【作者】 刘刚；

【导师】 郭孔辉；

【作者基本信息】 吉林大学 ， 工程硕士（专业学位）， 2017， 硕士

【摘要】 环境压力与科技创新推动着汽车产业的变革,促使政府、各大汽车厂商持续加大对汽车低碳化、智能化核心技术的研发投入。汽车低碳化、智能化的发展要求悬架能更加高效地衰减振动,保证轮胎的抓地能力。半主动悬架能有效地协调车身与车轮的运动,且辅助能量需求小,成为当前的研究热点,其与整车集成的动力学及控制是亟待解决的核心问题。目前,半主动悬架与整车集成的研究大多关注在车辆的稳态响应方面,缺乏对汽车的瞬态特性细致考虑,不能充分表达悬架运动学和动力学的耦合行为以及轮胎的松弛效应。这对车辆状态的观测、轮胎力的分配、稳态边界的求解等需要车辆模型的动力学控制带来了严重的影响。此外,实际汽车行驶时多处于瞬态工况,但当前的多数悬架功能分配中缺乏对瞬态特性目标的充分考虑,影响着车辆的综合性能。本文采用理论与数值模拟相结合的方法对汽车瞬态动力学特性的描述及其悬架功能分配展开研究,旨在建立一种准确描述汽车瞬态动力学特性的方法,并在此基础上建立半主动悬架汽车瞬态动力学特性功能分配策略,为半主动悬架与整车的集成提供有效的手段。本文主要研究内容及结论如下:1.精细车辆动力学建模。首先,建立包含瞬态轮胎模型的车辆侧、垂向耦合动力学模型,修正悬架K&C特性,并通过分析汽车侧、垂向动力学耦合机理,实现整车14自由度车辆动力学模型的一体化建模;其次,建立单轮随机路面,并应用相干函数和高频补偿函数表达路面输入的相关性和差异性,实现四轮随机路面重构;最后,采用CarSim与Simulink联合仿真对所建模型进行验证。2.汽车瞬态动力学特性分析。探究悬架K&C特性与轮胎瞬态特性对汽车瞬态动力学特性的影响以及粗糙路面对汽车操纵稳定性的影响规律。仿真结果表明:悬架K&C特性减小了横摆角速度与侧向加速度的响应时间和超调量;轮胎的松弛效应增加了响应时间,对超调量影响较小;悬架K&C特性对平顺性存在着重要影响,但会随车速、路面等级变化而异;粗糙路面改变车轮垂向载荷分布,进而使车轮侧偏刚度降低。3.路面垂向输入信息与车辆状态的在线识别。首先,针对一类非线性系统建立了状态与未知输入同时观测算法,对整车状态与路面不平度输入进行统一观测,转向(前轮转角2°)与随机路面(B级,70km/h)同时输入下考虑悬架K&C与轮胎瞬态特性可使状态参数的观测精度提升3%~6%;其次,采用有效均方值的方法对路面输入主频进行在线辨识,并参考ISO 8608路面等级分类标准在线估计路面等级;最后,采用递推最小二乘法对车辆簧载质量及转动惯量进行辨识,并建立载荷自适应律,为半主动悬架的工况自适应控制奠定基础。4.半主动悬架功能分配策略研究。首先,集成载荷、路面垂向输入信息及运行工况的识别结果,建立工况自适应的半主动悬架汽车瞬态动力学特性的功能分配策略;其次,引入状态反馈与前馈,根据ITAE指标配置理想二自由度车辆模型的零极点,求解最优附加横摆力矩,根据轮胎负荷率求解各车轮最优驱动力矩,改善车辆瞬态响应,探究悬架K&C特性对轮胎力分配的影响,仿真结果表明悬架K&C特性的考虑降低了轮胎的平均负荷率和最大负荷率;最后,建立滚动优化控制方法,求解满足动力学耦合、执行器饱和约束以及轮胎力约束条件下的最优悬架阻尼力,为汽车瞬态响应的控制留出稳定裕度,综合改善车辆的平顺性与操纵稳定性。更多还原

【Abstract】 Nowadays,the automobile industry is changing driving by the pressure of environment pollution and the innovation of vehicle technology.To master the core technology of low-carbon and intellectualization,the government and the major automobile manufacturers have spent lot of money in new energy vehicles and autonomous vehicle.The development of low-carbon and intellectualization requires the suspension to isolate the vibration effectively and ensures the grasping ability of the tires.Due to the low energy consumption and excellent performance,the semi-active suspension which can effectively coordinate the movement of the body and the wheels has attracted lot of attention.At present,most researches of semi-active suspension are lacking of consideration on vehicle transient behavior,which influences the vehicle state observation,tire force distribution and steady boundary solution.What’s more,it becomes the key obstacle of the semi-active suspension coordinated control with consideration of both the handling and the ride comfort.The relaxation effect of tyre and the suspension K&C characteristics will bring the vehicle system response delay.The actuator saturation will constrain the system control input,the vehicle dynamic of each direction couple together.the handling and the ride comfort vary from the road input and driving condition.In this paper,we will combine the theory with numerical simulation to study the transient dynamic respone of vehicle and its coordinated control.We will establish a simple and accurate method to describe the real-time transient characteristics of automobile and explore a coordinated control strategy of semi-active suspension to solve the time-delay,dynamic coupling and actuator saturation constraints of the vehicle transient performance.This paper is orginized as follows:1.Accurate vehicle dynamics modelingFirstly,we established the lateral and vertical dynamics model together with the transient tire model,modified suspension K&C characteristics.Secondly,we established the random road of the four wheels based on the correlation function and time delay between the four wheels.Finally,we verified this model by the joint simulation of CarSim and Simulink.2.Transient dynamic analysis of vehicleBased on the simulation,we analysised the effects of the K&C characteristics and transient tire model on the vehicle transient dynamic response.Besides,we also studied the influence of rough road on the handling stability.The simulation results show that the response time of the yaw rate and lateral acceleration was reduced with the consideration of suspension K&C characteristic,besides,the overshoot was also reduced.The response time of the yaw rate and lateral acceleration increased with the consideration of tire relaxation effect and the overshoot was basically unchanged.the effect of suspension K&C characteristics on ride comfort varied with the vehicle speed and road level.Rough pavement change wheel vertical load distribution and the wheel side slip angle increases.3.Online acquisition of road information and vehicle stateFirstly,we introduced a class of nonlinear systems’ s observation algorithm.We used this algorithm to estimate vehicle state and road roughness.Based on the simulation(front wheel angle 2 degrees and B class random road with 70km/h),we found that when considering the suspension K&C,the observation accuracy of the state could increase 3%~6%.Secondly,basised on the effective mean square method,we identified the input frequency of the road.Also,we identified the road grade referenced the ISO8608 pavement classification standard.Finally,the recursive least square method was used to identify the sprung mass,then built the load adaptive logic.4.Coordinated control strategy of semi-active suspensionFirstly,we consideried the load,working condition and road vertical input,then estabilished the coordinated control strategy of semi-active suspension including vehicle transient dynamics.Secondly,we introduced the state feedback and feedforward to the two degree of freedom vehicle model to acquire the optimal additional yaw moment according to the ITAE index,according to the principle of the load rate of the tire,we distributied the optimal wheel driving torque.The average load rate and the maximum load rate of tire is reduced with the consideration of the transient characteristics of the vehicle.Finally,the control objective was established by integrating the vehicle state and road surface information,and the MPC was used to solve the optimal suspension damping force under the dynamic coupling and actuator saturation constraints.更多还原