NL1041122B1

NL1041122B1 - Drive belt.

Info

Publication number: NL1041122B1
Application number: NL1041122A
Authority: NL
Inventors: Uhlenbrock Dietmar; Hautmann Nikolaus; Kulow Uwe
Original assignee: Bosch Gmbh Robert
Priority date: 2014-12-23
Filing date: 2014-12-23
Publication date: 2016-10-11
Also published as: CN105715743A

Abstract

A drive belt (300) for transmitting power between two rotating pulleys, having an endless, elongated shape and comprising a tension element (310) comprising a wire provided in at least one winding extending in the longitudinal direction of the drive belt (300) for transmitting a tensile force along the drive belt (300) and a number of support elements (350; 350a, 350b), each support element (350; 350a, 350b) being fixed in relation to the tension element (310) at least in the said longitudinal direction for supporting the tension element (310) on the two pulleys. The support elements (350; 350a, 350b) are arranged on the tension element (310) at a mutual separation or gap (3) in the longitudinal direction amounting to at least 1 mm, or to at least 10% of a dimension of the support elements (350; 350a, 350b) in the said longitudinal direction.

Description

DRIVE BELT

The present invention relates to a drive belt according to the preamble of claim 1 hereinafter. A drive belt as described above is generally used for the transmission of driving power between two shafts in a drive line. The drive belt is passed around a pair of pulleys, each pulley being provided on a different shaft. By frictional contact between a first pulley and the drive belt, a rotational motion of the first pulley is transformed into a translational motion of drive belt. By frictional contact between the drive belt and a second pulley, the translational motion of the drive belt is in turn transformed into a rotational motion of the second pulley. The second pulley is thus driven by the first pulley via the drive belt. A generally known use of a drive belt as described above is in the continuously variable transmission of a two-wheeled vehicle such as a scooter. In such a transmission, each pulley comprises a pair of pulley sheaves, each sheave having an inclined, inward facing flank for contacting a side surface of the drive belt. Depending on the distance of the two sheaves with respect to each other, the drive belt runs along a pulley at a larger or a smaller radius. By varying the distance of -the pulley sheaves in a driving pulley or in a driven pulley, the transmission ratio between the two pulleys can, subject to certain limitations, be freely chosen.

Conventionally, in scooters, a drive belt is applied having a tension element comprising an elastomeric or rubber ring, the ring having embedded therein a number of tension fibers, possibly with a protective cover layer provided between the (layer of) tension fibers and the rubber ring. Mounted on the rubber ring are a number of support elements for supporting the tension element on a pair of pulleys, each support element having a pair of contact surfaces for sustaining frictional contact with a pair of pulley sheaves. The support elements are made of a relatively hard and wear resistant material, typically a thermoplastic such as polyamide, in order to cope with the intense contact with the transmission pulleys in a durably manner. Each support element is positioned inside a notch provided in the outer surface of the rubber ring of the tension element, each support element thereby being fixed with respect to the tension element in the longitudinal direction of the drive belt. Because the rubber ring is provided with notches for accommodating part(s) of the support elements, a nominal height dimension thereof amounts to several times a diameter or height of the tension fibers.

The recent publications W02014-080288 A1 and W02014-080289 A1 teach that the rubber ring can be omitted from the tension element of the conventional drive belt. In this case, the tension element is composed of one or more tension cords or wires made from interwoven fibers such as aramid, possibly coated or otherwise provided with a cover layer. If such a coating or cover layer is applied, a thickness thereof will normally be less than the height the tension cord(s), in any case, such coating or cover layer is not provided with the said notches of the rubber ring that is applied in above-mentioned, conventional drive belt. Furthermore, if a single tension cord is used, this is typically arranged into a number of side-by-side lying, spiral windings. In this particular case, the required fixation between the tension element and the support elements in the longitudinal direction is realized either by the friction there between, by gluing or otherwise adhesively attaching these components together and/or by providing the support elements with parts that pierce -and thus interlock with- the tension cord(s) of the tension element.

