The Research On Trafficability Of Tractor Under Soft Clay Condition

Tire,the one and only vehicular component that has direct contact with road,plays an important role in the vehicle power performance.Especially for agricultural vehicles like tractors,the roads that these vehicles operate on provide poor adhesion condition making the driving wheel sliding,as a result,decreasing the operating efficiency.Therefore,in depth study on the tire trafficability is necessary to improve the trafficability of the tractors running on soft ground such as farm lands.This thesis mainly uses the empirical method to study the trafficability of tractor,trying to use the magic formula of tire on rigid pavement fitting the data of traction coefficient and slip on soft clay road.based on this we build up the tractor prediction model.The main contents of this thesis are as follows:(1)Theoretical analysis of tire trafficability.At first,the forces and motion states of the tire on soft ground were analyzed and the trafficability evaluation indexes were summarized.Besides,the dimensional analysis method was adopted to theoretically analyze the deformation and trafficability of tire.The trafficability coefficient a in the WES empirical formula was modified and the influence from tire pressure on trafficability was amplified.The simplified and theoretical formula for prediction of tire deformation and trafficability was built which offered guidance for latter tire deformation tests and single wheel trafficability experiments.(2)Design of the tire deformation tests.By the dimensional analysis method,the tire deformation tests were designed.The tire loads test bench was built according to tests requirements and the displacement sensor on that bench was calibrated.Deformation under different loads and pressure were tested,the data obtained was studied to fit the tire deformation prediction formula and modify the coefficient a in the WES empirical formula.(3)Design of the single wheel trafficability test.The dimensional analysis method was adopted to research tire trafficability,based on which the single wheel trafficability experiment was designed.Due to the measurement error of the traction force was comparatively large,the dragging part of the soil bin bench was improved.Besides,the sensors on that bench(dynamic torque sensor,tension and compression sensor)were calibrated and the data collection program was written based on Labview.The soil finishing craft for soil bin was studied and the water content,bulk density and cone index of soil in farm land were measured before experiments to simulate the soil in the open field.The data obtained was fitted by magic formula,within which the variables were determined by using genetic algorithm.Thus,the prediction model for tire trafficability was established.(4)Build real vehicle testing system and design farm land experiment.Forces analysis of the whole tractor was conducted to build the trafficability prediction model for the vehicle based on the single-wheel trafficability model.Then,the trafficability test system was developed based on the SNH550 tractor,the main contents of which includes,?design and calibrate the torque sensor of the driving wheel;?design the slip ration measurement scheme,GPS was adopted to evaluate the tractor speed and the Hall speed sensor designed was used to measure the speed of the driving wheel;?determine the traction force measurement scheme then calibrate the tension and compression sensor;?finish the data collection program based on Lab VIEW.The farm lands experiments was carried out by using the modified tractor,the data collected were compared to that from prediction,with the finding that though the gap between two data was comparatively large,them share the same tendency which implied that the modified magic formula can be applied to the vehicle trafficability prediction on soft ground.