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Title:
ONE-WAY CLUTCHED DAMPER FOR AUTOMATIC BELT TENSIONER
Document Type and Number:
WIPO Patent Application WO/2008/027369
Kind Code:
A2
Abstract:
A new asymmetrically damped tensioner is provided utilizing a bearing-ramp clutch (7). During normal operation, the bearing-ramp clutch (7) enables the tensioner arm (1) to pivot in a first direction (A) to take up belt slack with negligible frictional damping applied to the motion of the tensioner arm (1). When the tensioner arm (1) pivots in a second direction (B), away from the belt, however, in a condition commonly known as wind-up, the bearing-ramp clutch (7) locks against a fixed internal surface and creates a frictional damping force that is applied to the tensioner arm (1). This frictional linkage provides asymmetric frictional damping to the tensioner (21) to limit movement in the second direction (B) to mitigate wind-up.

Inventors:
PENDERGRASS JEFFREY A (US)
JOSLYN ROBERT C (US)
Application Number:
US2007/018903
Publication Date:
March 06, 2008
Filing Date:
August 29, 2007
Export Citation:
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Assignee:
DAYCO PRODUCTS LLC (US)
PENDERGRASS JEFFREY A (US)
JOSLYN ROBERT C (US)
International Classes:
F16H7/12
Foreign References:
US20050059518A1
US4557709A
US4572459A
Attorney, Agent or Firm:
BECKER, Robert, W. (Robert W. Becker & Associates, 707 State Hwy 333 Suite, Tijeras NM, 87059-7507, US)
Download PDF:
Claims:
CLAIMS

1. A tensioner comprising: an arm (1) pivotable about a pivot axis (15) in a first direction (A) and a second direction (B); a rotating bearing plate (2) coupled to the arm (1) for rotation therewith, the rotating bearing plate (2) comprising a first face, a second face, and a periphery; a bearing (3) in contact with the second face; and a brake bearing plate (4) comprising a friction face and a bearing face in contact with the bearing (3).

2. A tensioner as claimed in claim 1, further comprising a brake plate (5) that is substantially rotationally fixed relative to the first direction (A) and the second direction (B) and is in contact with the friction face.

3 ; A tensioner comprising: an arm (1) pivotable about a pivot axis (15) in a first direction (A) and a second direction (B); a rotating bearing plate (2) pivotable about said pivot axis (15) and translatable along said pivot axis (15), the rotating bearing plate (2) comprising a first face and a second face; a bearing (3) in contact with the second face; a brake bearing plate (4) pivotable about the pivot axis (15) and translatable along the pivot axis (15), the brake bearing plate (4) comprising a bearing face in contact with the bearing (3); and a brake plate (5) rotatably fixed to the pivot axis (15), the brake plate (5) comprising a friction face in contact with a brake face. 4. A tensioner comprising: a base cap (8) with an axle (9); an arm (1) comprising a cup (11) centered on the axle (9), the arm (1) being pivotable about said axle (9) in a first direction (A) and

a second direction (B); a rotating bearing plate (2) that rotates and translates along the axle (9) and is rotatably connected to the arm (1) for rotation therewith, the rotating bearing plate (2) comprising a first face and a second face; a bearing (3) in contact with the second face; a brake bearing plate (4) that rotates and translates along the axle (9), the brake bearing plate (4) comprising a friction face and bearing face in contact with the bearing (3); and a brake plate (5) substantially rotationally fixed to the axle (9) and in contact with the friction face of the brake bearing plate (4).

5. A tensioner as claimed in any one of claims 1-5, further comprising an end cap (6) that is substantially fixed to a point on the pivot axis (15) or axle (9) and is in contact with the friction face or the brake plate

(5).

6. A tensioner as claimed in any one of claims 1-5, further comprising a tab (13) on the periphery of the rotating bearing plate (2), whereby the rotating bearing plate (2) is coupled to the arm (1) for rotation therewith by the tab (13), wherein the arm (1) or cup (11) further comprises a slot (12) substantially aligned with the pivot axis (15), adapted to accept the tab (13), such that the tab (13) is substantially fixed to pivot in the first direction (A) and the second direction (B) while substantially free to translate along the pivot axis (15).

