WO2021129951A1

WO2021129951A1 - A transverse segment for a drive belt and a method for manufacturing such transverse segment

Info

Publication number: WO2021129951A1
Application number: PCT/EP2020/025583
Authority: WO
Inventors: Bert Pennings; Jozef Norbertus Mathias SCHNACKERS; Minh-Duc Tran
Original assignee: Robert Bosch Gmbh
Priority date: 2019-12-23
Filing date: 2020-12-16
Publication date: 2021-07-01
Also published as: NL1043518B1

Abstract

The present invention concerns a transverse segment (1) for a drive belt (50) comprising a row of such transverse segments (1) mounted on a ring stack (8). The transverse segment (1) defines a central opening (5) between a base part (10) of the transverse segment (1) and two pillar parts (11) thereof extending from a respective side of the base part (10) for accommodating the ring stack (8), as well as a respective pulley contact face (12) on either side of such base part (10). According to the invention a surface hardness of the transverse segments (1) at the location of a side face (16) of at least one of the pillar parts (11) is lower than at the pulley contact faces (12).

Description

A TRANSVERSE SEGMENT FOR A DRIVE BELT AND A METHOD FOR MANUFACTURING SUCH TRANSVERSE SEGMENT

This invention relates to a transverse segment that is destined to be part of a drive belt for a continuously variable transmission with two pulleys and the drive belt. Such a transmission is commonly known and is, for example, applied in the drive train of passenger cars and other motor vehicles. In the transmission, the drive belt runs around and between the pulleys that are each provided with two conical sheaves that define a V- groove wherein a respective circumference part of the drive belt is held. The width of the V-groove of the pulleys can be changed in mutually opposite directions, by moving the pulley sheaves towards, respectively away from one another, to control a radius at which the drive belt is (effectively) in friction contact with the respective pulleys, i.e. to control a speed ratio provided by the transmission within a continuous range between a smallest and a largest speed ratio.

A known type of drive belt comprises an essentially contiguous row of transverse segments made of steel that are mounted on and around the circumference of a ring stack composed of a number of flexible endless bands or rings that are mutually stacked, one around the other, and that are likewise made of steel.

In the above and below description, the axial, the radial and the circumference directions are defined relative to the drive belt when placed in a circular posture. A thickness direction and a thickness dimension of the transverse segments are defined in the said circumference direction, a height direction and a height dimension of the transverse segments are defined in the said radial direction and a width direction and a width dimension of the transverse segments are defined in the said axial direction. A thickness direction and a thickness dimension of the rings and of the ring stack are defined in the said radial direction, a width direction and a width dimension of the rings and of the ring stack are defined in the said axial direction and a length direction and a length dimension of the ring stack is defined in the said circumference direction. Up and down directions and above and below positions are respectively defined in radial outward and radial inward direction.

The known flexible ring is provided with an essentially rectangular cross-section, albeit with rounded sides, such that its thickness is much smaller than its width, typically by a factor of at least forty to one hundred or more. Also in absolute terms, the thickness of the ring is small and typically has a value of 185 to 200 micrometer, such that it can bend relatively easily in its circumference direction. In the ring stack, a number of such rings are arranged mutually concentric, i.e. are nested with minimal play, such that these share the load when the drive belt is operated in the transmission.

The known transverse segments each define a central opening that is open towards the radial outside of the drive belt and that accommodates and confines a respective circumference section of such ring stack, while allowing the transverse segment to move along the circumference thereof. This central opening is defined by and between a base part of the transverse segment that is located radially inward of the ring stack and two pillar parts thereof that respectively extend from a respective side of the base part in radial outward direction. The two pillar parts thus define respective axial boundaries of the central opening, whereas in radial inward direction the central opening it is bounded by the base part. In radially outward direction the central opening is at least partly closed by some means, in order to confine the ring stack to the central opening. This type of drive belt is, for example, known from the British patent GB1286777-A and, more recently, from the international patent publication WO2018/210456-A1. It is noted that according to these documents, the said means for confining the ring stack in radial outward direction are embodied by respective hook portions of the pillar parts that each extend axially towards the respectively other, i.e. axially opposite, pillar part at some distance away from the base part. These hook portions of the transverse segment can have equal axial extent or such axial extent can be different between the two hook portions, in which case these respective hook portions are preferably provided on opposite sides of the transverse segment for successive transverse segments in the drive belt, as a/o taught by WO2018/210456-A1.

