WO2007073158A1

WO2007073158A1 - Method for forming a carrying ring of a push belt for a continuously variable transmission

Info

Publication number: WO2007073158A1
Application number: PCT/NL2006/000639
Authority: WO
Inventors: Sytze Hessel Matthes Harkema; Cornelia Adriana Elizabeth Crebolder
Original assignee: Robert Bosch Gmbh
Priority date: 2005-12-19
Filing date: 2006-12-18
Publication date: 2007-06-28
Also published as: CN101330993A; JP5580534B2; JP2009519830A; NL1030704C2; CN101330993B

Abstract

A method for manufacturing a ring (8) of a push belt of a continuously variable transmission comprises the steps of providing a strip of basic material, bending the strip to a ring (8) , and fixing the distal ends (21, 22) of the strip to each other by welding. In order to prevent irregularities at the edges of the ring (8) to be formed, welding aids (31, 32) are applied, which are placed at opposite sides of the strip. The weld (41) is initiated in one of the welding aids (31, 32) , whereas the weld (41) is terminated in another of the welding aids (31, 32) . After the welding process, the welding aids (31, 32) are detached from the ring (8) . It is possible that a number of bent strips are placed in a row and closed by welding with a single welding movement. Furthermore, it is possible that outer rings (8) of a row of rings (8) are used as welding aids, wherein only the other rings (8) of the row are applied in a push belt.

Description

Method for forming a carrying ring of a push belt for a continuously variable transmission

The invention relates to a method for forming a ring that is destined to function as carrier of transverse elements in a closed- loop push belt for a continuously variable transmission, comprising the following steps: - providing a ribbon-shaped strip of basic material;

- forming a closed ring by bending the strip, wherein distal ends of the strip are placed against each other; and

- fixing the distal ends of the strip that has been formed to a ring to each other by welding. A push belt for a continuously variable transmission is generally known. Usually, such a push belt comprises two endless closed-loop sets of rings for carrying a relatively large number of transverse elements. The rings are relatively flat and wide, i.e. the radial distance between an inner circumference and an outer circumference of the rings is relatively small with respect to the dimension in an axial direction. In the push belt, the transverse elements are continuously arranged along the entire circumference of the rings, so that, during operation, they are able to transmit forces which are related to a movement of the push belt. In a continuously variable transmission, the push belt is disposed between two cooperating pulleys. During operation, the push belt transmits a torque from one of the pulleys to the other pulley, wherein a continuously variable ratio is realized.

During operation of the continuously variable transmission, the rings of the push belt are exposed to bending and pulling forces.

The bending forces are substantially determined by the thickness of the rings and the extent to which ring portions are bent at the moments that they are present in the pulleys. The pulling forces are substantially determined by the tensile force with which the push belt is suspended between both pulleys.

As a consequence of the said bending and pulling forces, fatigue in the material of a ring will play a role in a possible failure of the push belt. Fatigue is related to the type and the quality of the used material. For example, as a consequence of irregularities in the material, haircracks may occur. Usually, the occurrence of haircracks takes place first, at places where, as a result of large curvature at the surface, large concentrations of 5 tension occur. Therefore, it is important to manufacture rings of material having a high surface quality.

Basic material having the required high surface quality may be supplied with a proper width and thickness, adapted to the transverse dimensions of the final ring. By cutting off of this

10 basic material a strip having a proper length, bending the strip to a ring, and fixing the distal ends of the strip to each other by welding, a ring is realized which is applicable in a push belt after some finishing processes such as hardening and stretching. However, during the process of fixing the distal ends to each other by

15 welding, by applying a fusion welding method, imperfections occur at the ends of the welded seam as a consequence of contractions of the material. These contractions of the material are a result of the surface tension of the molten material in the welding bath and of a possible flow that takes place in the welding bath. The result is

20 that in a direction of the width, i.e. in the axial direction, an indentation occurs in the ring, at both sides. If a ring having such indentations would be used in a push belt of a continuously variable transmission, it is easily possible for haircracks to occur during operation as a consequence of concentrations of tension at the

25 indentations, wherein breaking of the ring may be the consequence.

It is an objective of the invention to manufacture a ring of a push belt for a continuously variable transmission of a strip of basic material having a high surface quality, wherein the occurrence 30 of indentations during joining the distal ends of the strip by welding is prevented.

To this end, the invention provides a method for forming a ring, wherein, prior to welding, at the position of the abutting distal ends, at opposite sides of the strip, a run-in welding aid 35 and a run-out welding aid are placed against the strip; wherein the welding process is initiated in the run-in welding aid and is terminated in the run-out welding aid; and wherein the welded ring and the welding aids are separated from each other after welding.

