WO2015101657A1

WO2015101657A1 - Drive belt equipped with an endless tension member and manufacturing method for it

Info

Publication number: WO2015101657A1
Application number: PCT/EP2015/050001
Authority: WO
Original assignee: Robert Bosch Gmbh
Priority date: 2014-01-02
Filing date: 2015-01-02
Publication date: 2015-07-09
Also published as: NL1040586C2; CN105874240B; CN105874240A

Abstract

The invention relates to an endless tension member (301) for a drive belt (300) for transmitting power between two rotating pulleys of a power transmission, the drive belt (300) having an endless elongated shape and comprising the endless tension member (301) for transmitting a tensile force along the drive belt (300) and a number of support elements (302) for supporting the tension member (301) on the pulleys, each support element (302) being fixed to the tension member (301) in the longitudinal direction of the drive belt. The tension member (301) includes a tension cord (302) and a carrier means (305) that encases the tension cord (302), at least in part, which carrier means (305) is made from a cured, liquid silicone rubber.

Description

DRIVE BELT EQUIPPED WITH AN ENDLESS TENSION MEMBER AND MANUFACTURING METHOD FOR IT

The present disclosure relates to a drive belt with an endless, i.e. largely ring- shaped, tension member according to the preamble to the claim 1 hereinafter. Such a drive belt and tension member for it is known from its application in drive belts that are used to transfer a drive power in a transmission wherein the drive belt is passed around two or more rotatable pulleys. Each pulley is provided with two conical discs facing one another thus defining a tapered groove wherein the drive belt is held in a tensioned state, such that the pulley can exert a driving force on the drive belt or vice versa by means of the friction there between. As a result, a rotation of a driving pulley of the transmission pulls the drive belt away from another, i.e. driven pulley of the transmission that is thereby brought into rotation.

A commonly known application of such a transmission is the so-called continuously variable transmission of 2-wheeled motor vehicles, such as scooters. In the continuously variable transmission the pulleys are adjustable in the sense that a separation between the conical discs thereof is variable, whereby a running radius of the drive belt on such pulley can be varied.

The present type of tension member and the drive belt incorporating it are described in detail in the International patent publication WO-A-2008/094035.

The known drive belt comprises a series of discrete support elements that are each individually fixed to the tension member thereof, typically by means of mutually interlocking parts. The support elements are provided with two main faces that are, at least predominantly, oriented in the forward and backward circumference directions of the drive belt and with two side faces that are placed at an acute angle relative to one another, each extending on a lateral side of the support element between the main faces thereof, and that serve to frictionally engage the transmission pulleys. The support elements further define an opening that, between all of the support elements of the drive belt, forms a continuous channel along the circumference of the drive belt, wherein the tension member is contained.

The known tension member is typically composed of a spirally-wound tension cord that is made of a stiff and tensile stress resistant material, such as a metal or a synthetic, typically fiber-reinforced material, and of a carrier means, wherein the tension cord is embedded and that is made of a hard, but still somewhat flexible synthetic rubber such as Hydrogenated Nitrile Butadiene Rubber (HNBR). The carrier means provides that the tension cord cannot be sharply bend ("kinked") and that the tension cord does not arrive in direct physical contact with the support elements. The known carrier means is provided with recesses and/or protrusions along its outer and/or the inner circumference, which recesses and/or protrusions interlock with relevant part(s) of the support elements at least in the circumference direction of the drive belt.

In order to achieve the highest torque transmitting capacity of the known drive belt, i.e. in order to maximally utilize the tension strength provided by the traction cord thereof, the carrier means thereof is made of relatively tough material such as HBNR containing reinforcing fibers. This latter material is able to cope with the forces that are exerted between the transverse segments and the tension cord during operation of the drive belt. This known drive belt design functions quite well in practice, but according to the present disclosure it does suffer from the disadvantage that the carrier means is not only strong and tough, but is also relatively stiff and difficult to bend in its circumference direction. Thus, during operation of the drive belt, the known carrier means is subjected to considerable bending stresses that typically cause the ultimate failure thereof, i.e. that determine the service life of the drive belt.

