NL1039973C2

NL1039973C2 - Drive belt with a carrier ring and transverse segments.

Info

Publication number: NL1039973C2
Application number: NL1039973A
Authority: NL
Inventors: Michael Fleig
Original assignee: Bosch Gmbh Robert
Priority date: 2012-12-24
Filing date: 2012-12-24
Publication date: 2014-06-25
Also published as: JP2016502055A; CN104937307A; JP6391591B2; CN104937307B; WO2014102225A1

Abstract

The disclosure relates to a transverse segment (33) for a drive belt with a carrier ring and with a plurality of these transverse segments (33) that are placed slideably on the carrier ring, which transverse segments (33) are each provided with two main surfaces (38, 41), where between the transverse segment (33) extends in thickness direction and with two friction surfaces provided on either side thereof, where between the transverse segment (33) extends in width direction, whereof on a front main surface (38) is provided with a largely cylindrically shaped protrusion (39) and whereof a rear main surface (41) is provided with a largely cylindrically shaped indentation (40). A circumference surface (43) of such indentation (40) or of such protrusion (39) is corrugated.

Description

DRIVE BELT WITH A CARRIER RING AND TRANSVERSE SEGMENTS

The present invention relates to a drive belt for a continuously variable transmission for motor vehicles, as defined in the preamble of claim 1.

5 Such a drive belt is well-known and is, for instance, described in the European patent applications EP-A-0 329 206 and EP-A-0 626 526. The known drive belt is composed of a plurality of transverse segments and at least one endless or ring-shaped carrier that extends through an opening or a recess of each of the segments such that these are supported thereby. The transverse segments are neither fixed to 10 one another nor to the carrier ring, such that they can move relative to the carrier at least in the circumferential or length direction thereof. In the drive belt, adjacent transverse segments abut one another through their respective front and back main surfaces, which main surfaces face, at least predominantly, in the said circumferential direction. Typically the transverse segments and the carrier ring are 15 made of steel. The carrier ring is typically composed of a number of individual bands that are narrowly fitted one around the other.

On either axial side thereof, the known transverse segment is provided with a friction surface. By means of these friction surfaces the transverse segment arrives in (frictional) contact with a driving pulley and a driven pulley of the transmission such 20 that a rotation of the driving pulley can be transferred to the driven pulley via the likewise rotating drive belt. An effective thickness of the transverse segment is defined as the dimension of these friction surfaces in the said circumferential direction, i.e. the part of the friction surfaces that is directly available for the contact with the pulleys. This effective thickness is typically less than an overall thickness of 25 the transverse segment because of, for instance, the presence of rounded or slanted transition edges between these friction surfaces and the main surfaces of the transverse segments.

The known transverse segment is further provided with an essentially cylindrical, possibly slightly tapering, protrusion or stud on its front main surface and 30 a, likewise essentially cylindrical indentation or hole on its back main surface. In the drive belt the stud of a first transverse segment is inserted in the hole of a second, adjacent transverse segment. As a result, the consecutive transverse segments in the drive belt mutually align each other in a plane that is oriented parallel with the said main surfaces thereof, i.e. perpendicular to the said circumferential direction.

35 As is explained in the European patent application EP-A-1 676 049, such 1 03 9973 2 interaction between the stud and the hole of two adjacent transverse segments also limits a rotation of the transverse segments relative to the carrier ring, both about the axial direction of the drive belt, i.e. a pitching of the transverse segments, and about the radial direction of the drive belt, i.e. a yawing of the transverse segments.

5 Several shapes and sizes have been proposed in the art in relation to the stud and the hole, however, in practice a predominant cylindrical shape is applied both for stud and for the hole. Such predominantly cylindrical shape is mostly somewhat tapered towards the end of the stud and the bottom of the hole, i.e. is slightly conical, to facilitate the insertion of the stud into the hole. Some clearance is necessarily 10 applied between the outer circumference of the stud and the inner circumference of the hole, i.e. in radial outward direction relative to the stud. This radial stud/hole-clearance allows, but at the same time limits a relative movement between the said consecutive transverse segments in the plane of the said main surfaces, also during the said pitching and yawing thereof relative to the carrier ring. This radial stud/hole-15 clearance may be designed such that is varies along the circumference of the stud, however, in practice it is mostly set to the same value in every direction.

