WO2008080911A1

WO2008080911A1 - Drive belt

Info

Publication number: WO2008080911A1
Application number: PCT/EP2007/064527
Authority: WO
Inventors: Arjen Brandsma
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2006-12-28
Filing date: 2007-12-24
Publication date: 2008-07-10
Anticipated expiration: 2009-06-28
Also published as: CN101589246A; CN101589246B; NL1033145C2

Abstract

The invention relates to a drive belt (20) which is flexible in the circumferential direction for the transmission of mechanical power between two rotating pulleys (1, 2), which drive belt (20) is provided with a self-contained thin, flat (or ribbon-shaped) tension element (25) that is completely enclosed by a supporting element (21) of the drive belt (20) having two largely axially directed mutually radially outwardly diverging side faces (23) intended for frictional contact with the pulleys (1, 2), which the side faces (23) at the radial height of the tension element (25) and around the circumference of the supporting element (21) are provided with a recess (27) which is directed axially towards the centre of the supporting element (21).

Description

DRIVE BELT

The present invention relates to the drive belt according to the preamble of Claim 1 below. Such a drive belt is generally used for the transmission of driving power, the drive belt being passed around two or more pulleys and clamped between them. A generally known use of such a transmission is the continuously variable transmission for two-wheeled motor vehicles, such as, for example, scooters.

A continuous aim in the technological development of the known drive belt is to have a belt by means of which the transmission can transmit ever increasing power levels, or by means of which power transmission is at least constant for quite a long operational period. More particularly, such an aim amounts to achieving an increase in the tensile and/or fatigue strength of the drive belt, and also an increase in the resistance to wear of particularly the side faces or running faces of said belt, which are intended for frictional contact with the pulleys. It is also important here to limit any power loss as much as possible, not only in order to improve the efficiency of the transmission, but also in order to reduce the thermal load on the drive belt in particular, such a thermal load occurring through the development of heat as a result of friction losses. All this should preferably be achieved in such a way that air cooling will suffice, as against cooling with a recirculating liquid medium.

It is a basic object of the present invention to provide a new drive belt design which produces one or more of the technological developments described above. To that end, the invention provides three solutions for the basic principle, which are set out in the appended Claims 1, 3, and 14, and which are described in greater detail below with reference to the accompanying figures. Figure 1 shows diagrammatically a cross section of a continuously variable transmission provided with two pulleys and a drive belt according to the prior art.

Figure 2 shows a first example of the known drive belt in cross section.

Figure 3 shows a side view in cross section of a second example of the known drive belt.

Figure 4 is a diagrammatic view in cross section of a drive belt according to a first embodiment of the basic principle of the present invention.

Figure 5 is a diagrammatic view in cross section of a drive belt according to a second embodiment of the basic principle of the present invention.

Figure 6 is a diagrammatic view in cross section of a drive belt according to a third embodiment of the basic principle of the present invention.

Figure 7 is a diagrammatic view in cross section of a drive belt according to a fourth embodiment of the basic principle of the present invention.

Figure 8 is a diagrammatic view in cross section of a drive belt according to a fifth embodiment of the basic principle of the present invention.

Figure 9 shows a possible version of the drive belt according to the third, fourth or the fifth embodiment of the basic principle of the invention.

Identical or similar structural parts of the drive belt are always indicated by the same reference numerals in the figures. Figure 1 shows diagrammatically a cross section of a continuously variable transmission according to the prior art. The known transmission comprises a primary pulley 1 which can be driven by a motor (not shown) with a power torque Tp, and comprises a secondary pulley 2 which can drive a load (not shown) with power torque Ts. The two pulleys 1 and 2 are provided with a pulley sheave 5 fixed on the respective pulley shaft 6, 7, and with a pulley sheave 4 which is axially movable relative to said respective shaft 6, 7. A drive belt 20 is clamped between the pulley sheaves 4, 5, so that by means of friction mechanical power can be transmitted between the two shafts 6 and 7.

