AN ENDLESS METAL BAND WITH A COATED SURFACE, A DRIVE BELT PROVIDED WITH THE ENDLESS METAL BAND AND METHOD FOR SHAPING THE DRIVE BELT The invention relates to a drive belt for use with a continuously variable transmission having two variable pulleys, each pulley defining a circumferential V-groove. The drive belt is provided with an endless carrier that typically consists of two band sets, each band set comprising at least one, but usually a number of mutually nested, flexible and endless metal bands and with a number of metal transverse elements arranged on and in sliding relationship with the endless carrier. Each transverse element is provided with one or more cut-outs, each cut-out accommodating a respective band set. A drive belt of this type is known from EP-A-0014013.

When describing the directions with respect to the drive belt and/or a transverse element thereof, it is always assumed that the transverse element (s) is/are in an upright position, such as is illustrated in Figure 2 in a front view thereof. In this Figure 2 the circumference or length direction L of the drive belt is at right angles to the plane of the figure. The transverse or width direction W is from left to right and the radial or height direction H is from top to bottom in the plane of Figure 2.

During operation of the drive belt in the transmission, the transverse elements are pressed against the inside of the endless carrier at least at the location of the transmission pulleys, whereby the bottom surface of the cut-outs of the transverse element arrive in close contact, in particular a sliding friction contact, with the radial inside surface of the radially innermost band of each band set of the endless carrier, which bottom surfaces are referred to as saddle surfaces hereinafter. It has been proposed in the art to design the said saddle surface thereof with a convex curvature as seen in the width direction of the transverse, i.e. between the front and back of the transverse element. Several advantageous effects are attributed in the art to such convex curvature, such as a reduced (Hertzian) contact stress between the transverse element and the endless carrier and a reduced (local) bending angle and stress of the endless metal bands thereof, whereby the drive belt can be loaded higher and/or longer until failure, and reduced friction losses, whereby the operating efficiency is improved .

However, in the currently preferred manufacturing method of the transverse elements, these are cut from a sheet or strip of basic material in the same front-to-back direction in a process step of fine blanking, so that the saddle surface (s) cannot be provided with the said convex curvature simultaneously with such cutting of the transverse element. Therefore, in the art, several methods have been suggested for reshaping the saddle surface into a convexly curved shape after it has first been cut out as a flat surface. In particular, several grinding methods have been proposed in the art for this purpose, for example as discussed in EP- 0231985 (Al), EP-1366855 (Al), US-4281483 (A), JP-S61-152362 (A), JP-2014-145423 (A), etc. These known grinding methods disadvantageously add to the complexity and cost of the manufacturing of the transverse element.

The present disclosure aims to provide a cost effective alternative to the known processes for providing the saddle surface (s) of the transverse elements with a convex curvature.

According to the present disclosure the above aim is realized by providing a coating with abrasive properties at the radial inside of the endless carrier, i.e. to the radial inside surface of the radially innermost band of the band set or band sets thereof. By virtue of such abrasive coating in combination with the circumstance that, during operation of the drive belt in the transmission, the transverse elements are pressed in radial outward direction against the radial inside surface of the endless carrier band, while a relative motion or speed difference exists there between, the saddle surfaces of the transverse elements are abraded. The extent of such abrasion is proportional to the contact force between the transverse elements and the endless carrier and is thus highest, at least initially during operation of the drive belt in the transmission, at the front and back side edges of the saddle surfaces in the most tightly curved part of the drive belt. Thus, by the said abrasive coating of the endless carrier, the saddle surfaces of the transverse elements are ground into a convexly curved shape, favourably without requiring an additional process step to be included in the manufacturing of the transverse element for such purpose.

Of course, it is still possible to include such abrading of the saddle surfaces of the transverse elements as a process step in the overall manufacturing process of the drive belt. To this end the drive belt, after the assembly thereof, is mounted on and around two pulleys, a clamping force is applied by the pulleys onto the drive belt to press the transverse elements thereof against the inside of the endless carrier and the pulleys and drive belt are rotated for a period of time to carry the abrasion process. Only hereafter the drive belt is mounted and used in the continuously variable transmission.

It is advantageous to stop the abrasion of the saddle surfaces once these have obtained the said convexly curved shape and thus to prevent the continued removal of material from the saddle surface. Therefore and in accordance with the present disclosure, the abrasive coating of the endless carrier is expendable, e.g. is abraded itself by the interaction with the saddle surfaces. Another option is to use an abrasive coating that dissolves in the lubricant that is applied in the transmission. In this case the abrasive coating will typically be composed of harder abrasive particles embedded in a softer, (gradually) dissolvable matrix .

Furthermore, and also in accordance with the present disclosure, it is advantageous that the rate of abrasion of the saddles surface is not too high. Otherwise, the size of the abraded particles will be too large and/or too much heat will be generated in the abrasion process. Furthermore, the higher the abrasion rate, the less predictable and consistent end-result of the abrasion process can be expected. Obviously, the abrasion rate is determined in part by the properties of the abrasive coating. For example, the hardness, size and number of abrasive particles of the coating will all influence the rate of abrasion of the saddle surfaces in the transmission that is realised thereby. However, according to the present disclosure a particularly favourable solution is found in providing the abrasive coating at only a part of the radial inside surface of the radially innermost band. The abrasive coating may, for example, be applied in the form of one or more strips spanning the width of the said band.

