WO2021129954A9

WO2021129954A9 - A drive belt provided with a plurality of transverse segments and a ring stack confined in a central opening of these transverse segments

Info

Publication number: WO2021129954A9
Application number: PCT/EP2020/025598
Authority: WO
Inventors: Robert Van Den Heuvel; Michael Keersmaekers; Dirk Jan DE KUYPER; Roderick BIJKERK; Dirk TWISK; Joep VAN DE VEN; Tom VAN LOCHEM; Benny SEITZINGER
Original assignee: Robert Bosch Gmbh
Priority date: 2019-12-24
Filing date: 2020-12-24
Publication date: 2022-08-04
Also published as: NL1043521B1; JP2023508966A; WO2021129954A1; CN114945759A

Abstract

The present invention concerns a transverse segment (1) for a drive belt (50) comprising a row of such transverse segments (1) mounted on a ring stack (8). The transverse segment (1) defines a central opening (5) between a base part (10) of the transverse segment (1) and two pillar parts (11) thereof extending from a respective side of the base part (10) for accommodating the ring stack (8). According to the present invention the drive belt (50) is designed to provide the ring stack (8) with a clearance in axial direction relative to the transverse segments (1) that is larger for the radially innermost (81) of the ring stack (8) than for at least one other ring thereof.

Description

A DRIVE BELT PROVIDED WITH A PLURALITY OF TRANSVERSE SEGMENTS AND A RING STACK CONFINED IN A CENTRAL OPENING OF THESE TRANSVERSE SEGMENTS

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

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

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

The known flexible ring is provided with an essentially rectangular cross -section, albeit with rounded sides, such that its thickness is much smaller than its width, typically by a factor of at least twenty-five up to one hundred or so. Also in absolute terms, the thickness of the ring is small and typically has a value of 185 to 200 micron, such that it can bend relatively easily in its circumference direction. It is common practice in the art to roughen the inner surface of the rings, as part of the manufacturing process thereof, in the sense that a regular or irregular pattern of indentations and/or ridges is impressed on it, with the aim of drawing-in and/or holding lubricant between the adjacent rings in the ring stack to reduce friction and wear in a sliding contact between the rings of the ring stack.

The known transverse segments each define a central opening that is open towards the radial outside of the drive belt and that accommodates and that confines a respective circumference section of such ring stack, while allowing the transverse segment to move along the circumference thereof. This central opening is defined by and between a base part of the transverse segment that is located radially inward of the ring stack and two pillar parts thereof that respectively extend from a respective side of the base part in radial outward direction on either side of the central opening. The two pillar parts thus define respective axial boundaries of the central opening, whereas in radial inward direction the central opening it is bounded by the base part, in particular by a radially outward facing, so-called bearing surface thereof. In radially outward direction the central opening is at least partly bounded by some means in order to confine the ring stack to the central opening. This type of drive belt is, for example, known from the British patent GB1286777- A and, more recently, from the international patent publication WO2018/210456-A1. According to these documents, the said means for confining the ring stack in radial outward direction of a transverse segment are embodied by hook portions of the pillar parts extending over the central opening thereof. In particular, a respective hook portion extends from a respective pillar part in the general direction of the other, i.e. axially opposite pillar part, at some distance radially outward of the base part, which radial distance exceeds the thickness of the ring stack somewhat. Moreover, an axial distance that separates the hook portions from one another, is somewhat less than the width of the ring stack.

The hook portions of the transverse segment can have equal length in the axial direction or such length can be different between the two hook portions, in which latter case the respective hook portions of mutually different length are preferably provided on opposite sides of the transverse segment for successive transverse segments in the drive belt, as a/o taught by WO2018/210456-A1. In this latter known design, the hook portions extend essentially equally far towards the axial middle of the transverse segment. However, since one pillar part is more narrow than the other one pillar, i.e. is provided with an undercut relative to the said other one pillar part, the hook portion of that one pillar part is longer than the hook portion of the said other one pillar part. In the WO2018/210456-A1 design of the drive belt, the said undercut of the one pillar part relative to the said other one pillar part serves to enable the transverse segments to be mounted on the ring stack with a favourably small clearance there between in the radial direction. In the drive belt, the undercut is provided to mutually opposite (left and right) axial sides of the successive transverse segment in the said row thereof, such that -in the drive belt- the ring stack is confined in axial direction between the said other one pillar parts without the undercut of such successive transverse segments.

