WO2018210457A1

WO2018210457A1 - A transverse segment for a drive belt for a continuously variable transmission and a drive belt including it

Info

Publication number: WO2018210457A1
Application number: PCT/EP2018/025143
Authority: WO
Inventors: Francis Maria Antonius Van Der Sluis; Hendrikus Franciscus LAMERS
Original assignee: Robert Bosch Gmbh
Priority date: 2017-05-19
Filing date: 2018-05-22
Publication date: 2018-11-22
Also published as: CN110637175A; JP2020521088A; NL1042390B1

Abstract

The invention concerns a transverse segment (1) for a drive belt (50) with a ring stack (8) and with transverse segments (1) mounted on the ring stack (8) along its circumference, comprising a base part (10) and two pillar parts (11), which pillar parts (11) extend from the sides of the base part (10) in height direction with an upper side of the base part (10) between the pillar parts (11) defining a support surface (13a, 13b), and which pillar parts (11) each include a hook portion (9) extending in the direction of the respectively opposite pillar part (11). The support surface (13a, 13b) comprises an essentially axially oriented central section (13b) and, to at least one side thereof, a side section (13a) that is oriented downwards away from the central section (13b). Hereby, the mounting of the transverse segment (1) on the ring stack (8) to assemble the drive belt (50) is facilitated.

Description

A TRANSVERSE SEGMENT FOR A DRIVE BELT FOR A CONTINUOUSLY VARIABLE TRANSMISSION AND A DRIVE BELT INCLUDING IT

This disclosure relates to a transverse segment that is destined to be part of a drive belt for a continuously variable transmission with two pulleys and the drive belt. Such a drive belt is commonly known and is mainly applied running around and between the two transmission pulleys, which pulleys each define a V-groove of variable width wherein a respective circumference part of the drive belt is held.

A known type of drive belt comprises an essentially contiguous row of transverse segments that are mounted on and around the circumference of a number of endless bands or rings that are mutually stacked in the radial direction. Each such transverse segment defines a central opening that is open towards the radial outside of the drive belt and that accommodates and confines a respective circumference section of such ring stack, while allowing the transverse segments to move along the circumference thereof. This particular type of drive belt is known, for example, from the British patent number GB1286777 and the European patent publication No. EP-1219860-A1 .

In the above and the below description, the axial, radial and circumference directions are defined relative to the drive belt when placed in a circular posture. A thickness dimension of the transverse segments is defined in the circumference direction of the push belt, a height dimension of the transverse segment is defined in the said radial direction and a width dimension of the transverse segment is defined in the said axial direction. A thickness dimension of the ring stack is defined in the said radial direction and a width dimension of the ring stack is defined in the said axial direction.

The known transverse segment comprises a base part and two pillar parts that extend from the base part at either axial side thereof in radial outward direction, i.e. upwards in height direction. The said central opening accommodating the ring stack is defined by and between the base part and the two pillar parts. In between the pillar parts, the said opening is bound by an essentially axially aligned, i.e. radially outward facing, support surface of the base part, which support surface interacts with and supports the ring stack from the radial inside thereof. At least one, but preferably both of the pillar parts of the known belt are provided with a hook portion extending in axial direction over the central opening that is thereby partly closed in radial outward direction as well. A bottom, i.e. radially inner surface of such hook portion thus engages the ring stack from the radial outside thereof, whereby the latter is contained inside the central opening of the transverse segment in radial outward direction.

In order to assemble the drive belt, it is generally not possible to fold the ring stack in axial direction for allowing it to pass between the hook portions of the transverse segments and to unfold in the central opening thereof. In particular, the ring stack would in practice be damaged by such folding and unfolding thereof. Therefore, i.e. in order to mount the transverse segments onto the ring stack, the transverse segments are individually slid onto the unfolded ring stack, i.e. having a more or less rectangular cross-section, in a rotated orientation and, thereafter, are rotated into axial alignment with the ring stack. To allow for such mounting, an overlap in axial direction, i.e. overhang, of the hook portions of the transverse segment and the ring stack must be small in relation to the width of the ring stack. However, when such overlap is small, in particular smaller than a play in axial direction of the transverse segments relative to the ring stack in the assembled drive belt, it may occur during operation of the drive belt that a transverse segment separates from the ring stack, compromising its integrity and continued operation.

