Abstract:
A tensioner for tensioning a belt includes a support housing that defines, at least in part, a spring cavity and an arm pivotably attached to the support housing. A spring is disposed in the spring cavity and is operatively connected to the arm and support housing to bias the arm to pivot relative to the support housing. The spring is a round wire coil spring having an unloaded axial height and wherein the spring cavity has a height greater than the unloaded axial height of the spring.

Description:
TECHNICAL FIELD 
     The present application relates generally to belt tensioners and more particularly to a belt tensioner with a round wire spring. 
     BACKGROUND 
     A tensioner is frequently utilized in a belt system to tension an endless belt that transmits power to accessories in an automobile engine. Tensioners typically use a spring, such as a flat wire or round wire spring to bias a pivot arm toward the belt. In tensioners employing a round wire spring, the round wire spring is compressed axially during assembly and is used to apply an axial force to the pivot arm. This axial spring force is used to maintain pivot arm alignment during use. 
     SUMMARY 
     In one aspect, a tensioner for tensioning a belt includes a support housing that defines, at least in part, a spring cavity and an arm pivotably attached to the support housing. A spring is disposed in the spring cavity and is operatively connected to the arm and support housing to bias the arm to pivot relative to the support housing. The spring is a round wire coil spring having an unloaded axial height and wherein the spring cavity has a height greater than the unloaded axial height of the spring. 
     In another aspect, a tensioner for tensioning a belt includes a support housing, an arm pivotably attached to the support housing and a compression member configured to bias the arm and the support housing together with an axial force. A round wire spring is operatively connected to the support housing and the arm to bias the arm to pivot relative to the support housing. The round wire spring is disposed within the support housing such that the axial force exerted by the compression member is not exerted on the spring. 
     In still another aspect, a method of assembling a belt tensioner comprising a support housing and an arm pivotably attached to the support housing is provided. The method includes coupling the support housing and the arm together through a round wire spring so as to bias the arm to pivot relative to the support housing, biasing the arm and support member together using a compression member and locating the round wire spring within the support member. According to this aspect, the round wire spring is isolated from the compressive force exerted by the compression member. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section view of a belt tensioner according to one embodiment; 
         FIG. 1A  is a side view of an unloaded round wire spring of the belt tensioner of  FIG. 1 ; 
         FIG. 2  is an exploded view of the belt tensioner of  FIG. 1 ; 
         FIG. 3  is a perspective view of a pivot arm of the belt tensioner of  FIG. 1 ; 
         FIG. 4  is a perspective view of a support housing of the belt tensioner of  FIG. 1 ; 
         FIGS. 5A-5C  are perspective views of the belt tensioner of  FIG. 1  with the pulley removed; and 
         FIG. 6  is a schematic view of the belt tensioner of  FIG. 1  engaging an automotive transmission belt. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a belt tensioner  10  includes a support housing  12  and a pivot arm  14  rotatably mounted to the support housing to form a spring cavity  16  therebetween. Located within the spring cavity  16  and operatively connected to both the pivot arm  14  and the support housing  12  is a round wire, helical spring  18 . The round wire spring  18  applies a force to the pivot arm  14  during use to bias the pivot arm toward an unloaded position. The pivot arm  14  carries a pulley  20 , such as a front or backside idler pulley, that can rotate relative to the pivot arm. The pulley  20  has a belt-engaging surface  22  for engaging a belt  116 , such as an automotive transmission belt ( FIG. 6 ). As will be described in greater detail below, the spring cavity  16  has a height H that is greater than an unloaded height h of the round wire spring  18  ( FIG. 1A ) effectively isolating the round wire spring from axial compression forces applied, for example, to maintain pivot arm alignment and to provide friction damping. 
     Referring also to  FIG. 2 , the support housing  12  includes a base  26 , an outer wall  28  and an alignment member  30  extending upwardly from the base and centrally located within a recess  42  formed by the outer wall and the base. The alignment member  30  has an enlarged proximal portion  32 , a relatively narrower distal portion  34  and a transition therebetween ( FIG. 1 ) forming a seating surface  36  that is shaped to receive a base portion  38  of a pivot bushing  40  (e.g., formed of molded plastic). 
     The pivot arm  14  includes a sleeve  44  sized to receive both the pivot bushing  40  and the alignment member  30 , an upper wall  46  extending outwardly from the sleeve, an opening  74  sized to receive an end  76  of the alignment member  30  and a pulley support  52  connected to the upper wall at a location offset from the opening  74 . Each of the pivot arm  14  and support housing  12  can be formed of any suitable material, including metal or polymer and can be formed by any suitable method, such as casting, machining and/or molding. 
     Positioned between the pivot arm  14  and the support housing  12  is a spring bushing  54  (e.g., formed of molded plastic). Spring bushing  54  has an upper surface  56  that can be placed in continuous (i.e., unbroken) annular contact with a lower edge  58  of the pivot arm  14  and a lower surface  60  that that can be placed in continuous annular contact with an upper edge  62  of the support housing  12 . This continuous annular contact can maximize surface area contact between the spring bushing—pivot arm—support housing assembly, which can provide increased friction damping of the pivot arm during use. Alternatively, in other embodiments, contact between the upper surface  56  and lower edge  58  and/or contact between lower surface  60  and upper edge  62  may not be continuous. 
