| Engine oil has important functions such as lubrication,cleaning,sealing,cooling and oxidation resistance.As the engine is running,the performance and the viscosity of the lubricating oil will gradually decrease.When the oil viscosity reaches the change index,it needs to be replaced to avoid engine wear and failure.Therefore,it is very important to carry out online detection for the viscosity of lubricating oil.This paper designs a new type of engine oil viscosity online detection sensor,the main contents include:Based on the principle of viscosity generation and the traditional rotation method,the research of the new viscosity sensor principle was carried out,and a method for indirectly measuring oil viscosity by motor current is proposed.The theory of fluid mechanics is applied to analyze the lubricating oil flow state and viscous moment when the rotor rotates.At the same time,the working characteristics of the DC motor is studied and related parameters are calculated,the mathematical relationship between the viscosity of the lubricating oil and the speed,torque and current of the motor is determined.And the mathematical model of the sensor was established.For the structural design of the sensor rotor,4 types of rotors are designed.Through the simulation analysis and numerical calculation of the 4 rotors by Fluent,the viscous torque and motor current under different oil viscosity were obtained and compared.The results show that the 4 rotors have certain resolutions for lubricating oil with different viscosity.When the lubricating oil working temperature is 70°C~100°C,the cylindrical rotor viscosity measurement accuracy reaches 0.01A/(mm~2/s),and it has good stability and reliability.The relationship between viscosity and sensor current is obtained by numerical fitting,and the measurement error caused by the density of lubricating oil is further discussed.In addition,the viscosity sensor has been designed with a rotating bearing and seal.Sensor hardware and software are designed according to the principle of viscosity measurement.With the main control board and viscosity detection module as the main hardware,the sensor control and detection circuit are designed,and the sensor data acquisition and processing system is established.The viscosity sensor is processed and tested,including rotor comparison test,sensor calibration test and sensor verification test.The rotor comparison test shows that the four rotors have certain resolutions for different viscosities.The numerical calculations and test results of the motor currents in different oils are close,and the overall relative error is between 0.0467%and 3.365%.Taking the cylindrical rotor as the research object,the current test was carried out in different viscosity oils at 20°C~100°C.The results show that the sensor measurement accuracy is higher in the high temperature oil above 70°C.The calibration test of the sensor is carried out by using the lubricating oil diesel mixture.The calibration equation of the sensor viscosity detection is obtained.The calibration equation is verified by further tests.The error between the test value and the standard value is 2.619%~5.380%.Especially at low viscosity,the sensor has a good detection performance. |
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