Abstract:
Belt tensioners for a power transmission belt system are disclosed. The belt tensioners have a support member, an arm, a torsion spring operatively coupled therebetween, and an improved damping assembly. The arm includes a housing section pivotally mounted to the support member for rotation about the arm. This housing section has a rub surface against which the damper assembly is seated. The damper assembly has a body having a friction surface frictionally contacting the rub surface of the arm and a damper spring integrated with the body. The improvement of the damper assembly is that the rub surface of the arm includes a trough concentric about the axis of rotation and the friction surface of the body includes an annular protrusion seated in the trough.

Description:
BACKGROUND 
     The present invention is directed to a belt tensioner for a transmission belt system and, more specifically, to an improved damper assembly for the belt tensioner and a method for constructing the belt tensioner incorporating the improved damper assembly. 
     The main purpose of a belt tensioner that automatically responds to fluctuations in the movements of an endless belt is to prolong the life of the belt itself or of engine components such as accessories operating in conjunction with the belt. Such belt tensioners are typically used in/on front-end accessory drives in an automobile engine. A front-end accessory drive often includes pulley sheaves for each accessory the belt is required to power, such as the air conditioner, water pump, fan and alternator. Each of these accessories requires varying amounts of power at various times during operation. These power variations, or torsionals, create a slackening and tightening situation of each span of the belt. The belt tensioner is utilized to absorb these torsionals through use of an internally mounted torsion spring. 
     Various embodiments of belt tensioners include an arm pivotally mounted to a base housing or spring case, where a torsion spring is operatively coupled between the arm and the base housing so as to force the distal end of the arm against the drive belt and, in turn, to provide sufficient tension force on the drive belt as desired. The size of torsional loads experienced by the drive belt is sometimes large enough to significantly move the arm away from the belt, causing the tension in the belt to be temporarily reduced. This is not favorable above a certain degree and squealing and squeaking of the belt may result. Therefore, typical belt tensioners incorporate damping devices to slow the pivotal movement of the arm. 
     In the belt tensioners illustrated and described in U.S. Pat. No. 6,575,860 and U.S. Pat. No. 6,206,797 an arm plate was included as a damping mechanism. The arm plate was deflectable or deformable to apply an axial force on other components of the tensioner, referred to herein as a deflection force. In these embodiments, when the arm plate deflection angle is less than the tapered angle of the sheath, the deflection force can only exist at the outer edge of the plate, and conversely when the arm plate deflection angle is greater than the tapered angle of the sheath, the deflection force can only exist at the edge of the plate&#39;s inner diameter. In either situation, when the sheath wears the deflection force either moves radially inward or outward, depending on where the force is applied. Since the location of the force is able to vary depending on the amount of deflection angle set during assembly and amount of wear, tensioner damping becomes increasingly difficult to manage. 
     An improved dampening device for belt tensioners is needed to solve these problems, especially a design where the deflection force does not move locations as the damping assembly wears over the life of the tensioner. 
     SUMMARY 
     The present invention provides a belt tensioner for a transmission belt system that includes an improved damper assembly; and, furthermore, a method for manufacturing such a belt tensioner that includes the improved damper assembly. 
     A first aspect of the present invention is directed to belt tensioners that have a support member, an arm, a torsion spring operatively coupled therebetween, and an improved damping assembly. The arm includes a housing section pivotally mounted to the support member for rotation about the arm. This housing section has a rub surface against which the damper assembly is seated. The damper assembly has a body having a friction surface frictionally contacting the rub surface of the arm and a damper spring integrated with the body. The improvement of the damper assembly is that the rub surface of the arm includes a trough concentric about the axis of rotation and the friction surface of the body includes an annular protrusion seated in the trough. 
     In one embodiment, the annular protrusion includes a wear-resistant material and is positioned below an edge of the damper spring that defines the outer diameter of the damper spring. The annular protrusion, when viewed in a longitudinal cross-section of the damper assembly, has an arcuate profile. In one embodiment, the arcuate profile is a semi-circular arc, an elliptical arc, or a lobular shape. 
