This invention relates to a method for manufacturing a transverse segment that is destined to be part of a pushbelt for a continuously variable transmission. The pushbelt is commonly known and typically comprises two sets of a number of mutually nested continuous bands or rings each, as well as a plurality of the transverse segments that are mounted on these ring sets in an essentially contiguous row along the circumference thereof. Such a pushbelt is for example described in the European patent EP 3063432 B1 that also discloses a method for blanking the transverse segment from a strip of basic material.

In the following description of the transverse segment, the mentioned directions and dimensions refer to the situation in which the transverse segment is part of the pushbelt. Thus, a longitudinal or thickness direction of the transverse segment thus corresponds to a circumferential direction of the pushbelt; a vertical or height direction of the transverse segment thus corresponds to a radial direction of the pushbelt; and a horizontal or width direction of the transverse segment corresponds to an axial direction of the pushbelt.

The known transverse segment defines two, horizontally extending slots that open towards a respective side of the segments, wherein a circumference section of a respective ring set is located. In the vertical direction, the slots are respectively defined between a body portion below the slots, a neck portion between the slots and a head portion above the slots. Also in the vertical direction the transverse segment comprises a lower part that has a thickness that is less than a thickness of an upper part of the transverse segment. By this design, two successive transverse segment in the pushbelt can mutually rotate -and the pushbelt as whole can curve- while remaining in mutual contact at an edge between the said upper and lower parts thereof. Typically, one main side of the transverse segment is formed as a flat surface, whereas its other, opposite main side includes the said edge that is referred to the rocking edge hereinafter. In the pushbelt, the rocking edge is preferably located close to the ring sets in radially inward direction, i.e. is preferably located just below the said slots wherein the ring sets are located.

Still, as explained in EP 3063432 Bl, the rocking edge cannot be provided arbitrarily close to the slots, because of a limitation of the conventional blanking method wherein the transverse segment is cut out of basic material. In particular, a convexly rounded transition is formed between a main side of the transverse segment and its circumference surface that is formed when the transverse segment is blanked, i.e. is cut from basic material, and that includes the bottom boundary surface of the slots. Such rounded transition is referred to as rollover or draw- in (when translated from the corresponding term in German: "Einzug"). In order for the pushbelt to function properly, the rocking edge must not coincide with the said rollover and must thus be formed at some distance below the slots, which distance at least exceeds the extend of the rollover in the height direction.

EP 3063432 Bl discloses a special blanking method that allows the rocking edge to be formed favourably close to slots defined by the transverse segment, in particular at a distance below the slots that would be within the extent of the rollover obtained with a more conventional blanking method. According to EP 3063432 Bl, the transverse segment blanking method includes the process steps of:

- first roughly forming the slots of the transverse segment by punching two elongated pieces out of the basic material, while leaving a layer of basic material between the thus formed holes in the basic material and -at least- the bottom boundary surface of the slots to be finally formed later; of

- secondly, inserting a support in each hole formed in the first process step, preferably by reinserting the punched-out pieces back into the holes; and of thirdly, finally forming the slots by cutting the transverse segment in whole or in part from the basic material surrounding it.

Effectively in this known blanking method, the rollover that is formed in the first process step, i.e. when the holes are formed, does not become part of the transverse segment as it is cut loose in the third process step, i.e. when the slots of the transverse segment are finally formed. At the same time, the rollover that is formed in the third process is comparatively small. Moreover, by the presence of the said support in the third process step, it is realised that -at least at the location of the said layer- the transverse segment is favourably sheared off from the rest of the basic material.

A general development trend in the design of the pushbelt is the downsizing thereof, in particular by utilizing the increased fatigue strength of the ring set that is obtainable with modern, i.e. highly optimised basic material compositions and/or the heat treatment thereof. Thus, in recent years, the number of rings incorporated in the ring sets has decreased, whereby the height of the slots and the height of the transverse segments as a whole could be decreased as well.

Although such downsizing of the pushbelt is favourable and sought after per se, this also makes it problematic or even impossible to apply the known blanking method according to EP 3063432 B1. In particular, a smallest possible height of the elongated piece that is punched out in the said first process step thereof (corresponding to a smallest height of the hole) is known to be linearly proportional to a thickness of the basic material (corresponding to a nominal thickness of the transverse segment). For example, the publication "Cold Forming and Fineblanking: A handbook on cold processing steel material properties component design" (2007; ISBN-13: 978-3446413504) mentions that the height of an elongated hole should amount to at least 0.6 times the basic material thickness. Otherwise, blanking becomes impractical and/or uneconomical by the then insufficient stiffness and/or strength of a blanking tool for punching the said elongated piece, i.e. a piercing punch.