As seen in radial direction, an outer portion of the known transverse segment is provided with an essentially constant thickness, whereas a thickness of an inner portion thereof decreases in radially inward direction. In between the said inner and outer portions, a front surface of the transverse segment, facing in a circumference direction of the drive belt, includes a width-wise extending surface part that is curved in radial direction and that is often referred to in the art as a rocking edge or a tilting zone. The rocking edge allows successive transverse segments in the drive belt to mutually rotate about the axial direction, while these remain in contact at the rocking edge, whereby the drive belt as a whole follows a curved trajectory. Although the rocking edge can be located in the base part of the transverse segment, it is preferably located at least partly in the pillar parts thereof.

It is common practice in the art to provide the transverse segment with a protrusion projecting from the said front surface or from an oppositely facing rear surface thereof and with a corresponding, however somewhat larger cavity in its respectively opposite main surface. In the row of transverse segments in the drive belt, the protrusion of a first transverse segment is received in the cavity of a second, i.e. adjacent transverse segment, at least in part. Hereby, a mutual displacement of the successive transverse segments perpendicular to the circumference direction of the drive belt is limited to a play of the protrusion inside the cavity. The protrusions and cavities thus serve to both mutually align the transverse segments in a row in the straight parts of the drive belt’s trajectory and to limit a rotation thereof in the said curved trajectory parts. In particular, at least a pitching (i.e. rotation about the axial direction) and a yawing (i.e. rotation about the radial direction) of the transverse segments and preferably also a rolling (i.e. rotation about the tangential direction) of the transverse segments relative to the ring stack is limited thereby. The known transverse segments each include a single protrusion (and corresponding cavity) provided centrally in its base part and/or two protrusions (and corresponding cavities), one provided in each of it pillar parts.

During operation in the transmission, the ring stack is tensioned by the transverse segments being urged in radial outward direction at the two pulleys by being clamped between the conical discs thereof. At these pulleys, the drive belt thus follows a curved trajectory, in which curved trajectory parts the transverse segments bear against the radial inside of the ring stack through, at least, a part of the surface of their base part that is located between the pillar parts, which surface part is denoted a bearing surface hereinafter. Due to the said tensioning thereof at the pulleys, the ring stack extends essentially straight between the two pulleys, while guiding the transverse segments as these traverse from the one pulley to the other in such straight trajectory parts.

In the presently considered design of the drive belt, the ring stack is thus confined in opposite axial directions, i.e. width-wise, in the central openings of the transverse segments, by and between the pillar parts thereof. The width of the ring stack is somewhat smaller than the width of the central openings of the transverse segments to accommodate a mutual misalignment of, i.e. axial offset between the pulley V-grooves that occurs during operation of the transmission in dependency on the speed ratio, as a/o discussed in US4820242. Nevertheless, such axial clearance of the ring stack relative to the transverse segments cannot prevent contact in axial direction between the ring stack and the pillar parts altogether during operation of the drive belt.

Underlying the present invention is the general development aim to improve upon the existing drive belt design and existing design considerations in terms of the wear resistance and/or the fatigue strength of the known drive belt. According to the present invention, an improvement can in this respect be obtained by a modification of the known manufacturing process of the transverse segments.

The known manufacturing process of the transverse segments includes at least the process step of hardening the transverse segment in a carburizing or carbo-nitriding heat treatment. This known heat treatment is applied to provide the transverse segments with an additional hardness, as well as with a compressive residual stress in a surface layer thereof, which properties are highly desirable for the transverse segments to withstand the friction contact with the pulleys with minimal wear. For example, W02017/108206 describes the known carburizing heat treatment in relation to the transverse segments. In particular, by hardening the transverse segments by carburizing or carbo-nitriding, these are typically provided with a surface hardness of 61 to 63 HRC (-770-850 HV1.0) compared to a core hardness of 58 to 60 HRC (-700-750 HV1.0). The thus additionally hardened surface layer of the transverse segment typically extends between 100 to 250 micron from the outer surface thereof.