The transmission ratio Rs/Rp of the transmission is determined by the ratio between a secondary running radius Rs and a primary running radius Rp of the drive belt 20, in other words the effective radial position thereof between the pulley sheaves 4, 5 of the respective pulleys 1 and 2. The abovementioned running radii Rp and Rs, and therefore the transmission ratio Rs/Rp of the transmission defined according to the invention, can be varied by making the movable sheaves 4 move in an axial direction opposite each other along the respective pulley shaft 6, 7. In Figure 1 the transmission is shown by way of example with a low transmission ratio Rs/Rp, in other words with a relatively large primary running radius Rp and a relatively small secondary running radius Rs.

Figure 2 shows in cross section a first example of the known drive belt 20, which drive belt 20 is disclosed in, for example, European Patent specification EP-A-I 217 254. The known drive belt 20 is provided with a self-contained tension element 25, which is composed of a number of pulling cords 31 embedded in an intermediate element 33. The tension element 25 is supported by a circumferential element which is substantially V-shaped in cross section or a supporting element 21 of the drive belt 20, which supporting element is provided with two largely axially directed, mutually radially outwardly diverging side faces 23 intended for frictional contact with the pulley sheaves 4, 5, which likewise diverge radially outwards with an angle φ between them (see Figure 1) . On the outermost radial outside of the drive belt 20 said drive belt is provided with a relatively rigid covering layer 27, which covers the supporting element 21. The covering layer 27 prevents the supporting element 21 from bulging excessively in the radial direction under the influence of the clamping force exerted by the pulley sheaves 4, 5 upon the drive belt 20.

As shown in Figure 3 in a side view in cross section of a second example of the known drive belt 20 disclosed in Japanese Patent Application JP-A-2003/222197, it is also known to use discrete so-called transverse elements 40 in the drive belt 20, instead of the continuous supporting element 21. These transverse elements 40 absorb the abovementioned clamping force and provide the frictional contact with the pulley sheaves 4, 5.

In both of the abovementioned cases the forces, or force components, acting upon the supporting element 21, or the transverse elements 40, in the radial and tangential direction or circumferential direction are transmitted to the tension element 25, which is consequently subjected to a varying tensile stress. The tension element 25 is also subjected to a varying bending stress through the fact that said tension element 25 is alternately bent and stretched again during rotation thereof around and between the pulleys 1, 2 of the transmission .

The present invention provides a number of new versions of the abovementioned known drive belt types, or at any rate design aspects of said drive belt types, for which in particular the possibility of providing the drive belt 20 with great rigidity in not only its tangential or circumferential direction, but also in its axial or transverse direction was a point of departure. According to the invention, the load-bearing capacity of the drive belt 20 can be improved to a considerable extent in particular by increasing the rigidity in the abovementioned directions. This last design aspect is achieved according to the invention in all of the embodiments of the basic principle of the drive belt according to the invention to be discussed below, and at least in the tangential direction, by using a thin, flat or ribbon-shaped tension element 25 made of a rigid, strong material, preferably a metal, and more particularly an iron alloy, such as spring steel or maraging steel. In particular, if metal is used for it, the tension element 25 is preferably provided with, i.e. completely enclosed by, a corrosion-resistant covering layer, such as a metal oxide skin, a DLC

(diamond-like carbon) coating or a Teflon coating.

In a first embodiment of the drive belt 20 according to the invention, which is illustrated in Figure 4 in a side view and in a cross section (A-A) , said drive belt comprises two or more of the abovementioned ribbon- shaped tension elements 25 placed mutually concentrically, an external diameter of a radially innermost tension element 25 [a] of the two adjacent tension elements 25 corresponding to an internal diameter of a radially outermost tension element 25 [b] of said two adjacent tension elements, and an axial width dimension of the abovementioned two tension elements 25 [a], 25 [b] being adapted to each other in such a way that only the radially innermost tension element 25 [a] can come into frictional contact with the pulley sheaves 4, 5 during operation.