In relation to a typical thickness of the basic material of between 1.4 and 1.8 mm, the said smallest height of the hole formed in the first process step of the known blanking method thus amounts to between 0.8 and 1.1 mm. However, in a pushbelt that is provided with only seven or even less mutually nested rings per ring set, the maximally allowed height of the hole is less than 0.8 mm and, for example, is equal to about 0.65 mm while taking into account a minimally required thickness of 0.15 to 0.4 mm for the said layer left in the first process step.

The present invention seeks to improve upon the known blanking method in relation to, for example, the downsized pushbelt. In particular, the present invention aims to reduce the said smallest height of the hole that can be reliably formed in the said first process step thereof.

According to the present invention, the pieces of basic material that are punched out in the said first process step to roughly from the slots of the transverse segment, are provided with a height that increases in width direction from its centre to at least one side thereof. Thus, the piercing punch that is used in the first process step to punch out the said piece of basic material, is provided with a side part that is higher than a central part thereof, as seen in a cross-section of the piercing punch perpendicular to a direction of movement thereof, i.e. perpendicular to the punching direction. By such higher side part the overall mechanical strength of the piercing punch is increased, such that its central part can be relatively small in the height direction of the transverse element without excessive deformation thereof when in use.

It is noted that in the typical design of the transverse segment, its body portion extends further below the slots than its head portion extends above the slots. This design allows the said higher side part of the piercing punch to be favourably located next to the head portion of the (still to be formed) transverse segment. In particular in this case, a first main face or underside of the piercing punch extends in an essentially flat plane, essentially in parallel with the body portion of the (still to be formed) transverse segment, whereas the opposite, second main face or topside thereof includes a protrusion.

Preferably, the piercing punch is provided with such higher side part on both sides of the said central thereof to further enhance its strength and, thus, to further reduce the smallest height of the hole that can be reliably formed in the said first process step thereof. In this case, both such higher side parts of the piercing punch preferably protrude towards the head portion of the (still to be formed) transverse segment rather than to the body portion thereof, by respective protrusions of the said topside of the piercing punch. One such protrusions is located next to the head portion of the (still to be formed) transverse segment, whereas the other protrusion is located next to the neck portion thereof, which latter protrusion thus creates a recess in the head portion of the transverse segment. Such recess can, however, be allowed without a major negative impact on the strength of the transverse segment and/or the longevity of the pushbelt as a whole. To the contrary, if the higher side parts, i.e. protrusions would protrude towards the body portion, portion of the (still to be formed) transverse segment, a significant and disadvantageous reduction of such strength and/or longevity would have resulted.

The above-described transverse segment and method for manufacturing it will now be explained in more detail by means of non-limiting, illustrative embodiments thereof and with reference to the drawing figures, whereof: figure 1 is a schematic side view of a continuously variable transmission including a pushbelt; figure 2 is a front view of a transverse segment for a pushbelt for a continuously variable transmission; figure 3 is a side view of the transverse segment which is shown in figure 2; figure 4 schematically illustrates a process step in the transverse segment manufacturing method in a known embodiment thereof; figure 5 schematically illustrates the same process step as figure 4, however in a first novel embodiment thereof according to the present invention; figure 6 schematically illustrates a second novel embodiment according to the present invention of the said process step; and figure 7 is a cross-section of a piercing punch used in the second novel embodiment of the said process step according to the present invention.

Figure 1 schematically illustrates a continuously variable transmission, such as for utilization in a motor vehicle. The continuously variable transmission is indicated in general by the reference sign 1. The continuously variable transmission 1 comprises two pulleys 4, 5, each arranged on a respective pulley shaft 2, 3. A pushbelt 6 is provided in a closed loop around the pulleys 4, 5 and serves for transmitting torque between the pulley shafts 2, 3. The pulleys 4, 5 are each provided with two pulley sheaves, where between a respective circumference section of the pushbelt 6 is located and clamped, so that a rotation may be transmitted between the pulleys 4, 5.

The shown pushbelt 6 comprises at least one ring set 7 composed of a bundle of mutually nested continuous bands or rings. A plurality of transverse segments 10 are arranged on the ring set 7 forming an essentially contiguous row along the entire circumference thereof. In the pushbelt 6, the transverse segments 10 are provided movable with respect to the ring set 7, at least in the circumferential direction thereof. For the sake of simplicity, only a few of these transverse segments 10 are shown in figure 1.

