its side.

[0019] Figure 1 is an elevation view of an engine 13 for a vehicle (not shown), and an endless drive arrangement 915 for the engine 13. The engine 13 is shown in simplified form as a simple rectangle, however it will be understood that the engine 13 could have any suitable form. The engine 13 includes an engine block 13a and a cylinder head 13b, and a crankshaft 913 that is driven by pistons (not shown) that reciprocate in the engine block 13a. the engine 13 may be powered by any suitable fuel such as gasoline or diesel fuel.

[0020] The vehicle further includes a secondary drive device 916, which may be, for example, a motor/generator unit (MGU) or any other type of suitable drive device such as an electric motor. Accessories such as a water pump, an air conditioning compressor or other items may be provided with pulleys also. However, to simplify the system for the purpose of the present disclosure, only the secondary drive device 916 is shown.

[0021] The endless drive arrangement 915 includes an endless drive member 11 , a crankshaft pulley 912 mounted to the crankshaft 913, a secondary drive device pulley 950 mounted to the shaft 952 of the secondary drive device 916, and a tensioner 10 (shown schematically in Figure 1). The endless drive member 11 connects the crankshaft pulley 912 and the secondary drive device pulley 950. In the view shown in Figure 1 , the crankshaft pulley 912 and the secondary drive device pulley 950 may rotate clockwise. A first span 11a of the endless drive member 11 is, in use (i.e. during operation of the vehicle) driven towards the secondary drive device pulley 950, and a second span 11 b of the endless drive member 11 is, in use (i.e. during operation of the vehicle), driven away from the secondary drive device pulley 950. The first span 11a of the endless drive member 11 engages a first side 950a of the secondary drive device pulley 950, and the second span 11a of the endless drive member 11 engages a second side 950b. For greater certainty, the term ‘in use’ is intended to mean, during use of the vehicle.

[0022] The endless drive arrangement 915 is operable in a first mode in which the crankshaft pulley 912 drives travel of the endless drive member 11 and the secondary drive device pulley 950 is driven by the endless drive member 11. In embodiments in which the secondary drive device 916 is an MGU, the first mode of operation may be referred to as a Tegen’ mode since it is in this mode that the MGU can operate as a generator, driven by the endless drive member 11 in order to charge a battery (not shown) of the vehicle.

[0023] The endless drive arrangement 915 is operable in a second mode in which the secondary drive device pulley 950 drives travel of the endless drive member 11. In this mode, the secondary drive device 916 may be used to drive travel of the endless drive member 11 in cooperation with the crankshaft pulley 912, thereby adding power to the crankshaft pulley 912, which in turn helps to drive wheels (not shown) of the vehicle. In such an instance, the second mode may be referred to as a boost mode, since the secondary drive device 916 boosts the power of the engine 13. Alternatively, or additionally, in the second mode, the secondary drive device 916 may be used to drive accessories of the vehicle (not shown) via additional pulleys engaged with and driven by the endless drive member 11 while the engine 13 is off. For example, if the vehicle is equipped with a stop/start system in which the vehicle shuts off the engine 13 when the vehicle is stopped for more than a few seconds (e.g. while stopped at a red light), then the secondary drive device 916 may be used to drive the endless drive member 11 and thereby drive the accessories even though the engine 13 is off. Alternatively, or additionally, in the second mode, the secondary drive device 916 may be used to start the engine 13 when the engine 13 is off, by driving the endless drive member 11 , which in turn drives rotation of the crankshaft pulley 912. Such a start function may be used for any type of vehicle, such as for vehicles that have stop/start functionality, whereby the secondary drive device 916 is used to start the engine 13 when the vehicle is ready to start moving (e.g. when the vehicle was waiting at a red light, and the red light then turns green). Providing the ability to start the engine 13 by driving the endless drive member 11 using the secondary drive device 916 may be referred to as providing a BAS function (belt-alternator start function) for the secondary drive device 916.

[0024] The endless drive member 11 may be a belt, or alternatively, it may be any other suitable type of endless drive member. In instances where the endless drive member 11 is a belt, it may be any suitable type of belt, such as a flat belt, a V belt, a poly-V belt, or even a timing belt.

[0025] The tensioner 10 is shown more clearly in Figures 2-4. The tensioner 10 includes a base 12 that is mountable to a stationary structure such as the engine block 13a. The base 12 may be in the form of a hollow shaft that defines a tensioner arm pivot axis A. The base 12 has a pass-through aperture 19 that has a mounting fastener (e.g. a threaded fastener - not shown) that passes therethrough and that mounts into a mounting aperture (e.g. a threaded aperture) in the stationary structure. The base 12 has a pivot shaft shown at 23.