An advantageous aspect of this first embodiment of the drive belt 20 according to the invention is its simple structure, in which the innermost tension element 25 [a] provides the frictional contact with the pulleys and to a great extent the transmission of torque between them, and in which the outermost tension element 25 [b] advantageously increases the axial rigidity of the drive belt 20 and absorbs part of the nominal tensile stress in the drive belt 20, which last aspect advantageously benefits the rigidity of said drive belt in the tangential direction.

The tension elements 25 [a] and 25 [b] are preferably provided with a corresponding axial width. The tension elements 25 [a] and 25 [b] are also preferably connected to each other, the connection permitting at least some mutual movement in the circumferential direction. This will mean that little or no power loss will occur as a result of the friction between the individual tension elements 25 [a] and 25 [b] . The tension elements 25 [a] and 25 [b] are also preferably connected by means of an elastically deformable adhesive. This means that a tensile and/or shear load of the adhesive can advantageously be limited in the circumferential direction .

In a second embodiment of the drive belt 20 according to the invention, which is illustrated in cross section in

Figure 5, said drive belt also comprises the abovementioned ribbon-shaped tension element 25, which in this case is provided with a number of local protuberances 26 separated from each other in the circumferential direction.

An advantageous aspect of this second embodiment of the drive belt 20 according to the invention is likewise its simple structure, in which the axial rigidity of the drive belt 20 is at least partially provided, or advantageously increased, by the abovementioned protuberances 26 of the tension element 25 of said belt. The protuberances 26 preferably extend over at least virtually the total axial width dimension of the tension element 25. The protuberances 26 are also preferably provided on the tension element 25 only on the radial inside and in the axial direction centrally relative to the axial centre thereof, the axial width of the protuberances 26 being less than that of the tension element 25. In this way the tensile and/or shear load upon the tension element 25 can advantageously be limited, and at the same time it can be ensured that frictional contact between the protuberances 26 and the pulley sheaves 4, 5, which is detrimental at least in potency, is avoided. Such a shape of the protuberances 26 is shown diagrammatically in Figure 5 by means of the dashed contour of the central protuberance of the three protuberances 26 shown in the figure.

In a further development of the first or second embodiment of the drive belt 20 according to the invention at least the largely axially directed side faces of the tension element 25 are provided with a wear-proof and/or traction-increasing covering layer, preferably completely enclosing the tension element 25.

In a third embodiment of the drive belt 20 according to the invention, which is illustrated in cross section in Figure 6, said drive belt likewise comprises the abovementioned ribbon-shaped tension element 25, which in this case is embedded in, or is completely enclosed by, the abovementioned supporting element 21 provided with the side faces 23 intended for the frictional contact with the pulley sheaves 4, 5. The supporting element 21 here is provided on either side, and at the radial height of the tension element 25, with a recess 27 which is directed axially towards the tension element 25, or the centre of the supporting element 21, and preferably extends around the entire circumference of the drive belt 20, or its supporting element 21. An advantageous aspect of this third embodiment of the drive belt 20 according to the invention is again its simple structure, in which the axial rigidity of the drive belt 20 is at least partially provided by, or is advantageously increased by, the supporting element 21. At the same time, possible damage to the supporting element 21, in particular by the effect upon it of the relatively sharp edges of the thin tension element 25 under the influence of the clamping force exerted by the pulley sheaves 4, 5 ("cutting in") can be largely avoided in a particularly effective manner.

In a fourth embodiment of the drive belt 20 according to the invention, which is illustrated in cross section in Figure 7, said drive belt likewise comprises the abovementioned ribbon-shaped tension element 25, which in this case is fitted on the radial outside of the abovementioned supporting element 21 provided with the side faces 23 intended for the frictional contact with the pulley sheaves 4, 5.

