NL1043486B1

NL1043486B1 - A transverse segment for a drive belt and a continuously variable transmission with a drive belt including the transverse segment

Info

Publication number: NL1043486B1
Application number: NL1043486A
Authority: NL
Inventors: Johannes Maria Van Der Meer Cornelis
Original assignee: Bosch Gmbh Robert
Priority date: 2019-11-28
Filing date: 2019-11-28
Publication date: 2021-08-31
Also published as: CN112855855A; JP2021085530A

Abstract

The present invention concerns a drive belt (6) for a belt-and-pulley-type continuously variable transmission comprising a row of transverse segments (10) mounted on a stack (9) of several, mutually nested rings. The transverse segments (10) are provided with a tilting edge (18) in the form of a convexly curved area of their front surface (11) that provides the mutual pushing contact between the successive transverse segments (10) when these are in a relatively tilted position. According to the invention, a radially outer extent of tilting edge (18) is oriented at an obtuse angle ó relative to a surface part of the front main body surface (11) adjoining such radially outer extent of the tilting edge (18).

Description

A TRANSVERSE SEGMENT FOR A DRIVE BELT AND A CONTINUOUSLY VARIABLE

TRANSMISSION WITH A DRIVE BELT INCLUDING THE TRANSVERSE SEGMENT This invention 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 known from the international patent application publication WO02015/063132-A1 and comprises a row of metal transverse segments slideably mounted on a stack of several, mutually nested continuous metal bands, i.e. flat and thin rings. This particular type of drive belt is also referred to as a push-type drive belt or pushbelt.

In the following description the axial, radial and circumference directions are defined relative to the drive belt when placed in a circular posture outside the transmission. Furthermore, a thickness dimension of the transverse segments 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 comprise a base portion, a middie portion and a top portion. The middle portion of the transverse segments extends in radial direction interconnecting the said base and top portions thereof. Between the base portion and the top portion and on either side of their middle portion of the transverse segment a respective slot for accommodating a respective ring stack of the drive belt is defined. At each slot, a radially outward facing bottom surface thereof contacts and supports the ring stack in radial outward direction. These bottom surfaces of the slots that are associated with the base portion of the transverse segments are denoted bearing surfaces hereinafter.

In the row of transverse segments of the drive belt, at least a part of a front main body surface (facing in a direction of belt rotation) of the transverse segment abuts against at least a part of the back main body surface (facing backward relative to the belt rotation direction) of a respectively leading transverse segment in the said row, whereas atleast a part of the back main body surface of the transverse segment abuts against at least a part of the front main body surface of a respectively trailing transverse segment. At least one of these front and back main body surfaces of the transverse segment, for example the front main body surface includes an axially extending, convexly curved surface part. This curved surface part divides the front main body surface into a radially outer and a radially inner surface parts that are oriented at an (obtuse) 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 at such curved surface part that is denoted tilting edge hereinafter, but that is also designated as rocking edge in the art. The tilting edge thus allows the row of transverse segments of the drive belt to smoothly follow a local curving of the ring stacks imposed by the transmission pulleys, while continuing to exert (a pushing) force on each other.

In relation to such tilting edge, US 6,440,023 B2 for example teaches to provide the tilting edge with a circular arc-shape, whereof the radius of curvature is linked to certain design and operating parameters of the drive belt. In particular, US 6,440,023 B2 prescribes a minimum radius of curvature for the tilting edge that is based on a maximum allowable Hertzian contact stress between the transverse segments, i.e. on a maximum allowable rate of wear of the tilting edge. In fact, such a minimum allowed tilting edge radius is typically preferred in practice for minimising a radial inward displacement of the contact line between the abutting transverse segments in dependence on a tilting angle there between. However, to the contrary, JP 2009216145 A teaches a tilting edge whereof a radius of curvature increases in radial inward direction. In this way, JP 2009216145 A takes into account that, during operation of the drive belt, the contact force between the abutting transverse segments at the pulleys varies in dependence on the tilting angle there between. In particular, according to JP 2009216145 A, such contact force is highest when the tilting angle is largest, i.e. when a radius of curvature of the drive belt on the pulleys is smallest.

It is an object of the present invention to further improve the performance of the known drive belt in terms of its wear resistance versus its operating efficiency. More in particular, the present invention aims to optimise the design of the transverse segment in this respect.

According to the present invention, the convex curvature of the tilting edge starts at an obtuse angle relative to the said radially outer surface part of the front main body surface thereof, which obtuse angle corresponds to, or is larger than 180 degrees minus a smallest tilting angle between the abutting transverse segments at the pulleys. Alternatively, the tilting edge may be provided in at least an outer section and an inner section in radial direction, whereof the outer section is convexly curved according to a smaller radius or radii of curvature than the inner section, while an extent in radial direction of the outer section is less than a third of that of the inner section and, preferably, amounts to between a fifth and a third thereof.

