Dynamic Characteristic Research Of A Three-Degree Seat Suspension

Engineering machineries have made a great development in recent years in China, but suspension technics of off-road vehicles such like agriculture vehicles, engineering vehicles and military vehicles are developing very slow, and the existing suspensions behave poor performance, that make vehicles unsafe and short lifetime; vehicles usually work in harsh conditions, and drivers bear low frequencies and high intensity vibration, their physical and mental health have been threated. Install the tractor with a seat suspension is a simple way to solute the problem. It matters to research the dynamic characteristic and to improve the dynamic performance, and to improve comfortableness of these vehicles.This subject is to develop the drivers’working environment, and a three-degree seat suspension system could damp vibrations of x, y and z axes was designed; driver’s body was simply equivalent to a mass and placed on the seat suspension, the differential equations were listed out according to the Newton second law; the seat a multi body system (MBS) prototype model of the suspension together with body was created using ADAMS software; body and seat suspension were placed in the cabin, a full tractor MBS model was created; some simulations were carried out. Tasks have been finished and conclusions have been drawn are as below:(1) A seat suspension was designed, and the way how to arrange the components was analyzed; and a "body-seat" system was created; a differential equation about how did the body move along x, y and z axes was created using multi-body dynamic theory; equations of equivalent stiffness in the forward direction and the driver’s left hand direction were derived and together with acceleration equations in three axes directions; additionally, the equations about nature frequencies in pitch and roll direction were also derived; factors that influence the suspension system’s vibration characteristic were analyzed. The result showed that vibration characteristic was influenced commonly by tractor mass attribute, tires properties, running speeds, and properties of the suspension structure.(2) Parts of the suspension were designed and the connect relations and drive connections were analyzed. The suspension system includes boards, air spring, torsion spring and magneto-rheological (MR) damper. Overall dimensions and working stroke were assured; types of air spring and MR damper were chosen, and strength of critical parts was verified.(3) According to the suspension structure, MBS model of the seat suspension was created; Parameters of tires were calculated, and tire model files were compiled; the tractor body model of CF700was created with Pro/E software; parameters of the drive’s body, parts and the tractor body were gained; a rougher road file (.rdf) for simulation was compiled according to the national standard, full tractor MBS virtual prototype was created with ADAMS software.(4) The body’s acceleration time domain signal were collected in x, y and z directions when the CF700tractor running on the runways of field tests; results of simulation and test were compared and verified, and showed that the simulation values were approximately equal to the field test value, which means parameters of the non-seat virtual prototype were reasonable; based on the simulation before, the simulation with seat suspension was carried out, vertical direction used way of low frequency damping, pitch and roll direction used way of high frequency damping; and the result showed that the best frequencies of vertical, pitch and roll directions should be1.5Hz,23Hz and15Hz.Researches of this subject have important and practical significances for accelerating speed of suspension research, improving driver’s comfortableness, and decreasing the harm to physical and mental health.