CHICAGO. Freightliner Custom Chassis Corp. (FCCC) rolled out a pilot model of a hydraulic-hybrid version of its MT-55 walk-in van chassis here at the Work Truck Show and 45th annual convention of the National Truck Equipment Assn. Powered by a 200-hp Cummins ISB 2007, the FCCC hydraulic hybrid chassis does not require a transmission and uses a Parker hydraulic-propulsion system.

The hydraulic hybrid chassis was designed and engineered in partnership with Parker Hannifin Corp. to address environmental and cost-savings concerns, according to FCCC, which said it would both improve fuel economy and reduce brake wear due to its regenerative braking system.

"The hydraulic hybrid chassis not only offers a reduction in operating costs, it also decreases exhaust emissions, providing a substantial environmental benefit," said Jonathan Randall, director of sales and
marketing for FCCC. "As the first chassis manufacturer to launch hybrids into the walk-in van market, we are very proud to continue that tradition by introducing our hydraulic hybrid as another option for customers."

Randall said that predictions based on preliminary testing have shown that the hydraulic hybrid improves fuel economy “between 50 to 70% over traditional diesel-powered vehicles with automatic transmissions in stop-and-go applications.” He said the hydraulic hybrid improves fuel economy in three significant ways: recovered braking energy; improved engine efficiency; and its engine-off feature.

According to FCCC, the hydraulic-hybrid system stores energy during the braking process in an “accumulator.” The energy stored in the accumulator is then used to accelerate the vehicle on the next
launch. Upon reacceleration, the vehicle utilizes the energy stored in the accumulator and once depleted, the engine is restarted.

"The hydraulic hybrid is able to recover and reuse about 70% of the energy that otherwise would have been wasted during the braking process," said Rich Kimpel, engineering manager for the Parker Hydraulic Group Technology and Commercialization Support Team. "On the other hand, typical electric hybrids can only recapture about 25% of the brake energy."

Another feature of the hydraulic system that was noted is that since the engine is not connected to the rear wheels of the vehicle, it can run more efficiently as it doesn't need to track road speed. Furthermore, the advanced engine-off feature allows the engine to turn off while idling at a stop. The engine only restarts when the energy stored in the accumulator is not enough to meet driving demands.

"The hydraulic hybrid differs from a hybrid-electric vehicle because the accumulators recharge much faster than batteries while the overall hydraulic system offers nearly 10 times the power density of electric hybrids," Kimpel said. "This factor also contributes to improved fuel economy by allowing the capture of more brake energy."

The hydraulic hybrid also requires less traditional friction braking because of its regenerative braking system, resulting in less brake wear and extended brake life, according to the two suppliers. They said that the regenerative braking system saves energy by recycling and storing it as hydraulic power, which can then be reused to propel the vehicle instead of losing it to heat as is the case with traditional brakes. Thus the friction braking system is minimally used when the regenerative system is working, further extending brake life and lowering maintenance costs.

FCCC and Parker Hannifin developed a prototype hybrid hydraulic chassis for FedEx Ground in 2008, and are currently running driver evaluation tests. UPS also received a hydraulic hybrid prototype for fleet testing. "Based on our application, hybrid hydraulics technology appears to be very promising," said Taki Darakos, project manager of vehicle maintenance at FedEx Ground.

"Our new hybrid hydraulic chassis is another option for customers interested in reducing their fuel consumption and carbon footprint without losing the outstanding performance, ride and handling of a FCCC chassis," added FCCC’s Randall.

www.freightlinerchassis.com