It is noted that, in principle, such overlap could be increased by increasing the height of the central opening of the transverse segments defined as the smallest distance in radial direction between the support surface and the bottom surface of the hook portion, in particular relative to the thickness of ring stack, thus increasing a radial clearance there between. However, in practice such radial clearance must be small in relation to the thickness of the ring stack to ensure the desired, i.e. optimum performance of the drive belt. Therefore, in practice, it is resorted to alternative means for containing the ring stack in the central opening of the transverse segment after it is mounted thereon. However, even though many such alternative means have been suggested in the art over the years, these typically add to the cost and/or the complexity of drive belt or its assembly and have therefore not been brought into mass-manufacture.

Against the above-described background, the present disclosure sets out to improve the known drive belt, equipped with transverse segments whereof the pillar parts are each provided with a hook portion. In particular, the present disclosure sets out to increase the amount of overlap between such hook portions and the ring stack, without compromising the customary high performance and low cost of the known drive belt.

According to the present disclosure, the support surface, to at least one axial side thereof, includes a side section that is oriented not only in axial direction but also in radial inward direction, i.e. at an angle relative to an essentially axially oriented, central section of the support surface. By the provision of such side section at an angle, an angle of insertion of the ring stack into the central opening of such novel transverse segment is increased in comparison with such insertion angle allowed by the known transverse segment design. In turn, such increased insertion angle allows for a wider ring stack to be fitted, whereby the said overlap is favourably increased.

Based on geometric considerations, the side section of the support surface preferably extends over a distance that is equal to or larger than the height of the central opening, in particular up to 2 times, preferably about 1 .5 times such height. Furthermore, the said side section preferably extends in an essentially straight line, at least for a predominant part thereof. Preferably also, a convexly curved transition is provided between the said side section and the central section of the support surface to avoid a sharp edge there between and the resulting unfavourably high contact stress between the ring stack and the transverse segment during drive belt operation.

In this latter respect, it is noted that the support surface is typically also convexly curved. By such convex shape of the support surface, a preferred, i.e. centred alignment of the ring stack relative to the support surface of the transverse segments is aimed for, as described in for example the United States patent number 4,080,841 . According to the present disclosure, the radius of curvature of the support surface is, however, much larger than -and thus clearly distinguishable from- a radius of curvature of the said transition. More in particular, the radius of curvature of the support surface is at least 1 and preferably about 2 orders of magnitude larger than the radius of curvature of the transition between the said side section and the central section of the support surface.

More in particular according to the present disclosure, the said extension surface preferably essentially coincides with, or lies radially inward of an imaginary, i.e. virtual straight line drawn through both:

- a first point defined by the transition between the side section of the support surface and the central section thereof; and

- a second point on the outer contour of the hook portion of the pillar part on the axial side of the support surface opposite to the first point, which second point defines the axial extent of the entrance to the central opening towards that pillar part.

This latter geometry of the transverse segment allows it to be mounted onto the ring stack favourably without having to bend the latter, while realizing a relatively small value of the said radial clearance in combination with a relatively large value of the said overlap.

It is noted that within the context of the present disclosure, i.e. for the mounting of the transverse segment onto the ring stack, a single extension surface, provided at one axial side of the support surface, suffices. However, it may be preferable to provide an extension surface on both axial sides of the support surface, such that the overall design and mass-distribution of the transverse segment can be (mirror) symmetric relative to the radial direction, as is customary in the art of transverse segment design.

The above novel transverse segment design according to the present disclosure will now be explained further with reference to the drawing, in which:

- figure 1 is a simplified and schematic side elevation of a 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 side elevation of only the transverse segment thereof;

- figure 3 schematically illustrates a drive belt assembly step of mounting the transverse segment on the ring stack after the folding thereof;

- figure 4 schematically illustrates a drive belt assembly step of mounting a transverse segment on the ring stack in the natural, i.e. free-shape or non-deformed state thereof;

- figure 5 schematically illustrates a novel transverse segment according to the present disclosure in a front elevation thereof;

- figure 6 is an enlargement of a detail of the novel transverse segment of figure 5 and

- figure 7 illustrates a further design detail of the novel transverse segment of figure 5.

Figure 1 schematically shows the central parts of a continuously variable transmission 100 for use in a driveline of, for example, passenger motor vehicles. This transmission 100 is well-known and comprises at least a first variable pulley 101 and a second variable pulley 102. In the driveline, the first pulley 101 is coupled to and driven by a prime mover, such as an electric motor or a combustion engine, and the second pulley 102 is typically coupled to and drives a driven wheel of the motor vehicle via a number of gears.

