ASSEMBLED DRIVING BELT

Abstract: In a continuous variable transmission cross elements of a driving belt are provided with coupling means in the shape of at least one projection (6) at one main side (1) and a recess (7) at the other main side (2). In order to improve the transition of cross elements going in and out of the pulleys in the transmission the contour of the projections and of the corresponding recesses is approximated by a circular arc R.

Description: The invention relates to a driving belt having a substantially trapezoidal cross-section for use on V-shaped pulleys, said driving belt consisting of one or more endless carriers as well as of a number of cross elements butting against one another with their main sides and being movably provided on the carrier, said cross elements being tapered radially inwardly in order to enable the driving belt to curve, whereby the cross elements are in contact with one another at the location of a tilting zone, the zone where the taper blends with the main side and whereby the cross elements above the tilting zone are provided with coupling means in the shape of at least one projection at one main side and a complementory recess at the other main side, the projection and the recess both having mutual cooperating tapered contact surfaces. Such a driving belt is known form GB-A-2,013,116. The coupling means of the cross elements ensure a sufficient centring of the cross elements in the straight parts of the driving belt between the two pulleys. The coupling means become disengaged in the curved parts of the driving belt, i.e. at the location of the V-shaped pulleys, so that the mutual centring is lost there, which provides the cross elements with some freedom to locate themselves into a position which makes a good grip of the cross elements in the pulleys possible. This known driving belt is satisfactory but nevertheless it has a number of drawbacks. The coupling means namely become disengaged only with difficulty or only partly, as a result of which there will be an overlocating of the cross elements between the pulleys. Because of this overlocating, whereby the positioning of the cross element is not only determined by the pulley but also by the adjacent cross elements and the carriers, the grip of the cross elements will not be optimal. All this can be compensated by accepting a greater clearance between the coupling elements. This has a negative effect on the centring of the cross elements in the straight parts, however. In this known driving belt it will always be necessary to search for a compromise between overlocating and clearance, therefore. The purpose of the invention is to obviate the above drawbacks. For this purpose the driving belt according to the invention is characterized in that the projection has an upper edge, seen in cross-section in the lengthnoise direction of the belt, approximating an axe, the radius thereof having its origin at the location of a fulcrum point, which fulcrum point is situated substantially on the tilting zone that seperates the taper from the main side. As a result of the measure according to the invention the movement of the coupling means towards and away from one another is facilitated considerably, whereby sufficient clearance between the coupling means is produced in the curved parts to release the engagement and therewith the overlocating, whilst a much smaller clearance is present in the straight parts, as a result of which an optimum centring in the straight parts is obtained. According to a further elaboration of the invention the projection, seen in cross-section in the lengthnoise direction of the belt is conical. The flank of the conical projection, which can be approximated by the above-mentioned circular arcs because of the limited height of the projection, thereby preferably includes an angle with a normal on the main side of the cross element which is of a magnitude that corresponds with that of the acute angle between the plane of the main surface side the tapered surface of the cross element. The invention furthermore relates to a cross element such as can be used in the aforesaid driving belt according to the invention and is described in the claims. The invention will be explained hereinafter with reference to two embodiments and a drawing. In the drawing: fig 1 is an embodiment of a cross element with coupling means according to the invention; fig 2 is a side view of the cross element according to fig 1; fig 3 is another embodiment of a cross element with conical coupling means according to the invention; fig 4a is a side view of the cross element according to fig 3; fig 4b is a detail of a coupling means according to fig 4a, and fig 5 shows an assembled driving belt according to the invention. The assembled driving belt according to the invention consists of a carrier 27, which may e.g. consist of one or more metal bands, and cross elements 26 placed thereon. The assembled driving belt 23 is put on a primary pulley 21 with a primary shaft 24 and a secondary pulley 22 with a secondary shaft 25. The driving belt 23 describes two straight parts between the primary and the secondary V-shaped pulleys 21 and 22 respectively and describes curved parts at the location of the primary pulley 21 and at the location of the secondary pulley 22. The cross element 26 (figs 1 - 4) is provided with two main sides 1, 2 which come into contact with the main sides of adjacent cross elements in the assembled driving belt. The main side 1 is provided with a taper 3 extending radially inwardly. The plane of the main side 1 and the taper 3 include an acute angle. The transition from the part of the main side 1 parallel to the main side 2 to the taper 3 is formed by the roll-off zone or tilting zone 4. During curving of the driving belt the cross elements will keep in contact with one another at the location of said tilting zone 4. The cross element 26 is constructed trapezoidally with side flanks 8 for engagement with the V-shaped pulleys 21, 22. The cross element is provided with one (figs 1, 2) or more (figs 3, 4) recesses for accommodating the carrier 27, carriers 27 respectively. The cross element is furthermore provided with one (figs 3, 4) or more (figs 1, 2) coupling means. The coupling means comprise projections 6 on the main side 1 and corresponding recesses 7 in the main side 2. With successive cross elements the projections 6 engage in the recesses 7 of the abutting element, at least in a straight part of the driving belt, so that a mutual centring of the cross elements can take place. The coupling means are provided above the tilting zone so that the projection 6 of the cross element and the recess 7 of an adjacent cross element move away from each other as soon as the driving belt is curved. The centring effect is thereby released so that the cross elements will get some mutual freedom of movement and can locate themselves for a certain grip in the pulleys. The known coupling means according to the state of the art are satisfactory by themselves but do not function optimally. Usually the projections 6 and the recesses 7 do not become disengaged completely so that the adjacent cross elements keep influencing one another's positioning in the curved part. The cross element also wants to adjust its position to the pulley so that the cross element is overlocated in said curved part. This results in a grip of the cross element in the pulleys which is not optimal, causing loss of power and limitation of the life span. By itself the overlocating of the coupling means in the pulleys can be released by means of a greater clearance between the projection 6 and the recess 7, so that a mutual contact in the pulleys is no longer possible. On the other hand a greater clearance has a negative effect on the necessary centring effect in the straight part. The above drawbacks can be obviated according to the invention by giving the projection a contour which can at least partly be approximated by one or more circular arcs which are described by radii having their origin at the location of the tilting zone, the recess at least partly having a complementary contour. In the embodiment according to figs 1 and 2 the contour of the upper half of the projection 6 can at least partly be described by means of circular arcs having radii R, R′, R″ etc. which have their origin on the tilting zone 4. The lower half of the projection 6, i.e. that half which is located under the centre line of the projection which runs parallel to the tilting zone 4, is provided with a correspondingly mirrored contour. The top of the projection 6 is flattened. The recess 7 has a contour which is complementary to the contour of the projection. As a result of this measure it will be possible to keep the clearance between the projection 6 and the recess 7 very small, which results in an optimum centring effect in the straight part whilst on the other hand the overlocating in the curved part has been eliminated. In the embodiment of a cross element according to fig 3 and figs 4a, 4b the recess 7 and the projection 6 are conical. The upper half of the conical projection 6 can be approximated with circular arcs whose radii have their origin at the location of the tilting line, as the flanks of the conical contour must be described with a limited segment of the circular arcs only, because of the limited height of the conical projection. The recess 7 again has a complementary contour. The angle β which the flank of the conical projection 6 includes with a normal on the main side 1 is as a good approximation of the circular arcs preferably of a magnitude which corresponds with that of the acute angle α between the main side 1 and the taper 3. As the tilting zone generally does not describe a clearly defined angle but more or less a roll-off area the angle β is preferably a few degrees greater than the angle α in order to compensate the effect of said roll-off area. It will be apparent that the invention has not been described exhaustively with reference to the embodiments and that within the scope of the invention various modifications will be apparent to the person skilled in the art. Thus the part of the projection according to figs 1 and 2 or 3 and 4 which lies under the centre line of said projection 6 which runs parallel to the tilting line may e.g. be omitted, whilst the illustrated contour of the recess is maintained. Also it will be possible for the recess and the projection to have greatly different contours which are only complementary over a limited functional area.

