Abstract:
A tensioner comprising a base, a pivot arm pivotally engaged with the base, a torsion spring engaged between the base and the pivot arm for biasing the pivot arm, a first damping member and a second damping member disposed between the pivot arm and the base, the first damping member wedgingly engagable between the pivot arm and the second damping member, and the second damping member frictionally engaged between the first damping member and the base.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a tensioner, and more particularly, to a tensioner comprising a first damping member wedgingly engagable between a pivot arm and a second damping member. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the automobile industry it is common to operate various vehicle accessories, such as the power steering pump, oil and air pumps, air conditioning and alternator, by a single endless belt driven by a pulley connected to the engine crankshaft. This system is referred to as a serpentine drive belt system. To ensure optimum operating efficiency for these various accessories, it is necessary that the drive belt be maintained at a predetermined tension to assure efficient performance of the accessories as well as satisfactory service life for the belt. Due to the relatively greater length for the single drive belt which replaces a plurality of smaller belts, there is a greater tendency for the belt to stretch which will affect the operating characteristics of the driven accessories. Therefore, it is desirable that a belt tensioning device be used for these endless belts to provide reliable service over an extended period of time and to maintain a constant amount of tension thereon regardless of the amount of belt stretch. 
         [0003]    Numerous devices have been proposed and used to accomplish this purpose. One type of tensioner uses a bushing formed of an elastomeric material which is placed in compression by some mechanical means for continuously exerting a tensioning force on the belt. These tensioner constructions, which use an elastomeric material, have the disadvantages in that the high load rate which they exert on the belt results in the rapid loss of tensioning as the belt stretches, and this load rate limits the stroke of the belt-engaged idler pulley to a shorter distance than desired. Also, sudden acceleration and deceleration of the drive belt can cause a whipping action to occur which creates a time lag before full damping is achieved. 
         [0004]    Other types of tensioning devices and arrangements are provided with some type of mechanical retaining means which limits the movement of the belt tensioning member in an opposite nontensioning direction, thereby maintaining a constant tensioning force on the endless drive belt and eliminating the undesirable effects of belt whipping. 
         [0005]    Representative of the art is U.S. Pat. No. 4,392,840 (1983) to Radocaj which discloses a device which maintains a predetermined tensioning force on the endless drive belt for vehicle accessories by use of a one-way clutch which prevents return of the tensioning means from its forward most tensioning position. In the preferred embodiment, a cylindrical shaft is mounted in a fixed position adjacent the drive belt. A roller clutch assembly is mounted on the shaft and includes an outer clutch housing rotatably mounted on the shaft. An outwardly extending lever is attached to the clutch housing and has an idler pulley rotatably mounted on the extended end of the lever. The pulley is moved into tensioning engagement with the drive belt by a torsional spring which is telescopically mounted on the shaft and clutch housing. The spring moves the pulley in a belt tensioning direction. The one-way clutch assembly preferably includes a roller clutch which consists of a plurality of rollers which are interposed between and are biased by a plurality of leaf springs into a wedging relationship with the shaft surface and ramps formed on a bearing cup. The rollers permit free movement of the clutch housing and attached lever in the belt tensioning direction while preventing movement of these components and associated idler pulley in the opposite nontensioning direction because of the wedging action of the rollers. 
         [0006]    What is needed is a tensioner comprising a first damping member wedgingly engagable between a pivot arm and a second damping member. The present invention meets this need. 
       SUMMARY OF THE INVENTION 
       [0007]    The primary aspect of the invention is to provide a tensioner comprising a first damping member wedgingly engagable between a pivot arm and a second damping member. 
         [0008]    Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings. 
         [0009]    The invention comprises a tensioner comprising a base, a pivot arm pivotally engaged with the base, a torsion spring engaged between the base and the pivot arm for biasing the pivot arm, a first damping member and a second damping member disposed between the pivot arm and the base, the first damping member wedgingly engagable between the pivot arm and the second damping member, and the second damping member frictionally engaged between the first damping member and the base. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention. 
           [0011]      FIG. 1  is an exploded view of the tensioner. 
           [0012]      FIG. 2  is a perspective view of the first damping member. 
           [0013]      FIG. 3  is a plan view of the damping member in  FIG. 2 . 
           [0014]      FIG. 4  is a cross-sectional view of the tensioner. 
           [0015]      FIG. 5  is a graph showing a comparison between load and arm angle. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]      FIG. 1  is an exploded view of the tensioner. Tensioner  100  comprises a base  10 . Pivot arm  20  is pivotally engaged with base  10  through shaft  11 . Pivot bushing  22  reduces friction between the pivot arm  20  and shaft  11 , thereby facilitating pivotal movement. Seal plate  24  prevents debris from entering between bushing  22  and shaft  11  or pivot arm  20  and provides pivot arm location and retention against the axial force of the spring. 
