NL1042192B1 - A drive belt for a continuously variable transmission with transverse segments and a ring stack and its manufacutring method - Google Patents

Abstract

The present invention concerns a drive belt (6) for a belt-andpulley- type continuously variable transmission comprising a row of transverse segments (10) mounted on a stack (9) of several, mutually nested continuous rings (5), with a radially outward facing carrying surface (42) of the transverse segment (10) supporting the ring stack (9) during operation. According to the invention, transverse segments (10) of varying width are included in the drive belt (6) with a maximum variation of such transverse segment width satisfying a prescribed criterion.

Description

Patent center

The Netherlands

Θ 1042192 (21) Application number: 1042192 © Application submitted: 22/12/2016

BI PATENT (51) Int. Cl .:

F16G 5/16 (2017.01)

Application registered: (73) Patent holder (s): 29/06/2018 Robert Bosch G.m.b.H. at Stuttgart, Germany, DE. (43) Application published: (72) Inventor (s): (47) Patent granted: Cornelis Johannes Maria van der Meer 29/06/2018 in Tilburg. (45) Patent issued: 05/07/2018 (74) Agent: ir. G.A.J.M. Plover in Tilburg.

(54) A DRIVE BELT FOR A CONTINUOUSLY VARIABLE TRANSMISSION WITH TRANSVERSE SEGMENTS AND A RING STACK AND ITS MANUFACUTRING METHOD © The present invention concerns a drive belt (6) segments (10) mounted on a stack (9) or several, mutually nested continuous rings (5), with a radially outward facing carrying surface (42) or the transverse segment (10) supporting the ring stack (9) during operation. According to the invention, transverse segments (10) or varying width are included in the drive belt (6) with a maximum variation or such transverse segment width satisfying a prescribed criterion.

NL BI 1042192

This patent has been granted regardless of the attached result of the research into the state of the art and written opinion. The patent corresponds to the documents originally submitted.

A DRIVE BELT FOR A CONTINUOUSLY VARIABLE TRANSMISSION WITH

TRANSVERSE SEGMENTS AND A RING STACK AND ITS MANUFACUTRING METHOD

This disclosure relates to a drive belt for a continuously variable transmission with two pulleys and the drive belt. Such a drive belt is known from the international patent application publication WO2015 / 063132-A1 and comprises a row of transverse segments mounted on a stack of several, mutually nested continuous bands, i.e. flat and thin rings, each. The transverse segments define a slot for accommodating and confining a respective circumference section of the ring stack, while allowing the transverse segments to move along the circumference of the ring stacks. This particular type of drive belt is also referred to as a push-type drive belt or push belt. This disclosure also relates to a method for manufacturing the drive belt or either design.

In the following description the axial, radial and circumference directions are defined relative to the drive belt when placed in a circular posture. Furthermore, a thickness dimension of the transverse segment is defined in the circumference direction of the drive 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.

The known transverse segments each include a base portion, a middle portion and a top portion. The middle portion of the transverse segments extends in radial direction interconnecting the said base and top portions thereof. On either side of the middle portion of the transverse segments define a slot between the base portion and the top portion for accommodating a respective ring stack or the drive belt. At each end, a radially outward facing bottom surface contacts and supports the ring stack in radial outward direction. These bottom surfaces of the slots are associated with the base portion of the transverse segments are denoted carrying surfaces hereinafter.

In the row of transverse segments of the drive belt, at least a part of a front main body surface or the transverse segment abuts against at least a part of the rear main body surface or a respectively preceding transverse segment in the said row, whereas at least a part of the rear main body surface or the transverse segment abuts against at least a part of the front main body surface or a respectively succeeding transverse segment. At least one of these front and rear main body surfaces or the transverse segment, for example the front main body surface includes an axially extending, convexly curved surface part. This curved surface divides the front main body surface into a radially outer and a radially inner surface that is oriented to an angle relative to one other. Abutting transverse segments in the drive belt are able to tilt relative to one another, while remaining in mutual contact and through such a curved surface part that is therefore denoted tilting edge hereher. The tilting edge allows the row of the transverse segments of the drive belt to follow a local curving of the ring stacks imposed by the transmission pulleys.