[0026] The tensioner 10 further includes a first tensioner arm 14 (which may be referred to as a lower tensioner arm) and a second tensioner arm 16 (which may be referred to as an upper tensioner arm). The first tensioner arm 14 is pivotably mounted to the base 12 for pivoting about the tensioner arm pivot axis A. In the example, shown the first tensioner arm 14 has a pass-through aperture 18 for mounting to the base 12. The second tensioner arm 16 also includes a pass- through aperture 24 for pivotably mounting the second arm 16 to the base 12. In the embodiment shown, the first and second tensioner arms 14 and 16 are mounted on the pivot shaft 23 such that the second tensioner arm 16 is mounted on top of the first tensioner arm 14.

[0027] A bushing arrangement is provided, that includes a first bushing 20 that is positioned radially between the pivot shaft 23 and the first tensioner arm 14 and a second bushing 26 that is positioned radially between the pivot shaft 23 and the second tensioner arm 16. A first bushing 20 protects against direct contact between the base 12 and the first arm 14. A second bushing 26 protects against direct contact between the base 12 and the second arm 16. The first and second bushings 20 and 26 may be made from any suitable material such as polyamide 4.6 or 6.6.

[0028] A tensioner arm biasing member 30 is provided and has a first end 32 that is engaged with a drive face 34 on the first tensioner arm 14 and a second end 36 that is engaged with a second drive face 38 on the second tensioner arm 16 so as to bias the first and second arms 14 and 16 in respective first and second free arm directions into the endless drive member 11. The free arm direction is the direction that the tensioner arm 14 or 16 would be moved in by the biasing member 30 if there were no endless drive member present to resist the arms’ respective movements. By contrast, the load stop direction is the direction the arm 16 would be moved in in if the belt tension were sufficiently high to overcome the biasing force of the biasing member 30. In general the free arm direction for a tensioner arm 14 or 16 is a direction of movement that bring the tensioner arm 14 or 16 into the endless drive member 11 , and the load stop direction is a direction of movement that brings the tensioner arm 14 or 16 away from the endless drive member 11. The tensioner arm biasing member 30 may be any suitable type of biasing member such as, for example, a torsion spring, which optionally includes a plurality of coils shown at 31. The tensioner arm biasing member 30, when in the form of a torsion spring, may be formed from a spring wire having any suitable cross-sectional shape such as a rectangular shape (shown in Figure 5), or a circular shape (shown in Figures 3 and 4).

[0029] Each of the first and second tensioner arms 14 and 16 has a pulley (shown at 46 and 48 respectively) rotatably mounted thereto for rotation about first and second pulley rotation axes AP1 and AP2 respectively. A mounting fastener (e.g. a threaded fastener) 52 is used to mount the pulley 46, 48 to the respective tensioner arm 14, 16.

[0030] As shown in Figure 2, a first centerline CL1 extends from the tensioner arm pivot axis A to the first tensioner pulley rotation axis AP1 , and a second centerline CL2 extends from the tensioner arm pivot axis A to the second tensioner pulley rotation axis AP2.

[0031] As shown in Figure 1 , each pulley 46, 48 is engaged with a respective first or second span 11a or 11 b of the endless drive member 11. The first and second spans 11 a and 11 b are on either side of the MGU pulley 950.

[0032] The first span 11a of the endless drive member 11 , in use, is driven towards the secondary drive device pulley 950 and, as noted above, engages the first side 950a of the secondary drive device pulley 950. The second span 11 b of the endless drive member 950b, in use, is driven away from the secondary drive device pulley 950 and, as noted above, engages the second side 950b of the secondary drive device pulley 950. For greater clarity, the first side 950a and the second side 950b of the secondary drive device pulley 950 are defined by a radial line extending from the centerpoint of the wrap angle of the endless drive member 11 on the secondary drive device pulley 950. The centerpoint is shown in Figure 1 at 951 . It will be noted that the centerpoint 951 will move depending on which mode the endless drive arrangement 915 is operating in, since the tensions in the first and second spans 11a and 11 b of the endless drive member 11 will vary, thereby affecting the positions of the tensioner arms 14 and 16 and the resultant amount of wrap that results in the endless drive member 11 on the secondary drive device pulley 950. [0033] The endless drive member 11 encloses an internal area 99.

[0034] The tensioner 10 operates on those spans 11a and 11 b to ensure that belt tension is maintained in the belt spans 11a and 11 b regardless of whether the MGU 916 is being operated in the first mode (in which case the tension in the second span 11 b will be relatively high and the tension in the first span 11a will be relatively low), or whether the endless drive member 11 is being driven by the engine 13 and the secondary drive device 916 is either off or is acting as a generator.

