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 in a radial direction. A lever 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. In one embodiment, the apparatus allows the user to switch the position of the biasing element and alter the direction of torque on the lever arm. In another embodiment, the lever arm and pulley are removable from the housing and replaceable with other arms and pulleys having different configurations.

Description:
RELATED APPLICATIONS 
   This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application No. 60/414,861, filed Sep. 30, 2002, which is hereby incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates generally to belt tensioners, and more specifically to mechanical spring-actuated or biased belt tensioners for use in continuously maintaining tension in endless drive belts in power transmission drive systems. 
   BACKGROUND OF THE INVENTION 
   The known belt tensioners are mostly related to designs that are used in maintaining belt tension in serpentine belt drives for automotive applications. While the majority of the known tensioners pertain to automotive application tensioners, there are other industrial applications where machines have drive systems that have motors driving pulleys with endless belts that need to be tensioned. One example of the prior art is shown in U.S. Pat. No. 4,557,709. 
   The known belt tensioners are constructed of a base part, a lever arm and a spring. The lever arm has a mounting feature onto which a pulley is attached. The pulley rides against the belt that is to be tensioned. The base is mounted on or in proximity to the device containing the drive belt. The base part contains a feature that houses the spring and also fixes one end of the spring from moving. The base typically has a hole axially through its central area and through the center of the spring that receives a pivot feature on the lever arm. 
   The lever arm has a pivot feature that usually has a shaft with a hole through it. The arm may also have a feature onto which one end of the spring is affixed. On the lever arm at a distance from and parallel to the pivot axis is a feature where a pulley can be attached. The pulley is forced against the belt and the drive system by the torque from the spring. 
   The spring in the known art is either a torsion spring or a spiral spring. The spring has one end fixed to the base and the other fixed to the arm. As the arm is moved in a radial manner about the pivot, the base is fixed and does not move, so the end of the spring fixed to the base does not move. The spring is compressed by the radial movement of the lever arm, which stores energy in the spring. The stored energy applies a steady force or torque to the arm and the pulley, pressing the pulley into engagement with the belt. The pulley adds tension in the belt by deflecting the shape of the belt. The added tension maintains the belt in a tight arrangement in the drive system. 
   A bolt is usually placed through the arm and the hole, through the pivot and base and threaded or fixed to the drive system. The bolt keeps the base from moving relative to the drive system. The pivot feature allows the lever arm to move when the bolt is tightened. The base is mounted so that there is some amount of compression in the spring when the belt is mounted against the pulley. As stated earlier, this compression exerts torque on the lever arm to press the pulley into engagement with the belt. The pulley maintains tension in the belt and compensates for changes in the length of the belt. When slack develops in the belt due to belt expansion or stretching, the spring has sufficient stored energy to exert additional torque on the lever arm and press the pulley further into the belt to remove any slack. 
   SUMMARY OF THE INVENTION 
   The present invention is an assembly for maintaining tension in a drive belt. The assembly features a housing mounted on a fixed base. The housing contains a biasing element having a first end that engages the housing and a second end that engages the base. The biasing element exerts a torque on the housing to bias the housing in a first rotational direction relative to the base. A lever 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 is pressed into engagement with the drive belt in response to the bias on the lever arm. The pulley deflects the shape of the belt to provide tension in the belt. 
   In one embodiment, the apparatus has a modular construction that provides the user with flexibility to assemble the apparatus in a manner that applies torque in either a clockwise or counterclockwise direction. In another embodiment, the device has a multi-part modular construction that allows lever arms and pulleys having different sizes and shapes to be used with the same housing and base. The lever arm, pulley, or both may be removed from the apparatus and replaced with a different sized lever arm and/or pulley to accommodate a different belt drive system or a different tensioning arrangement. Lever arms and pulleys having very simple configurations may be used with the housing and base. As such, the manufacturing costs for the lever arms and pulleys are reduced in comparison to prior art tensioning apparatuses. The housing portion of the modular arm may be constructed with a pivot feature that incorporates ball bearings. The ball bearings reduce the effects of frictional resistance generated when torque is provided in the tensioning apparatus. 