Furthermore, and also in accordance with the present disclosure, it is advantageous that the other surfaces of the bands of the band set (i.e. other than the said radial inside surface of the radially innermost band thereof) are relative smooth. In particular these other surfaces are neither provided with the abrasive coating, nor with a surface profile, such as is known from EP 0 014 013 Bl and is currently universally applied in drive belts. More in particular the so-called Ra surface roughness according to the ISO standard of these other band surfaces value is preferably 0.1 micron or less. It has namely been observed that, apart from the said convexly curved shape thereof, also a relatively smooth surface with a minimal Ra roughness value is obtained for the saddle surface. Such a smooth saddle surface exerts only a relatively small friction force on the radially innermost band, in which case it is known to be advantageous if also the friction between the bands of the band set themselves is small.

The above novel insights and technical concepts will now be explained by way of exemplary embodiments of a drive belt with reference to the drawing, in which:

figure 1 provides a schematic perspective view of the continuously variable transmission with a drive belt running over two pulleys;

figure 2 shows a cross section of the known drive belt viewed in the circumference direction thereof;

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

figure 4, in a close-up of figures 3 illustrates a design and manufacturing aspect of the transverse element that underlies the present disclosure;

figure 5 provides a schematic perspective view of first embodiment of a flexible, endless metal band in accordance with the present disclosure;

figure 6 provides a schematic perspective view of a second embodiment of a flexible, endless metal band in accordance with the present disclosure; and

figure 7 provides a schematic perspective view of several further embodiments of a flexible, endless metal band in accordance with the present disclosure.

The schematic illustration of a continuously variable transmission in Figure 1 shows a drive belt 3 which runs over two pulleys 1, 2 and which includes an endless band set 31 that carries an essentially contiguous row of transverse elements 32 that are arranged over the circumference of the band set 31. The drive belt 3 and the pulleys 1, 2 are in friction contact, whereto the conical discs 4, 5 of each pulley 1, 2 are urged towards each other thereby exerting respective clamping forces on the drive belt 3. In the illustrated position, the upper pulley 1 rotates more quickly than the lower pulley 2. By changing the distance between the two conical discs 4, 5 from which each pulley 1, 2, 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 transmitting power between an input shaft 6 and an output shaft 7 of the transmission, with a continuously variable rotational speed ratio between these input and output shafts 6, 7.

In Figure 2, the drive belt 3 is shown in a cross section thereof facing in its circumference direction L. This figure 2 shows an embodiment of the drive belt 3 that is equipped with two band sets 31, each shown in cross-section. The band sets 31 carry and guide the transverse elements 32 of the drive belt 3, whereof one transverse element 32 is shown in front elevation in Figure 2. The transverse elements 32 and the band sets 31 of the drive belt 3 are typically made of metal, usually steel. The band sets 31 hold the drive belt 3 together and, in this particular exemplary embodiment, are composed of five individual endless bands 44 each, which endless bands 44 are mutually concentrically nested to form the band set 31. In practice, the band sets 31 often comprise more than five endless bands 44. The transverse elements 32 are able to move, i.e. slide along the length direction L of the band sets 31, so that when a force is transmitted between the transmission pulleys 1, 2, this force is transmitted -at least in part- by the transverse elements 32 pressing against one another and, thus, pushing each other forward in a direction of rotation of the drive belt 3 and the pulleys 1, 2.

The transverse element 32, which is also shown in side view in Figure 3, is provided with two cut-outs 33 that are located opposite one another and that open towards opposite sides of the element 32. Each cut-out 33 accommodates a respective one of the two band sets 31. A first or body part 34 of the transverse element 32 extending radially inwards from or, in height direction H, below the band sets 31, a second or neck part 35 of the transverse element 32 being situated in between and at the same (radial) height of the band sets 31 and a third or head part 36 of the transverse element 32 extending radially outwards or, in height direction H, above the band sets 31. The lower or radially inward side of a respective cut-out 33 is delimited by a so- called bearing surface 42 of the body part 34 of the transverse element 32, which bearing surface 42 faces radially outwards or upwards in the general direction of the head part 36. The bearing surfaces 42 contact, i.e. bear on the radially inner circumference of the band sets 31, i.e. on the radially inside surface of the radially innermost band 44i thereof.