         [0017]    Pulley  30  is journalled to pivot arm  20  through a bearing  31 . Dust shield  32  prevents debris from coming in contact with bearing  31 . Bearing  31  and thereby pulley  30  are fastened to pivot arm  20  by a bolt  33 . Bearing  31  comprises either a ball bearing, sleeve bearing, needle bearing or other suitable bearing known in the art. 
         [0018]    Torsion spring  40  is engaged between base  10  and pivot arm  20 . Torsion spring  40  is used to apply a spring force through pivot arm  20  to a belt (not shown) through pulley  30 . 
         [0019]    Tensioner  100  further comprises a first damper  50  and a second damper  60 . First damper  50  engages a surface  23  of pivot arm  20 . Damper  50  is described in  FIG. 2  and  FIG. 3 . 
         [0020]    Second damper  60  comprises a damper support  61 , a first damper friction portion  62  and a second damper friction portion  63 . Portion  63  is keyed to base  10  so that portion  63  does not rotate with respect to base  10 . Support  61  comprises a flange  65  which extends radially. Portion  62  and  63  frictionally engage flange  65 . First damper  50  also engages an inner surface  64  of damper support  61 . 
         [0021]    Torsion spring  40  applies an axial force to press portion  62  against flange  65  of support  61 . In turn, flange  65  presses portion  63  against base  10 . 
         [0022]    The tensioner is mounted to a mounting surface (not shown), such as an engine, by a fastener such as a bolt engaged through bore  12  of shaft  11 . 
         [0023]      FIG. 2  is a perspective view of the first damping member. Damping member  50  comprises a plurality of planar members  53  disposed around the circumference of ring  54 . In an alternate embodiment members  53  need not be planar, but instead may have any form which allows contact with surface  23  and  64 . Each planar member  53  comprises a surface  51  and a second surface  52 . Surface  51  engages surface  64 . Surface  52  engages surface  23 . 
         [0024]    Each planar member  53  is further disposed at an angle α with respect to a radial drawn from the center of ring  54 . Since it is a part of pivot arm  20 , surface  23  is rotationally moveable with respect to support  61 . Due to the angle (α) when the pivot arm rotates in direction D+, since member  53  is engaged with each surface  23  and  64  such that each member  53  partially rotates with respect to ring  54 . This causes each member  53  to wedge between each surface  23  and  64  such that further relative rotation of pivot arm  20  with respect to support  61  is prevented. This in turn causes support  61  to be rotated between damping portions  62  and  63 . Due to the normal force imparted by torsion spring  40  upon damping member  60 , the frictional forces between damping portions  62  and  63  and support  61  resist rotational movement of pivot arm  20 , thereby damping a movement of pivot arm  20 . 
         [0025]    A movement of pivot arm  20  in direction (D−) causes members  53  to disengage from surfaces  23  and  64 , thereby disengaging the pivot arm  20  from the damping effect of damping member  60 . 
         [0026]    Angle (α) is in the range of approximately 25° to approximately 65°. Angle (α) is determined with respect to a point on a radius (R) located at a distance of ⅓(R) from the ring  54 . 
         [0027]      FIG. 3  is a plan view of the damping member in  FIG. 2 . A plurality of members  53  are spaced about the circumference of ring  54 . Damping member  50  comprises an elastomeric material. Damping member  50  may be molded, cast or cut as a single part. Due to its inherent flexibility, elastomeric materials allow each member  53  to flex or pivot with respect to ring  54  during operation as each member  53  wedges between each surface  23  and  64 . 
         [0028]      FIG. 4  is a cross-sectional view of the tensioner. Damper  50  is disposed between support  61  and surface  23 . Shaft  11  is fixedly connected to base  10 . 
         [0029]      FIG. 5  is a graph showing a comparison between load and arm angle. The graph describes relative values for load and arm travel and therefore does not include specific numerical values or ranges. 
         [0030]    In section (A), the first damper  50  is being loaded as a result of rotation of pivot arm  20  in direction D+. This is also characterized as 1 st  stage damping. As arm angle increases the belt load gradually increases until damping member  50  begins wedging between surface  23  and  64 . This is represented by the vertical line ( 1 ). 
         [0031]    In section (B), 2 nd  stage damping occurs as represented by line ( 2 ). This means that damping is being caused by friction between damping portions  62 ,  63  and support  61 . This is the result of damping member  50  being fully wedged between surface  23  and  64 . Wedged engagement between first damper  50 , surface  23  and surface  64  forces support  61  to move between portions  62  and  63 . 
         [0032]    In section (C) damper member  50  “unloads” and thereby the damping caused by damping portions  62  and  63  is rapidly diminished since damper  50  is being disengaged. This is represented by line ( 3 ). In section (D) damper  50  is unloaded by the reverse rotation (D−) of pivot arm  20 . Line ( 4 ) represents the tensioner fully unloading. 
         [0033]    In section (E), damper  50  is preloaded, meaning surfaces  51  and  52  are engaged with and are just becoming wedged between surfaces  23  and  64 . Some preload is required to avoid the situation where there is undesirable “free-play” between the loaded and unloaded conditions. 
         [0034]    Although a form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein.