WO2014102358A1

WO2014102358A1 - Transverse segment for a drive belt with a carrier ring and multiple transverse segments

Info

Publication number: WO2014102358A1
Application number: PCT/EP2013/078097
Authority: WO
Inventors: Guillaume Gerard Hubertus Rompen; Lucas Hendricus Robertus Maria Prinsen
Original assignee: Robert Bosch Gmbh
Priority date: 2012-12-28
Filing date: 2013-12-29
Publication date: 2014-07-03
Also published as: NL1039981C2

Abstract

Transverse segment for a drive belt for a continuous variable transmission provided with two cut-outs that are each bounded in one direction by a radially outwardly facing saddle surface (42) of the transverse segment, which saddle surface (42) is provided with a convexly curved contour (NC), whereof a highest, most radially outward located point (HP2) is located outside a geometric midpoint (MP) of the contour (NC) and whereof a longer side relative to the said highest point (HP2) is curved less sharply than the opposite, i.e. shorter side of that contour (NC).

Description

TRANSVERSE SEGMENT FOR A DRIVE BELT WITH A CARRIER RING AND MULTIPLE TRANSVERSE SEGMENTS

The present disclosure relates to a transverse segment for a drive belt for a continuously variable transmission, in particular for motor vehicles, as defined in the preamble of the claim 1 hereinafter.

Such a transverse segment and the drive belt incorporating it are well-known and are, for instance, described in the European patent applications EP-A-0 626 526 and EP-A-1 566 567. The known drive belt is composed of a plurality of steel transverse segments and two endless, i.e. ring-shaped carriers, each extending through a recess provided on either lateral side of the segments such that these segments are supported and guided by the carrier ring. Typically the carrier rings are also made of steel and are each composed of a number of individual continuous bands that are narrowly fitted, one around the other. The transverse segments are neither fixed to one another nor to the carrier rings, such that they can move relative to the carrier rings at least along the circumference, i.e. the length thereof. In the drive belt, adjacent transverse segments abut one another through their respective front and back main surfaces, which main surfaces face, at least predominantly, in the said circumferential direction. The known drive belt is operated in a lubricated or oiled environment, both to reduce belt-internal friction losses and to cool the belt and the pulleys of the transmission.

The known transverse segment is provided with a friction surface on either axial, i.e. lateral side thereof. By means of these friction surfaces the transverse segment arrives in (frictional) contact with a driving pulley and a driven pulley of the transmission such that a rotation of the driving pulley can be transferred to the driven pulley via the likewise rotating drive belt. The known transverse segment is further provided with a stud on its front main surface and a hole on its back main surface. In the drive belt the stud of a first transverse segment is inserted in the hole of a second, adjacent transverse segment. As a result, the consecutive transverse segments in the drive belt mutually align each other in a plane that is oriented parallel with the said main surfaces thereof, i.e. perpendicular to the said circumferential direction.

During operation of the drive belt, a relative movement may exist between the transverse segments and the carrier rings the said circumferential direction thereof. Furthermore, the transverse segments that are urged radially outwards by the pulleys during operation are contained in that direction by the carrier rings. Thus a transverse segment arrives into contact with the carrier rings via the radial inner surfaces of the recesses thereof that contain the carrier rings. These latter surfaces are referred to in the art as the saddle surfaces of the transverse segments.

A width-wise shape or contour of the saddle surfaces is known to be shaped slightly convex to promote the preferred alignment of a respective carrier ring relative to (the axial width of) a respective saddle surface. In this latter respect it is known that the carrier ring tends to centre itself on the highest, i.e. most radially outward point of the saddle surface during operation. This highest point of the saddle surface does not necessarily lie in the middle thereof. In some specific transmission designs it may be considered more favourable to minimise a contact between the carrier ring and the transverse segments in the axial direction, in which case said highest point is located more towards the lateral side of the transverse segment, an example whereof is provided by EP-A-1 566 567. However, the opposite design, wherein a contact between the axial side of the carrier ring and the pulleys is preferred to be avoided and wherein the highest point of the width-wise contour of the saddle surface is offset relative to the said middle thereof and away from the lateral side of the transverse segment, is also suggested in the art.

It is presently proposed to take the axial or width-wise offset of the highest point of the saddle surface into consideration in the further design of that saddle surface. In particular, it is proposed to define the width-wise contour of the saddle surface such that both ends thereof lie at essentially the same height, i.e. at essentially the same radial distance below the highest point of such contour. In other words, the width- wise contour of the saddle surface is steeper at a shorter side of contour relative to the highest point thereof the contour as compared to the other, longer side thereof. Preferably, both such short(-er) side and long(-er) side of the width-wise contour of the saddle surface are convexly curved according to a radius or (a plurality of) radii of curvature that are smaller, at least on average, on the short side of the contour as compared to the long side thereof.

