Of all the alternative fuel and power options available to the world of construction trucks and equipment, nothing holds more promise than hybrid diesel-electric systems. These designs use an internal combustion engine to turn a generator that pumps electricity into a big battery and then tap either the mechanical or the electrical system – or a blended mix of both – to move the vehicle or equipment.
Hybrid designs aren’t new. You’ll find them in vehicles as diverse as the 2,800-pound Toyota Prius and the world’s biggest mining trucks. Engineers estimate that hybrid diesel-electric machines could offer users potential fuel savings of 35 to 60 percent. And when it comes to cutting emissions and greenhouse gases and reducing our dependence on foreign oil, no other technology comes close.
So why haven’t manufacturers developed anything between the Prius and the mining truck? Why no hybrid excavators, wheel loaders or dozers?
The answer is a complicated tangle of issues. Manufacturers face big, long-term R&D costs. Politics and social policy play a role. And design engineers, especially those who work with off-road equipment, struggle with high torque demands, battery limitations, component space constraints and the constant pressure of making all this work within a cost/benefit ratio that will attract customers.
But make no mistake, hybrids are coming. And while there is no production-level hybrid earthmoving equipment available today, the truck industry will likely go to market late this year with the first production-level diesel electric hybrids for use in the utility industry. This small but history-making event will mark a turning point in the future of the internal combustion engine and increase the velocity of a process that will a decade to reach its full potential.
First up – trucks
“This is the most exciting technology I’ve ever been around with this corporation, and I’ve been with them for 40 years,” says Jim Williams, director of sales and distribution, new products, International Truck. The technology he’s referring to is a parallel diesel electric system (see “Series vs. parallel hybrids” in box below) for International’s 4000 series DuraStar utility bucket trucks that taps battery power to maneuver the bucket and assist in vehicle propulsion. Some 50 demo models of these trucks have been working in the field for almost two years now and full production models are expected to start rolling off the assembly lines late this year.
In addition to powering the bucket, the batteries in International’s hybrids will also provide juice to the power take off, what the company calls its “ePTO.” The horsepower required of the ePTO is not large, 20 to 30 horsepower is the sweet spot, Williams says. But you can run the ePTO with the engine off, rather than idling as you must with a mechanical or hydraulic PTO. This not only saves considerable amounts of fuel, but cuts greenhouse gases and helps in states that have strict anti-idling regulations. Drawing on electrical power only, operators will be able to use the bucket with the engine off for up to a two-hour duty cycle. Bucket trucks were chosen as the first application, but the ePTO can easily be adapted to a wide range of traditional PTO applications such as lifting cranes, tree trimmers and roll-off trucks.
The hybrids will be more expensive than traditional trucks, Williams says, but the savings in fuel and maintenance will help provide a payback. The targeted payback period, as volumes increase and costs are reduced, needs to be within five years on trucks with a 10-to 15-year duty cycle. Larger systems that can generate more powerful electrical output are coming, but they’re not here yet, Williams says. The current Eaton system generates 340 volts and will work on trucks up to 33,000 pounds. “But to get up to 60,000 or 65,000 pounds we need heavier components. We’re using 800-foot-pound transmissions at this point, and you need something in the 1,000- to 1,200-foot-pound pound range for those applications,” he says.
The heart of International’s hybrid design is an Eaton electric motor-generator between the output of an automated clutch and the input of the transmission. International is not the only truck company that’s putting the Eaton system to good use. Eaton has already produced 220 hybrid vehicles for testing and evaluation among truck manufacturers and customers including public utility fleets. Terex, PACCAR, Kenworth, Freightliner and Peterbilt are also working the Eaton design into their plans.
The ability to mix and match dual sources of power on a truck would not have been possible without multiplexed wiring systems using what’s known as a CAN-Bus “architecture.” Before CAN-Bus, a signal went down one wire to a component or sensor and then that component or sensor sent its response back up to the engine or dashboard via a different wire. The end result was a lot of wires and no interactivity between the systems. With CAN-Bus systems, signals travel both ways on a single wire and stop frequently in a series of “nodes” that act like mini-computers and determine where the signal goes next, if it’s important, or if it needs to be shared with any other component. End result: fewer wires and a smart machine in which all the components share information and help each other out.
International jumped on the CAN-Bus several years ago with its Diamond Logic Electrical system, using it to enhance some performance characteristics and as a maintenance and diagnostic tool. But Williams says the complex demands of a diesel-electric hybrid could not have been answered without smart wiring. “It has been an enabler for doing many other things downstream,” he says.
Despite a flurry of activity earlier in the year, most of the talk of diesel-electric off-road equipment has died down. At World of Concrete in January, New Holland and Kobelco showed a prototype 7-ton diesel-electric excavator. Masayuki Komiyama, manager of Kobelco’s hybrid group said that if the technology works it could boost fuel economy by 40 percent. But at the German construction trade show Bauma in April, the company was discouraging any notion that the project was anything other than an engineering experiment.
Also at Bauma, Atlas Weyhausen displayed a wheel loader that sported a four-cylinder, 50-horsepower Deutz hybrid diesel-electric engine with a flywheel mounted E-motor/ generator. On the electrical end, the Deutz E-motor contributes 10 kilowatts (equal to 13 horsepower) and 30 kilowatts peak power (40.2 horsepower) using lithium-ion batteries for storage. According to Willi Schiele, a senior vice president for research and development at Deutz, the hybrid design enabled the machine engineers to downsize the engine 30 percent and improve fuel economy about 20 percent. But Deutz says the project was a prototype and no further developments have been announced.
Play it again, I-SAM
The Volvo Group, on the other hand, is forging ahead with its I-SAM design as a solution for both trucks and equipment. I-SAM stands for Integrated Starter, Alternator-Motor. First introduced to the public in March 2006 at a press conference in Stockholm, this diesel electric hybrid was shown in the United States for the first time in January on a Mack Granite truck, a prototype developed in conjunction with the U.S. Air Force.
I-SAM is a parallel hybrid design with the starter, alternator-motor mounted between the engine flywheel and transmission. The model demonstrated in January was fitted to a 365-horsepower/11-liter Mack MP7 diesel engine and an automated 12-speed transmission and generated 120 kilowatts of electric power at 600 volts.
According to the company, I-SAM in truck applications can yield fuel savings up to 35 percent depending on application and driving conditions. The first commercially available I-SAM models will go into production in 2009, the company says.
When Volvo says the starter, alternator-motor is “integrated,” that means two things.
First, the three components are in essence one large device, and quite robust. The electric machine can serve as a motor or an alternator, either consuming or producing power as needed. “A normal alternator is 35 to 39 percent efficient. The I-SAM is 95 percent efficient,” says Lasse Sj