In September, the EPA, in partnership with Parker Hannifin and others, 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. (Earlier post.) Class 6 yard hostlers differ from on-road Class 6 vehicles in that they have lower top speeds in their unique drive cycles (around 25 mph).

The hydraulic hybrid drivetrain uses hydraulic accumulators 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.

Compared to batteries as an energy storage device for hybrids, the hydraulic accumulators offer a higher power density, but a lower energy density. The accumulators support a higher energy flow, not limited by overheating, and are more efficient at charging/discharging.

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 degrees. 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.

A full suite of Parker products, including specifically-designed pump/motors, hoses, fittings, valves, electronic controls, and Parker high-efficiency accumulators are incorporated into the design. A working demo vehicle is projected to be available for FedEx Ground within the next 12 months.

The United States Environmental Protection Agency (EPA), as part of a Cooperative Research and Development Agreement (CRADA), will continue providing Parker additional technical assistance in the development of the vehicle as it has for four years. These include in-kind engineering services, test equipment and facilities. Initial EPA simulation modeling of city driving confirms greater than 50% potential improvement in fuel mileage efficiency.

Parker expects the technology to have applications with other classes of vehicles.

FedEx is participating in the WestStart CalStart Hybrid Truck User Forum’s (HTUF) hybrid parcel delivery truck working group (WG), which is currently focused on hydraulic hybrids only—the hybrid-electric parcel delivery truck industry already being relatively mature.

Key performance parameters set out by the HTUF WG include:

• >50% fuel economy improvements compared to baseline Class 4/6 vehicles<
• Walk-in Van Chassis
• Reliability ≥ baseline truck
• Lifecycle costs ≤ baseline truck
• No reduction in cargo capacity
• Serviceability/maintainability ≥ baseline truck
• Durability ≥ baseline truck
• Cargo bed height ≤ baseline truck
• Range ≥ 400 miles/day
• Exterior and interior noise levels ≤ baseline truck
• Acceleration ≥ baseline truck
• Gradeability ≥ 5% at 37.5 mph for a Class 6 truck

This relationship with FedEx Ground marks the latest chapter in Parker’s 10-year history of energy saving hydraulic drive systems for commercial vehicles. We are extremely pleased FedEx Ground is working with us as a collaborator for this program.

—Dr. Joseph A. Kovach, Vice President of Technology and Innovation for Hydraulics

The day prior to the FedEx announced, Dr. Kovach had presented Parker’s hydraulic hybrid technology to financial analysts and shareholders during the company’s annual Investor Day at the company’s Cleveland headquarters.

Resources

• Hydraulic Hybrid (FedEx Ground WestStart CalStart presentation)