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

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

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

During operation in the transmission, the ring stack is tensioned by the transverse segments being urged in radial outward direction at the two pulleys by being clamped between the conical discs thereof. At these pulleys, the drive belt thus follows a curved trajectory, in which curved trajectory parts the transverse segments bear against the radial inside of the ring stack through, at least, a part of the surface of their base part that is located between the pillar parts, which surface part is denoted a bearing surface hereinafter.

Due to the said tensioning thereof, the ring stack extends essentially straight between the two pulleys, while guiding the transverse segments as these traverse from the one pulley to the other in such straight trajectory parts. Moreover, due to the said tensioning and starting from a radially innermost ring thereof, the rings of the ring stack elongate elastically, such that, at least at maximum tension, i.e. at full load during operation, any play in radial direction between the adjacent rings of the ring stack is absent, i.e. is removed due to the said elongation thereof. In this condition, all rings of the ring stack are mutually in contact along their complete circumference and all rings of the ring stack take a respective share in carrying the load.

Underlying the present invention is the general development aim to improve upon the existing drive belt design and existing design considerations in terms of the wear resistance and/or the fatigue strength of the known drive belt. More in particular, the present invention relies on the observation that the wear and/or the ultimate fracture of the individual rings in the ring stack is not equally distributed between them. Rather, the radially innermost ring of the ring stack was observed by applicant to experience the most wear, at least on average, at the axial sides thereof. Therefore, according to the present invention, it is beneficial to the overall performance of the drive belt, to reduce the severity of the axial contact between the transverse segments and the radially innermost ring of the ring stack, e.g. in terms of a rate of incidence and/or an intensity thereof.

In a first principle embodiment of the drive belt according to the present invention, an improvement is in this respect obtained by orienting at least a part of a side surface of at least one of the pillar parts facing the central opening of the transverse segment, towards the bearing surface, i.e. such that it is oriented partly in axial and partly in radially inward direction. In particular, such inclined part of the side surface is located within a range of radial positions corresponding to the ring stack when it is in contact with the bearing surface of the base part. As a result, an axial width of the central opening is smallest at some radial position radially outward from the radially innermost ring of the ring stack. In this way, the said axial contact between the transverse segments and the radially innermost ring of the ring stack is favourably reduced. According to the present invention, in absolute terms, a difference in width of the central opening that is required for realising the desired effect is favourably small, e.g. in the order of 0.1 to 1 mm, or between 0.5 to 5% of the central opening width. Preferably both pillar parts are provided with a thus inclined part of their respective side surface facing the central opening of the transverse segment.

Preferably according to the present invention and at least within a range of radial positions covered by the ring stack when it is in contact with the bearing surface of the base part, the said inclined part of the side surface is angled at an inclination angle relative to the radial direction, i.e. relative to a direction perpendicular to the width direction of the ring stack and/or of the bearing surface of the transverse segment, of less than 45 degrees. Thus, the inclined side surface of the pillar part according to the present invention is still predominantly oriented in the axial direction. Otherwise, the ring stack could become wedged between the said side surface and the bearing surface. Preferably, such inclination angle relative to the radial direction has a value in the range between 10 and 30 degrees.

In this respect, it is noted that a bottom surface of the hook portions that are predominantly oriented in radial inward direction, typically are also oriented somewhat in axial direction towards the axial middle of the transverse segment. In particular, these bottom surfaces are typically angled relative to the radial direction by more than 80 degrees, i.e. less than 10 degrees relative to the axial direction. However, in the transverse segment according to the present invention, a radial distance between such bottom surface and the bearing surface exceeds the (radial) thickness of the ring stack, such that the ring stack can also not become wedged between these latter two surfaces. A concavely curved transition surface can be provided between such bottom surface of the hook portion of a respective pillar part and the said side surface thereof that spans the remaining angle there between.

