Patent Description:
It is common for vehicle engines to drive a plurality of accessories using an accessory drive system that includes a belt. In some vehicles, a motive device is provided such as a motor/generator unit (MGU) that can be used for a number of purposes, such as, for example, driving one or more accessories via the belt when the engine is temporarily off while the vehicle is stopped for a short period of time (e.g. at a stoplight). Another purpose is for use as part of a belt alternator start (BAS) drive system wherein the MGU is used to start the engine through the belt. Another purpose is to supply additional power to the engine when needed (e.g. when the vehicle is under hard acceleration). In such situations special tensioning devices are typically needed to ensure that the belt is under the appropriate amount of tension regardless of whether it is being driven by the MGU or by the engine. In many instances however such tensioning devices are not optimal and result in relatively high belt tensions and hub loads on the various pulleys in the system, thereby negatively impacting fuel economy and component life.

It would be desirable to provide a tensioning system that at least partially addresses one or more of the problems described above and other problems. <CIT> discloses a tensioner for an automative engine accessory drive system, which can be used in connection with a motor-generator unit (MGU), wherein a ring portion is rotatably connected to the axis of a generator unit. One tensioner pulley is rotatably mounted and connected to said ring portion. Another tensioner pulley is provided on a tensioner arm, which is slidable and retractable along a circumferential direction along said ring portion around the pivot axis of the ring portion. Said tensioner arm is spring loaded relative to said ring portion, so that both pulleys are urged into contact with the two spans driving and/or being driven by the generator unit. <CIT> discloses a belt tensioning device for being used with a motor generator, with two tensioning arms being pivotable relative to one another around a common pivot axis, which coincides with the axis of the generator. A tensioning spring is provided between a counter-arm and one of the tensioning arms for biasing both tensioner arms relative to each other, so that the two tensioner pulleys are moved towards one another tending to increase the wrap of the belt around the pulley of the generator. <CIT> is directed at a driving gear for bicycles and discloses a means for taking up the slack of driving chains when used with elliptical chain wheels. A frame is loosely mounted on a boss for oscillation on the boss of the chain wheel. A short arm with a first chain wheel is pivoted to the frame and a coil spring biases the arm outward against the under side of the chain. A second chain wheel is provided on the frame.

The claimed use of a tensioner according to the present invention has the features as defined in claim <NUM>. An automotive engine accessory drive belt system according to the present invention has the features of claim <NUM>.

The foregoing and other embodiments of the invention will be more readily appreciated by reference to the accompanying drawings, wherein:.

Reference is made to <FIG> , which shows a crankshaft <NUM> from an engine <NUM> from a vehicle (not shown). It will be noted that the engine <NUM> is shown as a simple rectangle for illustrative purposes. It will be understood that the engine <NUM> may have any suitable shape and may be any suitable type of engine such as a spark-ignition engine or a diesel engine. The vehicle may be any suitable vehicle, such as an automobile, a truck, a van, a minivan, a bus, an SUV, a military vehicle, a boat or any other suitable vehicle.

The crankshaft <NUM> has a crankshaft pulley <NUM> thereon. The crankshaft pulley <NUM> drives one or more vehicle accessories via a belt <NUM>. The term 'belt' is used herein for convenience, however for the purpose of the claims and for the scope of this disclosure it will be understood that the belt <NUM> may alternatively be any other type of suitable endless drive member. It will further be noted that, in cases where the endless drive member is a belt, it may be any suitable type of belt, such as a flat belt, a V belt, a poly-V belt, a timing belt, or any other suitable type of belt. The term 'pulley' is similarly used for convenience and any other suitable rotary drive member may be used instead, such as a sprocket.

The accessories may include, for example, the MGU <NUM>, an air conditioning compressor <NUM>, a water pump <NUM>, a power steering pump <NUM> and/or any other suitable accessories. The system further includes a plurality of idlers <NUM> that are positioned to provide a selected amount of belt wrap about the pulleys of some of the accessories.

Each of the driven accessories has a shaft, and a pulley that may be connectable and disconnectable from the shaft via a clutch. For example, the MGU shaft, clutch and pulley are shown at <NUM>, <NUM> and <NUM> respectively. In another example, the air conditioning compressor shaft, clutch and pulley are shown at <NUM>, <NUM> and <NUM> respectively. Clutching each of the accessories permits each to be disconnected when not needed while the belt <NUM> itself is still being driven by the crankshaft <NUM>.

