GB2041116A

GB2041116A - A V-belt drive

Info

Publication number: GB2041116A
Application number: GB8000578A
Authority: GB
Original assignee: Volvo Car BV
Current assignee: Volvo Car BV
Priority date: 1979-01-09
Filing date: 1980-01-08
Publication date: 1980-09-03
Also published as: IT1129056B; NL7900152A; IT8067021A0; DE3000264A1; FR2446425A1; JPS5594051A

Abstract

A V-belt drive particularly for a variable transmission has a driven pulley and a driving pulley. To ensure that the maximum clamping force in the belt, as it passes over each pulley, occurs at a point intermediate the points at which the belt enters and leaves the pulley, the two halves 2, 3 of each pulley are arranged on non-coaxial axes H. K. Each pulley has a fixed half 2, on a shaft 4 which has an axis H, and an axially moveable half 3 rotatable about an axis K which is set at an angle to axis H. This causes the minimum spacing between the pulley halves 2 and 3 to occur at the location where the belt is fully engaged between the pulley halves 2 and 3. <IMAGE>

Description

SPECIFICATION A V-belt drive The invention relates to a V-belt drive com prising a driving pulley and a driven pulley over which a V-belt extends.

Such V-belts are known in many embodi ments, including fixed as well as variable transmissions, and using different materials for the belts such as rubber, canvas and metal.

All these drives have the disadvantage, that the belt is clamped most firmly when running into and out of the pulleys. This results from the fact that the pulleys are eccentrically loaded by the belt and therefore they bend. In displaceable pulleys the tolerance is removed in a number of cases so that the bending of the pulleys is apparently increased.

The above factors have a disadvantageous influence on the duration of life of the belts.

More rigid pulleys and less tolerance can reduce but not remove this disadvantage.

An object of this invention is to alleviate the above disadvantage and according to the invention this is achieved, by arranging that the two halves of at least one of the pulleys are so positioned with respect to one another that at the locations where the belt runs in and out of the pulleys, the distance apart of the pulley halves is greater than in the region where the belt extends fully between the pulley halves.

Preferably the axes of said two halves of at least one of pulleys intersect at an obtuse angle.

In a V-belt drive for a variable driving mechanism, in which the halves of one or both pulleys are displaceable in axial direction with respect to one another, but cannot rotate with respect to one another the invention is preferably applied such that the bearing points of the displaceable pulley halves are eccentrically positioned.

The invention will further be elucidated on the basis of the drawing, in which as example an embodiment of a V-belt drive according to the invention is indicated. In the drawing: Figure 1 shows diagrammatically the clamping force in a belt running between the two halves of a conventional pulley; Figure 2a is a schematic axial cross section through a pair of pulleys of a variable driving mechanism in which is embodied the invention; Figure 2b shows, on smaller scale, a schematic representation of the positions of the pairs of pulleys; Figure 3 shows a scheme of the clamping force in the belt running between the two halves of each pulley indicated in Fig. 2a and 2b; and Figures 4a--d shows a schematic diagram for the elucidation of the location of the theoretical connection point of the forces on the pulleys in various positions of the belt.

In Fig. 1 a belt 1 is indicated running between two halves of a pulley which are not indicated, but of which the common axis coincides with a line H which passes through the intersection point of the chain dotted lines and is perpendicular to the plane of the drawing. As appears from this drawing, the clamping force which is indicated by the successive arrows A, is at its maximum when running into and out of the pulley halves.

By tilting the axis of rotation of the two halves of each pulley somewhat with respect to one another a completely different distribution of the clamping force is reached in the belt. The greatest clamping force can be found somewhere between the points where the belt runs into and out of the pulley.

Fig. 2a, shows the case of a variable driving mechanism, an axial cross if a pair of pulleys fixed by a belt 1. Each pulley has two pulley halves 2 and 3 which are displaceable relatively to each other in an axial direction. Each pulley half 2 is secured to a shaft 4 which has a horizontally extending axis H, i.e.

the same axis as is perpendicular to the place of the drawing in Fig. 1 and 3.

The pulley halves 3 and shafts 4 cooperate in such a way, that the the pulleys 3 cannot be displaced in axial direction along the shaft 4, but cannot rotate with respect to the axially stationary pulley halves 2.