As mentioned, readabove, in the drive belt the transverse segments can move relative to the ring stacks along the circumference. This has the advantage that during operation of the drive belt the ring stack is tensioned to a relatively low level in relation to a torque transmitted by the drive belt between the pulleys, at least compared to other types of drive belt. However, on the other hand, such a sliding movement or slip between the transverse segments and the ring stack is known to bring about a small, but notional friction loss. It is known that such sliding movement can be favourably minimized by arranging the tilting edge of the transverse segments as close to the radial inside of the ring stack as possible in the height direction. In theory, in this respect, the tilting edge is preferably arranged to coincide with the carrying surfaces or the transverse segment in question.

In practice, the tilting edge is typically arranged at a distance of around 1 mm radially inward of the carrying surfaces. However, in particular by employing a special manufacturing process in the production of the transverse segments, for example as taught by WO2015 / 063132-A1, the said distance can be reduced to 0.9 mm down to 0.6 mm or even less.

The above design aspect of the transverse segments and the efficiency improving effect have been tested and confirmed in practice. However, in some but not ail cases these tests also revealed a small, but principally highly undesirable reduction of the service life of the drive belt as a whole, which phenomenon was neither expected nor understood.

The present disclosure aims to improve the service life of the drive belt, in particular of the drive belt incorporating transverse segments whereof the tilting edge is located within 0.9 mm radially inward of the carrying surface, more in particular within 0.6 mm.

According to the present disclosure such improvement can be surprisingly realized by controlling a deviation in the width dimension of the said base portion of the transverse segments of the drive belt, in particular by controlling such width deviation in relation to a radius or curvature of a transition edge between a carrying surface and a main body surface of these transverse segments.

According to an insight underlying the present disclosure, a position in radial direction or an individual transverse segment or the drive belt on the transmission pulleys, is determined by its width. Thus also a radial position of the carrying surfaces or the individual transverse segment is determined by its width. Therefore, the carrying surfaces of a wider transverse segment or a pair of abutting transverse segments protrudes relative to the carrying surfaces of the other, narrower transverse segment or the said pair. As a consequence, the ring stack does not only come in contact with these carrying surfaces, but is also bend around the said transition edge between the carrying surface and the main body surfaces or, at least, the said wider transverse segment. Such contact between the transition edge and the radial inside of the ring stack raises a ring stress level, in particular if the transition edge is a relatively sharp edge. In fact, it may just happen that the yield stress or the radially innermost ring or the ring package is exceeded, compromising the service life or that innermost ring.

With hindsight knowledge of the above phenomenon, it can be concluded in the known drive belt it is not critical, because the transition edges of the transverse segments are smoothly rounded at a relatively large radius or curvature, in particular in relation to a typical variance of width of these transverse segments in mass manufacture. However, together with the above-described reduction of the distance between the carrying surface and the tilting edge, the radius or curvature of the transition edges had to reduce as well.

More in particular, according to the present disclosure, the following, empirically derived relationship approximates the allowed maximum width deviation AWm in millimeters between each pair of abutting transverse segments in the drive belt and the radius of curvature Rte millimeters of the transition edges between the carrying surfaces and the main body surfaces:

AWm <0.005 * e ^A (10 * Rte) (1) with the representing the natural exponential base number equation (1) accuracy of cutting the

For the known drive belt with the distance of around 1 mm between its tilting edge and carrying surface features, the radius or curvature of the transition edge Rte can be 0.5 mm or more, which gives a maximum width deviation AWm or 0.742 mm according to This The latter value is easily realized within the commonly used manufacturing processes or transverse segment from strip material by (fine) blanking followed by deburring and quench hardening, such that the above described phenomenon does indeed not occur in the known drive belt. However, once the curvature of the transition edge Rts is reduced to 0.3 mm or less, for example for realizing the preferred location of the tilting edge within 0.7 to 0.4 mm radially inward of the carrying surface, the maximum width deviation AWm drops to 0.1 mm or less, which can be critical to achieve with the said commonly employed manufacturing processes.

The above novel design requirement according to the present disclosure could, in principle, be implemented by improving the accuracy of the blanking process, or the tumbling process and / or the quench hardening process. However, such may not be economical or practically feasible. As an alternative, the present disclosure proposes to (a) measure the width W of the transverse segments before these are mounted on the ring stack and to (b) select only those transverse segments for mounting on the ring stack that satisfy a prescribed criterion in relation to such width. Such prescribed criterion may, for example, be a width range that every transverse segment or the drive belt must satisfy. Alternatively or additionally, the maximum width deviation may be defined for every consecutive transverse segment that is mounted on the ring stack in relation to abutting, i.e. previously mounted transverse segment in the row or transverse segments of the drive belt.