In some vehicles, such as some hybrid vehicles, the engine <NUM> may be stopped temporarily in some situations (such as when the vehicle is stopped at a stoplight) and may then be started again when it is time for the vehicle to move. In such situations, the MGU <NUM> can be operated as a generator when the engine <NUM> is running so as to generate electricity for storage in a vehicle battery (not shown). In some arrangements, the MGU <NUM> operated as an electric motor to drive the crankshaft <NUM> via the belt <NUM>, enabling the engine <NUM> to be started via the belt <NUM> (i.e. a belt-alternator start (BAS) drive system).

The MGU <NUM> may instead be some other type of motive device such as an electric, hydraulic or pneumatic motor, which may be used to drive accessories or to start the engine <NUM>. The MGU or other motive device <NUM> may be referred to generally as a supplemental motive device, as it is a supplemental means for driving the belt <NUM>, whereas the engine <NUM> is a primary motive device for driving the belt <NUM>. Furthermore, in some arrangements, the engine <NUM> may instead be some other type of motive device, such as an electric motor. Instead of, or in addition to, being used to start the engine <NUM> and/or to drive accessories while the engine <NUM> is off, the supplemental motive device may be used to provide a power boost to the engine <NUM> via the belt <NUM> (e.g. to provide a burst of acceleration for the vehicle).

Providing tension in the belt <NUM> is beneficial in that it reduces the amount of slip that can occur between the belt <NUM> and the driven accessory pulleys, between the belt <NUM> and the MGU <NUM>, and between the belt <NUM> and the crankshaft <NUM>. In <FIG> , the direction of rotation of the crankshaft <NUM> is shown at DIR1. When the engine <NUM> is driving the belt <NUM> and the MGU <NUM> acts as a generator, it will be understood that a relatively higher tension will exist on the trailing belt span, shown at 914a, and a relatively lower tension will exist on the leading belt span, shown at 914b, where the terms 'trailing' and 'leading' are relative to the crankshaft pulley <NUM> in this context. In general, the belt tension will decrease progressively through each belt span along the belt routing between the span 914a and the span 914b. By contrast, when the MGU <NUM> is driving the belt <NUM> and the engine <NUM> is off, the trailing belt span, shown at 914c (trailing relative to the MGU <NUM>) has the highest belt tension, and the leading belt span 914d (leading relative to the MGU <NUM>) has the lowest belt tension. Thus it can be seen that the belt tension in the spans 914c and 914d can vary significantly during operation of the vehicle in the two different modes (i.e. in a first mode where the engine <NUM> is the sole driver of the belt <NUM> as compared to a second mode where the MGU <NUM> is the sole driver of the belt <NUM>). Tensioners have been proposed for some vehicles in which the tensioner has two arms that are fixedly connected to one another to form a V, wherein each arm has a pulley, and wherein the V is pivotally mounted to a base that is fixedly mounted to a region of the engine inside the contained area of the belt. The pulleys engage two different spans of the belt, (e.g. a span on either side of an accessory such as an MGU). As a result of their configuration, such a tensioner is capable of maintaining tension in both spans so that the belt tension is kept in the span needing it the most, regardless of whether the MGU is being driven as a generator or is being operated as a motor.

Such a tensioner, however, can be bulky and there is not always sufficient room in the aforementioned region to locate it.

In accordance with an arrangement of the present invention, an orbital tensioner <NUM> is provided for tensioning the endless drive member <NUM>, which is engaged with the rotary drive member <NUM> on the shaft <NUM> of the motive device <NUM>. With reference to <FIG> and <FIG>, the tensioner <NUM> includes a base <NUM>, a ring <NUM>, a tensioner arm <NUM>, a first tensioner pulley <NUM> and a second tensioner pulley <NUM>.

The base <NUM> may be made from aluminum or some other suitably strong material and is fixedly mountable to the MGU <NUM>. In the example shown in <FIG> the base <NUM> includes a plurality of fastener apertures <NUM>, which receive fasteners <NUM> (<FIG>) for mounting the base <NUM> to a housing of the MGU <NUM>.

The ring <NUM> may also be made from aluminum or another suitable material and is rotatably supported by the base <NUM> in surrounding relationship with the shaft <NUM> of the motive device <NUM><NUM> and is rotatable about a ring axis shown at AR in <FIG> and <FIG>. As shown in <FIG> , the ring axis AR may be coaxial with the axis of rotation of the MGU shaft <NUM>, which is shown at As.

