3556 拖拉机差速器零件的机械加工工艺规程设计

3556 拖拉机差速器零件的机械加工工艺规程设计,拖拉机,差速器,零件,机械,加工,工艺,规程,设计 Failure analysis of an automobile differential pinion shaftAbstractDifferential is used to decrease the speed and to provide moment increase for transmitting the movement coming from the engine to the wheels by turning it according to the suitable angle in vehicles and to provide that inner and outer wheels turn differently. Pinion gear and shaft at the entrance are manufactured as a single part whereas they are in different forms according to automobile types. Mirror gear which will work with this gear should become familiar before the assembly. In case of any breakdown, they should be changed as a pair. Generally, in these systems there are wear damages in gears. The gear inspected in this study has damage as a form of shaft fracture.n this study, failure analysis of the differential pinion shaft is carried out. Mechanical characteristics of the material are obtained first. Then, the microstructure and chemical compositions are determined. Some fractographic studies are carried out to asses the fatigue and fracture conditions.Keywords: Differential; Fracture; Power transfer; Pinion shaftIntroductionBy ordinary differential planetary gear, the planet round rack (differential shell) and half axle gears, etc parts. By the power of the engine, direct drive shaft into differential planetary wheel frame, again by the planets wheel drive left, right, two half shaft are respectively driven wheels left and right. Differential design requirements meet: (left) + (right shaft speed shaft speed) = 2 (planets wheel frame speed). When the automobile moher, left, right wheel and planetary wheel frame three speed equal in balance, while in the car when turning three equilibrium state is destroyed, cause the medial wheel speed decreases, and the lateral wheel RPM increases. Automotive differential is driven axle Lord pieces. Its function is to both sides half shaft transmission power, while allowing both sides half shaft in different speed rotating, satisfy both sides wheel as pure rolling forms do isometric driving, reducing tire and the surface friction. Differential this adjustment is automatic, here involves minimal energy consumption principle, namely earth all objects are inclined to consumption minimum state. For example a grain of beans into a bowl, beans will automatically stays in the bowl bottom and never stay in bowl wall, because bowl bottom is lowest energy position (potential), it automatically select static (minimum) without constantly kinetic energy movement. In the same way, Wheel in cornering would also automatically tendency of the lowest energy consumption in accordance with state, automatically turning radius adjusting right wheels speed. 1 Below is a brief introduce two differential1 . Off differentialThe structure of the Cherokee open-die differential is typical of planetary gear set structure, only the sun wheel and the number of teeth gear ring outside are the same. In this planetary gear set, active wheel is the planet frame, passive round is two SUNS chakra. Through the planetary gear set transmission properties we know, if planet shelf as ZhuDongZhou, two SUNS rounds of speed and rotation direction is uncertain, even two SUNS rounds of rotation direction is the opposite.Vehicle condition, this differential went to feature is two and a half shaft transmission torque is same. In a drive wheels impending cases, if transmission shaft is uniform rotation, have the drive wheels is no adhesion of driving force transmission speed rotation, if there is the driving wheels, adhesion driving wheels Angle acceleration is equal to the impending product and moment of inertia.Vehicle turn tires dont skid condition, differential connection of two and a half shaft torque direction is instead, give the vehicle driving forward, only the inside of the wheel, the planet shelf and medial sun round by constant transmission between became deceleration transmission, driving sensation is accelerated speed curve more powerful than straight.The advantages of open differential is installed in the pavement turned the best effect. Driving Weakness is in a drive wheels, under the situation of loss of adhesion another no driving force.2. Limited slip differential Limited slip differential used for parts make up open-die