WO2024141176A1 - A drive belt with transverse members and a ring stack for a continuously variable transmission - Google Patents

Abstract

The present invention concerns a transverse member for a drive belt for a belt-and- pulley-type continuously variable transmission comprising a row of these transverse members mounted on a stack of several, mutually nested rings. The transverse members are provided with a trapezoidal base portion (13) having two contact surfaces (37) that are provided with grooves (38) between ridge parts (39) thereof. According to the invention, an uppermost ridge part (39-b) and a lowermost ridge part (39-a) of the contact surfaces (37) lie in the same plane (VTP) and have essentially the same width as the ridge parts (39) thereof that are located between the grooves (38) thereof.

Description

A DRIVE BELT WITH TRANSVERSE MEMBERS AND A RING STACK FOR A CONTINUOUSLY VARIABLE TRANSMISSION

This invention relates to a transverse member or segment that is destined to be

5 part of a drive belt for a continuously variable transmission with two pulleys and the drive belt. Such a drive belt is known from the European patent application publication WO2015/097293-A1 and comprises a row of metal transverse members that are jointly mounted on and along the circumference of at least one stack of a number of mutually nested, continuous metal bands, i.e. flat and thin rings. The transverse members each define at least one slot for accommodating and confining a respective circumference section of the at least one ring stack, while allowing the transverse members to move, i.e. to slide along the circumference thereof. This particular type of drive belt is known as a push-type drive belt or pushbelt.

In the following description the axial, radial and circumference directions are

15 defined relative to the drive belt when placed in a circular posture outside the transmission. Furthermore, a thickness dimension of the transverse members is defined in the said circumference direction of the drive belt, a height dimension of the transverse member is defined in the radial direction of the drive belt and a width dimension of the transverse member is defined in the axial direction of the drive belt.

20 The known transverse members each comprise a base portion, a middle portion and a top portion. The middle portion of the transverse members extends in radial direction between the said base and top portions thereof, while the said slot or slots are defined between the base portion and the top portion of the transverse member, to the side of the said middle portion thereof. At such slot or slots, a radially outward facing

25 surface of the base portion of the transverse member is intended to contact and support the ring stack in radial outward direction. This particular surface or surfaces are denoted as bearing surface(s) hereinafter.

In the row of transverse members of the drive belt, at least a part of a front main body surface (facing in the predominant direction of belt rotation in the transmission) of the transverse member abuts against at least a part of the (oppositely facing) back main body surface of a respectively leading transverse member in the said row, whereas at least a part of the back main body surface of the transverse member abuts against at least a part of the front main body surface of a respectively trailing transverse member. At least one of these front and back main body surfaces of the transverse member, for

35 example the front main body surface includes an axially extending, convexly curved surface part. This curved surface part divides the front main body surface into a radially

Received at EPO via Web-Form on Dec 30, 2023 outer and a radially inner surface parts that are oriented at an angle relative to one another. Abutting transverse members in the drive belt are able to tilt relative to one another, while remaining in mutual contact at such curved surface part that is denoted tilting edge hereinafter, but that is also designated as rocking edge in the art. The tilting

5 edge allows the row of the transverse members of the drive belt to follow a local curving of the ring stack(s) imposed by the pulleys.

The transverse member is further provided with a protrusion, i.e. stud that protrudes from its front main body surface and with a cavity, i.e. hole that is recessed in its back main body surface. In the row of transverse members of the drive belt, the protrusion of the said trailing transverse member is at least partially located in the cavity of the said leading transverse member. Hereby, a mutual displacement of the abutting transverse members in a plane perpendicular to the circumference direction of the drive belt is prevented or, at least, is limited. Typically, the protrusion and the cavity are of a similar overall shape, e.g. predominantly cylindrical with a slight conicity, i.e. taper. The

15 protrusion is sized somewhat smaller than the cavity, such that in the drive belt a clearance exists between the inner circumference of the cavity of leading transverse member and the outer circumference of the protrusion of the trailing transverse member that is inserted in the cavity of the leading transverse member, in particular that is fully inserted therein. Thus, in case of the said predominantly cylindrical shape of the cavity

20 and the protrusion, the outer diameter of the protrusion is less than the inner diameter of the cavity. In this latter respect it is noted that, since the cavity and the protrusion are typically somewhat tapered, i.e. are slightly cone shaped, the diameter of the cavity and the diameter the protrusion are compared at an equal distance perpendicular to the rear and the front main body surface of the transverse member respectively.

25 Parts of the circumference surface of the transverse member that extends between the front and back main body surfaces thereof, are intended for (frictionally) contacting the pulleys by being clamped between two conical discs of each pulley. One such pulley disc engaging part of the circumference surface of the transverse members is provided on either axial side thereof and is denoted as (pulley) contact surface. Such contact surfaces of the transverse member are mutually oriented at an angle and a so- called belt angle is defined as the nominal value, i.e. average of that angle for all of the transverse members of the drive belt.