Figures 2 and 3 illustrate the transverse segment 10 of the known pushbelt 6 in more detail. In the illustrated embodiment thereof, the transverse segment 10 is intended for a pushbelt 6 equipped with two ring sets 7, whereto it defines two slots 23 wherein a circumference section of a respective ring set 7 is accommodate in the pushbelt 6.

A front surface of the transverse segment 10 is indicated in general by the reference sign 11, whereas a back surface of the transverse segment 10 is indicated in general by the reference sign 12. In the vertical direction, the transverse segment 10 successively comprises a body portion 13 of predominantly trapezoidal shape, a relatively narrow neck portion 14 and a head portion 15 of predominantly triangular shape. In the pushbelt 6, the body portion 13 is located below, i.e. radially inward of the ring sets 7, whereas the head portion 15 is located radially outward of the ring sets 7. Thus, the said slots 23 for accommodating the ring sets 7 are defined to the left and the right of the neck portion 14 of the transverse segment 10 in between the body portion 13 and the head portion 15 thereof. The slots 23 are bound in radial inward direction by respective boundary surfaces 16 that arrive in contact with and support the radial inside of ring sets 7 and that are referred to as support surfaces 16 hereinafter.

On either axial side thereof, the body portion 13 comprises a pulley sheave contact surface 17 through which the transverse segment 10 arrives in friction contact with the pulley sheaves of the pulleys 2, 3 in the transmission.

At the front surface 11 of the transverse segment 10 a projection 21 is provided. In the shown example, the projection 21 is arranged in the head portion 15, and corresponds in position to a slightly larger hole provided in the back surface 12 of the transverse segment 10. In figure 3, the hole is indicated by means of dashed lines and the reference sign 22. In the pushbelt 6, the projection 21 of the transverse segment 10 is at least partially located inside the hole 22 of a neighbouring transverse segment 10. The projection 21 and the corresponding hole 22 serve to prevent or at least limit mutual displacement of adjacent transverse segments 10 in a plane perpendicular to the circumferential direction of the pushbelt 6.

Also at the front surface 11 of the transverse segment 10, however in the body portion 13 thereof, a so-called rocking edge 18 is defined. The rocking edge 18 is represented by a convexly curved area of the front surface 11 between an upper part of the transverse segment 10 of essentially constant thickness and a tapered lower part thereof. The rocking edge 18 allows neighbouring transverse segments 10 in the pushbelt 6 to mutually rotate while remaining in pushing contact by the rocking edge 18 of one transverse segment 10 bearing on the back surface 12 of another, neighbouring transverse segment 10. The rocking edge 18 is located close to, but still at some distance below, i.e. radially inward of, the support surfaces 16. The rocking edge 18 preferably extends along the full local width of the transverse segments 10.

It is well-known in art to manufacture the transverse segment 10, at least as a semi-finished part, by blanking it from strip-shaped basic material 50. Such blanking process can in principle be carried out in a single step, i.e. in a single stroke of a blanking device. However, in a special embodiment of the known blanking method, it is carried out in at least three steps, whereof a first process step is illustrated in figure 4.

Figure 4 represents a section of the strip of basic material 50 that is pierced by a piercing punch 51 (first process step) to form a hole 52 in the strip 50 at the location of the slots 23 of the transverse segment 10 to be finally formed later (as indicated in figure 4 by the dashed contour). Subsequent to the first process step, a support is inserted in the hole 52 (second process step), where after the transverse segment 10 is blanked in its final shape (third process step).

In the said first process step, a dimension of the hole 52 in the height direction H is smaller than a height dimension of the slots 23 and a layer 53 of basic material 50 is left between the holes 52 and the body portion 13 of the transverse segment 10. Preferably, a layer of basic material 50 is also left between the hole 52 and the neck and head portions 14, 15 of the transverse segment 10 in this first process step.

When the hole 52 is formed by the piercing punch 51 in the first process step, it is formed with a rounded transition edge that is known as rollover. When the transverse segment 10 is subsequently blanked from the basic material 50, the said layer 53 does not become part of the transverse segment 10 including the extent of the rollover that is present in such layer 53. Thus, the finally formed slots 23 each have only a minimal transition edge towards the front and/or rear surfaces 11, 12 of the transverse segment 10 and the rocking edge 18 can be located favourably close to the support surface 16 in the height direction H, outside the said transition edges thereof.

