Abstract:
An assembly for maintaining tension in a drive belt features a housing mounted on a base. The housing contains a biasing element that exerts torque on the housing to bias the housing. An arm is connected to the housing and rotates with the housing in response to the bias of the biasing element. A pulley is connected to the lever arm and engages a drive belt in response to the bias force of the biasing element on the lever arm. The pulley deflects the shape of the belt to provide tension in the belt. A sealing element provides prevents migration of debris into the housing and provides a biasing force to impede translatory movement of a first half of the housing from a second half of the housing, while allowing rotation of the first half relative to the second half.

Description:
FIELD OF THE INVENTION  
       [0001]    The present invention relates generally to tensioners, and more specifically to mechanical spring-actuated or biased tensioners for use in continuously maintaining tension in endless drive belts or chains in power transmission drive systems. 
       BACKGROUND  
       [0002]    A variety of tensioners are known in the art for tensioning power transmission drives, such as belts. One type of tensioner uses compression springs to provide the biasing force. Such tensioners are an inexpensive and efficient way to maintain tension in drive belts or chain. However, the known tensioners may face premature failure when operating in harsh environments. 
       SUMMARY OF THE INVENTION  
       [0003]    In order to overcome the problems associated with premature failure of tensioner assemblies operating in harsh environments, the present invention provides a tensioner assembly adapted to reduce the effects of the environment. Accordingly, the present invention provides a tensioner for tensioning a belt, comprising a housing, an arm attached to the housing and a biasing element positioned within the housing for providing a tensioning force. A sealing element impedes migration of debris into the device that could impair rotation of the arm. 
         [0004]    According to one aspect of the invention, a tensioner is provided which includes a housing having a base and a cap that cooperates with the base to form a chamber. A shaft engages the base in such a manner to impede rotation of the shaft relative to the base. A bearing element may be provided between the shaft and the cap to facilitate rotation of the cap relative to the shaft. A biasing element within the chamber biases the cap relative to the base. An elongated arm connected with the housing has an end adapted to be connected with a pulley. A sealing element is provided to impede migration of debris into the housing. In one instance, the sealing element impedes migration of debris into a space between the shaft and the bushing. The sealing element may be deformable and a head of the shaft may deform the sealing element. Additionally, the sealing element may provide a biasing force impeding translatory displacement of the cap relative to the shaft without significantly impeding rotary displacement of the cap relative to the base. 
         [0005]    Additionally, according to one aspect of the invention, the sealing element comprises a rim circumscribing the head of the shaft, and a cover projecting inwardly from the rim to cover the bushing. Accordingly, the sealing element may impede migration of debris into a space between the shaft and the bushing. 
     
    
     
       DESCRIPTION OF THE DRAWINGS  
         [0006]    The foregoing summary and the following detailed description of the preferred embodiments of the present invention will be best understood when read in conjunction with the appended drawings, in which: 
           [0007]      FIG. 1  is a perspective view of a tensioner assembly partially in section in combination with an idler pulley. 
           [0008]      FIG. 2  is a perspective view of the tensioner illustrated in  FIG. 1  without an idler pulley. 
           [0009]      FIG. 3  is an enlarged fragmentary sectional view of the tensioner illustrated in  FIGS. 1 . 
           [0010]      FIG. 4  is a plan view of a sealing element of the tensioner illustrated in  FIG. 1 . 
           [0011]      FIG. 5  is a section view of the sealing element illustrated in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    Referring now to the drawings in general, and to  FIGS. 1 and 3  specifically, a tensioner apparatus is generally designated  10 . The tensioner  10  is operable to bias an idler pulley  7  into engagement with a belt, chain or conveyor. The tensioner  10  includes an arm  15  attached to a housing  20 . The arm  15  and a portion of the housing  20  pivot together relative to a base and are under bias from one or more biasing elements  70  in the housing  20 . The pulley  7  is connected to the end of the arm  15  and is configured to engage a belt to apply tension to the belt under the bias from the biasing element  70 . 