The friction contact between the contact surfaces of the transverse members and the pulley discs allows a force to be transmitted there between, such that the drive belt

35 can transfer a drive torque and a rotational movement from one pulley to the other. Furthermore, because of the conical shape of the pulley discs, the transverse members

Received at EPO via Web-Form on Dec 30, 2023 also experience a radially outward directed force component of the clamping force that is exerted at/by each pulley. This latter radial force component puts the drive belt and in particular the ring stack thereof under tension and also enables a displacement of the respective parts of the drive belt located between the pulley discs of each pulley in

5 mutually opposite radial directions between a smallest and a largest radial position thereof. The respective radial positions of the drive belt at the two pulleys determine a speed (and torque) ratio of the transmission between the pulleys thereof.

In relation to the belt angle, WO2015/097293-A1 teaches to design the transverse members such that the belt angle exceeds a -so called- pulley angle that is defined by and between the conical discs of input pulley of the transmission, which is the pulley that is directly connected to an engine or motor, i.e. that rotates at a speed that is the same as, or that is at least proportional to a rotational speed of the said engine or motor. By this difference between the belt angle and the pulley angle, a coefficient of friction between the drive belt and the input pulley is favorably increased, as is a

15 maximum drive torque that can be transmitted by the transmission at given pulley clamping forces. In particular according to WO2015/097293-A1 , the belt angle hereto exceeds the pulley angle by at least 0.2 degree and at most 1.2 degree.

A further known design measure for increasing the coefficient of friction between the drive belt and the pulleys is described in JP2000-179626-A and EP3835618-A1 that

20 both teach to offset the protrusion of the transverse members of the drive belt relative to the cavity thereof in radial inward direction. Hereby, a (virtual) central axis of a predominantly cylindrical or conical protrusion is located radially inward of a (virtual) central axis of the correspondingly shaped cavity. Thus, in this design of the transverse members the aforementioned clearance of the protrusion inside the cavity in the drive

25 belt is smaller at the underside of the protrusions than at the upper side thereof. In fact, according to EP3835618-A1 , such clearance can be removed completely, meaning that the radially inner extend, i.e. the underside of the protrusion essentially coincides with the underside of the cavity, or is even located radially inward thereof.

By this offset between the protrusions and cavities thereof, the transverse members are inclined -or at least have a tendency to incline- backwards in the row of the drive belt, even when otherwise traveling in a straight trajectory between the pulleys, because of the forced insertion of the protrusion into the (higher lying) cavity. Thus, the transverse members enter between the pulley discs in such backwards inclined orientation, whereby the said friction thereof with the pulley in tangential direction is

35 known to be favorably increased.

It is common practice in the art to provide a number of essentially equally spaced

Received at EPO via Web-Form on Dec 30, 2023 grooves in the otherwise flat surface of the contact surfaces, which grooves extend between and essentially perpendicular to the front and back main body surfaces of the transverse member. These grooves serve to accommodate and/or drain transmission fluid away from the contact surfaces when the higher-lying contacting parts thereof,

5 located between the grooves, arrives in (friction) contact with the pulleys. In fact, in relation to such macroscopic surface structure of the contact surfaces many design variants have been suggested in the art (see e.g. W02013/000493-A1 , JP2011-075089- Al , JP2010-0236663-A1 , EP2119939-A1 , JP2007 -303520-A1 , EP-0994275-A1) and for each such design variant several design variables are applicable, such as a groove pitch (i.e. as measured center-to-center between adjacent grooves in a virtual tangent plane of the contact surfaces), a groove depth (i.e. as measured perpendicular to the said tangent plane) and a contact ratio (as calculated by the groove pitch minus a groove width -as measured along the said tangent plane of the contact surfaces-, all divided by the groove pitch). It is thus not at all evident what detailed shape of the contact surfaces -i.e. what

15 surface structure thereof- is to be preferred in practice.

In consideration of the above-mentioned state of the art with partly diverging, incomplete and/or even confliction teachings, the present invention aims to provide a detailed shape of the contact surfaces that delivers the optimum between manufacturability of the transverse member, operating performance of the drive belt and

20 its longevity and, thus, to consolidate the known technical insights.

According to the present invention, the grooved contact surfaces of the transverse members are provided with a flat, or at most only minimally convexly curved surface part at both its upper end, where the contact surface transitions into the bearing surface via a convexly curved transition surface, and at its lower end, where the contact

25 surface transitions into a bottom surface of the base portion of the transverse member, likewise via a convexly curved transition surface. These flat or minimally convexly curved surface parts coincide with the virtual tangent plane of the respective contact surface, such that these provide for contact areas with the pulley discs that are maximally spaced along the height direction of the transverse member. Such maximum spacing being advantageous in providing the stable contact between the transverse members and the pulley discs, in particular resisting a rotation of the transverse members relative to the radial direction of the pulley discs that would otherwise disadvantageously reduce the friction.

Preferably, these upper and lower end parts of a respective contact surface

35 extend in the height direction over about the same distance as the said contacting parts of that contact surface extend between a pair of adjacent grooves. Otherwise, i.e. if

Received at EPO via Web-Form on Dec 30, 2023 these end parts are too short, there is a risk that the said convexly curved transition surface transitions directly to the uppermost or lowermost groove of the contact surface respectively, after stone tumbling the transverse member in manufacturing. Stone tumbling is conventionally applied to round-off the edges of the transverse member and

5 remove burr after these are cut, in particular blanked from basic material.