The performance of the known drive belt, in particular in terms of the longevity thereof, can thus, in principle, be improved by making the carrier means from a more flexible material and thus reducing the said bending stresses. However, in the art, such latter, more flexible materials generally lack the strength and toughness that is required for the drive belt application and these materials are thus rejected from being used for the manufacture of drive belts.

The present disclosure aims to provide an alternative to the conventionally applied endless tension member in terms of the material of the carrier means thereof. The drive belt according to the present disclosure is described in claim 1 hereinafter.

According to the present disclosure, the carrier means is made of a Liquid Silicone Rubber (LSR). Although LSR is widely used in industry in general, it has not previously been discussed or suggested as a basic material in or for the present drive belt application. In particular, LSR is mostly known for its chemical and temperature stability, whereas the present drive belt is neither subjected to corrosive chemicals nor to temperature extremes. Instead, the presently considered drive belt application of LSR relies on the inherent flexibility thereof that, surprisingly, was found to be accompanied by a material strength and toughness sufficient for such application as well. Additionally, in order to dampen or prevent torsion oscillations of the above drive belt design that can occur if the so-called shaft or center distance between the transmission pulleys large and/or in response to torque spikes originating from the engine or the load that are connected to the input and output side of the transmission respectively, the present disclosure teaches to mutually interconnected the tension cord windings thus forming an endless tension band. The stiffness of such tension band is remarkably higher than that of the conventional tension cord with a number of axially separate, i.e. loose, spiral windings, at least in the axial direction relative to the tension band, i.e. transversely to its circumference. As a result, the transverse stiffness of the tension member is increased and the said torsion oscillations of the drive belt are effectively and favorably suppressed.

In a more detailed embodiment of the drive belt according to the present disclosure, the individual tension cord windings of the tension band are interconnected by means of an adhesive, preferably an adhesive that hardens or cures. In this latter respect, in particular an epoxy resin is well-suited for coating the tension cord windings of the tension band. Epoxy (resin) is well known from many applications to form a chemically stable, strong and stiff matrix after curing. Additionally and in relation to the generally preferred type of tension cord that is made of interwoven aramid fibers, in particular epoxy resin was found to favorably bond with the aramid fibers and thus to (additionally) stiffen the tension cord and the tension band in the said transverse direction.

The present disclosure also concerns a method for providing a tension band for a drive belt, which method includes the process steps of:

- providing a tension cord, preferably a tension cord made of (interwoven) aramid fibers;

- immersing the tension cord in an epoxy resin bath to at least partly coat the tension cord with epoxy;

- winding the tension cord onto a cylindrical mandrel to from several, side-by-side lying tension cord windings; and

- applying a layer of epoxy resin to the radial outside of the tension cord windings.

Preferably, these process steps are carried out in the order that they are listed. Preferably also, the final process step of applying a layer of epoxy resin to the radial outside of the tension cord windings is carried out before the epoxy resin coating of the tension cord has cured. Furthermore, the layer of epoxy resin is preferably applied to the radial outside of the tension cord windings with force, for example by being sprayed from a nozzle.

Further, by using LSR the endless tension member can be favorably and easily manufactured by means of an injection molding process. In particular the endless tension member is formed by placing a spirally wound tension cord centrally in a mold cavity that is provided with the shape of the carrier means. LSR is injected into the mold cavity, filling the space between the tension cord and the walls of the mold cavity. Once injected into the mold cavity the LSR is cured, i.e. hardened, by forming chemical bonds between individual LSR polymers (or polysiloxanes), which process can be accelerated by heating the mold.