In a first elaboration of this first embodiment, the said side surface of the pillar part is oriented towards the bearing surface over the entire a range of radial positions covered by the ring stack, i.e. starting from a radial position of the bearing surface up to, essentially, a radial position of the bottom surface of the hook portion. As a result, an axial width of the central opening continually decreases in radially outward direction from the radial position of the radially innermost ring of the ring stack to the radial position of the radially outermost ring thereof.

In a second elaboration of this first embodiment, only an upper, i.e. radially outer section of the said side surface of the pillar part is oriented towards the bearing surface. In particular in this second elaboration, a radially inner section of the side surface is aligned in radial direction. As a result, an axial width of the central opening is largest at, at least, the radial position of the radially innermost ring of the ring stack and is smallest at, at least, the radial position of the radially outermost ring of the ring stack. In this second elaboration, the said axial contact between the radially innermost ring of the ring stack and the transverse segment favourably occurs in a radially, i.e. perpendicularly aligned, radially inner section of the side surface of the pillar part.

In a third elaboration of the first principle embodiment, only a middle section of the said side surface of the pillar part is oriented towards the bearing surface. In particular in this third elaboration, both a radially inner section and a radially outer section of the said side surface are aligned in radial direction. In this third elaboration, the axial contact with the transverse segment of both the radially innermost ring of the ring stack and the radially innermost ring thereof favourably occurs in respective, radially aligned sections of the side surface of the pillar part.

Preferably according to the present invention, the said radially inner section of the side surface of the pillar according to the above, second and third elaborations, extends in radial direction alongside at least 25% and at most 75% of the radially inner rings of the total number of rings of the ring stack. More preferably this radially inner section extends to essentially half the thickness, i.e. half the total number of rings of the ring stack. This preferred radial extend also applies to the said radially outer section of the side surface of the pillar according to the above third elaboration, however in relation to the radially outer rings of the ring stack.

In a fourth elaboration of this first principle embodiment, the said side surface of the pillar part is provided with a middle section in radial direction that protrudes towards the axial middle of the transverse segment relative to both a radially inner section and a radially outer section of thereof. In this way, the axial contact between the transverse segments and the ring stack is favourably concentrated at a ring of the ring stack between the radially innermost and outermost rings thereof, which ring is not otherwise in contact with the transverse segments.

In a second principle embodiment of the drive belt according to the present invention, the radially innermost ring of the ring stack is provided with a width that is smaller than a width of at least one other ring of the ring stack. Thus, a relatively large axial clearance is present between the radially innermost ring of the ring stack and the transverse segments of the drive belt, at least compared to the said at least one other ring of the ring stack. As a result, the radially innermost ring of the ring stack favourably does not, or at least not as severely as the said at least one other ring of the ring stack, arrive in axial contact with the transverse segments during operation of the drive belt in the transmission. According to the present invention, in absolute terms, a ring width difference that is required for realising the desired effect is favourably small, e.g. in the order of 0.1 to 1 mm, or between 0.5 to 5% of the ring width.

In an elaboration of this second embodiment, the radially outermost ring of the ring stack is provided with the largest width among all rings of the ring stack. In this case, the width of the rings of the ring stack may be provided to continually increase in radially outward direction between the successive rings of the ring stack. Preferably, however, several adjacent radially outer rings of the ring stack, including the radially outermost ring thereof, are provided with essentially the same, i.e. largest width. Moreover, several adjacent radially inner rings of the ring stack, including the radially innermost ring thereof, are preferably provided with essentially the same, i.e. smallest width. Hereby, these radially inner rings of the ring stack, which radially inner rings are subjected to a higher tension during operation of the drive belt as compared to the radially outer rings of the ring stack, do favourably not arrive in axial contact with the transverse segments, at least not as severely. More preferably, these several adjacent radially inner rings of the ring stack include at least 25% and at most 75% of a total number of rings included in the ring stack. This latter range preferably also applies to the said several adjacent radially outer rings of the ring stack provided with the largest width. In particular, the radially inner approximately 50% of rings of the ring stack is provided with the same, i.e. smallest width, while the other approximately 50% of rings thereof are provided with the same, i.e. largest width.