Claims: 1. A driving belt having a substantially trapezoidal cross-section for use on V-shaped pulleys, said driving belt consisting of one or more endless carriers (27) as well as of a number of cross elements (26) butting against one another with their main sides (1, 2) and being movably provided on the carrier (27), said cross elements (26) being tapered radially inwardly (at 3) in order to enable the driving belt to curve, whereby the cross elements (26) are in contact with one another at the location of a tilting zone (4), the zone (4) where the taper blends with the main side (1) and whereby the cross elements (26) above the tilting zone (4) are provided with coupling means (6, 7) in the shape of at least one projection (6) at one main side (1) and a complementary recess (7) at the other main side (2), the projection (6) and the recess (7) both having mutual cooperating tapered contact surfaces, characterised in that the projection has an upper edge, seen in cross-section in the lengthwise direction of the belt, approximating an arc, the radius thereof having its origin at the ation of a fulcrum point, which fulcrum point is situated substantially on tilting zone (4) that separates the taper (3) from the main side (1). 2. A driving belt according to claim 1, characterized in that the projection, seen in cross-section in the lengthwise direction of the belt , is conical. 3. A driving belt according to claim 1 or 2, characterised in that the flank of the projection includes an angle β with a normal on the main side (1) which is of a magnitude that corresponds with that of the acute angle between the plane of the main side (1) and the taper (3). 4. A driving belt according to claim 3, characterised in that the angle β which the flank of the projection includes with a normal on the main side (1) is a few degrees greater than the acute angle between the main side (1) and the taper (3). 5. Cross element (26) suited for application in a driving belt according to anyone of the proceeding claims, characterised in that it has all the features of the cross element as specified in claim 1.

Inventors: VAN LITH, JOHANNES HENDRIKUS
Applicants: VAN DOORNE'S TRANSMISSIE B.V.
Application year: 1989
Main classification: F16G5
IPC codes: F16G5