Although this latter known drive belt avoids the energy loss due to the deformation of the rubber ring during operation and, moreover, reduces manufacturing cost by obviating the rubber ring, a somewhat reduced service life was observed relative to the conventional drive belt that includes such rubber ring as part of the tension element thereof. Based on such observation applicant set out to investigate the main cause of such reduced service life and to devise a solution thereto based on the thus obtained understanding thereof. Accordingly, underlying the present disclosure is the desire and aim to improve the service life of the known drive belt.

According to the present disclosure, in the latter known drive belt, i.e. in the absence of the rubber ring, a bending of the tension element that occurs where the drive belt wraps in arc on and around the pulleys, is concentrated in between the support elements of the drive belt, whereas in the conventional drive belt such bending is more gradually distributed along such wrapped pulley arc. Because the tension element is rigidly fixed to the support elements, no bending in the longitudinal direction thereof can occur at these support elements. Thus the required bending of the tension element occurs at the edges of the support elements. The trajectory of the tension element in the wrapped pulley arc can thus be thought of as a number of consecutive, sharp bends or kinks that are separated by straight sections corresponding to the locations of the support elements. As a result, a bending stress in the tension element is concentrated at the said kinks therein, which was found to compromise the durability and/or service life thereof. It is favorable to reduce such bending stress, in particular by providing for the tension element to bend more gradually along the wrapped pulley arc.

In a first alternative elaboration of the drive belt according to the present disclosure, the bending of the tension element is favorably influenced by providing a separation, i.e. gap between the consecutive support elements in the longitudinal, i.e. circumferential direction of the drive belt. As a result of this measure, the bending of the tension element occurs in the gap between the support elements, which allows for a more gradual, i.e. less sharp bending thereof. Preferably, such gap is at least 10% of a dimension of the support elements in the said longitudinal direction, i.e. a thickness dimension thereof, and can amount to twice such support element thickness or even more. Preferably, in absolute terms, such gap is between 1 and 5 mm long, more preferably between 2 and 4 mm, in particular in combination with support elements that have a thickness between 2 and 9 mm, preferably between 3 and 6 mm.

In a practical elaboration of this first embodiment, a protective cover layer is applied to the tension cord(s) of the tension element in the said gap between the consecutive support elements. By this cover layer, the said bending of the tension element is favorably influenced by being even more equally distributed throughout the gap in between the consecutive support elements. Preferably in this respect, a thickness of the cover layer is largest where it adjoins the support elements and gradual reduces towards the center of the gap where the cover layer is thinnest. Hereby, the bending of the tension element at the edges of the support elements is suppressed, at least relative to the bending of the tension element where it spans the gap between the support elements.

Alternatively, in a second alternative elaboration of the drive belt, the bending of the tension element is favorably influenced by providing a resilient member between the support elements and the tension element that allows the latter to bend (also) at the location of the support elements. This resilient member thus allows for a more gradual, i.e. less sharp bending of the tension element. Such resilient member can be embodied by a layer of elastically compressible material, such as an elastomere, that is adhered either to the support element, to the tension element or to both.

In a practical elaboration of this second embodiment, the resilient member also embodies the said protective cover layer of the tension cord(s) of the tension element. In case the resilient member completely encloses, i.e. embeds the tension cord(s), the layer thickness thereof can be varied, whereby the bending of the tension element will be concentrated at the relatively thin portions thereof. Preferably, such thin portions are provided in a gap that is provided between the support elements in the first embodiment of the drive belt.

These and other aspects, features and advantages of the present invention will be further explained by the following description of one or more preferred embodiments with reference to the drawings, in which same reference numerals indicate same or similar parts, and in which: figure 1 schematically shows in perspective view a drive belt mounted on a pair of pulleys of a continuously variable transmission; figure 2 schematically shows in perspective view a drive belt according to the state of the art; figure 3 schematically shows in perspective view a portion of a drive belt in a first embodiment according to the present disclosure; figure 4 shows, in a schematic cross-section, a portion of a drive belt in a second embodiment according to the present disclosure; figure 5 shows, in a schematic cross-section, a portion of a drive belt in third embodiment according to the present disclosure; and figure 6 shows, in a schematic cross-section, a portion of a drive belt in fourth embodiment according to the present disclosure

Figure 1 shows a continuously variably transmission 2 comprising a first pulley 100a and a second pulley 100b. Each pulley 100a, 100b is mounted on a pulley shaft 200a, 200b. Running on the two pulleys 100a, 100b is a drive belt 1.

