|The hydraulic hybrid refuse truck. Click to enlarge.|
The New York City Department of Sanitation (DSNY) has launched field tests of Bosch Rexroth’s Hydrostatic Regenerative Braking (HRB) parallel hydraulic hybrid system to assess HRB’s viability for use as an alternative drive system for the department’s refuse trucks.
Bosch Rexroth says that for refuse collection vehicles with high start-stop frequencies, fuel savings of up to 25% are possible with the hydraulic hybrid system. 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.
The Rexroth HRB system uses a hydraulic pump/motor (axial piston unit) coupled to the mechanical drive train through a gearbox. 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.
|Video of Parallel HRB System. Description of powertrain begins at 1:30 in. Click to open. (Hat-tip to Geoff!)|
During acceleration, the pressurized gas pushes fluid out of the accumulator, actuating the axial piston unit, which now works as a motor. Hydraulic energy is converted into kinetic energy. The axial piston unit remains coupled to the mechanical drive train until the pressure accumulator is discharged. The valve manifold controls the filling and discharge process and protects the accumulator from excess pressure. The electronic BODAS controller regulates the HRB. In “normal” drive operation the Hydrostatic Regenerative Braking system is decoupled.
System components of the parallel HRB include:
- A4VSO variable axial piston pump with gearbox for pump/motor operation
- High-pressure bladder accumulator
- HIC valve manifold
- Electronic controller
Sponsored by the New York State Energy Research and Development Authority (NYSERDA), 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 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.
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.
He added that Crane is excited by the opportunity to partner with Bosch Rexroth and DSNY in the field evaluations. “These HRB-equipped collection vehicles are the first in New York City’s Department of Sanitation fleet of Hybrid Collection vehicles—a fleet that will prove to be more fuel efficient, less costly to operate, and environmentally friendly to the neighborhoods and communities they serve.”
Bosch Rexroth started in-field testing of HRB last summer with a refuse customer in Berlin, Germany and is now introducing this proven technology in North America.
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 the 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.
Bosch Rexroth also offers a series-hybrid package of its HRB. Bosch Rexroth is a division of the Bosch Group, a leading global supplier in the areas of automotive, industrial, consumer goods and building technology. Bosch has been involved in hybrid technology for more than 30 years, and has over 500 specialists globally dedicated to the development of both electric and hydraulic hybrid systems for light, medium, and heavy-duty vehicles worldwide.