The Urbane Powertrain

The Volvo Group is preparing for its commercial production launch of diesel-electric hybrid technology for heavy-duty applications-a launch the U.S. Air Force helped fuel.
By Ron Kotrba | March 15, 2007
For decades, Volvo Group has been a leading maker of 9- to 18-liter diesel engines for the world's heavy-duty vehicle markets. Diesel engines exhibit exceptional pulling power, fuel efficiency and longevity when judged against comparable gasoline outfits, which is why it's the internal combustion engine of choice for big jobs. Volvo Group, a $31 billion company built on its technological diesel prowess, is well on its way to a diversified portfolio of dual-powered drivetrains-diesel-electric hybrids-for the same markets in which Volvo already has an established presence. In 2009, the company expects to launch production of its first commercial lineup of these efficient, high-tech workhorses, the applications for which are many. With growing numbers of fleets guided by public or corporate policies to reduce petroleum consumption and increase the use of alternatively fueled vehicles in their fleets, hybrids and biodiesel used in tandem can reduce the impact of environmental footprints left by humanity's global stampede.
"We need to care for the environment, and the trucking industry needs to do what it can," says Marten Wikforss, head of media relations with Volvo Group. "We are part of the problem, yes, but we are also part of the solution."

An Air Force Entrance
Volvo Group, and its subsidiary Mack Truck, has been working with the U.S. Air Force (USAF) on diesel-electric hybrid technologies since 2003. Mike Mead, head of the Advanced Power Technology Office (APTO) at Robins Air Force base in Georgia, tells Biodiesel Magazine that the USAF initiated a bid process for vehicle technologies capable of utilizing electrical power with a diesel engine that, when coupled, would use significantly less fuel and yet still perform the rigorous activities required by specified military duties. "The Air Force looked at possible applications of this technology," Mead says. "The heavy-duty vehicles that would be most useful in demonstrating the benefits were selected to be developed by Mack." The APTO acted as the practical, technical liaison between Volvo-Mack and the Air Force at large. The resulting prototype was dubbed the "R-11," a 6,000-gallon refueling truck.

The R-11 is a mild hybrid, meaning the electric motor only assists in powering the wheels, whereas a full hybrid can be mobilized by either the electric or diesel motor. "The technology has outstanding potential to improve overall vehicle efficiencies while lowering emissions and enhancing performance," Mead says. The leap from passenger hybrid vehicle technology to heavy-duty applications has taken considerably more work. "Heavier vehicles require larger power storage devices for more torque at launch of the vehicle," he says. "Also, the operational needs of heavier vehicles are greater since they serve as platforms for other work, such as fueling aircraft, refuse collection and dump trucks, whereas additional power requirements are not a consideration for smaller passenger vehicles." In a full hybrid, the vehicle can run on electricity alone under certain operating conditions, such as the stop-and-go itinerary kept by transit buses or intra-city parcel and goods distribution.

Another prominent distinction between hybrids is whether the two onboard sources of power operate in series or parallel configurations. A serial hybrid moves only by the electric motor. Even if the conventional drivetrain is providing the bulk of power, that is still channeled through the electric motor before the vehicle is mobile. When the diesel engine isn't running during certain load or speed conditions, the electric motor takes a primary role. A generator affixed to the diesel-powered engine produces electricity that can be stored in the battery, which also contains electrical energy recuperated from regenerative braking. Friction from braking creates energy that is routed to the onboard batteries. Regenerative braking is also featured on most parallel hybrids. The simplified difference between serials and parallels is that the parallels have the ability to achieve direct mobilization of the vehicle with power from either the diesel or electric motor through complex electromechanical design.

The test work on the R-11 mild-hybrid refueler truck that began between the USAF and Mack back in 2003 helped Volvo-Mack hone its technology for future applications. "This technology will evolve into a full-hybrid vehicle, where the electric machine will be able to power the vehicle and auxiliary equipment without the diesel engine running," Mead says.

