| The all-terrain tracked vehicles are widely used in many fields such as transportation,emergency rescue,and forest fire protection.For this kind of tracked vehicle,the track is composed by a rubber track and rigid grousers connected by bolts,that is to say a rigid-flexible coupled track.In addition,the road wheels of the track system without support sprocket are non-pneumatic elastic tires,and the sprocket and idler wheel are attached with nylon.What’s more,an independent suspension with torsion bar spring is applied in the vehicle.Based on the unique configuration of the vehicle,the existing methods for analyzing the traditional tracked vehicle are not enough for this type of articulated tracked vehicles.In this thesis,it explored the mechanism of track-ground coupling for the articulated vehicle.The research on the ground pressure,fatigue life of track and initial track tension were conducted,which can provide theoretical references and engineering value for the vehicle.Based on the finite element theory,the rigid-flexible coupled track was divided into flexible and rigid elements.Their coupling relationships with the soil were analyzed respectively according to the existing mechanism rules.A mathematical model of predicting ground pressure under the rigid-flexible coupled track for straight driving was proposed which can contain the key information of soil and vehicle.Then the ground pressure model for steering driving,pivot steering and climbing were constructed according to their kinematics and dynamics equations.The results obtained from the detailed model were compared with the results of vehicle tests.The results shown that the predictions made by the detailed model were in good agreement.The mathematical models provided the basis on research for the fatigue life of track,and optimization of initial track tension.On the basis of strength theory and vehicle terramechanics theory,the mechanics model of the interaction between track and soil was created.The stresses of track resulted from the sprocket,road wheels,idler wheel and soil were obtained.Then,the fatigue life of track was calculated based on Manson-Halford model.Furthermore,the effects of track system,soil characteristics to the fatigue life were analyzed in detail.The methods to approve the fatigue life of track were proposed which can provide a direction for the design of track system.A simulation model of an all-terrain articulated tracked vehicle was constructed,and PID control method was introduced to control the driving state.Furthermore,the vertical load and vertical displacement of road wheels under different conditions and soil characteristics were studied.Then the ground pressure under road wheels were deduced.The proposed theoretical results were further verified by the simulation model.The pressures of steering hydraulic cylinder under driving steering and pivot steering were obtained,and their change trend were basically consistent with the experimental results.The simulation model for fatigue life of track was also established.Therefore,the fatigue life of track under different track system parameters and soil characteristics were simulated,which further verified the theoretical model of fatigue life.The relationship between the initial track tension and the vibration characteristics of track system was investigated.Then,the functions presented the relationship between initial track tension and dynamic displacement variation of a track shoe were created.A new method for predicting the initial track tension was proposed,which can improve comprehensively the performance of tracked vehicles on soft ground.The method aimed to reduce the ground pressure,the vertical dynamic displacement variation of a track shoe,and improve the fatigue life of the track.Based on NSGA-II,the initial track tension was optimized under four driving conditions,and the Pareto fronts were obtained.The ground pressure,fatigue life of track and dynamic displacement variation were calculated or tested again when the initial track tension changed.The results of the above researches were in good agreement. |
