WO2011076234A1

WO2011076234A1 - Drive belt for a transmission with convex pulley sheaves

Info

Publication number: WO2011076234A1
Application number: PCT/EP2009/009243
Authority: WO
Inventors: Lucas Hendricus Robertus Maria Prinsen
Original assignee: Robert Bosch Gmbh
Priority date: 2009-12-23
Filing date: 2009-12-23
Publication date: 2011-06-30
Also published as: CN102667233A; CN102667233B; JP5818807B2; KR20120101562A; JP2013515916A

Abstract

The invention relates to a drive belt for continuously variable transmission for motor vehicles, provided with two pulleys, each comprising two substantially conical pulley sheaves, between which the drive belt can be held at a variable radial position, which drive belt is provided with transverse elements (32), which on both lateral sides are provided with a flank (40) that is intended for frictional contact with the pulleys, in which flank (40) one or more grooves (41) of two different types are provided, whereof a first type of groove (50) is deeper than a second, more shallow type of groove (51).

Description

DRIVE BELT FOR A TRANSMISSION WITH CONVEX PULLEY

SHEAVES

The present invention relates to a drive belt, in particular intended for use in a continuously variable transmission with two variable pulleys with convex pulley sheaves, as described in the preamble of Claim 1 hereinafter. An example of a drive belt of the present type and associated transmission is described in the international patent application publication WO 2006/062400 Al . This known drive belt is characterized by, inter alia, an array of transverse elements mounted slideably on a continuous, i.e. endless tension element .

When describing the directions with respect to the transverse element, it is always assumed that the transverse element is in an upright position, such as is illustrated in figure 2 in a front view thereof. In this figure, the longitudinal or circumferential direction of the drive belt is at right angles to the plane of the figure. The lateral or width direction is from left to right and the radial or height direction is from top to bottom in the plane of figure 2.

The known transverse element comprises a bottom portion, a middle portion and a top portion. The endless tension element is -in this example- formed by two sets of a number of nested, flat and flexible, i.e. relatively thin, metal rings. Edges of the bottom portion of the transverse element, which edges face upwards in the direction of the top portion, form bearing surfaces for these ring sets. The substantially arrowhead-shaped top portion of the transverse elements is located above or radially outside the ring sets and encloses the latter in the height direction. The middle portion, which is located at the level of the ring sets, connects the bottom portion and the top portion to one another and the laterally oriented edges thereof form stop surfaces that each limit axial displacement of a respective ring set relative to the transverse element. The transverse elements are held in the drive belt such that they can move with respect to the circumferential direction of the endless tension element. In this example, one main surface of each transverse element, for example the rear surface, is provided with a recess, and the respective other main surface thereof, for example the front surface, is provided with a projection, with the projection of one transverse element in the drive belt being held in the recess of another, i.e. adjacent one. In addition, the bottom portion of the transverse elements is provided with what is known as a rocking edge, namely a generally slightly rounded transition between a topside of the transverse element of virtually constant thickness and a tapering underside. The rocking edge permits a relative rotation of adjacent transverse elements, allowing the drive belt to follow a curved trajectory in its circumferential direction, as is required at the position of the transmission pulleys.

In the known drive belt, the transverse elements fill virtually the entire circumference of the endless tension element and, at the position of the transmission pulleys, are clamped between the convexly curved sheaves thereof, so that a driving force can be transmitted between the pulleys and the drive belt with the aid of friction. As a result, a rotation of one pulley can be transmitted to the other by the transverse elements pushing each other forward in the direction of rotation, while being guided by the endless tension element.

As seen in the front view of thereof, the laterally oriented flanks or side faces of the bottom portion of the transverse element are in this case provided with a convex curvature in the height direction. These side faces are intended for frictional contact with the slightly bulging, i.e. likewise convexly curved, sheave surfaces of the pulleys, as seen in a cross-section thereof including its central axis (of rotation) . The side faces of the known transverse element include one or more grooves, which grooves are defined relative to the general or overall convexly curved contour of a respective side face. These grooves are provided for accommodating lubricant, as is applied in the present type transmission, and for realising a favourably high coefficient of friction between the drive belt and the pulleys .