In EP-A-1 676 049 a maximum value is prescribed for the stud/hole-clearance, at least in the axial direction of the drive belt, i.e. width-wise relative to the transverse segments. Such known maximum stud/hole-clearance should prevent that the 20 transverse segments can damage the carrier ring by an excessive yawing motion. More in particular, EP-A-1 676 049 teaches that, as the overall thickness and/or the effective thickness of the transverse segments gets smaller, an increasingly smaller (maximum) stud/hole-clearance is required (and vice versa), which known teaching can be quantified as follows: 25 RCL = 0.8 *TaU Te^ (1)

W

wherein - Tall is the overall thickness of a transverse segment, - Teff is the effective thickness of the transverse segment, - W is the width of the transverse segment, 30 - RCL is the calculated one-sided clearance that is denoted the radial stud/hole-clearance in the present disclosure and wherein - the factor 0.8 accommodates the inaccuracies between theory and practice.

The known drive belt is operated in a lubricated, i.e. oiled environment, both to reduce belt-internal friction losses and to cool the belt and the pulleys of the 3 transmission. The lubrication oil will, however, also enter into the holes of the transverse segments, at least in a bent part of the trajectory of the drive belt on the transmission pulleys, where the adjacent transverse segments are mutually oriented at an angle and where the studs are not fully inserted in the holes. As the transverse 5 segments transit from such bent trajectory part into a straight part of the drive belt's trajectory in-between the transmission pulleys, where the adjacent transverse element are mutually oriented in parallel and where the studs are inserted fully into the holes, lubrication oil must thus be expelled or discharged from the holes to receive the studs. The mechanical power that is required for discharging the 10 lubrication oil from the holes is effectively lost, i.e. such power is provided by the input shaft of the transmission, but is not transmitted to the output shaft thereof.

The above-identified power loss is mostly negligible and has, as such, never been addressed in the art. However, as the radial stud/hole-clearance becomes smaller, i.e. when the opening or channel between a stud and a hole that is available 15 for discharging the lubrication oil from the hole becomes smaller, increasingly more mechanical power is required to insert the stud into the hole. It is presently put forward that for a small enough radial stud/hole-clearance such detrimental impact on the operating efficiency of the drive belt is very well noticeable. In fact, when the radial stud/hole-clearance drops below a certain value, the lubrication oil in the hole 20 may resist being expelled by the stud to such an extent that the stud is not inserted fully into the hole, at least not during the transit of a respective transverse segment from the said bent trajectory part into the said straight trajectory part. This configuration of the drive belt is, however, to be avoided, because it may adversely affect the reliability of operation of the drive belt. In practice a noticeable decrease of 25 the operating efficiency of the drive belt is expected at a radial stud/hole-clearance of 25 microns or less. Below a radial stud/hole-clearance of 10 microns the efficiency decrease may become especially pronounced, due to the studs of the transverse segments not being inserted fully into the holes thereof during the above-mentioned transit.

30 On the other hand, in general and in particular in combination transverse segments that are formed progressively, i.e. that are produced from plate material towards their final shape in a number of cutting and shaping stages, which manufacturing technology is for example described in EP-A-1 968 760, there is a desire to apply a stud/hole-clearance of 25 microns or less on average between the 35 transverse segments, in case of the lower limit for the spread or tolerance in 4 manufacturing. For example, when applying this known manufacturing technology to obtain the more or less standard and commonly applied transverse segment with a nominal width of 24 mm and a nominal thickness of 1.5 mm, the effective thickness thereof will typically amount to less than 0.70 mm. In this case, the equation (1) 5 prescribes a maximum of 35 microns for the radial stud/hole-clearance for the standard, 24 mm wide transverse segment. Depending on the (statistical) spread or tolerance that is allowed in manufacturing, a practical range for the radial stud/hole-clearance will normally include a value of less than 25 microns. For example, a practical manufacturing tolerance range based on the equation (1) can be: 25 ± 10 10 microns, which range has a minimum value of 15 microns. Thus, already when a slightly larger manufacturing tolerance is allowed, such minimum value will drop to 10 microns or less.

