Variable Valve Actuation Systems for Environmentally Friendly Engines

INTRODUCTION VEHICLE engines have made remarkable progress since they first appeared and the operating range of engines in terms of rpm (revolutions per minute) and torque have expanded significantly. However, optimum engine design becomes difficult if the operation timing of the engine valves is fixed. For this reason, variable valve actuation has been used to optimize the valve timing in response to the operating conditions since the 1980s. Although the technique was initially used in a limited way for applications such as simultaneously achieving both higher output and stable combustion when idling, its effectiveness has grown as fuel economy and exhaust emission regulations have tightened and it has been adopted as a means of complying with these regulations. Hitachi was ahead of its Japanese competitors in commercializing use of VTC (valve timing control) to OVERVIEW: Use of variable valve actuation in engines has become more common in recent years as an effective technique for improving fuel economy and exhaust emissions as well as engine output, and it is growing in importance as a promising technique for reducing CO2 in response to environmental problems in particular. Hitachi commercialized VTC in the mid-1980s and commenced mass production of VEL in 2007. VTC is becoming a standard feature in gasoline engines and the fuel economy benefits of VEL when used in combination with VTC have seen it adopted increasingly wider. Hitachi is working on further enhancements to variable valve actuation which has a key role as a technology for complying with fuel economy regulations.