The transmission pulleys 101 , 102 each typically comprise a first conical pulley sheave that is fixed to a pulley shaft 103, 104 of the respective pulley 101 , 102 and a second conical pulley sheave that is axially displaceable relative to the respective pulley shaft 103, 104 and that is fixed thereto only in rotational direction. A drive belt 50 of the transmission 100 is wrapped around the pulleys 101 , 102, while being accommodated between the pulley sheaves thereof. As appears from figure 1 , the trajectory of the drive belt 50 in the transmission 100 includes two straight parts ST and two curved parts CT where the drive belt 50 is wrapped around a respective one of the two transmission pulleys 101 , 102. 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 these transverse segments 1 are shown in figure 1 . In the drive belt 50 the transverse segments 1 are movable along the circumference of the ring stack 8, which ring stack 8 is typically composed of a number of flexible metal bands or rings, which metal rings are stacked one around one another, i.e. are mutually nested. During operation of the transmission 100, the transverse segments 1 of the drive belt 50 at the first pulley 101 are driven in the direction of rotation thereof by friction. These driven transverse segments 1 push preceding transverse segments 1 along the circumference of the ring stack 8 of the drive belt 50 (which ring stack 8 may itself be rotating) and, ultimately, rotationally drive the second pulley 102, again by friction. In order to generate such friction (force) between the transverse segments 1 and the transmission pulleys 101 , 102, the said pulley sheaves of each pulley 101 , 102 are forced towards each other, whereby these exert a clamping force on the transverse segments 1 in the axial direction thereof. To this end, electronically controllable and hydraulically acting movement means (not shown) that act on the moveable pulley sheave of each pulley 101 , 102 are provided in the transmission 100. In addition to exerting a pinching force on the drive belt 50, these movement means also control respective radial positions R1 and R2 of the drive belt 50 at the pulleys 101 , 102 and, hence, the speed ratio that is provided by the transmission 100 between the pulley shafts 103, 104 thereof.

In figure 2 the known drive belt 50 is schematically illustrated. On the left side of figure 2 the drive belt 50 is shown in cross-section and on the right side of figure 2 a side elevation of only the transverse segment 1 thereof 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 transmission pulleys 101 , 102, are mutually oriented at an angle that closely matches an angle that is present between the conical pulley sheaves of the transmission pulleys 101 , 1 02. These pulley contact faces 12 are either corrugated by a macroscopic profile or are provided with a rough surface structure, such that only the higher lying peaks of the corrugation profile or of the surface roughness arrive in contact with the transmission pulleys 101 , 102. This particular feature of the transverse segment design provides that the friction between the drive belt 50 and the transmission pulleys 101 , 102 is optimised by allowing cooling oil that is applied in the known transmission 100 to be accommodated in the lower lying parts of the corrugation profile or of the surface roughness.

Each transverse segment 1 defines a base part 10 and two pillar parts 1 1 , whereof the base part 10 extends mainly in the axial direction of the drive belt 50 and whereof the pillar parts 1 1 extend mainly in the radial direction of the drive belt 50, each from a respective axial sides of the base part 10. In its thickness direction, each transverse segments 1 extends between a front surface 3 and a rear surface 2 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 1 1 and the base part 10 of each transverse segment, wherein a circumference section of the ring stack 8 is accommodated. A radially outward facing part 13 of the circumference surface of the base part, forming the radially inner boundary of the central opening 5, supports the ring stack 8 from the radial inside and is denoted support surface 13 hereinafter. This support surface 13 is typically convexly curved for promoting a preferred, centred alignment of the ring stack 8 during operation, i.e. rotation of the drive belt 50 in the transmission 100.

In the row of transverse segments 1 of the drive belt 50, at least a part of a front main body surface 3 of the transverse segment 1 abuts against at least a part of the rear main body surface 2 of a respectively preceding transverse segment 1 in the said row, whereas at least a part of the rear main body surface 2 of the transverse segment 1 abuts against at least a part of the front main body surface 3 of a respectively succeeding transverse segment 1 . The abutting transverse segments 1 are able to tilt relative to one another, while remaining in mutual contact at and through an axially extending and radially, convexly curved surface part 4 of the front surfaces 3 thereof and is denoted tilting edge 4 hereinafter. Below, i.e. radially inward of such tiling edge 4, the transverse segment is tapered, as can be seen in the side elevation thereof in figure 2, to allow for such mutual tilting without interference of the respective base parts 10 of the abutting transverse segments 1 below the tilting edge 4. It is noted that, although in figure 2 the tilting edge 4 is located in the base part 10 of the transverse segment 1 , it is also known to at least partly locate it in the pillar parts 1 1 , i.e. in two axially separate, but radially aligned, sections (not shown).

The pillar parts 1 1 of the transverse segments 1 are each provided with a projection

6 that protrudes from the respective front surface 3 in, essentially, the said circumference direction. In the drive belt 50, the projection 6 is inserted in a recess 7 provided in the opposite, i.e. rear surface 2 of an adjacent transverse segment 1 to limit a relative movement between the adjacent transverse segments 1 , at least in radial direction, but typically also in axial direction.