The above-described drive belt and its manufacturing method will now be explained further with reference to the drawing, in which equal reference signs indicate equal or similar parts and in which:

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

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

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

- figure 4 is an enlargement of a relevant part of the transverse segment depicted in figure 3;

- figure 5 is a schematic view of the transverse segment clamped between two sheaves of a pulley;

- figure 6 schematically illustrates a curved trajectory part of the drive belt; and

- figure 7 provides a graph with a modeled ring stress or is plotted in relation to a maximum width deviation AWm between the transverse segments 10 or the drive belt 6.

Figure 1 shows schematically a continuously variable transmission, such as for utilization in a motor vehicle between the prime mover and the drive wheels. The continuously variable transmission is indicated in general by the reference sign

1. The continuously variable transmission 1 comprises two 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 sheaves 7, 8, whereof a first pulley sheave 7 is fixed to the pulley shaft 4 or the respective pulley 2, 3 and whereof a second pulley sheave 8 is axially displaceable relative to such a pulley shaft 4, while being fixed thereto in rotational direction. During operation of the transmission 1, the drive belt 6 is clamped at a running radius R at each pulley 2, 3 by and between the respective pulley sheaves 7, 8, which running radii R can be varied to vary the speed ratio of the transmission by moving the pulley sheaves 7, 8 of the pulleys 2, 3 towards, respectively away from each other.

The drive belt 6 comprises two sets of mutually radially stacked continuous bands or rings, denoted ring stacks 9 hereinafter. Transverse segments 10 of the drive belt 6 are arranged on the ring stacks 9 forming an essentially contiguous row along the entire circumference. For the sake of simplicity, only a part of these transverse segments 10 are shown in figure 1.

The transverse segments 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 transmission pulleys 2, 3 by means of friction and by the transverse segments 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 segments 10 and the (rings of the) ring stacks 9 or the drive belt 6 are typically made of steel. This particular type of transmission 1 and its principal operation are well-known per se.

In figure 2, an exemplary embodiment of the drive belt 6 is shown in the cross section oriented in length or circumference direction C, ie perpendicular to the width or axial direction A and the height or radial direction R of the drive belt 6. In figure 3, only the transverse segment 10 or figure 2 is shown in a side elevation in the axial direction A.

In figure 2, the ring stacks 9 are shown in cross-section and one transverse segments 10 or the drive belt 6 is shown in a front elevation. The ring stacks 9 are in this case composed of five individual flat, thin and flexible endless rings 5 each, which endless rings 5 are mutually concentrically stacked in the radial direction R to form the respective ring stack 9. In practice, however, these ring stacks 9 often include more than five endless rings 5, eg nine or twelve or possibly even more.

In figures 2 and 3, the transverse segment 10 are shown to successively include in the radial direction A base portion 13 or predominantly trapezoidal shape, a relatively narrow middle portion 14 and a top portion 15 or predominantly triangular shape. On either side of the middle portion 14 a slot is defined between the base portion 13 and the top portion 15, the ring stack 9 is accommodated. At each slot 33, a radially outward facing carrying surface 42 or the base portion 13 contacts the radial inside or a respective ring stack 9 during operation.

A front surface of the transverse segment 10 is indicated in general by the reference sign 11, whereas a back surface of the transverse segment 10 is indicated in general by the reference sign

12. In the following, the front surface 11 and the back surface 12 are generally indicated as main body surfaces 11, 12. In the drive belt 6, at least a part of the front surface 11 or the transverse segment 10 abuts against at least a part of the back surface 12 or a succeeding transverse segment 10, whereas at least a part of the back surface 12 or the transverse segment 10 abuts against at least a part of the front surface 11 or a preceding transverse segment 10.

The transverse segment 10 takes-up a clamping force between the discs 7, 8 or each pulley 2, 3 via contact faces 37 Nam, one such contact face 37 Being provided at each axial side of the transverse segment 10. These contact faces 37 are mutually diverging in radial outward direction such that an acute angle is defined there between that is denoted the belt angle and that closely matches a pulley angle defined between the pulley sheaves 7, 8 of the pulleys 2, 3.