<FIG> and <FIG> show exploded views of the tensioner <NUM>. It will be noted that the base <NUM> shown in <FIG> and <FIG> is a minor variant of the base shown in <FIG> and <FIG>, with a principal difference being a different distribution of mounting apertures <NUM>. Referring to <FIG> and <FIG> a first ring bushing <NUM> and a second ring bushing <NUM> are provided. The ring bushings <NUM> and <NUM> can be configured to apply any desired amount of friction to the ring <NUM> to provide any desired amount of damping to the movement of the ring <NUM> on the base <NUM>. When used intentionally to apply a selected amount of damping to the movement of the ring <NUM>, the ring bushings <NUM> and <NUM> may be referred to as first and second ring damping members <NUM> and <NUM>. Suitable material of construction for the bushings <NUM> and <NUM> may be, for example, polyamide <NUM> or <NUM> or some other suitable polymeric material.

In the arrangement shown, a clamping member <NUM> is provided and is connected to the ring <NUM> such that the clamping member <NUM> cooperates with the ring <NUM> to clamp the base <NUM> and the first and second ring damping members while still permitting sliding movement of the ring <NUM> relative to the base <NUM>. With this arrangement, the first ring bushing <NUM> is positioned between the clamping member <NUM> and a first face <NUM> (<FIG>) of the base <NUM>, and the second ring bushing <NUM> is positioned between the ring <NUM> and the a second face <NUM> (<FIG>) of the base <NUM>. During movement of the ring <NUM> when the tensioner <NUM> is in use, the sliding occurs by the clamping member <NUM> on the first bushing <NUM> and/or by the first bushing <NUM> on the base <NUM>, and sliding also occurs by the ring <NUM> on the second bushing <NUM> and/or by the second bushing <NUM> on the base <NUM>. As a result of the aforementioned sliding movement, the first and second ring bushings <NUM> and <NUM> apply a frictional force (i.e. a damping force) to the ring <NUM>.

In the arrangement shown, the first ring bushing <NUM> is a complete circle, covering the entire circumference of the ring <NUM> and base <NUM>. However, the second ring bushing <NUM> covers less than the entire circumference of the ring <NUM> and base <NUM> (and in the arrangements shown, less than <NUM> degrees of arc). The second ring bushing <NUM> is positioned in a first region of the tensioner <NUM> that is outside of a second region that lies under the belt <NUM> (<FIG>). In the first region there is less of a height constraint on the tensioner components, whereas in the second region there can be significant height constraint. The part of the circumference of the ring <NUM> and base <NUM> where the second ring bushing <NUM> is not routed is in the second region of the tensioner <NUM>, so as help keep the height of the tensioner <NUM> sufficiently low to avoid interference with the belt <NUM>.

Optionally, the clamping member <NUM> may be threadably connected to the ring <NUM> (e.g. via engagement of threaded fasteners <NUM> with threaded apertures <NUM> in the ring <NUM>) so as to permit adjustment of a gap between the clamping member <NUM> and the ring <NUM>, and therefore adjustment of the clamping force therebetween. This permits adjustment of a damping force exerted on the ring <NUM> via the first and second ring damping members <NUM> and <NUM>.

It will be noted that the first and second ring bushings <NUM> and <NUM> have radially extending portions, shown at <NUM> respectively, which are the portions of the bushings <NUM> and <NUM> that act on the first and second faces <NUM> and <NUM> of the base <NUM>. Additionally however, the bushings <NUM> and <NUM> further include axially extending portions <NUM> (<FIG>) that act between the radially outer face <NUM> of the ring <NUM> and the radially inner ring-receiving wall <NUM> of the base <NUM>.

A sectional side view of the tensioner <NUM> is shown in <FIG>, however, in this view it can be seen that the first and second ring bushings <NUM> and <NUM> are replaced by a single bushing <NUM> that includes a first portion <NUM> (see also <FIG>) that is similar to the first bushing <NUM> (<FIG>) and acts between the clamping member <NUM> and the base <NUM>, and a second portion <NUM> that is similar to the second bushing <NUM> and acts between the ring <NUM> and the base <NUM>.

