Sensors for a lubrication-monitoring-system

For automotive applications, the condition of the engine oil is estimated by means of indirect methods mainly relying on operating parameters like engine speed, performance, and temperature. A study on the development of an on-line lubrication-monitoring system for combustion engines was carried out. The system was based on a set of physical sensors being directly immersed in the lubricating oil, and an algorithm processing the associated sensor signals. The viscosity of mineral oils could be reliably measured by a microacoustic sensor. The sensor was not suited to detect the viscosity grade of an engine oil containing viscosity modifier additives of high molecular weight. Experiments with artificially deteriorated oils indicated that the relative increase in the sensor signal provides more direct information on the oil's age in terms of oxidation, than the classically measured macroscopic kinematic viscosity. The sensor signal correlated much better with the degree of oxidation of the oil because oxidative deterioration causes an increase of the base oil's viscosity. The measured permittivity of used diesel engine oil samples yielded a strong correlation with the soot content only. This is an abstract of a paper presented at the Technische Akademie Esslingen 14th International Colloquium Tribology (Stuttgart/Ostfildern, Germany 1/13-15/2004).