In a series hybrid hydraulic system, the conventional vehicle driveline is replaced by the hybrid power system.

The conventional transmission and driveline are replaced by the hybrid hydraulic powertrain and energy is transferred from the engine to the drive wheels through fluid power.

The system is suited to a broader number of applications than parallel hydraulic hybrids, though - as with all hybrids - benefits will be highest in vehicles that operate in stop-and-go duty cycles.

Working with the Environmental Protection Agency under a Cooperative Research and Development agreement, Eaton is helping 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.

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.

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.

In a series hybrid hydraulic system, demonstrated fuel economy improvements between 50 and 70 percent is achieved in three ways::

• braking energy that normally is wasted is recovered and reused;
• the engine is operated more efficiently;
• and the engine can be shut off when not needed, such as when stopped or decelerating.