In a more detailed alternative embodiment of the above manufacturing process of the endless tension member, the injection molding of the carrier means takes place in two stages. In a first stage of the injection molding of the carrier means, the tension cord is wound around a cylindrical core part of an injection mold and a second mold part is placed around such core part, which second mold part is shaped to define a mold cavity that corresponds with a radially outer part of the carrier means. LSR is injected into this mold cavity and is cured. Thereafter, in a second stage of the injection molding of the carrier means, the core part of the mold is removed from radially inside the tension cord, whereof at least the radial outside surface is now encased by the radially outer part of the carrier means and is replaced by a third mold part that is shaped to define a further mold cavity that corresponds with a remaining, i.e. radially inner part of the carrier means. LSR is injected into this further mold cavity and is cured to complete the manufacturing process of the endless tension member.

It is noted that the tension cord need not necessarily be positioned exactly halfway a radial extent of the tension member. Instead, the optimum position of the tension cord relative to such radial extent will normally depend on the design of the carrier means, in particular of the said recesses and/or protrusions thereof, and/or on the specific LSR type or composition used, in particular in relation to its ability to cope with compression and with tension respectively. For instance, by positioning the tension cord in the radially outer half of the tension member, the carrier means will be loaded more by compression than by tension. Generally speaking, the carrier means made from LSR can cope better with compressive forces than with tensile forces. Furthermore, it is noted that in the latter embodiment of the manufacturing process including two injection molding stages, it is even favorably possible to use a different specific LSR composition for/in each such stage. Preferably the tension cord is made, at least predominantly, from Aramid fibers, which material provides the required tension strength and bonds well with the carrier means made from LSR. Some carbon fiber content may be added to further enhance such bonding.

The above-described basic features of the present disclosure will now be elucidated by way of example with reference to the accompanying figures.

Figure 1 represents a schematic side view of a drive belt of known design, whereto the present disclosure pertains.

Figure 2 schematically shows a first cross section of the drive belt of figure 1 . Figure 3 schematically shows a second cross section of the drive belt of figure

1 .

Figure 4 schematically shows a second, known drive belt design.

Figure 5 schematically shows a first embodiment of the drive belt design according to the present disclosure in a cross section corresponding to that of figure 2.

Figure 6 schematically illustrates a second embodiment of the drive belt according to the present disclosure.

In the figures, the same or similar structural parts of the drive belt are respectively indicated with the same reference numerals.

Figures 1 , 2 and 3 show the known drive belt 300, wherein figure 1 represents a side view thereof, figure 2 the cross section A-A thereof facing in the circumference direction of the drive belt 300, and figure 3 the cross section B-B thereof facing in the axial direction of the drive belt 300, i.e. widthwise. The known drive belt 300 is provided with two endless tension members 301 that each comprise a tension cord 302 and a carrier means 305 with the tension cord 302 having a predominantly circular cross-section and being embedded in a carrier means 305 in a spiral shape. The tension cord 302 thus extends several times the circumference length of the tension member 301 . In addition, the known drive belt 300 comprises a series or row of so-called support elements 303 that are placed along the circumference of the tension members 301 at regular intervals and that are connected to the tension members 301 at least in the circumference direction thereof through mutually interlocking parts 307 of the tension members 301 and the support elements 303.

Each support element 303 includes two side faces 304a; 304b that are placed at an acute angle to each other and that are intended for the frictional contact with pulleys of the transmission wherein the drive belt 300 is to be applied. The support elements 303 further describe two openings, through which the tension members 301 are led.

The support elements 30 are coupled to the tension members 301 in the circumference direction of the drive belt 300, so that considerable forces can be transferred there between for the benefit of the torque transfer between the transmission pulleys during operation. In figure 3, it can be seen that, in the presently illustrated example of the known drive belt 300, such coupling is achieved by a radially outwardly directed bulge or ridge 307 of the tension member 301 that engages with a recess or groove in the support element 303.

