Belt tensioner

[0001] The present application relates generally to belt tensioners and more particularly to a belt tensioner with a round wire spring.

[0002] 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.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0014] 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.

[0015] 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).

[0016] 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.

[0017] 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.

[0018] 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'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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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'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.

[0023] 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.