Abstract:
A compliant tensioner arm assembly including an arm, an elastically deformable body disposed on a surface of the arm, and a sliding surface disposed on the elastically deformable body is disclosed. The elastically deformable body allows the sliding surface to yield to a load condition of the sliding surface so that the sliding surface yields to the load condition.

Description:
INCORPORATION BY REFERENCE 
     The following documents are incorporated herein by reference as if fully set forth: U.S. Provisional Application No. 62/066,975, filed Oct. 22, 2014. 
     FIELD OF INVENTION 
     The present invention relates to a tensioning device for a drive system. 
     BACKGROUND 
     Drive systems typically include a flexible drive member, such as a belt or chain, to transfer torque from a drive sprocket to one or more driven sprockets. Under various operating conditions, the tension in the chain can vary greatly, requiring adjustment in chain tension to improve the operating condition of the chain which may improve performance, lessen wear, and reduce noise. 
     Tensioners are used as a control device for a chain drive in automobile drive systems, for example in an automatic transmission. Temperature and the linear expansion among the various parts of the drive system, as well as wear to the drive system components can produce a decrease in the tension of the chain. A tensioner is used to take up the slack in the chain or belt that connects the drive sprocket and a driven sprocket to adjust the tension in the slack side of a chain. 
     SUMMARY 
     In an embodiment of the present invention, a compliant tensioner arm assembly comprises an arm, an elastically deformable body disposed on a surface of the arm, and a sliding surface disposed on the elastically deformable body. The deformable body reacts to a load condition of the sliding surface so that the sliding surface yields to the load condition. 
     In an embodiment of the present invention, a compliant tensioner arm system comprises an arm supported for rotation about a pivot point, an elastically deformable body disposed on a surface of the arm, a sliding surface disposed on the elastically deformable body, and a resilient extension element coupled to the tensioner arm to provide a rotational force about the pivot point. The deformable body reacts to a load condition of the sliding surface so that the sliding surface yields to the load condition. 
     Other and further embodiments of the present invention are described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side sectional view of a compliant tensioner arm assembly  100  in accordance with an embodiment of the present invention. 
         FIG. 2  is an exploded view of the tensioner arm assembly of  FIG. 1 . 
         FIG. 3  is a side view of the tensioner arm assembly of  FIG. 1 . 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common in the figures. The figures are not drawn to scale and may be simplified for clarity. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. 
     While described in reference to automotive transmissions, the present invention may be modified for a variety of applications while remaining within the spirit and scope of the claimed invention, since the range of the potential applications is great, and because it is intended that the present invention be adaptable to many such variations. 
     DETAILED DESCRIPTION 
     Certain terminology is used in the following description for convenience only and is not limiting. The words “front,” “rear,” “upper”, “lower”, “above”, and “below” designate directions in the drawings to which reference is made. “Longitudinal axis” and forms thereof refers to a direction along the long axis of a part. The terminology includes the words specifically noted above, derivatives thereof and words of similar import. 
       FIG. 1  depicts a tensioner arm assembly  100  in accordance with an embodiment of the present invention. The tensioner arm assembly  100  includes a generally elongate arm  102  with a pivot point  104  at a first end  108 . The pivot point  104  may be the center point of a through bore as illustrated, the through bore configured to accept a shaft (not shown) to support the arm  102  for rotation about the pivot point  104  which is fixed with respect to a frame of reference. At least an upper portion  106  of the arm  102  has a generally curvilinear shape. 
     The upper portion  106  of the arm  102  is formed with opposing side walls  202   a ,  202   b  and a support surface  204  forming a pocket or recess  206  as shown in  FIG. 2 . The recess  206  may have an end walls at or near the first end  108  and/or the second end  110 . 
     The arm  102  may be formed from any suitable material, for example plastic or reinforced plastic, aluminum or steel to form a rigid support surface  204 . The body of the arm  102  adjacent to and below the recess  206  may be formed by a series of wall segments arranged as a truss-like structure  208 , which may beneficially provide sufficient strength and rigidity to at least the support surface  204 , while reducing the weight of the arm  102 . As used herein, “rigid” means the arm resists deflection when used as intended in a tensioner arm assembly and system. 
     A projection  112  extends from a lower portion  114  of the arm  102  and is configured to cooperate with a resilient member  116  to urge the arm in rotation about the pivot point  104 . The resilient member  116  is illustrated as a compression spring for ease of illustration only. Other elements suitable for urging the arm  102  in rotation may be used, for example a piston and cylinder arrangement. The resilient member  116  is seated at a first end against a portion of the arm  102 . A second end of the resilient member is seated against the end wall of a blind hole  120  formed in a portion of a wedge  118 . The blind hole  120 , resilient member  116 , and projection  112  are coaxially arranged and configured to allow axial movement of each member along the common axis. Extension of the resilient member  116  urges the arm to rotate about the pivot point in a counterclockwise direction as illustrated. 
