DRIVE ASSEMBLY FOR A TWO-WHEELED VEHICLE

Abstract

A drive assembly for a two-wheeled vehicle, wherein a closed chain is guided around a drive pinion and a sprocket for output. The chain is formed by pins, on each a bush rotatable about the center longitudinal axis of the pin, a roller provided on each bushing, for rotation around the bushing and has play, and the pins being connected to each other at two opposite ends by means of plates. The outer surface of the bushings and the rollers is coated with pure ta-C, having no further chemical elements except for unavoidable trace elements resulting from production in a PVD method. An R.sub.a roughness between 0.03 m and 0.2 m and/or an R.sub.z roughness between 0.3 m and 2 m is adhered to the surface of the coatings. The surfaces of the pinion and the sprocket in contact with the rollers do not have a coating of diamond-like carbon.

Claims

1. A drive assembly for a two-wheeled vehicle, in which a closed chain is guided around a drive pinion and a sprocket for the output and the chain is formed by pins, on each of which there is arranged a bushing which is rotatable about the center longitudinal axis of the pin, and a roller is provided on each bushing, which roller is arranged for rotation around the bushing and has play, the pins are connected to each other at two opposite end faces by means of plates; wherein the outer surface of each of the bushings and of each of the rollers is coated with a coating of pure ta-C and there are no further chemical elements in the coatings except for trace elements which are unavoidable in a PVD method, by means of which the coatings have been formed; an R.sub.a roughness of between 0.03 m and 0.2 m and/or an R.sub.z roughness of between 0.3 m and 2 m is maintained at the surface of the coatings; and the surfaces of the pinion and of the sprocket that are in contact with the rollers of the chain do not have a coating of diamond-like carbon.

2. The drive assembly as claimed in claim 1, wherein an R.sub.a roughness of between 0.05 m and 0.15 m and/or an R.sub.z roughness of between 0.5 m and 1.5 m is maintained at the surface of the coatings.

3. The drive assembly as claimed in claim 1, wherein the layer thickness of the ta-C coating on the outer surfaces of the bushings is greater than that on the outer surfaces of the rollers.

4. The drive assembly as claimed in claim 1, wherein the layer thickness of the ta-C coating on the outer surfaces of bushings is at least twice as great as that on the outer surfaces of the rollers.

5. The drive assembly as claimed in claim 1, wherein a gasket is arranged between the face ends of the bushings and the plates engaged on the pins respectively, which gasket is pushed onto the respective pin, and the gaskets are provided with a friction-reducing external coating or are formed of a friction-reducing material.

6. The drive assembly as claimed in claim 1, wherein a friction-reducing coating or a friction-reducing material is PTFE.

7. The drive assembly as claimed in claim 1, wherein in that a solid lubricant is contained between the outer surfaces of the pins, the inner surfaces of the bushings and the gaskets.

8. The drive assembly as claimed in claim 1, wherein the surfaces of the plates are provided with a coating that protects against corrosion and wear, or the material of the plates is modified in that manner in the region close to the surface, wherein a coating is not formed with diamond-like carbon.

9. The drive assembly as claimed in claim 1, wherein a surface of a coating that protects against corrosion and wear is modified with nitrogen, boron or phosphorus, or the coating that protects against corrosion and wear is formed by a nitride or phosphate compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0037] The invention will be described in greater detail hereinbelow.

[0038] The chain belonging to the drive assembly is substantially a conventional chain, as is usual for use on two-wheeled vehicles. This applies both to the form and dimensioning of the individual elements forming the chain, and to the materials of which those elements are formed. Thus, pins, bushings, rollers and plates are usually made of a steel. The surfaces of the pins, bushings and rollers have been mechanically processed and thereby smoothed.

[0039] In the invention, conventional pinions and sprockets are also used for the input and output.

[0040] The bushings and rollers which can be used in the invention form a type of semi-finished product and are supplied as bulk goods in the roughly cleaned and slightly greased state. Prior to the formation of the ta-C coatings, the working operations of degreasing, ultrasound-assisted wet cleaning in an alkaline bath and rinsing in deionized water, immediately followed by drying in a hot-air oven, are carried out.

