Hybrid Drive Systems

The essentials of their operation, care and safety

With all the emphasis today on improved fuel economy, energy conservation, environmental protection and enhanced vehicle functionality, commercial truck and component manufacturers have been busy developing "green" technologies. Increasingly, fleets are adopting hybrid and hybrid electric technology.

Vehicle fleet managers understand that delivery and transportation are the lifelines of any business. These managers are under constant pressure to lower operational costs without sacrificing performance and durability.

The performance characteristics of hybrid electric vehicles are enticing, and the tough duty cycle of a commercial vehicle is the ideal application to experience the full range of benefits from hybrid electric technology. For example, many commercial vehicles experience frequent idle time, such as school buses or delivery trucks at a drop-off. Hybrid electric offers engine-off at idle which can significantly reduce fuel and emissions, while still having the hybrid system support ancillary vehicle applications like climate control.

Depending on the application, hybrid electric truck users can experience an improvement of 30 to 35 percent in fuel economy compared to a traditional diesel-engine powered truck in a variety of operations. In an increasingly "green" world, the hybrid electric also reduces green house emissions by a wide margin.

Hybrid electrics provide other benefits. Along with extending engine life, hybrid systems assist in deceleration through regenerative braking, reducing brake wear, resulting in lower maintenance and lifecycle costs. The clean, quiet operation of hybrid electric vehicles are particularly suitable for those applications that require power takeoffs (PTO) to operate tools and equipment, where non-hybrid vehicles would otherwise be idling normally and exposing surrounding areas and vehicle operators to excessive noise and diesel exhaust for extended periods.

While hybrid electric technology itself presents a compelling story, there are external factors that are also helping to set the stage for accelerated growth in the commercial sector. Among these are access to government stimulus money, the threat of higher oil prices, greater recognition and appreciation for environmental issues and better understanding of hybrid technology in general.


Hybrid electric systems combine an engine with a combination electric motor/generator and high-capacity batteries to augment engine torque with electrical motor torque, say officials at Eaton Corporation, a global technology leader in electrical components and systems, including truck and automotive drivetrain and powertrain systems for performance, fuel economy and safety. Advanced powertrain controls monitor driving conditions and automatically select the ideal power mode, smoothly switching among electric only, combined diesel and electric and diesel-only power modes.

The hybrid drive system recovers energy normally lost during braking and stores this energy in the hybrid system's batteries, Eaton officials explain. This technology is called regenerative braking.

During the next vehicle launch cycle, this electric energy is pulled from the batteries and supplied to the hybrid motor, which converts the electric energy to torque and horsepower, continue the officials. When blended with engine torque, the stored energy is used to improve fuel economy and vehicle performance.

The main components of a parallel electric hybrid drive system are the diesel engine; hybrid drive unit (HDU) - electric motor and automated manual transmission; power electronics carrier (PEC), commonly referred to as the battery box; motor inverter controller; hybrid cooling system; DC/DC converter for ePTO (electrical power takeoff) application only; and battery charger.

Among the truck manufacturers currently offering a range of hybrid electric drive trucks are Freightliner, International, Kenworth and Peterbilt - all with systems that are supplied by Eaton.

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