Referring to <FIG>, the tensioner arm <NUM> is made from aluminum or another suitable material and is pivotally mounted to the ring <NUM> for pivotal movement about an arm pivot axis AA. The tensioner arm <NUM> has the first tensioner pulley <NUM> rotatably mounted thereon, for rotation about a first pulley axis A P1, which is spaced from the arm pivot axis A A. Referring to <FIG>, cthe tensioner arm <NUM> is biased in a free arm direction towards a first span 914d of the endless drive member <NUM> on one side of the rotary drive member <NUM>. The tensioner arm <NUM> may be biased in the free arm direction by a tensioner arm biasing member <NUM> (<FIG>, <FIG> and <FIG>). For example, the tensioner arm biasing member <NUM> may be any suitable kind of biasing member, such as for example, a torsion spring having a first end <NUM> (<FIG>) that engages a first drive wall <NUM> (<FIG>) on the arm <NUM>, and a second end <NUM> (<FIG>) that engages a second drive wall in a spring housing portion <NUM> on the ring <NUM>.

The tensioner arm <NUM> is part of a tensioner arm assembly that further includes a shaft member <NUM> which mounts (e.g. via threaded engagement) to the ring <NUM>, a pivot bushing <NUM> that pivotally supports the tensioner arm <NUM> on the shaft member <NUM>, and an optional damping structure <NUM> that includes a polymeric (e.g. unfilled (non-reinforced) nylon) tensioner arm damping member <NUM> and a metallic (e.g. steel) sleeve <NUM> that holds the damping member <NUM> and protects the damping member <NUM> against damage from engagement with the torsion spring <NUM>. The damping member <NUM> provides damping for the movement of the tensioner arm <NUM>. The components of the tensioner arm assembly may be similar to the analogous components described in <CIT>, the contents of which are incorporated herein in their entirety. The tensioner arm assembly may alternatively be as described in patent publications <CIT> , <CIT> , and <CIT>, the contents of all of which are incorporated herein by reference in their entirety.

Referring to <FIG>, the second tensioner pulley <NUM> is rotatably mounted at least indirectly to the ring <NUM> for rotation about a second pulley axis Ap2. In the arrangement shown in <FIG>, the pulley <NUM> is mounted directly to the ring <NUM>, via a fixed projection <NUM> on the ring <NUM>.

The second tensioner pulley <NUM> is biased towards a second span 914c of the endless drive member <NUM> on another side of the rotary drive member <NUM>. This biasing occurs by virtue of the forces transferred to the ring <NUM> by the tensioner arm biasing member <NUM>. More specifically, during operation of the tensioner <NUM>, when the first pulley <NUM> is engaged with the belt span 914d, the belt span 914d applies a hub load to the first pulley <NUM>. This hub load acts on the arm <NUM> through the pulley <NUM>. The force on the arm <NUM> is transferred through the biasing member <NUM>, and into the ring <NUM> itself, urging the ring <NUM> to pivot about axis AR in the opposite rotational direction to the direction of pivoting of the arm <NUM>. This force transfer into of the ring <NUM> urges the second tensioner pulley <NUM> in a second free arm direction, into the second belt span 914c. Thus the ring <NUM> is rotatable about the ring axis A Rin response to hub loads in the first and second tensioner pulleys <NUM> and <NUM> that result from engagement with the first and second spans 914d and 914c of the endless drive member <NUM>.

Each of the pulleys <NUM> and <NUM> may have the same construction. For example, each pulley <NUM>, <NUM> may include a pulley body <NUM>, a bearing <NUM>, and a pulley mounting fastener <NUM> used to mount (e.g. by threaded engagement) the pulley <NUM>, <NUM> to the tensioner arm <NUM> or to the projection <NUM>. Optional first and second dust shields <NUM> are provided to protect the bearing <NUM> from dust during operation of the tensioner <NUM>. The dust shields <NUM> may be separate components that sandwich the bearing <NUM> to inhibit the migration of dust and debris into the bearing <NUM>. As can be seen one of the dust shields <NUM> for the pulley <NUM> is provided as an integral portion of the tensioner arm <NUM>.

The bearing <NUM> may be a ball bearing, as shown, or it may be any other suitable type of bearing. The bearing <NUM> could also be a bushing in some arrangements.

Reference is made to <FIG>, which shows the tensioner <NUM> with some modified features. As can be seen in <FIG>, the second ring bushing is shown at <NUM> and extends about the entire circumference of the ring <NUM> and the base <NUM>. This provides improved stability of the ring <NUM> in terms of resistance to yaw.

