WO2011076235A1

WO2011076235A1 - Drive belt and transverse element for a drive belt

Info

Publication number: WO2011076235A1
Application number: PCT/EP2009/009244
Authority: WO
Inventors: Guillaume Gerard Hubertus Rompen
Original assignee: Robert Bosch Gmbh
Priority date: 2009-12-23
Filing date: 2009-12-23
Publication date: 2011-06-30
Also published as: CN103339408B; CN103339408A; EP2516889A1

Abstract

Drive belt (3) provided with a band set (31) and with a number of transverse elements (32), each transverse element (32) being provided with a cut-out (33) for accommodating the band set (31), with a base part (34) in height direction extending below the cut-out (33), with a head part (36) in height direction extending above the cut-out (33) and with a neck part (35) connecting the base part (34) to the head part (36), the cut-out (33) being delimited in part by a saddle surface (42) of the base part (34). The saddle surface (42) is provided with at least one groove (50) between two, higher lying parts (p1; p2; p3) of the saddle surface (42).

Description

DRIVE BELT AND TRANSVERSE ELEMENT FOR A DRIVE BELT

The invention relates to a drive belt for use with a continuously variable transmission having two variable pulleys, each forming a V-groove. The drive belt is provided with a carrier consisting of two adjacent band sets, each band set comprising at least one, but usually a number of concentrically nested, relatively thin and flat endless metal bands and with a number of metal transverse elements arranged on and in sliding relationship with the band sets. Each transverse element is provided with two cut-outs located opposite one another for accommodating the band sets, in such a manner that a first part of the transverse element extends below the band sets, a second part of the transverse element is situated between the band sets and a third part of the transverse element extends above the band sets. A drive belt of this type is known from EP-A-0014013. When describing the directions with respect to the transverse element, it is always assumed that the transverse element is in an upright position, such as is illustrated in figure 2 in a front view thereof. In this figure, the longitudinal or circumference direction of the drive belt is at right angles to the plane of the figure. The transverse or width direction is from left to right and the radial or height direction is from top to bottom in the plane of figure 2. Specifically at the location of the cut-outs, the surface of the transverse elements has to meet certain requirements in order to ensure a good operation of the drive belt. For example, during operation of the drive belt in the transmission, the transverse elements are pushed radially outwards against the band sets by the transmission pulleys. As a result, the (radial inside of the) band set is contacted by a radially outwardly facing surface part of the said first part of the transverse element that forms the bottom of the respective cut-out, which surface part is referred to as the saddle surface. The finishing and shape of the saddle surface have a significant impact on the performance and/or durability of the band set and, hence, on the drive belt as a whole.

It is known, for example from GB-A-2013116, to design the saddle surface as a smooth, doubly curved surface, that is to say both width-wise and in the said longitudinal direction. It being understood that the width-wise curvature of the saddle surface is defined in a cross- sectional plane of the transverse element including the width and height directions, i.e. in a cross-section of the transverse element oriented in the longitudinal direction, and that the longitudinal curvature is defined in a cross- sectional plane of the transverse element including the height and longitudinal directions, i.e. in a cross-section of the transverse element oriented in the width direction. Although not perfectly smooth, the known saddle surface is provided with surface roughness of about 0.55 μπι Ra roughness value at most, typically around 0.4 μπι Ra.

The known longitudinal curvature of the saddle surface describes, or at least may be approximated by, a circular arc with a radius of curvature that is referred to as the short saddle radius. The short saddle radius is set smaller than the smallest running radius of the drive belt on the pulleys of the transmission, e.g. in the range from 15 to 30 mm. As a result of this measure, a longitudinal curvature of the band sets largely corresponds to a longitudinal curvature of the drive belt on the pulleys, at least in comparison with a drive belt provided with transverse element having longitudinally straight saddle surfaces. In the latter case, where the drive belt is curved in longitudinal direction, the band sets assume a more or less polygonal shape composed of straight sections alternated by sharply curved sections at the front and rear edge of the saddle surface of each transverse element. Of course, such sharply curved sections significantly increase the stress level in the band sets during operation and hence decrease the load carrying capacity and/or the service life of the drive belt.

The known transverse element is cut or blanked out of a strip-shaped base material by a cutter that moves through the material in the above-defined longitudinal direction of the drive belt. This cutting process does, in principle, not allow for a cut surface, such as the saddle surface, to be curved in the cutter movement direction. The said longitudinal curvature of the saddle surface thus needs to be created in a further step in the manufacturing process, such as by means of grinding, which adds to the overall manufacturing cost of the drive belt.

