A power transmission belt, and more particularly a toothed power transmission belt, comprising a longitudinally extending tensile member composed of one or more carbon fiber cords, wherein the belt exhibits belt growth of not more than 0.1 % based on its original length after 48 hours under High Temperature Belt Growth Analysis performed at 100°C, a method for producing such belts exhibiting reduced belt growth, and a method for reducing the angular vibration of a camshaft in relation to a crankshaft in an internal combustion engine wherein the camshaft is to driven by a timing belt.
Attorney Docket No. B99-031 PCT POWER TRANSMISSION BELT AND METHOD
BACKGROUND The invention relates to power transmission belts including V-belts, multi-v- ribbed belts and toothed power transmission belts, and more particularly to such belts comprising a longitudinally extending tensile member comprising one or more cords, at least one of which being formed of a carbon fiber yarn, and to a toothed belt for providing piston-to-valve synchronization in automotive internal combustion engine, and to a method for reducing the angular vibration of a camshaft in relation to a crankshaft in an internal combustion engine in which the camshaft is driven by a toothed belt..
Power transmission belts are commonly used to transmit power as between pulleys. They may be subjected to extremes in temperature and in loading during normal operation. By virtue of their composite structure, comprising both relatively low modulus cured elastomer body portions and a relatively high modulus tensile member defining the primary load carrying component of the belt, and the extremes in loading and temperature to which they may be routinely put, a high degree of durability, flexibility, and consistency are required of each of the component parts. One particular problem associated more commonly but not exclusively with the utilization of toothed belts is that of belt growth, which constitutes a permanent deformation of the belt, and can occur as a result of extended operation, extreme dynamic loading, extreme temperatures, improper component selection, or combinations of the foregoing. In particular, if the materials surrounding the tensile member are insufficiently heat resistant, operation at relatively high temperature can so embrittle those materials that they no longer effectively bond the tensile member to the surrounding belt body, leading to a drop in belt tensile strength and hence rapid belt growth. Such permanent deformation of the belt leads to improper tooth- groove interaction, tensile failure and ultimately to catastrophic failure of the tensile cord.
The introduction of carbon fiber as a reinforcement material in rubber composite articles has presented the possibility of improved performance for some applications due to its relatively high modulus compared to conventional fibers, e.g., glass cord.