Variable effective diameter pulley

Details Variable effective diameter pulley Variable effective diameter pulley

1996-02-05

1998-01-20

Schoeppel, Roger J.

Endless belt power transmission systems or components

Pulley with belt-receiving groove formed by drive faces on...

474 87, 474141, 474148, F16H 5552

Patent

active

057096244

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION OF INVENTION

This invention relates to a drive arrangement including an endless flexible drive element such as a belt, and a pulley with which the flexible drive element co-operates and whose effective diameter is variable in order to achieve a variable transmission ratio between the pulley and another pulley or pulleys with which the flexible drive element co-operates.
More particularly, the invention relates to a drive arrangement including a pulley which comprises a pair of sheave members rotatable about an axis and supported for movement relative to one another in the direction along said axis, the sheave members having generally frusto-conical driving surfaces facing one another to define a generally V-section annular groove therebetween; and a drive ring disposed between the sheave members and having an external circumferential surface engageable by the flexible drive element and side surfaces engaging said facing generally frusto-conical driving surfaces of the sheave members, the drive ring being constrained between the sheave members and being able to assume an eccentric position relative thereto when permitted by the dimensions of the groove defined between the sheave members, in accordance with their relative axial position. A drive arrangement incorporating such a pulley of variable effective diameter will be hereinafter referred to as a drive arrangement of the kind specified.
As the distance between the driving surfaces of the sheave members increases (i.e. the V-section groove therebetween becomes wider) the drive ring is able to assume an increasingly eccentric position relative to the sheave members, and is forced to do so by the tension of the flexible drive element entrained around it. It may be the tension in the drive element which causes the drive ring to assume an eccentric position and force the sheave members apart. As the speed at which the drive ring is driven by the sheave members is dependent on the effective diameter at which they are engaged by the drive ring, the effective diameter of the pulley is decreased as the eccentricity of the drive ring increases.
A drive arrangement of the kind specified may comprise the auxiliary drive system of an internal combustion engine for a motor vehicle. It is usual to arrange for the auxiliary, which may comprise one or more of the following, namely an alternator, water pump, cooling fan, power steering pump, air conditioning pump, and so on, to be driven from the engine crankshaft by a belt. If a pulley of variable effective diameter is provided on the engine crankshaft, a variable transmission ratio may be provided between the crankshaft and the auxiliary so that the latter can be driven at a reasonably high speed when the engine is running slowly, and yet not be over-speeded when the engine is being operated at its maximum speed. A means for maintaining the required tension in the drive belt, or for causing a speed-dependent increase in belt tension, is, of course, additionally required in the drive arrangement.
One problem which can arise in a drive arrangement of the kind specified is that the drive ring may, instead of running stably in an eccentric position, be unstable in that the axis of rotation of the drive ring does not remain exactly parallel to the axis about which the sheave members rotate. The drive ring can tend to tilt or wobble, which leads to wear in the pulley. It is an object of the present invention to solve or at least reduce this problem in a drive arrangement of the kind specified.
According to the present invention, we provide a drive arrangement of the kind specified wherein there is provided stabilising means co-operating with the drive ring so as to maintain the axis of rotation of the drive ring parallel or substantially parallel to the axis of rotation of the sheave members.
Preferably the stabilising means engages a peripheral region of the drive ring, preferably said circumferential surface thereof engageable by the drive element.
Preferably the stabilising means comprises a stabilising rolle

REFERENCES:
patent: 2952167 (1960-09-01), Nelson
patent: 3590649 (1971-07-01), Fischer

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