【作者】 程云建；

【导师】 王小椿；

【作者基本信息】 北京交通大学 ， 机械设计及理论， 2012， 博士

【摘要】 随着汽车工业的快速发展、轿车家庭化的快速普及,汽车安全已经成为当今汽车领域重要的研究课题。在众多控制汽车安全的技术中,车辆的防滑控制技术一直是人们的研究重点和难点。车辆行驶速度的不断提高及路况条件的日益苛刻对车辆的防滑能力提出了更高的要求。目前,以控制车辆失稳、增大车辆牵引力为目标的控制方法有很多,效果也很明显,但仍存在一定问题亟待解决。为此,本文围绕车辆的防滑控制问题,对车辆限滑差速系统的原理、实现方式及限滑性能进行了深入的研究和探讨。对目前存在的各种限滑差速器产品或限滑差速器方案进行分析,针对它们存在的问题,提出并设计了一种新型的液力自举式限滑差速器。与其它主动控制式限滑差速器相比,它的创新之处在于将一个完整的液压系统集成于差速器总成内部,且不需要额外安装传感器测量车辆在行驶过程中的相关参数的变化,如驱动轮转速等,没有微处理器单元,不需电路支持,可靠性更高。通过该差速器内空间凸轮机构的作用,它可以根据差速器两半轴间的转速差自动调整液压系统的工作状态,从而调节差速器的锁紧程度。该空间凸轮机构是由半轴齿轮和安装在半轴齿轮与差速器壳体之间的从动件组成的,是液压系统的关键元件。通过分析凸轮廓线的传统设计方法反转法,发现它并不适合求解工作廓面为复杂空间曲面的空间凸轮的工作廓面方程。因此,本文提出根据从动件数学模型及其运动规律,利用空间曲面包络原理及微分几何理论计算空间凸轮工作廓面的方法,并推导出空间凸轮机构在接触点处的诱导法曲率及压力角的计算公式。通过设计实例证明,该方法虽然不如反转法计算速度快、直观、便于理解,但可以精确求出空间凸轮机构在每一时刻的接触点的位置,以及在该位置上的压力角和诱导法曲率值,为优化凸轮机构提供条件。本文推导出了液压系统压力与泄漏缝隙大小之间的关系式,通过分析系统压力与差速器输入转速、液压系统泄漏缝隙之间的关系,得出液压系统的压力与缝隙的大小呈现出立方关系；可以通过调整泄漏缝隙的大小来改变液压系统的工作压力,从而达到调节差速器的限滑能力的目的。以北方汽车车辆研究所提供的某型车辆数据为基础,编写了限滑差速器工况仿真软件。该软件已经通过北方汽车车辆研究所验收,目前正应用于差速器摩擦片摩滑工况研究。在建立发动机数学模型时,发现常用于拟合发动机外特性曲线的多项式拟合方法存在缺陷,在原始实验数据点处存在误差,拟合精度不高。针对此问题,本文提出利用三次非均匀B样条拟合发动机外特性曲线的方法。该方法可以消除在实验数据点处的误差,拟合精度高,适于描述发动机数学模型。为了能精确反应路况条件对限滑差速器工况的影响,本文对现有汽车试验场的路线情况进行分析后,提出了一种路线自定义语言,它可以准确描述各种路线,再配以路面附着系数和路面不平度等信息就可以精确描述路面、路线模型,为限滑差速器工况仿真分析提供条件。最后,利用自行设计和搭建的液力自举式限滑差速器内嵌液压系统压力测试平台测试单柱塞式液压泵的工作压力随差速器输入转速的变化关系。通过交流电机带动差速器一侧半轴,模拟差速器的转速差,利用压力计测量系统内部作用腔中的压力变化,分析压力随输入转速差变化的情况。结果表明：当输入转速差达到一定值时,液压系统可以在作用腔中建立起压力环境；且系统压力随输入转速的增大而增大,但存在极大值。实验结果和分析结论再次验证了本文提出的供轮式车辆使用的新型液力自举式限滑差速器系统的正确性和可行性。更多还原

【Abstract】 With the rapid development of the auto industry and the widespread popularity of the family car, vehicle safety has become an important research subject in auto industry field. Anti-slip control of the cars is always the emphasis and difficulty on the vehicle safety control. There is a higher requirement of anti-slip ability due to the faster and faster driving speed and more and more dreadful driving conditions. Current control methods mainly aim at controling vehicle stability and increasing the traction of the vehicle. Although these control methods have a significant effect, there are still some problems that must be solved urgently. The anti-slip control principle, realizing way and limited slip performance of the limited slip system were studied in this paper.According to the problems existed in limited slip differential (LSD) mechanism used widely in wheeled vehicle currently, a novel hydraulic bootstrapped limited slip differential was proposed. Compared with the other initiative anti-slip differential, one of its obvious characteristic is that a complete hydraulic system is integrated within the differential case. It does not need the sensors to measure the variation of the car driving parameters during the working period and has higher reliability for that there is no circuit within it. By the space cam mechanism, this new LSD can adjust the output pressure automatically to regulate the lock degree of the differential according to the speed difference between the two half axles.The cam mechanism, which is composed of half axle gear and the follower located between the differential case and the half axle gear, is the key part of the differential.A new method was introduced because that the traditional reversal method was not suitable to calculate the work profile surface of the space cam mechanism. Based on the conjugated surface meshing theory and the differential geometry theory, the formulas of the induced normal on contact points, the pressure angle and the working profile surface of the new LSD cam mechanism were deduced clearly. The designing example showed that the value of the pressure angle and the induced normal curvature on every contact point could be got directly by the new method although it was not understandable as reversal method. The conclusion that there was cubic relationship between the hydraulic pressure and the size of the clearance was obtained from those functions. The differential anti-slip ability could be adjusted by changing the size of the clearance. The differential simulated software was developed on the basis of the experiment data provided by North Vehicle Research Institute. The software had been used in the friction disk working condition research after it was checked and accepted by North Vehicle Research Institute. Polynomial fitting is the traditional method to describe the mathematic model of the engine, but the low precision is the great problem and even there are fitting errors on the experiment data points. A new method was developed to establish the engine mathematic model because of the flaws of the traditional way by the Polynomial fitting instead of cubic B-spline algorithm. This method has higher precision and no fitting error on the experiment data points. In order to reflect the influence of the differential working condition affected by road exactly, a custom program language was defined to describe the routine and the road surface condition mathematic model. The Road model could be got exactly by adding friction ratio and surface roughness of the road for analyzing the differential working condition.Finally, the experiment of testing the relationship between the pressure of hydraulic system output and the rotational speed difference of the differential was implemented on the experimental platform made by myself. A half axle was motored by an AC asynchronous motor with the belt, and the pressure of the acting room was measured by a hydraulic pressure meter. The results showed that the pressure environment in the acting room could be established if the rotational speed difference between the two axles exceeded some limit. The system output pressure became higher as the speed difference got bigger, but there was a maximum. The experiment results and the conclusions indicated that the novel hydraulic bootstrapped limited slip differential was correct and practicable.更多还原