A Compact Dual CAM Variable Valve Operation System to Improve Volumetric Efficiency of Small Engines

摘要

Setting the correct valve timing and lift based on the operating speed will be the key to achieving good volumetric efficiency and torque. Continuously variable valve timing systems are the best choice but are too expensive. In this work a novel two stage variable valve actuation system was conceived and developed for a small single cylinder three wheeler spark ignition engine. The constraints were space, cost and complexity. The developed system uses one cam for low speeds and another cam that has a higher lift and duration for high speeds. The shift between the cams occurs through the mechanism even as the engine runs by the operation of a stepper motor which can be connected to the engine controller. A one dimensional simulation model validated with experimental data was used to predict the suitable valve timings and lifts in low and high speed ranges. Two profiles were then selected. The mechanism to achieve shifting between cams was conceived and modeled in standard software for verifying the kinematics. A prototype of the mechanism was made and tested on the engine under motored conditions. A stepper motor with a controller was employed to operate the mechanism. The developed system resulted in improved volumetric efficiency and smooth shifting between the cams at specified speeds without difficulty. This system can be easily integrated into the existing vehicle.