The transverse segment 10 is provided with a projection 40 that is protrudes from its front surface 11 and with a corresponding hole 41 that is provided in its rear surface 12. In the drive belt 3, the projection 40 or the trailing transverse segment 10 is at least partially located in the hole 41 of the leading transverse segment 10, such that mutual displacement or these adjacent transverse segments 10 in a plane perpendicular to the circumference direction C or the drive belt 3 is prevented or, at least, limited.

At the front surface 11 in the base portion 13 or the transverse segment 10, a rocking edge 18 is defined. The rocking edge 18 is represented by a convexly curved area of the front surface 11, 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 other. An important function of the rocking edge 18 is to provide the mutual pushing contact between the adjacent transverse segments 10 when these are in a slightly rotated, ie tilted position relative to one another at the pulleys 2, 3. In order to favourble realize a minimal contact stress in the said pushing contact, as well as for the stability of such contact, the rocking edge 18 preferably extended along the full local width of the transverse segments 10. Within the context of the present disclosure, the width W of the transverse segments 10 is defined at the rocking edge 18.

The rocking edge 18 is preferably located close to the carrying surfaces 42, i.e. at minimal distance Drc radial inward. However, the smaller such distance is Drc, the sharper a transition edge 50 between the front surface 11 and the carrying surfaces 42 of the transverse segment 10 will be. This latter aspect of the design of the transverse segment 10 is illustrated in figure 4 in an enlargement of the area E or figure 3 indicted by the dotted circle. On the left side of figure 4, a relatively large rocking edge-to-carrying surface distance Drc is illustrated, allowing the transition edge 50 to be provided with a relatively large radius or curvature Rte, at least in comparison with the design of the transverse segment 10 on the right side of figure 4 with a relatively small rocking edge-to-carrying surface distance Drc. In practice and as illustrated in figure 4, the radius of curvature Rte is somewhat narrower than the rocking edge-to-carrying surface distance Drc in order to ensure reliably in mass manufacture that the rocking edge 18 does not overlap with the transition edge 50.

In Figure 4, the transition edge 50 is depicted as a circular arc or radius Rte. In practice, however, the transition edge 50 may not be uniformly shaped, in which case its contour is approximated by a (closest fit of a) circular arc or radius Rte, at least within the context of the present disclosure. As such, the transition edge radius Rte between the carrying surfaces 42 and the main body surfaces 11, 12 might seem unimportant. However, at least for the relatively wider transverse segments 10 of the drive belt 6, this transition edge 50 does in practice arrive in contact with the radial inside of the ring stack 9 raising the overall stress level.

In figure 5 it is illustrated in an exaggerated manner that, when clamped between the pulley sheaves 7, 8, a wider transverse segment 10-b or larger width Wb will be located at a somewhat larger radial position Rb relative to a radial position Ra more narrow transverse segment 10-a or lesser width Wa. In other words, the said running radius R of the drive belt 6 at the pulleys 2, 3 in fact varies slightly between the individual transverse segments 10 in relation to the respective width W-a, W-b thereof. A difference AR in the said radial positions R being directly related to the difference hW in the said widths W-a, W-b:

AR = ^ AW / tan (^ 0) (2)

This latter aspect is further schematically illustrated in figure 6 by a set of seven transverse segments 10, whereof only the base portion 13 is depicted, in mutually tilted positions thus forming a curved trajectory part of the drive belt 6. On the left side of figure 6, all transverse segments 10 are of the same width W, such that these run at the same radial positon R between the pulley sheaves 7, 8, as indicated by the dashed line. On the right side of figure 6, the said transverse segments 10-a, 10-b or different width W-a, W-b are present in such curved trajectory part. From figure 6 it can be appreciated that when a more narrow transverse segment 10 is followed by a wider transverse segment 10 in the row of transverse segments 10, the transition edge 50 or the latter impinges on the radial inside of the ring stack 9, as indicated by the dashed line.

The overall stress level in the inner ring of the ring stack 9 of the drive belt 6 has been modeled including the stress raising effect of the contact of such a ring with the transition edge 50. Figure 7 provides a graph of such modeled stress or in ring relation to a maximum width deviation hWm of the transverse segments 10 occurring in the drive belt 6 and for several values of the radius or curvature Rte transition edge 50. Also drawn in figure 7 is a dashed line representing a critical ring stress orcrit for designing the drive belt 6 that should not be exceeded during operation. Within the context of the present disclosure this critical design ring or stress is derived from the yield stress or the ring by subtracting a safety margin or 10%. From this figure 7, the relationship between the edge radius transition Rte and the maximum width deviation AWm according to equation (1) can be derived.