     As shown in  FIG. 3 , a lower surface  302  of the wedge  118  is supported on an incline plane  304  that is fixed with respect to the same reference as the pivot point  104 . The wedge  118 , the plane  304 , and the resilient member  116  cooperate to advance the arm  102  to take up slack in the chain as it is created in the drive system. 
     An elastically deformable body  130  is disposed on support surface  204  within the walls  202   a ,  202   b , and end walls if present. A lower surface  138  of the elastically deformable body  130  is formed to closely fit against the support surface  204  and is smaller than the recess  206  in at least the longitudinal length direction. As illustrated in  FIG. 1 , a space  122 ,  124  is formed between each of the ends  132 ,  134  of the elastically deformable body  130  and the longitudinal ends of the recess  206 . 
     The elastically deformable body  130  may be formed with voids  136  formed generally transverse to the longitudinal axis as shown in  FIG. 1 , or at other angles to the longitudinal axis, for example parallel to the longitudinal axis. Internal cylindrical surfaces define the illustrated voids  136 , although voids of other shapes may be similarly formed. The voids  136  may form a honeycomb-like body of the elastically deformable body  130 . Alternately, the elastically deformable body  130  may be formed without voids. 
     The elastically deformable body  130  may be formed as a rubber pad from a natural or synthetic rubber suitable for use in contact with, or immersed in, fluids commonly found in an automotive transmission environment, for example natural or synthetic lubricating oils used in automotive engines or transmissions. In non-limiting examples, the elastically deformable body  130  may be formed from alkyl acrylate copolymer (ACM) or other materials suitable for contact with the fluids similar to those described above in a temperatures range of about −40 degrees C. to 140 degrees C. The elastically deformable body  130  may have a Shore hardness of between 40 and 80, for example 60. 
     In some embodiments, one or more of the lower or upper surfaces  138 ,  140  of the elastically deformable body  130  may be formed with a pattern of raised surfaces, for example ribs or bumps, extending away from the top surface  140  of the elastically deformable body  130 . 
     A chain guide  150  is disposed on the upper surface  140  of the elastically deformable body  130  with an outwardly facing sliding surface  156 . The chain guide  150  is adapted for attachment to the arm  102  with the elastically deformable body  130  disposed between the arm  102  and the chain guide  150 . For example, as shown in the figures, the first end  152  of the chain guide  150  is formed with a U-shaped return  158  to engage a portion of the first end  106  of the arm  102 . The second end  154  of the chain guide  150  is formed with an interference fit structure to engage a feature (not shown), for example a through hole, formed at the second end  110  of the arm  102 . Other features may be used to secure the chain guide  150  to the arm  102 , at, for example, the ends  152 ,  154  of the chain guide or along the longitudinal edges  153 ,  155 . The sliding surface  156  is adapted to support a chain in a drive system under high temperature conditions in an oil-rich environment as discussed above. 
     The chain guide  150  may be formed from a low wear and low friction plastic material suitable for use in contact or immersed in the fluids, and at the temperatures, discussed above. Non-limiting examples of suitable materials include polyamides, for example nylon  46  or nylon  66 . 
     Assembled as described above and shown in the figures, the chain guide  150  is above and supported by the upper surface  140  of the elastically deformable body  130 . The lower surface  138  of the elastically deformable body  130  is above and supported by the support surface  204  of the arm  102 . In practice, the sliding surface  156  of the chain guide  150  is brought into contact with a belt or chain on the slack (i.e., no chain load) side of the drive system according to one embodiment. In another embodiment, the sliding surface  156  of the chain guide  150  is brought into contact with a belt or chain on the tight side (i.e., side with the chain load) of the drive system. 
     The force provided by the resilient member  116  causes counter clockwise (as drawn) rotation, or forward stroke as drawn, of the tensioner arm  102 . The forward stroke presses the sliding surface  156  against the chain at a force determined by the design of the resilient element  116  to deflect and lengthen the path of the chain until the spring force of the resilient member  116  and the slack side chain load are balanced. The path of the chain is thereby lengthened and the slack in the chain is reduced at the slack side to adjust the tension in at least the slack portion of the chain. 
     When the tight side load decreases and the chain shortens, or when full load reversal occurs so that the slack side becomes tight and the tight side becomes the slack side, the chain will push against the chain guide  150  and ultimately against the arm  102 . The wedge  118  is designed so that it will lock in place against the plane  304  due to friction to keep the chain in control at all times. Therefore, when the chain shortens, the slack side chain load will increase. Since the wedge is locked in place, the increase in the chain load may be dramatic, especially under the load reversal, or shock, conditions. It is during the shock conditions that the deformable body  130  deforms to shorten the chain path and reduce the peak load on the chain. 
     In some systems, such as automotive transmissions, the condition of the slack side of the chain can vary due to many factors, for example, misalignment in assembly, changes in temperature, or changes in the direction of power transmission as may occur during deceleration. The disclosed tensioner arm assembly  100  may beneficially create a compensation for variations in chain load during operation.