According to the folks at Autoblog, the first vehicles to get Eaton's SHH system are several UPS delivery trucks due to arrive next year. Eaton is already working with the Environmental Protection Agency under a Cooperative Research and Development agreement in order to “develop a series hydraulic hybrid power system that combines a high-efficiency diesel engine and a unique hydraulic propulsion system to replace the conventional drivetrain and transmission,” according to a report published on the company's official website.
Basically, the fuel economy is enhanced by three ways: braking energy, which is now recovered and reused for recharging the batteries, upgraded engine that is said to operate more efficiently and several engines modes that shut down the unit when it is not needed (during stopping or decelerating).
“The engine operates at its “sweet spot” of fuel consumption facilitated by the continuously variable transmission (CVT) functionality of the series hybrid hydraulic system and by regenerative braking,” Eaton explained the working principle of the SHH system. “The vehicle uses hydraulic pump/motors and hydraulic storage tanks to recover and store energy, similar to what is done with electric motors and batteries in hybrid electric vehicles.”