WO2022128043A1

WO2022128043A1 - Method for manufacturing a metal ring for a ring-set of a drive belt for a continuously variable transmission

Info

Publication number: WO2022128043A1
Application number: PCT/EP2020/025582
Authority: WO
Inventors: Jeihad Zeadan
Original assignee: Robert Bosch Gmbh
Priority date: 2020-12-16
Filing date: 2020-12-16
Publication date: 2022-06-23

Abstract

The invention concerns a method for manufacturing metal rings (41) for a drive belt (3) comprising a laminated set (31 ) of such metal rings (41), wherein the rings (41 ) are formed by cutting (IV) these from a tube (22) and wherein the cut rings (41 ) are rolled (V) to reduce their thickness, while increasing their length. According to the invention, the process step of cutting (IV) the rings (41) from the tube (22) is arranged to vary the width of a ring (41) cut from the tube (22) in relation to, in particular, a wall thickness of the tube (22) before cutting (IV).

Description

METHOD FOR MANUFACTURING A METAL RING FOR A RING-SET OF A DRIVE BELT FOR A CONTINUOUSLY VARIABLE TRANSMISSION

This disclosure relates to a method for manufacturing a metal ring for a ring-set of a drive belt for a continuously variable transmission, as well as to a drive belt including such metal ring. The drive belt is, as such, well-known, for example from the British patent publication GB1286777 (A) or from the more recent international patent publication WO2015/177372 (A1 ). This known drive belt consists of a number of mutually nested, endless flexible metal bands or rings, i.e. that are mutually concentrically stacked into a set of rings, i.e. ring-set, and a number of metal transverse segments that are arranged along the circumference of such ring-set in an essentially contiguous row. The transverse segments each define a central opening that is defined by and between a base part of the transverse segment and two pillar parts, each pillar part extending from a respective axial side of the base part in radial outward direction, in which central opening a respective circumference section of the ring-set is accommodated, while allowing the transverse segments to move, i.e. slide along the circumference thereof. For containing the ring-set in the central opening, the central opening is partly closed in radial outward direction by a respective axially extending portion of at least one and possibly both of the pillar parts. In particular, such axially extending portion of a respective pillar part extends partly over the ring-set towards the other, i.e. axially opposite, pillar part of the transverse segment and is denoted a hook portion of the pillar part hereinafter.

In the above and below description, the axial, radial and circumference directions are defined relative to the drive belt when placed in a circular posture. The thickness direction and thickness dimension of the transverse segments are defined in the circumference direction of the drive belt, the height direction and height dimension thereof are defined in the radial direction of the drive belt and the width direction and width dimension thereof are defined in the axial direction of the drive belt. The thickness direction and thickness dimension of the ring-set and of the individual rings thereof are defined in the radial direction of the drive belt, the width direction and width dimension of the ring-set and of the individual rings thereof are defined in the axial direction of the drive belt and the length direction and length dimension of the ring-set and of the individual rings thereof are defined in the circumference direction of the drive belt. Up and down directions and above and below positions are defined relative to the radial direction, i.e. in the height direction of the transverse segments and in the thickness direction of the rings/ring-set.

In the continuously variable transmission the drive belt is wrapped around and in friction contact with two pulleys that each define a V-groove of variable width, in which pulley V-grooves respective parts of the drive belt are held at a variable radius. By varying such belt radius at the transmission pulleys, a speed ratio of the transmission can be varied. This type of transmission is commonly applied in the drive train of passenger cars and other motor vehicles.

In an alternative known design of the drive belt the transverse segments thereof each define two lateral openings, one on either lateral side of a central or neck part of the segment, which neck part is located between and connects a bottom or body part and a top of head part of the segment. This type of drive belts includes two sets of nested rings, each accommodate in a respective one of the lateral openings of the transverse segment. In this latter drive belt design that is for example known from WO2015/097293, the two ring-sets are considerably less wide individually than the single ring-set of the first- mentioned drive belt design.

The basic setup of the overall manufacturing method of such drive belts is also well- known and entails a considerable number of process steps that are carried out with very high accuracy, i.e. with very narrow tolerances, realising a high quality end-product with an exceptional mechanical strength and wear resistance. In particular in relation to the ringset, such basic setup is for example described in WO2018/122397 and a/o entails forming the rings of the ring-set from a coil of basic material, including the process steps of:

- cutting a plate-shaped section from the coil;

- bending this plate into a cylinder;

- welding the bend plate section to form a tube;

- cutting subsequent ring-shaped sections from the tube; and of

- rolling these ring-shaped sections or rings individually, by compressing each ring between a pair of rolling rolls, while being rotated in circumference direction, to decrease its thickness, while increasing its (circumference) length.