According to the present invention, the said additional surface hardness of the transverse segments, although highly sought after to withstand their contact with the pulleys, is in fact less favourable in their contact with the ring stack. In particular, by such additional surface hardness, any mechanical wear due to the said axial contact between the pillar parts of the transverse segments and the ring stack during operation will concentrate in the latter, i.e. will mostly affect the axially oriented sides of the individual rings thereof. In turn, such wear of the rings will reduce their (fatigue) strength and of the drive belt as a whole.

The present invention sets out to reconcile the technical desire for a hard and wear resistant transverse segment with the desire to minimise a mechanical wear of the ring stack. Thereto, the surface hardness of the transverse segments is differentiated between the side faces of the pillar parts facing the central opening and the faces of the transverse segments that arrive in contact with the transmission pulleys, i.e. pulley contact faces. In particular, such surface hardness is set lower at the said pillar side faces of the transverse segments than at the pulley contact faces thereof.

According to the invention, this surface hardness differentiation can be obtained by applying a coating to the pillar side faces of the transverse segment as part of the manufacturing process thereof, which coating can be applied either prior to the said carburizing or carbo-nitriding heat treatment thereof or following it. In the first case, the coating is primarily aimed at preventing carbon diffusing through the pillar side faces from the gas phase in the carburizing or carbo-nitriding heat treatment and, thus, to locally prevent the said additional surface hardness from being created therein. In the second case, the coating is applied on top of the hardened surface layer of the transverse segments and thus takes over the said axial contact with the ring stack.

Alternatively, the surface hardness differentiation can be obtained by locally removing the said hardened surface layer, at least in part, in particular by grinding down the side faces of the pillar parts of the transverse segments that face the central opening thereof as part of the manufacturing process thereof and following the said carburizing or carbo-nitriding heat treatment thereof. According to the present invention at least 50% and preferably 100% of the thickness of the additionally hardened surface layer is removed, i.e. between 50 and 250 micron in absolute terms, over the full width of the side faces, i.e. over the entire thickness of the transverse segment.

Although other means and methods are conceivable, preferably a flexible grinding belt is applied. Such preference not only being related to the pillar side faces of the transverse segment being difficult to reach otherwise, but also to the possibility to provide these pillar side faces with a convex curvature along the thickness of the transverse segment as is commonly preferred in the art.

The above-described invention and the technical working principles underlying the invention will now be explained further with reference to the drawing figures, whereof:

- figure 1 is a simplified and schematic side elevation of a known transmission with two pulleys and a drive belt consisting of a ring stack and a row of transverse segments mounted on the ring stack along the circumference thereof;

- figure 2 schematically illustrates the known drive belt in a cross-section thereof facing in its circumference direction and also includes a separate, transverse cross-section of only the transverse segment thereof;

- figure 3 is a schematic representation of the presently relevant part of the known manufacturing method for the transverse segment; and

- figure 4 schematically illustrates a first novel embodiment of the transverse segment manufacturing method in accordance with the present invention;

- figure 5 schematically illustrates a second novel embodiment of the transverse segment manufacturing method in accordance with the present invention;

- figure 6 schematically illustrates a third novel embodiment of the transverse segment manufacturing method in accordance with the present invention; and

- figures 7 and 8 schematically illustrate a detail of the third novel embodiment of the transverse segment manufacturing method illustrated in figure 6.

Figure 1 schematically shows, in a cross-section thereof, the central parts of a continuously variable transmission 51 for use in a driveline of, for example, passenger motor vehicles. This transmission 51 is well-known and comprises at least a first variable pulley 52, a second variable pulley 53 and a drive belt 50 fitted around these pulleys 52, 53. In the driveline, the first pulley 52 is coupled to and driven by a prime mover of the vehicle, such as an electric motor or a combustion engine, and the second pulley 53 is coupled to and drives a driven wheel of the vehicle, typically via a number of gears. The pulleys 52, 53 each typically comprise a first conical sheave that is fixed to a respective pulley shaft 54, 55 and a second conical sheave that is axially displaceable relative to such respective pulley shaft 54, 55 and that is fixed thereto in rotational direction. As appears from figure 1, the trajectory of the drive belt 50 in the transmission 51 includes two straight parts ST, where the drive belt 50 crosses over between the pulleys 52, 53 and two curved parts CT where the drive belt 50 is wrapped around the two pulleys 52, 53 while being accommodated between the conical sheaves thereof.