In the known blanking method, a minimum height of the hole 52 is required to provide the piercing punch 51 with sufficient strength, in particular in mass production. This minimum height of the hole 52 is proportional to the thickness of the basic material 50 and puts a limit on the minimum height of the slots 23 that can be realised with the known blanking method.

In order to enable a downsizing of the pushbelt 10 with the known blanking method and in accordance with the present invention, a novel piercing punch 54 is provided with a protrusion 54pl in the height direction H on at least one side 54s thereof. In other words -and as illustrated in figure 5 that otherwise correspond to figure 4- such side part 54s is higher than a central part 54c of the novel piercing punch 54. By this protrusion 54pl, the central part 54c of the novel piercing punch 54 can be comparatively narrow, in particular more narrow than the known, elongated piercing punch 51, also when applied in mass production.

The novel piercing punch 54 can make use of the design aspect of the transverse segment 10 that its body portion 13 extends further in width direction W below the slots 24 than its head portion 15 does above the slots 23. The protrusion 54pl of the novel piercing punch 54 can thus be accommodated beside the head portion 15 in the width direction W while still being located above the body portion 13 in the height direction H.

Preferably and as illustrated in figure 5, the protrusion 54pl defines a concave transition surface 54t towards the narrow central part 54c of the novel piercing punch 54, having a radius of (concave) curvature that is larger than a radius of (convex) curvature of a tip 15t of the head portion 15 located beside the protrusion 54pl. Preferably also, the transition surface 54t extends in width direction W for more than half of a total extent of the protrusion 54pl in width direction W. Moreover, the novel piercing punch 54 preferably does not extend beyond the extent of the transverse segment 10 in the width direction W. These latter three design aspects of the novel piercing punch 54 favourably support its strength.

In figure 6 the novel piercing punch 54 is illustrated in a second embodiment thereof according to the present invention. In this case, two protrusions 54pl, 54p2 in the height direction H are provided, one on each side 54s of the novel piercing punch 54. Both protrusions 54pl, 54p2 extend upwards in the height direction H relative to the central part 54c of the novel piercing punch 54. By adding a second protrusion 54p2, the mechanical strength of the novel piercing punch 54 is favourably supported further and/or a an even more narrow central part 54c can be allowed in mass production.

In order to accommodate the protrusion 54p2 of the novel piercing punch 54 that is located beside the neck portion 14 of the transverse segment 10 to be finally formed later (as indicated in figure 6 by the dashed contour), the contour of the head portion 15 thereof is modified. In particular and relative to a conventionally applied, continually concavely curved recess 15cr in the head portion 15 beside the neck portion 14 (as indicated in figure 4), a modified recess 15mr is extended in width direction W. Preferably, such extension of the modified recess 15mr is by way of a straight contour section inserted between two concavely curved contour sections.

Figure 7 illustrates the second embodiment of the novel piercing punch 54 in more detail. In this second embodiment, the novel piercing punch 54 is provided with the protrusions 54pl, 54p2 in the height direction H at both side parts 54s thereof, i.e. on both sides of its central part 54c. The height hi of the central part 54c is essentially constant, at least when compared to the side parts 54s thereof. Still, the whole of the underside 54u of the novel piercing punch 54 on the opposite side of the protrusions 54pl, 54p2 is preferably concavely curved to match a convex curvature of the support surface 16, such as is typically applied in the art with a radius of curvature in excess of 100 mm, in particular of around 150 mm. Moreover, concavely curved transition surfaces 54t are provided in the opposite side of the novel piercing punch 54 relative to the said underside 54u thereof, which transition surfaces 54t each extend from the central part 54c towards a high point of a respective protrusions 54pl, 54p2.

Preferably according to the present invention, a smallest height hi of the central part 54c is smaller than 0.6 times the thickness of the basic material 50, whereas a largest height h2 of the side parts 54s with the protrusions 54pl, 54p2 is larger than 0.6 times such basic material thickness. Preferably also, the largest height h2 of the side parts 54s of the novel piercing punch 54 amounts to between 1.5 to 3 times the height hi of the central part 54c thereof.

In figure 8 the abovementioned third process step of the known transverse segment blanking method is illustrated, however, in a novel embodiment thereof according to the present invention. In this third process step the transverse segment 10 is blanked from, i.e. is cut out of the basic material 50. It is noted that prior to this third process step, two holes 52 have been punched in the basic material 50 in the first process step, by removing two pieces 55 of the basic material 50, and, in the second process step, these basic material pieces 55 have been reinserted, i.e. have been pressed back into their corresponding hole 52 in the basic material 50.

The present invention, 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 is 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.