Although the known curved saddle surface was previously conceived to represent the optimum shape for the saddle surface, according to the invention such shape can still be improved upon-. More in particular, a disadvantage was found to be associated with the known shapes of the saddle surface (whether flat, longitudinally curved and/or curved width-wise) , namely that during operation a significant amount of friction can occur in the sliding contact between the transverse elements and band sets, which causes a loss of efficiency and/or a build up of heat in that sliding contact. This build up of heat can in turn cause excessive wear, and/or a decrease in fatigue strength of the transverse element and/or the band set and as such can limit the power transmitting capacity of the drive belt.

The present invention aims to provide a viable alternative to the known, longitudinally straight and curved cross- sectional contours of the saddle surface of the transverse elements. Preferably, such novel design of the saddle surface provides an improvement in terms of efficiency of the drive belt and/or in terms of its production. According to the invention the above aim is realized with the transverse element according to the claim 1 hereinafter. The saddle surface of the transverse element according to the invention is provided with at least one groove located between two, higher lying parts of the saddle surface. The said higher lying parts being intended to arrive in contact with the band set, whereas -a bottom surface of- the said groove is not. Preferably, a long axis of the groove is oriented at least predominantly in the width direction, i.e. perpendicular in the direction of movement of the drive belt.

In this groove, a cooling and/or lubricant agent, such as automatic transmission fluid (ATF) or oil, as typically applied in the present type transmission, will accumulate during operation, which is considered to have a positive effect on the sliding contact between the transverse element and the band set. In particular, the lubrication of the said sliding contact is believed to be enhanced thereby, for instance in terms of a thicker oil film there between, resulting in a reduced wear rate and/or decreased energy losses through friction.

It is noted that a surface profile of grooves and ridges that is typically provided to at least the radial inside of the band sets, i.e. to the radially inwardly oriented surface of the radially innermost band thereof, as is for example described in US-4,332,575 can potentially be favourably omitted by the provision of several grooves in the saddle surface in accordance with the present invention .

In a more detailed embodiment, the said higher lying parts of the saddle surface on either side of the width-wise oriented groove may be provided with mutually different heights. In this manner, the transverse element may support the preferred, non-sharply curved, longitudinal curvature of the band set, without its saddle surface -or at least the part or parts thereof that actually arrive in contact with the band set- having to be provided with the known longitudinal curvature. In this respect, it may be preferred to provide the saddle surface with at least two such grooves and to provide the central part of the saddle surface located in between these two grooves with a height that exceeds the height of the side parts thereof that are located on the respective other side of the two grooves relative to the said central part. In this manner, the said central and side parts of the saddle surface may approximate the conventionally applied, convexly curved shape, however, favourably without these saddle surface parts as such having to be provided with a longitudinally curved cross-sectional contour.

In an alternative embodiment of the invention, also the upper or radially inwardly facing boundary surface of the cut-out, which is defined by the said third part of the transverse element and which also may arrive into contact with (in this case the radial outside of) the band set, is provided with at least one groove in a manner corresponding to and to the same effect as the groove or grooves provided in the saddle surface as described herein in detail. In order to illustrate the invention, an exemplary embodiment of a drive belt will be described with reference to the drawing, in which:

Fig. 1 diagrammatically shows a continuously variable transmission with a drive belt running over two pulleys;

Fig. 2 shows a cross section of the drive belt viewed in the longitudinal direction thereof;

Fig. 3 shows a width-wise oriented view of a transverse element of the drive belt;

Fig. 4 schematically shows a cross-section of the transverse element according to a first embodiment of the invention;

Fig. 5 schematically shows a cross-section of the transverse element according to a second embodiment of the invention;

Fig. 6 schematically shows a cross-section of the transverse element according to a third embodiment of the invention; and

Fig. 7 schematically shows a top view of a part of the transverse element in a variant of the first embodiment of the invention. The diagrammatic illustration of Figure 1 shows a drive belt 3 which runs over two pulleys 1, 2. In the illustrated position, the top pulley 1 rotates more quickly than the bottom pulley 2. By changing the distance between the two parts, in this case conical discs 4, 5 from which each pulley 1, 2 is composed, the so-called running radius R of the drive belt 3 on the respective pulleys 1, 2 can be changed, as a result of which the speed difference between the two pulleys 1,2 can be varied as desired. This is a known manner of varying a difference in rotational speed between two shafts.