Preferably also, these upper and lower end parts, as well as the said contacting parts of a respective contact surface are all minimally convexly curved with a radius of curvature of not less than 1 mm and preferably not more than 10 mm. Hereby, initially during a so-called running-in phase of drive belt operation in the transmission, a relatively high wear rate of the contact surfaces occurs, due to the initially limited contact area with the pulley discs, allowing the transverse member to quickly and optimally settle to the pulleys, in particular to the precise angle defined by and between the pulley discs thereof.

Preferably also, the grooves are each defined by a concavely curved groove

15 bottom with convexly curved groove edges on either side thereof, which groove edges align with a respective contacting part or one of the upper and lower end parts of the contact surface. Such a curved groove contour being advantageous to manufacture, in particular in a blanking process for cutting the transverse member out of strip material. Moreover, the convex design of the groove edges ensures that the contact ratio of the

20 contact surfaces increases favorably quickly after the said running-in phase of drive belt operation, thus minimizing further wear of the contact surfaces during prolonged drive belt operation, provided that the contact ratio after running-in wear is large enough. Ideally in this latter respect, the radius of curvature of the groove bottom and groove edges is about an order of magnitude less than that of the said contacting parts of the

25 contact surface, having a value in the range from 0.03 to 0.1 mm, preferably about 0.05 mm.

By minimizing the wear of the contact surfaces, the groove depth can be favorably small, in particular having a value in the range from 25 to 50 micron only, preferably about 30 microns. Such a shallow groove contour being advantageous to manufacture, in particular in the said blanking process. In combination with the aforementioned preferred radius of curvature of the groove bottom and groove edges and a preferred extend of the contacting parts of between 0.1 to 0.2 mm, the preferred groove depth enables a favorably small groove pitch of 0.15 to 0.35 mm, preferably about 0.25 mm. For reference, the overall height of the contact surface from its upper end part to its

35 lower end part is in the order of millimeters, typically about 7 mm, meaning that around 28 grooves are present in the contact surface in total.

Received at EPO via Web-Form on Dec 30, 2023 The above preferred dimensions of the grooved contact surfaces enable an initial contact ratio in the range between 0.4 to 0.6 and a contact ratio after running-in wear of more than 0.65, preferably about 0.75. Such relatively small initial contact ratio provides the desired quick running-in of the drive belt, while such relatively large contact ratio after

5 running-in wear minimizes further wear of the contact surfaces during prolonged drive belt operation and while providing adequate transmission fluid drainage.

As an independent further aspect thereof, the present invention relates to a taper that may be applied to the middle portion of the transverse member in height direction and that is known in the art from EP2325523-A1 . By such known taper the width of the middle portion increases from the base portion to the top portion of the transverse member. Hereby, the height and the weight of the transverse member could be favorably lowered. This known design relies on the circumstance that the pulley discs are conical, such that the tapering of middle portion of the transverse member in radial direction is possible without reducing the space between the pulley discs and the middle portion

15 available for accommodating the ring stack. Optimally, according to EP2325523-A1 , a taper angle of the middle portion of the transverse member, i.e. the angle defined by and between the side surfaces thereof, is the same as the belt angle that in turn corresponds to the angle defined between the pulley discs of the pulleys, i.e. the pulley angle. In the customary design of the transmission the pulley angle and the belt angle amount to

20 about 22°, although a value of 18° is applied in practice as well.

According to the present invention it has been recently discovered that this known design of the transverse member comes with a hidden disadvantage. Namely, when assembling the drive belt, the ring stack is inserted in the said slot of the transverse members in axial direction and there is a risk of the ring stack impacting

25 against the side surface of the middle portion, if it is inadvertently inserted too far. When the middle portion is tapered such impact is disadvantageously concentrated at the top corner of ring stack and thus more readily results in damage to the ring stack. In fact, the larger the taper angle of the middle portion is, the less clearance in axial direction is available at such top corner of the ring stack, in particular in comparison with the axial clearance available at the bottom corner thereof, and the larger the risk of a detrimental contact between the transverse member and the ring stack in drive belt assembly becomes. Such risk and damage have hitherto gone unnoticed, since it does not immediately affect the operation of the drive belt in the transmission. However, it can lead to premature failure of the drive belt, in particular the fatigue failure of the outermost

35 ring of the ring stack that was previous attributed to other causes.

The present invention seeks to reconcile the desire to minimize the mass of the

Received at EPO via Web-Form on Dec 30, 2023 transverse members (by setting the taper angle of the middle portion thereof equal to the pulley angle) with the desire to minimize the risk of damaging the ring stack in drive belt assembly (by setting the taper angle of the middle portion of the transverse members equal to zero). According to the present invention this objective is realized by setting the

5 taper angle in the range from 50% to 90% of the belt angle, which in the said customary transmission design corresponds to the range from 11 ° to ~20°. More preferably, the taper angle is set in the range from 14° to 18° (i.e. ~60% to ~80% of the belt angle with 17° (i.e. ~75% of the belt angle) as a typically applicable most preferred value.

