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Enova Hybrid Drive Systems Significantly Reduce Emissions

Recent dynamometer test results conclude that IC Bus school buses using post-transmission hybrid drive systems from Enova Systems can improve fuel efficiency by more than 70 percent compared to standard diesel-powered school buses. The Enova hybrid drive systems installed in the IC Bus school buses also significantly reduce carbon dioxide, NOx and particulate matter emissions. Advanced Energy, a resource for innovative and market-based approaches to energy issues, has facilitated the adoption of IC Bus plug-in hybrid school buses in school districts in the U.S. and Canada.

These route-specific test results, along with the recent announcement by IC Bus of their intention to reduce the price of their school buses equipped with plug-in hybrid electric systems by up to $40,000, shows that significant progress has been made in developing, engineering and deploying fuel efficient and cost competitive hybrid electric buses.

“Our unique post transmission system offers original equipment manufacturers a non-invasive solution to enter the hybrid vehicle market in either the retrofit or new vehicle segment. Being the only supplier of this technology offers us and our customers a tremendous competitive advantage,” states Mike Staran, Enova’s President and CEO.

The extensive series of fuel consumption and emissions tests were conducted to simulate actual route cycles and conditions using the West Virginia University Suburban Test Cycle. The tests were conducted at an independent commercial laboratory accepted by the California Air Resources Board that is properly equipped to perform specialized tests in accordance with applicable federal and California test procedures.

Tests were conducted on the following buses equipped with the Enova plug-in hybrid electric systems:

  • 2007 model year IC Bus CE Series school bus with a VT365 engine and Allison 2500 transmission
  • 2008 model year IC Bus CE Series school bus with a MaxxForce 7 engine and Allison 2500 transmission

The results shown below reflect a comparison of the plug-in hybrid buses to identical IC Bus school buses with standard diesel engines and drive systems. These results are based on the route-specific conditions defined by the West Virginia University Suburban Cycle and do not necessarily reflect fuel consumption and emissions data that may be generated from other route conditions. Selecting routes with frequent stops and starts and minimal highway miles allows the bus to get the most out of the hybrid system and is a key element to obtaining similar results.

Test Results from Both 2007 and 2008 IC Bus CE Series with Enova Systems

Fuel Economy:

  • Over 70% increase over the standard diesel system


  • Over 40% reduction in CO2
  • Over 30% reduction in Particulate Matter
  • Over 20% reduction in NOx

“We are very pleased with the test results, and will now focus our attention to understanding school bus routes and determining the types and duration of routes that can strongly benefit from plug-in hybrid electric systems,” says Ewan Pritchard, Hybrid Program Manager for Advanced Energy. “This proves that significant benefits are available as long as we put these in the right place,” Pritchard states.

“We believe these results show the success of our system in obtaining fuel economy and air quality improvements without major changes to standard production engines,” said David Hillman, Marketing Director for IC Bus. “But this is only the first phase of development. IC Bus and Enova are committed to developing ‘engine off’ technology to obtain additional fuel economy and emissions control improvements.”

In March 2007, the first plug-in hybrid electric school bus was delivered to Manatee County Schools in Bradenton, FL., by IC Bus, Enova Systems and Advanced Energy. Today, 19 hybrid school buses are on the road in 11 states thanks to the efforts of Advanced Energy and its partners.

Enova’s unique post transmission parallel hybrid system is one in which the electric drive system is integrated behind the factory-installed transmission. The Enova Hybrid has proven to be a non-invasive system that requires little or no modification to OEM chassis, body or instrumentation. However, the hybrid systems are designed to communicate with many other electronic systems on the bus, such as engine, transmissions, emissions and ABS systems controllers. An important competitive advantage that IC Bus and Enova Systems have generated by working together is to integrate and coordinate all of these electronic systems on the bus.

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