The present disclosure aims to reconcile the desire to apply a small radial stud/hole-clearance with the desire to minimise the adverse affect that such small 15 clearance can has on the transmission efficiency. Thus, effectively, this disclosure is aimed at facilitating or otherwise enhancing the discharge of lubrication oil from the hole of the transverse segment by a stud of an adjacent transverse segment that is inserted into it.

An obvious measure for improving such discharge would be to apply the said 20 small radial stud/hole-clearance only in the width direction of the transverse segment and to apply larger clearance in other directions, in particular in the height direction of the transverse segment perpendicular to the width and thickness directions thereof, for example by flattening an underside and a topside of the stud relative to its conventional round cross-sectional shape, or by shaping the hole more or less like an 25 ellipse with its long-axis in the height and its short-axis in the width direction. However, since the preferred production method is to form the stud from material that is made available by the (press-)shaping of the hole, the stud and the hole are preferably provided with a largely similar shape.

A more preferable measure for improving such discharge is provided by the 30 present disclosure, in particular by the features of the claim 1 hereinafter. According to the claim 1, the circumference surface of the stud anc(/or of the hole is corrugated in the sense that it is provided with ridges and grooves, mutually alternating along the circumference of the stud and/or the hole. Such corrugation was found to be surprisingly effective in improving the discharge of lubrication oil from the hole in 35 comparison with the many other conceivable shapes of the stud and/or the hole.

5

Moreover, by such corrugation, the radial stud/hole-clearance can be approximately and favourably the same in every direction, i.e. along the entire circumference of the stud and hole.

The advantageous lubrication oil discharge feature of the surface corrugation is 5 attributed to a twofold effect thereof. Firstly, the grooves of the corrugation form channels that accommodate the lubrication oil and that facilitate the discharge thereof, in particular if the corrugation is applied to the stud of the transverse segment. Secondly and probably most importantly, by the corrugation the pressure exerted by the stud on the lubrication oil when it enters into the hole is increased, at 10 least locally at the protruding ridges thereof, which pressure serves to set the lubrication oil in motion towards an area of lower pressure, i.e. to the corrugation grooves and, ultimately, to the outside of the hole. Although this latter effect does not reduce the mechanical work involved in discharging the required volume of lubrication oil, it does reduce the time required there for and thus also reduces the 15 mechanical power that is expended thereby to the benefit of the said operating efficiency of the drive belt. This latter effect also occurs when the ridges and grooves are provided only to the circumference surface of the hole, which is highly preferable in manufacturing the transverse segments.

To optimise the pressure-increasing effect of the corrugation, it is provided 20 preferably along the entire circumference of the stud and/or hole and preferably on a fine scale. In this latter respect, the top surfaces of the ridges of the corrugation may each be between 10 and 100 microns wide and may be mutually separated by between 25 and 250 microns, at least for the said commonly applied transverse segment.

25 The invention will now, by way of example, be elucidated further along a drawing in which: figure 1 provides a schematically representation of the known continuously variable transmission with two pulleys and a drive belt; figure 2 illustrates a transverse segment of the drive belt according to figure 1, 30 both in a side and in a front elevation thereof; figure 3 schematically indicates the feature of rotation of the transverse segments of the belt at a pulley ("element yawing"); figure 4 provides a novel embodiment of the transverse segment in a cross-sectional perspective view of a top part thereof including a stud and a hole, and 35 figure 5 provides a different view of the novel embodiment of the transverse 6 segment according to figure 4.

In the figures, identical reference numbers relate to identical or at least comparable technical features.

Figure 1 shows the central parts of a known continuous variable transmission, 5 as is commonly applied in the drive line of personal vehicles between the engine and the drive wheels thereof. The transmission comprises two pulleys 1, 2, each provided with two pulley sheaves 4, 5, and a drive belt 3 that is wrapped around the said pulleys 1, 2, located clamped between the respective pulley sheaves 4, 5 thereof. The pulley sheaves 4, 5 are shaped generally conical and at least one pulley sheave 10 4 is incorporated in the transmission axially moveable along a respective pulley shaft 6, 7 over which it is placed. The transmission also comprises activation means that impose on the said at least one sheave 4 an axially oriented force Fax directed towards the respective other pulley sheave 5, such that the belt 3 is clamped there between and a rotational movement and accompanying torque can be transmitted 15 between the pulleys at a variable transmission ratio.