In another elaboration of this second embodiment, one or more rings of the ring stack between the radially innermost and outermost rings thereof is provided with the largest width among all rings of the ring stack. As a result, the axial contact between the transverse segments and the ring stack is favourably concentrated at such in-between ring or rings that is/are not otherwise, i.e. in radial direction, in contact with the transverse segments.

The above, first and second principle embodiments of the present invention are preferably applied together in the design of the drive belt, such that a ring width difference, a radial extend of the inclined section of the said side surface of the pillar part and/or its inclination angle relative to the radial direction, can each separately remain favourably small, while only in combination realising the desired effect.

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

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

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

- figure 3 schematically illustrates the known drive belt in an alternative basic design;

- figure 4 illustrates a technical insight underlying the present invention;

- figure 5 schematically illustrates an elaboration of a first principle embodiment of the novel drive belt in accordance with the present invention;

- figures 6A-C schematically illustrates several further elaborations of the such first principle embodiment according to the present invention;

- figure 7 schematically illustrates an elaboration of the such second principle embodiment according to the present invention specifically in relation to the alternative drive belt design illustrated in figure 3;

- figure 8 schematically illustrates an elaboration of a second principle embodiment of the novel drive belt in accordance with the present invention; and

- figure 9A-C schematically illustrates several further elaborations of the such second principle embodiment according to the present invention.

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

The drive belt 50 is composed of a ring stack 8 and a plurality of transverse segments 1 that are mounted on the ring stack 8 along the circumference thereof in an, at least essentially, contiguous row. For the sake of simplicity, only a few of the transverse segments 1 of the drive belt 50 are shown in figure 1, which transverse segments 1 are, moreover, not drawn to scale in relation to, for example, the diameter of the pulleys 52, 53. In the drive belt 50, the transverse segments 1 are movable along the circumference of the ring stack 8, which ring stack 8 is composed of a number of relatively thin and flexible endless steel bands or rings that are mutually nested, as can be seen more clearly in figure 2 that shows the ring stack 8 with eight individual rings. In practice between 6 and 12 rings are typically applied in the ring stack 8.

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

It is noted that, because only one of the sheaves of each pulley 52, 53 is axially displaceable, a varying amount offset in the axial direction exists there between in relation to the said speed ratio. In practice, the maximum axial pulley offset typically amounts to between 0.35-0.75 mm in either axial direction (i.e. both to the left and to the right of dead centre) depending on the transmission design, in particular in terms of a speed ratio range thereof and an angle defined by and between the conical sheaves of these pulleys 52, 53. The drive belt 50 must be able to accommodate such axial pulley offset by leaving and entering the pulleys 52, 53 at an angle relative to the radial direction thereof. Hereto, a clearance is provided in the drive belt 50 in axial direction between the ring stack 8 and the transverse segments 1.

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

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

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

As illustrated in figure 2, the bearing surface 13 is a central part of a boundary surface of the central opening 5 defined by the base part 10 in radially inward direction, which bearing surface 13 predominantly extends in the axial and circumference directions of the drive belt 50. The bearing surface 13 is marginally convexly curved in, at least, the axial direction in a well-known manner, for realising, or at least promoting, a desired contact and interaction between the transverse segment 1 and the ring stack 8. On either side of bearing surface 13, the said boundary surface of the base part 10 further includes a transition surface 15 forming a transition between the bearing surface 13 and a radially aligned side surface 16 of a respective pillar part 11 facing the central opening 5. Typically, such transition surfaces 15 include a convexly curved part adjoining the bearing surface 13 and a concavely curved part adjoining the said side surface 16 of the respective pillar part 11. It is noted that the convexly curved part of the transition surfaces 15 is much more sharply curved than the bearing surface 13 with a factor of 10 or more between the respective radii of curvature.

