|The UPS hydraulic hybrid|
The US EPA and its industry partners today unveiled the world’s first diesel-hydraulic series-hybrid delivery truck. (Earlier post.) The hydraulic hybrid offers an improvement in fuel economy of up to 60-70% and a reduction in CO2 emissions of 40% or more compared to a conventional diesel-powered truck.
The hydraulic series hybrid uses an engine/pump to pressurize and transfer hydraulic fluid to the rear drive pump/motor and/or high pressure accumulator. The hydraulic drivetrain replaces the conventional drivetrain and eliminates the need for a conventional transmission.
The hydraulic hybrid vehicle (HHV) offers features comparable to an electric hybrid for maximizing fuel efficiency:
Regenerative Braking. When stopping the vehicle, the hybrid controller uses the energy from the wheels by pumping fluid from the low pressure reservoir into the high pressure accumulator. When the vehicle starts accelerating, this stored energy is used to accelerate the vehicle. This process recovers and reuses more than 70% of the energy normally wasted during braking.
Optimum Engine Control. The engine pump pressurizes and transfers fluid from the low pressure reservoir to the rear drive pump-motor, and under certain operating conditions, to the high pressure accumulator. As in other series hybrid designs, the engine operates at its maximum efficiency sweet spot to achieve optimum vehicle fuel economy.
Shutting Engine Off When Not Needed. The engine can be completely shut off during certain stages of operation, to be activated by the controller only when it is needed. As a result, in stop and go urban city driving engine use is cut almost in half.
|The hydraulic hybrid powertrain. Click to enlarge.|
The powertrain. A high-pressure accumulator stores energy as a battery would in a hybrid electric vehicle using hydraulic fluid to compress nitrogen gas. A low-pressure reservoir stores the low pressure fluid after it has been used by the pump/motor.
The engine pump-motor pressurizes and transfers hydraulic fluid to the rear drive pump/motor and/or high pressure accumulator. The rear drive pump-motor converts the pressure from the hydraulic fluid into rotating power for the wheels, and recovers breaking energy which is stored in the high pressure accumulator.
The hybrid controller monitors the driver’s acceleration and braking, and commands the hybrid system components.
EPA estimates that the added costs for the hybrid components, produced in high volume, for a package delivery vehicle have the potential to be less than $7,000, which would be recouped in less than three years by the lower fuel and brake maintenance costs.
In today’s dollars, the net lifetime savings over this vehicle’s typical 20 year lifespan are estimated to be more than $50,000. If fuel prices continue to increase at a faster rate than inflation, the lifetime savings would be even greater.
EPA and UPS plan to evaluate the demonstration vehicle in on-the-road service during 2006.
EPA is also developing a second UPS demonstration vehicle in a second phase of this partnership in order to explore the cost effectiveness of a different full hydraulic hybrid system configuration under a variety of load and driving cycle conditions.
EPA also plans to install an EPA Clean Diesel Combustion (CDC) engine in the phase 2 vehicle. (Earlier post.) The CDC engine does not need NOx aftertreatment to achieve 2010 NOx standards.
Eaton played a key role in developing this HHV with EPA. The other organizations that contributed to the development of the UPS hydraulic hybrid demonstration vehicles are UPS, International Truck and Engine Corporation, and the US Army-National Automotive Center. Major technical support was provided by FEV Engine Technology, Inc., Southwest Research Institute and Morgan-Olson.