An advantageous aspect of this fourth embodiment of the drive belt 20 according to the invention is again its simple structure, in which the axial rigidity of the drive belt 20 is at least partially provided by, or is advantageously increased by, the supporting element 21. At the same time possible damage to the supporting element 21, in particular by the effect upon it of the relatively sharp edges of the thin tension element 25 under the influence of the clamping force exerted by the pulley sheaves 4, 5 ("cutting in") can be largely avoided in a particularly simple manner. Furthermore, in this case the tension element 21 is subjected to an advantageously low degree of tensile bending stress, while the bending stresses in the tension element 25 consistent with a given running radius Rp, Rs of the drive belt 20 are advantageously minimized. The supporting element 21 is preferably provided on its radial inside with notches 28 extending over its axial width, which notches preferably extend in the radial direction to over half the total radial height dimension of the supporting element 21. This will limit the pushing bending stress in the supporting element 21. Such notches 28 are also shown diagrammatically in Figure 7 and can be used to the same effect and advantage in the drive belt 20 according to the third embodiment of the invention.

In a fifth embodiment of the drive belt 20 according to the invention, which is illustrated in side view in cross section in Figure 8, said drive belt likewise comprises the abovementioned ribbon-shaped tension element 25, which in this case is fitted centrally in the radial direction in the abovementioned supporting element 21, which element 21 is provided with the abovementioned notches 28 both on its radial inside and on its radial outside. The central position of the tension element 25 means that an advantageously stable frictional contact with the pulley sheaves can be achieved, while the presence of the notches 28 will ensure that both the tensile stresses and the pushing bending stresses remain limited in the supporting element 21. To this end, the notches 28 preferably extend in the radial direction almost to, but not entirely to the tension element 25. Furthermore, the axially directed recesses 27 shown in Figure 6 can also be used to the same effect and advantage in the drive belt 20 according to this fifth embodiment of the invention .

In a further development of the third, fourth or fifth embodiment of the drive belt 20 according to the invention, which is illustrated in side view in cross section in Figure 9, the drive belt 20, or at any rate its supporting element 21, is provided with a reinforcing element 29 for increasing the axial rigidity of said drive belt. The reinforcing element 29 preferably comprises a self-contained thin, flat (or ribbon-shaped) ring 29 [a] with a contour which is undulating in the circumferential direction and/or a number of preferably cylindrical transverse pins 29 [b] . The reinforcing element 29 is preferably made of a metal or a rigid plastic or plastic composite such as a reinforced polyamide, for example reinforced with glassfibre. The reinforcing element 29 preferably extends therein almost, but not completely over the full axial width dimension of the supporting element 21, so that detrimental direct contact, at least detrimental in potency, between the reinforcing element 29 and the pulley sheaves 4, 5 can be avoided. The reinforcing element 29 can be embedded in the supporting element 21 with some play, so that a tensile and/or shearing load exerted upon the supporting element 21 can advantageously be limited. The reinforcing element 29 is preferably situated radially inside the tension element 25.

In yet a further development of the third, fourth or fifth embodiment of the drive belt 20 according to the invention the supporting element 21 is made of an elastomeric plastic or plastic composite, and its abovementioned side faces 23 are preferably provided with a wear-proof and/or traction-increasing covering layer .

In yet a further development of the third, fourth or fifth embodiment of the drive belt 20 according to the invention at least one of the two substantially radially directed main sides of the tension element 25 is provided with one or more grooves, preferably substantially axially directed grooves. This will advantageously influence, i.e. reinforce, an adhesion between the tension element 25 and the supporting element 21, on the one hand through the fact that the surface available for adhesion is increased and, on the other hand through the fact that the adhesion then at least partially achieves mutual engagement or positive locking of the tension element 25 and the supporting element 21.

Claims

1. Drive belt (20) which is flexible in the circumferential direction for the transmission of mechanical power between two rotating pulleys (1, 2) which drive belt (20) is provided with a self-contained thin, flat (or ribbon-shaped) tension element (25) and with a supporting element (21) with two largely axially directed mutually radially outwardly diverging side faces (23) intended for frictional contact with the pulleys (1, 2), characterized in that the tension element (25) is completely enclosed by the supporting element (21) and in that the side faces (23) of the supporting element (21) around its circumference and at the radial height of the tension element (25) are provided with a recess (27) which is directed axially towards the centre of the supporting element (21) .

2. Drive belt (20) according to Claim 1, characterized in that in the radial direction the tension element (25) is fitted centrally in the supporting element (21) , and in that elongated notches (28) are provided in the radial inside and in the radial outside of the supporting element (21) .