More in particular according to the present invention, the radius of curvature of the radially outer section of the tilting edge can be smaller than what is prescribed for the radially inner section in terms of the said maximum allowable Hertzian stress and/or rate of wear.

In this respect, it is noted that the limiting case of the radius of curvature of the radially outer section of the tilting edge being equal to zero, corresponds with the first mentioned embodiment of the present invention.

However, in practice, a transition section in the form of the outer section of the tilting edge will typically be present between the said radially outer surface part of the front main body surface and the inner section of the tilting edge, because of plastic deformation and/or wear of the transverse segment during operation, or even because of practical limitations in its manufacturing process.

Underlying the present invention is an aspect of the operation of the drive belt in the transmission.

Namely, as seen in the direction of rotation of the drive belt in the transmission, a relatively leading transverse segment rotates relative to a trailing transverse segment as it transits from a straight trajectory part of the drive belt located between the pulleys into a curved trajectory part thereof located on the pulleys.

In particular, in the said curved trajectory part, the transverse segments are mutually oriented at a tilting angle a that is determined -or, at least, can be approximated- by a radius of curvature Rr of the curved trajectory part and a thickness t of the transverse segment as follows: (180-t)/(7r-Rmin) 2 a [deg] 2 (180-t)/(1r-Rmax) (1) with Rmin and Rmax respectively representing a minimum and a maximum occurring radius Rr of the curved trajectory paths of the drive belt on the pulleys.

A tilting angle a smaller than (180-t)/(1r:Rmax) thus occurs only briefly during the transitions of the said relatively leading transverse segment from the straight trajectory part of the drive belt to the curved trajectory paths thereof and vice-versa.

According to the present invention, the radially outer section of the tilting edge may thus be curved according to a smaller radius of curvature then a bottom section thereof that defines the tilting angles a according to equation (1) without causing excessive wear of the tilting edge.

Quantitatively and in relation to the typical design and dimensions of the transmission and the drive belt, the following preferred parameter values apply in accordance with the present invention: - the said outer section of the tilting edge is preferably convexly curved according to a radius or radii of curvature smaller than 6 mm, in particular between 2 and 4 mm; and/or - the said inner section of the tilting edge is preferably convexly curved according to a radius or radii of curvature equal to, or larger than 6 mm, in particular between 10 and 20 mm; and/or

- the said outer section of the tilting edge preferably spans an angle of at least 1 degree, in particular between 1 and 2 degrees; and/or - the said outer and inner sections preferably merge smoothly with each other, as well as with the said radially outer surface part and the said radially inner surface part of the front main body surface respectively.

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 provides a perspective view of a continuously variable transmission with a drive belt running over two pulleys; - figure 2 provides a cross-section of the known drive belt oriented in the circumference direction thereof; - figure 3 provides a width-wise oriented view of a transverse segment of the known drive belt; - figure 4 illustrates the contact between two successive, mutually abutting transverse segments in the known drive belt in an enlarged section thereof; — figure 5 depicts the tiling edge of the known transverse segment in detail; — figure 6 depicts the tiling edge of the transverse segment in a first embodiment thereof in accordance with the present invention; and — figure 7 depicts the tiling edge of the transverse segment in a second embodiment thereof in accordance with the present invention.

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

Figure 1 schematically shows a continuously variable transmission, such as for utilization in a motor vehicle between the prime mover and the drive wheels thereof.

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 of the respective pulley 2, 3 and whereof a second pulley sheave 8 is axially displaceable relative to such pulley shaft 4, while being fixed thereto in rotational direction.

During operation of the transmission 1, the drive belt 6 is clamped at a so- called running radius Rr at each pulley 2, 3 by and between the respective pulley sheaves 7, 8 thereof, which running radii Rr can be varied between a minimum running radius Rmin and a maximum running radius Rmax 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 thereof.

For the sake of simplicity, only some of these transverse 5 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 of 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 cross-section oriented in length or circumference direction C thereof, i.e. 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 of 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 segment 10 of 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 comprise more than five endless rings 5, e.g. nine or twelve.

In figures 2 and 3, the transverse segment 10 is shown to successively comprise in the radial direction R, a base portion 13 of predominantly trapezoidal shape, a relatively narrow middle portion 14 and a top portion 15 of predominantly triangular shape.

On either side of the middle portion 14 slots 33 are defined between the base portion 13 and the top portion 15, wherein the ring stacks 9 are accommodated.

At each slot 33, a radially outward facing bearing surface 42 of the base portion 13 contacts the radial inside of a respective ring stack 9 during operation.