The support elements 303 of figures 1 and 3 are shaped with a tapered bottom part 308 located to the radial inside of the tension members 301 , which allows the tension members 301 and hence the drive belt 300 to curve along in its circumference. Alternatively to this latter end, it is known to provide a free space between the successive support elements 303 on the tension member 301 , as is indicated in figure 4 in an alternative embodiment of the known drive belt 300 that is provided with a single, axially centered endless tension member 301 . In this particular embodiment, the tension member 301 of the drive belt 300 is alternately provided with axially extending ridges 307 and grooves 306, with the support elements 303 being fitted at the location of the grooves 306 and thus being mutually separated by the ridges 307 that thus also serve to couple the support elements 303 to the tension member 301 in its circumference direction.

The support elements 303 of the known drive belts 300 are made of a rigid and, preferably, wear-resistant plastics, such as fiber-reinforced nylon. The tension cord 302 of the tension member 301 thereof is made from synthetic fibers that are both stiff and strong, such as Aramid fibers, which fibers are woven together to form a continuous cord that is impregnated with resin to protect the fibers and to prevent an unweaving thereof. The carrier means 305 of the tension member 301 of the known drive belts 300 is made of a tough, but still somewhat flexible material, such as an elastomere (rubber).

According to the present disclosure, the carrier means 305 of the tension member 301 is made of a Liquid Silicone Rubber (LSR) by using an injection molding process with a mold wherein the tension cord 302 is pre-positioned. After the said injection molding the Liquid Silicone Rubber (LSR) of the carrier means 305 is solidified by curing. Thereafter the tension member 301 is taken from the mold and the support elements 303 are mounted thereon to form the drive belt 300. As shown in figure 5 in a front elevation of one such support element 303, it is provided in two parts 303a, 300b, where between an opening is defined for accommodating a small section of the tension member 301 . By the two separate parts of the support element 303, the opening is closed by fitting the second part of the support element 303a; 303b only after a first part thereof 303a; 303b has been mounted on the tension member 301 . Then, finally, the two parts 300a; 300b of the support element 300 are glued or welded together to form the drive belt 300, preferably by means of an ultrasonic welding process. By initially providing the support elements 303 in two separate parts 303a; 303b, these parts 303a; 303b can be formed favorably by injection molding, i.e. separately from the tension member 301 and thus avoiding a deterioration of the carrier means 305 material (LSR) by the heat required for the injection molding of the support elements 303.

It is noted that the carrier means 305 of the tension member 301 can be formed in two stages, wherein in one stage of such forming process a radially outer part 305a of the carrier means 305 is formed and in another stage thereof a radially inner part 305b of the carrier means 305 is formed. This latter forming process favorably allows the use of a different LSR composition for each respective part 305a and 305b of the carrier means 305.

In figure 6 a second novel embodiment of the drive belt 300 in accordance with the present disclosure in a cross section thereof facing in the circumference direction of the drive belt 300. In this second embodiment, the tension cord 302 is provided in multiple windings that are mutually interconnected by being embedded in a cured epoxy layer 306. By the epoxy layer 306, that is first applied to the windings of the tension cord 302 in resin form, the windings of the tension cord 302 stick together, such that an integral part is formed in the form of an endless tension band 307. In particular in its axial direction, the tension band 307 is thus provided with a considerable stiffness, such that the axial stiffness of the tension member 301 is increased considerably relative to the tension member 301 of the known drive belt 300, wherein the windings of the tension cord 302 are individually embedded directly in the relatively flexible material of the carrier means 305. As a result, during operation in the transmission, the novel drive belt 300 is considerably less prone to torsion oscillations.

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

Claims

1 . Drive belt (300) for transmitting power between two rotating pulleys of a power transmission, the drive belt (300) having an endless elongated shape and comprising an endless tension member (301 ) for transmitting a tensile force along the drive belt

(300) and a number of support elements (302) for supporting the tension member

(301 ) on the pulleys, each support element (302) being fixed to the tension member

(301 ) in the longitudinal direction of the drive belt, the tension member (301 ) includes a tension cord (302) and a carrier means (305) that encases the tension cord (302), at least in part, characterized in that, the carrier means (305) is made from a cured, liquid silicone rubber.