7. A tensioner as claimed in any one of claims 1-6, wherein the bearing (3) is selected from the group comprised of roller bearing, tapered bearing, and ball bearing, wherein when the rotating bearing plate (2) moves relative to the brake bearing plate (4), the bearing (3) is urged by the rotation to increase the distance between the rotating bearing plate (2) and the brake bearing plate (4) such that the first face of the rotating bearing plate (2) engages with the arm (1) with a force to dampen the movement of the arm (1),

or whereby the first face of the rotating bearing plate (2) is in contact with said arm (1) to couple the rotation of the rotating bearing plate (2) to the pivoting of the arm (1), wherein the second face further comprises a bearing raceway (22) and the bearing face further comprises a mating bearing raceway (23), wherein the bearing raceway (22) and the mating bearing raceway (23) are configured to substantially retain the bearing (3), whereby the bearing raceway (22) and the mating bearing raceway (23) each further comprise a deeper portion (26) and a tapered portion (27).

8. A tensioner as claimed in any one of claims 1-7, further comprising a torsional spring (63) linking the rotation of the rotating bearing plate (2) to the brake bearing plate (4).

9. A tensioner of claim 7, wherein the bearing raceway (22) and the mating bearing raceway (13) are located in the four quadrants of the circumference of the respective rotating bearing plate (2) and the brake bearing plate (4), and are between about 35 degrees and about 80 degrees arc length.

10. A tensioner as claimed in any one of claims 1-9 where a rotation of the arm (1) in a second direction (B) causes a rotation of the rotating bearing plate (2) in the second direction (B) thereby urging the bearing (3) to translate relative to the brake bearing plate (4) such that the friction face of the brake bearing plate (4) engages the brake plate (15) with a force to dampen the movement of the arm (1).

Description:

ONE-WAY CLUTCHED DAMPER FOR AUTOMATIC BELT

TENSIONER

Technical Field

The present invention relates generally to tensioners and more particularly to an asymmetrically damped tensioner utilizing a bearing-ramp plate clutch operatively engaged with the tensioner arm. Background Art

It is common for a belt tensioner to have a means to dampen movement of the tensioner arm caused by belt tension fluctuation. The required magnitude of this damping depends on many drive factors including geometry, accessory loads, accessory inertia, engine duty cycle and others. For instance, drive systems that have higher torsional input or certain transient dynamic conditions may require higher damping to sufficiently control tensioner movement. Although higher damping is very effective at controlling arm movement, it can also be detrimental to other critical tensioner functions (e.g. slow or no response to slack belt conditions). In addition, variation or change in damping that occurs as a result of manufacturing variation, operating temperature and component break-in or wear can also cause the tensioner to be unresponsive.

Timing belt systems have benefited from the use of asymmetric damping to address this problem. An asymmetrically damped tensioner provides damping when additional belt tension is encountered, but is free to respond to slack belt conditions. Although asymmetric functionality may not be required for all other front end accessory drive tensioners, the potential for increased service life, solving other transient dynamic system problems including belt slip during a 1-2 gear shift, or simply making the tensioner less sensitive to damping variation make it a desirable design option.

One current solution to this problem uses a viscous linear damper mechanism, such as a shock absorber, attached to a pivoting arm. Asymmetric damping is achieved through, for example, check valves and

different orifice sizes in the shock absorber. This solution, however, tends to be expensive and requires more packaging space than a conventional tensioner. Other solutions use wedges that increase damper friction during wind-up or spring loaded self-energizing brake shoe elements. These designs, however, tend to be complex with many small parts to assemble.

One-way clutch mechanisms have been proposed, for example in U.S. Patent Nos. 4,583,962 and 6,422,962, for timing belt tensioners for the purpose of preventing or limiting back travel to prevent tooth jump. These "ratcheting" tensioners, however, lack the ability to relieve belt tension sufficiently when not required. Other timing belt tensioner proposals including, for example, U.S. Patent Nos. 4,832,665 and 6,375,588, use a oneway device coupled to a viscous damper. Although these devices offer good functionality, retention of the viscous fluid throughout the service life can be difficult. Yet another design, disclosed in U.S. Patent App. Publication 2003/0008739, uses friction generated by the clamping action of a wrap spring clutch to provide damping.