The latter process step of rolling is described in detail in W02004/050270. According to this latter document, the thickness of the ring before rolling is measured and the process parameters of the rolling process are determined in dependence of such measured thickness. In particular, such rolling process parameters are determined to obtain the desired thickness and length of the ring after rolling. Typically, in drive belt manufacturing, such desired thickness is the same for all rings of the ring-set, whereas their desired length is required to vary as they are later mutually nested to from the ringset. Still, the desired thickness can be set to vary as well, for example in dependence on the intended position of the specific ring within the ring-set.

In the known rolling process, i.e. by allowing the width of the rings after rolling to vary, the thickness and length thereof can be controlled towards the said desired values with high accuracy, which favourably enables the application of a well-defined and narrowly controlled clearances between the rings in the ring-set. Further according to W02004/050270, such width variation of the rings after rolling can, at least to a certain extent, be controlled by relating the said measured thickness before rolling to the said desired ring length after rolling. In this case, thicker rings are rolled to a longer ring length and vice versa.

The present invention aims to further improve upon the drive belt manufacturing method in terms of at least the accuracy of the thickness and the length of the rings obtained after rolling and preferably also their width. Even though such further dimensional accuracy improvement is expected to only marginally increase the mechanical strength of the ring-set, it can still be beneficial in terms of the performance and/or durability of the drive belt as a whole. In particular, by reducing the dimensional tolerances of ring-set, favourably less clearance between the transverse elements and the ring-set needs to be included in the design of the drive belt. For example, in the first-mentioned drive belt design, a clearance required between the transverse segments and the ring-set in radial direction is determined not only by the thickness of the ring-set, but also by its width, because of the way the transverse segments have to be mounted on the ring-set in this design.

According to the present invention, such aim is realised in the said process step of cutting a ring-shaped section from the tube. In particular according to the invention, the cutting process is arranged to cut rings of varying width from the tube. For example, if the rings are cut from the tube by laser cutting, the distance that the laser is displaced relative to and in the axial direction of the tube after cutting a first ring from the tube, which axial distance determines the width of the ring that is subsequently cut from tube, is variable. The invention thus provides a further parameter for the control of the manufacturing method of the drive belt ring component, allowing the dimensional accuracy of the ring after rolling to be favourably increased.

In the known drive belt manufacturing method, the rings are cut from the tube with the same width, such that a variation in the (wall) thickness of the tube results in a variation in the volume of the rings that are subsequently cut from the tube. Even though, after the next process step of rolling, different ring lengths are required (i.e. to mutually, concentrically nest the rings, i.e. to form the ring-set), such required length variation does -in practice- not fully compensate for the said volume variation, meaning that after rolling the width of the rings necessarily, however, disadvantageously, varies as well. By employing the manufacturing method according to the present invention, such known ring width variation can be favourably reduced.

In a more detailed embodiment of the present invention, the width of the ring cut from the tube in cutting is controlled, i.e. can be adapted in relation to an actual, i.e. measured thickness of either the coil, the plate or the tube. By measuring such thickness before cutting the rings from the tube and by controlling the width of the cut rings in relation to such measured thickness, the said variations in ring volume can be favourably reduced, as are the ring width variations after rolling. Ideally, the thickness of the coil, plate or tube is measured at multiple locations, preferably each such location corresponding to each ring that is later cut from such coil, plate or tube. This latter aspect of the present invention is most easily and also most effectively implemented in the cutting process. In particular in this respect, the cutting process is additionally arranged to measure the thickness of the tube close to an end thereof, before a ring is cut from such tube end.

Alternatively or additionally, the width of the ring cut from the tube in cutting is controlled in relation to one or more of:

(ii) an actual diameter of the tube determined before cutting,

(iii) a desired length of the ring after rolling,

(iv) a desired thickness of the ring after rolling, and/or of

(v) a desired width of the ring after rolling.

By such control of the width of the cut ring, the accuracy of the dimensions of the ring after rolling can be remarkably improved.

