Sensor Gives Early Warning of Engine Failure

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U.S. Army Research Laboratory scientists have reported inventing a method to detect and predict mechanical failure due to lubrication loss in machines and movable components, by monitoring gas concentration in a gearbox or machinery enclosure.

According to a patent for the process dated Aug. 25, imminent catastrophic failure can be predicted when torque or power transfer is lost. An estimate of when failure will likely occur through the operation of the machinery may be determined after the liquid lubrication supply has ended or becomes inadequate to lubricate the machinery components effectively.

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The scientists –Stephen Berkebile of Havre de Grace, Maryland, and Kevin Radil of Brunswick, Ohio – said that while attaching temperatures sensors to the gearbox housing could provide some useful information on the gearbox’s health, it doesn’t offer a real-time approach. Instead, a delay would occur that is equal to the time it takes for the heat generated at the failing gear and bearing contacts to be transmitted to the housing.

In a different method, sensors located on the airframe and engine collect vibrations through a health monitoring system. If any vibration reaches a critical level, they noted, the pilot is trained to safely land the aircraft. “Using vibration measurements as an indicator for a loss-of-lubrication event in the machinery may result in a late report to the operator,” they wrote.

The scientists instead invented a different solution for detecting and predicting mechanical failure of movable components. It calls for setting a predefined threshold gas concentration level in a substantially enclosed machine.

“By monitoring the concentration of gas species and the rate of change in concentration of the gas in the gearbox or machinery enclosure after the supply of the primary lubricant ends, determinations may be made about the time to failure and the damage state,” the inventors stated in the patent’s abstract. “The determinations may be based on thermomechanical and chemical processes, on measurement of a baseline system, or by setting a threshold of expected change in gas concentration.” The system can then transmit the information for further decision-making and response.

The patent’s background contends that such a system would be advantageous for helicopters. The scientists explained that a number of sensors that are part of the lubrication system could act as possible indicators for loss-of-lubrication in a rotorcraft gearbox. However, they noted, their limited functionality generally makes them unable to provide the detailed information required to estimate machine operating life until total failure nor a gearbox’s health during the event.

“When the lubrication system loses pressure, the pilot of the aircraft receives a warning that a problem has occurred, but it does not indicate the severity of the event or how long the gearbox is expected to function,” they noted. “The temperature of the oil sump is collected and usually transmitted to the cockpit, but a loss of the lubricant renders this temperature meaningless until the housing to which it is attached increases in temperature, perhaps after the gearbox has already failed.”

According to a report on the invention by TechLink, a key benefit is the provision of indications to an operator or automated system control unit that a situation of loss-of-lubrication has occurred in high speed gears, gearbox, or machinery. This includes reports on the time that is estimated until catastrophic failure occurs, and the ability to report if catastrophic failure is imminent. The method is also designed to prevent costly wear, damage, and failure of expensive machinery by indicating when loss of lubrication has started in the early stages. Since it is designed to continuously monitor the concentration change of gases in real-time, the health of the gears is continually known and the time to failure can be predicted. Techlink is the authorized, nationally focused technology transfer partnership intermediary for the U.S. Department of Defense and Department of Veterans Affairs.

The patent may be viewed at the United States Patent and Trademark Office website.