Post R-11, so to speak, the USAF continues to work with Volvo-Mack. Three Mack Granite dump trucks and two Low Entry refuse trucks are on order Mead says. "Further developments are concentrating on increasing fuel efficiency, reducing idling times, enabling full electric launch of the vehicle, reducing diesel engine parasitic losses, external drive of auxiliary loads electrically and the supply of off-board power while stationary," he tells Biodiesel Magazine. "Air Force engineers and program managers worked with an exchange of ideas on how the technology might be expanded for future vehicles to include electric auxiliary power. Mack then developed a drivetrain to meet all these requirements."

I-SAM, U-Save
While the Volvo Group is working on multiple hybrid configurations for a variety of heavy-duty requirements, an integral component of the Volvo Group's technology is the Integrated Starter Alternator Motor (I-SAM). In a detailed Volvo Group press release on the breakthrough engineering, the company states: "The I-SAM consists of a permanent magnet unit including power converter, energy storage system and a powertrain management unit (PMU). The [permanent magnet] unit has a high diameter-to-length ratio and is placed between the clutch and an automatic mechanical transmission, the new generation of Volvo gearboxes. The PMU contains the key logics on gear-shifting strategies and power split between diesel engine and electric machine. The high power and torque output from the [permanent magnet] unit allows for downsizing of the diesel engine. The high power and torque capabilities are used in an electric retardation system and the generated energy is stored in the energy system for later reuse."

Ultimately, I-SAM can perform as a starter, an electric drive motor and a generator. Real-time speed and load information is relayed to the sophisticated onboard computer, which, through its electronic controls, tells I-SAM what to do and when to do it. Since the permanent magnet unit can meet the high power and torque requirements of heavy-duty operations, the onboard diesel engine can be smaller, another angle to the system's ability to conserve energy.

Much of what Volvo has accomplished wouldn't be possible if not for battery technology advances, and Volvo has done its part on that front, as well. Volvo Technology Transfer, part of Volvo Group, is a principal shareholder in Effpower, a Swedish company formed in 1999 to commercialize breakthroughs in bipolar battery technology. "Effpower has advanced the well-known lead-acid chemistry to a new level," Volvo Group states. "The key to its high performance characteristics (long life, cost-efficient, high power and environmentally sound) lies in a bipolar battery design utilizing a patented lead-acid infiltrated ceramic plate and a patented sealing method."

Biodiesel-Electric
Wikforss tells Biodiesel Magazine that this I-SAM-equipped lineup will bring more savings for some applications than others. "It will serve a viable purpose and different applications, but the biggest savings would be in city distribution and transit buses, where there's a lot of stopping and going," he says. Fuel savings there can reach 35 percent or more, but the natural flip side to using less fuel is producing less emissions. As this technology takes off in urban settings, where air quality suffers from mobile emissions sources the worst, the benefits mount. "Another aspect to pollution is noise pollution," Wikforss says. "There's less noise with a hybrid, and those living in urban settings will appreciate that."

Mead says the USAF's R-11, along with the subsequently ordered Mack hybrid prototypes soon expected, are all capable of running on B20-the Air Force standard. Wikforss, on the other hand, says that while biodiesel is a good fuel and serves a purpose, Volvo doesn't make a practice of pledging its allegiance to just one fuel, no matter its appeal, until one fuel becomes the worldwide-accepted standard. He doesn't object to using biodiesel in such applications, though. Considering Europe's diesel-fuel specification allows for up to 5 percent biodiesel without distinction, it's a moot position either way regarding low-level blends. He expresses concerns over different fuels and emissions regulations when crossing national boundaries. "We want to see international harmonization on that, and decisions must be taken up by the United Nations," Wikforss says. "Those trucks run across borders all the time."

Leif Johansson, president and CEO of AB Volvo, stated Volvo's position on renewable fuels and his company's hybrid systems in a corporate press release last year. "The hybrid power system is a long-term and highly interesting solution for efficient and environmentally adapted transport activities," Johansson said. "We are aware that oil prices for our customers will rise, and therefore all solutions that reduce fuel consumption are highly attractive. The diesel engine in our hybrid solution can also be operated using biofuels, and consequently transport activities can be conducted without carbon dioxide emissions. This paves the way for interesting developments toward long-term sustainable transport solutions."

Ron Kotrba is a Biodiesel Magazine staff writer. Reach him at rkotrba@bbibiofuels.com or (701) 746-8385.
 
 
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