     In one embodiment, the damper spring is an annular plate having a generally conical shape and includes a convex side facing towards the rub surface of the arm, wherein the generally conical shape of the damper spring biases the body of friction material axially against the rub surface of the arm. 
     In another embodiment, the body includes a plastic material and the plastic material is molded over the damper spring or coaxially molded thereto. After the molding process, the body may be a disc-shaped body of plastic material wrapped around the outer diameter of the damper spring. 
     In one embodiment, the support member includes a pivot shaft extending therefrom, and the damper assembly is substantially disk-shaped and is coaxially mounted on the pivot shaft. The damper spring has a center opening through which the pivot shaft extends and the center opening fixedly attaches the damper spring to the pivot shaft and thereby retains the support housing, arm, and damper assembly together. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top plan view of one embodiment of a belt tensioner acting upon a power transmission belt of a power transmission belt assembly. 
         FIG. 2  is a perspective, exploded view of one embodiment of a belt tensioner having an improved damping mechanism. 
         FIG. 3  is an elevational, cross-sectional view of one embodiment of a belt tensioner having an improved damping mechanism. 
         FIG. 4  is a magnified view of portion B enclosed by the circle in  FIG. 3 . 
         FIG. 5  illustrates a step of deforming a damping assembly. 
         FIG. 6  is the damper assembly of  FIGS. 3 and 5  after the deforming step, illustrating the conically shaped spring plate. 
         FIG. 7  is an elevational, cross-sectional view of another embodiment of a belt tensioner having an improved damping mechanism without a labyrinth seal and with the plastic material separate from the damper spring. 
         FIG. 8  is an elevational, cross-sectional view of another embodiment of a belt tensioner having an improved damping mechanism with a labyrinth seal and with the plastic material separate from the damper spring. 
         FIG. 9  is a magnified view of a portion of an alternate embodiment showing the reversal of the positions of the trough and annular protrusion. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description will illustrate the general principles of the invention, examples of which are additionally illustrated in the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. 
     Disclosed herein is an improved damper assembly for belt tensioners and methods for constructing the belt tensioners incorporating the improved damper assembly. 
     As shown in  FIGS. 1-4 , an exemplary embodiment of a belt tensioner  10  for providing a predetermined amount of tension upon a transmission belt  12  of a transmission belt system includes an arm  14  pivotally mounted to a support housing or spring case  16  and a torsion spring  18  operatively coupled between the arm  14  and the support housing  16 . The torsion spring  18  applies a torsional force on the arm  14  in the direction shown by arrow A ( FIG. 1 ), such that the distal end  20  of the arm  14  applies a corresponding tension force upon the transmission belt  12 . The arm  14  and support housing  16  may be manufactured from die-cast aluminum and the torsion spring  18  may be manufactured from steel, but other suitable alternative materials (or combination of materials/components) to construct such components are also contemplated. Additionally, while the torsion spring  18  in the exemplary embodiment is a coil spring, it may be any other suitable spring, such as a flat wire spring. 
     As illustrated in  FIGS. 1 and 2 , a pulley  22  is mounted for rotation to the distal end  20  of the arm  14  by a bolt  24  extending through the hub  26  of the pulley  22  and into a threaded bore of the distal end  20  of the arm  14 . The pulley  22  is preferably journaled to the distal end  20  of the arm  14  by roller bearings  30 . A dust cover  32  in the shape of a washer with an annular flange  34  ( FIG. 2 ) extending axially inwardly from the hub of the washer is coaxially mounted between the bearings  30  and the head  36  of the bolt  24  to protect the bearings  30  from contamination. 
     Referring again to  FIGS. 1-4 , the support housing  16  is generally bowl-shaped and includes a pivot shaft  38  extending coaxially upward from the inner surface of the convex side of the bowl-shaped housing. A tubular, wear resistant plastic bushing  40  is positioned around the outer circumferential surface of the pivot shaft  38 . The proximal end  42  of the arm  14  is a complementary bowl-shaped pivot housing  45  that includes a cylindrical pivot tube  44  extending axially downward from the convex side thereof, where the pivot tube  44  is coaxial with the pivot shaft  38  and has an inner diameter that substantially matches (or is slightly larger than) the outer diameter of the bushing  40 . Accordingly, the cylindrical pivot tube  44  is used to pivotally mount the arm  14  on the pivot shaft  38  of the support housing  16 . It will be understood that while the bushing  40  in this exemplary embodiment is a wear resistant plastic, it is within the scope of the invention to use other suitable bushing materials or bearing structures. 