This latter, novel design of the transverse segment and of the saddle surfaces in particular, has the advantage that the carrier rings are more evenly loaded during operation. Moreover, by more evenly loading the carrier rings, the maximum stress level experienced by the carrier rings during operation is favourably reduced.

The novel transverse segment will now be elucidated further with reference to the attached drawing figures, whereof: figure 1 provides a schematic perspective view of the continuously variable transmission with a drive belt running over two pulleys, which drive belt includes an endless carrier and a number of transverse segments;

figure 2 shows a cross section of the known drive belt, which cross-section is oriented in the circumference direction of the belt;

figure 3 provides a width-wise oriented view of a transverse segment of the known drive belt;

figure 4 provides a close-up of a saddle surface of the known transverse segment, schematically illustrating a convexly curved contour thereof;

figure 5 is another schematic representation of the saddle surface contour of the known transverse segment; and

figure 6 is a schematic representation of the saddle surface contour similar to figure 5, however, depicting the saddle surface shaped in accordance with the present disclosure.

In the drawing figures equal reference signs indicate equal or similar structures and/or parts.

The schematic view of a continuously variable transmission in Fig. 1 shows a drive belt 3 that runs over two pulleys 1, 2 and that includes a flexible endless carrier or carrier ring 31 and an essentially contiguous row of transverse segments 32 that are mounted on and arranged along the circumference of the carrier ring 31. In the illustrated configuration of the transmission, the upper pulley 1 will rotate more quickly than the lower pulley 2. By changing the distance between the two conical sheaves 4, 5 of the pulleys 1, 2, the so-called running radius R of the drive belt 3 on each pulley 1, 2 can be changed in a mutually coordinated manner and, as a result, the (transmission) ratio between the rotational speeds of the two pulleys 1, 2 can be varied.

In Fig. 2, the drive belt 3 is shown in a cross section thereof facing in the circumference or length direction L (fig. 3) of the belt 3, i.e. facing in a direction perpendicular to the axial or width direction W and the radial or height direction H thereof. This Fig. 2 shows the presence of two carrier rings 31, shown in cross- section, that carry and guide the transverse segments 32 of the drive belt 3, whereof one transverse segment 32 is shown in front elevation.

The transverse segments 32 and the carrier rings 31 of the drive belt 3 are typically made of metal, usually a steel alloy. The transverse segments 32 take-up a clamping force exerted between the sheaves 4, 5 of each pulley 1, 2 via contact faces 37 thereof, one such contact face 37 being provided at either axial side of the transverse segment 32. These contact faces 37 are mutually diverging in radial outward direction such that an acute angle is defined there between that is denoted the contact angle O_c of the drive belt 3, which contact angle essentially matches a V- angle defined between the two sheaves 4, 5 of each pulley 1, 2, which latter angle is denoted the pulley angle Φ_Ρ.

The transverse segments 32 are able to move, i.e. can slide along the carrier rings 31 in the circumference direction L, so that a torque can be transmitted between the transmission pulleys 1, 2 by the transverse segments 32 pressing against one another and pushing each other forward along the carrier rings 31 in a direction of rotation of the drive belt 3 and the pulleys 1, 2. In the exemplary embodiment of this Fig. 2, the carrier rings 31 are composed of five individual endless bands each, which endless bands are mutually concentrically nested to form the carrier ring 31. In practice, the carrier rings 31 often comprise more than five endless bands, e.g. nine or twelve or possible even more.

The transverse segment 32 of the drive belt 3, which is also shown in a side elevation in Fig. 3, is provided with two cut-outs 33 located opposite one another, which cut-outs 33 each open towards a respective axial side of the transverse segment 32 and each accommodate (a small section of) a respective carrier ring 31. A first or base portion 34 of the transverse segment 32 thus extends radially inwards from the carrier rings 31, a second or middle portion 35 of the transverse segment 32 is situated in between the carrier rings 31 and a third or top portion 36 of the transverse segment 32 extends radially outwards from the carrier rings 31. The radially inner side of each cut-out 33 is delimited by a so-called saddle surface 42 of the base portion 34 of the transverse segment 32, which saddle surface 42 faces radially outwards, generally in the direction of the top portion 36 of the transverse segment 32, and contacts the inside of an carrier ring 31.