The aforementioned tensioner designs are not ideal. Accordingly, a new tensioner design is desired. Brief Description of the Drawings

The features of the invention, and its technical advantages, can be seen from the following description of the preferred embodiments together with the claims and the accompanying drawings, in which:

Figure 1 is an exploded perspective view of one embodiment of a new tensioner with a bearing-ramp plate clutch.

Figure 2A and 2B show details of two embodiments of the bearing-ramp plate clutch.

Figure 3 is a view of a partial assembly of the bearing-ramp plate clutch within a tensioner arm.

Figure 4 details the assembled bearing-ramp plate clutch within a tensioner arm.

Figure 5 highlights specific features of one embodiment of a brake plate.

Figure 6 is an exploded perspective view of a new tensioner according to another embodiment with an angled bearing-ramp plate clutch.

Figure 7 is a cut away view of a new tensioner according to another embodiment with an angled bearing-ramp plate clutch. Disclosure of the Invention

The new tensioner disclosed herein uses a one-way, bearing- ramp clutch that produces asymmetric friction such that substantial frictional damping is applied to the tensioner only during wind-up (i.e. untensioning). Wind-up results when increasing belt tension causes the belt to lift the tensioner arm in a direction away from the belt. The present invention resists wind-up with a frictional damping force but does not substantially resist movement of the tensioner arm toward the belt with the same frictional damping force. This characteristic is generally known as asymmetric damping. Detailed Description of Preferred Embodiments

Referring now to the embodiment depicted in Fig. 1, the tensioner 21 herein achieves asymmetric damping in part, by the use of a bearing-ramp clutch 7 that connects the tensioner arm 1 to a brake plate 5. During normal operation, the bearing-ramp clutch 7 is not engaged and the tensioner 21 is biased normally using a spring. During wind-up, the bearing- ramp clutch 7, which is linked to the tensioner arm 1, expands in size and locks to increase the normal force applied by the bearing-ramp clutch 7 to the brake plate 5, thereby increasing the frictional damping force and resisting the movement of the tensioner arm 1 away from the belt. Due to the frictional nature of the asymmetric damping, the tensioner 21 will also respond to high belt tension once the frictional force of the damper is overcome, i.e., the tensioner 21 will not restrict all motion in the wind-up direction regardless of the belt tension.

- A -

The tensioner 21 includes a tensioner arm 1 and a bearing-ramp clutch 7. The bearing-ramp clutch 7 is comprised of three primary elements, a rotating bearing plate 2, bearings 3, and a brake bearing plate 4. The brake bearing plate 4 is in factional contact with the brake plate 5. The interactions between the roller clutch 7 and the brake plate 5 produces the frictional force that generates the asymmetric damping for the tensioner arm 1.

The tensioner arm 1 is pivotable in a first direction A and a second direction B about a pivot axis 15. As is known in the art, the tensioner arm 1 may be biased by, for example, a torsional spring (not shown) in, for example, the first direction A, to tension an associated power transmitting belt or chain. A pulley (not shown), which is rotatably attached to the distal end 16 of the tensioner arm 1, is thereby brought into engagement with the belt with a force to tension the belt. The tensioner arm 1 shown in this embodiment also has a cup 11 with a substantially channel shaped cut in the wall of the cup 11 to create a locking slot 12 substantially aligned with the pivot axis 15 of the tensioner arm 1.

In the embodiment depicted in Fig. 1, the tensioner 21 further comprises an end cap 6 and tensioner base 8. The tensioner base 8 is mounted to the opposite side of the tensioner arm 1 from the bearing-ramp plate clutch 7. The tensioner base 8 has a tensioner axle 9 emerging from the center of the tensioner base 8. The tensioner axle 9 is substantially parallel to the pivot axis 15. Near the distal end of the tensioner axle 9 there is a series of locking teeth 10 oriented substantially along the pivot axis 15. The locking teeth 10 are sized to engage the inner locking teeth 14 located around the center of the brake plate 5. The engagement of the locking teeth 10 with the inner locking teeth 14 substantially prevents the rotation of the brake plate 5 about the pivot axis 15 while substantially allowing the translation of the brake plate 5 along the pivot axis 15. The end cap 6 is affixed to the distal end of the tensioner axle 9 to cover the end of the tensioner 21 and create an axial force along the pivot axis 15 that compresses the bearing-ramp plate clutch 7 against the brake

plate 5.