     The support housing  16  includes a circumferential outer wall  46  that mates with the complementary circumferential outer wall  48  of the pivot housing  45  of the arm  14 . An annular space is provided between each of the circumferential outer walls  46 ,  48  and the cylindrical pivot tube  44  of the arm  14 , which extends along a substantial portion of the axial length of the pivot shaft  38  extending from the support housing  16 . This annular space provided within the circumferential walls  46 ,  48  provides an annular cavity  50  for seating the torsion spring  18  therein. A first end  52  of the torsion spring is attached to the inner surface of the support housing  16  and the opposite end  54  of the torsion spring is attached to the inner surface of the pivot housing  45  of the arm  14 . 
     An annular outer bushing  56  formed from wear resistant plastic is positioned axially between the circumferential walls  46  of the support housing  16  and the circumferential walls  48  of the pivot housing  45  of the arm  14 . The outer bushing  56 , which includes axially extending annular flanges  57  seated within complementary annular grooves  59 ,  61  of the respective housings  16 ,  45 , acts as a bearing surface between the circumferential outer walls  46 ,  48  of the respective housings  16 ,  45  and also acts to seal the annular cavity  50  seating the torsion spring  18  therein from external contaminants. Again, it will be understood that while the outer bushing  56  in this exemplary embodiment is a wear resistant plastic, it is within the scope of the invention to use other suitable bushing materials or bearing structures. 
     In the exemplary embodiment, the pivot tube  38  is a solid steel (or other suitable material, such as aluminum or powdered metal) insert that includes a center bore  58  for receiving an attachment bolt  60  therein and a larger diameter counter-bore  62  extending into its upper end  64  to provide a seat for the head  66  of the attachment bolt  60  ( FIG. 2 ) and is also useful in assembly process, as will be described in further detail below. The retaining O-ring  68  shown in  FIG. 2  is used to prevent the attachment bolt  60  from exiting out from the central bore  58  of the pivot tube  38  during shipment. The outer circumferential surface of the pivot housing  45  of the arm  14  includes a radially extending projection  70  and the outer circumferential surface of the support housing  16  includes a radially projecting and upwardly extending projection  72  having an axial position substantially matching that of the projection  70  on the arm (most easily seen in  FIG. 1 ). Accordingly, the projection  70  acts as an arm stop for abutting against the projection  72  to limit rotation of the arm  14  in the direction indicated by arrow A, thereby prohibiting the torsion spring  18  from unwinding completely. Additionally, a certain amount of rotational travel of the arm  14  is required to install the belt tensioner on the appropriate drive. Accordingly, to avoid over stressing of the torsion spring  18  during this installation process, a second radially extending projection  74  ( FIG. 1 ) is provided on the arm  14  to limit rotation of the arm during the installation process. It will be understood by those of ordinary skill in the art that other suitable pivot assemblies for pivotally coupling the arm  14  to the support housing  16  are available and are thus within the scope of the invention. 
     Referring primarily to  FIGS. 2 ,  3  and  4 , the belt tensioner  10  includes a damper assembly  76  that also acts as a clamping plate for axially clamping the various components of the belt tensioner  10  together at the proximal end  42  of the arm  14 . The pivot housing  45  has an upper, exterior surface  83  facing the damper assembly  76  and upon which the damper assembly is seated. The upper surface  83  includes an annular shoulder  92  defining the outer diameter of the pivot housing  45  at the upper surface. Juxtaposed to this annular shoulder  92  is a rub surface  84  that defines a trough  85  that frictionally contacts the damper assembly  76 . 