Lateral side surfaces 37 of the said body part 34 of the transverse element 32 that arrive in contact with the pulley discs 4, 5 are oriented at an angle φ with respect to one another, which corresponds, at least predominantly, to a V- angle between these discs 4, 5. A first or rear main face 38 of the transverse element 32 facing in the circumference direction L of the drive belt 3 is essentially flat, while a so-called rocking or tilting edge 18 is provided on an opposite facing, second or front main face 39 of the transverse element 32. In height direction H above the rocking edge 18, the transverse element 32 in side view has an essentially constant thickness and, in height direction H, whereas below the rocking edge 18, said body part 34 tapers towards the bottom side of the transverse element 32. The rocking edge 18 is typically provided in the form of a slightly rounded section of the front main face 39 of the transverse element 32. In the drive belt 3, the front main face 39 of the transverse element 32 arrives in contact with the rear main face 38 of an adjacent transverse element 32 at the location of the rocking edge 18, both in the straight parts of the drive belt 3 stretching between the pulleys 1, 2 and in the curved parts thereof located between the conical pulley discs 4, 5 of the transmission pulleys 1, 2. The transverse element 32 is also provided with a protuberance 40 on its front main face 39 and a hole 41 in its rear main face 38. The protuberance 40 and the hole 41 of two adjacent transverse elements 32 in the drive belt 3 are mutually engaging in the sense that the protuberance 40 of a first of the adjacent transverse elements 32 is at least partly inserted in the hole 41 of a second one thereof. Hereby, a relative displacement between and/or rotation of the said two adjacent transverse elements 32 is limited to a clearance provided between the said protuberance 40 and hole 41.

In the art, it is known to provide the bearing surfaces 42 of the transverse elements 32 with a convex curvature in the circumference direction L of the drive belt 3 in order to limit the contact stress introduced in the radially innermost band 44i by the contact with the transverse elements 32. A radius Rs of such curvature is typically adapted to, i.e. is chosen equal to or smaller than the smallest running radius R of the drive belt 3 at the pulleys 1, 2.

The transverse elements 32 are cut from strip-shaped basic material by a cutter that moves through the material in the above-defined circumference direction L of the drive belt 3. This cutting process does, in principle, not allow for the surfaces that are created therein, such as the bearing surfaces 42, to be provided with a contour in the cutter movement direction, such as the said convex curvature in the circumference direction L of the drive belt 3. The bearing surfaces 42 are thus initially created without the said convex curvature, as illustrated on the left side and middle of figure 4 in a side view of the transverse element 32 and of an enlargement of a part thereof. The convex curvature of the bearing surfaces 42 of the end-product transverse elements 32, which is illustrated on the right side of figure 4, thus needs to be shaped by and in a further process step in the overall manufacturing process of the end-product transverse element 32. Several examples of such further process step are provided by the art that mostly concern grinding down, in particular, the edges of the bearing surfaces 42.

According to the present disclosure, the above known process step of shaping the bearing surfaces 42 of the transverse elements 32 can be favourably omitted from the overall manufacturing process thereof. According to the present disclosure, instead, a coating 50 with abrasive properties is applied to the radial inside surface 51 of the radially innermost band 44i of the band sets 31. In figure 5 such feature is schematically illustrated in a perspective view of the said innermost band 44i.

By virtue of such abrasive coating 50 in combination with the circumstance that during operation of the drive belt 3 in the transmission a relative motion or speed difference occurs between the transverse elements 32 and the band sets 31 in the circumference direction of the drive belt 3, the saddle surfaces 42 of the transverse elements 42 are ground into a convexly curved shape. Furthermore and also according to the present disclosure, in a particularly favourable embodiment of the innermost band 44i, the abrasive coating 50 is provided in a strip-shape that does traverse the full width of the radial inside surface 51, but traverses only a (small) part of the circumference length thereof. This latter embodiment of the innermost band 44i is illustrated in figure 6. By the width of such strip-shape, a rate of abrasion of the saddles surfaces 42 can be predetermined. Furthermore, such strip- shape allows a harder and/or more wear-resistant material to be used as the said coating, without the rate of wear of the bearing surfaces 42 caused thereby becoming excessive.

Additionally, it may be desirable to vary the rate of abrasion of the saddles surfaces 42 along the width thereof. For example the lateral sides of saddles surfaces 42 may be abraded less, or possibly not at all, to improve the lubrication of the contact between the saddles surfaces 42 and the radial inside surface of the said innermost band 44i. In the later case, the abrasive coating 50 may be applied only in a width-wise central part of the innermost band 44i, as is illustrated in figure 7 in one possible embodiment 50a thereof. In the former case, the abrasive coating 50 may be provided in shape that narrows from such width-wise central part of the innermost band 44i to the axial sides thereof, as is illustrated in figure 7 in two possible embodiments 50b and 50c thereof. Alternatively, it may be required to abrade in particular the said lateral sides of saddle surfaces 42, in which case the abrasive coating 50 may be provided in shape that widens from such width-wise central part of the innermost band 44i to the axial sides thereof, as is illustrated in figure 7 in one possible embodiment 50d thereof. Yet another option is to abrade one lateral side of saddle surfaces 42 more than the respective other lateral side thereof, in which case the abrasive coating 50 may be provided on one axial side of the innermost band 44i only, as is illustrated in figure 7 in one possible embodiment 50e thereof. Alternatively, the abrasive coating 50 may still extend the entire width of the innermost band 44i, while being tapered in the width direction, e.g. while being provided with a trapezoidal shape, as is illustrated in figure 7 in one possible embodi ^¬ ment 50f thereof.

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.