Figure 2A shows one embodiment of a bearing-ramp clutch 7, comprised of a rotating bearing plate 2, a brake bearing plate 4, and bearings 3. Figure 2B details another embodiment of the rotating bearing plate 2 and the brake bearing plate 4. In both Figure 2A and 2B, the rotating bearing plate 2 has a locking tab 13. The locking tab 13 is sized to engage the locking slot 12 on the tensioner arm 1. When the locking tab 13 is engaged with the locking slot 12, the rotating bearing plate 2 is able to translate along the pivot axis 15 while substantially linking the rotation of the rotating bearing plate 2 to the rotation of the tensioner arm 1 about the pivot axis 15. Although the embodiments shown detail a single locking tab 13, multiple locking tabs may be used to fix the rotation of the rotating bearing plate 2 about the pivot axis 15 to the rotation of the tensioner arm 1. Alternative structures known to those of ordinary skill in the art can be used to achieve similar functionality including, but not limited to, locking teeth, or mating ovoid or rectilinear profiles. In yet other embodiments, described in more detail below, the locking tab 13 is eliminated and instead frictional forces generated at the interface of the rotating bearing plate 2 and the cup 11 of the tensioner arm 1 urge the rotating bearing plate 2 to follow the rotation of the tensioner arm 1.

The two embodiments shown in Figures 2A and 2B depict the rotating bearing plate 2 and the brake bearing plate 4 with two different embodiments of the respective bearing raceways 22 and 23. Figure 2 A shows a bearing raceway 22 on the surface of the rotating bearing plate 2 and a mating bearing raceway 23 on the surface of the brake bearing plate 4. The mating bearing raceway 23 is on the opposite side of the brake bearing plate 4 from the brake surface (not shown in Fig. 2A and 2B). When assembled the bearing raceway 22 and the mating bearing raceway 23 face each other and they form a confined space for the roller bearing 3 to travel. Similarly, a second embodiment of the bearing raceway 22 and the mating bearing raceway 23 are shown in Figure 2B. The width and depth of the bearing

raceway 22 and the mating bearing raceway 23 vary according to the overall arc length. So, for example in the embodiment shown in Figure 2A, the bearing raceway 22 and the mating bearing raceway 23 are longer than the same structures in the second embodiment in Figure 2B. The bearing raceway 22 and mating bearing raceway 23 arc length as depicted in Fig. 2A is approximately 80 degrees, while the bearing raceway 22 and mating bearing raceway 23 arc length as depicted in Fig. 2B is approximately 35 degrees. In addition to the overall arc length, the taper, and both the depth and width of the bearing raceway 22 and mating bearing raceway 23 relative to the arc length traveled, vary. The changing arc length and taper increases the rate of separation between the rotating bearing plate 2 and the brake bearing plate 4, which increases as the roller bearing 3 travels within the space formed between the bearing raceway 22 and the mating bearing raceway 23.

The arc length and taper directly effect how much wind-up is necessary for the bearing-ramp clutch 7 to expand and increase the frictional force generated between the brake bearing plate 4 and the brake plate 5 and effectively lock thereby transferring the frictional forces to the tensioner arm 1. Adjusting the rate of taper of the bearing raceway 22 and the mating bearing raceway 23 thus effectively adjusts the rate of application of asymmetric frictional damping applied to the tensioner 21 during wind-up. The bearing raceway 22 and mating bearing raceway 23 shown in Fig. 2A in the first embodiment have a relatively shallower slope; thus the rate of change of the position of the bearing 3 changes more slowly than in the case of a shorter arc length bearing raceway 22 and mating bearing raceway 23 shown in the second embodiment in Fig. 2B. The shorter arc length of the second embodiment, shown in Figure 2B, means that for a given displacement of the tensioner arm 1 away from the belt being tensioned, the rotating bearing plate 2 and brake bearing plate 4 will separate further than with the first embodiment shown in Figure 2A. The resulting increase in separation increases the frictional damping applied to the tensioner 21 to prevent wind-

up.

