Development of a Variable Valve Timing System for Improving the Performance of a Small Two Wheeler Engine

A novel, fully mechanical, simple, compact and cost effective variable valve timing system for two-wheeler application was developed. The details of the system and the performance are discussed. The system uses flyweights to exert a force on a cam, which floats on a shaft against a spring. The movement of the cam is axial and rotational due helical groves on the shaft. The system could start retarding the cam phasing after a predetermined speed. The system when implemented on a small scooter engine of 125 cc resulted in an increase in the volumetric efficiency at low speeds by 8%. The torque was improved by 10%. There was a reduction in the fuel consumption due to reduced throttling losses and leaner mixtures. When the system was implemented on a two-wheeler and tested on a chassis dynamometer on the Indian Driving Cycle a reduction in fuel consumption of 5% was noted. The emissions were also within limits. On the whole it is concluded that this system can be implemented on small engines for better performance.