Study On New Profile High Speed Timing Roller Chain Sprocket

Roller chain drive was widely used in timing mechanism of motorcycle engine. However, because of the chordal action and the meshing impact effect, conventional roller chain drive was not suitable for high-speed transmission. It is necessary to develop a new kind of roller chain drive to improve the dynamic performance of roller chain mechanism in high speed condition. In order to reducing fluctuation of chain, improving balance of chain drive and minishing the meshing impact between chain and sprocket in high speed situation, the new tooth profile sprocket was designed and studied in this paper.First of all, theoretical analysis was carried out for the traditional roller chain drive; it was found that the main reason for the chordal action and the meshing impact of conventional roller chain drive was the irregular centrode. On this basis, a theoretical deducing model of new tooth profile sprocket was established. By preestablishing centrode of chain and sprocket, promising all the parameter of standard chain was constant and setting several hypotheses, theoretical equation of new tooth profile sprocket which could conjugate mesh with standard chain was deduced. What's more, in order to verify the dynamic performance of the new tooth profile sprocket, the multi-body dynamics model of simple chain transmission mechanism model is established, and dynamic simulation experiment is conducted.Secondly, to verify dynamic performance of the new tooth profile under real mechanism of engine, the multi-body dynamics model of double overhead camshaft timing chain transmission mechanism of engine were respectively established and simulated under various rotating speed varies 1,000r/min from 8,000r/min as using national standard GB1244-85 sprocket, German standard DIN8196 and new teeth profile sprocket. After analysing fluctuation of chain, meshing impact between sprocket and roller, the nonuniformity coefficient of driven sprocket angular velocity and the tension of chain, the new tooth profile sprocket is proved to have a better dynamic performance under high speed compared with others. Finally, the paper made a research on the serious deterioration of dynamic performance of the new tooth profile sprocket when the speed of crankshaft sprocket is 8000r/min, finding that elongation of the chain link and the input inaccuracy of the new tooth profile were responsible for the deterioration, and a method called profile optimization was proposed. With the purpose of verifying the profile optimization method, the simulation of the optimizational tooth profile sprocket timing chain transmission mechanism at high speed is proceed, also other sprockets. The simulation results show that the optimizational new tooth profile sprocket has a better dynamic performance, also, the new tooth profile equation is errorless at high speed.