【作者】 张立浩；

【导师】 郭孔辉；

【作者基本信息】 吉林大学 ， 车辆工程， 2014， 博士

【摘要】 随着汽车工业的高速发展，人们对于汽车的操控性和舒适性的要求也越来越高。而悬架系统决定着汽车的稳定性，舒适性和安全性等。钢板弹簧非独立悬架里的钢板弹簧存在重量较重，刚度大，舒适性差，纵向尺寸较长，转向干摩擦大，KC特性不理想等缺点，主要应用在一些性能要求不高的越野车和货车、客车等商用车上。独立悬架系统的具有质量轻，减少了车身受到的冲击，并提高了车轮的地面附着力；设计的自由度大，可得到较理想的K&C特性，侧倾角刚度较大，可用刚度小的较软弹簧，改善汽车的舒适性；可以使发动机位置降低，汽车重心也得到降低，从而提高汽车的行驶稳定性等优点，主要应用在轿车等乘用车上。从悬架性能来说独立悬架远远强于非独立悬架。但是独立悬架系统存在着结构复杂、成本高、维修不便、承载能力差等缺点，很少应用于载荷较大的商用车上（目前不少商用车的前悬架也开始采用独立悬架）。商用车的前悬架，由于非独立悬架布置的原因，主销与轮胎的相对偏距都较大，这常常会带来前轮摆振、刹车跑偏等问题。所谓“中心转向”悬架系统，是指车轮转向主销垂直穿过轮胎中心的悬架系统。这样可以避免因轮胎的不平衡力引起的前轮摆振，或出现刹车跑偏问题；但在低速行驶时，通常这种悬架系统在车轮转向时没有自动回正能力。为了解决上述问题，全面提升商用车的操纵性和平顺性，本文提出了一种自回正中心转向独立悬架，可以明显减小轮胎中心与主销的偏距：既可满足商用车的承载能力，同时悬架布置灵活；转向时球销摩擦阻力小，为改善回正性与转向路感打下良好基础，转向时利用弹簧横向刚度实现中心转向系统的回正性能，有希望使商用车的性能品质得到明显的提高。本文开展了以下研究工作：首先，对中心转向独立悬架系统以及与其匹配的转向系统进行初步设计。对多杆中心转向独立悬架的结构形式和特点进行分析，并着重对转向自回正性能的原理进行了分析。以某非独立悬架车型为例，把其前悬架升级为中心转向独立悬架，对悬架系统主要参数的设计和计算。定性的分析了中心转向独立悬架导向机构的设计方法。设计了与中心转向独立悬架系统相匹配的转向系统。以转向的转角传动比以及左、右车轮的阿克曼转角关系为优化目标，对转向系统各部件进行了优化设计。其次，基于合理的悬架K&C特性和阿克曼转向特性对悬架和转向系统进行优化设计。根据中心转向独立悬架的基本结构原理以及悬架系统的主要参数，建立中心转向独立悬架动力学模型。文中创新性的把弹簧模型实体化，建立了弹簧柔性体模型，并装配到独立悬架模型中。弹簧的各个方向运动，以及产生的各个方向的力都可以准确的反馈到转向节以及车身上。弹簧的横向运动产生的横向载荷，会对主销产生回正力矩。然后研究了基于合理的悬架的K&C特性的中心转向独立悬架模型的硬点优化。建立了与悬架系统匹配的转向系统模型，并基于合理的转向特性对中心转向独立悬架模型进行硬点优化。根据优化后的悬架及转向系统的硬点位置，悬架与转向系统的结构，对悬架导向杆系，转向节，弹簧支座，减振器支座进行了结构设计。建立悬架系统的三维运动模型，并进行运动校核，保证结构设计的可行性。以悬架主要承载部件转向节为例，进行强度分析，保证结构设计的安全性。然后，对中心转向独立悬架的回正性能进行了设计与分析。通过研究转向阻力矩产生的原因，以及转向阻力矩中的主要阻力及其测量方法，确定回正力矩的设计目标。影响转向回正性能的主要因素有弹簧横向刚度以及弹簧的布置角度。首先研究了转向回正力矩和弹簧横向刚度的关系。先分析了弹簧横向刚度与弹簧参数的关系以及弹簧横向刚度的计算方法。通过对中心转向独立悬架的转向试验仿真分析，得到转向过程中弹簧的横向位移值。根据方向盘转角为600°的弹簧下点的横向位移值结合目标回正力矩推导出弹簧横向刚度的大小。基于弹簧横向刚度对弹簧进行尺寸优化，得到满足回正力矩的弹簧模型。分析了不同弹簧横向刚度对于悬架K&C特性的影响。然后分析了不同弹簧内倾角和转向回正力矩的关系，并研究了弹簧内倾角对悬架K&C特性的影响。最后对中心转向独立悬架的回正性能仿真分析与试验的验证，得了准确的悬架模型。最后，建立了以中心转向独立悬架为前悬架的整车模型，对整车的平顺性试验和操纵稳定性试验进行仿真分析。在ADAMS/Car中建立了整车多体动力学模型，并对前悬架中心转向独立悬架和转向系统模型以及后悬架钢板弹簧非独立悬架模型进行K&C特性的仿真分析与试验验证。针对本文所研究的车辆进行了平顺性脉冲输入试验和随机路面输入试验和相关的仿真分析，对平顺性试验的结果分析可以得出，总加权加速度均方根值在合理范围内，中心转向独立悬架的设计可以满足整车的平顺性要求。由于本研究的重点放在前独立悬架，原车的后悬架不作改动，未对该车的平顺性作进一步的挖掘。从转向回正性试验结果可以看出方向盘转角的响应时间在正常范围内，中心转向独立悬架完全满足整车的回正性要求，可以实现自动回正。本文主要创新点如下：1、提出了一种商用车新型的多杆独立悬架结构，该型独立悬架虚拟主销在车轮中心平面内，转向阻力小，路感良好。2、提出了中心转向独立悬架系统从悬架结构设计，硬点优化设计，到悬架运动及强度校核的悬架正向开发流程，实现该悬架的开发。3、提出了中心转向独立悬架回正性能的设计方法，即把弹簧柔性体引入到悬架多体动力学模型中，根据弹簧横向刚度和弹簧布置形式进行设计，使其产生适当的绕虚拟主销的回正力矩。更多还原

【Abstract】 With the rapid development of automobile industry, the vehicle performancerequirements in handling stability and ride comfort are also increasing. The suspensionsystem plays a vital role on the stability, comfort and security et al. The conventional leafspringtype non-independent suspension，mainly used in some hardcore off-road vehicles andcommercial vehicles, has many shortcomings such as heavy weight, high stiffness, poorcomfort et al. While the independent suspension system, mainly used in passenger cars,possess many advantages:1)Relative light weight in unsprungmass, which can reduce thebody shock and improve the traction of the wheels;2)softer spring can be used to improvethe ride comfort;3)the positionof the engine and the vehicle center of gravity can be loweredto improve the vehicle handling performance. From the view of suspension performance,the independent suspension is better than non-independent suspension. However, theindependent suspensionis rarely appliedon the larger commercial vehiclesdue to itsdrawbacks such as complex structure, high cost, inconvenience to repair and poor bearingcapacity.Considering the aforementioned problems, a self-aligningindependent suspension ofsteering on center is proposed in this dissertation:1)the carrying capacity of commercialvehiclescan be met, while the suspension layout is flexible;2)the turning ball bin has smallfriction;3)the self-aligning performance is realized by utilizingthe spring lateral stiffnesswhen turning. This paper is carried out by following aspects:1)the independent suspension system of steering on center and its matched steeringsystem are preliminary designed.Firstly, the structure and characteristics of multi-rodindependent suspension of steering on centerare analyzed, furthermore, the principle ofself-aligning performanceis analyzed.Secondly, the front