As a consequence of the measures of the invention, it is '4ø ^"v prevented that indentations are forming at the edges of the ring as a result of contractions of the material during welding. Because of the fact that the welding aids are positioned against the ring to be welded, a transition of air to material of the ring is present nowhere in the welding direction. Welding is initiated somewhere in the run-in welding aid, as a result of which it will seem as if welding takes continually place in material, also at the transition of the run-in welding aid to the ring. The same is true for the transition of the ring to the run-out welding aid. The molten material in the welding bath will not be inclined to retract against the respective edges of the ring under the influence of the surface tension. As a consequence, at the position of the edges of the ring, the welded seam will look the same as in the ring. However, as a consequence of the above-described steps, the welding aids are fixed to the ring by welding. Therefore, as a last step of the method according to the invention, the welding aids are additionally separated from the ring.

Preferably, two or more strips to be welded to rings are placed between the welding aids. Of course, the above-described advantages which occur at the transition between the ring and a welding aid are also applicable to the transition between two rings. With this, in principle, an unlimited number of rings may be welded in a single welding movement.

As an alternative, the welding aids may also be formed by strips to be welded to rings as well, comprising the same basic material. By continually adding a new ring to a set of rings to be welded, it is possible to let the welding process of the rings take place in a continuous process. In that case, separating the rings, which is performed afterwards, may also take place in a continuous process . In clamping the at least one ring for the purpose of applying the weld, it is preferred when an area of the ring that is located at the inner circumference of the ring, at a position corresponding to the area where the weld is applied, is left free.

The method according to the invention is suitable for application in fusion welding methods such as (plasma) arc welding, laser welding and electron beam welding.

Preferably, the welding aids comprise the same material as the strip to be welded to a ring, because, in such a case, it is guaranteed that there is practically no transition between the welding aids and the ring, not only in a physical sense, but also in the sense of composition of material. When the welding aids are formed by a strip which is to be welded to a ring, this will surely be the case, assuming that the rings to be formed are identical.

For sake of completeness, it is noted that, at the side of the weld to be formed, a surface of the welding aids is in one plane with a surface of the ring, at least at the position of the weld to be formed, so that there is actually practically no transition between the welding aids and the ring. Preferably, a thickness dimension of the welding aids is at least equal to that of the ring to be welded. In order to realize a good connection of the welding aids to the ring, it is preferred when a side surface of the welding aids facing the ring constitutes a flat delimiting surface, which is oriented substantially perpendicular to the surface on which the weld is applied.

The invention also relates to a push belt which is provided with at least one ring that has been manufactured consistent with the method according to the invention.

Besides, the invention relates to a continuously variable transmission which is provided with the above-referred push belt.

Various aspects, features and advantages of the present invention will be further explained by the following description with reference to the drawing, in which equal reference signs indicate equal or similar components, and in which: figure 1 diagrammatically shows a side view of a continuously variable transmission having a push belt; figure 2 shows a perspective view of a strip bent to a ring, prior to welding; figure 3 diagrammatically shows a detail of a welded joint according to the state of the art; and figure 4 diagrammatically shows a welding configuration according to the invention.

Figure 1 diagrammatically shows a continuously variable transmission, such as for utilization in a motor vehicle. The continuously variable transmission is indicated in general by the reference sign 1.

The continuously variable transmission 1 comprises two pulleys 4, 5 which are arranged on separate pulley shafts 2, 3. An endless closed-loop push belt 6 is arranged around the pulleys 4, 5, and serves for transmitting torque between the pulley shafts 2, 3. Each of the pulleys 4, 5 comprises two pulley sheaves, wherein the push belt 6 is positioned and clamped between said two pulley sheaves, so that a force may be transmitted between the pulleys 4, 5 and the push belt 6 with the help of friction.

The push belt 6 comprises at least one endless carrier 7, which is usually composed of a number of rings. Along the entire length of the carrier 7, transverse elements 10 are arranged, wherein the transverse elements 10 are mutually adjacent to each other. For the sake of simplicity, only a number of these transverse elements 10 is shown in figure 1.

Figure 2 shows a strip 9 of a metal alloy, which is bent to a ring, prior to welding, wherein the distal ends 21, 22 are still free from each other. In the welding process, the distal ends 21, 22 of the strip 9 are placed against each other, after which they are fixed to each other by welding. Due to this, a closed ring 8 is realized, which, in principle, after having been subjected to some finishing processes, is applicable in a push belt 6.

In the context of manufacturing a carrier 7 for a push belt 6 for a continuously variable transmission 1, it is a usual thing when the strip is less than 1 mm thick, for example, 0.4 mm or even 0.2 mm after rolling/stretching. Preferably, the strip 9 is made of maraging steel.

Figure 3 shows a detail of a welded ring at the position of the distal ends 21, 22 interconnected by welding. A strip of metal bent round, such as shown in figure 2, has been welded to a ring by a welding process according to the state of the art, by applying a fusion welding method. Welding has taken place in the direction indicated by an arrow in figure 3. A circumference of the welded seam 23 realized due to this is indicated by dotted lines.

Figure 3 clearly shows that an indentation 24, 25 is present at both edges of the welded seam 23. Both the welded seam 23 and the indentations 24, 25 are depicted in a relatively exaggeratedly large fashion. In reality, the welded seam and the indentations are much smaller with respect to the transverse dimension of the ring.