Although the known drive belt inherently functions well, it was found that after prolonged operation of the drive belt in the transmission, the said side faces are disadvantageously prone to wear. As a result, the said coefficient of friction was found to gradually, but noticeably decrease during operation. In particular, such wear was found to be problematic, if it is unevenly distributed such that the convex contour of the side faces changes during operation. It was found that in an extreme case, a part of the side face may loose its initial convex contour completely. It is an object of the present invention to reduce the side face wear during operation, or least to reduce the unevenness thereof. According to the invention, this object can be achieved by applying the features of the characterising portion of Claim 1 hereinafter in the design of the known drive belt.

According to the invention, the side faces of the transverse element are, at least initially, provided with a surface profile comprising protruding parts separated by both comparatively shallow and comparatively deep grooves. The deeper grooves are provided for the purpose of accommodating the lubricant just like in the known belt, whereas the shallower grooves are provided to reduce at least the initial area of contact between the protruding parts of a side face in-between the grooves and a pulley sheave, at least relative to the known belt. As a result, a so-called running-in effect occurs during the initial operation of the transmission. Namely the protruding parts of the side faces wear off relatively quickly. By the provision of the shallow grooves, the said contact area of the protruding parts increases relatively rapidly and a contact pressure between the drive belt and the pulleys decreases in accordance therewith until the wear rate drops off to (almost) zero and a steady state, minimal wear rate is reached. During the initial, running-in wear of the (surface profiles) of the side faces of the transverse elements they form and settle naturally to provide a general side face contour that provides a favourably low and/or evenly distributed wear rate during the prolonged operation of the transmission.

The present invention is explained in more detail below by way of example with reference to the appended figures, in which: Figure 1 diagrammatically depicts a continuously variable transmission provided with two pulleys and a drive belt according to the prior art,

Figure 2 shows a tangentially oriented cross section of the transmission shown in Figure 1 at the location of a pulley sheave,

Figure 3 shows a side view of a transverse element of the drive belt according to the known art,

Figure 4 shows an enlargement of a part of the known transverse element, as seen in the direction of movement or circumferential direction of the drive belt, which part includes a side face of the transverse element provided with a surface profile comprising grooves, and in which

Figure 5 shows an enlargement of a part of the face provided with a surface profile defined accordance with the invention.

Figure 1 diagrammatically depicts a view of the central parts of a continuously variable transmission according to the prior art. The known transmission comprises a primary pulley 1 on an input shaft 6 of the transmission, which can be driven by an engine (not shown) with a primary couple (of forces) Tp and a secondary pulley 2 on an output shaft 7 of the transmission, which can drive a load (not shown) with a secondary couple Ts. Both pulleys 1, 2 are provided with a substantially conical pulley sheave 5 that is fixedly secured to the respective pulley axle 6, 7 and with a likewise substantially conical pulley sheave 4 that can be displaced in the axial direction withrespect, to the said axle 6, 7. A drive belt 3 is clamped between the pulley sheaves 4, 5 of the two pulleys 1, 2, this drive belt in each case describing a path which is substantially in the form of a segment of a circle, i.e. running radius R. A mechanical power can be transmitted between the two pulley axles 6, 7 with the aid of friction between the drive belt 3 and the pulleys 1, 2, the transmission ratio of the transmission 1 being given by the quotient of the running radius R of the drive belt 3 at the location of the primary and secondary pulleys 1 and 2, respectively.

The drive belt 3 shown here is of the so-called push belt type, which comprises an essentially continuous series of transverse elements 32, each composed of a bottom portion 33, a top portion 35 and a middle portion 34 which connects the bottom portion 33 and the top portion 35 to one another. Part of a top side of the bottom portion 33 that faces towards the top portion 35, i.e. radially outwardly oriented edges 36 of the bottom portion 33 on either side of the middle portion 34, forms a bearing surface 36 for a continuous, i.e. endless tension element 31. In this example, the endless tension element 31 is formed by two sets 31a, 31b of a number of nested, i.e. concentrically stacked, flat and relatively thin, flexible rings. Both the rings of the endless tension element 31 and the transverse elements 32 are made from metal, typically, respectively a maraging steel and a carbon steel.

The top portion 35 of the transverse elements 32 is located radially outside the endless tension element 31 and encloses the latter in the height direction, while the middle portion 34 is located between the sets of rings 31a, 31b of the endless tension element 31. The axially laterally oriented edges 37 of ^' the middle portion in this case each form a stop surface 37 in the axial direction for a set of rings 31a, 31b.

