RESEARCHERS DEVELOP NEW TECHNIQUE TO DETECT ENGINE MISFIRES
COLUMBUS, Ohio -- Researchers here have developed a new way to detect engine misfire in vehicles, an approach that is more accurate than the systems currently available.
The method will help auto manufacturers meet new pollution control regulations in California that require warning lights in cars that alert drivers when the engine is misfiring. Other states are also looking at enacting similar legislation.
Engine misfire can lead to the release of excess exhaust emissions into the environment and can damage the catalytic converter in an automobile, said Giorgio Rizzoni, an assistant professor of mechanical engineering and researcher at Ohio State University's Center for Automotive Research.
Rizzoni and his colleagues developed a technique that uses existing on-board sensors to look for a change in the engine's velocity that is characteristic of a misfire. It can distinguish between a drop in energy caused by a misfire and changes caused by road conditions or driver action.
"You can't hear an engine misfire," he said. "In fact, even an experienced mechanic may not detect the presence of misfire.
That's one reason it's important to be able to detect a misfire."
Regulations in California and in Europe require automobile manufacturers to provide on-board detection of engine misfire in all new cars. The sensors are part of an emission control system called On-board Diagnostics phase II.
A misfire is a complete lack of combustion in one or more cylinders in an engine and is most commonly caused by bad spark plugs or a faulty fuel injector system.
In a normal crankshaft revolution, air and fuel flows through an inlet valve and is compressed by the engine. A spark is applied, causing an explosion that releases energy to the piston. The piston raises, an exhaust valve opens, and the exhaust gases are sent to the catalytic converter, which oxidizes and reduces the gases. The exhaust is filtered and released through the tailpipe.
When an engine misfires, it produces a mixture of air and fuel which the engine cannot burn. The mixture is sent to the catalytic converter, which normally operates at temperatures of greater than 800 degrees Fahrenheit. The high temperatures cause the mixture to burn. Continual combustion in the catalytic converter can cause the device to malfunction and release excess exhaust.
Manufacturers have implemented different types of misfire detection techniques in new cars, but Rizzoni said many of those methods have met with complaints of false alarms.
Engine misfire cause a momentary drop in engine torque -- the energy sent to the engine following combustion. Most misfire detection sensors look for any drop in energy, but these drops can be caused by outside events, such as bumps in the road or changing gears.
"If one of the cylinders misfires, it will have disturbed the natural rotation of the engine in a very special way that is different from a disturbance caused by an external factor," Rizzoni said. "Our technique looks for a pattern that is unique to engine misfire."
Under normal conditions, engine combustion follows a specific periodic pattern. Rizzoni's system is tuned into the normal crankshaft revolution and is highly sensitive to the change in engine pattern that occurs when a cylinder misfires. At the same time, it is insensitive to outside "noise," or disturbances that occur outside the engine.
"Our method takes the measurement of engine rotation that is electronically provided by sensors in the on-board computer system and conditions it using a microcomputer to eliminate the noise as much as possible, minimizing the probability of error in detecting the misfire," Rizzoni said.
Rizzoni's technique has been tested by several auto manufacturers in the United States, Asia and Europe. Rizzoni developed the technique with William Ribbens, professor and director of the Vehicular Electronics Laboratory at the University of Michigan.
The research was published in a recent issue of the Journal of Dynamic Systems, Measurement and Control.
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Contact: Giorgio Rizzoni, (614) 292-3331
Written by: Kelli Whitlock, (614) 292-9475