The total number of bearings 3 and bearing raceways 22 and mating bearing raceways 23 (collectively, raceways) is determined by the length of the raceways, the taper of the raceways, the size of the bearings 3. The number of bearings 3 is also dictated by the need for the bearings 3 to adequately support and separate the rotating bearing plate 2 and the brake bearing plate 4. The smallest number of bearing 3 elements for the design is three, and the maximum number is dictated by the size of the bearings 3 and the length and taper of the raceways necessary to achieve a specific damping profile. In the case of the two embodiments shown in Figures 2A and 2B, the total number of raceways and bearings 3 is four. The bearings 3 and raceways are equally distributed along the circumference of the rotating bearing plate 2 and the brake bearing plate 4. Although the embodiments have all of the bearing elements oriented along a single arc line, it is possible to orient the bearings 3 and the raceways in multiple arc lines so they are effectively staggered along the circumference of the bearing-ramp clutch 7.

A partial assembly of the bearing-ramp plate clutch 7 with a tensioner arm 1 is shown in Figure 3. The tensioner arm 1 is shown with the tensioner cup 11 facing upward. A rotating bearing plate 2 is inserted into, and sits in, the base of the tensioner cup 11. The locking tab 13 slides into the locking slot 12 on the interior surface of the tensioner cup 11. Four bearings 3 are placed in the bearing raceway 22 in the deepest portion of the bearing raceway 22 or the free running position. The base cap 8 is installed in the opposite side of the tensioner arm 1 and the base cap axle 9 and the base cap locking teeth 10 are protruding from the center of the tensioner cup 11. The tensioner arm 1 rotates along the pivot axis 15 about the base cap axle 9. The rotating bearing plate 2 is rotationally coupled to, and rotates with, the tensioner arm 1.

Figure 4 is an isometric view of another step in an exemplary assembly process whereby the bearing-ramp clutch 7 is now fully assembled

inside the tensioner cup 11. The frictional face or brake surface of the brake bearing plate 4 is shown facing outward, thereby completing the assembly of the bearing-ramp clutch 7. The opposite side of the brake bearing plate 4 has the mating bearing raceway 23 that is aligned with the bearing raceway 22 with the bearing 3 substantially constrained within. The assembly of the embodiment shown in Figure 4 has an assembled bearing-ramp clutch 7.

The brake plate 5 is detailed in Figure 5. The brake plate 5 has a series of inner locking teeth 14. The inner locking teeth 14 are sized to intermesh with the base cap axle locking teeth 10. A brake material 50 is located on the periphery of the brake plate 5. The brake material engages with the mating surface of the brake bearing plate 4 when assembled inside the tensioner arm 1. The mating frictional interfaces on the brake plate 5 and the brake bearing plate 4 may take many forms other than the flat face to flat face embodiment depicted. Some examples of alternative physical forms for the mating frictional interface between the brake plate 5 and the brake bearing plate 4 include a cup and cone or ball and socket configuration to maximize surface area, discrete brake pads, and other combinations for creating a surface suitable for a friction interface between the elements to provide frictional damping to the tensioner 21. The frictional surface itself can be fabricated with numerous processes such as heat and surface treatments, surface etching, and processing coupled with material selection in order to control the friction properties of the interface. In the alternative, a dissimilar frictional surface with the desired friction properties is adhered, bonded, glued, welded, or otherwise affixed to the surface. The various techniques for creating effective friction contacts between parts such as these may be selected by those of ordinary skill in the art.

Although the particular embodiments shown in the figures depict the use of roller ball bearings, many different types of bearings may be utilized, including, for example, ball, taper, needle, roller, and cylindrical bearings. Additionally, the various components of the bearing-ramp clutch 7

can be fabricated in either fewer or greater numbers of elements. Regardless of the physical structure selected, the bearing-ramp clutch 7 uses a rolling bearing element, bearing 3, and the interaction between the rolling bearing element inside the bearing-ramp clutch 7 assembly to enable free movement of the tensioner in the tensioning direction and to enable frictional locking during a wind-up condition typified by rotation in the opposite direction. The rolling bearing element is guided by the bearing raceway 22 and the mating bearing raceway 23 and is substantially retained within the bearing-ramp clutch 7 by the rotating bearing plate 2 and the brake bearing plate 4.

