| In view of the low level of agricultural mechanization in hilly and mountainous areas in China and the phenomenon that traditional agricultural machinery is prone to bump or suspension tilt when driving and operating on uneven roads in hilly and mountainous areas,a four-wheel drive mobile chassis with balanced rocker arm mechanism was designed.The chassis adopts the h-type transmission form of the balanced rocker arm suspension,which is mainly composed of four modules: the main structure,the balanced rocker arm mechanism,the two side transmission mechanism and the two side steering mechanism.This paper mainly studies the following contents:First of all,aiming at working environment,the design idea is reorganized and a new balanced rocker arm mechanism four-wheel drive moving chassis for hilly and mountainous work is proposed.The moving chassis adopts the balanced rocker arm suspension,whose structure can guarantee the landing of all four wheels at the same time and improve the characteristics of traction adhesion.And in order to achieve the purpose of the average distribution of torque,the four-wheel drive chain drive design.Besides,in order to solve the problem that the steering trapezoid structure can not be arranged in the h-type drive,the hydraulic steering scheme is adopted.According to the theoretical calculation of the chassis traction,the dynamic configuration is determined,and the basic design parameters of the moving chassis are finally determined.Secondly,on the basis of determining the overall structure design of the moving chassis,according to the chassis performance requirements,the output half shaft and multi-stage chain drive sprocket on the full-time four-drive chain drive system were designed and the wheels were selected.A new full hydraulic steering structure without steering trapezoid is designed.In order to realize ackerman steering,MATLAB genetic algorithm is used to optimize the displacement relation of steering cylinder of the steering system,determine its best installation position,and select and calculate the steering hydraulic cylinder.Thirdly,the finite element method is used to analyze the static and dynamic performance of the drive axle to verify the reliability of the chassis design.As the main loadbearing structure of the new design,it is very important to establish the geometric model of the movable chassis drive axle.The structural performances of the drive axle under full load bending,emergency turning and emergency braking are analyzed,and the max stress value and max deformation of driving axle is smaller than the permitted value.The dynamic characteristics of the drive axle in the free state were analyzed,and the natural frequencies and modes of the first six orders of the drive axle were calculated.The natural frequency of the first order is 27.96 Hz,which is much higher than the excitation frequency of the rated engine speed of 18.3Hz,so as to avoid the resonance phenomenon caused by external excitation.Finally,a mathematical model is established to analyze the maximum theoretical climbing angle,longitudinal and lateral stability of the chassis.The results show that the theoretical climbing angle of moving chassis is 26.1°,which is greater than that of similar front and rear driven chassis.The ultimate tilting angle and transverse ultimate tilting angle of the upper and lower slopes of the chassis are 52°,50.9° and 46.7° respectively,and the stability can meet the requirement of agricultural machinery.The motion theory analysis and structure design of the balanced rocker arm suspension are carried out,and the maximum theoretical obstacle clearance height of the chassis is 554 mm.The simulation results show that the moving chassis with balanced rocker suspension has a small fluctuation in the center of mass,a small lateral offset,and a stable grounding force,which proves that its performance of unilateral obstacle crossing is more excellent than traditional tractor chassis. |