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

The transverse segment 10 takes-up a clamping force exerted between the discs 7, 8 of each pulley 2, 3 via contact faces 37 thereof, 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 8 defined between the pulley sheaves 7, 8 of the pulleys 2, 3. The transverse segment 10 is provided with a protrusion 40 that protrudes from its front surface 11 and with a corresponding cavity 41 that is provided in its back surface

12. In the drive belt 6, the protrusion 40 of the trailing transverse segment 10 is at least partially located in the cavity 41 of the leading transverse segment 10, such that a relative displacement between these successive transverse segments 10 in a plane perpendicular to the circumference direction C of the drive belt 6 is prevented or, at least, limited.

At the front surface 11 of the transverse segment 10, a tilting edge 18 is defined in the base portion 13 thereof. The tilting edge 18 is represented by a convexly curved area of the front surface 11, which area separates two parts of the said front surface 11 in the radial direction R, which two parts are oriented at an (obtuse) angle relative to one other such that below, i.e. radial inward of the tilting edge 18 the transverse segment 10 is tapered. An important function of the tilting edge 18 is to provide the mutual pushing contact between the successive transverse segments 10 when these are in a slightly rotated, i.e. tilted position relative to one another at the pulleys 2, 3. This function of the tilting edge 18 is illustrated in more detail in figure 4 in an enlargement of a part P of the transverse segment 10 of figure 3.

Figure 4 represent an axially oriented view of two successive, mutually abutting transverse segment 10a, 10b, both in an aligned, i.e. parallel orientation thereof and when mutually oriented at an tilting angle a. In the said parallel orientation thereof, the successive transverse segments 10a, 10b are in contact above, i.e. radially outward of the tilting edge 18. However, as the respectively leading transverse segment 10b rotates relative to the respectively trailing transverse segment 10a, its back surface 12 rolls-off over the tilting edge 18 of such trailing transverse segment 10a. This rotating and rolling- off occurs when the leading transverse segment 10b of the successive transverse segments 10a, 10b just enters or departs from between the two pulley sheaves 7, 8 of a pulley 2, 3. When these are both located between the sheaves 7, 8 in a curved trajectory part of the drive belt 6, the tilting angle a between the successive transverse segments

10a, 10b remains essentially constant, as does the radial position of the contact there between on the tilting edge 18 of the trailing transverse segment 10a. Hereby, the tilting angle a can be approximated by: a [deg] = (180:t)/(TT:Rr) (2) with t representing a thickness dimension of the transverse segments 10 in the circumference direction of the drive belt 6.

As illustrated in figure 5, the tilting edge 18 of the known transverse segment 10 is provided with a fixed radius 18R whereof a basis or centre point 18C coincides with the radially outer extent of the tilting edge 18, such that the tilting edge 18 smoothly merges with the part of the front surface 11 that lies above, i.e. radially outward of the tilting edge

18. The tilting edge 18, i.e. the convex curvature of the front surface 11 extends in radial inward direction to such an extent that it can accommodate any tilting angle a between the successive transverse segments 10a, 10b that occurs during operation of the drive belt 5 in the transmission 1, i.e. between Rr=~ and Rr=Rmin in equation (2). For example, with typical parameter values of Rmin=25 mm and t=1.5 mm, the tilting edge 18 spans an angle B of at least 3.5 degrees, i.e. from being aligned vertically at its radially outer extent to being oriented at 3.5 or more degrees relative to vertical at its radially inner extent. Thus, with a typically applied rocking edge radius 18R of 6 mm, an arc length 18L of the rocking edge 18 of only ~0.37 mm is minimally required.

Since the running radius Rr of the drive belt 6 varies between Rmin and Rmax in the curved trajectory parts at the pulleys 3, 4, while it is essentially infinite in the straight trajectory parts between the pulleys 3, 4, smaller tilting angle a values between 0 and (180-t)/(r-Rmax) occur between the successive transverse segments 10a, 10b only briefly when the leading transverse segment 10b transits between the said straight and curved trajectory parts. Consequently, a radially outer section of the tilting edge 18 that represents the said smaller tilting angle a values, experiences less wear than a radially inner section thereof that represents the range of relatively larger tilting angle a values according to equation (1) hereinabove. According to the present invention, this operational aspect of the drive belt 6 enables a favourable design modification of the transverse segment 10, in particular of the tilting edge 18 thereof.

A first embodiment of the novel transverse segment 10 according to the present invention is illustrated in figure 6. In this first embodiment thereof, the said radially outer extent of tilting edge 18 is oriented at an obtuse angle & relative to a surface part of the front main body surface 11 adjoining such radially outer extent of the tilting edge 18. This novel design feature effectively entails that the centre point 18C of the radius of curvature 18R of the radially outer extent of the tilting edge 18 is located above, i.e. radially outward of the tilting edge 18. Preferably in this case, a range of tilting angles a defined by the rocking edge 18 is reduced compared to that of the known transverse segment 10 and, in particular, does not include the said smaller tilting angle a values. As a consequence, the radial extent and the arc length of the rocking edge 18 can be favourably reduced compared to that of the known transverse segment 10. Alternatively, the radius 18R of the tilting edge 18 can be favourably increased compared to that of the known transverse segment 10 without increasing the arc length 18L thereof. Hereby, a contact stress between the successive transverse segments 10 in the said curved trajectory part is reduced, thus favourably reducing elastic compression and/or wear of the transverse segment 10.