suspension of a non-independentsuspension vehicle is upgradedto the independent suspension of steering on center, then thedesign and calculation of the main parameters of the suspension system,such asthe stiffness of the suspension, the offset frequency, static deflection, spring parameters, the suspensiondamping, are carried out. Thirdly the design methods of the steering mechanism areanalyzedqualitatively and the steering system matched with independent suspension ofsteering on center is designed. Finally, the length and layout of steering arm and the middlerod, the length and angle of the steering tie rod and the steering knuckle are optimizedtakingthe steering angle ratio, the relationship of left and right wheelsAckermanangle as theoptimizedtarget. on the work of the preliminary designed for the independent suspensionsystem of steering on center and its matching steering system make it easier to study theaccurate suspension and steering model.2)Theoptimal design for the suspension and steering systems are conducted,based onthe suspension K&C characteristics and steering characteristics.The independent suspensionsystem of steering on center dynamics model is built via the multi-body dynamics softwareMSC.Adams, based on the structure principle and the main parameters of the proposedsuspension.In conventional manner, the spring is simulated by building the spring unit andthe properties file, it only reflect the influence of the axial stiffness of the spring onsuspension kinematics. However, the self-aligning performance of the independentsuspension system of steering on center is realized by utilizing lateral stiffness of the spring,besides the vertical movement, the spring has lateralmovement, and compound movementwith vertical and lateral movement, which can’t be simulated by the conventional springunit.In this dissertation, the spring model is materialized innovatively, a flexible springmodel is establised, and then applied to the independent suspension.The movement of thespring inEach direction, and the force generated in all directions can be accurately fed intothe knuckle and the vehicle body.Lateral loads generated by the lateral movement of thespring, will produce kingpin aligning torque. Furthermore, the hard point optimizations ofthe proposed suspension are studied based on the K&C characteristics. Then the steeringsystem is builtto match the suspension system, and the hard point optimizations of theproposed suspension are studied based on the steering characteristics. In order to ensurethat the design of the proposed suspension system to meetthe reasonable suspension K&C characteristics and steering characteristics, the multi-objective optimization of frontsuspension is carried out based on the above two features.According to the optimized hardpoint locations of the suspension and steering systems, the structure of suspension andsteering system,the suspension guide bar, steering knuckles, spring bracket and the shockabsorber bearing are designed.A three-dimensional motion model of suspension system isadoptto conduct the motion check to ensure the feasibility of structural design. Taking themain load bearing component and the suspension knuckle for example, the strength analysisis carried out to ensure the safety of structural design.3)Aligning performance of on-center independent suspension is designed and analyzed.The design objective of aligning moment is set via studying the causes of aligning resistancemoment and the calculation method of main resistance. The main factors influencing thesteering aligning performance are the transverse stiffness of spring and arrangement angle ofspring.Firstly, the relationship between the aligning moment and the transverse stiffness isstudied. The relationship between the transverse stiffness of spring and the spring parametersis analyzed and the calculation method of the transverse stiffness of spring is obtained. Thetransverse displacement value of the spring in the process of steering is obtained accordingto the steering simulation of on–center independent suspension. The transverse stiffness ofspring is