Feb 4, 2009 10:54 AM

A prototype heavy-duty tractor equipped with ArvinMeritor’s first Meritor diesel-electric drivetrain has been placed into service with Wal-Mart Stores.

Most hybrid systems are best suited for start-stop applications, said Carsten J Reinhardt, president of ArvinMeritor’s Commercial Vehicle Systems (CVS) business. However, the Meritor dual-mode hybrid drivetrain, which combines both mechanical and electrical propulsion systems, is specifically designed for linehaul, over-the-road trucks.

At less than 48 miles per hour, vehicle propulsion is delivered entirely through an electric motor with power from lithium ion batteries. These batteries are recharged through regenerative braking and/or an engine-driven generator.

As highway speed is approached, the drivetrain phases to a diesel-powered system with the electric motor providing power—only as required—allowing for total system optimization.

The key difference with this system is its ability for zero-emission mode over a wide range of vehicle driving conditions, Reinhardt said. Additionally, the batteries provide continuous power for hotel loads during an overnight rest period, eliminating the need for engine idling or other redundant anti-idling systems.

The Meritor diesel-electric drivetrain was developed specifically for Wal-Mart in collaboration with Navistar and Cummins. The program was announced in January 2007.

The consortium is working on building a second-generation hybrid truck, expected to be completed by December 2009.

Wal-Mart will test and evaluate the prototype tractor in regular linehaul service at one of its distribution centers for the next year.

The retailer is also testing trucks that operate on reclaimed grease fuel made with the waste brown cooking grease from Wal-Mart stores, and on an 80/20 blend of biodiesel made of reclaimed yellow waste grease. In addition, it is evaluating trucks that use Eaton’s diesel-electric hybrid power systems, as well as trucks powered by liquid natural gas.

Wal-Mart Transportation operates nearly 7,200 heavy-duty trucks in North America and has committed to doubling its fleet efficiency by 2015.