The powertrain in the new Hyundai Sonata Hybrid is significantly different from those in other hybrids. One result is class-leading highway fuel economy.
The Sonata Hybrid can go up to 75 mph propelled by its electric motor. This velocity far surpasses the top speeds in electric-vehicle mode of competitive hybrids, including the Ford Fusion Hybrid and Nissan Altima Hybrid, and cuts the Sonata's fuel consumption. The EPA rates the Sonata's highway fuel economy at 40 mpg.
Better aerodynamics help boost fuel economy: Shutters behind the grille close at highway speeds and the car's underbody is sculpted to reduce drag. But the new Sonata's fuel economy is mainly because of its innovative powertrain.
The challenge, says Mark Guin, Hyundai senior development engineer at the Hyundai-Kia America Technical Center in Chino, Calif., was to "come up with our own hybrid system while working around existing patents."
Says Guin: "We believe that the solution we came up with is elegantly simple."
Hyundai's solution replaces a typical hybrid's transmission-motor assembly with a standard automatic transaxle modified to work with what Hyundai calls a transmission-mounted electrical device. The TMED includes two main parts: a powerful electric drive motor and a solenoid-activated clutch pack. These parts fit in about the same space as a traditional torque converter.
"The fine control we can exert over the wet clutch pack makes it possible for us to use a conventional automatic transmission without a torque converter," a notorious energy drain, Guin says.
"The TMED enables our 40 mpg highway mileage and high-speed EV operation. Because the torque from the motor runs through all of the transmission's six gears, we can keep the motor running at its optimal rpm," Guin says. Electric motors are more efficient running at lower speeds.
The clutching system enables the gearbox to receive power from the 30-kilowatt (40.8-hp) electric motor, the 166-hp 2.4-liter Atkinson cycle four-cylinder gasoline engine, or both.