The drive belt manufacturing method according to the present disclosure will now be explained further with reference to the drawing figures, whereof:

Figure 1 is a schematic illustration of a known transmission incorporating two variable pulleys and a drive belt;

Figure 2 illustrates two known drive belt types in a schematic cross-section, each provided with a set of nested, flexible metal rings and with a plurality of metal transverse segments that are slidably mounted on such ring-set along the circumference thereof;

Figure 3 provides a diagrammatic representation of the presently relevant part of the known overall manufacturing method of the drive belt;

Figure 4 is a schematic representation of a novel setup of a process step of cutting in the overall manufacturing method of the drive belt;

Figure 5 illustrates a step of measuring a wall thickness preceding the process step of cutting of figure 4.

Figure 1 shows the central parts of a known continuously variable transmission or CVT that is commonly applied in the drive-line of motor vehicles between the engine and the driven wheels thereof. The transmission comprises two pulleys 1 , 2 that are each provided with a pair of conical pulley discs 4, 5 mounted on a pulley shaft 6 or 7, between which pulley discs 4, 5 a predominantly V-shaped circumferential pulley groove is defined. At least one pulley disc 4 of each pair of pulley discs 4, 5, i.e. of each pulley 1 , 2, is axially moveable along the pulley shaft 6, 7 of the respective pulley 1 , 2. A drive belt 3 is wrapped around the pulleys 1 , 2, located in the pulley grooves thereof, for transmitting a rotational movement and an accompanying torque between the pulley shafts 6, 7.

The transmission typically also comprises activation means (not shown) that -at least during operation- impose on the said axially moveable pulley disc 4 of each pulley 1 , 2 an axially oriented clamping force that is directed towards the respective other pulley disc 5 of that pulley 1 , 2, such that the drive belt 3 is clamped between each such disc pair 4, 5. These clamping forces not only determine a friction force that can maximally be exerted between the drive belt 3 and a respective pulley 1 , 2 to transmit the said torque, but also radial positions R of the drive belt 3 in the pulley grooves. These radial position(s) R determine a speed ratio of the transmission. This type of transmission and its operation are well-known per se.

In figure 2, two known examples of the drive belt 3 are schematically illustrated in a cross-section thereof facing in the circumference direction thereof. In both examples, the drive belt 3 comprises transverse segments 32 that are arranged in a row along the circumference of an annular carrier in the form of one or two sets 31 of metal rings 41 . In either example of the drive belt 3, the ring-set 31 is laminated, i.e. is composed of a number of mutually nested, flat, thin and flexible individual rings 41. A thickness of the transverse segments 32 is small relative to a (circumference) length of the ring-set 31 , in particular such that several hundred transverse segments 32 are comprised in the said row thereof. Although in the accompanying figures the ring-set 31 is illustrated to be composed of 5 nested rings 41 , in practice, mostly 6, 9, 10 or 12 rings 41 are applied in such ring-set 31 .

On the right-side of figure 2 an embodiment of the drive belt 3 is illustrated incorporating only a single ring-set 31. In this case, the ring-set 31 is accommodated in a centrally located recess of the transverse segment 32 that opens towards the radial outside of the drive belt 3. Such central opening is defined between a base part 39 and two pillar parts 36 of the transverse segment 32 that respectively extend from either axial side of the base part 39 in radial outward direction. In such radial outward direction, the central opening is partly closed-off by respective, axially extending hook parts 37 of the pillar parts 36.

On the left-side of figure 2 an embodiment of the drive belt 3 is illustrated including two such ring-sets 31 , each accommodated in a respective laterally oriented recess of the transverse segment 32 that opens towards a respective, i.e. left and right, axial sides thereof. Such lateral openings are defined between a body part 33 and a head part 35 of the transverse segment 32 on either side of a relatively narrow neck part 34 that is provided between and interconnects the body part 33 and the head part 35.

On either side thereof, the transverse segments 32 of both of the drive belts 3 are provided with contact faces 38 for arriving in friction contact with the pulley discs 4, 5. The contact faces 38 of each transverse segment 32 are mutually oriented at an angle <p that essentially matches an angle of the V-shaped pulley grooves. The transverse segments 32 are typically made from metal as well.

It is well-known that, during operation in the transmission, the individual rings 41 of the drive belt 3 are tensioned by a/o a radially oriented reaction force to the said clamping forces. A resulting ring tension force is, however, not constant and varies not only in dependence on a torque to be transmitted by the transmission, but also in dependence on the rotation of the drive belt 3 in the transmission. Therefore, in addition to the yield strength and wear resistance of the rings 41 , also the fatigue strength is an important property and design parameter thereof. Accordingly, maraging steel is used as the basic material for the rings 41 , which steel can be hardened by precipitation formation (ageing) to improve the overall strength thereof and additionally be surface hardened by nitriding (gas-soft nitriding) to improve wear resistance and fatigue strength in particular.

