This disclosure relates to a method for manufacturing a ring from steel basic material that is suitable to function as a carrier of transverse elements in a closed- loop drive belt for a continuously variable transmission, comprising the following steps:

- providing a plate of basic material;

- bending the plate into a tube shape, whereby two side faces are placed against each other,

- fixing the said two side faces together in a welding process to form a tube,

- separating a ring-shaped section from the tube and

- processing the ring-shaped tube section to form a carrier ring for a drive belt, which processing at least includes elongating the ring-shaped tube section in a rolling process. To avoid fracturing or damaging the tube and or the ring- shaped tube section at the location of the weld and/or in the so-called heat-affected zone of the welding process when the ring-shaped section is separated from the tube, the tube is annealed prior to such separating. In such tube annealing process the brittleness that is introduced in the welding process in the weld and heat affected zone is removed by the recovery and the re-crystallization of the material at a temperature considerably above 600 degrees Celsius, e.g. at about 800°C.

It is noted that the tube annealing process is required for the same reason also in view of the rolling process, i.e. for allowing the ring shaped tube section to be elongated without being accompanied by unwanted deformation or even fracturing from within the weld or the heat affected zone thereof.

A drive belt for a continuously variable transmission is generally known. Usually, such a drive belt comprises two sets of endless, i.e. closed-loop rings that carry a multitude of transverse elements of the drive belt, which transverse elements are arranged in an essentially contiguous row along the entire circumference thereof. These carrier rings of the drive belt are relatively flat, i.e. the radial distance between an inner circumference and an outer circumference of the carrier rings is relatively small with respect to the dimension in an axial direction .

In a continuously variable transmission, the drive belt is disposed between two cooperating pulleys where between a continuously variable speed ratio is realized. During operation, the drive belt transmits a torque from one of the pulleys to the other one pulley, a/o by the transverse elements thereof pushing each other from the said one pulley to the said other one pulley.

During operation of the continuously variable transmission, the carrier rings of the drive belt are exposed to bending and pulling forces and, as a consequence, metal fatigue of a carrier ring will play a role in a possible failure of the drive belt. The resistance of the carrier rings against such metal fatigue is largely determined by the type, quality and treatment of the used steel. A preferred basic material that provides the required material properties for drive belt application of the carrier ring is maraging steel.

The separating of a ring-shaped section from the tube is commonly performed by one or more rotating cutting blades that are forced into the material of the tube, which is rotated as well. Several basic arrangements of such separating process are known in the art, as, for example, described in the international patent applications WO2005/039812-A1 and WO2004/089568-A1 and in the European patent applications EP-1130282-A and EP-1108919-A. However, in all such cases, the cutting blade or blades exert considerable (shear) stresses on the tube that can only be accommodated without fracturing or unwanted deformation, if the material of the tube is sufficiently ductile. In practice this means that after the welding of the tube and prior to separating a ring-shaped section there from, the tube must be annealed.

According to the present disclosure, by using a laser, plasma beam or similar heat source to separate a ring- shaped section from the tube by melting in a melt cutting process, the said shear stresses do not occur. Consequent ^¬ ly, with such melt cutting process the ductility or brittleness of the tube is hardly of influence on the quality of the cut, i.e. of the ring-shaped tube section. In any case the above-mentioned unwanted deformation or fracturing thereof will not occur, not even without annealing the tube prior to the melt cutting thereof.

At first sight, this latter aspect of the melt cutting process appears irrelevant in practice, because the tube annealing process must be carried out anyway, in order for the rolling process to be carried out without damaging or fracturing the ring-shaped tube section. However, based on an insight underlying the present disclosure, this aspect could still be favorably applied. In particular in accordance with the present disclosure, the annealing after welding is postponed until after separating the ring-shaped tube section from the tube in a melt cutting process. Hereby the overall effectiveness, in particular cost effectiveness of the carrier ring manufacturing method is improved.

The above-described basic features of the present disclosure will now be elucidated by way of example with reference to the accompanying figures.

Figure 1 is a schematic illustration of a part of the known drive belt including two ring sets, each represented by a number of mutually nested carrier rings, as well as a plurality of transverse elements.

Figure 2 is a diagram representing a known sequence of process steps in a known method for manufacturing a ring set for a drive belt from plate-shaped base material;

Figure 3 illustrates a known setup of the process step of separating a ring-shaped section from a tube in the known ring set manufacturing method.

