Freightliner Custom Chassis Launches Hydraulic Hybrid

March 5, 2009
Freightliner Custom Chassis Corporation (FCCC) introduced the newest addition to its alternative powertrain chassis development program

Freightliner Custom Chassis Corporation (FCCC) introduced the newest addition to its alternative powertrain chassis development program -- the pilot hydraulic hybrid walk-in van chassis – new powertrain features, including the Vehicle Acceleration Rate Management System (VARMS) and the Load-Based Shift Scheduling (LBSS).

Boasting improved fuel economy and less brake wear due to regenerative braking, the hydraulic hybrid chassis is designed and engineered in partnership with Parker Hannifin Corporation to address environmental and cost-savings concerns. The pilot hydraulic hybrid chassis is on display in Chicago at The Work Truck Show's Hybrid Pavilion (booth #5407) as well as showcased in the Ride & Drive as a demonstration unit.

"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."

Hydraulic hybrid chassis utilizes stored energy Predictions based on preliminary testing have shown that the hydraulic hybrid improves fuel economy between 50 to 70 percent over traditional diesel-powered vehicles with automatic transmissions in stop-and-go applications. The hydraulic hybrid improves fuel economy in three significant ways: recovered braking energy; improved engine efficiency; and its engine-off feature.

Built on the FCCC MT-55 chassis, 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 percent 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 percent of the brake energy."

Another feature of the hydraulic system is that the engine is not connected to the rear wheels of the vehicle, allowing it to 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.

The Vehicle Acceleration Rate Management System (VARMS) and the Load-Based Shift Scheduling (LBSS) have been fully tested and validated, proving that when combined, both features achieve more than an 8 percent increase in fuel economy versus a comparably specified vehicle without these features.

Working with engine manufacturer Cummins, testing included the development and validation of the VARMS. This new, optimized programming system, implemented for use with the Allison 1000/2000 series transmission, includes a means for programming the vehicle's acceleration rate and has been carefully integrated with the chassis powertrain components.

Acceleration rate management, which controls the vehicle acceleration rate to a maximum predetermined value, provides improved fuel economy and vehicle component life. The VARMS is engaged at low speeds to discourage fast starts, thereby improving fuel economy and tire life, and will disengage automatically to allow the vehicle to meet the operational requirements of normal driving conditions.

In addition to the introduction of new engine programming, FCCC also worked with Allison to validate and introduce new transmission programming. Testing shows that LBSS has been proven to provide additional fuel economy improvements, while not sacrificing vehicle performance.

Using advanced technology to calculate real-time vehicle load and operating grades, LBSS selects the appropriate shift schedule for the task at hand. As the load of the vehicle (physical of increased grade) changes, the transmission calibration can switch between performance-based shifting and economy mode. LBSS automatically selects between an Economy 2200 RPM variable shift schedule or a Performance 2500 RPM variable shift schedule based on the actual load and grade in which the vehicle is operating.

More information at