It is noted that in JPH04-83941-A discloses a transverse member and a ring stack with a rotation angle being defined between an axially aligned position of the transverse member relative to the ring stack and a maximally rotated position of the transverse member relative to the ring stack. In order to provide a linear contact in axial direction between the ring stack and the side surfaces of the middle portion of the transverse member when these are in the said relatively rotated position, the middle

15 portion is tapered by its side surfaces being are mutually oriented at an angle corresponding to twice the said rotation angle. In the customary design of the known drive belt, the said rotation angle amounts to approximately 1 ° to 2°, such that the corresponding taper angle of the middle portion of the transverse member would amount to 2° to 4° (i.e. less than 20% of the belt angle). It will be clear that the said rotation angle

20 is determined by the clearance that is provided between the transverse member and the ring stack in radial direction in combination with the overall width of the ring stack in axial direction. In any case, this latter known taper angle of the middle portion of the transverse member is considerably smaller than the taper angle according to the present invention.

25 As yet a further independent aspect thereof, the present invention also aims to optimize the design of the continuously variable transmission as a whole. Underlying this particular aspect of the present invention is the inventors’ new insight that, in terms of a respective friction increase between the drive belt and the pulleys that is respectively realized, these known design features are in fact not complementary. That is to say that the said friction increase that can be realized by applying the known difference between the belt angle and the pulley angle cannot increased further by also applying the known offset between the protrusion and the cavity or vice versa.

According to the present invention, the protrusion of the transverse members of the drive belt still is preferably offset in radial inward direction relative to the cavity

35 thereof in the known manner, however, the optimum difference between the belt angle and the pulley angle is less than 0.4 degree and more preferably has a value in the

Received at EPO via Web-Form on Dec 30, 2023 range between 0.02 and 0.2 of a degree. By applying such a small difference between the belt angle and the pulley angle, a (highest) contact pressure between the drive belt and the pulleys is favorably small, as is their wear during operation, while still realizing a favorably high coefficient of friction there between by applying the known offset between

5 the protrusion and the cavity.

More in particular according to the present invention, the offset between the protrusion and the cavity of the transverse members is optimally defined such that the underside of the protrusion essentially coincides with the underside of the cavity, at least within a tolerance of 10 micron or less between the transverse members of the drive belt. Thus, in case of the said predominantly cylindrical shape thereof, the said offset preferably amounts to approximately half the difference between outer diameter of the protrusion and the inner diameter of the cavity. Nevertheless, in the context of the present invention, a practical range for such offset is between 40 and 80% of such diameter difference.

15 In the following, the continuously variable transmission according to the present invention and the associated drive belt design are explained further and in more detail by way of example embodiments and with reference to the drawings, whereof:

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

20 - figure 2 provides a schematic cross-section of the known drive belt oriented in the circumference direction thereof;

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

- figure 4 is an enlargement of a detail of the transverse member depicted in figure

25 2;

- figure 5 schematically illustrates the same detail of the transverse member as depicted in figure 4, however designed in accordance with the said further aspect of the present invention;

- figure 6 provides an enlargement of a detail of figure 5;

- figure 7 is an enlargement of another detail of the transverse member depicted in figure 2;

- figure 8 schematically illustrates the same detail of the drive belt as depicted in figure 7, however showing only the transverse member;

- figure 9 is an enlargement of yet another detail of the transverse member depicted

35 in figure 2;

Received at EPO via Web-Form on Dec 30, 2023 - figure 10 schematically illustrates a section of a straight trajectory part of a drive belt incorporating transverse members as depicted in figure 9;

- figure 11 schematically illustrates the friction contact between the drive belt incorporating transverse members as depicted in figure 9 and the pulley.

5 Inter alia, it is noted that these drawing figures are of a schematic nature and, in particular, are not drawn to scale.

Figure 1 schematically illustrates a continuously variable transmission, such as for utilization in a motor vehicle between the prime mover and the driven wheels thereof. This known continuously variable transmission is indicated in general by the reference sign 1. The continuously variable transmission 1 comprises two adjustable pulleys 2, 3 and a drive belt 6 that is provided in a closed loop around the pulleys 2, 3. The pulleys 2, 3 are each provided with a pulley shaft 4 and with two pulley discs 7, 8, whereof a first pulley disc 7 is fixed to the pulley shaft 4 of the respective pulley 2, 3 and whereof a second pulley disc 8 is axially displaceable relative to such pulley shaft 4, while being

15 fixed thereto in rotational direction. During operation of the transmission 1 , the drive belt 6 is clamped at a running radius Rr at each pulley 2, 3 by and between the respective pulley discs 7, 8 thereof, which running radii Rr can be varied to vary the speed ratio of the transmission by moving the pulley discs 7, 8 of the pulleys 2, 3 towards, respectively away from each other.

20 In the presently illustrated general design thereof, drive belt 6 comprises two sets of mutually radially stacked continuous bands or rings 5 (see figure 2), denoted ring stacks 9 hereinafter (and whereof only one is visible in figure 1). Transverse members 10 of the drive belt 6 are arranged on the ring stacks 9 forming an essentially contiguous row along the entire circumference thereof. For the sake of simplicity, only some of these

25 transverse members 10 are individually illustrated in figure 1.

