【作者】 吴英龙；

【导师】 赵华；

【作者基本信息】 西南交通大学 ， 工程力学， 2013， 博士

【摘要】 车辆舒适性及碰撞安全性能与减振器密切相关,目前国产减振器的开发、设计多停留在模仿设计、经验设计和试验修正上,缺乏减振器的先进设计理论,导致国产减振器故障问题多、成本高、开发周期长。因此,通过理论、试验和仿真手段深入研究减振器的工作原理和故障机理,完善减振器的设计理念,优化减振器结构,具有重要的理论意义和工程价值。本文从理论上建立了阻尼力和油液压强的换算公式、减振器节流计算的公式、三种受力形式下阀片变形的计算公式,并通过Java编程进行迭代计算获得了阀片和弹簧座的分离点位于环形槽内(d≤a)时阀片径向线变化的过程曲线。发现常通孔节流是平行平面缝隙节流,开阀后的节流为平行平板间径向节流。在二类节流分析中均考虑了局部节流损失、沿程节流损失；在第二类节流中对起始段被活塞部分填充后的节流内径、考虑常通孔存在后的节流高度作了等效处理。由节流公式获得的油液压强与由换算公式获得的油液压强具有很好的一致性。研究了阀片与弹簧座的三种接触方式：集中接触,分布接触(未接触区域全部受油液压强作用),分布接触(未接触区域部分受油液压强作用)。在假定分布载荷下,基于板壳理论的阀片变形计算与由有限元计算结果吻合很好。从理论上分析了示功图(F-S曲线图)偏斜的原因、示功图上各曲线相互穿透的原因、及影响示功图饱满的因素。阀系灵敏度不足会导致阻尼力变化滞后于活塞速度变化,从而形成“残余力”(激励速度为零而阻尼力不为零),并使示功图偏斜、阻尼力-速度过程图(F-V曲线图)复原或压缩行程前半段曲线与后半段曲线分离。当高速度点曲线的分离过大时,示功图上该曲线会穿透低速度点曲线。速度点(Vmax)和开阀速度对示功图饱满的影响可忽略；当开阀阻尼力(Fo)和阻尼力-速度特性曲线第二段的斜率(k2)确定,开阀后的饱满情况确定；当F0确定,适当减小k2时,减振器总做功减小；阻尼力迟滞则示功图不饱满现象严重。通过系列试验发现,阻尼力异常波动与加工质量、设计分析有对应关系,减振器的异响与开阀状态(F0/V0)有对应关系。质量问题主要有漏油、气压抗力降低、阻尼力偏离设计值和松退力矩不合格等。摩擦力换向、螺母松动、换向空程、损伤、开阀、阀片与阀门盖碰撞、补偿阀阀片被卡住和阀片翘曲等造成的阻尼力异常波动在示功图、F-V图及解析结果上有不同特点。通过172型减振器咔咔声异响的试验分析发现,异响件加速度、阻尼力信号的时频特征都普遍比正常件大；异响件的阻尼力异常由开阀引起,其开阀状态普遍比正常件大。提出了两种阻尼力-速度特性曲线(F-Vmax曲线)仿真预测的方法；开发了筒式减振器瞬态双向流固耦合仿真系统并完成了相应预测方式下阻尼力的预测；建立了减振器流固耦合冲击响应仿真系统,并联合活塞杆固定环压装仿真完成了活塞杆冲击破坏仿真分析。F-Vmax曲线仿真预测的方法为：①使用准稳态方式获得各个速度点的阻尼力值；②获得F-V图中Vmax=1500mm/s的曲线。通过瞬态双向流固耦合仿真获得了阻尼力、阀片应力和位移分布及变化的特点,筒内流场分布及变化的特点,并验证了理论方法的合理性,探讨了降低仿真计算规模和提高计算精度的方法。完成了某特种车辆空投降落的碰撞仿真。发现其最薄弱的部位是车轴,其次为发动机附近区域；车辆与地面接触碰撞的时间与地面的刚度密切相关。当地面为混凝土材料时,碰撞时间最短,车辆的动态应力及其波动幅度也最大。这为进一步研究减振器对车辆空投降落的影响及减振器自身的冲击破坏提供了基础。更多还原

