Endless belt power transmission systems or components – Pulley with belt-receiving groove formed by drive faces on... – Speed responsive
Patent
1994-05-19
1996-05-07
Schoeppel, Roger J.
Endless belt power transmission systems or components
Pulley with belt-receiving groove formed by drive faces on...
Speed responsive
74336B, F16H 5900
Patent
active
055140408
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a pulley located at the end of an engine-driven shaft, in which pairs of flyweights having a substantially cylindrical shape engage toothed racks in order to vary, under the influence of the centrifugal force, the winding diameter of the pulley around which is winded a trapezoidal belt. This pulley, called driving pulley, is part of a type of drive called variable-speed belt drive. In addition to the driving pulley described hereinafter, the drive comprises another pulley, called driven pulley, on which is winded the other end of the belt. The driven pulley is designed in a way that the winding diameter varies in reverse of the driving pulley, the belt having a fixed length. This type of drive is used particularly in vehicles such as snowmobiles, motorcycles, all-terrain vehicles or some small automobiles.
The object for varying the winding diameter of the pulleys is to have a diameter ratio allowing an important torque during the acceleration of the vehicle and a reasonable engine rotation speed at high speeds. If the engine rotation speed is low or if the load is high, the driving pulley has a small winding diameter and it increases as the engine rotation speed increases or as the load becomes smaller. On the other hand, the pulley has to reduce its winding diameter when the engine rotation speed decreases or if the required torque is increasing.
In a traditional type of variable-grooved pulley, flyweights sliding along smooth walls are used for allowing the winding diameter of the pulley to vary. The pulley usually has two flanges, one called fixed flange and the other called movable flange, which are mounted around a shaft. The axial movement of the movable flange is made by sets of flyweights which are resting against two inclined walls, the first being solid with the movable flange and the other being solid with an end member provided on the shaft, at the end opposed to the fixed flange.
When the shaft of the pulley is in rotation, it brings the fixed flange into rotation along with the end member. This end member transmits its rotation motion with the side walls of a guide located between the end member and the movable flange, to the flyweights which then move, with the side walls of the guide of the movable flange, the movable flange. Additionally, since they are rotated, the flyweights are subjected to centrifugal forces and, deplacing radially, take respectively contact on the two ramps of the movable and the end member. Because of their trapezoidal shape, they produce an axial push on the movable flange which then slides towards the fixed flange. For a given rotation speed of the pulley, an equilibrium is reached when the axial push is counter-balanced by a first axial return force, exerted by a return spring mounted between the movable flange and a shoulder of the shaft, and by a second return force which is the axial component of the pressure exerted by the belt. Following this equilibrium, the belt with a trapezoidal cross-section has a changing winding diameter taking a value more or less important according to the rotation speed of the pulley.
An example of a driving pulley of the type mentioned hereinabove is described in Canadian patent No. 1,212,559.
In dynamics, when the rotation speed is increasing, the centrifugal force on the flyweights is increasing proportionally. Their axial push on the ramps is also increasing and the equilibrium is shifted towards a closeness of the two flanges. The winding diameter is then increased. Additionally, when the rotation speed decreases, the axial push of the flyweights decreases and the equilibrium is shifted towards a distancing of the two flanges. The winding diameter is then decreased.
The movement of the movable flange being generated by the sliding of the flyweights along the contact walls, the axial push is modified by the friction between the flyweights and the contact walls. When the vehicle is in an accelerating phase, the friction is tending to reduce the axial push which becomes inferior to the desired val
REFERENCES:
patent: 3395587 (1968-08-01), Casini
patent: 3638744 (1972-02-01), Washizawa
patent: 3685366 (1972-08-01), Schupan
patent: 4800768 (1989-01-01), Kazuta
Powerbloc IBC Canada Inc.
Schoeppel Roger J.
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