A first or rear surface 38 of the two main body surfaces 38, 39 of transverse segment 32 that face in mutually opposite circumference directions L, is essentially flat. The other or front main body surface 39 of the transverse segment 32 is provided with a so-called rocking edge 18 that forms, in the radial direction H, the transition between an upper part of the front surface 39, extending essentially in parallel with its rear surface 38, and a lower part thereof that is slanted such that it extends towards the rear surface 38. In Fig. 2 the rocking edge 18 is indicated only schematically by way of a single line, however, in practice the rocking edge 18 is mostly provided in the shape of a convexly curved transition surface. The said upper part of the transverse segment 32 is thus provided with an essentially constant dimension between the main body surfaces 38, 39, i.e. as seen in the circumference direction L, which dimension is typically referred to as the thickness of the transverse segment 32.

It is noted that in order to realise a favourable contact between the transverse segments 32 and the carrier rings 31, in particular to promote the preferred alignment of a respective carrier ring 31 relative to the (width of) respective saddle surfaces 42 of the transverse segments 32, these saddle surfaces 42 are typically curved at least slightly convexly and at least in the axial direction. In this respect, it is known that during operation of the drive belt 3 the carrier rings 31 tend to be centred on the highest point of the convexly curved saddle surfaces 42. The convexity of the saddle surfaces 42 that is applied in practice is, however, so small that it cannot be discerned on the scale of Fig. 2.

Fig. 4 provides a schematically drawn enlargement of a detail of the transverse segment 32, including the saddle surface 42 thereof. Even at the scale of Fig. 4, a radius of curvature Rs of the saddle surface 42 has been exaggerated by about 5 times to be able to illustrate this design feature. To give a numeric example; in a practical design of the drive belt 3, the saddle surface 42 may extend for about 10 mm in the width direction W and is convexly curved at about 200 mm radius Rs. This means that a highest point HP1 of the saddle surface 42 lies about 62 microns above (i.e. radially outward from) a left side endpoint LE and/or a right side endpoint RE of the saddle surface 42. Still, it is known from practice that even this minimal convexity of the saddle surface 42 supports and benefits the operation, in particular the longevity of the drive belt 3.

It is noted that the left and right side endpoints LE, RE of the saddle surface 42 correspond to locations were a local radius of curvature of the contour of the transverse segment 32 changes sharply between the relatively large radius of curvature Rs of the saddle surface 42 to a much smaller radius of curvature that defines the transition between the saddle surface 42 and the middle portion 36 of the transverse segment 32 or between the saddle surface 42 and a respective contact face 37 of the transverse segment 32. Typically, such change of the local radius of curvature at the endpoints LE, RE of the saddle surface 42 is by two orders of magnitude, for example from the said 200 mm radius Rs to a value close to 1 mm. Thus, the saddle surface 42 of the transverse segment 32 is well-defined and the size and shape thereof, including the location of the said endpoints LE, RE thereof can be accurately determined with high certainty.

In Fig. 5 the arc-shaped contour of the saddle surface 42 is indicated by the dashed contour line SC. The dashed contour line SC extends symmetrically between the respective left side and right side endpoints LE, RE thereof, such that a geometric midpoint MP of the dashed contour line SC, which corresponds with the middle of the saddle surface 42, also represents the highest point HP1 of this contour SC, i.e. of the saddle surface 42. With such symmetric contour, the carrier ring 31 will be urged towards such midpoint MP of to the saddle surface 42 during operation of the drive belt 3. It is, however, also known to provide the saddle surface 42 with an asymmetric contour, which asymmetric contour is indicated by the solid contour line AC in Fig. 5. The highest point HP2 of this solid contour line AC lies -in this example- to the right of the midpoint MP of the saddle surface 42, which particular asymmetric contour of the saddle surface 42 may be applied to minimise a contact between the carrier ring 31 and the transverse segment 32, since the carrier ring 31 is thereby urged towards the respective axial side of the transverse segment 32 during operation.

It can be seen in Fig. 5 that the said asymmetric contour of the saddle surface 42 (as represented by the solid contour line AC) is not only asymmetrical in terms of the highest point HP2 thereof being offset in the width direction W relative to the midpoint of the MP of the saddle surface 42, but also in terms of the location of the left side endpoint LE relative to that of the right side endpoints RE in the height direction H. In particular it can be seen that, when the saddle surface 42 is shaped according to the asymmetric contour line AC, the left side endpoint LE of the saddle surface 42 is located radially inward from the right side endpoint RE thereof. Again, even though such height difference between these end points LE and RE of the saddle surface 42 will be minimal in absolute terms and, for example, amounts to only 10 microns or so, it may still negatively affect the optimal functioning of the drive belt 3. In particular, a tensile stress in the carrier ring 31 may not be optimally distributed therein during operation, such that the fatigue strength of the carrier ring 31 may also be suboptimal.

