1.0. INTRODUCTION NCAT, formerly known as EPA's Clean Automotive Technology program, has been researching technology systems to improve vehicle fuel economy and reduce greenhouse gases since the early 1990's. In 1993, President Clinton initiated the Partnership for a New Generation of Vehicles (PNGV), a cooperative research and development program comprised of several Federal Agencies and the U.S. Council for Automotive Research (USCAR), which was comprised of the three U.S.-based car companies. The centerpiece of PNGV was to “Develop vehicles to achieve up to three times the fuel efficiency of comparable 1994 family sedans.” ( National Research Council of the National Academy of Sciences 2001 ) The EPA played a key role in this public-private partnership and directed substantial research activities towards demonstrating a new type of hybrid technology that used hydraulic rather than electric components.From 1993 through 2004, NCAT worked through various automotive industry partnerships to demonstrate the potential of hydraulic hybrid vehicle (HHV) technology to significantly reduce greenhouse gases (GHGs) and increase fuel economy in light-duty passenger vehicles, sport utility vehicles and pickup trucks. From 2005 through 2012, NCAT demonstrated series HHV solutions for commercial package delivery vehicles, non-road yard-hostler service trucks, and finally , passenger shuttle buses. Descriptions of EPA's demonstration vehicles can be found at: www.epa.gov/otaq/technology/ or www. archive.epa.gov/otaq/technology During the HHV research program, EPA obtained over 50 patents for hydraulic components and control strategies. ( Gray Jr, “Methods of operating a series hybrid vehicle” 2008 ) (Gray Jr, “Hydraulic hybrid vehicle method of safe operation” 2012 ) The work in this area has stimulated a wide range of other research, demonstration, and commercialization projects. ( Beretti 2012 ) (Gallo 2014 )Design and Demonstration of EPA's Integrated Drive Module for Commercial Series Hydraulic Hybrid Trucks and Buses John Kargul, Andrew Moskalik, Kevin Newman, Daniel Barba, and Jeffra Rockwell US Environmental Protection Agency ABSTRACT The United States Environmental Protection Agency's (EPA) National Center for Advanced Technology (NCAT), located at its National Vehicle and Fuel Emissions Laboratory in Ann Arbor, Michigan, has been a global leader in development and demonstration of low-greenhouse gas emitting, highly fuel efficient series hydraulic hybrid drivetrain technologies. Advances in these exciting new technologies have stimulated industry to begin manufacturing hydraulic hybrids for both commercial truck and non-road equipment markets. Development activities are continuing for other markets, including light-duty vehicles. Given the commercial emergence of these low-greenhouse gas emitting series hydraulic hybrids, EPA has passed the leadership for further development to industry. This paper focuses specifically on the design and demonstration of the final series hydraulic hybrid drive for commercial trucks and buses as designed, built and demonstrated by EPA, incorporating many of innovative hydraulic technologies designed and advanced throughout EPA's hydraulic hybrid program. The unique integrated hydraulic drive module and its transmission in a series hydraulic hybrid vehicle (HHV) configuration were installed in a 30-foot class 6 diesel midibus. This HHV was able to achieve 50-180% better mpg over various urban stop-go drive cycles and 30% better mpg over the EP A highway cycle in chassis dynamometer testing. The paper shows design, control and integration techniques necessary for a cost-effective series hybrid for the commercial truck and bus market. Benefits include significant improvements in hydraulic pump/motor efficiency , maximum fuel economy for stop-go cycles while also improving mpg on highway operation, simple installation and removal of system components, and incorpor