[0035] Referring to Figure 4, one or more (in this instance, three) axial preload members 40 are positioned between a surface on a preload holder 41 on the base 12 and the second tensioner arm 16, and are positioned to apply an axial compression force on the first and second tensioner arms 14 and 16 urging the first and second tensioner arms 14 and 16 towards one another between the preload holder 41 and a shoulder 43 on the base 12. The aforementioned compression force may be referred to as an axial preload. The preload holder 41 may be held in place by being press-fit onto the pivot shaft 23 of the base 12.

[0036] The axial preload members 40 may be any suitable type of biasing members such as, for example, Belleville washers, which can generate large biasing forces and which are compact. The axial preload members 40 do not directly engage the second tensioner arm 16; instead, a support member (e.g. a flat metallic washer) 44 is provided between the biasing members and the second tensioner arm 16. Furthermore, the second bushing 26 has a flange portion 46 that is also present between the axial preload members 40 and the second tensioner arm 16, to prevent direct sliding movement between the second tensioner arm 16 and the support member 44. The axial preload may be applied about the circumference of the lower arm 14, at an average radius r, as shown in Figure 5. The function of the axial preload members 40 is described further below.

[0037] A slide disc shown at 60 is provided between the second tensioner arm 16 and the first tensioner arm 14 to support the rotation of the two tensioner arms 14 and 16 relative to one another. The slide disc 60 may be polymeric or may be made from any suitable material to allow low friction relative movement between the first and second tensioner arms 14 and 16.

[0038] Figure 5 shows a partially sectional view of the tensioner 10 with a focus on the first tensioner arm 14. During operation, the endless drive member 11 (Figure 1 ) applies a hub load shown at F1 to the first pulley 46 (represented as an arrow at the center of the first pulley 46), which results in a force on the first arm 14. This hub load F1 introduces a tipping force to the first tensioner arm 14 that, if unaddressed, can result in yaw in the first tensioner arm 14. This can, in turn, result in noise and wear problems with the endless drive member 11 , and can furthermore cause uneven wear in the bushings 20 and 22. The uneven wear in the bushing 20 can lead to progressively increasing play between the arm 14 and the base 12 and over time, premature failure of the tensioner 10. To counteract the tipping force caused by the hub load F1 , the axial preload members 40 are selected to apply a sufficiently high axial preload (shown at F2 in Figure 5) to the first arm 14 that a resulting radially directed counterforce applied to the bushing 20 from the axial preload is at least approximately as great as the bushing hub load applied to the bushing 20 as a result of the hub load F1 . Because the axial preload F2 is applied about the entire circumference of the arm 14, the axial preload F2 is always positioned to counteract the bushing hub load (BHL) that results from the hub load F1. The formula for the bushing hub load (BHL) may be expressed as BHL = F1 x L1 / BL, where BHL is the bushing hub load as noted above, F1 is the hub load, L1 is the axial distance from the hub load to the bottom of the bushing 20, and BL is the axial length of the bushing 20.

[0039] The counterforce applied to the bushings 20 and 22 that are the result of the axial preload members 40 is determined as follows: CF = F2 x L2 / (BL 12), wherein CF is the counterforce, F2 is the axial preload, and L2 is the radius r of the axial preload. If the counterforce CF exceeds the bushing hub load BHL, no moment is introduced that causes uneven wear to the bushing 20. As a result, the bushing 20 wears evenly, which can result in a longer life for the tensioner 10. It will be noted that, while an example was described with the arm 14 at a particular position, the counterforce generated by the axial preload members 40 may be sufficiently high so that it is at least approximately as great as the bushing hub load throughout a range of positions of the tensioner arm 14 and preferably throughout substantially all of the positions that the arm 14 will move to during operation within the design conditions of the engine 13 (Figure 1 ).

[0040] The mechanics of the second tensioner arm 16 will now be described with less detail than with the first tensioner arm 14. The hub load on the second pulley 48 is shown at F3 and a force by the biasing member 30 is applied on the second tensioner arm 16 to resist rotation thereof. The sum of these forces applies a tipping force that is resisted by a reaction force through the second bushing 26. Providing a reaction force that is approximately centered axially on the second bushing 26 results in more even wear and a resulting longer life for the bushing 26 and therefore, optionally greater longevity for the tensioner 10.

[0041] It will be noted that, while an example was described with the arm 16 at one particular position, the reaction force generated at the second bushing arrangement may be approximately centered axially along the second bushing arrangement throughout a range of positions of the tensioner arm 16.