In Figure 2, the drive belt 3 is shown in cross section. This figure shows a cross section of two band sets 31 and a front view of a transverse element 32, of which the drive belt 3 comprises a considerable number, arranged over the periphery of the band sets 31. Both the transverse elements 32 and the bands of the band sets 31 are made of metal. The transverse elements 32 are able to move freely in the longitudinal direction of the band sets 31, so that when a force is transmitted between the pulleys 1, 2, this force is transmitted by the transverse elements 32 pressing against one another. The band sets 31 in this case guide the transverse elements 32. In the exemplary embodiment illustrated here, a band set 31 consists of five bands, although in practice a band set 31 can comprise more bands, even up to twelve or more. Each transverse element 32, which is also shown in side view in Figure 3, is provided with two cut-outs 33 located opposite one another, each for accommodating one of the two band sets 31, so that a first or base part 34 of the transverse element 32 extends below the band sets 31, a second or neck part 35 of the transverse element 32 is situated between the band sets 31 and a third or head part 36 of the transverse element 32 extends above the band sets 31. A respective cut-out 33 is delimited at the bottom by a so-called saddle surface 42 of the base part 34 that faces upwards, i.e. in the general direction of the head part 36. The saddle surface 42 is provided with a convex curvature in the longitudinal direction of the drive belt 3, i.e. as seen in figure 3. A radius of curvature of the saddle surface 42 is referred to as the short saddle radius SSR.

The lateral or pulley contact surfaces 37 of said base part 34 of the transverse element 32 are oriented at an angle φ with respect to one another, which corresponds at least substantially to a V-angle φ defined between the conical discs 4,5 of the pulleys 1,2 (see Fig. 1).

A rear side 38 of the transverse element 32 is substantially flat, while a so-called tilting line 18 is provided on a front side 39 of the transverse element 32. Above the tilting line 18, the transverse element 32 in side view has an essentially constant thickness and below the tilting line 18 said base part 34 tapers towards the bottom side of the transverse element 32. The tilting line 18 is typically provided in the form of a slightly rounded section of the front side 39 of the transverse element 32. In the drive belt 3, the front side 39 of the transverse element 32 comes into contact with the rear side 38 of an adjacent transverse element 32 at the location of the tilting line 18, both in the straight sections of the drive belt 3 between the pulleys 1, 2 and in the curved sections thereof on the pulleys 1, 2. The transverse element 32 is also provided with a protuberance 40 on the front side 39 and a recess 41 on the rear side 38, the protuberance 40 and the recess 41 of two transverse elements 32 abutting in the drive belt 3 mating, as a result of which a displacement with respect to one another in a direction oriented at right angles to the longitudinal direction of the drive belt 3 is limited to a tolerance of the protuberance 40 in the recess 41 in this direction.

In figures 4, 5 and 6 three embodiments of the transverse element 32 according to the invention are represented by a cross-section of only the base part 34 thereof in the cross-sectional plane A-A indicated in figure 2, which plane includes the height direction H (see figs.2&3) and the longitudinal direction L (see fig.3) of the belt 3 and which plane is thus oriented in the width direction W (see fig.2) .

In its first embodiment in figure 4, the saddle surface 42 is provided with a single groove 50 that is oriented in the width direction of the transverse element 32. In this embodiment example, the groove 50 is located centrally in the saddle surface as seen in the longitudinal direction. The groove 50 is designed such that at least a bottom surface part thereof does not contact the band set 31.

During operation of the drive belt 3 with transverse elements 32 designed in accordance with the figure 4 embodiment, lubricant is accommodated in the groove 50 for the lubrication of the sliding contact between the transverse element 32 and the band set 31 to reduce a wear rate thereof and/or to decrease friction there between.

Within the context and scope of the invention, various shapes, sizes and numbers of the grooves 50 are possible. Preferably, the groove or grooves 50 are 25 to 250 micron (i.e. μπι) deep (when measured perpendicular and relative to an imaginary contour of the saddle surface 42 uninterrupted by the grooves 50) , more preferably around 50 to 100 micron, and make up 5 to 50%, more preferably around 25%, of an overall (imaginary, uninterrupted) surface area of the saddle surface 42.

