NREL Analysis Finds Fuel Savings in Route-Based Controls for Hybrid Electric Vehicles
November 28, 2007
After investigating advanced control strategies for hybrid electric vehicles (HEVs), researchers in NREL's Vehicle Systems Analysis team have modeled a promising new approach that could reduce fuel consumption in energy-efficient HEVs even more. In fact, the new approach could result in 2% to 4% more fuel savings during several drive cycles.
With this new approach, known as route-based control, the HEV's control system utilizes specific information about an upcoming driving profile to help ensure fuel-efficient operation of the vehicle on the particular route anticipated. The route predictions used for the approach could be obtained "on the fly" with the assistance of a Global Positioning System (GPS) navigation device in the vehicle.
"Today's HEV controls do not necessarily provide optimal performance during all travel patterns because of operating limits associated with the vehicle's battery," said Jeffrey Gonder, NREL Vehicle Systems Analysis team member. "Integrating predictive information about the upcoming driving route into the vehicle controller's decision-making capability could improve fuel efficiency at potentially minimal cost, since relatively modest changes to the HEV control software would be the only requirement."
Gonder noted that the savings are limited by practical considerations, such as computational time and the need to work with a vehicle's existing control architecture. "But the aggregate fuel displacement could be considerable if this approach were applied across the entire HEV fleet," he said. "For instance, based on another NREL study that estimated the total U.S. HEV fleet fuel consumption in 2006, reducing HEV fuel use by 3% across the board would save nearly 6.5 million gallons of fuel annually."
Potential follow-on work for the project includes the following:
- Collaborations with an HEV R&D partner to demonstrate route-based HEV control benefits in hardware
- Further investigation of the sensitivity of the approach to variations in drive cycles
- Application to a plug-in HEV (PHEV) configuration
- Using route-based control enhancements to extend battery life, reduce vehicle emissions, or achieve other benefits.
Results (PDF 650 KB) of NREL's research and simulations will be published at the SAE World Congress in April 2008. For more information, contact Jeff Gonder, NREL, 303-275-4462, or jeff_gonder@nrel.gov. Download Adobe Reader.
NREL Researchers Estimate Fuel Savings from Hybrid Electric Vehicles
September 28, 2007
Hybrid electric vehicles (HEVs) saved close to 230 million gallons (about 5.5 million barrels) of fuel between 1999, when they were first introduced into U.S. markets, and 2006, according to estimates from an analysis conducted at NREL by researchers in the Vehicle Systems Analysis team of the Center for Transportation Technologies and Systems.
NREL's researchers used a combination of sales and fuel economy data to estimate the total amount of fuel saved by HEVs in comparison to the amount that would have been consumed by conventional vehicles during the same period. They based the fuel economy data on new mpg ratings from the Environmental Protection Agency (EPA) as well as older EPA ratings and the miles-per-gallon values reported by drivers.
They also made use of VISION modeling software developed by Argonne National Laboratory to determine the total number of HEVs in use in a given year and estimate HEV stock. The stock estimates and sales data helped in estimating fuel savings.
Kevin Bennion, a research engineer in the Vehicle Systems Analysis team, said that sales of HEVs have increased an average of 72% per year for the past five years. The sales-weighted average HEV fuel economy in 2006 was 35 mpg for new models sold in the United States.
Team leader Matthew Thornton added that, as HEV technologies continue to mature and sales keep increasing, these vehicles will have a significant impact on transportation fuel use in our nation.
For more information, see the full press release and contact NREL Public Relations at (303) 275-4090.
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy, operated by Midwest Research Institute and Battelle.
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