As can be seen in <FIG> and <FIG> , a different damping structure is used to provide damping for the tensioner arm <NUM>. The damping structure is shown at <NUM> and includes a damping member <NUM>, a support member <NUM> and a damping member biasing member <NUM>. The damping member <NUM> may be made from any suitable material such as a suitable polymeric material, such as polyamide <NUM> or polyamide <NUM>. The damping member <NUM> slidingly engages a damping surface <NUM> on the tensioner arm <NUM> (<FIG>). A support member <NUM> supports the damping member <NUM>, and the biasing member <NUM> acts between a support surface <NUM> on the ring <NUM> and the support member <NUM>. The biasing member <NUM> may be any suitable type of biasing member, such as, for example, a steel Belleville spring washer. The support member <NUM> may be made from a suitable material such as steel, so as to prevent damage (e.g. gouging) to the damping member <NUM> by the biasing member <NUM> due to the relative softness of the damping member <NUM> as compared to the biasing member <NUM>.

The damping structure <NUM> may be similar to the damping structure disclosed in US patent application publication <CIT>, the contents of which are incorporated herein in their entirety. Providing a damping structure similar to the damping structure <NUM> is advantageous in arrangements where it is desirable to providing damping to the movement of the tensioner arm <NUM> that is independent of the hub load incurred by the first pulley <NUM>.

Another difference between the arrangements shown in <FIG> and the arrangement shown in <FIG> is that the clamping member <NUM> in <FIG> is not threaded, but instead includes clip portions that clip onto receiving members on the ring <NUM>. In the arrangement shown in <FIG>, the flange portion of the clamping member <NUM> (which is shown at <NUM>) may be relatively thin in cross-section so as to render it resilient, and may be shaped to apply a spring force on the damping member <NUM>. This arrangement can be configured so that a consistent force is applied to the damping member <NUM> by the clamping member <NUM> reducing the need for assembly worker expertise.

It will be further noted that the damping members <NUM> and <NUM> also provide damping that is substantially independent of the hub load incurred by the pulleys <NUM> and <NUM>. Additionally, it will be noted that the use of two damping members <NUM> and <NUM> both of which are at relatively large diameters (i.e. large moment arms) from the ring axis A R, reduces the average amount of force that each damping member <NUM> and <NUM> must apply to achieve a selected damping load.

The damping members <NUM> and <NUM> may have surface properties that provide symmetric damping in the sense that the damping force exerted by the damping members <NUM> and <NUM> may the same irrespective of the direction of movement of the ring <NUM>. Alternatively, however, the damping members <NUM> and <NUM> may be provided with surface properties (e.g. a fish-scale effect) that provides lower damping in one direction and higher damping in the opposite direction. Other means for achieving asymmetrical damping are alternatively possible, such as the use of a ramp structure whereby the ring <NUM> rides up the ramp structure urging it into progressively stronger engagement with a damping member (so as to increase the damping force) during rotation in a first direction and wherein the ring <NUM> rides down the ramp structure urging it into weaker engagement with the damping member thereby reducing the damping force during movement in the second direction.

In other arrangements, the members <NUM> and <NUM> may be configured to provide as little damping as possible thereby increasing the responsiveness of the tensioner <NUM>.

Reference is made to <FIG>, <FIG> and <FIG>, which show an installation pin <NUM> that facilitates installation of the belt <NUM> (<FIG>) on the pulleys <NUM>, <NUM> and <NUM> when the tensioner <NUM> is already installed on the motive device <NUM>. The installation pin <NUM> can be passed through an optional tensioner arm pin aperture <NUM> into an optional ring pin aperture <NUM>, to lock the tensioner arm <NUM> in a position that is away from a free arm stop position and that is towards a load stop position. The free arm stop position represents one end of a range of movement of the arm <NUM>, and is the position that the tensioner arm <NUM> would end up in if there were no belt present to resist the arm's movement. The load stop position represents the other end of the range of movement of the arm <NUM> and is the position the arm <NUM> would end up in if the belt tension were sufficiently high to completely overcome the biasing force of the biasing member <NUM>.

