Thin autotensioner

Abstract

An autotensioner comprises a torsion coil spring interposed between a base and a rocking arm, and a tubular bushing provided between an inside surface of the base and an outside surface of the rocking arm. The torsion coil spring pushes and biases the rocking arm toward the bushing, and brings the pushing direction substantially in coincidence with the axial load direction of the force, acting on a stepped bolt supporting the rocking arm, from a belt. When the belt tension becomes high, the arm axial center displaces slightly from the base axial center, an extremely large first damping force acts on the rocking arm. When the belt tension becomes low, the smaller second damping force acts on the rocking arm.

1 . A thin autotensioner comprising:
 a base that has a cup having an inside diameter;   a rocking arm that is rotatably supported by said base; and   a torsion coil spring that biases said arm in a predetermined direction, said torsion coil spring having an outside diameter larger than said inside diameter, said torsion coil spring being twisted in a direction in which said outside diameter is compressed so as to be housed inside said cup.   
   
   
       2 . A thin tensioner according to  claim 1 , wherein said torsion coil spring is engaged at one end with a first engagement part provided inside said base, and engaged at the other end with a second engagement part provided inside said rocking arm, and relative positions of said first engagement part and said second engagement part differing when said torsion coil spring engages with the first engagement part and the second engagement part and when said rocking arm is attached to said base. 
   
   
       3 . A thin tensioner according to  claim 1 , wherein an axial length of said torsion coil spring is shorter than said outside diameter. 
   
   
       4 . A thin tensioner according to  claim 1 , further comprising at least one friction member that is interposed between said cup and said rocking arm, and gives a frictional resistance to the rocking of said rocking arm. 
   
   
       5 . A thin tensioner according to  claim 4 , wherein said friction member is composed of a tubular part, and a flange projecting from a bottom of said tubular part to an inside direction of said cup and rocking arm, said friction member exhibiting an L-shape in cross-section. 
   
   
       6 . A method of assembly of a thin tensioner comprising:
 a first step of twisting a torsion spring coil having an outside diameter larger than an inside diameter of a cup to make the outside diameter smaller than said inside diameter; and   a second step of interposing said twisted torsion coil spring between said cup and rocking arm.   
   
   
       7 . A method of assembly of a thin tensioner comprising:
 a first step of engaging one end of a torsion coil spring having an outside diameter larger than an inside diameter of a cup, with said cup;   a second step of engaging another end of said torsion coil spring with a rocking arm;   a third step of rotating said rocking arm to twist said torsion coil spring and make the outside diameter smaller than said inside diameter;   a fourth step of bringing said rocking arm into proximity with said cup to compress said torsion coil spring and house it in said cup; and   a fifth step of rotatably fastening said rocking arm to said cup.   
   
   
       8 . A friction member in an autotensioner rotatably attaching a rocking arm to a base, characterized by being provided between said rocking arm and said base, and being formed by a material mainly comprised of a polyphenylene sulfide resin.