3. Drive belt (20) which is flexible in the circumferential direction for the transmission of mechanical power between two rotating pulleys (1, 2), in particular according to Claim 1, which drive belt (20) is provided with a self-contained thin, flat (or ribbon-shaped) tension element (25) and with a supporting element (21) with two largely axially directed mutually radially outwardly diverging side faces (23) intended for frictional contact with the pulleys (1, 2), characterized in that the tension element (25) is fitted on the radial outside of the supporting element (21) .

4. Drive belt (20) according to Claim 1 or 3, characterized in that the supporting element (21) is provided on its radial inside with notches (28) extending over the axial width of the supporting element (21), which notches extend therein in the radial direction to over half the total radial height dimension of the supporting element (21) .

5. Drive belt (20) according to Claim 2 or 4, characterized in that the notches (28) extend in the supporting element (21) in the radial direction almost to, but not entirely to the tension element (25) .

6. Drive belt (20) according to one or more of the preceding claims, characterized in that the supporting element (21) is provided with a reinforcing element (29) which is embedded in the supporting element (21) in order to increase its axial rigidity.

7. Drive belt (20) according to Claim 6, characterized in that the reinforcing element (29) comprises at least one self-contained thin, flat (or ribbon-shaped) ring (29 [a]) which is corrugated in the circumferential direction .

8. Drive belt (20) according to Claim 7, characterized in that the reinforcing element (29) comprises at least a number of preferably cylindrical transverse pins (29[b]) .

9. Drive belt (20) according to one or more of Claims 6 - 8, characterized in that the reinforcing element (29) is made of a metal or a rigid plastic or plastic composite .

10. Drive belt (20) according to one or more of Claims 6 - 9, characterized in that the reinforcing element (29) extends therein almost, but not completely over the full axial width dimension of the supporting element (21) .

11. Drive belt (20) according to one or more of Claims 6 - 10, characterized in that the reinforcing element

(29) is embedded in the supporting element (21) with some play, so that movement is possible between them to a limited extent at least in the circumferential direction .

12. Drive belt (20) according to one or more of Claims 6 - 11, characterized in that the reinforcing element (29) is situated radially inside the tension element (25) .

13. Drive belt (20) according to one or more of Claims 6 - 12, characterized in that the supporting element (21) is made substantially of an elastomeric plastic or plastic composite.

14. Drive belt (20) which is flexible in the circumferential direction for the transmission of mechanical power between two rotating pulleys (1, 2), in particular according to one of the preceding claims, which drive belt (20) is provided with a self-contained substantially ribbon-shaped tension element (25) , characterized in that the tension element (25) is provided with a number of local protuberances (26) separated from each other in the circumferential direction.

15. Drive belt (20) according to Claim 14, characterized in that the protuberances (26) extend over at least virtually the total axial width dimension of the tension element (25) .

16. Drive belt (20) according to Claim 15, characterized in that the protuberances (26) are provided in the axial direction centrally relative to the axial centre of the tension element (25) , in that the axial dimension of the protuberances (26) is less than that of the tension element (25) , and in that the protuberances (26) are provided only on the radial inside of the tension element (25) .

17. Drive belt (20) according to one or more of the preceding claims, characterized in that the tension element (25) and/or the tension elements (25 [a] , 25 [b] ) thereof is/are at least partially embedded in a covering layer, and is/are preferably fully embedded in said covering layer, which covering layer is preferably a wear-proof and/or traction-increasing covering layer.

18. Drive belt (20) according to one or more of the preceding claims, characterized in that a radially directed main side of the tension element (25) is provided with one or more grooves, preferably substantially axially directed grooves.

19. Drive belt (20) according to one or more of the preceding claims, characterized in that the tension element (25) is made of a metal, preferably an iron alloy such as spring steel or maraging steel.

20. Drive belt (20) according to Claim 19, characterized in that the tension element (25) is provided with a corrosion-resistant covering layer, such as a metal oxide skin, a DLC (diamond-like carbon) coating or a Teflon coating.