【Abstract】 Vehicle comfort and collision safety performance is closely related with the shock absorber. At present, the development and the design of shock absorber stay in imitation of design, experience design and experimental correction. The lack of advanced design theory of shock absorber leads to problems of failure, high cost and long development cycle. In hence, study on the working principles, failure mechanism theories, perfect design concepts, optimizations of damper structure by experiment and simulation have important theoretical significance and engineering value.Based on the theoretic research, this paper established the conversion formula of damping force and oil hydraulic pressure, throttling formulas, valve deformation formulas under three different equilibrium models of forces. Further, through the Java iterative calculation, we obtained the change history of valve radial line when the separation point between valve disc and spring basement was out of the ring groove(d≤a). We found that it was a parallel flow during the period the valve wasn’t open and it was a radial flow between two parallel flat planes during the period the valve was open. In the analysis of the two throtting calculation, the local head loss and the frictional head loss were considered. The rod padding effect to the inner radius and the throttle orifice flow effect to the throtting thickness were considered in the second throttling calculation. Oil pressure obtained by the throttle formula and obtained by the conversion formula had a good consistency. The contact types between valve disc and spring seat were circumference line contact, circumference surface contact (the untouched section is entirely subjected to the hydraulic pressure) and circumference surface contact (the untouched section is partially subjected to the hydraulic pressure). Under the assumed distribution load, valve disc deformation calculation based on the theory of shells and the finite element showed a good agreement.Based on the theoretic research, we pointed out the causation of the indicator diagram (F-S diagram) deviation, the causation of the curve penetrating, the factors which influenced the indicator diagram plumpness. The valve system sensitivity deficiency would lead to the variation of damping force behinds the piston speed change, and to form a "residual force"(the incentive speed was zero but damping force wasn’t zero), and the indicator diagram deviation. On the damping force vs. velocity diagram (F-V diagram), the first half of the recovery curve or the compression curve would separate from the second half. When the separation of a high speed curve was too large, this curve would pass through a low speed curve on the indictor diagram. Effects of the velocity point (Vmax) and the open gate velocity to the indicator diagram plumpness were neglectable; when the open gate damping force and the slope of the second segment of the F-Vmax curve (k2) were determined, the indicator diagram plumpness was certain; when Fo was certain and k2reduced, work would decline; the damping force hysteresis would induce serious un-plumpness of the indicator diagram.Through tests and anatomizations, we pointed out that abnormal fluctuations of damping force were corresponding to the processing quality and the design analysis, there was a correspondence between the abnormal noise and valve opening state (Fo/Vo)-The main quality problems were the oil leak, the gas pressure resistance loss, the aberrancy of damping force and the pine twisting moment loss. Friction direction swerve, lack of valve sensitivity, loss of pine twisting moment, irrational design and valve disc wrap had different features in the anatomization results and the F-S curves and the F-V curves. The acceleration time characteristics and the acceleration frequency characteristics of withdraws with noisy problem were generally bigger than the normal ones’, so were the damping force time characteristics and the damping force frequency characteristics of withdraws with noisy problem; those abnormities were caused by opening the valve, and their open status were generally bigger than the normal ones.Two simulation methods for forecasting the damping force characteristics, a dynamic fluid-structure interaction (FSI) finite element system and a dynamic fluid-structure interaction finite element impact system were promoted. The predicting methods of F-Vmax curve were:①aining the damping force at each velocity point by using quasi-statics method;②Gaining the F-V curve of Vmax=1500mm/s. Through a series of simulations, we gained the damping force vs. velocity characteristics, the distribution and the history of the valve disc stress and the fluid field. Meanwhile, simulation results had verified the rationality of the theoretic method. Also, we probed into ways, such as sub cycling, to promote the computation speed and the computation precision.Also, this paper had accomplished an airdrop landing simulation of a vehicle for special services. We pointed out that the axle was the weakest part; the contact time and the ground stiffness were closely related. When the ground was a concrete material, the contact time was the shortest, vehicle dynamic stress and its fluctuation was the biggest. For further understanding the effects of the shock absorber to the vehicle safety and its damage, this part has a good help.更多还原