calculated based on aligning moment and transverse displacement value of thespring. Optimization of spring size was carried out based on the transverse stiffness, and thenspring model meeting aligning moment is achieved.The variation of the spring transversestiffness influencingon the suspension K&C characteristics is analyzed. The relationshipbetween spring inclination angle and aligning moment and the spring inclination angleinfluencing on the suspension K&C characteristics is studied.According to the suspensionhard point set in chapter3, the hard points of suspension guiding mechanism and steeringpart, and the design of spring size and inclination angle, all structural parameters ofon–centerindependent suspension is achieved. Finally, the accurate model of the suspension isobtained via simulation analysis and experimental verification.4)A vehicle model with on–center independent suspension as front suspension is built to study the vehicle ride comfort and handling stability of the proposed suspension system. Afull-car vehicle model, including the front suspension model, the rear suspension, steeringsystem model, tire model, and the body modelis buildedin ADAMS/Car. Simulation analysisand experimental verification are carried out focusing on K&C characteristics of frontsuspension, steering system model and rear suspension. UniTire tire model proposed byguo konghui academician is selected as Tire model, to obtain higher simulation accuracyunder large lateral acceleration. In order to identify parameters of UniTire tire model, the sixdegrees freedom tire testing machine developed by guo konghui academician and his team isused to test tire performance.The simulation model is verified by ride comfort test andhandling stability test. The validation results show that the simulation results fells well withexperimental results, sothe vehicle multi-body dynamics model is accurate enough todescribe the linear and nonlinear dynamic of the vehicle characteristics. Ride comfort testresults show that the total weighted acceleration root mean square value is reasonable; thedesign of on–center independent suspension can satisfy the requirement of the vehicle ridecomfort. Steering portability test results show that the steering wheel torque is small in theprocess of steering, and vehicle with on–center independent suspension as front suspensionhas light steering characteristic.Returnability test results shows that response time of the yaw rate is within the normalrange, meanwhile the yaw rate is reduced into the limit range. the steering testresults showthat the on–center independent suspension satisfy the requirement of aligning performanceand can realize automatic correction.Major Innovations of the Dissertation:(1) A new type of independent suspension with following adavantages is proposed in thispaper: the ball pin has small friction resistance and long applying time.a)smallfriction resistance in the ball pin prolong its lifespan; b)small steering resistance whilestreering led to good road feeling; c)wheel move around its center when Steering,which reducing the wear of the tire; d)due to spring load through the center ofimprinting, the roll moment of the wheel assembly is reduced;e)the layout of height ofthe two connecting rod is flexible. (2) A car is taken as an example, the design method of on–center independent suspension isput forward: from the basic parameters’ selection of suspension form, basic space layout,and initial design of suspension hard point to optimization of suspension hard pointbased on the suspension K&C characteristics and steering characteristics, thenmovement checking and strength calculation of the suspension is carried.(3) Design method on the aligning performance of on–center independent suspension is putforward, namely, based on transverse stiffness of spring and the spring inclination angel,to make its produce aligning moment around the virtual king pin; The spring as flexiblebodyassemble into the suspension dynamic model, which can accurately simulate thespring stiff influencing on the suspension kinematics and steering aligning performance.更多还原