|Chassis layout for the hydraulic series hybrid yard hostler. Click to enlarge.|
The US Environmental Protection Agency (EPA) has launched a project to develop hydraulic series hybrid systems for Class 6 port yard hostlers—the heavy-duty diesels that move goods and products from ships to trucks at ports.
EPA’s hydraulic series-hybrid drive technology is currently being tested in several UPS vehicles. (Earlier post.) The hydraulic hybrid offers an improvement in fuel economy of up to 74% compared to conventional diesel-powered versions of those trucks, depending on the operating mode .
|The bent-axis pump/motor. Click to enlarge.|
The hybrid vehicles will use a diesel-hydraulic system that will combine the cleanest available diesel engine technology with components that use hydraulic fluid compression to store energy. Power to the drive axles is provided by a hydraulic pump/motor.
The goal is to develop a hybrid drive system that will include a diesel engine that meets the 2007 and 2010 on-road diesel standards. An engine meeting the 2010 standard will also achieve 93% reductions in NOx and 93% reductions in particulate matter compared to an ordinary diesel yard tractor. The hydraulic hybrid technology is expected to further reduce emissions by eliminating emissions from the internal combustion engine during idling.
|Accumulators for energy storage.|
Hydraulic accumulators are used to store energy. As hydraulic fluid enters either accumulator, the nitrogen (N2) in that accumulator compresses and its pressure rises. Like other hybrid systems, energy saved when applying the brakes is reused to help accelerate the vehicle.
The system uses bent-axis pump/motors that can deliver 330 hp at 5,000 psi at 45 degrees and 510 hp at 7,000 psi at 45 deg. The current system is planned for maximum pressure of 5,000 psi. Future systems will utilize 7,000 psi.
The system adjusts to power demands using the variable position yoke assembly. At 0 degrees, no power is produced or absorbed; at 45 degrees, maximum power is produced or absorbed.
|Hydraulic primary drive assembly integrated into rear differential. Click to enlarge.|
The hydraulic hybrid technology is expected to improve the fuel efficiency of the yard tractor by 50 to 60%, reduce or eliminate emissions during idling, and decrease brake wear.
Key partners in the project include the Port Authority of New York and New Jersey, A.P.M. Terminals, Kalmar Industries, Parker Hannifin Corporation and the Port of Rotterdam, with which EPA will share project information.
For the longer term, the EPA is interested in exploring a number of different high-efficiency engines for use in the series-hybrid architecture, including:
The EPA-International-Ford Clean Diesel Combustion Engine (earlier post);
Optimized E85 or M85 engines;
HCCI gasoline engines;
Free piston engines;
HyTEC—Hybrid Thermal Energy Converter that recovers energy from engine exhaust heat