2000 Traverwood DriveAnn Arbor, MI 48105

Phone: (734) 214-4200

www.epa.gov/otaq/technology

United StatesEnvironmental Protection

Agency

National Vehicle and FuelEmissions Laboratory (NVFEL)

The technical organizations that contributed to thedevelopment of the hydraulic hybrid yardhostler are: U.S. EPA, APM Terminals, Parker-Hannifin, Kalmar Industries, FEV, Inc., R. H. SheppardCo., Inc., and Webasto.

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

• Achieve ultra-low pollution emissions• Reduce greenhouse gases• Increase fuel efficiency

By developing cost-effective technologies, theClean Automotive Technology program also en-courages manufacturers to produce cleaner andmore fuel-efficient vehicles. Fleets owners benefitby being able to recoup the initial hybrid systemcosts through lower operating costs within a fewyears.

EPA does not endorse any specific company or enterprise.

EPA-420-F-09-051October 2009

www.epa.gov/otaq/technology

Additional support was provided by:

Port Authority of New York and New Jersey, and the New

Jersey Department of Environmental Protection.

Special Thanks to the Port of Rotterdam for their

cooperation.

Series Hydraulic HybridSeries Hydraulic Hybrid“Yard Hostler”“Yard Hostler”

Using innovative series hydraulic hybrid technology,

EPA and its industry partners have created a highly

efficient and cost-effective hybrid. This system is

projected to improve the stop-and-go fuel efficiency

of off-road container tractors known as yard hostlers

by 50-60 percent and reduce climate change CO2

greenhouse gas emissions by over 30 percent. The

unique energy recovery technology used to stop a

hydraulic hybrid vehicle also reduces brake wear by

up to 75 percent, increasing the net operating sav-

ings substantially.

Even more remarkable, when manufactured in high

volume there is the potential to recoup the hybridi-

zation costs from fuel and maintenance savings in

three to five years.

Hydraulic hybrid vehicles rely on proven tech-

nology which is being evaluated in package

delivery vehicles, shuttle buses, and refuse

trucks.

H O W I T W O R K S

This innovative technology is simple. The main compo-nents in a full series hydraulic hybrid vehicle are:

• High pressure accumulator — stores energy byusing hydraulic fluid to compress nitrogen gas much asa battery is used to store energy in a hybrid electricvehicle.

• Rear drive pump/motor (acting as a motor) —converts pressurized hydraulic fluid into rotating powerfor the wheels .

• Low pressure reservoir — holds the spent fluid afterit has been used by the rear drive pump/motor.

• Rear drive pump/motor (acting as a pump) —captures braking energy by pumping hydraulic fluidback into the high pressure accumulator.

• Engine pump/motor (acting as a pump) — createsadditional high pressure fluid needed to drive the vehi-cle, storing any excess in the high pressure accumulator.

• Hybrid controller — monitors the driver’s accelera-tion and braking, and sends operating commands tothe various hybrid system components.

The three key design features that contribute to im-proving the fuel efficiency of hydraulic hybrid vehiclesare:

1. Regenerative Braking — To slow or stop the

vehicle, the rotating energy of the wheels is used topump fluid from the low pressure reservoir into thehigh pressure accumulator. This stored energy isthen used to accelerate the vehicle. Up to 70 per-cent of the energy normally wasted during brakingis recovered and reused.

2. Engine Shutoff (idle reduction) — Over 40 per-

cent of a yard hostler’s working hours are spentwaiting at the port with the engine idling. The vehi-cle’s engine-off power steering and heating systemsallow the engine to be shut off during these waitingperiods. The unique series hybrid design also en-ables the engine to be automatically turned offwhen it is not needed, such as during braking.These features reduce vehicle emissions, as well asoperating and maintenance costs.

3. Optimum Engine Control — In the full series

hybrid design, there is no conventional transmissionand driveshaft to connect the engine dirctly to thewheels. This frees the engine to be operated at itsbest efficiency “sweet” spot, achieving optimumvehicle fuel economy.

The lifetime fuel savings for thisvehicle’s typical 12 year lifespan couldbe over $35,000 (assuming fuel costs of$3/gallon).

Each high efficiency yard hostler couldsave a terminal operator over 1,000gallons of fuel per year.

A typical yard hostler vehicle used to move containers at a sea port terminal.