The drive belt 50 is composed of a ring stack 8 and a plurality of transverse segments 1 that are mounted on the ring stack 8 along the circumference thereof in an, at least essentially, contiguous row. For the sake of simplicity, only a few of the transverse segments 1 of the drive belt 50 are shown in figure 1, which transverse segments 1 are, moreover, not drawn to scale in relation to, for example, the diameter of the pulleys 52, 53. In the drive belt 50, the transverse segments 1 are movable along the circumference of the ring stack 8, which ring stack 8 is composed of a number of relatively thin and flexible endless steel bands or rings that are mutually nested, as can be seen more clearly in figure 2 that shows the ring stack 8 with eight individual rings.

During operation of the transmission 51, the transverse segments 1 of the drive belt 50 can be driven by the first pulley 52 in the direction of rotation thereof by friction. These driven transverse segments 1 push preceding transverse segments 1 in the circumference direction of the ring stack 8 and, ultimately, rotationally drive the second pulley 53, again by friction. In order to generate such friction (force) between the transverse segments 1 and the pulleys 52, 53, the said pulley sheaves of each pulley 52, 53 are urged towards each other, whereby these clamp the transverse segments 1 between them in the respective curved trajectory part CT of the drive belt 50. To this end, electronically controllable and hydraulically acting movement means (not shown) that act on the moveable pulley sheave of each pulley 52, 53 are provided in the transmission 51. These movement means also control respective radial positions R1 and R2 of the drive belt 50 at the pulleys 52, 53 and, hence, the speed ratio that is provided by the transmission 51 in the driveline between the pulley shafts 54, 55 thereof.

Also during operation of the transmission 51 drive belt 50, the transverse segments are urged radial outward by being clamped between the conical pulley sheaves and are being forced into contact with the radial inside of the ring stack 8 that is tensioned thereby. Since, as mentioned hereinabove, in the drive belt 50 the transverse segments 1 can move relative to the ring stack 8 along the circumference thereof, the ring stack 8 is tensioned to a relatively low level in relation to a torque transmitted by the drive belt 50 between the pulleys 52, 53, at least compared to other types of drive belt.

In figure 2 the known drive belt 50 is schematically illustrated in more detail. On the left side of figure 2 the drive belt 50 is shown in a cross-section thereof facing in circumference direction and on the right side of figure 2 a cross-section A-A of only the transverse segment 1 is included. From figure 2 it appears that the transverse segments 1 of the drive belt 50 are generally shaped similar to the letter "V", i.e. are generally V- shaped. In other words, side faces 12 of the transverse segments 1 through which it arrives in (friction) contact with the pulleys 52, 53, are mutually diverging in radial outward direction by being oriented at an angle that closely matches an angle that is present between the conical sheaves of these pulleys 52, 53. The pulley contact faces 12 of the transverse segment 1 are typically either corrugated by a macroscopic profile or are provided with a rough surface structure, such that only the higher lying peaks of the corrugation or of the surface roughness arrive in contact with the pulleys 52, 53. This particular feature of the transverse segment design provides that the friction between the drive belt 50 and the pulleys 52, 53 is optimised by allowing cooling oil that is applied in the known transmission 51 to be accommodated in the lower lying parts of the corrugation or of the surface roughness.

Each transverse segment 1 includes a base part 10 and two pillar parts 11, whereof the base part 10 extends mainly in the axial direction of the drive belt 50 and whereof the pillar parts 11 extend mainly in the radial direction of the drive belt 50, each from a respective axial side of the base part 10. In its thickness direction, the transverse segment 1 extends between a front main body surface, i.e. front surface 2 and a rear main body surface, i.e. rear surface 3 thereof that are both oriented, at least generally, in the circumference direction of the drive belt 50. An opening 5 is defined centrally between the pillar parts 11 and the base part 10 of each transverse segment 1, wherein a circumference section of the ring stack 8 is accommodated. In radial outward direction the central opening 5 is partly closed-off by respective hook portions 9 of the pillar parts 11. Each such hook portion 9 extends from a respective pillar part 11 generally in the direction of the respectively opposite pillar part 11. Thus, the hook portions 9 confine the ring stack 8 to the central opening 5 of the transverse segment 1 in radial outward direction. In between the pillar parts 11, the base part 10 defines a bearing surface 13 for confining and supporting the ring stack 8 in radially inward direction.