     The damper assembly  76  includes a damper spring, or spring plate  78 , substantially in the form of a Belleville spring integrally molded with, or co-molded with an annular sheath  80 . The annular sheath  80  may entirely comprise a wear resistant plastic material or at least a portion thereof may include the wear resistant plastic materials, such as a friction surface that frictionally contacts the pivot housing  45 . Although not shown in the drawings, the spring plate  78  includes a plurality of teeth or projections extending radially outwardly from its outer circumferential surface and into the sheath for prohibiting rotation of the sheath  80  with respect to the spring plate  78 . The spring plate  78  is, in the exemplary embodiment, a hardened steel plate and the wear resistant plastic material of the sheath  80  is, in the exemplary embodiment, a polyamide 46 nylon material. Of course, it is within the scope of the invention to utilize suitable alternative materials (or combinations of materials and components). For example, suitable alternative friction materials include, but are not limited to, all polyamides (PA) including 66 nylon, 6 nylon, 11 nylon, 12 nylon, 69 nylon, 612 nylon, and 610 nylon; polyethermides (PEI); polysulfones (PSU); polyethersulfones (PES); polyoxymethylenes (POM), or acetals; polyetheretherketones (PEEK); polyphenylene sulfides (PPS); polypthalamides (PPS), or amodels; polyphenylene sulfides (PPO); and amorphous nylons. 
     Referring to  FIG. 5 , the damper assembly  76  is constructed by first over-molding the sheath  80  over a substantially flat hardened steel washer  78 ′, also referred to as the non-deflected spring plate  78 ′ herein. This co-molded component  102  must then be acted upon by a deforming work piece  104  to deform the non-deflected spring plate  78 ′ into its preferred, substantially conical shape as shown in  FIG. 6 . The change in the orientation of the non-deflected spring plate  78 ′ from being perpendicular to the axis of rotation A of the tensioner to being conical, angled toward the axis of rotation A at an angle less than 90° thereto, is the deflection angle D. The work piece  104  has a substantially conical or frustoconical working end  106 , where the sloping angles S of the working end  106  slope at the desired angle of deflection for the spring plate  78 . The work piece  104  is coaxially applied against the co-molded piece  102  (or vise-versa) to deform the non-deflected spring plate  78 ′ until it achieves its desired conical shape. As will be appreciated by those of ordinary skill in the art, the greater the sloping angles S, the greater the deflection angle D, the greater the biasing force to be applied by the spring plate  78 . 
     Referring to  FIGS. 2-4 , the sheath  80  of the damper assembly  76 , molded over the non-deflected spring plate  78 ′ (shown prior to being deformed), includes an exterior surface  82  opposite the spring plate  78  and facing the upper surface  83  of the pivot housing  45 . The exterior surface  82  is generally a planar, annular surface except for an annular protrusion  86  protruding therefrom toward the pivot housing  45 . The annular protrusion  86  is disposed on the exterior surface  82  of the sheath  80  in a position that seats the protrusion  86  in the trough  85  on the pivot housing  45 . In the exemplary embodiment in  FIGS. 3 and 4 , the protrusion  86  is positioned under the edge of the non-deflected spring plate  78 ′ that defines the spring plate&#39;s outer diameter. As used herein, with respect to the components illustrated in  FIG. 3 , outer and inner are relative to the axis of rotation A, where being proximate or more proximate the axis of rotation A is “inner” and being distal or more distal the axis of rotation A is “outer.” The protrusion  86  when viewed in a longitudinal cross-section of the damper assembly  76  has an arcuate profile. The arcuate profile of the protrusion may have a constant radius or a varying radius. In one embodiment, the arcuate profile is a semi-circular arc. In another embodiment, the arcuate profile is an elliptical arc. In another embodiment, the arcuate profile is a lobular shape. 
     As seen in  FIG. 4 , the sheath  80  also includes an annular clamp segment or flap  88  extending around a circumferential outer surface of the non-deflected spring plate  78 ′ and at least partially over an upper annular surface of the non-deflected spring plate  78 ′ so as to retain the sheath  80  to the non-deflected spring plate  78 ′. The sheath  80  also includes an annular bead or flange  90  extending axially downward from an outer circumference of the sheath  80  over an annular shoulder  92  extending into an upper surface of the pivot housing  45 . This flange  90  completely encircles the annular shoulder  92 , providing a labyrinth seal  93  between the damper assembly  76  and the arm  14 . Further, while the flange  90  in the exemplary embodiment is generally in the shape of an annular bead, it is within the scope of the invention to utilize alternative shapes for the flange  90  and/or alternative structures for the labyrinth seal provided by the flange  90 . 