The transverse elements 32 are held in the drive belt 3 such that they can move with respect to the circumferential direction of the endless tension element 31. In this arrangement, one main surface of each transverse element, for example the rear surface 46, is provided with a recess (not shown) , and the respective other main surface thereof, for example the front surface 43, is provided with a projection 44, the projection 44 of a transverse element 32 in each case being received in the recess of an adjacent transverse element 32. The bottom portion 33 of the transverse elements 32 is provided with what is known as a rocking edge 45, namely a generally slightly rounded transition between a top side of the transverse element 32 of virtually constant thickness and an effectively tapering underside thereof, which rocking edge 45 extends in the transverse direction in the front surface 43 of the transverse element 32. The rocking edge 45 permits a rocking or rolling tilting movement between adjacent transverse elements 32, with the result that the drive belt 3, as seen in the circumferential direction, can follow a curved path between the sheaves 4, 5 of the pulleys 1, 2.

It is known from the prior art to make the conical surface of the sheaves 4, 5 of the two pulleys 1, 2 spherical or convex, as is diagrammatically depicted in Figure 2 in a tangentially oriented cross section of the transmission at the location of a pulley sheave 4, 5. In this example, the conical surface 10 of the pulley sheave 4, 5 is slightly convexly curved in the cross-sectional plane defined by the radial and axial directions, with a constant radius of curvature RrlO. The laterally oriented flanks or side faces 40 on either side of the bottom portion 33 of the transverse elements 32 are also provided with a convex curvature with radius of curvature Rr40. In practice, both these latter two radii of curvature RrlO, Rr40 are much larger than as depicted in Figure 2 (and further figures) ; they are exaggerated in the figures for the sake of clarity. Still, the said radii of curvature RrlO, Rr40 are defined such that an angle between the radial direction and the pulley sheaves 4, 5 and between the radial direction the side faces 40 varies to a significant extent, i.e. for several degrees, e.g. for about four degrees between 7.5 and 11.5 degrees. In addition, in practice, contrary to the above-mentioned constant radius of curvature RrlO, Rr40, radii of curvature that vary in the radial or height direction are also employed. In the transmission described above, a liquid lubricant is used in order to limit wear and/or damage of the sheave surfaces 10 and the side faces 40 in the frictional contract there between as far as possible. The side faces 40 of the known transverse element 32 include one or more grooves 41 that are provided for accommodating the said lubricant and, hence, for realising a favourably high coefficient of friction in the said frictional contact.

The side face 40 of the transverse element 32 is shown in more detail in Figures 3 and 4 that respectively show a side view and a front view of the transverse element 32 at the location of a side face 40 thereof. The side face 40 is shown to comprise a number of grooves 41 separated by higher lying parts 42 of the side face 40 that define the general or overall convexly curved contour thereof and that actually arrive in (direct, i.e. physical) contact with the pulley sheave surface 10 during operation.

The grooves 41 are oriented substantially in the thickness direction of the transverse element 32, i.e. in the circumferential direction of the drive belt 3, extending between the rear surface 46 and the front surface 43 thereof. The dimension of an individual groove 41 in the height or radial direction of the drive belt 3, i.e. the groove width, is preferably approximately equal to 1 to 5% of the total dimension of the side face 40 in that direction. The depth of a groove 41 is a less critical parameter and preferably amounts to between 25% and 50% of its width.

The above known surface profile of the side faces 40 could be improved upon, in particular in view of the typically application of the drive belt 3 in a transmission for passenger motor vehicles that are operated in a single transmission ratio for prolonged periods of time, which can cause a local, hence uneven and highly undesirable wear of the sides face 40.

According to the invention, the side faces 40 of the transverse element 32 are, at least initially, provided with a surface profile comprising protruding parts 52 separated by both comparatively shallow grooves 51 and comparatively deep grooves 50. This surface profile according to the invention is illustrated in figure 5 by an enlargement of a part "A" of the transverse element 32, which part "A" corresponds to the one indicated in relation to the known transverse element 32 in figure 4.