Figure 3 illustrates a relevant part of the known manufacturing method for the ringset 31 , as it is typically applied in the art for the production of metal drive belts 3 for automotive application. The separate process steps of the known manufacturing method are indicated by way of Roman numerals.

In a first process step I a thin sheet or plate 20 of a maraging steel basic material, typically having a thickness in the order of 0.3 to 0.6 mm is bend into a cylindrical shape and the meeting plate ends 21 are welded together in a second process step II to form a hollow cylinder or tube 22, typically with a diameter in the order of 10-20 cm. In a third step III of the process, the tube 22 is annealed in an oven chamber 50 to reduce bending stress and welding homogeneity by recovery and re-crystallization of the ring material at a temperature considerably above 600 degrees Celsius, e.g. about 800 °C. Thereafter, in a fourth process step IV, the tube 22 is cut into a number of rings 41 , each typically with a width in the order of 5 to 15 mm.

After cutting IV, the rings 41 are rolled to a larger diameter -process step five V- while the thickness thereof is reduced to between 0.15 and 0.25 mm, typically to about 0.18-0.19 mm. Between cutting IV and rolling V an annealing process may optionally be applied (not illustrated). The rolled rings 41 are subjected to a further, i.e. ring annealing process step VI for removing the work hardening effect of the previous rolling process step V.

After annealing VI, the rings 41 are calibrated in a seventh process step VII by being mounted around two rotating calibration rolls and stretched to a predefined (circumference) length by forcing the said rolls apart. In this seventh process step VII of ring calibration, the ring 41 is typically also provided with a slight transverse curvature, i.e. crowning, and an internal residual stress is imposed upon the rings 41. Thereafter, the rings 41 are heat- treated in an eighth process step VIII of combined ageing, i.e. bulk precipitation hardening, and nitriding, i.e. case hardening. More in particular, this heat treatment involves keeping the rings 41 in an oven chamber 50 containing a process atmosphere composed of ammonia, nitrogen and hydrogen. It is noted that the illustrated, combined heat treatment can alternatively be followed or preceded by an aging treatment (without simultaneous nitriding). Such separate aging treatment is applied when the duration of the nitriding treatment is too short to simultaneously complete the precipitation hardening process.

A number of the thus processed rings 41 are assembled in a ninth process step IX to form the ring-set 31 by the radially nesting, i.e. the concentrically stacking of selected rings 41 . In order realize a minimal radial play or clearance between each pair of adjoining rings 41 in the ring-set, the subsequent rings 41 of the ring-set 31 are carefully selected in terms of the length thereof from a stock of rings of varying length. It is noted that it is also known in the art to instead assemble the ring-set 31 immediately following the seventh process step VII of ring calibration, i.e. in advance of the eighth process step VIII of ring ageing and ring nitriding.

It is known to be beneficial for the ultimate performance of the drive belt 3 that the ring-sets 31 and thus also the individual rings 41 thereof are manufactured with high accuracy in terms of their (circumference) length and (radial) thickness. After all, these two dimensions determine the clearances between the subsequent rings 41 in the ring-set 31 . In this respect, it is known to control the rolling process step V in dependence on the thickness of the ring 41 that is measured before rolling. In this way, it was found possible to roll the rings 41 to the desired length and thickness with high accuracy, while variations in the volume of the rings 41 predominantly result in variations in the width of the rolled rings 41. Nevertheless, also these width variations are preferably minimized as much as possible, such that favourably less clearance is needed in the design of the drive belt 3 between the transverse elements 32 and the ring-set 31. In particular, a safety margin added to such clearance to account for the said ring width variations can then be reduced.

According to the present invention, the cutting process (step IV) is arranged to cut rings 41 of variable width W1 , W2, W3 from the tube 22, as illustrated in figure 4, although not to scale. Hereby, a width variation between the rings 41 after the rolling process (step V) can be favourably reduced, in particular by adapting the width W1 , W2, W3 of the rings 41 cut from the tube 22 in step IV in relation to one or more of the parameters of: (i) an actual thickness of the basic material determined before cutting,

(ii) an actual diameter of the tube 22 determined before cutting,

(iii) a desired length of the ring 41 after rolling,

(iv) a desired thickness of the ring 41 after rolling, and/or of

(v) a desired width of the ring 41 after rolling.