differential transmission in off-road defects, it is in the open differential institution improved, and the differential shell side increase friction between gear piece, corresponding to the planetary gear set speaking, is the planet shelf and the sun round between increased friction slices, increase the sun wheel and planet shelf free rotating resistance torque. Limited slip differential provide additional torque, and friction slices transfer of power and two driving wheel rotation difference of concerned. In open-die differential structure to improve on LSD, cannot produce 100% limited slip, because the limited slip coefficient, the higher the vehicles to the characteristics of the poor. LSD have open-die differential transmission characteristics and mechanical structure. Advantage is to provide certain limited slip torque, defect is turning performance becomes poor, friction slices limited life. LSD is the suitable scope paving road surface and mild off-road. Usually used for the drive. Former drove generally does not installed, because LSD interfere steering, limited slip coefficient, the greater the steering the more difficult. The final-drive gears may be directly or indirectly driven from the output gearing of the gearbox. Directly driven final drives are used when the engine and transmission units are combined together to form an integral construction. Indirectly driven final drives are used at the rear of the vehicle being either sprung and attached to the body structure or unsprung and incorporated in the rear-axle casing. The final-drive gears are used in the transmission system for the following reasons 1:(a) to redirect the drive from the gearbox or propeller shaft through 90_ and,(b) to provide a permanent gear reduction between the engine and the driving road-wheels.In vehicles, differential is the main part which transmits the movement coming from the engine to the wheels. On a smooth road, the movement comes to both wheels evenly. The inner wheel should turn less and the outer wheel should turn more to do the turning without lateral slipping and being flung. Differential, which is generally placed in the middle part of the rear bridge, consists of pinion gear, mirror gear, differential box, two axle gear and two pinion spider gears.A schematic illustration of a differential is given in Fig. 1. The technical drawing of the fractured pinion shaft is also given in Fig. 2. Fig. 3 shows the photograph of the fractured pinion shaft and the fracture sectionis indicated.In differentials, mirror and pinion gear are made to get used to each other during manufacturing and the same serial number is given. Both of them are changed on condition that there are any problems. In these systems, the common damage is the wear of gears 24. In this study, the pinion shaft of the differential of aminibus has been inspected. The minibus is a diesel vehicle driven at the rear axle and has a passenger capacity of 15 people. Maximum engine power is 90/4000 HP/rpm, and maximum torque is 205/1600 Nm/rpm. Its transmission box has manual system (5 forward, 1 back). The damage was caused by stopping and starting the minibus at a traffic lights. In this differential, entrance shaft which carries the pinion gear was broken. Various studies have been made to determine the type and possible reasons of the damage.These are:_ studies carried out to determine the material of the shaft;_ studies carried out to determine the micro-structure;_ studies related to the fracture surface.There is a closer photograph of the fractured surfaces and fracture area in Fig. 4. The fracture wascaused by taking out circular mark gear seen in the middle of surfaces.Fig. 1. Schematic of the analysed differential.2. Experimental procedurepecimens extracted from the shaft were subjected to various tests including hardness tests and metallographic and scanning electron microscopy as well as the determination of chemical composition. All tests were carried out at room temperature.2.1. Chemical and metallurgical analysisChemical analysis of the fractured differential material was carried out using a spectrometer. The chemical composition of the material is given in Table 1. Chemical composition shows that the material is a low alloy carburising steel of the AISI 8620 type.Hardenability of this steel is very low because