Inside job: sensors move into cylinders

  • 10-Mar-2009 09:04 EDT
Sensors are being embedded deeper inside engines. (General Motors)

­One way to get the utmost in precision is to place sensors right in the middle of the activity they are observing. That is si­mple for jobs such as airflow, but it is extremely difficult when engineers want to place sensors deep inside the engine.

These sensors are small si­licon chips, which is both good and bad. Small size makes it easier to embed them in cylinders. But silicon is fragile, so it has to be protected from high temperatures and harsh materials such as gasoline.

Those are big challenges slowing the adoption of in-cylinder sensing, which will provide exacting detail on engine operation. The sensor provides a feedback loop on the combustion process, which positively impacts both emissions and efficiency,” said Kristoff Coddens, Sensor Business Unit Manager at Melexis.

Along with size and ruggedness, sensors for this application must be fast enough to follow combustion-process dynamics. They are already seeing use in diesels, where sensors are integrated into glow plugs. There is optimism that they will migrate to gasoline before long.

“Cylinder-pressure sensing is likely to become a mainstream technology in the near future,” Coddens said. “It is currently being offered on high-end auto-combustion engines with glow plugs. The next step will be to offer the sensor as a stand-alone device on gasoline engines.”

This probably will not occur overnight. Observers note that it will be a while before this new advance is proven effective enough for widespread use.

“It looks like the Holy Grail, in cylinder pressure and temperature sensors, [both] becoming a reality outside the lab,” said Dave Monk, Automotive Sensors Product Manager at Freescale Semiconductor. “The industry’s looking at parts that may see use in five to seven years.”

Some note that, to improve ruggedness, engineers may have to turn to silicon-on-insulator, silicon gallium arsenide, or other alternatives. “In-cylinder sensors may not even be the same type material; they may be something besides silicon to get to the temperature needed and to meet corrosion levels,” Monk said.

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