An end cap 6 encloses the tensioner 21, as shown in Figure 1. The end cap 6 encloses the bearing-ramp clutch 7 and provides a compressive force oriented along the pivot axis 15 to the assembly that keeps individual elements of the assembly under compression. The end cap 6 is mounted to the end of the base cap axle 9 and stays substantially fixed relative to the motion of the tensioner arm 1. The end cap 6 may have an O-ring (not shown) around either or both the external edge and center hole of the end cap 6 to protect the internal elements of the tensioner 21 from dust and dirt and optionally to provide a barrier to prevent the escape of lubricant from inside the tensioner 21.

If the wind-up forces become large enough to overcome the asymmetric frictional damping generated by the interaction between the brake bearing plate 4 and the brake plate 5, the tensioner arm can still break free and rotate by overcoming the static friction at that interface. In this manner, the tensioner is protected against potential damage to the mechanism caused by extreme wind-up conditions while still providing asymmetric damping suitable to manage normal wind-up experienced during normal engine operation. The selection of the mating friction surfaces on the brake plate 5 and the brake bearing plate 4, including the bearing-ramp clutch 7 design itself, provide the designer with control over the amount of force necessary to overcome the frictional damping.

Through the selection of the mating friction surfaces, the type of bearing 3 used, and the configuration of the bearing raceway 22 and mating bearing raceway 23, the designer can control the relationship between the amount of asymmetric friction applied to the tensioner arm 1 relative to the amount of wind-up experienced. For example, for more aggressive damping, a shorter, more steeply tapering bearing raceway 22 and mating bearing raceway 23 can be used. The shorter, more steeply tapering raceways cause a given change in the position of the tensioner arm 1 to result in a greater displacement of the bearing 3 for a given rotation of the tensioner arm 1 in the direction of wind-up, direction B. The greater displacement moves the rotating bearing plate 2 and the brake bearing plate 4 apart at a faster rate, thereby increasing the normal force applied to the friction surface between the brake bearing plate 4 and the brake plate 5. The increase in the rate that the normal force is applied to the friction surface for a given change in tensioner arm 1 position, means an increasing rate of asymmetric damping applied to the tensioner arm 1 during wind-up to combat wind-up.

A perspective exploded view of a second embodiment of the bearing-ramp clutch 7 in a tensioner 21 is shown in Fig. 6. The tensioner cup 11 in the second embodiment is formed with a cup-shaped surface 61. The rotating bearing plate 2 in the second embodiment has a cone-shaped surface

60. The cone-shaped surface 60 is sized to mate with the cup-shaped surface

61. The cone-shaped surface 60 and the cup-shaped surface 61 are friction surfaces that together form a second mating frictional interface between the tensioner arm 1 and the rotating bearing plate 2. The frictional link causes the rotating bearing plate 2 to move in substantially the same direction and in substantially the same amount as the tensioner arm 1. The second embodiment shown in Fig. 6 utilizes the second mating frictional interface instead of an interlocking slot and tab to rotationally link the rotating bearing plate 2 with the tensioner arm 1.

Inside the rotating bearing plate 2, bearings 3 are located in

contact with bearing raceways 22. The bearing raceways 22 are fabricated on the interior surface of the rotating bearing plate 2. The bearings 3 are captured by the brake bearing plate 4, which has mating bearing raceways 23 (not shown). A torsional spring 63 links the rotating bearing plate 2 with the brake bearing plate 4 such that a rotation of the rotating bearing plate 2 manifests itself as a rotational urge applied to the brake bearing plate 4. The rotating bearing plate 2 and brake bearing plate 4 with the bearings 3 and the torsion spring 63 form the bearing-ramp clutch 7 assembly of the second embodiment.