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

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

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

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

To support the integrity of the drive belt 50 during operation, preferably a large overlap in axial direction is provided between the ring stack 8 and the hook portions 9 of the pillar parts 11 of the transverse segment 1. However, at the same time, preferably a small clearance is applied there between in the radial direction, which clearance effectively determines the maximum width of the ring stack 8 that can be fitted in the central opening 5 during assembly of the drive belt 50. In this respect, i.e. for maximising the said axial overlap for a given radial clearance, it is known to provided one of the pillar parts 11 of each transverse segment with an undercut 17, as illustrated in figure 3. By the undercut 17, the central opening 5 is extended on the side of the respective pillar part 11 in both axial and radial inward direction. By the provision of the undercut 17 the axial symmetry of the transverse segment 1 is lost.

During drive belt assembly, the individual transverse segments 3 are sequentially mounted on the ring stack 8, whereto the ring stack 8 is inserted into the undercut 17 of the respective pillar part 11, the transverse segment 1 is subsequently rotated to align its bearing surface 13 with the ring stack 8 that thereby passes the hook portion 9 of the opposite pillar part 11 (without an undercut) and the transverse segment 1 is translated in axial direction to centre its bearing surface 13 with the ring stack 8. The undercut 17 is applied to mutually opposite (i.e. left and right) pillar parts 11 between two types A and B of the transverse segment 1, which types A, B are successively included in the row of transverse segments 1 of the drive belt 50. In the drive belt 50, the ring stack 8 is confined in axial direction between the side surfaces 16 of the pillar parts 11 without the undercut of the said successive transverse segments 1. A corresponding side surface 18 of the pillar part 11 with the undercut 17 does thus not arrive in contact with ring stack 8, at least not during normal operation of the drive belt 50 when the projections 6 of the transverse segments 1 are engaged in the cavities 7 of respectively adjacent transverse segments 1.

However, irrespective of the particular basic design thereof, two contradictory design requirements that are schematically illustrated in figure 4 have to be satisfied therein according to the present invention. Namely, i.e. as separately discussed hereinabove, on the one hand a sufficient axial overlap AO must be realised between the hook portion 9 of the pillars parts 11 of the transverse segments 1 and the ring stack 8 and, on the other hand, a sufficient axial clearance AC must be realised between the side surface 16 of the respective pillar parts 11 of the transverse segments 1 and the ring stack 8. These contradictory design requirements become conflicting when their sum (i.e. AO+AC) exceeds the axial extend (AE) of the hook portion 9 relative to the side surface 16 of the respective pillar parts 11, as illustrated in figure 4 by an exaggerated amount. Based on this and other insights that are discussed hereinabove, the present invention sets out to improve the known drive belt 50.

In a first elaboration of the present invention that is illustrated in figure 5, the side surface 16 of a respective pillar part 11 is oriented partly towards the bearing surface 13, such that it is oriented not only in axial direction but also in radial inward direction. As a result, the width of the central opening 5 at the radial position of the innermost ring 81 of the ring stack 8 can be large compared to the width of the central opening 5 at the radial position of the radially outermost ring 82 of the ring stack 8. In this way, a favourably large axial clearance AC at the radial position of the innermost ring 81 of the ring stack 8 is combined with a favourably large axial overlap AO of the hook portion 9 with the radially outermost ring 82 thereof. In particular, such inclined part of the side surface 16 extends in radial direction between the radial position of the bearing surface 13 of the base part 10 and the radial position of a radially inwardly oriented bottom surface 19 of the hook portion 9.

Further examples of transverse segment designs according to the present invention, that likewise provide an increased axial clearance AC at the radial position of the innermost ring 81 of the ring stack 8 invention, are illustrated in figures 6A-C.

