In today's direct fuel injected, overhead camshaft engines, valves driven by belt- or chain-driven camshafts control the amount of air flowing in, and exhaust gases flowing out, of the cylinders. Timing, lift, and duration of intake and exhaust valve opening have significant impact on engine performance, emissions, and efficiency. Today's engines use variable valve control to manage timing of the valve’s opening and closing. Until now, variable valve control techniques could not regulate valve duration, as the valve’s closing timing was subordinate to opening timing and could not respond to diverse driving situations.
Hyundai addresses this with its new Continuously Variable Valve Duration (CVVD) technology that optimizes engine performance and fuel efficiency while reducing emissions. CCVD stretches or shortens the time intake valves are open, depending on engine speed and load. When the vehicle maintains a constant speed requiring low engine output, CVVD opens the intake valves from the middle to end of the compression stroke, improving fuel efficiency by reducing the resistance caused by compression. When high engine output is needed, intake valves are closed at the beginning of the compression stroke to maximize the amount of air for combustion.
CCVD brings a 4-percent boost in performance, a 5-percent improvement in fuel efficiency, and reduces emissions by 12 percent. It works as a complement to existing variable-valve-timing systems, not as a replacement. Hyundai is currently using CVVD on intake valves, but the technology can be used on exhaust valves as well. Hyundai's Smartstream G 1.6-liter engine is the first to feature the technology.