Based on figure 7, equation (1) and in particular when the transverse segments 10 are manufactured with a relatively small radius or curvature Rte of the transition edge 50 between their main body surfaces 11, 12 and carrying surfaces 42, the present disclosure proposes to measure the width W of the transverse segments 10 before these are mounted on the ring stack 9 and to select only those transverse segments 10 for mounting on the ring stack 9 that satisfy a pre-scribed criterion in relation to their measured width W.

The present disclosure, in addition to the whole 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, but are merely provided as non-binding examples or the respective features. The claimed features can be applied separately in a given product or process, as the case may be, but it is also possible to apply any combination of two or more or such features therein.

The invention (s) represented by the present disclosure is (are) not limited to the following and / or the examples that are explicitly mentioned, but also encompasses amendments, modifications and practical applications, in particular those that are within reach of the person skilled in the relevant art.

Claims (7)

CONCLUSIONS A drive belt (6) with a ring package (9) and with a number of cross sections (10) which are successively placed and movably placed on the ring package (9), which cross sections (10) are provided with an opening (33) for receiving the ring package (9), which opening (33) is bounded on its underside by a bearing surface (42) on an upper side of a base portion (13) of the respective transverse segment (10), which base portion (13) is also provided with a tilting edge (18), in the form of a convex curved portion across the width (W) of the base portion (13) and perpendicular to that width direction of a front surface (11) of the respective transverse segment (10), and of a convex transition edge ( 50) between the bearing surface (42) and the front surface (11) of the respective transverse segment (10), characterized in that the transverse segments (10), or at least the dimensions thereof, of the drive belt (6) satisfy the relationship: AWm <0.005 * e ^A (10 * Rte) (1), where Rte represents an (average) radius of curvature in millimeters from the transition edge (50), where e is the base of the natural logarithm and in which LWm is a range of width dimensions in millimeters represented within which the width of all transverse segments (10) of the drive belt (6) are located. The drive belt (6) according to claim 1, characterized in that the radius of curvature of the transition edge (50) of all transverse segments (10) of the drive belt (6) is equal to or smaller than 0.4 mm, in particular is equal to or less than 0.3 mm, more in particular equal to or less than 0.2 mm. The drive belt (6) according to claim 1 or 2, characterized in that the tilting edge (18) of all transverse segments (10) of the drive belt (6) is less than 0.9 mm below its bearing surface (42) , in particular less than 0.7 mm below, more in particular less than 0.6 mm below. Method for the production of a drive belt (6), such as for a continuously variable transmission, with a ring package (9) and with a number of successive and movable transverse segments placed on the ring package (9), which transverse segments (10 ) are provided with an opening (33) for receiving the ring package (9), which opening (33) is bounded on a underside thereof by a bearing surface (42) on an upper side of a base portion (13) of the respective transverse segment ( 10), which base portion (13) is also provided with a tilting edge (18), in the form of a portion of a front surface (11) which is arranged across the width (W) of the base portion (13) and curved convexly to that width direction of the respective transverse segment (10), and of a convex transition edge (50) between the bearing surface (42) and the front surface (11) of the respective transverse segment (10), according to which method, the width (W) of the transverse segments (10) ) is determined, or becomes commun before they are placed on the ring package (9), and in which only transverse segments (10) are placed on the ring package (9) which satisfy a criterion prescribed with respect to that width (W). The method for manufacturing a drive belt (6) according to claim 4, wherein said prescribed criterion relates to a width range within which the width (W) of all transverse segments (10) of the drive belt (6) must be located. The method for manufacturing a drive belt (6) according to claim 4, wherein said prescribed criterion relates to a maximum allowable difference in the width (W) of two cross sections (10) placed successively on the ring package (9). The method for manufacturing a drive belt (6) according to claim 5 or 6, wherein said width range in millimeters or said maximum allowable difference in millimeters is 0.005 * e ^A (10 * Rte), wherein Rte a (mean) radius of curvature in millimeters from the transition edge (50) and in which e is the base of the natural logarithm. 1/3