Hybrid Visions

Class 6 and 7 Electric-Diesel Commercial Trucks Are Helping Contractors See Green

By Mike Elwell

The challenge of providing a cleaner world coupled with the demand for a dwindling energy source is fueling innovation in the truck world. Construction and landscape crews utilize machines and trucks all day long — often seven days a week — which means they invest heavily in diesel and gas products that affect their bottom line every month.

To help balance these increasing fuel costs with more economical products, truck manufacturers are now offering fleets a greener and more fuel-efficient alternative — Class 6 and 7 hybrid-electric commercial trucks. These trucks offer a significant improvement in fuel economy, ranging from 30 to 60 percent depending on application. In addition, they also feature reduced emissions and noise, which make the trucks more community-friendly.

“We believe that hybrid technology is a critical and necessary development for commercial work trucks,” says Jim Williams, director of sales and distribution for new products at Navistar International. “A hybrid truck like the DuraStar Hybrid from International can deliver significant efficiency and cost-savings. This is especially true with today’s high fuel prices where just one truck can save thousands of dollars in fuel costs annually.”

In order to explain why hybrid trucks are so efficient and useful for delivery, utility, construction and many other applications, it’s important to understand how the primary components of a hybrid drive system work together.

Primary Components

The hybrid drive system is comprised of four main components, which include the hybrid drive unit, the Power Electronics Carrier (PEC), the Motor Inverter/Controller and the DC/DC Converter.

The hybrid drive unit consists of a mechanical automated transmission and a hybrid motor/generator, which adds horsepower and torque to the powertrain. The PEC includes the control electronics for the hybrid system and the hybrid’s lithium ion batteries. It also contains a cooler for the electronics system. The Motor Inverter/Controller includes the control system to make the hybrid system work.
The DC/DC Converter keeps the 12-volt system fully charged in any engine-off application. While the engine is off, the 12-volt electrical loads (lights, strobes, etc.) can deplete the 12-volt batteries. The DC/DC Converter eliminates this problem by using the hybrid batteries to charge the 12-volt battery system.

Putting it all together, a hybrid diesel electric commercial truck basically inserts a hybrid electric motor, powered by high-voltage batteries between the engine and the transmission. Along with starting the engine, the hybrid electric motor can operate the vehicle at low speeds on electricity only before the engine begins to help out at higher loads and speeds, saving precious fuel and lowering operating costs. In certain applications, it also has the capability of operating body equipment using the hybrid batteries to operate the power take off (PTO). This is different than a conventional truck where the engine must be running to operate the PTO.

Hybrid Applications

Hybrids are best suited for stop-and-go applications and applications that require the use of equipment without the engine running. Intercity and suburban pickup and delivery type applications provide the best opportunity to operate the truck under electric power, which is inherently fuel-efficient. They also allow for maximum use of the truck’s regenerative braking capability, which replaces used energy to the hybrid battery.

When the operator needs to slow or stop the truck, he or she simply takes a foot off the accelerator and the hybrid motor/generator goes into a generation mode, which brakes the truck electrically. This replaces used energy to the hybrid battery instead of wearing out the brakes and wasting energy — it adds to the overall productivity of the truck.

“For applications that don’t require engine-off operations like pickup and delivery or flat-bed stake trucks, Navistar’s base system includes the Eaton Hybrid Drive System,” Williams says. “In applications like these, customers can see fuel economy improvements of up to 30 to 40 percent.”

For engine-off applications, where truck equipment can be run without the engine running, like tree aerial bucket trucks, cranes, service utility trucks and recovery trucks, fuel economy improves even more.

“In an engine-off application where the hybrid battery is operating the hybrid motor/generator and the PTO, fuel economy improves up to 40 to 60 percent,” Williams states. “In the case of a hybrid utility bucket or aerial tree bucket truck, we measured the duty cycle and found it will operate the bucket for one to two hours with the engine off. This gives 100 percent reduction in fuel and emissions,” Williams adds.

As energy is used in the operation of the bucket, the hybrid battery will eventually discharge to a point that a recharge is required. Then, the truck automatically starts the engine and operates the PTO from the engine while it’s simultaneously recharging the hybrid battery. This is accomplished in five to seven minutes. When the battery is fully charged, the engine automatically shuts down and the truck operates the PTO using the hybrid battery once again.

What About Performance?

So, with an increase in efficiency comes a loss in performance, right? Wrong.
“Third party testing was done to quantify the performance improvements compared to a conventional vehicle, and part of that effort was to look at its acceleration in comparison to a base line unit,” says Williams. “Loaded to 27,500-lb GVW, the hybrid truck proved to be nine seconds faster in accelerating from 0 to 60 mph.”

The added electric power is more powerful at low speeds because of a basic difference in electric motor performance. Unlike an internal combustion engine, where torque and horsepower are increased as the engine’s rpm increases, an electric motor provides 100 percent of its rated torque and horsepower at 0 rpm. Mating the two provides a great performing truck.

Federal and State Grants

“For companies that choose to buy hybrid trucks, there are government incentives at the state and federal level available,” says Rob Durham, Lakeside International Trucks.

Some states and the federal government have funds available to help businesses offset the initial cost of a hybrid commercial truck. On a federal level, the Energy Policy Act of 2005 allows for tax credits of up to $12,000. The tax credit is dependent on the chassis gross vehicle weight (GVW) and the amount of fuel saved.
“More information about this federal funding can be found by talking to your local dealer,” says Williams.

There are also a substantial number of states that provide incentives for the purchase of medium-duty hybrid trucks. Currently, California, Connecticut, Louisiana, New Hampshire, New Jersey, New York, North Carolina, Ohio, Oregon and Texas offer incentives. Legislation is under way to add more states to the list. For more information visit the Environmental Defense Fund Web site, http://environmentaldefense.org/page.cfm?tagID=1123.

“Our network of International dealers is up-to-speed with current and upcoming legislation regarding hybrid incentives on a federal and state level,” says Williams. “Dealers are an excellent resource for companies looking to learn more about hybrid trucks and the tax incentives that are available.”

Going Green

The trend to go “green” has been on the rise over the last few years. Companies that are concerned about reducing their carbon footprint and increasing their fuel economy are starting to think about adding hybrid trucks to their current fleets.
“Hybrid trucks produce significantly lower emissions,” says Durham. “In some cities, the air coming out of the exhaust pipe is actually cleaner than the air going in.”

“Navistar has been producing hybrid commercial trucks for the last few years, and in October 2007 it became the first company to offer line assembly of hybrid commercial trucks,” says Williams. “To date, we have hundreds of hybrid trucks in the field, a number that will rise as we continue to educate potential adopters like the utility, tree care and landscape and construction industries about the benefits of hybrid technology.”

Mike Elwell is director, marketing, medium for Navistar International Corp., based in Warrenville, Ill.

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