|A series hydraulic hybrid. A pump/motor provides torque to the driveshaft. Source:NextEnergy|
The US Environmental Protection Agency and the University of Toledo have announced a three-year cooperative agreement worth about $1 million to improve and to optimize hydraulic hybrid vehicle components to maximize fuel economy benefits and minimize emissions. EPA will contribute up to $450,000 toward the agreement.
A hydraulic hybrid system uses an accumulator (which stores energy as highly compressed gas) and one or more hydraulic pump/motors rather than the battery pack, electric generator/motor and power electronics used in electric hybrids.
During acceleration, fluid in the high-pressure accumulator drives the pump/motor as a motor, thus providing torque to the driveshaft.
Hydraulic drivetrains are particularly attractive for vehicle applications that entail a significant amount of stop-and-go driving, such as urban delivery trucks, refuse trucks or school buses. A major benefit of a hydraulic hybrid vehicle is the ability to capture and use a large percentage of the energy normally lost in vehicle braking.
The collaborative EPA-UT effort is applicable to both light- and heavy-duty vehicles with high-efficiency hydraulic hybrid systems.
The partnership will focus on four main tasks:
Improving efficiency of hydraulic hybrid drivetrain components;
Refining hydraulic hybrid drivetrains for smooth and quiet operation;
Modeling improvements to hydraulic hybrid operation; and
Training a new generation of engineers with knowledge and skills in advanced automotive technology;
A number of hydraulic hybrid development projects are underway in the US and China, including a major push by the EPA to develop a full series hydraulic hybrid in which the engine drives a pump rather than the electric generator in an electric series hybrid.