Figure 4 illustrates an alternative setup of the process step of separating a ring-shaped section from a tube that is to be applied within the context of the present disclosure .

Figure 5 is a diagram representing a novel sequence of process steps as part of the manufacturing of the ring set in accordance with the present disclosure.

The known drive belt 3 that is schematically represented in part in figure 1 comprises two sets 31 of mutually nested, annular metal bands denoted carrier rings 32, as well as a several individual metal transverse elements 33, which transverse elements 33 are each provided with a recess 34 on either lateral side thereof wherein the ring sets 31 are provided. In the known drive belt 3 the transverse elements 33 form a row that spans and essentially continuously fills the entire circumference of the ring sets 31. During use in a transmission, the drive belt 3 is held between two transmission pulleys, whereby the ring sets 31 of the belt 3 are tensioned such that the row of transverse elements 33 can transmit a drive force from one pulley to another while being guided by the ring sets 31.

Figure 2 diagrammatically shows the major steps in a typical manufacturing method for forming the ring sets 31 of the drive belt 3, which includes the manufacturing of the intermediate product carrier ring.

In a first process step I, a plate 11 of basic material having a thickness of around 0.4 mm is bend into a cylindrical shape and the meeting side faces 12 of the plate 11 are welded together in a second process step II to form a hollow cylinder or tube 13. In a third step III of the process the tube 13 is annealed, to recover and re- crystallize the metal lattice, in an industrial oven 16 at a temperature considerably above 600 degree Celsius, e.g. around 800 degree Celsius. Thereafter, in a fourth process step IV, a ring-shaped section 14 is separated from the main body of the tube 13. In the next step -process step five V- the lateral side faces or edges 15 of the ring- shaped tube section 14 are treated to improve the surface quality and/or the shape thereof. In the illustrated example, the edge 15 treatment takes place by way of an edge melting process wherein the said edges 15 are reshaped by temporarily being melted by means of a heat source such as a laser 20, which edge melting process is, as such, known from WO-2012 /089228A1. Thereafter, the ring shaped tube section 14 is rolled in a sixth process step VI to reduce the thickness thereof to less than 0.2 mm, typically around 0.185 mm, while being elongated, thus forming the carrier ring 32.

The carrier ring 32 is then subjected to a further annealing process step VII for removing the work hardening effect of the previous rolling process (i.e. step five VI) Thereafter, in an eight process step VIII, the carrier ring 32 is calibrated, i.e. is mounted around two rotating rollers and stretched to a predefined circumference length by forcing the said rollers apart. In this eight process step VIII, also an internal stress distribution is imposed on the carrier ring 32. Thereafter, the carrier ring 32 is heat-treated in two separate process steps, namely a ninth process step IX of ageing or bulk precipitation hardening and a tenth process step X of nitriding or case hardening. More in particular, both such heat-treatments involve heating the carrier ring 32 in an oven chamber that is supplied with process gas that is typically composed of nitrogen and some, e.g. around 5 volume-% of hydrogen for ring ageing and of nitrogen and ammonia for ring nitriding Both heat-treatments typically occur within the tempera ^¬ ture range from 400 degrees Celsius to 500 degrees Celsius and can each last for less than 30 to over 120 minutes in dependence on the metal used for the carrier ring 32 (i.e. typically a maraging steel alloy) , as well as on the mechanical properties desired for the carrier ring 32.

Finally, a laminated ring set 31 is formed by radially stacking, i.e. nesting, a number of thus processed carrier rings 32, as is further indicated in figure 3 in the last depicted eleventh process step XI . Obviously, the carrier ring 32 of the ring set 31 have to be suitably dimensioned, e.g. have to differ slightly in circumference length to allow the carrier rings 32 to be closely fitted one around the other. To this end the carrier rings 32 of the ring set 31 are typically purposively selected from a stock of carrier rings 32 of varying dimensions.