of low carbon proportion. Therefore, surface area becomes hard and highly enduring, and inner areas becomes tough by increasing carbon proportion on the surface area with cementation operation. This is the kind of steel which is generally used in mechanical parts subjected do torsion and bending. High resistance is obtained on the surface and high fatigue endurance value can be obtained with compressive residual stress by making the surface harder 57.In which alloy elements distribute themselves in carbon steels depends primarily on the compound- and carbide-forming tendencies of each element. Nickel dissolves in the a ferrite of the steel since it has less tendency to form carbides than iron. Silicon combines to a limited extent with the oxygen present in the steel to form nonmetallic inclusions but otherwise dissolves in the ferrite. Most of the manganese added to carbon steels dissolves in the ferrite. Chromium, which has a somewhat stronger carbide-forming tendency than iron, partitions between the ferrite and carbide phases. The distribution of chromium depends on the amount of carbon present and if other stronger carbide-forming elements such as titanium and columbium are absent. Tungsten and molybdenum combine with carbon to form carbides if there is sufficient carbon present and if other stronger carbide-forming elements such as titanium and columbium are absent. Manganeseand nickel lower the eutectoid temperature 8.Preliminary micro structural examination of the failed differential material is shown in Fig. 5. It can be seen that the material has a mixed structure in which some ferrite exist probably as a result of slow cooling and high Si content. High Si content in this type of steel improves the heat treatment susceptibility as well as an improvement of yield strength and maximum stress without any reduction of ductility 9. If the microstructure cannot be inverted to martensite by quenching, a reduction of fatigue limit is observed. There are areas with carbon phase in Fig. 5(a). There is the transition boundary of carburisation in Fig. 5(b) and (c) shows the matrix region without carburisation. As far as it is seen in these photographs, the piece was first carburised, then the quenching operation was done and than tempered. This situation can be understood from blind martensite plates.2.2. Hardness testsThe hardness measurements are carried out by a MetTest-HT type computer integrated hardness tester. The load is 1471 N. The medium hardness value of the interior regions is obtained as 43 HRC. Micro hardness measurements have been made to determine the chance of hardness values along the cross-section because of the hardening of surface area due to carburisation. The results of Vickers hardness measurement under a load of 4.903 N are illustrated in Table 2.2.3. Inspection of the fractureThe direct observations of the piece with fractured surfaces and SEM analyses are given in this chapter. The crack started because of a possible problem in the bottom of notch caused the shaft to be broken completely. The crack started on the outer part, after some time it continued beyond the centre and there was only a little part left. And this part was broken statically during sudden starting of the vehicle at the traffic lights. As a characteristic of the fatigue fracture, there are two regions in the fractured surface. These are a smooth surface created by crack propagation and a rough surface created by sudden fracture. These two regions can be seen clearly for the entire problem as in Fig. 4. The fatigue crack propagation region covers more than 80% of the cross-section.Shaft works under the effect of bending, torsion and axial forces which affect repeatedly depending on the usage place. There is a sharp fillet at level on the fractured section. For this reason, stress concentration factors of the area have been determined. Kt = 2.4 value (for bending and tension) and Kt = 1.9 value (for torsion) have been acquired according to calculations. These are quite high values for areas exposed to combined loading.These observations and analysis show that the piece was broken under the influence of torsion with low nominal stresses and medium stress concentration 10.The scanning electron microscopy shows that the fracture has taken place in a ductile manner (Fig. 6). There are some