In practice, such width adaptation in cutting will be small compared to the width of the ring 41 to be cut, in particular less than 10% and typically in the order of 0.5% to 5%, i.e. much smaller than what is illustrated in figure 4.

In the illustrated example, the rings 41 are cut from the tube 22 by means of a laser 23 in a laser cutting process that is known as such. The distance D3 that the laser 23 is displaced in the axial direction of the tube 22 after cutting a previous ring 41 * from the tube 22 corresponds to the width W3 of the ring 412 that is to be cut from the tube 22 next. Alternatively to displacing the laser 23, the tube 22 can of course be displaced relative to the laser 23 over the same distance D3 in the opposite axial direction.

The invention thus provides a further parameter for the control of the manufacturing method of the drive belt ring 41 component, allowing the dimensional accuracy thereof to be favourably increased.

To most effectively improve the accuracy of the width of the ring 41 after rolling, i.e. to most effectively reduce variations thereof, at least the thickness Tm of the basic material before cutting is measured, which measured thickness Tm is then used to determine the width W1 , W2, W3 of the rings 41 to be cut from the tube 22 in step IV. Preferably, such measured thickness Tm is determined in relation to the tube 22, more preferably at the location of, and for each ring 412 that is to be cut therefrom next, as illustrated in figure 5.

The present invention, in addition to the entirety of the preceding description and all details of the accompanying figures, also concerns and includes all of the features of the appended set of claims. Bracketed references in the claims do not limit the scope thereof, but are merely provided as 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 that lie within reach of the person skilled in the relevant art.

Claims

9 CLAIMS

1. A method for manufacturing metal rings (41 ) intended for use in a drive belt (3) comprising a laminated set (31 ) of such metal rings (41 ), wherein the rings (41 ) are formed by subsequently cutting (IV) these from a tube (22) and wherein the cut rings (41 ) are rolled (V) to reduce their thickness while increasing their length, characterized in that the process step of cutting (IV) is arranged to be able to vary the width of the rings (41 ) cut from the tube (22).

2. The method for manufacturing a metal ring (41 ) according to claim 1 , characterized in that the width of rings (41 ) cut from the tube (22) is controlled in relation to one or more of the parameters of:

(i) an actual thickness of the basic material determined before cutting,

(ii) an actual diameter of the tube (22) determined before cutting,

(iii) a desired length of the ring (41 ) after rolling,

(iv) a desired thickness of the ring (41 ) after rolling, and/or of

(v) a desired width of the ring (41 ) after rolling.

3. The method for manufacturing a metal ring (41 ) according to claim 1 , characterized in that the tube (22) is formed by bending (I) and welding (II) a steel plate (20) and in that the width of rings (41 ) cut from the tube (22) is controlled in relation to at least the thickness of the steel plate (20).

4. The method for manufacturing a metal ring (41 ) according to claim 3, characterized in that the thickness of the steel plate (20) is measured at several locations along a direction that is perpendicular to a direction wherein the plate (20) will be bend to form the tube (22).

5. The method for manufacturing a metal ring (41 ) according to claim 1 , characterized in that the width of rings (41 ) cut from the tube (22) is controlled in relation to at least the wall thickness of the tube (22).

6. The method for manufacturing a metal ring (41 ) according to claim 5, characterized in that the wall thickness of the tube (22) is measured at a location (412) where the next ring (41 ) will be cut from the tube (22).

7. A drive belt (3) comprising a single laminated set (31 ) of metal rings (41 ) and a multitude of metal transverse segments (32) that are arranged along the circumference of such ring-set (31 ) in an essentially contiguous row and that each define a central opening between a base part (39) of the transverse segment (32) and two pillar parts (36) thereof, each pillar part (36) extending from a respective axial side of the base part (39) in radial outward direction, whereof at least one and preferably both pillar parts (36) are provided with a hook portion (37) that extends over the central opening in the general direction of the other pillar part (36), partly closing-off the central opening in radial outward direction, in which central opening a respective circumference section of the ring-set (31 ) is accommodated, while allowing the transverse segments to move, i.e. slide along the circumference thereof, characterized in that, the metal rings (41 ) of the ring-set (31 ) are manufactured with the manufacturing method according to a preceding claim.