     A flange  64  extends about a periphery of the spring bushing  54 . The flange  64  has inner surfaces  66  and  68  configured to extend over an outer surface  70  of the support housing  12  and an outer surface  72  of the pivot arm  14 , respectively, e.g., to provide a labyrinth-type seal between the pivot arm and the support housing. This seal can inhibit passage of foreign agents, e.g., dirt, oil, etc. into the spring cavity, which can affect the tensioner&#39;s operation. In some embodiments, the spring bushing may not include a flange or the flange may extend over only one of the outer surfaces  70  or  72 . 
     As noted above, round wire spring  18  biases the pivot arm  14  toward an unloaded position during use. Referring to  FIGS. 3 and 4 , to operatively connect the round wire spring  18  to each of the support housing  12  and the pivot arm  14 , slots  75  and  77  are provided. As shown, the slots  75  and  77  are L-shaped, however, any suitable shape can be used. Referring to  FIGS. 1A and 3 , the pivot arm  14  includes slot  77  that is sized to receive an inwardly facing end  78  of round wire spring  18 . In the illustrated embodiment, slot  77  extends only partially into sleeve  44  and through upper wall  46  at a location adjacent opening  74  ( FIG. 2 ). Referring now to  FIGS. 1A and 4 , the support housing  12  includes slot  75  extending through outer wall  28  that is sized to receive an outwardly facing end  80  of round wire spring  18 . The slot  75  is located near base  26  at a location spaced-apart from the upper edge  62  of the support housing  12 . In some cases, slot  75  extends only partially through outer wall  28 . 
     With the spring operatively connected to the pivot arm  14  and the support housing  12 , biasing force can be applied to the pivot arm merely by rotating one of the pivot arm and support housing relative to the other. Referring to  FIGS. 5A-5C , the support housing  12  and the pivot arm  14  each include cooperating stops  96  and  98 , respectively. Stop  96  extends upwardly from an upper surface  100  of support mount  102  and includes a relatively flat surface region  104 , a relatively angled surface region  106  and a stop surface  108  capable of engaging a stop surface  110  of stop  98 . Stop  98  also includes a relatively flat surface region  112  and a relatively angled surface region  114 . Referring particularly to  FIGS. 5A and 5B , the angled surface regions  106  and  114  of the stops  96  and  98  cooperate to allow stop  98  to slide along the flat surface region  104  of stop  96  during rotation. Referring particularly to  FIG. 5C , once stop surface  110  of stop  98  passes stop surface  108  of stop  96 , the stop surfaces engage to inhibit counter-rotation due to the biasing force, thus placing the pivot arm  14  in the unloaded position. 
     Referring back to  FIGS. 1 and 2 , the assembly is clamped or compressed together by an axial compression force using an armplate  82  (e.g., formed of spring steel) and plate bushing  84  (e.g., formed of plastic). The plate bushing  84  is sized to fit within a seating portion  86  of the pivot arm  14 . A raised rim  88  extends about the seating portion  86  to align the plate bushing once seated within the seating portion. As can be seen, the plate bushing  84  has an inner surface  88  that is spaced-apart from an outer surface  90  of the alignment member  30  forming a gap  92  therebetween. Referring particularly to  FIG. 1 , during radially riveting the armplate  82  to the alignment member  30 , inner edge  94  of the armplate is elastically deflected into gap  92  formed between inner surface  89  and outer surface  90 . This elastic deflection biases the assembly together thereby affecting sliding friction between the rotational and stationary parts of the tensioner  10  and serves to align the pivot arm  14  during use. Using an armplate and plate bushing to provide an axial clamping force is described in greater detail in U.S. Pat. No. 6,206,797, the details of which are incorporated by reference as if fully set forth herein. 
     As noted above, referring now to  FIGS. 1 and 1A , the height H (e.g., greater than 41 mm, such as about 42.2 mm) of the spring cavity  16  is greater than the unloaded height h (e.g., less than about 42.2 mm, such as about 41 mm) of the round wire spring  18 . As a result, no axial force is transmitted to the round wire spring  18  due to the axial compression force applied by the armplate  82 , nor does the axial compression force have to overcome any axial spring force applied by the spring to bias the assembly together. As such, the round wire spring  18  is effectively isolated from the axial compression force applied by the armplate  82 . Also, in some embodiments, because H of the spring cavity  16  is greater than h of the round wire spring  18 , an axial compression force need not be applied to maintain the pivot arm&#39;s spring biased, unloaded position as there is no axial spring force applied to the pivot arm that would cause the pivot arm to disengage the support housing  12 . Further, use of a round wire spring  18  can, in some cases, provide packaging benefits, such as in cases where it is difficult to package a flat wire spring. 
     A number of detailed embodiments have been described. Nevertheless, it will be understood that various modifications may be made. For example, while an armplate and plate bushing clamping arrangement has been described other suitable compression devices may be used, such as a Belleville or wave spring. Accordingly, other embodiments are within the scope of the following claims.