As illustrated in figure 2, the bearing surface 13 is a central part of a boundary surface of the central opening 5 that is defined by the base part 10 in radially inward direction and that thus predominantly extends in the axial and circumference directions of the drive belt 50. The bearing surface is convexly curved in, at least, the axial direction in a well-known manner, for realising, or at least promoting, a desired contact and interaction between the transverse segment 1 and the ring stack 8. On either side of bearing surface 13 the said boundary surface of the base part 10 further includes a transition surface 15 forming a transition between the bearing surface 13 and a side face of a respective pillar part 11 facing the central opening 5. Typically, such transition surfaces 15 include a convexly curved part adjoining the bearing surface 13 and a concavely curved part adjoining the said side face of the respective pillar part 11. It is noted that convexly curved part of the transition surfaces 15 is curved according to a much smaller (e.g. by factor of 0.1 or less) radius of curvature than the bearing surface 13 is curved.

Both pillar parts 11 of the transverse segment 1 are provided with a protrusion 6 that protrudes in thickness direction from the front surface 2 of the transverse segment 1 and with a corresponding, however somewhat larger cavity 7 in the opposite side of the respective pillar part 11, i.e. in the rear surface 3 of the transverse segment 1. In the row of transverse segments 1 in the drive belt 50, the protrusions 6 of a first transverse segment 1 are received in the cavities 7 of a second, i.e. adjacent transverse segment 1. By this engagement of the protrusions 6 and the cavities 7 of successive transverse segments 1, the transverse segments 1 mutually link to and align one another in radial direction and in axial direction in the said row thereof in the drive belt 50. In figure 2, the diameter of the cavity 7 is exaggerated relative to the diameter of the protrusion 6 to illustrate a play that exists there between.

Also in the said row of transverse segments 1 in the drive belt 50, at least a part of the front surface 2 of a first transverse segment 1 abuts against at least a part of the rear surface 3 of a second, i.e. adjacent transverse segment 1. Abutting transverse segments 1 are able to tilt relative to one another, while remaining in mutual contact at and through an axially extending, convexly curved surface part 4 of the front surface 2 thereof that is denoted rocking edge 4 hereinafter. Above, i.e. radially outward of such rocking edge 4, the transverse segment 1 has an essentially constant thickness, whereas below, i.e. radially inward of such rocking edge 4, the transverse segment 1 is tapered, i.e. has a thickness that decreases in radially inward direction (whether gradually, stepwise or by a combination thereof), to allow for the afore-mentioned relative tilting without interference between the respective base parts 10 of the abutting transverse segments 1.

It is noted that, although in figure 2 the rocking edge 4 is located partly in the pillar parts 11 and partly in the base part 10 of the transverse segment 1 such that it overlaps with the bearing surface 13 in radial direction, it is also known to locate the rocking edge 4 fully in the base part 10, i.e. radially inward of the bearing surface 13. In either case, the rocking edge 4 is preferably provided in two parts 4a, 4b separated by the central opening 5 and/or by a recessed area 14 in the front surface 2 of the transverse segment 1 that is recessed in thickness direction relative to the rocking edge 4. The recessed area 14 provides a channel between the abutting transverse segments 1, allowing lubricant to flow from radially inside the drive belt 50 to the radial inside of the ring stack 8. Such lubricant is supplied to the transmission during operation, not only for cooling it, but also for lubricating the dynamic contact between the transverse segments 1 and the ring stack 8, as well as between the individual rings of the ring stack 8. It is further noted that in the embodiment of the transverse segment 1 illustrated in figure 2, wherein the rocking edge 4 is located partly in the pillar parts 11 and the base part 10 of the transverse segment 1, the recessed area 14 is, in part, formed as a curved transition surface between the front surface 2 of the transverse segment 1 and the bearing surface 13 as an inevitable side- effect of the preferred manufacturing method of fine-blanking the transverse segment. In fine-blanking, the transverse segment 1 is cut from steel basic material by pressing a punch, having a contour corresponding to that of the transverse segment 1, through the basic material into a transverse segment-shaped hole of a die plate, while being supported by a counter punch on the opposite side thereof. An end face of the counter punch that contacts the basic material is a/o shaped to form the rocking edge 4 and is provided with a recess that serves as a mould for forming the protrusion 6, while the end face of the punch that contacts the basic material is protruding part to form the cavity 7.