The drive belt 3 comprises at least one endless or ring-shaped carrier 31 and a number of transverse segments 33, with the carrier ring 31 extending through an opening 37 of the transverse segments 33, such that these are moveable along the circumferential direction of the carrier ring 31.

20 As is shown in more detail on the left-hand side of figure 2 in a cross-section of the drive belt 3, the carrier ring 31 consists of two parts 31, each such part being composed of a number of individual bands 32 that are narrowly fitted around one another. The transverse segments 33 are basically metal plates that are facing in the circumferential direction of the carrier ring 31 and that are provided with a friction 25 surface 35 on either axial side thereof, for frictionally engaging the pulley sheaves 4, 5. In the drive belt 3, adjacent transverse segments 33 abut one another through their respective front and rear main surfaces 38, 41 as is shown for a pair of abutting transverse segments 33 on the right-hand side of figure 2.

To allow the drive belt 3 to bend easily, a bottom side of the transverse 30 segments 33 is tapered. An axially extending edge 42, between such tapered bottom side and a top part transverse segments 33 of largely constant thickness, on the front main surface 38 serves as and defines the axis of rotation between each pair of abutting transverse segments 33.

Further, the known transverse segments 33 include a stud 39 projecting from 35 the front main surface 38 and a hole 40 provided in the back main surface 41. In the 7 drive belt 3, the stud 38 of a first transverse segment 33 of a pair of abutting transverse segments 33 is at least partly inserted in the hole of a second transverse segment 33 of such pair, whereby these transverse segments 33 mutually align each other perpendicular to the said circumferential direction. When the stud 39 is fully 5 inserted into the hole 40, a clearance or play RCL there between in the radial direction of the stud, limits -i.e. determines the maximum possible- mutual displacement between the abutting transverse segments 33 in the plane of the main surfaces 38, 41. Additionally, when the transverse segments 33 are clamped in the axial direction between the sheaves 4, 5 of a pulley 1, 2, such radial stud/hole-10 clearance RCL also limits a rotation of the transverse segments 33 about the radial direction of the drive belt 3 as will be clarified with reference to figure 3.

Figure 3 provides a schematic view of a pair of abutting transverse segments 33 that are both clamped between the sheaves 4, 5 of a pulley 1, 2. From this figure 3 it appears that a rotation of the transverse segments 33 about the radial direction is 15 accompanied by a sliding movement between the front main surface 38 with the stud 39 and the rear main surface 41 with the hole 40 of the transverse segments 33, which sliding movement is thus limited to said radial stud/hole-clearance RCL. According to the art, it is preferred that this type of rotation of the transverse segments 33 is limited, such that the forces FnL, FnR exerted by the pulley sheaves 20 4, 5 on the friction surfaces 35 of the transverse segment 33 work to counteract such rotation. If the cross-sectional shape of the transverse segment 33 closely approximates a rectangle, this latter criterion can be quantified as follows: RCL = (2) w wherein 25 - Tall is the thickness of such theoretical transverse segment 33 and wherein - W is the width thereof.

However, in practice, a more or less rounded or slanted transition surface 25 is mostly present between the main surfaces 38, 41 and the friction surfaces 35 of the transverse segments 33, either as incorporated in the particular design of the 30 transverse segment 33 or as a result of the processes involved in the manufacturing thereof, such as blanking and (stone) tumbling. As illustrated in figure 3, the effective width Teff of this latter transverse segment 33 that available for contact with the pulley sheaves 4, 5, i.e. the breadth of the friction surfaces 35 thereof, is noticeably less than the largest or overall thickness Tall of that transverse segment 33. In this 8 case the equation (1) applies instead.

