A Review of Variable Valve Timing Benefits and Modes of Operation

An Electromechanical Valve Drive Incorporating a Nonlinear Mechanical Transformer

“…It has been reported that a net fuel efficiency gain (gas mileage) of up to 15% over a typical driving cycle was achieved over a conventional valvetrain system [3]. Fuel efficiency can also be improved by variable engine displacement.…”

“…If the valve open-duration and overlap can be optimized as a function of engine speed, pumping losses are minimized, and volumetric efficiency is improved [3]. It has been reported that a net fuel efficiency gain (gas mileage) of up to 15% over a typical driving cycle was achieved over a conventional valvetrain system [3].…”

“…With half the cylinders disabled, fuel efficiency is improved by 25% at low speed cruise and 40% at idle speed [2], [3]. Unequal lifts of paired valves can provide a variety of incylinder charge swirls and improve fuel efficiency by up to 30/0 in addition to better combustion stability, improved idle quality and lower emissions [2].…”

“…Timing and lift are a compromise among fuel efficiency, performance, and emission. On the other hand, we can improve fuel efficiency by 15-20% or more over a driving cycle, torque by 5-13% or more, depending on engine speeds, and t~missions significantly with a fully flexible variable valve actuation system that can adjust phase, duration and lift independently and flexibly [1], [2], [3]. The greater the flexibility which can be incorporated in the valvetrain, the greater the benefits that can be achieved.…”

“…In internal combustion engines, variable valve actuation (VVA) systems offer a flexible valve profile and may significantly improve fuel efficiency, engine performance, and emissions cOlmpared with conventional, fixed profile valvetrains [1], [2], [3]. One of the most advanced VVA systems is the electromechanical valve drive (EMVD), an electrically actuated, camless VVA which can flexibly control the duration, phase, and lift of a valve profile.…”