The indentations 24, 25 have occurred during welding as a result of contraction of the material in the welding direction indicated by the arrow. This contraction is the result of the surface tension of the molten metal in the welding bath, and of a possible flow that takes place in the welding bath, and occurs at both the start and the finish of the welded joint, at the position where the ends of the welded seam is a transition of metal to air.

Figure 4 diagrammatically shows a welding configuration according to the invention. In this figure, the distal ends 21, 22 of a strip 9 of metal bent round as shown in figure 2, which are placed against each other, are depicted. A run-in welding aid 31 and a run-out welding aid 32 are placed against the ring 8 at the position of the distal ends 21, 22 placed against each other. Subsequently, the distal ends 21, 22 have been interconnected by welding, wherein the welding process has been initiated in the run- in welding aid 31, and has been terminated in the run-out welding aid 32. In figure 4, the direction in which welding has taken place is indicated by means of an arrow. The welded seam 41, which is extending as far as in both welding aids 31, 32, is indicated by a dotted line at its circumference. The welded seam 41 is depicted in a relatively exaggeratedly wide fashion. In reality, the welded seam 41 is much narrower with respect to the transverse dimension of the ring 8.

After welding, the welding aids 31, 32 and the ring 8 are separated from each other, for example by breaking off or cutting loose. The area of the ring 8 at the position of the welded seam 41 is possibly subjected to a suitable finishing process.

The method according to the invention is applicable in the field of fusion welding such as (plasma) arc welding, laser welding and electron beam welding.

The invention offers the possibility of welding several rings 8 while being arranged next to each other. To this end, a number of bent strips 9 may be placed between the welding aids 31, 32, which are abutting against each other. In the process, the rings 8 are formed with a single welding movement. After welding, the rings 8 are detached from each other.

Within the framework of the present invention, it is also possible that outer rings 8 of a row of rings 8 are applied as welding aids. In that case, it is not necessary to apply separate welding aids. In such a case, the outer rings 8 are not applicable in a push belt 6, whereas all other rings 8 are.

In the foregoing, a method for manufacturing a ring 8 of a push belt 6 of a continuously variable transmission 1 has been described. This method comprises the steps of providing a strip 9 of basic material, bending the strip 9 to a ring 8, and fixing the distal ends 21, 22 of the strip 9 to each other by welding. In order to prevent irregularities ^"at the edges of the ring 8 to be formed, a run-in welding aid 31 and a run-out welding aid 32 are applied, which are placed at opposite sides of the strip 9. The weld 41 is initiated in the run-in welding aid 31, whereas the weld 41 is terminated in the run-out welding aid 32. After the welding process, the welding aids 31, 32 are detached from the ring 8. It is possible that a number of bent strips 9 are placed in a row and closed by welding with a single welding movement. Furthermore, it is possible that outer rings 8 of a row of rings 8 are used as welding aids, wherein only the other rings 8 of the row are applied in a push belt 6.

It will be clear to a person skilled in the art that the invention is not limited to the examples of embodiments discussed in the foregoing, but that various variants and modifications are possible within the scope of protection of the invention as defined in the attached claims.

Claims

1. Method for forming a ring (8) that is destined to function as carrier (7) of transverse elements (10) in a closed-loop push belt (6) for a continuously variable transmission (1), comprising the following steps:

5 - providing a ribbon-shaped strip (9) of basic material;

- forming a closed ring (8) by bending the strip (9), wherein distal ends (21, 22) of the strip (9) are placed against each other; and

- fixing the distal ends (21, 22) of the strip (9) that has been formed to a ring to each other by welding;

10 wherein, prior to welding, at the position of the abutting distal ends (21, 22), at opposite sides of the strip (9), a run-in welding aid (31) and a run-out welding aid (32) are placed against the strip (9) ; wherein the welding process is initiated in the run-in welding aid (31) and is terminated in the run-out welding aid (32); and

15 wherein the welded ring (8) and the welding aids (31, 32) are separated from each other after welding.

2. Method according to claim 1, wherein at least two strips (9) to be welded to rings (8) are placed between the welding aids (31, 32) .

20

3. Method according to claim 1 or 2, wherein at least one of the run-in welding aid (31) and the run-out welding aid (32) is formed by a strip (9) to be welded to a ring (8) .

25 4. Method according to claim 3, wherein placing the strips (9), welding the strips (9) to rings (8), and separating the rings (8) from each other takes place in a continuous process.

5. Method according to any of claims 1-4, wherein welding takes 30 place by means of a fusion welding process such as (plasma) arc welding, laser welding or electron beam welding.

6. Method according to any of claims 1-5, wherein the welding aids (31, 32) comprise the same material as the strip (9) to be welded to

35. a ring (8) .

7. Push belt (6), comprising at least one ring (8) that has been manufactured consistent with the method according to any of claims 1-6.

8. Continuously variable transmission (1), comprising the push belt (6) according to claim 7.