Continuing the evolution of its hydraulic drivetrain technology for commercial vehicle applications, Bosch Rexroth will supply its Hydrostatic Regenerative Brake (HRB) parallel hydraulic hybrid technology into prototype refuse vehicles for field testing and evaluation in two metro areas. The system will be installed into a prototype refuse chassis, and the project is sponsored by the New York State Energy and Research Development Authority and the National Association of State Energy Officials.
The Dept. of Sanitation–New York City (DSNY) and the City of Baltimore Bureau of Solid Waste (BSW) will host the field tests. American LaFrance LLC will provide each city with a prototype truck chassis into which the HRB system will be installed. Significant technical support is being provided by New West Technologies LLC, and additional sponsorship is provided by the New Jersey Board of Public Utilities, the Maryland Energy Administration and the Maryland Dept. of the Environment. NASEO’s support for this effort is part of the State Technology Advancement Collaborative, a program funded by the U.S. Dept. of Energy to promote multistate initiatives in new energy technology.
The overall goal of the project is to assist widespread application of hydraulic hybrid powertrains in vehicle fleets, such as refuse haulers, that have been identified as having high potential for successfully using this technology to reduce fuel consumption and emissions, along with reduced operating and maintenance costs and improved performance. The specific objective of the field tests is to validate the technical and economic characteristics of the HRB system, a key step in defining a program for deploying this product to large numbers of in-service and new vehicles. The two cities participating in the tests are expected to exhibit significant differences in operating conditions and will therefore provide a more thorough analysis of the HRB’s potential.
“The Dept. of Sanitation is pleased to participate in the planned field testing of Bosch Rexroth’s Hydrostatic Regenerative Brake System,” said John J. Doherty, New York City Dept. of Sanitation Commissioner. “Sanitation travels 6300 curb miles daily to collect 12,000 tons of refuse per day throughout the five boroughs of New York City. The daily house-to-house collection service provided by the Department in stop-and-go traffic is a true test for this type of technology. We await the results of the testing for further department evaluation.”
Bosch Rexroth’s HRB system targets vehicles and equipment where the duty cycle has many starts and stops.
The HRB system is essentially a hydraulic hybrid that uses the hydraulic energy stored in accumulators to assist in acceleration, then recovers energy during vehicle deceleration and braking. This allows the vehicle engine to function in a more consistent range, thereby reducing overall fuel consumption and engine emissions.
“There are two drivers of the technology of the system,” said Christine Ehret, engineering machine functions, platform projects project manager at Bosch Rexroth in Germany. “They are the reduction of fossil fuel use and the reduction of emissions.
“This can be done with electric or hydraulic hybrid systems. The important parameters of energy storage technologies are energy density and power density. A lead acid battery or fuel cell has a high energy density and a low power density. Hydraulic accumulators have a high energy density and a high power density and are very suitable for start-stop applications. We have seen fuel savings of up to 35% in some applications and a corresponding reduction in emissions.”
The Bosch Rexroth HRB system has been developed in two configurations, an integrated system for original equipment installations or retrofit. In both cases, the system is similar, consisting mainly of two hydraulic bladder accumulators, a hydraulic pump/motor and associated valves and sensors.
During braking, the pump/motor acts as a pump, directing hydraulic fluid into one accumulator. At the next acceleration event, the accumulator releases the stored energy in a controlled manner, driving the motor, which effectively reduces the load on the combustion engine. The bladder accumulators are nearly maintenance-free and are commonly used in hydraulic applications. Standard versions operate with nominal pressures between 5000 and 6000 psi.
A pressure sensor is used to control the braking torque and operating transitions. Integrated systems, such as those in lift trucks, can use the existing hydrostatic circuit and motor. Retrofit systems would require the addition of a variable axial piston pump and some coupling of the existing vehicle drive-train and the HRB system.
In development, Bosch Rexroth has developed systems on a 25 ton refuse truck with a 268 hp engine operating at speeds to 16 mph that would use 13.2 gal. accumulators. The company has also tested 10 ton lift trucks rated 114 hp operating at speeds up to 14 mph. In that system the HRB would incorporate 5.2 gal. accumulators. Fuel savings would vary depending on a range of factors, such as mass of the vehicle, speed, distance between starts and stops, etc.
But for nearly every configuration tested, Bosch Rexroth indicated that fuel savings ranged between 15 and 35%.
The system components in the HRB system are essentially all products currently in Bosch Rexroth’s product line, which the company said ensures high availability and reproducible quality in series production.
DATA COLLECTION KEY IN HYDRAULIC HYBRID REFUSE TRUCK TEST PROGRAM
The point of any field test program is to generate information on how the particular technology actually works in real-world conditions But the act of data collection has to be seamless and transparent to the operation itself since if it’s not–if it changes or inhibits the operator’s behavior and how he uses the vehicle–the information gathered is likely to be skewed and unreliable.
In a program such as the hydraulic hybrid refuse truck (see related story), the challenge of accurate data collection is complicated by the duty cycle and operating environment of the vehicle itself Refuse trucks in major metro areas such as New York and Baltimore have a hard life and the conditions don’t tolerate the presence of delicate monitoring and data gathering systems. Along with that, the program’s budget didn’t allow for the addition of local personnel dedicated exclusively to monitoring and data gathering.
The answer for New West Technologies LLC, which is providing technical support services for the project, was a wireless data system, and the company chose nCode’s eDAQ-Lite system.
“The ability to have high-speed wireless communication is critical to this project,” said Ziga Ivanic, project manager in New West’s Energy Systems Division who specializes in advanced transportation technologies. “nCode’s eDAQ-Lite system provided a superior overall data collection solution coupled with high-speed wireless communication capability, thus eliminating the need for an on-site engineer to monitor the project.”
Ivanic’s responsibility in the project is to oversee and manage the data collection and development of drive cycles for the hydraulic hybrid prototype. New West began in early 2006 by collecting baseline operating data from conventional refuse trucks in the DSNY fleet. It focused on more than 40 different parameters, such as route driven, engine torque engine speed, fuel consumption, accelerator and brake pedal position, etc.
In the current initial phase of the project, which is ongoing, New West is analyzing the data and providing Bosch Rexroth with the representative truck duty cycle data for the DSNY refuse truck fleet. Of particular interest to Bosch Rexroth are vehicle speed profiles and engine operating maps and operating characteristics which will allow for appropriate sizing of the hydraulic components and the development of a control strategy for capturing the maximum amount of regenerative braking and reusing it later for vehicle propulsion.
In Part 2 of the project, which is scheduled to begin early in the next year, New West will conduct comparative tests of the conventional refuse truck and the hydraulic hybrid prototype refuse truck in DSNY fleet service. The project presented several challenges to New West. The immediate need was for a rugged, portable data acquisition solution impervious to dirt, water and the vibrations resulting from driving a fully loaded 72,000 lb. DSNY refuse truck on New York City streets.