Each pulley 100a, 100b comprises a pair of pulley sheaves 101 a, 101 b. Each pulley sheave 101a, 101b has an inclined contact surface 102 facing the contact surface 102 of the other pulley sheave 101a, 101b. Within each pulley 100a, 100b, the pulley sheaves 101a, 101b are moveable with respect to each other in the axial direction of the respective pulley shaft 200a, 200b so that the distance between the contact surfaces 102 of the two pulley sheaves 101a, 101b can be varied. With the contact surfaces 102 of the two pulley sheaves 101a, 101b deviating with respect to each other in the radially outward direction of a pulley 100a, 100b, bringing the two pulley sheaves 101a, 101b closer together urges the drive belt 1 to move radially outward to continue running at a larger diameter. Vice versa, moving the two pulley sheaves 101a, 101b away from each other allows the drive belt 1 to move radially inward to continue running at a smaller diameter.

With the first pulley 100a being a driving pulley, the second pulley 100b is driven by the first pulley 100a via the drive belt 1. The transmission a portion ratio between the first pulley 100a and the second pulley 100b can be varied by changing the radius at which the drive belt 1 runs at each of the pulleys 100a, 100b in opposite directions.

Figure 2 shows a portion of a drive belt 1 according to the state of the art. The known drive belt 1 comprises a number of support elements 50, each support element 50 being substantially plate-shaped and arranged facing in the longitudinal direction of the drive belt 1. At the sides facing in the opposite axial directions, a support element 50 is provided with a contact surface 54a, 54b for coming into contact with the contact surface 102 of a pulley sheave 101a, 101b. The two contact surfaces 54a, 54b have an inclined position with respect to each other, so to fit an inclination of the contact surface 102 of the pulley sheaves 101a, 101b. The known support element 50 comprises a bottom piece 20 and a top piece 30, where between a slit-shaped opening 55 is defined. A portion of the support element 50, in particular a portion extending radially inward of an edge 56 on a front main face thereof, is tapered so as to facilitate the tilting of adjacent support elements 50a, 50b with respect to each other to allow bending of the drive belt 1.

The drive belt 1 further comprises a tension element 10 extending through the opening 55 of each support element 50. The tension element 10 comprises a tension wire 40 that is provided in the drive belt in a number of windings 41a, 41b, each extending in the longitudinal direction along the full circumference of the drive belt 1. The windings 41a, 41b of the tension wire 40 are positioned side by side, so as to substantially fill the width of the opening 55 of a support element 50. The tension wire 40 can be made of metal, plastic, or aramid fibers, in which latter case the wire 40 may be spun or have an otherwise woven structure. Other materials such as carbon fiber or glass fiber may also be used. The tension element 10 may include a coating or cover layer of the tension wire 40 to enhance the durability and/or wear resistance thereof, in particular in case the latter is made from fiber material.

In order for the known drive belt 1 to function as intended, the support elements 50 are fixed to the tension element 10, for example by means of an adhesive being provided there between, by being provided with mutually interlocking parts, or, possibly, by friction alone. As mentioned in W02014-080288 A1, adjacent, i.e. consecutively arranged support elements 50a, 50b are fixed to the tension element 10 at a mutual distance of about 0.1 mm, when measured in a longitudinally stretched part of the drive belt 1.

In the known drive belt 1, a bending of the tension element 10 that occurs where the drive belt 1 wraps in arc around a pulley shaft 200a, 200b, while being clamped between the pulley sheaves 101a, 101b of a respective pulley 100a, 100b, is concentrated in a number of relatively sharp kinks in between the adjacent support elements 50a, 50b thereof. At each such kink in the tension element 10, a considerable bending stress is generated in each winding 41a, 41b of the tension wire 40. According to the present disclosure, the durability and the known drive belt 1 can be improved, if the tension element 10 is allowed to bend more gradually.

