【作者】 高锐涛；

【导师】 杨洲；

【作者基本信息】 华南农业大学 ， 农业机械化工程， 2019， 博士

【摘要】 拖拉机作业地形复杂,来自田间的低频激励与人体内脏的固有频率接近时引起共振;发动机振动频率范围宽,作业时振动加剧,长时间暴露在振动环境下也会使驾驶者不舒适度增加;拖拉机振动会严重影响驾驶者舒适度及身体健康。拖拉机振动主要通过座椅传递至人体,减振座椅悬架是提升驾驶员舒适度的重要机构,传统拖拉机座椅悬架主要以普通弹簧阻尼机构为主,隔振频率高,不能有效隔离低频振动,而且对振动舒适度的评价也缺乏有效的客观评价方法,亟需开展相关研究。本文以国产大中型水旱两用轮式拖拉机为研究对象,围绕拖拉机座椅悬架隔振系统优化设计及振动舒适度评价展开研究,主要包括:(1)多工况下轮式拖拉机振动特性分析开展拖拉机发动机振源传递特性分析,试验研究了发动机振动频段内各振动传递路径的振动传递情况,发动机转速在900-1020 rpm范围内时,驾驶者感受到的发动机振动最小,有助于降低驾驶者的不舒适度。分别在水田、湿地和旱地等作业工况下,以及不同挡位的条件下,对拖拉机的低频激励特性展开试验研究,结果表明拖拉机在旱地作业时易引起拖拉机底盘在2-5 Hz频率范围内的垂向共振,水田中1挡作业时座椅底部在垂向也会产生8 Hz的共振,且在不同挡位均存在4-8 Hz范围内的共振频率点,这会造成人体对垂向振动敏感,影响驾驶者工作效率和身体健康,证明了减振座椅设计的必要性,并为其舒适度评价提供振动输入依据。(2)大行程近零刚度的拖拉机减振座椅悬架优化设计研究基于正负刚度并联机构减振原理,提出一种新型椭圆凸轮-滚轮负刚度减振机构,构建减振悬架的动力学建模并进行参数优化,通过对悬架垂向和水平弹簧选取及椭圆凸轮长短轴参数匹配,在±20 mm行程范围内得到垂向等效刚度为0.03456 N/mm的近零刚度。根据优化得到的参数加工减振座椅悬架样机。对样机进行负载的加载与卸载试验得到其力-位移特性曲线,并对样机进行田间试验,采集振动加速度数据以检验减振效果。试验结果表明:负刚度机构可有效抵消81.3%的正刚度,将最低隔振频率从3.87 Hz降低至1.67 Hz;与传统座椅悬架相比,该悬架的振动加速度平均幅值较座椅基座的降低比例从20%变为53%,显著提升减振效果,改善拖拉机驾驶员的乘坐舒适度。(3)基于拖拉机座椅振动的人体多生理指标测试与分析提出了基于拖拉机座椅振动的人体多生理指标测试与分析方法,设计并加工了六自由度振动模拟平台用于定量模拟拖拉机振动输入,研究了人体表面肌电、皮电、皮温和脉搏波等生理指标特征值的获取准则,试验结果表明随着人体不舒适度的增加,生理指标整体呈现以下趋势:人体表面肌电的中值频率值下降、皮电的均值上升、皮温斜率下降、脉搏波信号均值增加。因此,基于人体生理指标特征可以很好地评价振动舒适度。(4)基于人体多生理指标的振动舒适度评价方法研究提出了基于人体多生理指标的振动舒适度评价方法,构建了人工神经网络并通过对大量人体多生理指标试验样本进行训练得到神经网络模型,预测准确率达88.9%,不仅可以更客观地用于人体振动舒适度评价,还可以用于人体在其他恶劣工况下的舒适度评价。基于所建立神经网络模型对减振座椅舒适度进行评价,与普通座椅悬架相比,减振座椅显著降低了不舒适度等级,且随着时间增加,不舒适度均保持在可接受范围内。本文通过轮式拖拉机整车振动分析为减振座椅悬架设计提供依据,基于凸轮滚轮的负刚度机构和正负刚度并联的近零刚度减振原理实现拖拉机座椅悬架的低频隔振,并基于人体多生理指标构建和训练振动舒适度神经网络模型,通过模型来客观地评价减振座椅的效果,所建立模型也可用于客观反映人体在不同工况下的不舒适度,为结构设计优化提供依据。更多还原

【Abstract】 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.更多还原