26 June 2006

The US Environmental Protection Agency (EPA) has unveiled a diesel-hydraulic hybrid delivery truck, which can offer up to 60-70% improvement in fuel economy and a 40% CO2 emission reduction compared to conventional diesel trucks. The prototype truck—a UPS delivery vehicle—will be evaluated in onroad tests beginning this year.

In the hydraulic series hybrid, the diesel engine drives a pump to compress and transfer hydraulic fluid—nitrogen gas—to the rear drive pump/motor and/or to a tank, called the high pressure accumulator, where the compressed gas energy can be stored. The stored energy can be utilized to drive the pump/motor unit. The expanded gas is stored in another tank, called the low pressure accumulator. The hydraulic drivetrain replaces the conventional drivetrain and eliminates the need for a conventional transmission.

The hybrid hydraulic drivetrain increases vehicle fuel economy in three ways: (1) through regenerative braking it permits the recovery of energy (in the form of compressed gas in the high pressure accumulator) that is otherwise wasted in vehicle braking, (2) it allows the engine to be operated at much more efficient modes, and (3) it enables the engine to be shutoff during many operating conditions such as when the vehicle is decelerating and stopped at a light.

The demonstration vehicle was developed in cooperation between the EPA and industrial partners, including Eaton, UPS, International, US Army National Automotive Center, and Morgan-Olson. Major technical support was provided by FEV Engine Technology and Southwest Research Institute.

The added cost for the hybrid components in a production hybrid vehicle is estimated at $7,000. This could be recouped in less than three years by the lower fuel consumption and lower brake maintenance cost.

The EPA is also developing a second hydraulic hybrid demonstration vehicle under a second phase of the program, which will feature a different hybrid system configuration. The second phase vehicle would also utilize the EPA Clean Diesel Combustion (CDC) engine, meeting the 2010 NOx emission standards without the need for NOx aftertreatment.

Source: US EPA