In a first embodiment of a drive belt 300 according to the present disclosure, which embodiment is schematically illustrated in figure 3, a considerable mutual distance or gap 3 is provided between consecutive support elements 350a, 350b thereof. As a result of such gap 3, the tension element 310 is given space to bend, such that the resulting local bending radii of the tension element 310 are favorably increased and the bending stress is favorably decreased relative to the state of the art drive belt 1. In the shown example of the drive belt 300, the gap 3 is approximately the same size in the longitudinal direction of the drive belt 300 as the size of the support elements 350a, 350b in that direction, i.e. as a thickness thereof. By the application of such large gap 3, the service life of the drive belt 300 could be extended appreciably. However, already a smaller gap 3 of at least 1 mm, i.e. tenfold the conventionally applied separation, or at least 10% of the said thickness can provide a noticeable and favorable improvement of such service life.

In a second embodiment of the drive belt 300 according to the present disclosure, which is schematically shown in figure 4 in a cross-section of a tension wire 40 of the tension element 310 and of a support element 350, a resilient member is provided in the gap 3 between the consecutive support elements 350a, 350b of the drive belt 300 in accordance with the said first alternative embodiment thereof according to the present disclosure. In particular such resilient member 4 is made of a relatively compliant, i.e. elastically deformable material, such as rubber, that is attached to the tension wire 40 of the tension element 310. By this resilient member 4, the required bending of the tension element 310 will be favorably distributed throughout the gap 3 in between the consecutive support elements 350a, 350b. Preferably, such resilient member 4 completely embeds the tension element 310, where it would otherwise be exposed to the environment in between the support elements 350a, 350. To further enhance such gradual, more equally distributed bending of the tension element 310, a thickness of the resilient member 4 in radial direction reduces as seen from a respective support element 350a, 350b towards a centre or middle M of the gap 3, as is also illustrated in figure 4. By this latter feature, the required bending of the tension element 310 is optimally distributed in its longitudinal direction by increasing the local bending radii thereof.

In relation to this latter second novel embodiment of the drive belt 300 it is noted that, by not providing the resilient member 4 in radial direction between the tension wire 40 of the tension element 310 and the bottom piece 20 and the top piece 3 of the support elements 350, the required bonding there between is not detrimentally influenced. These latter components of the novel drive belt 300 can thus be favorably fixed together in a manner taught by W02014-080288 A1 or W02014-080289 A1, i.e. by applying an adhesive there between and/or by fusion through (ultrasonic) welding.

Inter alia, it is noted that such required bonding between the tension element 310 support elements 350 can be improved by incorporating both aramid and polyamide fibers in the tension wire 40. Further components and/or materials can of course be applied to optimize certain properties of the tension wire 40, however, already by adding a small share of polyamid fibers to the main constituent part of aramid fibers, the bonding of the tension wire 40 with the support elements 350 was found to be greatly improved, in particular when applying ultrasonic welding. More in particular, the aramid fibers then largely determine the tensile strength of the wire 40, whereas the polyamide fibers largely determine the bonding strength of the wire 40 with the support elements 350.

In a third embodiment of the drive belt 300 according to the present disclosure, which is schematically shown in figure 5 in a cross-section of a tension wire 40 of the tension element 310 and of a support element 350, a resilient member 5 is included therein in the form of inserts 5 of relatively compliant, i.e. elastically deformable material, such as rubber, at the edges of the opening 55 between the bottom and top pieces 20, 30 of the support elements 350 where the tension element 310 passes through (figure 2). By the presence of such inserts 5, which can be compressed by the tension wires 40 of the tension element 310 as indicated by the arrows, the tension element 310 can bend (also) at the location of the support elements 350, such that the resulting local bending radii of the tension element 310 are favorably increased and the bending stress is favorably decreased relative to the state of the art drive belt 1.

In a fourth embodiment of the drive belt 300 according to the present disclosure, which is schematically shown in figure 6 in a cross-section of a tension wire 40 of the tension element 310 and of a support element 350, a resilient member 6 is included therein in the form of a cover layer of the tension wire 40 of relatively compliant, i.e. elastically deformable material. The cross-section oriented in the longitudinal direction of the tension element 310 including such cover layer 6 in addition to the tension wire 40 fits inside the opening 55 of the support elements 350. By the presence of such cover layer 6, the tension element 310 can bend (also) at the location of the support elements 350. Furthermore, as is also illustrated in figure 6, a layer thickness of the said cover layer 6 is reduced from the support element 350 towards the middle M of the gap that is provided between the consecutive support elements 350a, 350b of the drive belt 300 in accordance with the said first alternative embodiment thereof according to the present disclosure.