The transverse members 10 are provided movable with respect to the ring stacks 9, at least along the circumference thereof. As a result, a torque can be transmitted between the pulleys 2, 3 by means of friction between these pulleys 2, 3 and the transverse members 10 and by these transverse members 10 pressing against one another and pushing each other forward along the circumference of the ring stacks 9 in a direction of rotation of the pulleys 2, 3. The transverse members 10 and the (rings 5 of the) ring stacks 9 of the drive belt 6 are typically made of (high grade) steel. This particular type of transmission 1 and its principal operation are well-known per se.

In figure 2, the known drive belt 6 is schematically illustrated in cross-section

35 oriented in length or circumference direction C thereof, i.e. perpendicular to an axial direction A and a radial direction R of the drive belt 6. Thus, the ring stacks 9 are

Received at EPO via Web-Form on Dec 30, 2023 illustrated in cross-section and one transverse member 10 of the drive belt 6 is illustrated in a front elevation in figure 2. The ring stacks 9 are illustrated with five individual flat, thin and flexible endless rings 5 each, which endless rings 5 are mutually concentrically stacked in the radial direction R, i.e. are mutually nested to form the respective ring stack

5 9. In practice, the ring stacks 9 often comprise more than five endless rings 5, i.e. typically up to twelve or more.

Also in figure 2, the transverse member 10 is shown to comprise, in radially outward direction, a base portion 13 of generally regular trapezoidal shape, a relatively narrow middle portion 14 and a top portion 15 of generally triangular shape. The middle portion 14 is centrally located in the transverse member, such that on either side thereof a slot 33 is defined between the base portion 13 and the top portion 15, wherein a respective one of the two ring stacks 9 is accommodated. At each slot 33, a radially outward facing bearing surface 42 of the base portion 13 of the transverse member 10 supports the radial inside of a respective ring stack 9.

15 A front main body surface of the transverse member 10 is indicated by the reference sign 11 , whereas a back main body surface of the transverse member 10 is indicated by the reference sign 12. In the drive belt 6, at least a part of such front surface 11 of the transverse member 10 abuts against at least a part of such back surface 12 of a respectively leading transverse member 10, whereas at least a part of such back

20 surface 12 of the transverse member 10 abuts against at least a part of such front surface 11 of a respectively trailing transverse member 10.

The transverse member 10 takes-up a clamping force exerted between the discs 7, 8 of each pulley 2, 3 via contact surfaces 37 thereof, one such contact surface 37 being provided at either axial side of the transverse member 10. These contact surfaces

25 37 are mutually diverging in radial outward direction such that an acute angle is defined there between that is denoted the belt angle cp and that closely matches a pulley angle 0 defined between the pulley discs 7, 8 of the pulleys 2, 3 (see figure 1).

The transverse member 10 is provided with a protrusion 40 that protrudes from its front surface 11 and with a corresponding cavity 41 that is provided in its back surface 12. In the drive belt 6, the protrusion 40 of the trailing transverse member 10 is at least partially located in the cavity 41 of the leading transverse member 10, such that a relative displacement between these successive transverse members 10 in a plane perpendicular to the circumference direction C of the drive belt 6 is prevented or, at least, limited to a play or clearance between the protrusion 40 and the cavity 41 in a respective

35 direction in thee said plane. In the accompanying figures, the protrusion 40 and the cavity 41 are depicted with a generally cylindrical shape, however differently shaped

Received at EPO via Web-Form on Dec 30, 2023 protrusions 40 and cavities 41 are known as well. In particular, it is customary in the art to provide these with a slight conicity, i.e. taper.

At the front surface 11 of the transverse member 10, a tilting edge 18 is defined. The tilting edge 18 is represented by a convexly curved area of the front surface 11 ,

5 which area separates two sections of the said front surface 11 in the radial direction R, which two sections are oriented at an angle relative to one another such that below, i.e. radial inward of the tilting edge 18 the transverse member 10 is tapered, as shown in figure 3 that schematically illustrates a side elevation of the transverse member 10 of figure 2. An important function of the tilting edge 18 is to provide the mutual pushing contact between the successive transverse members 10 when these are in a slightly rotated, i.e. tilted position relative to one another at the pulleys 2, 3. In particular, when a leading transverse member 10 of a pair of successive transverse members 10 enters between the two pulley discs 7, 8 of a pulley 2, 3, it is rotated relative to the trailing transverse member 10 of the said pair that has not yet entered the pulley 2, 3, while its

15 back surface 12 remains in contact at the tilting edge 18 on the front surface 11 of the trailing transverse member 10. In the accompanying figures, the tilting edge 18 is located in the base portion 13 of the transverse member 10, but it is also known to locate the tilting edge 18 at least partly in the middle portion 14 of the transverse member 10.