In the second embodiment, the function of the brake plate 5 is replaced by the end cap 6. The end cap 6 is fixed to the pivot axis 15 so it cannot rotate. A portion of the surface of the end cap 6, shown in Fig. 7, facing the tensioner arm 1 is a friction surface 70 that interfaces with a friction surface on the brake bearing plate 4. The mating frictional interfaces on the end cap 6 and the brake bearing plate 4 form a frictional linkage between the bearing-ramp clutch 7 and the fixed end cap 6. In an alternative embodiment, a brake plate 5, as described above, which is substantially unable to rotate about the base cap axle 9 (not shown in Fig. 6), is used between the bearing- ramp clutch 7 assembly. Regardless of whether or not a brake plate 5 is used in the embodiment, the mating frictional interfaces create a frictional linkage between the bearing-ramp clutch 7 and a substantially fixed surface.

Operationally, the tensioner 21 of the second embodiment operates in a similar manner to the first embodiment. When the bearing-ramp clutch 7 is urged due to wind-up of the tensioner arm 21, (i.e. direction B), the bearings 3 are urged away from the deeper portion, of the bearing raceways 22 and mating bearing raceways 23, and the rotating bearing plate 2 and the brake bearing plate 4 are urged apart. When the respective plates (2 and 4) are urged apart the greater normal force applied to the mating frictional interface and the second mating frictional interface increases the frictional force applied to the damper and thus results in increased asymmetric damping. Similarly, when the tensioner arm 1 is moving in toward the belt (i.e. direction A), the bearings

3 are urged toward the deeper portion of the bearing raceways 22 and the mating bearing raceways 23. The movement of the bearings 3 into the deeper portion reduces the distance separating the rotating bearing plate 2 and the brake bearing plate 4. The reduction in distance thus reduces the normal force applied to the mating friction surface and second mating friction surface, thereby reducing the friction applied to the tensioner arm 1 as it moves toward the belt (direction A).

In the second embodiment shown in Figs. 6 and 7, a torsional spring 63 creates a rotational linkage between the rotating bearing plate 2 and the brake bearing plate 4. The torsional spring 63 has a pair of tangs 64 at each end of the spring. In the sectional view of the embodiment of the tensioner shown in Fig. 7, the tangs 64 of the torsional spring 63 interface with the rotating bearing plate 2 and the brake bearing plate 4 respectively. The torsional spring 63 creates a rotational linkage that couples movement of the rotating bearing plate 2 through the torsional spring to cause a corresponding movement of the brake bearing plate 4. The rotating bearing plate 2 rotates due to the frictional interface of the cone-shaped surface 60 of the rotating bearing plate 2 with the cup-shaped surface 61 on the tensioner arm 1.

Other features depicted in the cut-away of the embodiment shown in Fig. 7 include the tensioner pulley 73 located at the distal end 16 of the tensioner 1 that applies a force generated by the tensioner 1 to the belt under tension (not shown). The tensioner pulley 73 rotates on tensioner bearings 71 to minimize friction. The tensioner pulley 73 and tensioner bearings 71 rotate about the tensioner axle 72.

Similar to the first embodiment of the tensioner 21, the second embodiment depicted has friction surfaces that enable the tensioner arm 1 to tolerate extreme wind-up excursions without damaging the tensioner 21 or its internal components. Specifically, the mating friction surface and second mating friction surface enable the tensioner arm 1 to overcome the asymmetric friction damping and continue to rotate so that in the event of extreme wind-up

it overcomes the frictional damping created by the bearing-ramp clutch 7. The second embodiment has a second mating friction surface between the tensioner arm 1 and the cup-shaped surface 60 inside the cup 11 that interfaces with the rotating bearing plate 2 in addition to the mating friction surface created by the brake bearing plate 4. The mating friction surface and second mating friction surface can be tailored to work together and selectively give in a way that minimizes the chance of damage to the tensioner 21 during extreme wind-up conditions.