   
     DESCRIPTION OF THE DRAWINGS 
     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: 
       FIG. 1  is a diagram of a typical application, including a belt, tensioner assembly and idler pulley. 
       FIG. 2  is an exploded perspective view of the present configuration of the belt tensioner assembly shown with a flat belt idler pulley and mounting hardware. 
       FIG. 3  is a front elevation view of the tensioner without the idler pulley. 
       FIG. 4  is a side elevational view of the tensioner device shown in FIG.  3 . 
       FIG. 5  is a bottom elevational view of the tensioner device shown in FIG.  3 . 
       FIG. 6  is a sectional view of the device in  FIG. 5  taken along the line  6 — 6 . 
       FIG. 7  is a sectional view of the device in  FIG. 3  taken along the line  7 — 7 . 
       FIG. 8  is a front view of the belt tensioner assembly illustrated in FIG.  2 . 
       FIG. 9  is a side elevational view of the tensioner assembly shown in FIG.  8 . 
       FIG. 10  is a detail showing the housing portion of the design along with the arm. It is the first in a sequence of FIGURES showing the “Bayonet” type of method that connects the arm to the housing. This particular detail shows the arm and the housing in an exploded view, with the tab sections on the arm aligned with the notch sections on the housing. The arrow shows that once the tabs are aligned with the slots, the arm can then be moved down, flush with the housing. 
       FIG. 11  is the next in the arm/housing assembly sequence, showing the arm with the tabs aligned with the slots in the housing, and with the bottom surface of the arm in contact with the top surface of the housing. 
       FIG. 12  is the last in the sequence of the arm/housing assembly sequence, showing the arm rotated in a clockwise direction relative to the housing, and the tabs on the arm engaged into the slots in the housing. This sequence can also be achieved in a counter clockwise manner, since the features are mirrored on both sides of the parts. 
       FIG. 13  is a perspective view of an alternative embodiment of a tensioner. 
       FIG. 14  is a plan view of the tensioner illustrated in FIG.  13 . 
       FIG. 15  is a sectional view of the tensioner illustrated in FIG.  13 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to the drawings in general, and to  FIGS. 1 and 2  specifically, a tensioner apparatus is generally designated  10 . The tensioner  10  biases an idler pulley  70  into engagement with a belt  7 . The tensioner  10  includes a pivotable arm  60  removably attached to a housing  40 . The arm  60  is under bias from a biasing element  35  in the housing  40 . The pulley  70  is connected to the end of the arm  60  and engages the belt  7  to apply tension to the belt under the bias from the biasing element  35 . 
   The tensioner  10  has a modular construction that allows the housing  40  to be readily assembled with arms  60  and pulleys  70  having a variety of sizes. As such, the tensioner  10  may be provided as an assembly or kit which comprises a biasing element  35 , a housing  40 , and a variety of lever arms  60  and pulleys  70  having different sizes. Depending on the application, a lever arm  60  and pulley  70  having appropriate dimensions may be selected and connected to the housing  40 . 
   The modular construction of the tensioner  10  permits easy disassembly and access to the biasing element  35 . Referring to  FIG. 2 , the tensioner  10  comprises a torsion spring  35 . The spring  35  is readily removable from the housing  40  and can be reinserted in an opposite or reverse configuration to change the direction of the bias exerted on the lever arm  60 . 
   Referring now to  FIG. 2 , the details of the tensioner will be described in greater detail. The housing  40  is mounted over a base  20 . The base includes a central boss or hub  22  projecting upwardly. The hub  22  is generally cylindrical having a central bore and a vertical slot  24  extending along the height of the hub. The central bore of the base  20  is sized to receive a cylindrical shaft  30 . The base  20  is preferably injection molded in a fiber reinforced nylon material. Alternatively, the base could be made using other mold types or manufacturing processes. 
   The shaft  30  is cylindrical, having a central bore that extends through the shaft. The shaft may be made from a steel tubing, or from a machined from a solid piece of metal, such as steel alloy. The bore through the shaft  30  aligns with the bore in the hub  22  to allow the insertion of a mounting bolt  65 . 