     Referring back to  FIG. 2 , the non-deflected spring plate  78 ′ includes a plurality of teeth  98  extending radially inwardly from the inner circumferential surface  94  of a center hole  96  extending therethrough. These teeth  98  become embedded into the outer circumferential surface  100  of the pivot shaft  38  at the upper end  64  of the pivot shaft to securely attach the damper assembly  76  to the pivot shaft  38  and, consequently, to retain the proximal end  42  of the arm  14  axially between the support housing  16  and the damper assembly  76 . This, in turn, retains the torsion spring  18  within the annular chamber  50 . The teeth  98  become embedded, as shown in  FIG. 3 , once the pivot bushing  40 , outer bushing  56 , housing  45  of the arm  14 , torsion spring  18  and damper assembly  76  have been stacked on the support housing  16 , or otherwise positioned coaxial with the pivot shaft  38 , and a diametrically expanding work piece  108 , having a final outer diameter slightly larger than the inner diameter of the counter-bore  62  extending into the upper end  64  of the pivot shaft  38 , is positioned into the counter bore  62  and diametrically expanded such that the circumferential walls  110  of the counter bore  62  are forced radially outwardly, into the teeth  98  on the inner circumferential surface  94  of the center hole  96  extending through the deflected spring plate  78 , as shown in  FIG. 6 , so that the teeth  98  become embedded into the circumferential walls  110 , thereby fixedly attaching the deflected spring plate  78  and damper assembly  76  to the pivot shaft  38 , and in turn, retaining the support housing  16 , outer bushing  56 , arm  14 , pivot bushing  40 , torsion spring  18  and damper assembly  76  altogether on the pivot shaft  36 . It will be appreciated that there are other suitable coupling/retaining methods available to those of ordinary skill in the art, such as the use of radial riveting, all of which fall within the scope of the invention. 
     The biasing properties of the spring plate  78  (due to the substantially conical shape of the spring plate after deformation) also acts to force the annular protrusion  86  against the trough  85  in the rub surface  84 , referred to herein as a deflection force. The resulting frictional engagement between the annular protrusion  86  and the trough  85  acts to dampen severe pivotal movements of the arm  14  due to the torsionals experienced by the drive belt  12 . In this protrusion-trough design the annular protrusion  86  keeps the deflection force directed to a single location provided by the location of the trough  85 . And, based on the annular protrusion&#39;s position, the deflection force of the damping assembly  76  is generally at the edge defining the outer diameter of the damper assembly  76 , and more particularly is at the edge defining the outer diameter of the spring plate  78 . The arcuate shape of the annular protrusion  86  is advantageous because it allows the damping assembly  76  to “rock over” as the non-deflected spring plate  78 ′ is deformed into the gap  120  during assembly, i.e., the arcuate shaped annular protrusion acts much like a cantilever allowing the spring plate to pivot along its axis when the arm plate is deformed into the gap. In the embodiment illustrated in  FIGS. 1-4  and  6 - 8 , the protrusion  86 ,  286  or  386 , respectively, is a smooth, constant diameter arc. This provides the advantage of a deflection force at a constant rate at a position where the damping force is the highest. In another embodiment, if it is preferred to have the deflection force rate increase more quickly as the arm plate is deflected, the cam may have an elliptical arc. However, in either version, the deflection force always stays in the same location which is what is desired. 
     As shown in the  FIG. 6 , the annular protrusion  86  sets firmly inside the trough  85  in the arm  14  as a result of the force applied thereto by the spring plate  78  once deflected (i.e., in its conical shape). This protrusion-trough meshing relationship does not change location regardless of the amount of wear experienced by the sheath  80  (in particular the wear of the protrusion  86 ) or the method of assembly. In the disclosed improved tensioner, the sheath  80  cannot be pinched between the spring plate  78  and the pivot housing  45  of the arm  14  at any point. Also, when wear of the protrusion  86  occurs, the surface area of the protrusion, and hence the protrusion to trough contact, will be increased because the tip of the arcuate surface will wear first. In this new improved tensioner, the wear that does occur at the protrusion  86  will not affect the deflection force, change the applied angle of the deflection force, as quickly or as severely as it would have in the embodiments discussed in the background section. As a result, the damping force is more reliable and consistent throughout the life of the part thereby improving engine efficiency for a longer period of time. 