Once the belt <NUM> (<FIG>) has been installed throughout the accessory drive system on the engine <NUM>, the installation pin <NUM> (<FIG>) may be removed from the apertures <NUM> and <NUM> permitting the biasing member <NUM> to drive the arm <NUM> and pulley <NUM> into the belt <NUM>. The pin <NUM> is shown in the installed position in <FIG>. The installation pin <NUM> is a pin in the examples shown herein, however it will be understood that the installation pin <NUM> may instead be any suitable type of arm locking member that locks the tensioner arm <NUM> in a selected angular position to permit the belt <NUM> to be installed on the pulleys <NUM>, <NUM> and <NUM>.

Reference is made to <FIG>, which shows the tensioner <NUM> with another variation in features. In this arrangement, the tensioner <NUM> includes a third tensioner pulley shown at <NUM>. The third pulley <NUM> permits the tensioner <NUM> have a selected amount of belt wrap about the MGU pulley <NUM> (<FIG>) while providing a selected orientation to the belt span 914c. As a result, the belt span 914c can be routed to avoid interference hazards near the engine <NUM>.

Reference is made to <FIG>, which shows the tensioner <NUM> with a second tensioner arm assembly. In other words, the tensioner arm <NUM> is a first tensioner arm, and the tensioner biasing member <NUM> is a first tensioner biasing member, and the tensioner <NUM> includes a second tensioner arm <NUM>' that may be similar but a mirror image of the first tensioner arm <NUM>, and which is biased in a free arm direction into the belt span 914c by a second tensioner biasing member <NUM>'. The introduction of the second biasing member <NUM>' introduces a different set of forces into the ring <NUM> during changes in belt tension and therefore changes in the hub loads on the pulleys <NUM> and <NUM> than exists with the arrangement shown in <FIG> and <FIG>.

Reference is made to <FIG>, which shows the tensioner <NUM> that uses an arcuate, helical compression spring <NUM> instead of a torsion spring as the tensioner biasing member. The compression spring <NUM> has a first end <NUM> that engages a first drive surface <NUM> on the tensioner arm <NUM>, and a second end <NUM> that engages a second drive surface <NUM> on the ring <NUM>.

The tensioner <NUM> as shown in <FIG> includes two helical compression springs, shown respectively at <NUM> and <NUM>', which act on first and second tensioner arms <NUM> and <NUM>' respectively. In the arrangement shown in <FIG>, each compression spring <NUM>, <NUM>' acts between a respective tensioner arm <NUM> and a drive surface on the ring <NUM>. By contrast, an arrangement shown in <FIG> includes a single spring that acts between the first and second tensioner arms <NUM> and <NUM>' and does not act directly on the ring <NUM>.

<FIG> are schematic views of the tensioner <NUM> with a single tensioner arm <NUM>, illustrating different situations. <FIG> illustrates a situation where the engine <NUM> (<FIG> ) is operating at a substantially constant load, (e.g. at idle with no MGU load). The belt tension in spans 914c and 914d may be substantially the same. <FIG> illustrates a situation where the MGU pulley <NUM> is driven by the MGU <NUM> (<FIG> ), either to operate accessories when the engine <NUM> is off, or to start the engine <NUM>, or to provide a boost of power to a running engine <NUM>. As can be seen, the ring <NUM> has rotated clockwise as a result of the increased tension in belt span 914d and the reduced belt tension in span 914c. <FIG> illustrates a situation where the engine <NUM> (<FIG>) is under high load, thereby increasing the belt tension in span 914c and reducing the belt tension in span 914d, while the MGU <NUM> is either not operating or is operating as a generator. As can be seen the ring <NUM> has rotated counterclockwise as a result of the reduced tension in span 914d and the increased tension in span 914c.

<FIG> shows an alternative engine layout that includes an accessory pulley <NUM> (in this instance for a water pump) and two idlers <NUM> that ensure that there is a selected amount of belt wrap around the crankshaft pulley <NUM> and around the accessory pulley <NUM> even when the MGU pulley <NUM> is being driven by the MGU <NUM> (<FIG>). This reduces the likelihood of slip at the crankshaft pulley <NUM> when the crankshaft pulley <NUM> represents a high load (e.g. during a BAS starting event).

<FIG> shows another alternative engine layout that includes only the MGU pulley <NUM>, the crankshaft pulley <NUM>, the tensioner <NUM> and an idler <NUM>.