In figure 6A, only an upper, i.e. radially outer section 161 of the side surface 16 of the respective pillar part 11 is oriented partly towards the bearing surface 13, whereas a lower, i.e. radially inner section 162 thereof is radially aligned, i.e. is oriented in axial direction. In particular, such inclined section 161 of the side surface 16 coincides with the radially outer rings of the ring stack 8, when the latter is in contact with the bearing surface 13 of the base part 10. With this particular transverse segment design, the said favourably large axial clearance AC exists for at least the radially innermost ring 81 and preferably several of the radially inner rings of the ring stack 8.

In figure 6B, only a middle section 163 of the side surface 16 of the respective pillar part 11, located between the radially outer and inner sections 161, 162 thereof that are radially aligned, is oriented towards the bearing surface 13. In figure 6C, such middle section 163 of the side surface 16 protrudes relative to the radially outer and inner sections 161, 162 thereof.

Figure 7 illustrates a possible elaboration of the present invention in relation to the drive belt design including two types A and B of non-axially symmetric transverse segments 1. In particular, the elaboration of figure 7 corresponds to that of figure 6A wherein a radially outer section of the side surface 16 of a respective pillar part 11 of the transverse segments 1 is oriented towards the bearing surface 13 thereof, i.e. both in axial and in radial inward direction, whereas a radially inner section thereof is radially aligned, i.e. is oriented in axial direction.

In this case, specifically the pillar part 11 without the undercut 17 is provided with the said side surface 16 that is at least partly oriented towards the bearing surface, namely the pillar part with the undercut 17. In fact, the side surface 18 of the pillar part 11 with the undercut 17 is preferably oriented somewhat in radial outward direction. In particular, an angle defined between this latter side surface 18 and the radial direction corresponds to an angle between the axial orientations of the transverse segment 1 and the ring stack 8 respectively, when the latter is located in the undercut 17 as part of the assembly of the drive belt 50 (see figure 3). Furthermore, the radially inwardly oriented bottom surface 19 of the hook portion 9 of both pillar parts 11 are designed to not arrive in contact the ring stack 8 upon axial displacement of the latter along the bearing surface 13 of the base part 10 of the transverse segment 1. In particular, a radial distance between the bottom surface 19 and the bearing surface 13 exceeds the (radial) thickness of the ring stack 8. In other words, upon such axial displacement, the ring stack 8 will enter into the undercut 17 without contacting the bottom surface 19 of the hook portion 9 until it finally contacts the side surface 18 of the respective pillar part 11.

Alternatively, according to the present invention and as illustrated in figure 8, highlighted by the dotted circles C, the design of the ring stack 8 is modified rather than the transverse segment 1. In particular in this elaboration of the present invention, a radially innermost ring 81 of the ring stack 8, is provided with a width that is less than the width of the other rings thereof. In this way, an intensity and/or frequency of a contact in axial direction between such innermost ring 81 of the ring stack 8 and the side surface 16 of a respective one of the pillar parts 11 of the transverse segments 1 is favourably reduced. Effectively, the said axial clearance AC at the radial position of the innermost ring 81 of the ring stack 8 is increased relative to the other rings and in particular a radially outermost ring 82 thereof. In particular, the said axial overlap AO favourably remains unaffected thereby. These effects can of course also be realised by providing the radially outermost ring 82 of the ring stack 8 with a width that is more than the width of the other rings thereof.

Further examples of ring stack designs according to the present invention, that likewise provide an increased axial clearance AC at the radial position of the innermost ring 81 of the ring stack 8, are illustrated in figures 9A-C. Figures 9A-C each depict an axial side of the ring stack 8 in cross-section with the individual rings thereof in an axially aligned state, such that the opposite axial side of the ring stack is a mirror image of the shown axial side.

In figure 9A, the width of the ring stack 8 increases in radial outward direction between the individual rings thereof, i.e. from the innermost ring 81 having the smallest width to the outermost ring 82 having the largest width. In this elaboration a width difference between two adjacent rings in the ring stack 8 can remain favourably small.