   The spring  35  is a spiral spring formed from a long piece of rectangular steel that is formed in a spiral fashion to create a plurality of overlapping convolutions. The inner end  37  of the spring  35  forms a tongue that is inserted into the slot  24  in the hub  22  of the base  20 . The outer end  38  of the spring  35  also forms a tongue, which engages the housing  40  as described further below. The inner convolutions of the spring  35  have a diameter that is larger than the outer diameter of the hub  22  so that the spring is disposed around the hub  22 , as shown in FIG.  6 . 
   The housing  40  is also preferably injection molded in a fiber reinforced nylon material, however the base could also be made using other manufacturing processes. The housing  40  is generally cylindrical, preferably having a height that is less than its diameter. A vertical opening or slot  46  is formed in the side of the housing  40  and is configured to receive the outer end  38  of the spring  35 . The top of the housing  40  includes a locking flange  42  and a gap  44  configured to cooperate with the arm  60  to releasably attach the arm to the housing, as discussed further below. 
   The housing  40  includes a central hub  41  having an opening in which one or more bearing assemblies  50  are disposed. The bearings  50  are radial ball bearings that can either be pressed into the central bore of the housing to form an interference fit or alternatively can be insert molded into the central bore during the molded process. The outer race  52  of each bearing is fixed to the central bore of the housing  40 . The shaft  30  extends through the bearings  50  so that the inner race  51  of each bearing engages the outer surface of the shaft  30 . In this way, the bearings allow the housing  40  to rotate relative to the shaft  30 , so that the shaft  30  forms a rotational axis around which the housing rotates. 
   The housing  40  along with the bearings  50  are assembled onto the base  20  by inserting the shaft  30  through the inner race  51  of each bearing  50  while also aligning the slot  46  in the housing with the outer end  38  of the spring  35 . The mounting bolt  65  and washer  66  are used to attach the housing  40  to the base. The bolt  65  extends through the bearings  50 , the sleeve  30  and the base  20 , and into the frame  7  of the device to which the tensioner is mounted. The head of the bolt  65  presses the washer  66  against the end of the shaft  30 . In this way, the housing  40  is mounted over the base  20  and the spring  35  so that the housing is rotatable relative to the base. Referring to  FIG. 4 , the lower edge of the housing  40  is preferably spaced apart from the top surface of the base  20  so that a gap is formed between the housing and the base. The gap allows the housing to readily rotate relative to the base without frictional resistance and consequent wear. Rotating the house in a first direction increases the bias in the spring biasing the housing in a second direction that is reverse the first direction. The bias of the spring can be reversed by flipping over the spring in the housing. 
   The arm  60  is releasably connected to the housing  40 . In this way, different arms of different length and configurations can be attached to the housing. The arm  60  is attached to the housing  40  by means of a bayonet-type connection. Specifically, the arm  60  includes a locking collar  62  that includes a locking tab  63  that cooperates with the locking flange  42  on the housing. The locking tab  63  on the arm is aligned with an opening or gap  44  in the locking flange  42  on the housing and is moved down through the gap and rotated either clockwise or counterclockwise, depending on which way the biasing force is to be applied by the tensioner  10 . When the arm is rotated, it slides under a ledge below the flange that retains the locking tabs  63  of the locking collar on the arm. In this way, the locking collar  62  and the locking flange  42  cooperate to retain the arm to impede axial displacement of the arm relative to the housing. Preferably, the mounting configurations on the arm and housing are mirrored. This adds flexibility to connecting the arm and base, with less concern for how the gap  44  is oriented relative to the desired position of the arm  60 . 
   An elongated portion of the arm  60  extends away from the locking collar, and includes a plurality of holes for mounting an idler pulley  70  to the arm. Specifically, the tensioner arm  60  includes one or more holes so that a bolt  72  can pass through the idler pulley  70  and the arm to attach the idler pulley to the arm with a nut  73 . 