Each shaft 4 is supported by a bearing 6b in a housing 5 and a sleeve 8 connected to the movable pulley half 3 is also supported by bearings 7 in the housing 5, but the axes of the bores in which the bearings 7 are included, are at an angle to the axes of the bores in which the bearings 6 are provided, so that the sleeves 8 and thereby the displaceable pulley halves 3 have an axis K tilted relatively to axis H. In Fig. 2a the movable pulley half 3 of each pulley is drawn at the same side for clarity. In practice the movable pulleys 3 would by provided at opposite sides.

Fig. 2b shows the positions of the axes again schematically.

The distribution of the clamping forces B indicated in Fig. 3 is clearly different from the clamping forces A indicated in Fig. 1, especially in that the maximum is no longer at the points where the belts run in and out. So, it is no longer the case, that the two peak loads are provided which are reached in rather irregular and often abrupt manner, but only one peak load occurs increasing in regular way and decreasing again. This is advantageous for the duration of life of the belt.

It is remarked, that the same favourable results are obtained whether the invention is applied in fixed or variable transmissions and also independently of whether the transmission means consist of rubber or canvas belts or metal belts.

Displaceable belts of variable driving mechanisms bend under certain circumstances such that the undesired effect of the highest belt load, when this belt runs in and out of the pulleys is reinforced by the removal of the tolerance. This, however, strongly depends on the location of the bearings of the pulleys, as will be further elucidated on the basis of the Fig. 4and.

In Fig. 4a-d an axial force D and a radial force E is executed on the pulley half 3 by the belt. The axial force is about four times the radial force.

When the resultant F of these forces intersects the axis of the pulley at a point S at a distance from the centre of gravity Z of the stationary pulley half, greater than the distance from the bearing 8 (Fig. 2a) of the pulley to said centre of gravity, the tolerance is, indeed, removed such that the pulley is more open at the outer side.

If, however, the resultant E intersects the axis of the pulley at a point positioned between the centre of gravity Z of the stationary pulley half and the bearing of the pulley, the pulley will tilt in the other direction as the result of the tolerance. This means, that the mutual distance of the pulleys will become smaller at the outer side, whereas the mutual distance at the side facing the other pair of pulleys will become greater. This also means that the effect aimed at is reached therewith, as only small differences are concerned, certainly in transmissions with steel belts.

In this arrangement it is important, that the location of the connection of the resultant of the forces on the pulley, only varies a little.

In a particular pair of pulleys the line of activities of the axial force executed by the belt on the pulley, will be almost constant.

This is effected, as appears from Fig. 4c and d, because when the diameter R of the belt increases the spanned arc a will also increase.

The above means that the effect aimed at cannot only be reached by having the axes of the pulley halves make an angle with one another, but it can also be reached by displacing the bearings of the pulleys from one another.

Claims

1. V-belt drive comprising a driving pulley and a driven pulley over which a V-belt extends, characterized in that the two halves of at least one of the pulleys are so positioned with respect to one another that, at the locations where the belt runs in and out of the pulleys, the distance apart of the pulley halves is greater than in the region where the belt extends fully between the pulley halves.

2. V-belt drive according to claim 1, characterized in that the axes of said two halves of the pulley intersect at an obtuse angle.

3. V-belt drive according to claim 1, characterized in that the bearing points on the common axis of the halves of a pulley are so far away from each other that, under the influence of the force exerted by the belt on the pulleys, the tolerances are taken up so that the spacing of the pulley halves at the sides inclined towards each other is greater than at the sides inclined away from each other.

4. V-belt drive according to any of claims 1 or 3, applied in a variable driving mechanism, in which the halves of a pulley are displaceable in axial direction with respect to one another but cannot rotate with respect to one another, characterized in that the bearing points of the displaceable pulley halves are eccentrically positioned.

5. V-belt drive according to claim 4, applied to a variable transmission system.

6. V-belt drive according to any of the preceding claims and in which both pulleys are arranged with their perspective halves positioned as set out in claim 1.

7. V-belt drive substantially as hereinbefore particularly described and as illustrated in Figs. 2 to 4 of the accompanying drawings.