By replacing a paper-based design process with The Mathworks Inc.'s software tools for model-based design, Nissan designed an emission reduction system that was first implemented in its 2000 Sentra Clear Air (CA) model. Sentra CA became the first gasoline-powered vehicle to be CARB certified for the PZEV standard.

"If you drove 10 miles to work, then home in the Sentra, you would still produce less pollution than an ordinary car sitting in a driveway all day with its engine off," claims Shigeaki Kakizaki, assistant manager, Engine Management System Engineering Group No. 2 at Nissan.

"It is difficult to reduce development time and costs with a traditional development process," says Kakizaki. "We had reached the limit of our capabilities and needed a new process."

To achieve objectives, Nissan would need to reduce development time, implementing a new, sophisticated controls strategy, and minimize system costs by reducing the number of sensors to achieve low emissions.

Nissan used Matlab, Simulink, and Stateflow from The Mathworks Inc. to develop models of its emission-control strategy. These models became the main tools for the system, which engineers reused throughout the development process. Using Simulink, engineers first created a plant model of the engine to validate designs and refine the emission control strategy.

"Simulink enabled us to perform simulations early in the design process," says Kakizaki. "This helped us quickly validate our design ideas and refine our control strategies." Kakizaki's team validated algorithms on real engine hardware and met the emission requirements. They then began implementing their design and developing software.

For third-generation emission control, Nissan used Simulink to implement a "Sliding Mode Control" strategy—one of the latest advancements in emission control. Nissan applied this strategy to its Maxima, Quest, Murano, Z-car, and Titan trucks, and was able to reduce the number of sensors without losing control capability.

"Simulink helped us to move an advanced control strategy like Sliding Mode Control from research to implementation in production vehicles," says Kakizaki.

Nissan is currently improving testing and verification by applying a concept they call "model-based testing." By generating test cases from Simulink models and comparing results against the actual hardware implementation, model-based testing will reduce program verification time and software quality quantification efforts. Nissan is working with MathWorks' partner, Reactive Systems, on the development of this technology.

"Evolving model-based design further into the testing phase will provide substantial improvements to the overall efficiency of our development process," notes Kakizaki. The improved tools and processes include:

• Reducing development time by 50%. "When applying advanced control theories, Matlab and Simulink are far superior to in-house tools for analysis and design," says Kakizaki. "MathWorks tools helped reduce our programming by half and improved communication among our engineering teams."
• Winning the U.S. Environmental Protection Agency Climate Protection Award for innovations in improving fuel economy and reducing zone-depleting hydrofluorocarbons. As of this writing, Nissan was the only automaker to receive such a commendation.
• Reducing the number of sensors needed, a strategy first applied to 2003 Nissan Sentra models.