As further illustrated in figure 2, the pulley contact faces 12 of the transverse segment 1 extend in radial direction from the underside of the base part 10 to somewhat above the rocking edge 4, i.e. partly in the pillar parts 11. However, such radial extend can also be less, e.g. the pulley contact faces 12 can be confined to the base part 10, or more, e.g. of the pulley contact faces 12 can extend in the pillar parts 11 to radially outward of the ring stack 8.

In figure 3 the relevant parts of a well-known method for manufacturing the transverse segments 1 are schematically illustrated. The known manufacturing method comprises the two basic process steps of:

A) cutting-out, i.e. blanking in particular fine-blanking, the transverse segments 1 from a strip 61 of the basic material by means of a blanking station 70, which strip 61 is gradually advanced and fed to the blanking station 70 by unwinding a coil 60, and of

B) heat treating, i.e. hardening, the transverse segments 1 by means of a hardening station 80 in a carburizing or carbo-nitriding process, which heat treatment includes

- an austenitizing stage I, wherein the transverse segments 1 are heated (e.g. to above ±780 °C in case of DIN 1.2003 steel) to austenitize the basic material in a carbon- containing gas atmosphere, whereof the carbon potential exceeds the carbon content of the basic material;

- a quenching stage II, wherein the transverse segments 1 are rapidly cooled (e.g. to below 110 °C) to form martensite, and

- a tempering stage III, wherein the transverse segments 1 are heated again, but to a temperature considerably below the austenitizing temperature (e.g. to around 200 °C), for reducing the brittleness thereof.

In case of carbo-nitriding, also a nitrogen-containing gas is added to the gas atmosphere, such that the surface layer of every transverse segment is enriched not only with carbon, but also with nitrogen.

The thus manufactured transverse segment 1 includes an additionally hardened surface layer of 100 to 250 micrometer thickness, in which surface layer the hardness gradually decreases from the surface to the bulk or core of the transverse segment 1.

According to the present invention, the above known manufacturing method can be improved upon in terms of the resulting properties of the transverse segments 1 in relation to their application in the drive belt 50. In particular according to the present invention, the additional surface hardness can accelerate the wear of the axially oriented sides of the individual rings of the ring stack 8 of the presently considered type of drive belt 50. After all, during operation of the drive belt 50, the ring stack 8 is constrained in axial direction by the pillar parts 11 of the transverse segments 1, in particular by a side face 16 thereof that faces the central opening 5 (see figure 2).

According to the present invention, the surface hardness of the transverse segment 1 is differentiated between the pulley contact faces 12 thereof and, at least, the said pillar side face 16 thereof that arrives in contact with the ring stack 8. In particular, such surface hardness is lower at the respective pillar side face 16 than at the pulley contact face 12. In this latter respect it is noted that, deviating from the symmetric design of the transverse segment 1 of figure 2, WO2018/210456 teaches an asymmetric transverse segment design in terms of, in particular the width of the pillar parts 11 thereof on either side of the central opening 5. In this case, only one of the pillar parts 11, i.e. the widest pillar part 11 of each transverse segment 1 actually arrives in contact with ring stack 8. Thus, in this case, only the side face 16 of the widest pillar part 11 of the transverse segment 1, needs to be provided with the lower surface hardness in accordance with the present invention.

