There's been a lot of news lately about hybrid technology, where electric-powered engines are mated to their gasoline and diesel counterparts in the same vehicle. Although hybrid systems have so far only seen real development in cars, they've started migrating to the truck world — and that could be a very good thing for light- and medium-duty fleets.
In addition to higher mpg and lower emissions, one of the biggest advantages of hybrids is that you don't have to plug them in every night to re-charge the batteries, or fuel them at hard-to-find natural gas stations. Just pump them full of gasoline and the engine will charge the battery as it operates. People are more likely to use them over other alternatively-fueled vehicles because they don't have to change their operating habits.
What does this have to do with trucks? A lot, actually. Eaton Corp.'s Kevin Beaty, who is working on the Hybrid Electric Vehicle project, says hybrid systems may be able to solve a lot of the drawbacks that have faced truck designers trying to incorporate alternative fuel technology. With electric- or natural gas-only powerplants, fleets face a wide range of weight, maintenance, fueling and distance issues. The beauty of hybrids, Beaty says, is that the technology has the potential to solve many of those problems, but in a different way than most people think.
“Look at the Toyota Prius. Its fuel economy is nominally two times better than comparable gasoline cars. However, it does not achieve that fuel economy simply through adding batteries and an electric motor,” he explains. “What's really changed is the design of the gasoline engine in the Prius. Combustion and emission control changes…have improved fuel economy and cut emission levels, but left drivability and performance way below what drivers would consider acceptable. That's where the electric motor comes in.”
Beaty says the key to hybrids is that the electrical powerplant adds torque to the vehicle, giving drivers the acceleration and performance they expect, as well as better fuel economy and lower emissions.
For trucks to get the same benefits, however, a few wrinkles need to be ironed out. Beaty says fleets now using gasoline-powered step vans would see the same level of fuel savings and emission reductions achieved by the Prius if they used a hybrid system.
But it's a different ballgame for diesel-powered trucks. Diesel engines designed to fit within a hybrid system are still experimental. They use Homogenous Charge Compression Ignition (HCCI), which is a completely different form of combustion than that used in today's diesels. Beaty says HCCI diesels don't deliver the torque response most fleets expect; but the electric motor could fill the gap.
Although the hybrid would help lower emissions, the jury is still out over whether it could meet EPA's '07 mandates without aftertreatment. Ironically, Beaty points out that a hybrid system may even help regulate engine temperatures with more predictability since the effectiveness of aftertreatment depends on keeping a diesel engine's exhaust stream within a certain temperature range.
Despite those challenges, Beaty believes a production-line light- and medium-duty hybrid truck could be available in four years. He admits that's an ambitious schedule, but the potential is there for hybrids to play a role in helping commercial truck fleets vastly improve fuel economy and cut emissions at the same time, without having to completely alter the way their equipment is fueled and maintained.
“The key to hybrid truck design is to take a systems approach: Look at how the engine, transmission, brakes, suspension, axles and chassis all work together,” he says. This provides “a lot of opportunity to really improve the efficiency of vehicles, for cars and trucks.”
