SEOUL, South Korea — Hyundai has developed a new six-speed automatic transmission to be used across its vehicle lineup that is capable of improving both fuel economy and acceleration.The transmission will debut on the redesigned V6 Azera in January. On the Azera, the new transmission improves fuel economy from 21.2 mpg to 23.8 mpg. Acceleration from zero to 60 mph drops by 0.2 seconds to 7.8 seconds, and passing acceleration also improves. Eventually, the new transmission will be used in 16 different Hyundai models.Hyundai is the fourth automaker to develop a six-speed transmission in-house, following Toyota and a joint venture between GM and Ford. Compared with the five-speed transmission it replaces, the new gearbox is 26.5 pounds lighter and has 62 fewer parts. It is also maintenance-free, with transmission fluid intended to last the life of the car.Hyundai's rear-wheel-drive Genesis uses a six-speed transmission, but that gearbox is built by ZF. The new transmission will be used in vehicles built with transverse engines.Inside Line says: Hyundai's plan to put six gears into 16 models is more confirmation that the Koreans are serious players. — Eric Tingwall, Correspondent