For the sake of completeness is noted that alternative general designs of the

20 presently considered type of drive belt are known in art, such as from the international patent publication WO2018/210456-A1 . This latter alternative drive belt design includes only a single ring stack located in a single, centrally located opening of each of the transverse members. This central opening is open towards the radial outside of the drive belt and is thus defined by and between the base portion and two pillar portions of the

25 transverse member that respectively extend from a respective side of the base portion in radial outward direction. Also the transverse members of this latter type of drive belt are provided with the above-described protrusion-and-cavity pair -either provided in a single instance, centrally in the base portion or in two instances, one in each pillar portion-, as well as with the above-described contact surfaces 37 on the axial sides of the transverse member thereof.

In the commonly adopted design of the transverse member 10, the contact surfaces 37 are provided with a number of essentially equally spaced grooves 38 in an otherwise flat surface of the contact surfaces 37, as shown in figure 4 in an enlarged view of one of the axial sides of the base portion 13 of the transverse member 10,

35 however while omitting a central part of the contact surface 37 located between the cutoff lines CL.

Received at EPO via Web-Form on Dec 30, 2023 In the illustrated embodiment the grooves 38 are each defined by a concavely curved groove bottom with convexly curved groove edges on either side thereof, which groove edges align with ridge parts 39 of the contact surface 37. These ridge parts 39 all lie in a common virtual tangent plane VTP, such that these parts 39 will arrive in common

5 contact with the pulley discs 7, 8 during operation of the drive belt 6 in the transmission 1. The grooves 38 serve to channel transmission fluid away from such contact.

At both ends of the contact surface 37 in height direction, a convexly curved transition surface 44 is provided between the contact surface 37 and, on the one hand, the bearing surface 42 and a bottom surface 45 of the base portion 13 of the transverse member 10 on the other hand.

Between the transition surface 44 at the lower end of the contact surface 37 and the lowermost groove 38-a therein, a relatively narrow ridge part 39-a is provided. Such lowermost ridge part 39-a provides for a favorably large extend of the contact surface 37 in height direction between such lowermost ridge part 39-a and an uppermost ridge part

15 39-b thereof.

Nevertheless, according to the present invention an improvement can realized by increasing the width of the lowermost ridge part 39-a, as is schematically illustrated in figure 5, wherein three pairs of adjacent dotted lines indicate such width for respective ridge parts 39-a, 39-b, 39-c between respectively neighboring grooves 38 or between a

20 respectively neighboring groove 38 and transition surface 44. Preferably, the lowermost ridge part 39-a of the contact surface 37 is provided with essentially the same width as the uppermost ridge part 39-b thereof. More preferably and as is illustrated in figure 5, all ridge parts 39; 39-a, 39-b, 39-c of the contact surface 37 are provided with essentially the same width.

25 Further according to the present invention and as is schematically illustrated in figure 6 in a further enlargement of the contact surface 37, the ridge parts 39 thereof are preferably provided with a minimal convex curvature. A radius of curvature R39 of the ridge parts 39 preferably amounts to between 1 and 10 mm and more preferably is at least an order of magnitude larger than a radius of curvature R38b of the concavely curved groove bottom and/or a radius of curvature R38e of the convexly curved groove edges. As is further illustrated in figure 6 and at least initially, i.e. before operation of the drive belt 6 in the transmission 1 , the width W39 of the ridge parts 39 (as measured in the said common virtual tangent plane VTP between the convexly curved edges of the neighboring two grooves 38) amounts to approximately 45% of a groove pitch GP (as

35 measured center-to-center between two neighboring grooves 38 in the said common virtual tangent plane VTP).

Received at EPO via Web-Form on Dec 30, 2023 Another aspect of the commonly adopted design of the transverse member 10 illustrated in figure 2, is the tapered shape of the middle portion 14 thereof, such that the width of that middle portion increases from the base portion 13 to the top portion 15 of the transverse member 10. In other words, the axially oriented side surfaces 43 of the

5 middle portion diverge in radial outward direction, defining a taper angle p therebetween. According to EP2325523-A1 , this taper angle p ideally corresponds to the pulley angle 0 and thus also to the belt angle cp. In the customary design of the transmission these pulley, belt and taper angles all amount to about 22 degrees (e.g. 22° ± 1 °). This known design relies on the circumstance that the pulley discs 7, 8 are conical, such that the tapering of middle portion 14 of the transverse member 10 is possible without reducing the space available for accommodating the ring stack 9 between the pulley discs 7, 8 and the middle portion 14.

Nevertheless, according to the present invention and as schematically illustrated in figure 7, when the ring stack 9 is inserted in axial direction into the slot 33 of the

15 transverse members 10 to assemble the drive belt 6, there is a risk that the ring stack 9, in particular the top corner 9C thereof, impacts against the side surface 43 of the middle portion 14 of one or more of the transverse members 10 and is damaged. When the taper angle p of the middle portion 14 is large, there is less clearance in axial direction available between the ring stack 9 and the that middle portion 14 then when the taper

20 angle p is smaller (Figure 7: dashed line 43’ versus solid line 43) and the risk of such detrimental impact is higher. According to the present invention, the drive belt 6 assembly process can therefore be facilitated by reducing the taper angle p of the middle portion 14 vis-a-vis the prior art, in particular by setting such taper angle p equal to 17° ± 1°.

