DETROIT – Nissan Motor Co. Ltd. says it has cracked the code to developing a smart hybrid electric vehicle control system, employing the navigation system to optimize the battery “state of charge” and improve fuel economy in its prototype hybrid.

Using a Tino hybrid vehicle, Nissan engineers plugged data from the vehicle’s navigation system – including real-time traffic data from Japan’s Vehicle Information and Communication System (VICS) – to determine the topographical layout of the road, as well as traffic flow.

The data compiled by the navigation unit and sent to the powertrain control system includes: road classification (whether it is an expressway, 2-lane, etc.), congestion level (as determined by the data supplied by VICS), road grade and exact distance of section of road measured.

The data was used to provide precise control of the vehicle’s powertrain control system, which adjusted the use of the engine and electrical power depending on traffic and road conditions.

Nissan engineer Yoshitaka Deguchi, who presented the auto maker’s findings during the Convergence 2004 conference here, says the navigation system data allows the vehicle to know ahead of time whether there is a downhill or uphill grade ahead and adjust the powertrain system accordingly.

For example, the battery’s charge state could be reduced in advance of entering a downgrade, at which point the energy provided by the vehicle’s regenerative braking could be recovered and used to replenish the battery.

“In a traditional system, the energy regenerated during a downhill maneuver would be lost because the battery would not have been used beforehand,” he says.

Deguchi says the use of navigation-system and traffic-control data could extend the life of the batteries used in hybrid powertrain systems, while also conserving fuel.

In real-world tests in Japan, Deguchi and his colleagues discovered the benefits of using navigation-system data. During their first test, which was run for 25 miles (41 km) through various elevations up to 2,952 ft. (900 m), the team measured a 3.5% improvement in overall fuel economy, when compared with a traditional hybrid vehicle.

The second test, which was conducted on a downhill 14-mile (22-km) route, netted a 7.8% improvement in fuel efficiency, while the final 26-mile (42-km) test on mainly congested freeways, provided a 0.5% improvement.

Deguchi says the minimal improvement in city driving is expected, because hybrid powertrains already are designed to provide maximum efficiency in stop-and-go city driving.