In figure 9B, the radially inner four rings of the ring stack 8 including the radially innermost ring 81 thereof, are all provided with essentially the same width that is smaller than the width of the radially outer four rings of the ring stack 8 including the radially outermost ring 82 that are likewise all provided with essentially the same width. This elaboration appears to perform better in practice, in particular more robustly, when compared to providing only one ring of the ring stack 8 with a smaller or larger width relative to all of the other rings of the ring stack 8. Of course, instead of the illustrated 4-to-4 split between the eight rings, other splits, such as a 6-to-2 split, are possible as well.

In figure 9C, an in-between ring 83 of the ring stack 8 is provided with the largest width among all rings of the ring stack 8, while the innermost ring 81 and the radially outermost ring 82 thereof are provided with a smaller width. As a result, the said axial contact between the ring stack 8 and the transverse segments 1 is favourably concentrated at such in-between ring 83 that is not otherwise in contact with the transverse segments 1. Obviously, the above described ring stack designs and the transverse segment designs according to the present invention can be combined in a single drive belt design. After all the said axial clearance AC is determined by such combination.

The present invention, in addition to the entirety of the preceding description and all details of the accompanying figures, also concerns and includes all the features of the appended set of claims. Bracketed references in the claims do not limit the scope thereof, but are merely provided as non-binding examples of the respective features. The claimed features can be applied separately in a given product or a given process, as the case may be, but it is also possible to apply any combination of two or more of such features therein. The invention is not limited to the embodiments and/or the examples that are explicitly mentioned herein, but also encompasses amendments, modifications and practical applications thereof that lie within reach of the person skilled in the relevant art.

Claims

1. A drive belt (50) with a ring stack (8) consisting of a number of mutually radially nested rings (81, 82, 83) and with a number of mutually consecutive transverse segments (1) that are movable arranged on the ring stack (8) and that each define a central opening (5) for accommodating the ring stack (8), which central opening (5):

- in radial inward direction is bounded by a base part (10) of the transverse segment (1) that is provided with a bearing surface (13) facing the central opening (5), which bearing surface (13) contacts a radial inside of the ring stack (8),

- in either axial direction is bounded by a respective pillar part (11) of the transverse segment (1) that each extend from respective axial side of the base part (10) in radial outward direction, whereof at least one pillar part (11) is provided with a side surface (16) facing the central opening (5), which side surface (16) can arrive in contact with a respective axial side of the ring stack (8), and

- in radial outward direction on either axial side thereof is bounded by a respective hook portion (9) of the pillar parts (11) that are each provided with a bottom surface (19) facing the central opening (5), characterized in that the side surface (16) of the said at least one pillar part (11) is at least partly inclined relative to the radial direction, oriented towards the bearing surface (13) of the base part (10).

2. The drive belt (50) according to claim 1, characterized in that the inclined part of the side surface (16) of the said at least one pillar part (11) is inclined relative to the radial direction at an angle of less than 45 degrees and preferably having a value in the range between 10 and 30 degrees.

3 The drive belt (50) according to claim 1 or 2, characterized in that a height dimension of the central opening (5) in the radial direction between the base part (10) of the transverse segment (1) and the hook portions (9) of the pillar parts (11) thereof, is larger than a thickness dimension of the ring stack (8) in the radial direction.

4. The drive belt (50) according to claim 1, 2 or 3, characterized in that the bottom surfaces (19) of the hook portions (19) of the pillar parts (11) of the transverse segment (1) are predominantly aligned in the axial direction, possibly inclined relative to such axial direction by up to 10 degrees at most.

5. The drive belt (50) according to a preceding claim, characterized in that the transverse segment (1) is provided with a concavely curved transition surface between the bottom surface (19) of the hook portion (19) of the said at least one pillar part (11) and the at least partly inclined side surface (16) thereof, spanning an angle there between.

