Demonstrating their utility: hybrid utility vehicles beginning to transition from test platforms to real-world production products.
A number of vehicle manufacturers, such as Peterbilt, Kenworth, Freightliner and others, have also progressed in the development of hybrid electric utility trucks for utility, telecom, municipal and other applications.
In short, it seems evident that over the next year or so, hybrid electric technology will have the chance to demonstrate its ability to do real work in the real world.
Hybrid electric trucks can pay off in significant fuel savings and reduced emissions for duty cycles that include lots of starts and stops. They are also attractive in applications where the engine operates in a lightly loaded or idling mode. Both of those conditions routinely exist in utility trucks, where engines supply power for aerial lift buckets, post hole drills, tree trimmers and other equipment at the work site. With hybrid electric technology, power take-off (PTO) devices can be powered by electricity supplied from batteries rather than having to run a diesel engine to power the hydraulic systems.
Here is a brief review of some of the vehicles being marketed or that are in expanded test applications.
The International diesel electric utility trucks are based on the International 4000 Series medium-duty truck powered by a MaxxForce DT inline, six-cylinder engine rated 225 hp with 600 lb.ft. of torque. The engine is teamed with Eaton Corp.'s hybrid electric drivetrain that incorporates a transmission, lithium-ion storage batteries, permanent magnet motor and hybrid controls. In this pre-transmission parallel hybrid configuration, a 44 kW permanent magnet electric motor is mounted directly in front of the Eaton Fuller medium-duty, automated manual, six-speed transmission.
The system recovers kinetic energy during regenerative braking and that energy is used to charge the batteries. Electric torque can be blended with engine torque to improve vehicle performance, allowing the engine to operate in its most fuel-efficient range for a given speed. The vehicle can also be operated on electrical power only and the hybrid system can also provide up to 25 kW of auxiliary power to operate lifts, tools, etc.
Results of prototype hybrid utility trucks used in the pilot program have shown reductions in fuel consumption of as much as 40 to 60% when measured against travel and work cycles typical of the utility industry. About two-thirds of the fuel savings result from the engine being shut off at the work site, and a side benefit is the relative silence of the engine-off operation.
The hybrid trucks used in the pilot program operated the utility bucket in an electric-only mode for as long as two hours, which was found to reduce engine idle times by as much as 87%.
The production versions of the International utility trucks are based on International's Class 6/7 chassis and are available in several different versions, including tree trimmers and telecom applications as well as standard truck designs that do not include a PTO.
Freightliner, also collaborating with Eaton, has developed a hybrid electric utility truck based on its Class 7 Business Class M2 106 truck. This proof-of-concept truck is a full-parallel hybrid with regenerative braking and electric launch capability. The electric motor is integrated with the engine and transmission, enabling operation with electric or diesel power, either separately or in combination. The truck launches with electric power and the diesel engine provides additional torque as required.
The 33,000 lb. GVWR truck is powered by an MBE 900 diesel engine rated 230 hp with 660 lb.ft. of torque. The combination of the engine and 44 kW electric motor can generate as much as 290 hp and 860 lb.ft. of torque when maximum power is needed. Again, lithium-ion batteries are used for energy storage.
The Freightliner hybrid utility truck integrates the hybrid system with the hydraulics for electric power take-off (ePTO) operation. At the job site, the engine remains off for the majority of the time, with the hydraulics being operated off of the batteries. When the batteries are depleted, the engine automatically starts and is used to recharge the batteries. The process takes approximately five minutes and when the batteries are fully recharged, the engine automatically turns itself off. Work is not interrupted during this process.
Besides the significant fuel savings, ePTO operation means utility personnel will be able to perform their duties with significantly less engine idle time, resulting in less noise and reduced exhaust emissions. A further side benefit--and one shared with virtually all hybrid electric systems--is that regenerative braking results in significantly extended brake life and reduced maintenance costs. Simulations and testing have shown significant fuel economy improvements over conventional diesel engines and promises to greatly reduce vehicle operating costs for customers.
Peterbilt's Model 335 hybrid-electric medium-duty truck, targeted for municipal and utility applications, is scheduled for limited production this year. The fully integrated bucket lift body and 55 ft. aerial was developed jointly between Peterbilt and Terex Utilities. The body was specially designed to allow for installation of the hybrid components on the chassis during manufacture, resulting in a true dedicated hybrid vehicle that also provides easy access to hybrid components for improved serviceability. Peterbilt said it expects the hybrid will result in a 30 to 40% reduction in fuel use through the combined improvement of on-road fuel economy and stationary jobsite operation.
The parallel hybrid system, which also used Eaton hybrid drive components, is driven by Paccar's new PX-6 six-cylinder diesel engine. The inline, 6.7 L engine is available in horsepower ratings of 200 to 325 hp with torques of 520 to 750 lb.ft. When mated to Eaton's Hybrid Drive Unit an additional 60 hp and 310 lb.ft. of torque is available, the company said.
The operation of the drivetrain and other systems are coordinated by a J1939 digital controller that senses hydraulic power demand from the onboard equipment and automatically engages the hybrid system. Under full charge, the PTO can operate for up to 25 minutes before the engine is started to recharge the lithium-ion batteries. A full recharge takes 4.5 minutes, Peterbilt said. In eight hours of operation, the diesel engine will run for less than one hour, according to Peterbilt.
Peterbilt has also engineered an Eaton hybrid system into its Class 6 Model 330 configured for local pickup and delivery applications and its Class 7 Model 335 equipped with a fully integrated Terex bucket lift body. The Model 330 is powered by a Paccar PX-6 engine rated 240 hp with 560 lb.ft. of torque. With the hybrid system, combined horsepower and torque are increased to 300 hp and 860 lb.ft.
This configuration, the company said, is ideal for stop-and-go use, such as urban pickup and delivery, with the hybrid system resulting in 30 to 40% greater fuel economy by using electric power to accelerate the vehicle from a stop.
The Model 335 truck is also powered by the Paccar PX-6 engine that regenerates lithium-ion batteries to electrically operate the PTO. Fuel use, emissions and noise are greatly reduced and the crane assembly can operate for up to 28 minutes solely on battery power. The engine automatically starts to regenerate the batteries, which takes approximately 4.5 minutes. During typical stationary operation of the PTO, the engine needs to run only about one-sixth of the time versus nonhybrid vehicles, the company said.
Both the Model 335 and the 330 are in limited production this year with full production expected for 2008. That's the same production schedule for Kenworth's new T270 Class 6 hybrid. The Kenworth T270 hybrid medium-duty conventional is powered by the Paccar PX-6 engine and features a similar transmission-mounted motor/generator, a frame-mounted 340 V battery pack and a dedicated power management system.
The goal for the T270 hybrid is to improve fuel economy by 30% in start-and-stop applications, such as utility trucks and pick-up and delivery. For medium-duty applications, such as for utility work, the T270 hybrid can be spec'd with an electric power take-off.
Bill Siuru, PhD, PE, is a Diesel Progress field editor based in Temecula, Calif.
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|Title Annotation:||TECHNOLOGY OF CLEAN AIR|
|Publication:||Diesel Progress North American Edition|
|Date:||Jun 1, 2007|
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