25 A further advantage of a reduced taper angle p of the middle portion 14 is that the side surfaces 43 thereof are oriented at a less sharp or larger angle relative to the bearing surface 42 of the base portion 13 as well. As illustrated in figure 8, this means that the curvature of a concave part of a curved transition 46 between such side surface 43 and a respective bearing surface 42 of the base portion 13 can be favorably decreased without increasing the size of a recess 33a that is created by such transition 46 in the base portion 13 as part of the slot 33. Or, alternatively, such recess 33a is reduced in size, when the conventional curvature of the said transition 46 is applied. Either way, the mechanical strength, in particular the fatigue strength of the transverse member 10 is improved.

35 In particular according to the present invention, the concave transition 46 between a respective side surface 43 and a respective bearing surface 42 is provided

Received at EPO via Web-Form on Dec 30, 2023 with a compound curvature consisting of at least two adjacent concave sections R1 , R2, whereof a first concave section R1 is connected to the side surface 43 and a second concave section R2 forms the bottom of the recess 33a, and at least one convex section R3 that is connected to the bearing surface 42. To minimize the size of the recess 33a, a

5 radius of curvature the first concave section R1 and a radius of curvature the convex section R3 are relatively small. To maximize the strength of the base portion 13, a radius of curvature the second concave section R2 is relatively large, in particular is 2 to 2.5 times as large as the radius of curvature the first concave section R1. The radius of curvature the convex section R3 preferably amounts to 0.5 to 1 time the radius of curvature the first concave section R1. The first and second concave sections R1 , R2 preferably span an angle of at least 45° up to at most 90° individually and of between 120° and 160° combined. In absolute terms, the radius of curvature of the first concave section R1 preferably amounts to between 0.4 and 0.5 mm and the radius of curvature of the second concave section R2 preferably amounts to between 0.8 and 1 mm.

15 Yet another aspect of the commonly adopted design of the transverse member 10 is that its protrusion 40 is positioned lower on, i.e. radial inward of its cavity 41 , as schematically illustrated in figure 9 in an enlargement of an upper, i.e. radially outer part of the transverse member 10. In particular, an offset CLO is applied between a (virtual) central axis CA40 of the predominantly cylindrical protrusion 40 relative to a (virtual)

20 central axis CA41 of the predominantly cylindrical cavity 41 in radial inward direction. By this design measure, the transverse members 10 are urged into a backwards inclined position in a straight trajectory part of the drive belt 6 between the pulleys 3, 4, as schematically illustrated in figure 10. Thus, the transverse segments enter the pulley in such backwards inclined orientation, whereby the friction between the drive belt 6 and

25 the pulleys 3, 4 is remarkably increased. Moreover, a substantial reduction of the noise generated by the operation of the drive belt 6 in the transmission 1 is realized by this known design measure,

According to another known design measure of the transverse member 10, its contact surfaces 37 are oriented at an angle, i.e. belt angle cp, that exceeds the pulley angle 0, as schematically illustrated in figure 11. In particular, the belt angle cp exceeds the pulley angle 0 by between 0.2 and 1.2 degree. Also by this latter design measure, the friction between the drive belt 6 and the pulleys 3, 4 is remarkably increased.

According to the present invention, the said friction increase realized by these two known design measures are, however, not complementary. Further according to the

35 present invention, an improvement can therefore be realized by applying a relatively small difference between the belt angle cp and the pulley angle 0 of less than 0.4 degree

Received at EPO via Web-Form on Dec 30, 2023 in combination with applying a relatively large offset CLO between the protrusion 40 and cavity 41 , preferably such that an underside 40a, i.e. a radially innermost part 40a of the protrusion 40 essentially coincides with an underside 41a, i.e. a radially innermost part 40a of the cavity 41 , at least on average between the transverse members 10 of the

5 drive belt 6. By this relatively large offset CLO, the known benefits of high belt/pulley- friction and low belt operation noise are realized, while the relatively small belt/pulley- angle difference favorably realizes a reduced wear during operation and -thus- an increased service life of the drive belt 6.

The present disclosure, in addition to the entirety of the preceding description and

10 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

15 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.

Received at EPO via Web-Form on Dec 30, 2023

Claims

1. A drive belt (6) for a continuously variable transmission (1) with two adjustable pulleys (2, 3) and with the drive belt (6), the drive belt (6) comprising a ring stack (9),

5 consisting of a number of mutually nested rings (5), and a number of transverse members (10) that are arranged on the ring stack (9) and that each define a slot (33) for accommodating the ring stack (9), which slot (33) on its radial outer edge is bounded by a top portion (15) of the transverse member (10), on an axial side thereof is bounded by a middle portion (14) of the transverse member (10), having a side surface (43) facing predominantly in axial direction towards the slot (33), and which slot (33) on its radial inner edge is bounded by a base portion (13) of the transverse member (10) having a bearing surface (42) facing predominantly in radial outward direction towards the slot (33), having a bottom surface (45) facing predominantly in radial inward direction, having a contact surface (37) facing predominantly in axial direction, and having respective

15 convex transition surfaces (44) provided at either end of the contact surface (37) between that contact surface (37) and the bearing surface (42) and the bottom surface (45) respectively, in which contact surface (37) a number of grooves (38) are provided, separated by ridge parts (39) of the contact surface (37), characterized in that, the two outermost ridge parts (39-a, 39-b) of the contract surface (37) are each directly

20 connected to a respective convex transition surface (44) and in that all ridge parts (39) of the contact surface (37), including the said outermost ridge parts (39-a, 39-b) thereof, together define a common virtual tangent plane (VTP) for friction contact with the pulleys (2, 3).