         [0013]    Referring now to  FIGS. 1-3  the details of the tensioner will be described in greater detail. The tensioner  10  includes a housing  20  that includes two compartments for housing the biasing elements  70 . The housing is generally cylindrical, and is formed of a lower portion or base  30 , and an upper portion or cap  40 . As discussed further below, the compartments housing the biasing elements are formed such that part of each compartment is in the base and part of each compartment is in the cap. In the present embodiment, the biasing elements are springs, so the compartments will be referred to as spring compartments in the following description, however, it should be understood that the biasing element may be in a form other than a spring, such as an elastomeric element. 
         [0014]    Referring to  FIG. 1 , the details of the base  30  will be described in greater detail. The base  30  is generally cylindrical, having a central bore  35 . A shaft  50  extends into the bore  35 , and a fastener extends through the bore and into the shaft to attach the tensioner to a machine element, as described further below. The base  30  also includes a pair of grooves  32 ,  34  that form the lower part of spring compartments. Walls between the grooves separate the grooves from one another. The walls operate as end walls that the springs  70  bear against during use of the tensioner. 
         [0015]    The grooves  32 ,  34  are formed in a curved shape. In the present instance, the grooves follow an arc-shaped curve. In the present embodiment, the second groove  34  is substantially a mirror of the first groove  32 . Additionally, in the present instance, the bottom surface of grooves  32 ,  34  are rounded to correspond to the curvature of the convolutions of the springs  70 . 
         [0016]    The cap  40  overlies the base  30  to enclose the springs  70  within the device. Additionally, an elongated arm  15  is attached to the cap. The arm  15  is configured to be connected with a machine element. For instance, in the present instance, the arm  15  includes a mounting hole positioned remote from the cap  40  that can be used to attach a pulley  7  to the arm so that the tensioner can be used to tension a belt. In the present instance, the arm is integrally formed with the cap so that the arm and cap are a single piece. However, it may be desirable to form the arm and the cap separately so that the arm can be removably attached to the cap if desired. 
         [0017]    The cap  40  is in the form of a generally cylindrically-shaped body that is similar to the base  30 . The cap also includes a central bore or opening for receiving the shaft  50 . The cap  40  comprises two grooves  42 ,  44  similar to the grooves  32 ,  34  in the base for housing the springs  70 . In this way, when the cap  40  is placed over the base  30 , the upper grooves  42 ,  44  overlie the lower grooves  32 ,  34  to form compartments for receiving the springs  70 . 
         [0018]    The tensioner includes at least one biasing element  70 . Although the number of biasing elements can vary, in the present instance the tensioner  10  includes two biasing elements  70  that are disposed symmetrically within the housing to balance the biasing forces when the device is rotated. Accordingly, the tensioner includes two similarly configured biasing elements, one in each of the spring compartments. 
         [0019]    The cap  40  and the attached arm  15  pivot about a shaft  50 , which is connected to the base  30 . The shaft is generally cylindrical, having a first end that forms an enlarged diameter head  52  and a second end  54  that forms a smaller diameter, which includes a threaded portion  54 . As discussed below, the threaded portion engages the base  30  to connect the shaft to the base in a manner that impedes rotation of the shaft relative to the base. 
         [0020]    The shaft  50  is hollow, having a central bore, and the length of the shaft between the head  52  and the threaded portion  54  is generally cylindrical. A shoulder  56  is formed in the shaft adjacent the threaded end  54 . The shoulder  56  confronts, but does not necessarily abut the base  20  when the threaded end  54  is threaded into the base  30 . The cooperation of the threaded end with the base operates as a stop limiting the distance that the shaft is inserted into the housing. However, as discussed below, in the present instance, the shoulder of the shaft contacts the base, acting as a stop to maintain the proper spacing between the base and the cap. 