The deeper grooves 50 are provided for the purpose of accommodating the lubricant just like in the known belt, whereas the shallower grooves 51 are provided to reduce at least the initial area of contact between the protruding parts 52 of a side face 40 in-between the grooves 50, 51 and a pulley sheave 4, 5, at least relative to the known belt 3. As a result, a so-called running-in effect occurs during the initial operation of the transmission. Namely the protruding parts 52 of the side faces 40 wear off relatively quickly. By the provision of the shallow grooves 51, the contact area of the protruding parts 52 increases relatively rapidly and a contact pressure between the drive belt 3 and the pulleys 1,2 decreases in accordance therewith until the wear rate drops off to (almost) zero and a steady state, minimal wear rate is reached. During the initial, running-in wear of the (surface profiles) of the side faces 40 of the transverse elements 32 they form and settle naturally to provide an overall side face contour that provides a favourably low and/or evenly distributed wear rate during the prolonged operation of the transmission.

Preferably, the protruding parts 52 of the surface profile are provided, at least initially with a smoothly rounded, convexly curved (cross-sectional) contour. Preferably, the shallow grooves 51 and the deep grooves 50 are provided intermittedly in the side faces 40. More preferably, both the shallow grooves 51 and the deep grooves 50 extend over the entire local thickness of the transverse element 32, i.e. the dimension thereof in the circumferential direction of the drive belt 3.

Preferably, the deep grooves 50 are 5 to 25 times as deep as the shallow grooves 51, a groove depth being measured relative and perpendicular to an imaginary, continuous convex curve that touches the (relatively) protruding parts 52 of the initial contour "C" of a respective side face 40. More preferably, the depth of the deep grooves is between 25 and 250 microns. More preferably, the depth of the shallow grooves 51 is between 2 and 20 microns. More preferably, the deep grooves 50 are more than 5 times as deep as the shallow grooves 51.

Preferably, the deep grooves 50 have a width of between 25 and 100 micrometer, whereas the width of the shallow grooves 51 amounts to between 100 and 250 micrometer. More preferably, the shallow grooves 51 are more than 2 times as wide as the deep grooves 50.

Preferably, at least the shallow grooves 51, but more preferably also the deep grooves 50, are provided, at least initially, with a smoothly rounded, concavely curved contour. More preferably, the concave contour of at least the shallow grooves 51 of the surface profile smoothly merges with the convex contour of the protruding parts 52 thereof, but preferably also with that of the deep grooves 50.

Claims

1. Drive belt (3) for a continuously variable transmission for motor vehicles with two pulleys (1, 2), each pulley (1, 2) having two substantially conical pulley sheaves (4, 5) between which the drive belt (3) is held at a variable radial position (R) , which drive belt (3) comprises transverse elements (32) that are provided with side faces (40) for frictional contact with the pulleys (1, 2) , which sides faces (40) are provided with a surface profile comprising grooves (41; 50; 51), characterized in that, the surface profile comprises at least two types of grooves (50; 51) separated by protruding parts (52) of the surface profile, whereof a first type of groove (50) is deeper than a second, more shallow type of groove (51).

2. Drive belt (3) according to Claim 1, characterized in that, the side faces (40) of the transverse elements (32) are convexly curved, at least when defined by an imaginary, continuous curve that touches the protruding parts (52) of the surface profile.

3. Drive belt (3) according to Claim 1 or 2, characterized in that the shallow grooves (51) and the deep grooves (50) are intermittedly provided in the said surface profile.

4. Drive belt (3) according to Claim 1, 2 or 3, characterized in that the depth of the grooves (50; 51) is measured perpendicular and relative to an imaginary, continuous convex curve that touches the protruding parts (52) of the said surface profile.

5. ' Drive belt (3) according to Claim 4, characterised in that a depth of the shallow groove (51) amounts to 2 to 20 micrometer and/or in that a depth of the deep (50) groove amounts to 25 to 250 micrometer.

6. Drive belt (3) according to any one of the preceding claims, characterised in that a width of the deep grooves (50) amounts to 25 to 100 micrometer.

7. Drive belt (3) according to any one of the preceding claims, characterised in that a width of the shallow grooves (50) amounts to 100 to 250 micrometer.

8. Transmission provided with two pulleys (1, 2), each comprising two substantially conical pulley sheaves (4, 5), between which the drive belt (3) according to one or more of the preceding claims is held at a variable radial position (R) , characterized in that the pulley sheaves (4, 5) of the pulleys are provided with a convex curvature in their radial direction.