Abstract
In this research, we investigated biodegradable hydraulic oil temperature characteristics by using an oil sensor and verified the correlation between sensor measurement values and oil properties as biodegradable hydraulic oil deteriorated, to apply oil condition monitoring to biodegradable hydraulic oil. The test results of temperature characteristics showed that biodegradable oil and mineral oil had equivalent kinematic viscosity characteristics. In contrast, the density of biodegradable oil was approximately 1.05 times that of mineral oil, and the dielectric constant was approximately 1.5 times that of mineral oil, showing a linear change trend with temperature change. This confirms that temperature correction is possible using the same method as used for mineral oil. Test results for degradation showed that, for biodegradable hydraulic oil, the change rate for total acid number increase in the sensor value was smaller than that for mineral oil, indicating that a new evaluation criterion is needed. Furthermore, it was confirmed that mineral oil, biodegradable oil, or a mixture of the two can be roughly estimated in a hydraulic excavator by using the characteristics of the difference in density and dielectric constant between biodegradable oil and mineral oil.