It is presently proposed to improve on the known design of the transverse segment 32 by defining the saddle surface(s) 42 thereof according to a new contour line NC that is asymmetric not only in terms of the off-centre location of the highest point HP2 thereof, but also in terms of the radius or radii of curvature thereof, respectively to the left side Rsl and to the right side Rsr of such highest point HP2. In particular, the radius or radii of curvature Rsr on the short(-er) side of the new contour line NC are designed to be smaller than the radius or radii of curvature Rsl on the long(-er) side of the new contour line NC.

In Fig. 6 an example of such new contour line NC of the saddle surface 42 is indicated by the solid line and is shown in comparison with the known, asymmetric contour line AC that is indicated by the dashed line. In this example, the radius of curvature Rsl of the longer, left side of the new contour line NC is left unchanged relative to the radius of curvature Rs of the known, asymmetric contour line AC, but the radius of curvature Rsr of the shorter, right side of the new contour line NC is much smaller than such longer side radius of curvature Rsl. In this latter, novel design of the saddle surface 42, the tensile stress occurring in the carrier ring 31 during operation of the drive belt 3, is more favourably, in particular more equally distributed therein, at least in comparison with the known design of the saddle surface 42.

In particular in this example of Fig. 6, these radii of curvature Rsl, Rsr of the new contour line NC of the saddle surface 42 are (mutually) chosen to completely remove any difference in height H between the left side endpoint LE and the right side endpoint RE of the saddle surface 42, as indicated by the horizontal dotted line HDL in Fig. 6. This design of Fig. 6 is considered to represent the most preferred embodiment of the new contour line NC, at least in terms of the (improvement in) resulting fatigue strength of the endless carrier 31.

It is noted that Fig. 6 (just like Figs. 4 & 5) is not drawn to scale and that in reality the difference between the left side radius of curvature Rsl and the right side radius of curvature Rsr of the saddle surface 42, according to the new contour line NC and relative to the highest point HP2 thereof, is much smaller. In fact, the said difference will normally be so small that it cannot be discerned with the naked eye, not even on the enlarged scale of the present drawing figures.

The present disclosure, in addition to the entirety of the preceding description and all details of the accompanying figures, also concerns and includes all the features of the appended set of claims. Bracketed references in the claims do not limit the scope thereof, but are merely provided as non-binding examples of the respective features. The claimed features can be applied separately in a given product or a given process, as the case may be, but it is also possible to apply any combination of two or more of such features therein. The invention(s) represented by the present disclosure is (are) not limited to the embodiments and/or the examples that are explicitly mentioned herein, but also encompasses amendments, modifications and practical applications thereof, in particular those that lie within reach of the person skilled in the relevant art.

Claims

1. Transverse segment (32) for a drive belt (3) for a continuously variable transmission, which drive belt (3) comprises at least two carrier rings (31) and a number of these transverse elements (33) that are mutually arranged slideably on the carrier rings (31), in which transverse segment (32) at least two recesses (33) are provided for the accommodation of at least one of the carrier rings (31) each, which recesses (33) extend over the thickness of the transverse segment (32) between a front main body surface (39) and a rear main body surface (38) thereof and which recesses (33) are delimited in one direction, being a radially inward direction relative to the drive belt (3), by radially outward facing saddle surfaces (42) of the transverse segment (32) that support a radial inside of the carrier rings (31) and that are provided with a convex curvature in the axial direction of the drive belt (3), a most radially outwardly located highest point (HP2) on the saddle surfaces (42) being located outside the geometric midpoint (MP) of the saddle surfaces (42), characterised in that the longer side of the saddle surfaces (42), relative to the said highest point (HP2) thereof, is less sharply curved than the opposite, shorter side thereof, at least on average.

2. The transverse segment according to the claim 1, characterized in that an average value of the radius of curvature (Rsl) of the said longer, less sharply curved side of the saddle surfaces (42) is larger than an average value of the radius of curvature (Rsr) of the said opposite, shorter side thereof.

3. The transverse segment according to the claim 1 or 2, characterized in that a left side endpoint (LE) and a right side endpoint (RE) of the saddle surface (42), i.e. of the convex contour (NC) thereof, are located at an at least approximately equal radial height.