变速器主减速齿轮对有限元分析

发布时间：2018-09-08 16:33

【摘要】：变速器是汽车的重要部件,而处于常啮合状态的变速器主减速齿轮对,作为变速器的重要零件,它承受着汽车传动的全部扭矩。同时因为汽车频繁的换档和车速变化,造成变速器主减速齿轮对的寿命缩短。主减速齿轮价格昂贵,不可随意调换,制造精度比较高。而齿轮的承载能力主要受接触强度和弯曲强度的限制,因此,对主减速齿轮副的弯曲应力和接触应力进行科学的分析,就显得十分必要。本文根据某企业提供的汽车手动变速器主减速齿轮对的结构及机械性能参数,实现了主减速斜齿轮的三维参数化精确建模。尽管很多研究人员在有关CAD/CAM/CAE软件上实现了“参数化”的斜齿轮建模,但这个“参数化”是在“事先手动参与”后的实现的“参数化”,并不是完全的全过程参数化。另外很多研究文献忽略了齿轮根部的精确造型,而这是进行轮齿根部弯曲强度有限元计算的重要前提。本文建立斜齿轮的完整的实用的数学模型,所谓“完整”,既包括渐开线齿廓,也包括过渡曲线齿廓;所谓“实用”,是指以齿厚中心线为对称轴建立了齿廓的数学模型,这有利于三维CAD建模。并基于APDL语言实现了斜齿轮的三维参数化精确建模。本文对变速器在发动机最大输出扭矩(变速器最大输入扭矩)时,齿轮副的受载和约束情况进行了分析,重点介绍了渐开线斜齿轮啮合最恶加载线的定义,并根据此定义对变速器主减速齿轮副的最恶加载线进行了计算,利用最恶加载线对齿轮施加载荷。求解计算后,分别对主动和从动齿轮的弯曲应力分布状况进行了研究,得出齿轮中较危险弯曲应力的位置,在实际的齿轮设计中可以作为理论参考,同时在齿轮制造和热处理过程中可以对弯曲应力最大的地方考虑特殊处理,以增加齿轮的寿命和可靠性。传统计算公式与有限元法算的结果相比较,计算公式得到的弯曲应力值偏小些,说明工程中,按有限元法进行设计和校核,是偏安全的。用有限元分析结果对弯曲强度进行了校核,应力最大值比材料弹性许用应力小,得出齿轮弯曲强度储备较大。这与主减速齿轮实际使用中很少发生弯曲折断的结论是一致的。本文为使齿轮副非线性接触分析的计算速度加快,结果更精确,对齿轮副啮合模型做简化,取大齿轮的四个齿和小齿轮的三个齿进行接触有限元分析。建立接触对(指定接触面和目标面、创建目标面和接触面单元、调整接触初始条件),计算在载荷和约束作用下的应力值,得出直观的齿轮副接触面上接触应力变化云图。从图分析知等效接触应力最大值为929.6 MPa,齿面接触应力成线形分布,即沿接触线分布,分布不均,两端靠近中间的位置接触应力相对较大,中间位置相对较小,最大的接触应力出现在节线附近靠近齿根处。分析得出的齿轮中较危险接触应力位置,在实际的齿轮设计中可以作为理论参考,同时在齿轮制造和热处理过程中可以对接触应力最大的地方考虑特殊处理,以增加齿轮的寿命和可靠性。与弯曲应力计算结果比较分析相似,计算公式得到的接触应力值偏小些,说明工程中,按有限元法进行设计和校核,是偏安全的。对接触强度进行了校核,其结果得到了合作企业的认可,精度较高。综上所述,本文对MT21变速器主减速齿轮副的弯曲强度和接触强度进行了详尽的分析,掌握了该齿轮副应力分布,对强度进行了校核,分析结果经设计方认证,认为具有较高的精度。本文的研究工作为齿轮的结构优化、轮齿修形、多物理场耦合分析等奠定了基础。鉴于齿轮强度计算的复杂性,应当说本文的研究仍属于基础性的工作。在本文研究基础上,可以方便地进一步研究齿轮的结构优化、轮齿修形、多物理场祸合分析、概率设计(可靠性设计)等。
[Abstract]:Transmission is an important part of automobile, and the main gear pair of transmission in constant meshing state, as an important part of transmission, it bears all the torque of automobile transmission. It is necessary to scientifically analyze the bending stress and contact stress of the main reducer gear pair.
According to the structure and mechanical performance parameters of the main reducer gear pair of the automobile manual transmission provided by an enterprise, this paper realizes the accurate three-dimensional parametric modeling of the helical gear pair of the main reducer. The parameterization after participation is not a complete parameterization of the whole process. In addition, many research papers neglect the precise modeling of the root of the gear, which is an important prerequisite for the finite element calculation of the bending strength of the root of the gear. Linear tooth profile also includes transition curve tooth profile; the so-called "practical" refers to the establishment of a mathematical model of tooth profile with the center line of tooth thickness as the symmetrical axis, which is conducive to three-dimensional CAD modeling.
In this paper, the load and restraint of gear pair in the maximum output torque of engine (maximum input torque of transmission) are analyzed. The definition of the worst load line of involute helical gear meshing is introduced emphatically. According to this definition, the worst load line of the main gear pair of transmission is calculated, and the worst load line is used. After calculating, the bending stress distribution of active and driven gears is studied, and the position of dangerous bending stress in gears is obtained. It can be used as a theoretical reference in actual gear design, and special consideration can be given to the place where the bending stress is maximum in gear manufacturing and heat treatment. Comparing with the result of finite element method, the value of bending stress obtained by traditional calculation formula is smaller, which shows that it is safe to design and check according to finite element method in engineering. The allowable stress is small and the reserve of bending strength of the gear is large, which is consistent with the conclusion that the bending fracture of the main reducer gear seldom occurs in actual use.
In order to speed up the calculation of non-linear contact analysis of gear pair and make the result more accurate, the meshing model of gear pair is simplified, and the contact finite element analysis of four teeth of big gear and three teeth of small gear is carried out. By calculating the stress value under load and restraint, the contact stress variation nephogram on the contact surface of gear pair is obtained intuitively. The maximum value of equivalent contact stress is 929.6 MPa, and the contact stress on the tooth surface is linear distribution, that is, along the contact line, the distribution is uneven, the contact stress at the two ends near the middle position is relatively large, and the middle position is relative. The position of the dangerous contact stress in the gear can be used as a theoretical reference in the actual gear design. At the same time, special treatment can be taken into account in the gear manufacturing and heat treatment process to increase the life and reliability of the gear. Similar to the calculation results of bending stress, the contact stress values obtained by the calculation formulas are slightly smaller, which shows that it is safe to design and check the contact strength by finite element method in engineering. The results are approved by the cooperative enterprise and have higher accuracy.
In summary, the bending strength and contact strength of the main reducer gear pair of MT21 transmission are analyzed in detail in this paper, the stress distribution of the gear pair is mastered, and the strength is checked. The analysis result is verified by the designer, and it is considered to have higher precision. In view of the complexity of gear strength calculation, this paper is still a basic work. On the basis of this study, it is convenient to further study gear structure optimization, gear tooth modification, multi-physical field coincidence analysis, probability design (reliability design) and so on.
【学位授予单位】：江西理工大学
【学位级别】：硕士
【学位授予年份】：2011
【分类号】：TH132.41

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