This invention relates to a variable-speed pulley and clutch adapted for use in snowmobiles and other small vehicles. Such pulleys are connected to the engine shaft and may operate at high speeds which subject the rotating parts to high centrifugal forces. The parts must be designed and constructed to withstand high centrifugal forces, and the pulley must be smooth and reliable in its response to operator-controlled changes in the engine shaft speed and to variations in operating conditions. The present invention relates especially to pulleys of the type in which centrifugal weights between the movable pulley flange and a reaction cone connected to the fixed pulley flange force the flange together and provide torque drive between the cone and the movable flange.
In accordance with the present invention, the fixed pulley flange is mounted on a pulley hub which has a cylindrical primary bearing surface at the opposite side of the pulley groove from the flange and has a hub extension of reduced diameter extending therebeyond and providing an elongated outboard bearing surface. The movable pulley flange is carried by a sleeve hub slidably and rotatably mounted on the pulley hub and its extension by means of an inboard bearing surface engaged with the primary bearing and an outboard bearing spaced therefrom and engaged with the bearing surface of the hub extension. The two hubs are counterbored at the inner diameter of the sleeve hub to define a spring chamber about the hub extension which contains a spring that acts on the hubs to urge the flanges apart. To prevent metal-to-metal contact between the two pulley flanges and consequent wear from relative rotation of such flanges, the two hubs are formed with axially-facing thrust faces, radially inward of the primary bearing sleeve and radially outward of the spring, which come together to limit closing movement of the pulley flanges.
The movable pulley flange is urged toward the fixed flange by a selected number of symmetrically disposed plate-like centrifugal weights mounted between the movable flange and a reaction cone fixed to the outer end of the hub extension. The weights are desirably molded plastic disks disposed in radial channels on the face of either the reaction cone or preferably the movable pulley flange, and frictionally engage a surface of revolution on the other of such cone and flange. The limit of opening movement of the flanges is determined by the engagement of the retracted centrifugal weights with the cone and flange, and in consequence the opening-limit position is fixed by the position of the reaction cone which is fixed on the hub extension. The spring applies a preload to the centrifugal weights so as to produce an initial frictional drive between the driven reaction cone and the rotatably mounted movable flange. The movable flange thus has a limited throw, between the closing-limit position determined by engagement of the thrust faces on the hubs and the opening-limit position determined by the position of the reaction cone.
Selective insertion of one or more spacers between the hub thrust faces will shift the closing limit position and thereby open the spacing between the flanges to suit wider belts. Corresponding selective insertion of spacers between the hub extension and the pulley hub, or otherwise in the connection between the reaction cone and the fixed pulley flange, will correspondingly shift the position of the opening limit of the movable flange, by moving the position of the reaction cone. Suitable selection of spacers will maintain the same or secure a different throw of the movable flange in response to action of the centrifugal weights.
Desirably, the hub extension is connected to the main hub by a threaded joint at which axially-facing faces on the two parts come together and which permits the insertion of the spacers between such faces so as to axially adjust the extension (and the reaction cone it carries) relative to the main hub and its fixed pulley flange. This joint is desirably at the end of the spring chamber and the spacers extend under the end of the spring. This has the effect of maintaining the same effective spring length, and the same preload on the centrifugal weights.
The pulley is adaptable to various applications, as by changing the number or mass of centrifugal weights, by shifting the opening limit or the closing limit or both limits of movement of the movable flange, by varying the shape of the reaction cone, etc. In one illustrated modification, the reaction cone is formed with an annular groove which restrains the centrifugal weights until a desired engine speed is attained.