For one type of transverse segment 33 that is actually applied in practice, the (cross-sectional shape of the) transition surface 25 between the friction surface 35 and the front main surface 38 can be approximated by arc with a radius of 0.3 mm, 5 whereas the transition surface 25 between the friction surface 35 and the rear main surface 41 can be approximated by a slanted plane with a dimension in the thickness direction of the transverse segment 33 of 0.5 mm. Thus the effective thickness Teff of such transverse segment 33 is 0.8 mm less than its overall thickness Tall, which overall thickness in this example amounts to 1.5 mm in combination with a width of 10 the transverse segment 33 of 24 mm. For this known transverse segment 33, the equation (1) prescribes a maximum radial stud/hole-clearance RCL of 35 microns, which maximum value can be controlled in manufacturing by means of a tolerance range of -for instance- 25 ± 10 microns.

Although, such small radial stud/hole-clearance RCL thus helps to avoid an 15 unfavourable loading of the drive belt 3, it does come with the disadvantage that, when the studs 39 are inserted into the holes 40, lubrication oil can only be discharged from the hole 40 through the small gap there between. The narrower such gap is, i.e. the smaller the radial stud/hole-clearance RCL, the more effort it takes to insert the stud 39 (further) into the hole 40. To mitigate this disadvantage, 20 i.e. to facilitate the insertion of the studs 39 into the holes 40 during operation of the drive belt 3, it is presently proposed to provide the circumference surface of the stud 39 and/or the circumference surface 43 of the hole 40 with a corrugation.

Figure 4 provides a cross-section section of such novel transverse segment 33, showing only the top part thereof with the stud 39 and the hole 40. In figure 4, 25 circumference surface 43 of the hole 40 is corrugated, i.e. is provided with a pattern of mutually alternating ridges 44 and grooves 45.

Figure 5 provides a further view of such novel transverse segment 33 shown in figure 4, in particular of the hole 40 with the corrugated circumference surface 43. Figure 5 provides a view of the rear main surface 41 of such novel transverse 30 segment 33, looking into the hole 40 thereof.

In the exemplary embodiment of thereof in the figures 4 and 5, forty-five ridges 44 and grooves 45 are provided in total along the circumference of the hole 40, with the breadth of each groove 45 amounting to about four time the breadth of the (top surface of the) ridges 44. By such corrugation of the circumference surface 43 of the 35 hole 40, i.e. by the provision of the said ridges 44 and grooves 45, lubrication oil that 9 may be present in the hole 40 is discharged there from more easily when the stud 39 is inserted (further) therein, in particular in comparison with the known stud 39 and hole 40 having a flat and/or smooth circumference surface. Firstly, such discharge appears to be facilitated by the grooves 45 of the corrugation forming channels 5 between the circumference surface 43 of the hole 40 and the circumference surface of the stud 39 that allow the lubrication oil to flow more freely there between. Secondly, such discharge appears to be promoted by the ridges 44 of the corrugation exerting a higher pressure on the lubrication oil as the stud 39 is inserted (further) into the hole 49 and as compared to the known smooth circumference surface, which 10 (higher) pressure is what sets the lubrication oil in motion towards to the outside of the hole 40 in the first place.

It is noted that the tops of the ridges 44 may be curved slightly concavely to closely follow the contour of the circumference surface of the stud 39, however, these ridge tops are preferably shaped as essentially flat or even slightly convexly surfaces 15 to further increase the pressure exerted by the ridges 44 on the lubrication oil when the stud 39 is inserted (further) into the hole 40.

For the above-mentioned dimensions of the transverse segment 33, the stud 39 and the hole 40 are typically provided with a diameter of approximately 2.0 mm. With these dimensions of the transverse segment 33, the corrugation shown in the figures 20 4 and 5 can be calculated to be on a fine scale with the ridge tops having a breadth of ± 28 microns, each pair of adjacent ridge tops being separated by ± 112 microns, which latter value thus represents the said breadth of the groove 45.