6. The drive belt (50) according to any one of the claims 1-5, characterized in that the inclined part of the side surface (16) of the said at least one pillar part (11) extends in the radial direction from the radial position of the bearing surface (13) of the base part (10) to radially outward of the ring stack (8).

7. The drive belt (50) according to any one of the claims 1-5, characterized in that the inclined part of the side surface (16) of the said at least one pillar part (11) extends in the radial direction from a radially aligned, radially inner part of the side surface (16) to radially outward of the ring stack (8), which radially inner part of the side surface (16) in radial direction coincides with at least the radially innermost ring (81) of the ring stack (8), preferably with several adjacent, radially inner rings thereof, more preferably with approximately the radially inner half of the rings included in the ring stack (8).

8. The drive belt (50) according to any one of the claims 1-5, characterized in that the inclined part of the side surface (16) of the said at least one pillar part (11) extends in the radial direction from a radially aligned, radially inner part of the side surface (16) to a likewise to radially aligned, radially outer part of the side surface (16), which radially inner and outer parts of the side surface (16) in radial direction each coincide with at least one ring (81; 82) of the ring stack (8), preferably with several adjacent rings thereof.

9. The drive belt (50) according to a preceding claim, characterized in that the other pillar part (11) of the transverse segment (1) is provided with an undercut (17) relative to the said at least one pillar part (11), whereof a side surface (18) facing the central opening (5) is at least partly inclined radially outward.

10. The drive belt (50) according to a preceding claim, characterized in that a width dimension in the axial direction of a radially innermost ring (81) of the ring stack (8) is smaller than such width dimension of at least one of the other rings of the ring stack (8). 19

11. The drive belt (50) according to claim 10, characterized in that the at least one of the other rings of the ring stack (8) is located between the radially innermost ring (81) and the radially outermost ring (82) of the ring stack (8).

12. The drive belt (50) according to claim 10, characterized in that the at least one of the other rings of the ring stack (8) is the radially outermost ring (82) of the ring stack (8).

13. The drive belt (50) according to claim 12, characterized in that such width dimension of the rings of the ring stack (8) continually increases in radially outward direction from the radially innermost ring (81) thereof, having the smallest width dimension, to the radially outermost ring (82) thereof, having the largest width dimension.

14. The drive belt (50) according to claim 12, characterized in that such width dimension of the rings of the ring stack (8) is essentially the same for several adjacent, radially inner rings of the ring stack (8) including the radially innermost ring (81) thereof, having the smallest width dimension, as well as for several adjacent, radially outer rings of the ring stack (8) including the radially outermost ring (82) thereof, having the largest width dimension.

15. The drive belt (50) according to claim 14, characterized in that the said several adjacent, radially inner rings of the ring stack (8) correspond to approximately the radially inner half of the rings included in the ring stack (8).

16. The drive belt (50) according to a preceding claim, characterized in that a difference between, on the one hand, a clearance in axial direction of the radially innermost ring (81) of the ring stack (8) relative to the respective side faces (16) of the pillar parts (11) of the transverse segments (1) that can arrive in contact with a respective axial side of that radially innermost ring (81), and, on the one hand, such axial clearance of the radially outermost ring (82) of the ring stack (8), either amounts to between 0.1 and 1 mm, or amounts to between 0.5 to 5% of a width dimension in the axial direction of the radially innermost ring (81) of the ring stack (8).

17. A continuously variable transmission (51) comprising two adjustable pulleys (52, 53) and the drive belt (50) according to a preceding claim that is wrapped around those pulleys (52, 53), between which pulleys (52, 53) a maximum offset in the axial direction occurs during operation of the transmission (51), characterized in that a clearance in axial 20 direction of the radially innermost ring (81) of the ring stack (8) relative to the respective side faces (16) of the pillar parts (11) of the transverse segments (1) that can arrive in contact with a respective axial side of that radially innermost ring (81), is approximately equal to or larger than the said maximum offset, whereas such axial clearance of the radially outermost ring (82) of the ring stack (8) is smaller than the said maximum offset.