The bearing-ramp clutch 7 enables the tensioner 21 to assume two primary operating states, a brake or damping state and a rotate state. As shown in Figure 2A, the bearing raceway 22 and the mating bearing raceway 23 provide a deeper portion 26 and a tapering portion 27 of the bearing raceway 22 and mating bearing raceway 23. The deeper portion 26 is configured to hold the bearing 3 during normal tensioning of the belt. During normal belt tensioning it is desirable to apply a majority of the spring force to the belt under tension with a minimal amount of friction generated by the bearing-ramp clutch 7. During normal belt tensioning, the spring, not shown in the figures, provides a preload to the tensioner arm 1 thereby urging the tensioner arm 1 toward the belt in direction A. As the tensioner arm 1 moves in direction A, the rotating bearing plate 2 rotates along with the tensioner arm 1. The rotation of the rotating bearing plate 2 in direction A urges the bearing 3 into the deeper portions 26 of the rotating bearing plate 2 and the brake bearing plate 4. When the bearing 3 is located in the deeper portions 26, the rotating bearing plate 2 and the brake bearing plate 4 are the closest together and occupy the least amount of volume inside the space defined along the pivot axis 15 between the end cap 6 and the inside of the tensioner cup 11. In other words, the distance between the rotating bearing plate 2 and the brake bearing plate 4 is minimized. Since the space occupied by the bearing-ramp clutch 7 is at a minimum, the normal force applied to the mating frictional interface is minimized. The brake bearing plate 4 forms the mating frictional

interface with either the frictional surface on the brake plate 5, or the end cap 6. With the minimal normal force at the frictional contact, the amount of frictional damping generated by the bearing-ramp clutch 7 is at a minimum and it is in a rotate state.

The second operating state for the bearing-ramp clutch 7 is the braking state. This condition occurs during tensioner 21 wind-up, when the tensioner arm 1 is pivoting away from the belt being tensioned. As the tensioner arm 1 rotates in direction B, the rotating bearing plate 2 is urged in direction B due to the linkage between the rotating bearing plate 2 and the tensioner arm 1. The rotation of the rotating bearing plate 2, as a result of the movement of the tensioner arm 1 from a backlash state, urges the bearings 3 along the bearing raceway 22 and mating bearing raceway 23 away from the deeper portions 26 along the tapering portions 27. The resulting movement of the bearings 3 into the tapering portions 27, forces the rotating bearing plate 2 and the brake bearing plate 4 apart from each other. As a result of the movement, overall space occupied by the roller plate clutch 7 increases and the brake bearing plate 4 is urged into the brake plate 5. Movement along the pivot axis 15 of the brake plate 5 is constrained by the end cap 6 and the movement along the pivot axis 15 of the rotating bearing plate 2 is contained by the tensioner cup 11. Therefore, the increasing separation of the rotating bearing plate 2 and the brake bearing plate 4 increases the normal force applied to the mating frictional interface formed by the brake bearing plate 4 and either the brake plate 5 or the end cap 6. The increasing normal force at the mating frictional interface increases the frictional damping. Further, the increasing separation of the rotating bearing plate 2 and the brake bearing plate 4 impedes the movement of the bearing 3 inside the bearing raceway 22 and the mating bearing raceway 23 that effectively locks the rotation of the rotating bearing plate 2 to the brake bearing plate 4. The effective locking action allows the frictional force generated at the mating frictional interface between the brake bearing plate 4 and the brake plate 5 or the end cap 6 to be

transferred to the tensioner arm 1, thereby creating the asymmetric frictional damping needed to resist wind-up of the tensioner 21.

The embodiments described herein include a number of frictional surfaces that are used to create asymmetric damping and effectively brake and/or link the various elements of the tensioner 21. Regardless of position, the frictional surfaces can take a number of alternative forms within the structure of the overall embodiment including a cup and cone or ball and socket configuration to maximize surface area, discrete brake pads, and other combinations for creating a surface suitable for a friction interface between the elements to provide frictional damping to the tensioner. The frictional surface itself can be fabricated with numerous processes such as heat and surface treatments, surface etching, and processing coupled with material selection in order to control the friction properties of the interface or a dissimilar frictional surface that is adhered to the surface. The various techniques for creating effective friction contacts between parts such as these may be selected by those of ordinary skill in the art.

The embodiments of this invention shown in the drawings and described above are exemplary of numerous embodiments that may be made within the scope of the appended claims. It is contemplated that numerous other configurations of the tensioner assemblies may be created taking advantage of the disclosed approaches. In short, it is the applicant's intention that the scope of the patent issuing herefrom be limited only by the scope of the appended claims.