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 variations, modifications and practical applications thereof, in particular those that lie within reach of the person skilled in the relevant art.

Claims

A drive belt (300) for power transfer between two rotating pulleys (100a, 100b) with an elongated, endless shape and comprising: - a tension element (310) comprising a cable (40) which extends in at least one in the longitudinal direction of the drive winding (300) is provided for transferring a tensile force in the drive belt (300), - a number of support elements (350; 350a, 350b), each of which is fixed relative to the tension element (310) in the said longitudinal direction and which support the tension element (310) at the location of the two pulleys (100a, 100b), characterized in that the support elements (350; 350a, 350b) are spaced apart or with a gap (3) on the tension element (310) are arranged, which gap (3) in the said longitudinal direction is either at least 1 mm or at least 10% of a dimension of the support elements (350; 350a, 350b) in that longitudinal direction.

The drive belt (300) according to claim 1, characterized in that the gap (3) in said longitudinal direction has a dimension in the range between 1 mm and 5 mm and preferably in the range between 2 mm and 4 mm .

The drive belt (300) according to claim 2, characterized in that the dimension of the support elements (350; 350a, 350b) in the said longitudinal direction has a dimension in the range between 2 mm and 9 mm and preferably in the range between 3 mm and 6 mm.

The drive belt (300) according to claim 1, 2 or 3, characterized in that the drive belt (300) further comprises a resilient member (4), which resilient member (4) is arranged in the gap (3) between mutually adjacent support elements (350; 350a, 350b) thereof.

The drive belt (300) according to claim 4, characterized in that the resilient member (4) is arranged on the tension element (310) and that a thickness dimension thereof, at least measured perpendicular to said longitudinal direction, varies and thereby near support elements (350; 350a, 350b) is larger than more to a center (M) of the gap (3).

A drive belt (300) for the power transfer between two rotating pulleys (100a, 100b), in particular the drive belt (300) according to claim 1, which drive belt (300) has an elongated, endless shape and comprising: - a tension element ( 310) comprising a cable (40) which is provided in at least one winding extending in the longitudinal direction of the drive belt (300) for transferring a tensile force in the drive belt (300), - a number of supporting elements (350; 350a, 350b ), each of which is fixed with respect to the tension element (310) in the said longitudinal direction and which support the tension element (310) at the location of the two pulleys (100a, 100b), characterized in that the drive belt (300) furthermore comprises resilient member (5, 6) disposed between the support elements (350; 350a, 350b) and the tension element (310).

The drive belt (300) according to claim 6, characterized in that the support elements (350; 350a, 350b) define an opening (55) between an upper part (20) and a lower part (30), where the pulling element (310) ), and that the resilient part (5) is arranged on at least one edge of the opening (55) and preferably on both edges thereof that belong to the lower part (30) of the supporting elements (350; 350a, 350b) is applied.

The drive belt (300) according to claim 6, characterized in that the resilient member (6) is arranged on the tension element (310) and preferably completely encloses it.

The drive belt (300) according to claim 8, characterized in that the support elements (350; 350a, 350b) are arranged on the tension element (310) at a mutual distance or with an intermediate space (3), which intermediate space (3) in said longitudinal direction being either at least 1 mm or at least 10% of a dimension of the support elements (350; 350a, 350b) in that longitudinal direction, and that a layer thickness of the resilient part (6) is smaller in the middle (M ) of the gap (3) then at the location of the support elements (350; 350a, 350b).

The drive belt (300) according to any of claims 6 to 9, characterized in that the resilient member (4; 5; 6) is made of elastic material such as rubber.

The drive belt (300) according to one of the preceding claims, characterized in that the cable (40) is made up of more than one type of fiber material, in particular a combination of mainly aramid fibers and fewer polyamide fibers, and that the support elements ( 350; 350a, 350b) are attached to the cable (40) by either an adhesive provided between them or by a welding process such as ultrasonic welding.