A second, alternative embodiment of the novel transverse segment 10 according _ to the present invention is illustrated in figure 7. In this second embodiment, the tilting edge 18 of the transverse segment 10 includes both a radially outer section 181 and a radially inner section 182, with the radius of curvature 18R1 of the radially outer section 181 being smaller than the radius of curvature 18R2 of the radially inner section 182 and with the radially outer section 181 defining (only) the said smaller tilting angle a values. In this second embodiment too, either the radial extent and the arc length of the rocking edge 18 can be favourably reduced, or its radius 18R can be favourably increased compared to that of the known transverse segment 10.

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

CONCLUSIONS

A transverse segment (10) for a drive belt (6) provided with a belt package (9) consisting of a number of inter-nested belts and of a number of such transverse segments (10) placed successively and movably on the belt package (9), which transverse segment (10) defines a recess (33) for receiving the belt package (9), which recess (33) is bounded on an underside thereof by a base part (13) of the transverse segment (10) having a bearing surface (42) for supporting the belt package (9), in which base part (13) a tilting edge (18) is provided in the form of a vertically convex curved part of a front face (11) of the transverse segment (10), characterized in, in that the convex curvature of the tilting edge (18) is at an angle to the part of the front surface (11) located above the tilting edge (18).

2. A transverse segment (10) for a drive belt (6) provided with a belt package (9) consisting of a number of inter-nested belts and of a number of such transverse segments (10) placed successively and movably on the belt package (9), in particular according to claim 6, which transverse segment (10) defines a recess (33) for receiving the belt package (9), which recess (33) is bounded on an underside thereof by a base part (13) of the transverse segment ( 10) with a bearing surface (42) for supporting the belt package (9), in which base part (13) a tilting edge (18) is provided in the form of a part of a curved shape convexly curved in the height direction according to a radius of curvature (18C). a front face (11) of the transverse segment (10), characterized in that a pivot point of the radius of curvature (18C) of the tilting edge (18) is located above the tilting edge (18).

A drive belt provided with a belt package (9) consisting of a number of inter-nested belts and of a number of such transverse segments (10), successively placed and movably placed on the belt package (9), according to claim 1 or 2.

4. A continuously variable transmission (1) provided with two pulleys (2, 3) and with a drive belt (6) wrapped around these pulleys (2, 3) with a belt package (9) consisting of a number of inter-nested belts and with a number of transverse segments (10), successively placed and movably placed on the belt package (9), each defining a recess (33) for receiving the belt package (9), which recess (33) is bounded on an underside thereof by a base part (13) of the respective transverse segment (10) with a bearing surface (42) for supporting the belt package (9), in which base part (13) a tilting edge (18) is present in the form of a vertically curved convex part of a front surface (11) of the respective transverse segment (10), which tilting edge (18) provides for the contact between two successive transverse segments (10) in the drive belt (6) at the position of the pulleys (2, 3) where the successive transverse segments (10) transverse segments (10) are oriented at a tilt angle (a), which tilt angle (a) is related to a walking radius (Rr; Rmax; Rmin) of the drive belt (6) around a respective pulley (2, 3) and which tilting edge (18) has an upper section (181) curved according to a relatively small radius of curvature (18R1) and a lower section curved according to a relatively large radius of curvature (18R2). section (182), characterized in that the upper section (181) of the tilt rim (18) spans an angle equal to or less than the tilt angle (a) between the successive transverse segments (10) at a maximum value of the running radius (Rmax) of the drive belt (6) occurring in the transmission (1).

The transverse segment (10) according to claim 4, characterized in that the radius of curvature (18C1) of the upper section (181) of the tilting line (18) is less than 6 mm and preferably has a value in the range between 2 and 4mm.

The transverse segment (10) according to claim 5, characterized in that the radius of curvature (18C2) of the lower section (182) of the tilt line (18) is equal to or greater than 6 mm and preferably has a value in the range between 10 and 20 mm.

The transverse segment (10) according to claim 4, 5 or 6, characterized in that the upper section (181) of the tilt line (18) spans an angle of at least 1 degree and preferably between 1 and 2 degrees.

The transverse segment (10) according to claim 4, 5 or 6, characterized in that the top section (181) of the tilt rim (18) extends vertically for less than one third of a dimension in height of the lower section (182) of the tilt rim (18) and preferably extends between a fifth and a third of that dimension in the height direction.