Internal-combustion engines are now all about the trade-off between power and efficiency. Until now, the tools to address that trade-off have been variable valve timing and variable valve lift, which control the mixture of air and gasoline.
Engineers at Hyundai Motor Group have added a new option for that tool kit. Continuously variable valve duration, referred to as CVVD, regulates the duration of valve opening and closing according to driving conditions.
Hyundai claims it achieves a 4 percent boost in performance, a 5 percent improvement in fuel efficiency and 12 percent reduction in emissions.
At low engine output, CVVD opens the intake valve from the middle to the end of the compression stroke for efficiency. At high output, the intake valve is closed at the beginning of the compression stroke to maximize air used for detonation, according to the automaker.
"Previous variable valve control technologies could not regulate valve duration, as the valve's closing timing was subordinate to opening timing and could not respond to diverse driving situations," the company said. "CVVD takes the technology in a new direction by adjusting how long a valve is open."
The first CVVD application comes in the 1.6-liter T-GDi Smartstream turbocharged four-cylinder engine in the 2020 Sonata sedan. But its use will increase, including its availability in the next-generation Kia Optima sedan, already on sale in Korea.