     Above, the damping mechanism  76  was described as being a spring plate over-molded with a sheath  80 . When over-molded, the sheath  80  defines a keyway  110  that has received the outer peripheral edge  112  of the non-deflected spring plate  78 ′ or spring plate  78  therein ( FIGS. 4 and 6 ). Over-molding, however, is not a required feature. In alternate embodiments, the non-deflected spring plate  78 ′ or spring plate  78  may be a separate piece from the sheath  80 . As illustrated in  FIG. 7 , the damping mechanism, generally referred to as  276 , for a belt tensioner  210  includes a spring plate  78  seated on an annular ring  279  of wear resistance material(s) having an annular protrusion  286 , similar to annular protrusion  86  described above, shaped and configured to seat in a trough  285  on the arm  214  of the belt tensioner  210 . As illustrated in  FIG. 8 , the damping mechanism, generally referred to as  376 , for a belt tensioner  210  includes spring plate  78  seated on an annular sheath  380  of wear resistance material(s) having an annular protrusion  386  seated in a trough  285  on the arm  214  of the belt tensioner  210 . Sheath  380  is similar to sheath  80  described above, except that there is no annular clamp segment or flap  88  (see  FIG. 4 ) extending around a circumferential outer surface of the spring plate and at least partially over an upper annular surface of the spring plate. Here, with the absence of the flap  88 , the spring plate  78  may be seated within a recess  388  in the upper surface off the sheath  380  rather than being molded thereto. In these alternate embodiments, if desired, the spring plate  78  may be merely seated on, adhered to, or keyed to the annular ring  279  ( FIG. 7 ) or sheath  380  ( FIG. 8 ). 
     As can be appreciated, the embodiments described above may alternately have the trough and the annular protrusions reversed, i.e., the trough is in the sheath and the annular protrusion is on the arm. As illustrated in  FIG. 9 , the damping mechanism, generally referred to as  476 , includes a spring plate  78  seated on an annular sheath  480  of wear resistance material(s) having a trough  485 , similar to trough  85  described above, shaped and configured to seat therein an annular protrusion  486 , similar to annular protrusion  86 , disposed on the rub surface  484  of the arm  414 . While  FIG. 9  is illustrated with a sheath  480 , the sheath may instead be any of the alternate configurations disclosed herein such as those shown in  FIGS. 7 and 8  or modifications thereof. 
     Some other advantages of the belt tensioner  10  and damper assembly  76  described above include, but are not limited to, an overall reduction in the amount of components needed for the belt tensioner; a reduced cost in manufacturing the belt tensioner; a damper assembly that has a dual purpose of dampening rotation of the torsion arm and coupling components of the belt tensioner to the base housing; a spring plate that has a dual purpose of dampening rotation of the torsion arm and coupling components of the belt tensioner to the base housing; a damper assembly that includes a labyrinth seal; and a single piece damper assembly utilizing a co-molded spring and friction material. It is to be understood, however, that it is not necessary to meet any or all of the identified advantages or objects of the present invention disclosed herein in order to fall within the scope of any claims, since the invention is defined by the claims and since inherent and/or unforeseen advantages of the present invention may exist even though they may not be explicitly discussed herein. 
     Following from the above description and summaries, it should be apparent to those of ordinary skill in the art that, while the apparatuses and processes herein described constitute exemplary embodiments of the present invention, it is to be understood that the invention is not limited to these precise apparatuses and processes, and that changes may be made therein without departing from the scope of the invention as defined by the claims. Additionally, it is to be understood that the invention is defined by the claims and it is not intended that any limitations or elements describing the exemplary embodiments herein are to be incorporated into the meaning of the claims unless such limitations or elements are specifically listed in the claims.