[0042] Thus by providing both of the features described above in relation to increasing the operating life of the bushings 20 and 22, and 26 and 28, the operating life of the tensioner 10 may be longer than that of other V tensioners of the prior art.

[0043] For greater certainty, it will be noted that the benefits described above for the bushings 20 and 22, and for the bushings 26 and 28 would be applicable to first and second bushing arrangements that each only included a single bushing.

[0044] It will be noted that, in the figures, the lengths of the arrows representing forces F1 , F2 and F3 are not to be taken as being indicative of the magnitudes of the forces being represented. [0045] An installation pin 64 may be provided which is insertable and removable from an aperture 66 in the second tensioner arm 16 and when inserted therethrough, engages a holder surface 68 on the first tensioner arm 14 to hold the arms 14 and 16 in a certain position to facilitate installation of the endless drive member 11 . Once the endless drive member 11 is installed, the installation pin (or more generally an arm locking member) can be removed, permitting the arms 14 and 16 to engage respective spans of the endless drive member 11 .

[0046] Referring to Figure 1 , it has been found that it is advantageous to position the first and second tensioner arms 14 and 16 and the base 12 such that the tensioner arm pivot axis A is positioned outside of the internal area 99, and on one of the first and second sides 950a or 950b of the secondary drive device pulley 950. Preferably, one of the first and second centerlines CL1 and CL2 extends without crossing any of the first and second spans 11 a and 11 b of the endless drive member 11 , and the other of the first and second centerlines CL1 and CI2 extends across both of the first and second spans 11 a and 11 b of the endless drive member 11. In particular, it has been found that this positioning of the first and second tensioner arms 14 and 16 and the base 12 results in relatively lower hub loads F1 and F3 on the pulleys 46 and 48 respectively.

[0047] In the specific embodiment shown in Figure 1 , the first and second tensioner arms 14 and 16 and the base 12 are positioned such that the tensioner arm pivot axis A is positioned on the first side 950a of the secondary drive device pulley 950, and the first centerline CL1 extends without crossing any of the first and second spans 11a and 11 b of the endless drive member 11 , and the second centerline CL2 extends across both of the first and second spans 11 a and 11 b of the endless drive member 11 .

[0048] By providing lower hub loads F1 and F3, it will be understood that the axial compression force applied by the at least one axial preload member 40 can be lower in order to inhibit uneven wear on the bushings 20 and 26. [0049] In some embodiments, it is possible to position the tensioner arms 14 and 16 and the base 12 such that each of the first and second centerlines CL1 and CL2 extends across at least one of the first and second spans 11a and 11b of the endless drive member 11 .

[0050] It can be seen that the first and second centerlines CL1 and CL2 are not the same length. More specifically, in the embodiment shown, since the base 12 is positioned on the first side 950a of the secondary drive device pulley 950, the second centerline CL2 is longer than the first centerline CL1. In the embodiment shown, the second centerline CL2 is about 1.8 times as long as the first centerline CL1. In other embodiments, the length of the second centerline CL2 may at least 1.5 times as long as the first centerline CL1 .

[0051] It is noted that the second tensioner arm 16 extends over at least some of the secondary drive device pulley 950 so as to reach the second span 11 b of the endless drive member 11 without interfering with the rotation of the secondary drive device pulley 950. By providing a relatively long length for the second centerline CL2, a greater amount of movement is available for the second tensioner arm 16, without a large angular change. It is also noted that the first tensioner arm 14 is oriented relative to the first span 11a of the endless drive member 11 such that it is nearly parallel to the first span 11a. As a result, changes in tension in the first span 11a can result in movement in the first tensioner arm 14 that is almost directly perpendicular to the first span 11a of the endless drive member 11 , which provides greater accommodation for changes in tension, with relatively little angular change in the first tensioner arm 14, even though it has a first centerline CL1 that is shorter than the second centerline CL2. Ultimately, the first and second pulleys 46 and 48 achieve engagement with the endless drive member 11 with relatively little wrap angle, which implies relatively little hub load when operating in the first mode or the second mode as compared to tensioners of the prior art. [0052] In the embodiment shown, it can be seen that the second tensioner arm 16 is arcuate and has a first side edge 16a that faces towards a rotation axis A2 for the secondary drive device pulley 950, wherein the first side edge 16a is convex. For greater clarity, the tensioner 10 as shown in Figure 1 is schematically shown and so the first and second tensioner arms 14 and 16 are not shown as being arcuate.

[0053] Those skilled in the art will appreciate that a variety of modifications may be made to the embodiments described herein without departing from the fair meaning of the accompanying claims.