Research On On-line Measurement Of Viscosity And Density Of Autombile Oil

Only under the protection of lubricating oil can the automobile engine,gearbox and other equipment operate normally,so the deterioration of lubricating oil will cause great harm to automobile mechanical parts.The traditional oil quality detection method that change lubricating oil according to mileage or time has poor real-time performance.Therefore,an on-line detector that can detect the viscosity and density of oil online in real time is an urgent need for future vehicles.This paper mainly studies the method of on-line detection of oil viscosity and density based on quartz tuning fork,especially the method of simultaneous detection of oil viscosity and density.The physical properties of quartz piezoelectric crystal,the electromechanical coupling model of quartz tuning fork and the influence of temperature change on the resonance state of quartz tuning fork were studied.Two kinds of measurement principles of viscosity and density based on quartz tuning fork were focused.One is the measurement principle of viscosity and density based on resonance frequency and equivalent impedance,the other is the measurement principle based on quality factor and resonance frequency.Methods of simultaneous measurement of oil viscosity and density based on aforementioned methods were also studied,and the calibration methods for tuning fork based on these two methods were summarized.Then the quartz tuning fork was selected and its modal was analyzed.In this paper,the influence of parasitic conductance and its processing method were analyzed,and the temperature compensation algorithm was studied.The calibration experiment of quartz tuning fork was carried out with standard liquid and impedance meter E4990a.The viscosity coefficient and the density coefficient were measured out for the method based on the resonance frequency and the equivalent impedance,and a three-dimensional curved surface of the viscosity varying with the variety factor and the vibration frequency for the method based on the quality factor and the resonance frequency.The error analysis after calibration showed that the measurement accuracy of the quartz tuning fork is similar to that of similar products at home and abroad.The circuit system of viscosity and density on-line measurement was designed,and software programs such as impedance and resonance frequency detection,resonance frequency quality factor calculation,viscosity and density simultaneous measurement calculation were developed,and have embedded to the hardwere.Experimental research by using the developed software and hardware for some oil products and comparative analysis of two measurement methods based on resonance frequency and equivalent impedance and quality factor and harmonic frequency showed that the measurement method based on quality factor and harmonic frequency has higher measurement accuracy,and can realize simultaneous measurement of viscosity and density.The measurement error of viscosity and density is less than 5%in the range of 6cp-73cp,and less than 1%in the range of 0.750g/cm~3-1.325g/cm~3.