2. The drive belt (300) according to claim 1 , characterized in that, the carrier means (305) thereof is made from two liquid silicone rubber compositions.

3. The drive belt (300) according to claim 2, characterized in that, the carrier means (305) thereof includes a radially outer part (305a) made from a first liquid silicone rubber composition and a radially inner part (305b) made from a second liquid silicone rubber composition different from the said first one.

4. The drive belt (300) according to claim 3, characterized in that, the tension cord

(302) thereof is located between such radially outer part (305a) and such radially inner part (305b) of the carrier means (305).

5. The drive belt (300) according to any one of the claims 1 to 4, characterized in that, the tension cord (302) thereof is off-centre relative to a radial extent of the carrier means (305) and is located more towards the radial outside of the carrier means (305) then towards the radial inside thereof..

6. The drive belt (300) according to a preceding claim, characterized in that, the tension cord (302) is spirally wound in a number of windings that are mutually interconnected forming an endless tension band (307) that is encased, at least in part, by the carrier means (305) of the tension member (301 ).

7. The drive belt (300) according to claim 6, characterized in that, the windings of tension cord (302) are mutually interconnected by means of a hardened adhesive.

8. The drive belt (300) according to claim 6 or 7, characterized in that, the windings of tension cord (302) are embedded, at least in part, in an epoxy layer (306).

9. The drive belt (300) according to a preceding claim, characterized in that, the tension cord (302) is made of interwoven aramid fibers with an epoxy coating.

10. Drive belt (300) according to a preceding claim, characterized in that, the support element (303) includes two parts (303a, 300b), between which parts (303a, 300b) of the support element (303) defines an opening for accommodating the tension member (301 ).

1 1 . Drive belt (300) according to claim 10, characterized in that, one such part (303a) of the support element (303) is generally U-shaped, in that the tension member (301 ) is fitted in an opening defined by such generally U-shaped part (303a) and in that the other one part (303b) of the support element (303) is likewise fitted in the opening defined by such generally U-shaped part (303a).

12. Method for manufacturing an endless tension member (301 ) for a drive belt (300) for transmitting power between two rotating pulleys of a power transmission, which endless tension member (301 ) includes a tension cord (302) provided in a number of side-by-side lying windings thereof and a carrier means (305), wherein the spirally wound tension cord (302) is contained, at least in part, wherein:

- a tension cord (302) is provided, preferably a tension cord made of aramid fibers;

- the tension cord (302) is wound onto a cylindrical mandrel to from several, side-by- side lying tension cord windings;

- a layer of epoxy resin (306) is applied at least to the radial outside of the windings of the tension cord (302);

- the epoxy resin layer (306) is allowed to cure forming an endless tension band (307); and

- the endless tension band (307) is encased in a synthetic rubber, preferably by means of injection molding using a mold defining a cavity containing the tension cord (302), to finally form the endless tension member (301 ).

13. The method for manufacturing the endless tension member (301 ) according to claim 12, wherein the tension cord (302) is first immersed in an epoxy resin bath to at least partly coat the tension cord with epoxy.

14. The method for manufacturing the endless tension member (301 ) according to claim 12, wherein the layer of epoxy resin is applied to the tension cord (302) with force, preferably by being sprayed from a nozzle.

15. The method for manufacturing the endless tension member (301 ) according to claim 12, 13 or 14, wherein prior to the said process step of liquid silicone rubber injection, the tension cord (302) is wound around a cylindrical core part of the mold and a second mold part is placed around such core part, which second mold part is shaped to define a mold cavity that corresponds with a radially outer part (305a) of the carrier means (305), wherein, in the said process step of liquid silicone rubber injection, liquid silicone rubber is injected into the said mold cavity, wherein the said core part of the mold is removed from radially inside the tension cord (302) and is replaced by a third mold part, which third mold part is shaped to define a further mold cavity that corresponds with a radially inner part (305b) of the carrier means (305), and wherein liquid silicone rubber is injected into the said further mold cavity.