   The tensioner assembly  10  may be attached to the frame of a device or onto a mounting assembly attached to a device. Referring to  FIG. 1 , the tensioner assembly  10  is assembled so as to engage the belt in the position shown (“engaging position”). Before the belt  7  is assembled, the tensioner assembly  10  would typically be assembled with the arm  60  pivoted into a position rotated approximately 90 degrees from the engaging position (such as that shown in phantom lines). This position (“relaxed position”) would not have any biasing load generated by the spring  35  because there would be no deflection in the spring. 
   When the belt is assembled, the tensioner arm  60  is rotated to the engaging position. During rotation of the arm  60 , the housing  40  rotates in a radial direction around the pivot axis. By rotating the housing  40 , the outer end  38  of the spring  35  moves in a radial direction because of its connection with the slot  46  in the housing  40 . The inner end  37  of the spring remains fixed in contact with the slot  24  in the base  20  while the outer end  38  moves radially. As a result, movement of the outer end  38  of the spring  35  relative to the inner end  37  causes deflection in the spring. The deflection in the spring  35  generates a load which is resisted by a bias force exerted by the spring. In general, the bias force in the spring is proportional to the amount of deflection caused by rotation. The bias force is transferred through the lever arm  60  to the idler pulley  70  at the end of the arm. The idler pulley  70 , in turn, pushes on the belt  7  and deflects the shape of the belt. The deflection of the belt form tension and removes the slack in the belt. The biasing force on the arm  60  also causes the bayonet-type attachment of the arm to the housing  40  to remain in engagement. 
   Referring now to  FIGS. 13-15 , an alternative embodiment of the tensioner is designated generally  110 . The tensioner  110  is similar to the embodiment discussed above, and illustrates an alternative and preferred connection between the arm and the tensioner housing. Specifically, the tensioner  110  includes a plurality of fasteners, such as nuts  182  and bolts  180  that attach the arm  16  to the housing  140 . 
   The tensioner  110  includes a base  120  that is similar to the base  20  in the first embodiment previously described. However, preferably, the base  110  includes a circular groove  126  that extends around the periphery of the top surface of the base, as shown in FIG.  15 . The groove  126  is configured to receive the lower edge of the housing  140 . Preferably, the groove  126  is wider than the thickness of the housing so that the housing can rotate in the groove as the housing is turned relative to the base. In this way, there is a gap between the lower edge of the housing and the bottom of the groove so that the housing can readily pivot relative to the base, but there is not an exposed gap that would allow dirt, dust and other contaminants to easily enter the housing. 
   The housing  140  is similar to the housing of the first embodiment, except that the housing includes a plurality of pins  142  and holes  143  for aligning and attaching the housing with the arm  160 , rather than the locking flange  42  used in the first embodiment. Specifically, the upper surface of the housing  140  includes a plurality of pins  142  projecting upwardly, circumferentially spaced apart around a central hub  141 . In addition, the upper surface of the housing includes a plurality of holes  143  circumferentially spaced apart around the central hub. 
   The arm  160  comprises a locking bracket  162  that includes a plurality of radial slots  163  circumferentially spaced apart. The slots are sized and configured to cooperate with the pins  142  on the top of the housing to align the arm  160  on the housing. In addition, the locking bracket includes a plurality of circumferentially spaced apart holes  164 . The locking bracket also includes a central aperture configured to fit over the central hub  141  of the housing. 
   To attach the arm  160  to the housing  140 , the mounting bracket  162  of the arm is placed onto the housing so that the pins  142  on the housing project into the radial slots  163  in the arm, and the holes  164  in the arm are aligned with the holes  143  on the top of the housing. The bolts  180  are then inserted through the aligned holes and threaded into the nuts  182  to attach the arm  160  to the housing  140 . The nuts  182  may be inserted into recesses formed inside the housing so that the nuts are attached to the housing. Alternatively, rather than using separate nuts, the holes  143  in the housing can be threaded so that the bolts can be threaded directly into the housing to attach the arm to the housing. In this way, a variety of arms  160  of different lengths and configurations can be used with the same housing and base so that the tensioner can be used in a variety of applications. 
   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. Accordingly, the invention incorporates variations that fall within the scope of the following claims.