In figure 4, the parts pi and p2 of the saddle surface 42 on either side of the groove 50, which parts pi, p2 do arrive in direct physical contact with the band set 31, are provided with the same dimensions. It may, however, be advantageous to provide these parts pi, p2 with mutually different heights. Such design principle is illustrated in figure 5 in a second embodiment of the transverse element 32 according to the invention. This second embodiment incorporates a groove 50 and a step 51 in the saddle surface 42, whereof the higher lying parts pi and p2 of the saddle surface 42 on either side of the groove 50 are flat and are provided with a mutually different height. In this manner, the saddle surface 42 may approximate the conventionally applied, convexly curved shape even though the said higher lying parts pi and p2 as such present an essentially flat surface. In a third embodiment of the invention that is illustrated in figure 6, the saddle surface 42 is provided with two grooves 50 that are both oriented in the width direction of the transverse element 32. Additionally, a central part p3 of the saddle surface 42 located in between the two grooves 50 extends in height direction to above side parts pi and p2 of saddle surface 42 that are respectively located on the opposite side of one of said two grooves 50. In this manner, the central part p3 and the side parts pi, p2 of the saddle surface 42 may approximate the conventionally applied, convexly curved shape, however, favourably without these saddle surface parts pi, p2 and p3 as such having to be provided with a curved cross-sectional contour. Preferably, the height of the respective parts pi, p2, p3 of the saddle surface 42 is chosen such that a virtual arc drawn through the mid-points thereof in the cross-section of figure 5, approximates a circle segment, preferably having a radius of curvature that approximates a running radius R of the drive belt 3 on the pulleys 1, 2 of the transmission, preferably the smallest running radius occurring during operation of the transmission. Finally, in figure 7 a variant of the above first embodiment of the transverse element 32 according to the invention is illustrated with a top view of a section of the saddle surface 42, viewed downwards in the height direction H (as indicated by arrow point B in fig. 3) . Figure 7 illustrates that, in accordance with the invention, a higher lying part pi, p2 of the saddle surface 42 need not necessarily be formed as a single continuous plane pi extending over the full (in this case width) dimension . of the saddle surface 42, but may just as well be formed . by two or more isolated islands p2 surrounded by a lower lying part or parts z of the saddle surface 42 that include the said groove or grooves 50.

Claims

1. Transverse element (32) for a drive belt (3) provided with a band set (31) and with a number of such transverse elements (32), which transverse element (32) is provided with a cut-out (33) for accommodating the band set (31), with a base part (34) in height direction extending below the cut-out (33), with a head part (36) in height direction extending above the cut-out (33) and with a neck part (35) connecting the base part (34) to the head part (36), the cut-out (33) being delimited in part by a saddle surface (42) of the base part (34), characterised in that, the saddle surface (42) is provided with at least one groove (50) between two, higher lying parts (pi, p2, p3) of the saddle surface (42) .

2. The transverse element (32) according to claim 1, characterised in that, the groove (50), in particular a long axis thereof, is at least predominantly oriented in the width direction, perpendicular to both the said height direction and a longitudinal direction.

3. The transverse element (32) according to claim 1 or 2, characterised in that, the higher lying parts (pi, p2, p3) of the saddle surface (42) are provided with a mutually different height relative to the groove (50).

4. The transverse element (32) according to claim 1, 2 or 3, characterised in that, the saddle surface (42) is provided with at least two grooves (50) and that a central part (p3) of the saddle surface (42) located in between those two grooves (50) extends in height direction to above respective side parts (pi, p2 ) of saddle surface (42) each located on the opposite side of a respective one of said two grooves (50) relative to the said central part (p3) .

5. The transverse element (32) according to a preceding claim, characterised in that, the groove (50) is between 25 micron and 250 micron deep and preferably between 50 micron and 100 micron deep.

6. The transverse element (32) according to a preceding claim, characterised in that, by the provision of the groove or grooves (50) the surface roughness of the saddle surface (42) exceeds 0.55 micron Ra .

7. The transverse element (32) according to a preceding claim, characterised in that, the radially inwardly oriented surface of the radially innermost band of the band set (31) is not provided with a surface profile of grooves and ridges.

8. The transverse element (32) according to a preceding claim, characterised in that, also the upper or radially inwardly facing boundary surface of the cut-out (33) defined by the head part (36) of the transverse element (32) is provided with at least one groove.

9. Drive belt (3) provided with a transverse element (32) according to a preceding claim.