In a first elaboration of the present invention that is illustrated in figure 4, a first novel process step Cl is included in the overall manufacturing method of the transverse segment 1 in between the said two basic process steps A and B thereof. In this first novel process step Cl, a coating 17 is applied to the blanked, but unhardened transverse segment 1 at, at least, the respective pillar side face 16 thereof by means of a coating station 90, while leaving at least the pulley contact faces 12 exposed. This latter coating 17 is specifically selected to be capable of limiting or preventing carbon and/or nitrogen in the gas atmosphere from entering into the transverse segment 1 by diffusion in the said austenitizing stage I of the following hardening process step B. Thus, the said additional surface hardness that is otherwise created in the quenching stage II of the hardening process step B is limited or prevented from being created at the location of the coating 17, i.e. at the respective side face 16 of the pillar part 11 of the transverse segment 1.

In a second elaboration of the present invention that is illustrated in figure 5, a second novel process step C2 is included in the overall manufacturing method of the transverse segment 1 following the said two basic process steps A and B thereof. Also in this second novel process step C2, a coating 18 is applied to the -in this case- blanked and hardened transverse segment 1 at, at least, the respective pillar side face 16 thereof by means of a coating station 90, while leaving at least the pulley contact faces 12 exposed. In this case, however, the coating 18 is specifically selected to provide a favourable dynamic contact with the sides of the individual rings of the ring stack 8. In particular, this specific coating 18 is relatively soft and has low friction and wear resistant properties.

In a third elaboration of the present invention that is illustrated in figure 6, a third novel process step C3 is included in the overall manufacturing method of the transverse segment 1 following the said two basic process steps A and B thereof. In this third novel process step C3, the respective pillar side face 16 is ground down by means of a grinding belt 100 that is pressed against and moved relative thereto. In particular, in this third novel process step C3 the additionally hardened surface layer of the transverse segment 1, resulting from hardening process step B, is locally removed, at least in part. According to the present invention, at least 50% and preferably 100% of the thickness of the additionally hardened surface layer is thus removed, i.e. between 50 and 250 micron in absolute terms.

Additionally in this third novel process step C3, as illustrated in figure 7 in a cross- section of the transverse segment 1 intersecting the respective pillar side face 16 thereof, and due to the lower stiffness of, even, the tensioned grinding belt 100 relative to the pillar part 11, the respective pillar side face 16 can be easily provided with a favourable convex curvature in the thickness direction of the transverse segment 1.

Such convex curvature can either extend symmetrically between the front surface 2 and the rear surface 3 of the transverse segment 1, as illustrated in figure 7, or asymmetrically as illustrated in figure 8A. In particular such asymmetric convex curvature is realised by orienting the respective pillar side face 16 at an angle relative to the grinding belt 100, as illustrated in figure 8B, rather than in parallel therewith as in figure 7. In this case the side Sa of the respective pillar side face 16 that is closest to the grinding belt 100, i.e. that arrives in contact with the grinding belt 100 first and/or with a higher force, is provided with a smaller radius of curvature after grinding than the opposite edge Sb thereof. Such an asymmetric convex curvature of the pillar side face 16 may be preferred, because it takes into account an axial offset between the pulley V-grooves that occurs during operation of the transmission, as a result whereof the ring stack 8 is typically not oriented exactly perpendicular to the front and rear surfaces 2, 3 of the transverse segment 1. In particular, the said asymmetry of the convex curvature of the side faces 16 thereof is preferably provided oppositely, i.e. mirrored in said thickness direction between the two pillar parts 11 of the transverse segment 1. This can be accomplished by grinding down the side faces 16 of these two pillar parts 11 simultaneously by two grinding belts 100 (or two sections of one and the same belt 100) extending in parallel, i.e. favourably without having to reorient the transverse segment 1 during the grinding process, as illustrated in figure 8B just before the respective grinding belts 100 engage a respective pillar part 11 to starting the grinding process.

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.

Claims

1. A transverse segment (1) for a drive belt (50) with a ring stack (8) composed of a number of mutually nested bands and with a number of such transverse segments (1) that are consecutively and movably arranged on the ring stack (8), which transverse segment (1) is provided with a central opening (5) for receiving the ring stack (8), which central opening (5) is bounded by a base part (10) of the transverse segment (1) at its underside and on either lateral side thereof by a respective pillar part (11) of the transverse segment (1), which base part (10) is provided with a pulley contact surface (12) on either lateral side thereof and which pillar parts (11) each define a side surface (16) facing the central opening (5), characterized in that the transverse segment (1) is provided with a surface hardness that is lower at the location of the side surface (16) of at least one of its pillar parts (11) than at the location of the pulley contact surfaces (12) of its base part (10).