25 2. The drive belt (6) according to claim 1 , characterized in that, a width of the outermost ridge parts (39-a, 9-b) of the contact surface (37) of each of the transverse members (10) of the drive belt (6) corresponds to the width of the other ridges (39), as measured between two successive grooves (38) in the contact surface (37).

3. The drive belt (6) according to claim 2, characterized in that,

- the said width of the outermost ridge parts (39-a, 9-b) and the ridges (39) has a value between 0.1 and 0.2 millimeters, and in that,

- a width of the grooves (38) as measured between two successive ridges (39) has a value between 0.4 and 0.6 times the said width of the outermost ridge parts (39-a, 9-b)

35 and the ridges (39). ceived at EPO via Web-Form on Dec 30, 2023

4. The drive belt (6) according to a previous claim, characterized in that, both the outermost ridge parts (39-a, 9-b) and the ridges (39) of each of the transverse members (10) of the drive belt (6) are provided with a convexly curved contour, each defined by radius of curvature between 1 and 10 mm and together defining the said virtual tangent

5 plane (VTP).

5. The drive belt (6) according to a previous claim, characterized in that,

- the base portion (13) of each of the transverse members (10) of the drive belt (6) has two contact surfaces (37), each facing predominantly in mutually opposite axial directions and defining a belt angle (cp) between them, and in that,

- the middle portion (14) of each of the transverse members (10) of the drive belt (6) has two side surfaces (43), each facing predominantly in mutually opposite axial directions and defining a taper angle (P) between that has a value between 50% and 90% of the belt angle (cp).

15

6. The drive belt (6) according to claim 5, characterized in that,

- the said taper angle (P) has a value between 60% and 80% of the belt angle (cp) and preferably amounts to 75% of the belt angle (cp), or in that,

- the said taper angle (P) has a value between 14 and 18 degrees and preferably

20 amounts to 17 degrees, with the belt angle (cp) amounting to approximately 22 degrees.

7. The drive belt (6) according to claim 5 or 6, characterized in that, between at least one of the two side surfaces (43) of the middle portion (14) of each of the transverse members (10) of the drive belt (6) and the bearing surface (42) of the base portion (13)

25 thereof, there is a curved transition (46), having a first part that is concavely curved and that connects to the respective side surface (43), having a third part that is convexly curved and that connects to the respective bearing surface (42) and having a second part that is concavely curved and that connects to both the first part and the second part, forming a radially inward bottom of the curved transition (46), and in that a radius of concave curvature R2 of the said second part is larger than both a radius of concave curvature R1 of the said first part and a radius of convex curvature R3 of the said third part, preferably is between 2 and 2.5 times larger than at least the radius of concave curvature R1 of the said first part, more preferably amounts to between 0.4 and 0.5 mm.

35 8. A continuously variable transmission (1) with two adjustable pulleys (2, 3), each comprising two pulley discs (7, 8) that define a pulley angle (0) between them, and with ceived at EPO via Web-Form on Dec 30, 2023 the drive belt (6) according to a preceding claim, characterized in that, each of the transverse members (10) of the drive belt (6), on a front face (11) thereof, is provided with a protrusion (40) and, in a rear face (12) thereof, is provided with a cavity (41), which protrusion (40) is located lower on the top portion (15), i.e. is located more radially

5 inward than the cavity (41) is located in the top portion (15) of the transverse member (10), and in that the average value of the belt angle (cp) of the transverse members (10) of the drive belt (6) is larger than the pulley angle (0) of at least one of the two pulleys (2; 3) by a margin of at least 0.02 and at most 0.4 of a degree, preferably of not more than 0.2 of a degree.

9. The continuously variable transmission (1) according to claim 8, characterized in that, the protrusion (40) of a respective transverse member (10) is sized somewhat smaller than the cavity (41) of that respective transverse member (10), such that an underside (40a) of the protrusion (40) in radial direction essentially coincides with an

15 underside (41a) of the cavity (41).

10. The continuously variable transmission (1) according to claim 8 or 9, characterized in that, the protrusion (40) and the cavity (41) of a respective transverse member (10) are of a predominantly cylindrical shape, with a diameter of the protrusion (40) being smaller than a diameter of the cavity (41) and with a central axis (CA40) of the protrusion (40) being located lower on the top portion (15) of that respective transverse member (10) than a central axis (CA40) of the cavity (41) is located in the top portion (15) of that respective transverse member (10) by a margin of 40 to 80% of a difference between the diameters of the protrusion (40) and of the cavity (41), preferably of 50% ±

25 5% of that diameter difference. ceived at EPO via Web-Form on Dec 30, 2023