Optimum Design Of Wheeled Tractor Seat Suspension And Comfort Evaluation Method For Human Vibration

Due to the complex terrain of the tractor in the field,the low-frequency excitation from the field causes resonance of human body when it is close to the natural frequency of the internal organs,which seriously affects the comfort and health of the driver.The engine has a wide vibration frequency range,and the vibration is intensified during operation,which is mainly transmitted to the human arm through the vehicle frame.Prolonged exposure to the vibration environment will increase the fatigue of the driver.Seat suspension is an important mechanism to improve the comfort of the driver because the vibration of the tractor is mainly transmitted to the human body through the seat.The traditional seat suspension is mainly based on the common spring damping vibration isolation mechanism,which has high vibration isolation frequency and cannot effectively reduce the low-frequency vibration from the field.There is also a lack of effective and objective evaluation method for the comfort of vibration.The research object of this paper is dual-use wheel tractor for flood and drought.This paper is focused on the optimization design and vibration comfort evaluation of tractor seat suspension vibration isolation system,mainly including:(1)Vibration characteristics analysis of wheeled tractor under multiple working conditionsThe transmission characteristics for the vibration of the tractor engine were analyzed,and the vibration transmission conditions of each vibration transmission path in the engine vibration frequency band were studied experimentally.The engine vibration felt by the driver’s arm was significant reducted when the engine speed was within the range of 900-1020 RPM.Experiments has been done for tractor under paddy fields,wetlands and dry land with different gear.The results show that the tractor in wetlands and paddy field operations,low vibration of 2 Hz with pitch and roll motion was generated,while the body is sensitive to transverse vibration frequency within 2 Hz.Resonance frequency of 8 Hz has been reached for the bottom of the seat in the paddy field.The human body is sensitive to vertical vibration which will reduce driving efficiency and harm one’s physical health.This proves the necessity of vibration seat design,and provide a basis for vibration input in the comfort evaluation.(2)Study on the optimization design method of the suspension of tractor seat with large stroke and nearly zero stiffnessBased on the principle of positive and negative stiffness parallel mechanism of vibration reduction,a new type of elliptical CAM-roller negative stiffness damping mechanism has been put forward.The dynamics modeling of suspension has been studied and parameter optimization has been done.The quasi zero stiffness is 0.03456 N/mm within the scope of 2cm by parameter matching.According to the optimized parameters,the prototype of vibration damping seat suspension has been processed.The force-displacement characteristic curve was obtained by loading and unloading test on the prototype,and the field test was carried out on the prototype to collect vibration acceleration data to test the effect of vibration reduction.The test results show that the negative stiffness mechanism can effectively offset the positive stiffness of 81.3% and reduce the lowest vibration isolation frequency from 3.87 Hz to 1.67 Hz.Compared with the traditional seat suspension,the average amplitude of vibration acceleration of the suspension reduces from 20% to 53% compared with the seat base,which significantly improves the vibration reduction effect and improves the ride comfort of the tractor driver.(3)Test and analysis of multiple physiological indicators of human body based on the vibration of tractor seatA method for testing and analyzing multiple physiological indexes of human body based on the vibration of tractor seat was proposed.The six-degree-of-freedom vibration platform was designed and processed for quantitative simulation of tractor vibration input.The criteria for obtaining the characteristic values of physiological indicators such as human surface electromyography,skin electromyography,skin temperature and human pulse were studied.The experimental results show that with the increase of human discomfort,the physiological indicators show a regular trend.The increasing of mean frequency of human surface electromyography and the slope of skin temperature imply the escalation of discomfort,while the increasing the mean value of skin electricity,and the mean value of pulse wave imply the escalation of discomfort.Therefore,the characteristics of human physiological are effective indicators for good evaluation of discomfort under vibration.(4)Study on vibration comfort evaluation based with multiple physiological indicators of human bodyArtificial neural network was constructed and a neural network model was obtained through training a large number of experimental samples,with prediction accuracy up to88.9%.It can not only be used to evaluate the comfort level of human body more objectively,but also be used to evaluate the comfort level of human body under other bad conditions.Base on the proposed neural network model,the comfort level of the cushioning seat was evaluated.Compared with the ordinary seat suspension,the comfort level of the cushioning seat was significantly reduced,and the discomfort level remained within the acceptable range as time went by.In this paper,the vibration analysis of the whole wheeled tractor vehicle provides a basis for the design of vibration isolation seat.Based on the negative stiffness mechanism of CAM roller and the near-zero stiffness isolation principle of parallel positive and negative stiffness,the low-frequency vibration isolation of the tractor seat suspension is studied.The neural network model for predicting the discomfort level for hunman body exposured to the vibration was constructed and trained based on multiple physiological indexes of human body,which can be used to objectively evaluate the effect of vibration isolation seat.The established neural network model can also be used to objectively reflect the discomfort of human body under different working conditions,which provides a basis for structural design optimization.