A known setup of the above fourth process step IV of separating the ring-shaped tube section 14 from the tube 13 is schematically illustrated in figure 3. Figure 3 depicts the tube 13 in cross-section; however, in reality the diameter of the tube 13 is much larger relative its wall thickness. The circles 17 indicate several consecutive radial positions of an essentially cylindrical and rotatable cutting tool 17 relative to the tube 13 during the cutting process. However, in reality the cutting tool 17 has a fixed radial position, whereas the tube 13 is rotated with respect thereto. On the inside the tube 13 a counter tool 18 provides a support for the tube 13 when the cutting tool 17 moves radially inward during the cutting process. The actual cutting occurs in two phases I, II. In a first phase I of the cutting, the cutting tool 17 is gradually moved through the wall thickness (positions Ia-Ic) of the rotating tube 13 thus following a spiral cutting line C in the material of the tube 1. Then, in a second phase II of the cutting, the ring-shaped section is fully separated from the tube 13 in one full rotation of the tube 13. It may be clear that in this known setup of the fourth process step IV a substantial cutting force is exerted on the tube 13 by the cutting tool 17.

An alternative setup of the process step IV of separating the ring-shaped tube section 14 from the tube 13 is schematically illustrated in figure 4. In this second embodiment a concentrated heat source (e.g. a laser beam) 19 is used to melt through the wall thickness of tube 13. In one full rotation of the tube 13 relative to the heat source 19, a complete circumferential cut is made from a start position S and the ring-shaped section 14 is separated from the tube 13. It may be clear that in this particular setup of the fourth process step IV only minimal forces are exerted on the tube 13 and/or the ring- shaped section 14.

In practice, the internal stress, which is introduced into the material of the tube 13 at welding, in combination with the forces exerted by a mechanical cutting tool 17, 18, such as the one illustrated in figure 3, cause the tube 13 and/or the ring-shaped tube section 14 to be damaged, e.g. by an unwanted deformation thereof, or even to fracture. However, in a melt cutting process, no substantial cutting forces are exerted and, hence, the tube 13 and/or the ring-shaped tube section 14 will not be damaged thereby. Thus, the third process step III of tube annealing need not necessarily be carried out if the ring- shaped section 14 is separated from the tube 14 (process step IV) by means of a melt cutting process instead of a mechanical cutting process. Still, the resulting ring- shaped tube section 14 must be annealed prior to the rolling thereof, i.e. prior to the sixth process step VI of the manufacturing of the carrier ring 32 and finally of the ring set 31 of the drive belt 3.

According to the present disclosure the annealing of the ring-shaped tube section 14 is favorably postponed, i.e. is carried out only until after the edges 15 thereof are treated in the fifth process step V. In this particular setup of the overall carrier ring manufacturing method, the fifth process step V of edge melting can be carried out in accordance with the known art, i.e. including the after treatment of annealing as taught by WO-2012 /089228A1 , however, favorably without a second annealing process step prior to the sixth process step VI of rolling the ring- shaped tube section 14. This novel setup of the relevant part of the manufacturing of the carrier ring is illustrated in figure 5.

According to figure 5, after the welding of the tube 13 in the second process step II, the tube 13 is immediately cut into a several ring-shaped sections 14 in a melt cutting process, i.e. in the fourth process step IV, thus skipping the third step III of annealing in the conventional manufacturing method. Thereafter, in the fifth process step V, the edges 15 of the ring-shaped tube section 14 are treated by a laser 20 that temporarily melts these edges 15. Only thereafter is the ring-shaped tube section 14 subjected to a process step V-b of annealing, in order to equalize the material properties throughout the ring- shaped tube section 14 by recovery and re-crystallization. In this latter process step V-b the heat affected zones resulting from the welding process step II, the separating process step IV and the edge melting process step V are all removed simultaneously, i.e. favorably in a single process step V-b. Thus in the said fourth process step IV of melt cutting and in the said fifth process step V of edge melting, the metal crystal structure of the tube 13 still includes the irregularities that were formed therein the second process step II of tube welding, i.e. still includes a weld structure and a heat affected zone.

Finally, it is noted that, even if it is not opted for an edge melting process to treat the edges 15 of the ring- shaped tube section 14 (process step V) , but instead another process such as stone tumbling or brushing is applied for this purpose, it can still be advantageous to anneal the ring-shaped tube section 14 only after such another edge treatment process is completed. After all, in this manner, only those intermediate products that meet the required quality standards after melt cutting (process step IV) and edge treatment (process step V) will (have to) be annealed (process step V-b) prior to rolling (process step VI) .

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 that 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.