Advancing hydraulic hybrids: test within refuse truck to incorporate Bosch Rexroth’s Hydrostatic Regenerative Brake system.
Published in: Diesel Progress North American Edition
Date: 7/1/2007
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 (NYSERDA) and the National Association of State Energy Officials (NASEO).
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.
Equally important, New West needed high-speed wireless communication capability integrated with the data acquisition system. Requirements included the ability to reliably and efficiently collect data remotely while not affecting operator behavior, as welt as identify and locate the test truck and communicate with it when needed.
“We looked at many different manufacturers of data acquisition systems in researching the right solution for this project,” Ivanic said. “Other data acquisition manufacturers were less expensive than nCode, but none of them provided the extensive capabilities that the EDAQ-Lite solution has. This expanded capability coupled with the ability to incorporate high. speed wireless communication, more than outweighed the additional cost and was key to our select on
The eDAQ-Lite is a stand-alone data acquisition system for field data testing. It is designed to allow collection of a wide range of analog, strain and thermocouple data directly from sensors, as well as digital data including vehicle network interfaces and GPS. The system is fully expandable and allows for user-defined, customized data acquisition solutions, nCode said.
eDAQ-Lite also incorporates an Ethernet communication port that enables integration of a broad-band wireless modem for high-speed wireless (WWAN) remote communication.
New West’s eDAQ-Lite system consisted of eDAQ-Lite ELCPU, ELDIO-GPS, EDIO-VBM-CAN and EDIO-VBM-1708 modules. “We needed a modular data collection solution to ensure we had adequate capability for whatever else might come at us, because we weren’t sure at the beginning of the project what additional information we would need to collect,” Ivanic said. “It was a positive feature for us, for example, that we could add more layers for additional thermocouples and pressure transducers, if needed.”
A small, rugged and portable unit was essential for New West to withstand the shock and vibration generated by the refuse truck chassis traveling New York City streets in all weather situations. With the ability to tolerate 20 g vibration in a sealed unit. eDAQ-Lite is engineered to minimize the potential for damage from shock and vibration, as well as from dirt and water intrusion.
A key benefit of the nCode system was its ability to be packaged into the vehicle. Designed for mobile applications, the system’s small footprint allowed it to be installed easily into the refuse truck without impacting or influencing the truck operator’s behavior or the vehicle’s performance.
A low power draw enabled both the eDAQ-Lite system and the wireless modem to be connected to the vehicle battery, allowing continuous system operation literally 24/7.
The eDAQ-Lite system also provides data collection flexibility, Ivanic noted. “We use one of the I/O channels as a trigger,” he said. “When it goes from high to low, that starts a test. When it goes the other way, that stops it.
“This allows us to record only operational data instead of having tests run continuously for 24 hours and saved us a lot of time from a data analysis perspective.”
High-speed wireless communication was needed to completely manage the data collection and analysis process remotely. New West’s eDAQ-Lite system incorporates a third-party high-speed wireless modem. Code s solution allows the flexibility for employing high-speed WWAN wireless Ethernet connection for super fast communication–up to 400 Kb/sec. for uploading and downloading at 156 Kb/sec.,” said Ivanic.
New West is using an Airlink Raven modem and, according to Ivanic, the system allows a 2 MB file (approximately one day’s worth of data) to be downloaded in a couple of minutes.
“It really doesn’t matter where you are if you have good wireless communication capability,” Ivanic added. “We’re mostly collecting time histories with a couple of computed channels. With the eDAQ-Lite, we can monitor our tests real-time at home, in the office or from a hotel room in Europe.”
The remote data retrieval also provides flexibility, Ivanic said. The eDAQ-Lite system’s internal system memory retains the acquired data locally, but it can be accessed selectively. “The fact that we download only that information we need as opposed to having to download the system’s entire memory is critical,” Ivanic said. “This way we can keep all that information saved on the system. The backup is all on the eDAQ-Lite, which gives us a lot of peace of mind.
“If we didn’t have this wireless capability we’d need an engineer on-site in New York City to physically connect to the data collection system and download the data. That more than pays for the additional cost of buying the modem and the monthly service fee.”
The advantages of remote data retrieval became clear early, as upon reviewing data at the end of a day of testing, New West realized it had lost the vehicle bus data. Sending out an engineer to check on the system the next day revealed that the vehicle bus cable became loose. Because of the remote data retrieval capability, New West was able to identify and correct this problem immediately.
nCode’s intuitive Test Control Environment (TCE) software is engineered to allow easy test setup and communication when the eDAQ-Lite is hard wired and used behind a corporate firewall. When communicating remotely with an outside ISP, however, the use of proprietary software can become difficult due to corporate firewall security measures, nCode offers a work-around solution to address firewall issues when connecting remotely. eDAQ-Lite hosts its own web browser, allowing remote users to simply use the Internet to connect with the system. “Using a web browser me s we can connect from anywhere and still easily look at individual data sets, runs or parameters as needed,” Ivanic said.
In addition, the traditional GPS capability was important in that it allowed for correlation of downloaded data to specific GPS coordinates for more in-depth analysis. In this way, a specific spike in the data could be related to a physical event–for example, a massive pothole at a precise point in the truck’s route.
And “if a truck needs to be located, GPS allows the engineer to quickly identify it from a parking lot full of trucks, rather than wasting time hunting around for it,” Ivanic said. “That’s a huge time saver.”
As part of the second phase of the project later this year, New West will install another eDAQ-Lite system with high-speed wireless capability into the prototype hydraulic hybrid truck in the DSNY fleet to do comparative testing.