Reduce grIncrease fuel 

By developing

facturers to 

EPA’s Clean Automotive Technology Program con-ducts this innovative research primarily to: 

• Achieve ultra-low pollution emissions • eenhouse gases • efficiency 

 cost-effective technologies, Clean Automotive Technology also encourages manu-

produce cleaner and more fuel-efficient vehicles.  Fleets and consumers benefit by being able to recoup the initial hybrid system costs through lower operating costs within a few years. 

P A R T N E R S  C L E A N  A U T O M O T I V E  T E C H N O L O G Y  

The organizations that contributed to the development of the UPS hydraulic hybrid demonstration vehicles are: U.S. EPA, UPS, Eaton Corporation, In-ternational Truck and Engine Corpora-tion, and the U.S. Army – National Automotive Center. Major technical support was provided by FEV Engine Technology, Inc., Southwest Research Institute and Morgan-Olson. 

United States  EPA420-F-06-043 Environmental  June 2006 Protection Agency Office of Air and Radiation 

H Y D R A U L I C  H Y B R I D S  

The Most Efficient  Lowest Cost  

Hybrids 

C O S T  E F  F E  C  T  I  V  E  H Y  B R  I  D  S  

CL

EA

N A

UT

OM

OT

IVE

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NO

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Environmental Protection Agency 

2000 Traverwood Drive Ann Arbor, MI 48105 Phone: (734) 214-4200 http://www.epa.gov/otaq/technology  

U.S. EPA National Vehicle and Fuel 

Emissions Laboratory  (NVFEL) 

World’s First Full Series Hydraulic Hybrid Delivery Vehicle Prototyped in a UPS “Package Car” 

http://epa.gov/otaq/technology/#hydraulic 

http://epa.gov/otaq/technology/#hydraulic

Through the use of innovative hydraulic hybrid 

technology EPA and its industry partners have 

been able to create the most efficient and 

cost-effective powertrain technology in the 

world. EPA has been able to improve city fuel 

economy of a UPS package car by 70% and 

reduce CO2 greenhouse gas emissions by 40%. 

The unique energy recovery technology used 

while braking reduces brake wear by 75% in-

creasing the net savings substantially. 

What is even more astounding is that the addi-

tional cost for this technology manufactured in 

high volume has the potential to be less than 

15% of the price of the base vehicle.  At cur-

rent fuel prices, this technology will pay for 

itself in two to three years.   

H H V - H Y D R A  U L I C  H Y B R  I D  V E H I C L E S   H I G H  E S T  E F  F I C I E N C Y  -  L O W  E  S T  C O S T  

H O  W  I T  W O  R K  S  

This innovative technology is simple. The main com-

ponents in HHVs are: 

• The high pressure accumulator stores energy as a battery would in a hybrid electric vehicle using hydraulic fluid to compress nitrogen gas . 

• The low pressure reservoir stores the low pres-sure fluid after it has been used by the pump/motor. 

• The rear drive pump/motor converts the pres-sure from the hydraulic fluid into rotatingThe net lifetime savings over this 

vehicle’s typical 20 year lifespan would be over $50,000.  

A fleet owner operating one of these high efficiency vehicles would save up to 1,000 gallons of fuel each year. 

There are three key design features enabling an 

HHV to provide maximum fuel efficiency: 

1.	 Regenerative Braking When stopping the vehi-

cle, the hybrid controller uses the energy from 

the wheels by pumping fluid from the low pres-

sure reservoir into the high pressure accumu-

lator. When the vehicle starts accelerating, 

this stored energy is used to accelerate the 

vehicle. This process recovers and reuses over 

70% of the energy normally wasted during 

braking.  

2.	 Optimum Engine Control The engine pump pres-

surizes and transfers fluid from the low pres-

sure reservoir to the rear drive pump-motor, 

and under certain operating conditions, to the 

high pressure accumulator.  In the full series 

hybrid design, there is no conventional trans-

mission and driveshaft connecting the engine 

to the wheels freeing the engine to be oper-

ated at its maximum efficiency “sweet” spot to 

power for the wheels, and recovers  braking achieve optimum vehicle fuel economy. 

energy which is stored in the high pressure 3.	 Shutting Engine Off When Not Needed The unique

accumulator Hydraulic Hybrid Vehicles (HHVs) rely on	 hybrid design not only allows the engine to be 

proven innovative technology which can be • The engine pump/motor pressurizes and trans-	operated at its maximum efficiency, but also

fers hydraulic fluid to the rear drive pump-applied to light duty work trucks, SUVs and 

motor and/or high pressure accumulator  enables the engine to be completely shut off 

heavy duty urban vehicles such as city transit	 during certain stages of operation because it is • The hybrid controller monitors the driver’s ac-

buses and garbage trucks. celeration and braking, and commands the 

activated by the controller only when it is 

hybrid system components.  needed. As a result, in stop and go urban city 

driving  engine use is cut almost in half.