JULY 2009

Hydraulic hybrids tested in NYC refuse trucks

Field tests of Bosch Rexroth’s Hydrostatic Regenerative Braking (HRB) parallel hydraulic hybrid system were launched by the New York City Department of Sanitation (DSNY), to assess HRB’s viability for use as an alternative drive system for the department’s refuse trucks. The field evaluations are designed to authenticate both the technical and economic benefits of the HRB system, and provide real-world operating data DSNY will use to consider large-scale deployment of the technology within the city’s in-service and new vehicle fleets.

Sponsored by the New York State Energy Research and Development Authority, this evaluation project identifies vehicle fleets which, when integrating technologies such as HRB, have high potential for reducing fuel consumption and emissions. The hydraulic hybrid evaluation is part of a larger program carried out by DSNY that will demonstrate the impact of utilizing multiple alternative drive technologies.

The HRB system-equipped trucks will be operated in all five of the City’s boroughs, to test fuel efficiency and other parameters in a wide range of neighborhoods, seasonal conditions, and operating environments.

“The HRB system provides optimum fuel efficiency when vehicles undergo frequent braking and acceleration,” said Michelle DuHadway, manager, Parallel HRB accounts, Bosch Rexroth. The trucks will be subjected to a variety of in-use testing, including braking tests, acceleration tests, route collection tests and dynamometer testing to evaluate emissions.

“New York City Department of Sanitation is thrilled to be the first refuse fleet in the nation to field test the Bosch Rexroth HRB system. This is an important step toward achieving the commercialization of heavy-duty hybrid hydraulic vehicles,” said Rocco DiRico, deputy commissioner, support services, DSNY.

The HRB system is installed onto a Crane Carrier Company LET2 truck, and will be integrated with a Heil Environmental refuse body. Two identical trucks equipped with a HRB system will be provided for the evaluation.

The Rexroth HRB system uses a hydraulic pump/motor, connected to the driveline, to capture kinetic energy during vehicle braking. When braking, the pump/motor acts as a pump, absorbs energy from the driveline and imparts a retarding force on the drivewheels, pumping hydraulic fluid into a nitrogen-pressurized accumulator. During acceleration, the pressurized gas pushes fluid out of the accumulator, and the pump/motor then acts as a hydraulic motor, assisting the engine and reducing the fuel required to launch the vehicle. This process is commonly referred to as regenerative braking.

Hybrid drive train technologies will become a “necessity” in the near future in the heavy truck market, said Glenn Pochocki, vice president of sales & marketing, refuse/chassis products, Crane Carrier Company. “Bosch Rexroth’s hybrid HRB technology and system can be integrated into most medium and heavy duty truck vocations without impacting the vehicle’s configuration,” he said. “The HRB system is designed to improve the vehicle’s fuel economy, while improving brake system life with improved acceleration – what better combination is there?”

According to Bosch Rexroth, the HRB technology has already undergone field testing in urban settings, with positive results. “We started our in-field testing of HRB last summer with a refuse customer in Berlin, Germany and are now introducing this proven technology in North America,” said Ed Greif, vice president, engineering development hydraulics, Bosch Rexroth. “Field testing has verified our simulations and we anticipate similar success in the United States.”

Hydraulic hybrids, due to their high power density, are well equipped to cope with the high power requirements of regenerative braking. Maintaining efficiency during energy conversion, hydraulic hybrid systems have the potential to capture a large portion of braking energy and make use of it more effectively.

Reduced brake maintenance costs and the associated vehicle downtime offer another significant system savings. Since it is possible to slow the vehicle without engaging the foundation brakes as often, the life of the vehicle’s brakes is extended and the amount of brake dust released into the environment is reduced.

“On average, the Department of Sanitation replaces brakes approximately once a year, which takes the truck out of service for at least two days. We hope to improve that figure by 50 percent or more,” DuHadway said.