         [0021]    The bore of the shaft  50  is configured to receive a fastener that is operable to attach the tensioner  10  to a machine element. As illustrated in  FIG. 1 , the shaft  50  may have an internally threaded bore for attaching the tensioner to a machine. For instance, a fastener, such as a bolt  8 , may extend through a plate attached to a machine. The head of the bolt bears against the back of the plate, and the bolt engages the threaded bore of the shaft to attach the tensioner  10  to a machine element. Alternatively, the bore of the shaft may be smooth rather than threaded. The fastener may extend through the bore and be connected via a nut that would bear down against the head of the shaft. Alternatively, the bolt may extend through the shaft so that the head of the bolt bears against the head of the shaft, and the bolt threadedly engages either a tapped hole in a mounting plate or other mounting surface, or the bolt engages a nut on the back side of the mounting surface. 
         [0022]    The tensioner  10  operates such that the spring  70  is disposed between the cap  40  and the base  30 , and the base is maintained stationary while the cap  40  pivots about the shaft  50  in response to the load on the item being tensioned. To improve the pivoting motion of the tensioner, it may be desirable to include one or more bearing elements between the various elements. For instance, as illustrated in  FIG. 1 , the present embodiment includes a bushing  60  disposed between the shaft  50  and the cap  40 . The bushing  60  is positioned within the cap so that the shaft  50  bears against the interior of the bushing. The bushing  60  is configured to be press fit into the bore though the cap  40  to form a bearing surface between the cap and the shaft. In this way, the bushing provides a smooth wear surface with a relatively low coefficient of friction so that the cap can pivot smoothly relative to the shaft. 
         [0023]    The bushing  60  is formed from a material that is softer and/or smoother than the material from which the base, cap and shaft are formed. In this way, the base, shaft and cap can be formed from materials with less regard to wear durability. For instance, the base and cap may be formed of aluminum, the shaft may be formed of steel, and the bushing  60  may be formed of bronze. 
         [0024]    The bushing  60  may be a simple cylindrical liner. However, it may be desirable to utilize a bushing having a flared head, as shown in  FIG. 1 . Specifically, the bushing  60  may include a head that flares outwardly so that the head of the bushing is disposed between the top surface of the housing and the bottom surface of the flared head  52  of the shaft  50 . A gap formed between the underside of the flared head  52  of the shaft and the top surface of the bushing  60 , ensures that the tensioner is free to rotate without binding. 
         [0025]    Referring to  FIG. 1 , in the present instance, the base  30  includes a boss  38  that forms an annular ridge protruding from the top surface of the base around the central bore  35 . The shoulder  56  of the shaft  50  rests on the boss  38  to maintain a gap between the cap and the base  30  to allow the cap to rotate relative to the base. To reduce wear between the base  30 , cap  40  and springs  70 , preferably the springs are coated with grease in the spring compartments. Additionally, to impede the migration of contaminants between the shaft and the bushing, a sealing element is provided between the head of the bushing  60  and the head of the shaft  50 . In the present instance, the sealing element is a resiliently deformable disk, illustrated in  FIG. 3-5 . 
         [0026]    The sealing element  80  comprises a cover that forms a seal between the shaft  50  and the cap  40 . The seal  80  comprises a rim  82  that circumscribes the bushing  60  and the bore of the cap  40 . In the present instance, the rim  82  is a substantially circular ring having an inner diameter that is greater than the outer diameter of the head of the bushing. 
         [0027]    A cover  83  extends inwardly from the rim  82 , forming a substantially continuous surface. An aperture  85  in the cover provides an opening to accommodate the body of the shaft  50 . The aperture  85  is smaller than the perimeter of the head of the shaft, so that the head overlies the cover  83 . In the present instance, the aperture is approximately the same diameter as the body of the shaft  50 , or slightly larger. However, if the cover is formed of resiliently deformable material, the aperture may be slightly smaller than the body of the shaft. 
         [0028]    Configured as described above, the rim  82  spaces the cover  83  from the surface of the cap  40  to impede interference between the cover  83  and the bushing  60 . The outer edge of the cover  83  is supported by the rim, while the interior of the cover, adjacent aperture  85 , is unsupported so that the cover is generally free to deform downwardly in response to a force applied downwardly on the cover. 