[0041] For incorporation into a PVD coating installation, the rollers and bushings are received on rods, wherein the number of rollers or bushings is governed by the maximum coating height of the installation. The rods with the rollers or bushings stacked thereon are installed in a position on a holder of a rotating cage of the coating installation, so that they are in triple rotation during coating.

[0042] Coating in the PVD installation begins, after pumping down to a sufficiently low starting pressure in the high vacuum range, with plasma etching, in which surface contamination, covering and oxide layers on the surfaces of the bushings and rollers are removed with argon ions. This process is followed by the deposition of a metallic adhesion promoter layer, generally chromium. This layer is applied by means of a vacuum arc or sputtering process. The layer thickness is to be approximately 0.2 m. Finally, in the next step, a ta-C coating is applied by means of vacuum arc vaporization of graphite. The vacuum arc vaporization technique can be a simple electric direct current arc technique or a pulsed electric arc technique. The latter can preferably be used via a laser-ignited electric arc technique (laser arc method) for forming the ta-C coatings on the outer surfaces of the bushings and rollers.

[0043] The layer thickness of the ta-C coatings is to be maintained between 0.5 m and 10 m, preferably 2.5 m on the rollers and 5 m on the bushings. The coatings are in each case homogeneous ta-C layers which are to have a hardness of preferably 50 GPa-70 GPa.

[0044] After coating, mechanical smoothing of the parts coated with ta-C is preferably carried out in order to reduce the roughness of the ta-C layer resulting from the process. Tumble smoothing can preferably be carried out for this purpose.

[0045] The bushings and/or rollers provided with a ta-C coating are thereby introduced, alone or together with tools provided with corresponding ta-C layers, into a barrel which is preferably configured with carriers on a barrel wall. The closed barrel is then rotated about its horizontal longitudinal axis. A temperature of 20 C. is thereby maintained, and a pressure of 0.5 N/mm.sup.2 is used.

[0046] The rotation of the barrel results in a tumbling movement of the amount of bushings and/or rollers in the form of loose bulk products, and optionally of the tools, in the barrel and thus in relative movements of the bushings and/or rollers with the tools optionally contained in the barrel at the surfaces provided with the ta-C coating. This leads to a mutual removal of roughness peaks on the surfaces of the ta-C coatings. After a sufficiently long time of about 15 minutes, the rotation is ended and the barrel is opened. The provided on the with the ta-C coatings and optionally the tools can then be removed from the barrel. The outer surfaces of the bushings and rollers so processed have a significantly reduced roughness R.sub.z of 0.5 m. It was possible to achieve an R.sub.a roughness of 0.05 m. Any wear debris that has formed can be removed by rinsing with a suitable solution, for example an aqueous medium as cleaning medium. This rinsing can be carried out both during the surface processing in the barrel and as a separate process step after completion of the surface processing and removal of the bushings and/or rollers from the barrel.

[0047] Smoothing can also be carried out by means of an oscillating linear movement or a random movement without a given pattern.

[0048] The ta-C coatings can have depressions or elevations which are formed by hard carbon particles which are formed during the formation of the ta-C coatings by means of the vacuum arc method. The hard carbon particles can be broken out of the ta-C coating during smoothing, and a depression remains there as a defect. The depression(s) have on average a width of 1 m.

[0049] The method of surface smoothing can be carried out without the addition of auxiliary substances, but an iron powder may also be introduced into the drum and/or applied to an outer surface of the ta-C coatings in order to assist with smoothing by a chemical-catalytic action of the iron.

[0050] A nickel phosphate layer on surfaces of plates can be formed as described below:

[0051] In the method for producing a metal coating by electroless deposition, the plates of a chain that are to be coated are immersed in an aqueous electrolyte which contains nickel cations and phosphinate ions. The proportion of nickel cations in the electrolyte can be kept between 79% by mass and 97% by mass and the proportion of phosphinate ions in the electrolyte can be kept between 2% by mass and 15% by mass. Small proportions of antimony and bismuth ions may also be present.

[0052] The nickel ions are thereby reduced to pure nickel. With hypophosphite ions, which are reduced in the process to orthophosphate, a coating formed by a nickel-phosphorus alloy can form on the surface of the plates. The production of such coatings is known per se and is offered commercially as durnicoating under the name Durni-Coat by AHC-Oberflchentechnik GmbH & Co. OHG, based in Kerpen DE.