In summary this disclosure concerns a transverse segment 33 for a drive belt 3 with a carrier ring 31 and with a plurality of transverse segments 33 that are placed 25 slideably on the carrier ring 31, which transverse segments 33 are each provided with two main surfaces 38, 41, where between the transverse segment 33 extends in thickness direction and with two friction surfaces 35 provided on either side thereof, where between the transverse segment 33 extends in width direction, whereof on a front main surface 38 is provided with a largely cylindrically shaped protrusion 39 and 30 whereof a rear main surface 41 is provided with a largely cylindrically shaped indentation 40, a diameter of the indentation 40 being somewhat larger than a diameter of the protrusion 39, whereby at least some radial clearance RCL is present between the protrusion 39 and the indentation 40 of two subsequent transverse segments 33 in the drive belt 3, with a circumference surface of the protrusion 39 or 35 a circumference surface 43 of the indentation 40 being ribbed, i.e. corrugated.

10

This disclosure also concerns the above-described transverse segment 33, wherein the corrugated circumference surface 43 is provided with a number of mutually alternating ridges 44 and grooves 45.

This disclosure also concerns any one of the above-described transverse 5 segments 33, wherein the ridges 44 and the grooves 45 extend over the circumference surface 43 in the axial direction thereof.

This disclosure also concerns any one of the above-described transverse segments 33, wherein the ridges 44 and the grooves 45 extend over the circumference surface 43 in the axial direction thereof.

10 This disclosure also concerns any one of the above-described transverse segments 33, wherein a dimension of the ridges 44 in the circumference direction of the circumference surface 43 amounts to between 10 and 100 microns and wherein a dimension of the grooves 45 in that direction amounts to between 25 and 250 microns.

15 This disclosure also concerns any one of the above-described transverse segments 33, wherein the diameter of the indentation 40 is at most 35 micron, preferably at most 25 micron, more preferably at most 10 micron larger than the diameter of the protrusion 39.

This disclosure also concerns a drive belt 3 with a carrier ring 31 and with a 20 plurality of any one of the above-described transverse segments 33 that are placed slideably on the carrier ring 31.

This disclosure also concerns the above-described drive belt 3, wherein, on average between all pairs of adjacent transverse segments 33 in the drive belt 3, the said radial clearance RCL is at most 25 micron.

25 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 30 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 35 particular those that lie within reach of the person skilled in the relevant art.

1 03 9973

Claims

1. Transverse segment (33) for a drive belt (3) with a carrier ring (31) and with a number of such transverse segments (33), which are slidably arranged on the carrier ring (31), which transverse segment (33) is provided with two main surfaces (38, 41), between which the transverse segment (33) extends in thickness direction and, on either side thereof, of two friction surfaces (35) between which the transverse segment (33) extends in width direction, one of which for main surface (38) of a substantially cylindrically shaped protuberance (39) is provided and of which a back main surface (41) is provided with a substantially cylindrically shaped indentation (40), a diameter of the indentation (40) being slightly larger than a diameter of the protrusion (40) 39), so that there is at least some play in the radial direction (RCL) between the protrusion (39) and the depression (40) of two successive transverse segments (33) in the drive belt (3), characterized in that a circumference of the protrusion (39) or a peripheral surface (43) of the depression (40) is ribbed.

The transverse segment (33) according to claim 1, characterized in that the circumferential surface (43) is provided with a number of mutually alternating ridges (44) and grooves (45).

The transverse segment (33) according to claim 2, characterized in that the ridges (44) and grooves (45) extend thereon in the axial direction of the peripheral surface (43). 25

The transverse segment (33) according to claim 2 or 3, characterized in that a dimension of the ridges (44) in the circumferential direction of the circumferential surface (43) is between 10 and 100 micrometers and a dimension of the grooves (45) in that direction is between 25 and 250 micrometers. 30

The transverse segment (33) according to one or more of the preceding claims, characterized in that in the diameter of the depression (40) a maximum of 35 microns, preferably a maximum of 25 microns and more preferably a maximum of 10 microns larger is then a diameter of the protrusion (39). 35 1039973

6. Drive belt (3) with a carrier ring (31) and with transversely arranged segments on the carrier ring (31), which transverse segments (33) are characterized according to one or more of the preceding claims.

The drive belt (3) according to claim 6, characterized in that the average of the radial clearance between the protuberance (39) and the indentation (40) over all pairs of successive transverse segments (33) in the drive belt (3) ) is not more than 25 micrometres. 1 03 9973