The pillar parts 1 1 of the transverse segments 1 are each also provided with a hook portion 9 that in axial direction hangs over the opening 5. The hook portions 9, in particular bottom, i.e. radially inward facing surfaces 14 thereof, partly close off the central opening 5 also in radial outward direction. In the drive belt 50, the hook portions 9 of the transverse segments 1 overlap with the ring stack 8 in axial direction and thus prevent or at least hinder that these can separate from the ring stack 8 in radial inward direction.

In order to assemble the drive belt 50 according to the above known design, the ring stack 8 must be bent considerably in axial direction, i.e. folded almost double, to fit through the entrance to the central opening 5 defined by and between the hook portions 9 of the transverse segments 1 , as is schematically indicated in figure 3. In practice, however, such a considerable elastic deformation of the ring stack 8 is typically not possible, due to the high stiffness and low yield strain of the ring material. In this respect, figure 4 schematically illustrates a more practical method of drive belt assembly, wherein the ring stack 8 need not be deformed, at least not considerably. In figure 4 the dashed, rectangular outline schematically indicates the position of the non-deformed ring stack 8 relative to the transverse segment 1 during drive belt assembly, i.e. during the mounting of the transverse segment 1 on the ring stack 8. It is noted that in practice the individual rings and thus also the non-deformed ring stack 8 as a whole are/is typically slightly curved width-wise, i.e. are/is crowned, such that an effective thickness of the ring stack 8 in the said non-deformed state thereof is somewhat larger than its physical thickness.

A limitation of the particular method of drive belt assembly illustrated in figure 4, is that the hook portions 9 of the transverse segment 1 can show only a small overlap with the ring stack 8 in axial direction. In other words, a width W8 of the ring stack 8 can only be a little larger than a width EW5 of the gap between the hook portions 9 thereof that provides the entrance to the central opening 5 of the transverse segment 1 . In particular, a maximum possible overlap between the ring stack 8 and the hook portions 9 (i.e. W8 minus EW5) can be geometrically related to a radial clearance RC between the ring stack 8 and the hook portions 9 in the assembled state of the drive belt 50. Typically in the present type drive belt 50 such radial clearance RC is, however, required to be limited, in particular to be less than 30% and preferably in the range between 15% to 25% of the (effective) thickness of the ring stack 8, such that the said maximum possible overlap is unfavourably small. Thus, with this drive belt design and method of assembly thereof, there is a risk that a transverse member 1 separates from the endless carrier 8 during operation of the drive belt 50. In particular such separation might occur when, in the row of transverse segments 1 of the drive belt 50, a gap is formed at either side of that transverse segment 1 , e.g. due to wear of the belt 50 over the service life of the transmission in combination with a high, instantaneous belt load. This separation risk could be decreased, if the said overlap could be increased somehow.

According to the present disclosure, the width W8 of the ring stack 8 can be increased relative to the gap width EW5 of the opening 5 between the hook portions 9, as is schematically illustrated in figure 5 in an exemplary embodiment of the novel transverse segment 1 , such that the said overlap, i.e. an amount of (combined) overhang of the hook portions 9 over the ring stack 8 increases as well. In the novel transverse segment 1 , the support surface 13 does not extend in, essentially, axial direction over the entire width of the opening 5 between the pillar parts 1 1 , but rather includes a side section 13a at either axial side of a central section 13b thereof, which side sections 13a are oriented in radial inward direction away from the said central section 13b of the support surface 13. In particular, such that a side section 13a is oriented at an acute angle relative to the central section 13b. A preferred, practically applicable range for such angle is 10 to 30 degrees, more specifically 15 to 25 degrees.

By this design feature of the novel transverse segment 1 , when it is being mounted on the ring stack 8, one axial side of the ring stack 8 extends to radially inward of the support surface 13, in particular more or less in parallel with one of the side sections 13a thereof. As a result, a much wider ring stack 8 can be inserted into the central opening 5 of the novel transverse segment 1 , as compared to the known transverse segment 1 of figure 4 with the central opening 5 of the same gap width EW5. Hereby, the said overlap of the hook portions 9 of the transverse segment 1 with the ring stack 8 is favourably increased in relation to the said radial clearance RC there between. Alternatively, the radial clearance RC can be favourably reduced, or a combination of both.