         [0029]    The cover  83  is interposed in the gap between the head of the bushing  60  and the head of the shaft  50 . The head of the shaft  50  bears down upon the cover  83  deflecting the cover downwardly. However, a gap remains between the cover  83  ad the head of the bushing to allow free movement between the head of the bushing and the head of the shaft. 
         [0030]    The cover may be formed of a variety of materials, such as metal plastic or rubber. In the present instance, the cover  83  is resiliently deformable, and is integrally formed with the rim  82 . In the present instance, the rim and cover are integrally formed as a single piece from plastic. Two exemplary plastics include polypropylene and acetal. 
         [0031]    Since the cover is formed of a resiliently deformable material, in the present instance, the cover acts as a biasing element to dampen displacement of the cap relative to the base  30 . For instance, as discussed above, a gap is formed between the head of the bushing and the head of the shaft. Without the gap, the shaft head would tend to bind against the head of the bushing, thereby preventing the tensioner arm from rotating freely to take up slack in the belt or chain being tensioned. Because of the gap between the head of the bushing and the head of the shaft, the cap may move axially relative to the base. The head of the shaft limits the ability of the cap to move upwardly away from the base. Additionally, as the cap moves upwardly away from the base, the sealing element compresses. As the sealing element  80  deforms, the resilience of the sealing element provides a biasing force biasing the cap  40  downwardly toward the base  30 . In this way, the sealing element  80  provides a dampening force impeding displacement of the cap away from the base. 
         [0032]    Configured as described above, the tensioner  10  is assembled as follows. The base bushing  60  is press fit into the central hub of the cap  40 . The springs  70  are inserted into the spring compartments. Grease is applied to the springs and the cap is placed over the base so that the grooves in the cap  42 ,  44  overlie the grooves in the base  32 ,  34 . The shaft is then inserted through the aperture  85  in the sealing element  80  and the bore of the cap so that the threaded end  54  threadedly engages the threaded bore  35  in the base. As the shaft is threaded into the base  30 , the head of the shaft engages the cover portion  83  of the sealing element  80 , deforming the sealing element downwardly toward the cap  40 . Since the sealing element is formed of a resiliently deformable material, the resilience in the sealing element biases the inner edge of the cover  83  against the underside of the shaft head  56 . At the same time, the compression of the sealing element urges the lower edge of the rim down into a sealing engagement with the cap  40 . 
         [0033]    In the present instance, a bonding element, such as LOCTITE is applied to the threads to bond the threaded portions together to substantially permanently fix the hub relative to the base. A machine element, such as a pulley is then attached to the end of the arm  15 . 
         [0034]    A connector, such as a bolt  8 , is then used to attach the tensioner to a mounting plate or machine element as described above. The fastener tightens down against the shaft  50  to tighten the base against the machine element. However, the shaft is fixed relative to the base, so that tightening down against the shaft does not significantly tighten the cap against the base. In this way, the cap  40  is free to rotate relative to the base after the device is mounted onto the machine element. 
         [0035]    The terms and expressions which have been employed are used as terms of description and not of limitation. There is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof. It is recognized, therefore, that various modifications are possible within the scope and spirit of the invention. For instance, in the foregoing description, the tensioner includes a bushing to improve the interface between the shaft, base and housing. In certain applications it may desirable to utilize bearing elements that incorporate ball bearings. Similarly, rather than using a separate bushing, the elements could be plated or coated with a material that provides the desired wear surface. Accordingly, the term bearing element for the shaft, base or housing is meant to include any type of liner, bushing, ball bearing, plating or coating, which provides a property or characteristic separate from the material from which the corresponding element (i.e. the hub, base or housing) is formed. Additionally, in the foregoing description, the biasing element is described as a coil spring in the form of a compression spring in spring chambers formed in the housing. Alternatively, the biasing element may be a spiral torsional spring with one end attached with the base and the other end attached with the housing to provide a biasing force when the cap is rotated relative to the base. In such an embodiment, the spring compartments need not be configured according to the shape of the spring. Instead, the housing may be generally hollow for accommodating the torsional spring. Accordingly, the invention incorporates variations that fall within the scope of the following claims.