Tough sensor makes gas burn better

Troy, MI-The federal government and auto industry continue to wrestle over fuel efficiency and exhaust emissions, trying to find a balance point between cost, safety, and pollution. It's a tough equation for politicians, but technology may provide a solution.

The goal is to burn the perfect proportion of oxygen and gasoline. Engine sensors have historically given a binary answer - is the mixture too lean (extra air) or too rich (extra fuel)?

But a new type of sensor will measure the ratio precisely, allowing engines to burn less fuel under low-power demand, and add more fuel only to accelerate, climb hills, or tow loads. That uses less gasoline, which leads to better fuel efficiency and cleaner emissions.

Delphi Corp. (Troy, MI) has created this "wide-range" sensor, using extensive CAE analysis and lab testing to learn how to manage the extreme temperature and vibration of an internal combustion engine.

"Customers are constantly trying to package sensors in smaller and smaller spaces," says Scott Nelson, a senior project engineer for Delphi. "As vehicle design changes, so do the packaging restraints; but the temperature requirements do not."

Design challenges include operating conditions from -40 to 1,000C. One way to handle that heat is with larger sensors-up to 66 mm tall-which hold their critical components further from the fire. But their size makes them more vulnerable to vibration, and tougher to install.

So Nelson designed a possible solution in 3D CAD, then took a 2D symmetric slice of the model and began running dozens of iterative tests with FEA from ALGOR (Pittsburgh, PA). Using its Heat Transfer Analysis Extender package, he put the virtual sensors through virtual hell, with 1,000C exhaust temperature, ambient heat of 150C, and no air flow.

He used the results to optimize the geometry and material properties, and reduced temperature at two locations by 20%. And his tests determined an optimal length of 51 mm (depending on the configuration).

Then Nelson verified his test results with a dynamometer in the lab, and found they agreed to within 4%. Those physical tests were even worse, he says: "accelerated extreme high temperature testing(>1,000C), thermal cycling (1,000 to 150C), extreme vibration, poisoning tests, physical testing (drop, impact, corrosion, etc.), and water immersion."

Sounds like a smooth design process. But until he got ALGOR, Nelson faced frustrating delays in waiting for analysis results from specialists in another department. When he got FEA on his desk, Nelson got results in seconds, allowing him to test dozens of creative iterations and use the real-time feedback to perfect his design. Using a simplified 2D slice speeded the process even more.

"As a product designer, I find that performing my own analysis leads to a much more interactive and informed design process," he says. "I can do far more iterations than would be logistically feasible if I turned the analysis work over to someone else."

ALGOR's Windows-based interface makes it easier for designers, not just specialists, to run analysis. Its latest version uses a single window to run various analyses, and to displays results for each. And the company's inCAD feature lets users capture CAD geometry from various sources; it's completely associative with Solid Edge and SolidWorks, and accepts Pro/ENGINEER, Autodesk, and Cadkey data. Its Superdraw III feature is a precision finite element model-building tool, still used by some specialists instead of 3D CAD.

Nelson uses Solid Edge to create his CAD models, and collaborates with other Delphi designers using Unigraphics. He also uses Superdraw III to make some simple models, and Excel and C++ to model mathematics.

His new, wide-range sensors are designed for use in 2004-model, lean-burn cars, though Nelson wouldn't specify which brand. They can also be used in standard (stoichiometric) and diesel engines, he says.

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