In particular, the side sections 13a lies completely under the hook portion 9 of the respective pillar part 1 1 , i.e. the side sections 13a remain within and the central section 13b starts within the axial extent of the respective hook part 9. Preferably, convexly curved transition sections 13c of the support surface 13 are provided between the said side sections 13a and the central section 13b thereof, as illustrated in more detail in figure 6 in an enlargement of the transverse segment of figure 5. By such transition sections 13c, sharp edged and the resulting unfavourably high contact stress between the ring stack 8 and the transverse segment 1 during operation drive belt 50 are avoided. Also in figure 6 it is indicated that the central section 13b of the support surface 13 is typically also convexly curved, however, at a considerably larger radius of curvature R300 of e.g. 300 mm compared to a radius of curvature R10 of e.g. 10 mm of the said transition section 13c.

Finally, in figure 7 two preferred geometric aspects of the novel transverse segment 1 are illustrated. Firstly, a respective side section 13a of the support surface 13 lies radially inward of a first virtual straight line L1 drawn through both:

- a first point P1 in-between such respective side section 13a and the central section 13b of the support surface 13 and

- and a second point P2 on the outer contour of the hook portion 9 of the pillar part 1 1 on the axial side of the support surface 13 opposite to the first point P1 , which second point P2 defines the axial extent of the entrance to the central opening 5 towards that pillar part 1 1 . Hereby, an adverse contact between the ring stack 8 and the respective side section 13a of the support surface 13 can be largely avoided in the assembly process of the drive belt 50.

Secondly, a respective top, i.e. radially outer surface 15 of the hook portion 9 of the pillar part 1 1 lies radially inward (or at most essentially coincides with in radially outward direction) of a second virtual straight line L2 drawn through the side sections 13a at the opposite side of the support surface 13 relative to such respective pillar part 1 1 . Hereby, an adverse contact between the ring stack 8 and the respective top surface 15 of the hook portion 9 can be largely avoided in the assembly process of the drive belt 50.

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

Claims

CLAIM

1 . A transverse segment (1 ) for a drive belt (50) with a ring stack (8) and with transverse segments (1 ) mounted on the ring stack (8) along its circumference, comprising a base part (10) and two pillar parts (1 1 ), which pillar parts (1 1 ) extend from the sides of the base part (10) upwards in height direction with an upper side of the base part (10) between the pillar parts (1 1 ) defining a support surface (13a, 13b), at least one of which pillar parts (1 1 ) includes a hook portion (9) extending widthwise in the direction of the respectively opposite pillar part (1 1 ), characterized in that the support surface (13a, 13b) comprises an essentially widthwise oriented central section (13b) and, to at least one side thereof, a side section (13a) that is oriented at an acute angle relative to the said central section (13b) downwards in the height direction away from the central section (13b), which side section (13a) is located in the height direction under the hook portion (9) of the at least one pillar part (1 1 ).

2. The transverse segment (1 ) according to claim 1 , characterized in that the hook portion (9) of the at least one pillar part (1 1 ) extends in the direction of the respectively opposite pillar part (1 1 ) over the full extent of the side section (13a) of the support surface (13a, 13b) in that direction.

3. The transverse segment (1 ) according to claim 1 or 2, characterized in that the side section (13a) of the support surface (13a, 13b) extends over a distance that is equal to or larger than the distance in height direction between the hook part (9) of the at least one pillar part (1 1 ) and the central section (13b) of the support surface (13a, 13b) and that is preferably equal to about 1 .5 times the latter distance.

4. The transverse segment (1 ) according to claim 1 , 2 or 3, characterized in that the central section (13b) of the support surface (13a, 13b) extends widthwise, essentially in parallel with and over the full width of a gap between the pillar parts (1 1 ), respectively the hook portion (9) or hook portions (9) thereof.

5. The transverse segment (1 ) according to claim a preceding claim, characterized in that the central section (13b) of the support surface (13a, 13b) is located centrally between the two pillar parts (1 1 ) in the width direction, in that both pillar parts (1 1 ) include a hook portion (9) extending in the width direction towards the respectively opposite pillar part (1 1 ) and in that the support surface (13a, 13b) is provided with the said side section (13a) under a respective hook portion (9) on both sides of the central section (13b) thereof.

6. A drive belt (50) with a ring stack (8) and with a number of the transverse segments (1 ) according to any one of the claims 1 -5, which transverse segments (1 ) are mounted on the ring stack (8) along circumference thereof while the ring stack (8) is located in the width direction essentially in the middle of the base part (10) of the respective transverse segments (1 ) and arrives in contact with the central section (13b) of the support surface (13a, 13b).

7. A drive belt (50) consisting of only one ring stack (8) and a number of the transverse segments (1 ) according to any one of the claims 1 -5 that are mounted on the ring stack (8) along circumference thereof.