2. The transverse segment (1) according to claim 1, characterized in that it is provided with a, compared to a core thereof, additionally hardened surface layer and in that a thickness of the said additionally hardened surface layer is less at the location of the said side surface (16) of at least one of its pillar parts (11) than at the location of the pulley contact surfaces (12) of its base part (10).

3. The transverse segment (1) according to claim 1, characterized in that it is provided with a, compared to a core thereof, additionally hardened surface layer and in that at the location of the said side surface (16) of at least one of its pillar parts (11) such additionally hardened surface layer is not provided.

4. The transverse segment (1) according to claim 1, 2 or 3, characterized in that a surface hardness thereof amounts to at most 60 HRC or 750 HV at the location of the said side surface (16) of at least one of its pillar parts (11) and amounts to at least 61 HRC or 770 HV at the location of the pulley contact surfaces (12) of its base part (10).

5. A method for manufacturing a transverse segment (1) for a drive belt (50), in particular the transverse segment (1) according to one of the claims 1-4, which transverse segment (1) is provided with a central opening (5) for receiving the ring stack (8), which central opening (5) is bounded by a base part (10) of the transverse segment (1) at its underside and on either lateral side thereof by a respective pillar part (11) of the transverse segment (1), which base part (10) is provided with a pulley contact surface (12) on either lateral side thereof and which pillar parts (11) each define a side surface (16) facing the central opening (5), wherein a coating is applied to the side surface (16) of at least one of the pillar parts (11), which coating is not applied to the pulley contact surfaces (12).

6. The method for manufacturing a transverse segment (1) according to claim 5, wherein the transverse segment (1) is provided with a hardened surface layer in a carburizing or carbo-nitriding hardening treatment and wherein the said coating is applied to the said the side surface (16) of at least one of the pillar parts (11) either before or following that hardening treatment.

7. A method for manufacturing a transverse segment (1) for a drive belt (50), in particular the transverse segment (1) according to one of the claims 1-4, which transverse segment (1) is provided with a central opening (5) for receiving the ring stack (8), which central opening (5) is bounded by a base part (10) of the transverse segment (1) at its underside and on either lateral side thereof by a respective pillar part (11) of the transverse segment (1), which base part (10) is provided with a pulley contact surface (12) on either lateral side thereof and which pillar parts (11) each define a side surface (16) facing the central opening (5), wherein the transverse segment (1) is provided with a hardened surface layer in a hardening treatment (B) and wherein following the hardening treatment (B) the said hardened surface layer is at least partially removed at the location of, at least, the side surface (16) of at least one of the pillar parts (11).

8. The method for manufacturing a transverse segment (1) according to claim 7, wherein, at the location of the said side surface (16) of at least one of the pillar parts (11) and over the entire thickness of the transverse segment (1) a layer of at least 50 micron thickness, preferably of at least 125 micron thickness is removed.

9. The method for manufacturing a transverse segment (1) according to claim 7, wherein, at the location of the said side surface (16) of at least one of the pillar parts (11) and over the entire thickness of the transverse segment (1) a layer of at least 100 micron thickness and at most 250 micron thickness is removed.

10. The method for manufacturing a transverse segment (1) according to claim 7, 8 or 9, wherein the said hardened surface layer is at least partially removed in a grinding process by means of a moving grinding belt (100) having a long direction that is pressed against the said side surface (16) of at least one of the pillar parts (11).

11. The method for manufacturing a transverse segment (1) according to claim 10, wherein the said side surface (16) of at least one of the pillar parts (11) is oriented at an angle relative to the long direction of the grinding belt (100).

12. The method for manufacturing a transverse segment (1) according to claim 10 or

11, wherein the side faces (16) of both pillar parts (11) of the transverse segment (1) are removed simultaneously, preferably by means of two grinding belts (100) or grinding belt sections that are mutually oriented in parallel and that are each pressed against a respective side surface (16).