<FIG> and <FIG> illustrate an engine layout similar to that shown in <FIG>, but where the ring axis AR is not co-axial with the axis As of the MGU shaft. <FIG> illustrates a situation where the ring axis AR is 'inboard' of the shaft axis AS, while in <FIG> the ring axis AR is outboard of the shaft axis AS. The terms 'inboard' and 'outboard' are used here to indicate position relative to the region of the engine <NUM> that is contained within the belt <NUM> (shown at <NUM>). While <FIG> and <FIG> illustrate arrangements in which the ring axis AR is not coaxial with the shaft axis AS, it can be seen that the ring <NUM> still surrounds the shaft <NUM>.

It will be understood that, in the arrangements shown herein, the tensioner arm <NUM> pivots about an arm pivot axis AA that is offset from the shaft axis As of the MGU <NUM>. This has several advantages. Firstly, under certain conditions, such as low frequency events such as a BAS starting event, the offset pivot axis of the tensioner arm <NUM> and the use of a ring <NUM> that can have a relatively high inertia and that moves along a relatively large diameter path can control the movement of the tensioner <NUM> so as to reduce the likelihood of slip. Arrangements that incorporate two tensioner arms <NUM> and <NUM>' are advantageous in that they can more effectively filter out events (i.e. belt tension fluctuations that are higher frequency), while providing an additional degree of freedom of movement which is the ring <NUM>.

It has been found during testing of a tensioner in accordance with the present disclosure that the average belt tension and the average hub loads are lower than with some other types of tensioner. This results in many advantages including: reduced fuel consumption during engine operation, reduced belt wear (and therefore increased belt life), and reduced loads (and therefore reduced wear) on the pulleys and bearings of the driven components such as for the air conditioning compressor, the water pump and the MGU itself. In particular, the reduced hub loads apply to arrangements with a single tensioner arm <NUM>, where the ring <NUM> simply moves to a position to accommodate the belt tension acting on the first pulley <NUM> and the belt tension acting on the second pulley <NUM>.

Another advantage of the arrangements described herein is that the tensioner <NUM> can be mounted to the MGU <NUM> to form a subassembly that can be installed in a vehicle relatively easily as compared to having an assembly line worker install the MGU, and then separately install a tensioner system. This can reduce the overall cost to manufacture the vehicle by some amount.

Claim 1:
The use of a tensioner (<NUM>) in an automotive engine accessory drive belt system, which system includes an endless belt (914b) entraining at least two pulleys, one pulley (<NUM>) being connected to a crankshaft (<NUM>) and one pulley (<NUM>) being connected to a motor-generator unit (MGU; <NUM>), the tensioner (<NUM>) comprising:
a base (<NUM>) mountable to the MGU (<NUM>);
a ring (<NUM>) rotatably supported by and slidably mounted to the base (<NUM>) in surrounding relationship with the rotational shaft axis of the MGU (<NUM>), the base (<NUM>) retaining the ring (<NUM>) axially and guiding the ring for rotation about an axis that is substantially coincident with the rotational shaft axis of the MGU (<NUM>) and its MGU pulley (<NUM>);
a bushing (<NUM>, <NUM>) disposed between the ring (<NUM>) and the base (<NUM>) for damping the rotational movement of the ring (<NUM>) relative to the base (<NUM>);
a tensioner arm (<NUM>) pivotally mounted to the ring (<NUM>) for pivotal movement about an arm pivot axis that is offset from the ring rotational axis;
a first tensioner pulley (<NUM>) rotatably mounted to the tensioner arm (<NUM>), the first tensioner pulley (<NUM>) positioned for engaging an outside surface of a first belt span on one side of the MGU pulley (<NUM>);
a second tensioner pulley (<NUM>) that is rotatably mounted to the ring (<NUM>) for rotation about a rotational axis that is fixed relative to the ring (<NUM>) and offset from the ring rotational axis, the second tensioner pulley (<NUM>) positioned for engaging an outside surface of a second belt span on another side of the MGU pulley (<NUM>); and
a torsion spring (<NUM>) acting between the ring and the tensioner arm (<NUM>) for biasing the tensioner arm (<NUM>) towards the first belt span and for biasing the first and second tensioner pulleys (<NUM>, <NUM>) to move towards one another, thereby tending to increase the wrap of the belt around the MGU pulley (<NUM>);
wherein the ring (<NUM>) is rotatable in response to hub loads received by the first and second tensioner pulleys (<NUM>, <NUM>) that occur as a result of the first and second tensioner pulley engagements with the first and second belts spans.