shear lips in the crack propagation region which is a glue of the plastic shear deformations. Fig. 7 shows the beach marks of the fatigue crack propagation. The distance between any two lines is nearly 133 nm.3. ConclusionsA failed differential pinion shaft is analysed in this study. The pinion shaft is produced from AISI 8620 low carbon carburising steel which had a carburising, quenching and tempering heat treatment process. Mechanical properties, micro structural properties, chemical compositions and fractographic analyses are carried out to determine the possible fracture reasons of the component. As a conclusion, the following statements can be drawn:_ The fracture has taken place at a region having a high stress concentration by a fatigue procedure undera combined bending, torsion and axial stresses having highly reversible nature._ The crack of the fracture is initiated probably at a material defect region at the critical location._ The fracture is taken place in a ductile manner._ Possible later failures may easily be prevented by reducing the stress concentration at the criticallocation.AcknowledgementThe author is very indebted to Prof. S. Tasgetiren for his advice and recommendations during the study.References1 Heisler H. Vehicle and engine technology. 2nd ed. London: SAE International; 1999.2 Makevet E, Roman I. Failure analysis of a final drive transmission in off-road vehicles. Eng Failure Anal 2002;9:57992.3 Orhan S, Akturk N. Determination of physical faults in gearbox through vibration analysis. J Fac Eng Arch Gazi University2003;18(3):97106.4 Tas_getiren S, Aslantas_ K, Ucun I. Effect of press-fitting pressure on the fatigue damages of root in spur gears. Technol Res: EJMT2004;2:219.5 Nanawarea GK, Pableb MJ. Failures of rear axle shafts of 575 DI tractors. Eng Failure Anal 2003;10:71924.6 Aslantas_ K, Tas_getiren S. A study of spur gear pitting formation and life prediction. Wear 2004;257:116775.7 Savas_ V, O zek C. Investigation of the distribution of temperature on a shaft with respect to the deflection. Technol Res: EJMT2005;1:338.8 Smith FW. Principles of materials science and engineering. 3rd ed. USA: McGraw-Hill Series; 1996. p. 51718.9 ASM metal handbook, vol. 1. Properties and selection, irons, steels, and high performance alloys; 1991.10 Voort GFV. Visual examination and light microscopy. ASM handbook metallography and microstructures. Materials Park(OH): ASM International; 1991. p. 10065.汽车差速器小齿轮轴的失效分析摘要差速器被用于减少的速度并且提供传输运动中的力矩。从发动机到轮子转动它根据适当的角度在车辆和提供内部和外部的车轮转是不同的。小齿轮啮合和轴在入口处是作为一个单独的部分而制造它们是在不同的形式根据车辆的类型。镜子齿轮将工作用这个前齿轮应该熟悉组装。如有任何故障,他们应该被改变成双。一般来说,在这些系统中有磨损的齿轮。齿轮检查这方面的研究以有一种轴断裂作为齿轮被破坏。在这项研究中,失效分析型差动齿轮轴被执行。材料力学特性获得第一。然后,材料的显微结构和化学成分已经决定了。一些显微研究学者进行疲劳断裂条件的分析关键词:差速器;断裂,动力装置,齿轮轴一 介绍对于整车的结构体系来说，差速器只是装在两个驱动半轴之间的一个小轴承。看似微不足道，但如果没有它，两个驱动半轴之间以刚性连接，左右车轮的转速保持一致，汽车将只能直线行驶，不能转弯。自从一百年前雷诺汽车公司的创始人路易斯雷诺发明出差速器后，它就在汽车上发挥着巨大作用。现在每辆汽车上都装有差速器。 顾名思义，差速器的作用就是使两侧车轮转速不同。当汽车转弯时，例如左转弯，弯心在左侧，在相同的时间内右侧车轮要比左侧车轮走过的轨迹要长，所以右侧车轮转的要更快一些。要达到这个效果，就得通过差速器来调节。差速器由差速器壳、行星齿轮、行星齿轮轴和半轴齿轮等机械零件组成。 发动机的动力经变速器从动轴进入差速器后，直接驱动差速器壳，再传递到行星齿轮，带动左、右半轴齿轮，进而驱动车轮，左右半轴的转速之和等于差速器壳转速的两倍。当汽车直线行驶时，行星齿轮，左、右半轴齿轮和驱动车轮三者转速相同。当转弯时，由于汽车受力情况发生变化，反馈在左右半轴上，进而破坏差速器原有的平衡，这时转速重新分配，导致内侧车轮转速减小，外侧车轮转速增加，重新达到平衡状态，同时，汽车完成转弯动作。以下简介两种差速器：一 开式差速器 切诺基的开式差速器的结构，是典型的行星齿轮组结构，只不过太阳轮和外齿圈的齿数是一样的。在这套行星齿轮组里，主动轮是行星架，被动轮是两个太阳轮。通过行星齿轮组的传动特性我们知道，如果行星架作为主动轴，两个太阳轮的转速和转动方向是不确定的，甚至两个太阳轮的转动方向是相反的。 车辆直行状态下，这种差速器的特性就是，给两个半轴传递的扭矩相同。在一个驱动轮悬空情况下，如果传动轴是匀速转动，有附着力的驱动轮是没有驱动力的，如果传动轴是加速转动，有附着力的驱动轮的驱动力等于悬空车轮的角加速度和转动惯量的乘积。 车辆转弯轮胎不打滑的状态下，差速器连接的两个半轴的扭矩方向是相反的，给车辆提供向前驱动力的，只有内侧的车轮，行星架和内侧的太阳轮之间由等速传动变成了减速传动，驾驶感觉就是弯道加速比直道加速更有力。 开式差速器的优点就是在铺装路面上转行行驶的效果最好。缺点就是在一个驱动轮丧失附着力的情况下，另外一个也没有驱动力。 开式差速器的适用范围是所有铺装路面行驶的车辆，前桥驱动和后桥驱动都可以安装。 二 限滑差速器 限滑差速器用于部分弥补开式差速器在越野路面的传动缺陷，它是在开式差速器的机构上加以改进，在差速器壳的边齿轮之间增加摩擦片，对应于行星齿轮组来讲，就是在行星架和太阳轮之间增加了摩擦片，增加太阳轮与行星架自由转动的阻力力矩。 限滑差速器提供的附加扭矩，与摩擦片传递的动力和两驱动轮的转速差有关。 在开式差速器结构上改进产生的 LSD，不能做到 100的限滑，因为限滑系数越高，车辆的转向特性越差。 LSD 具备开式差速器的传动特性和机械结构。优点就是提供一定的限滑力矩，缺点是转向特性变差，摩擦片寿命有限。 LSD的适用范围是铺装路面和轻度越野路面。通常用于后驱车。前驱车一般不装，因为LSD会干涉转向，限滑系数越大，转向越困难。最后一级齿轮（也就是输出齿轮)可以直接或间接被变速箱齿轮驱动，当发动机和传动装置结合在一起形成便成为一个完整的结构时，采用直接驱动器驱动。间接驱动最终驱动器在车尾处的弹簧连接车身结构或者非悬挂并纳入后轴套管中。最后的驱动齿轮应用在传输系统中有下列原因：（1）从变速箱和传动轴驱动改变 90 度重新定向驱动（2）提供在发动机和驱动轮之间的永久的齿轮减速在车辆中，差速器是主要部分用于传送从发动机到车轮的运动。里面的的轮子转动的少,外面的轮子转动的多就没有侧向的滑移和猛冲。差速器通常被放置在后桥的中部,由小齿轮啮合,镜子齿轮,齿轮箱,两轴差和两个小三角齿轮组成。图1为差速器的原理图，图二为断裂齿轮轴的技术图纸设计。通过图三的照片表明了齿轮轴的断裂。在差速器,镜子和小齿轮啮合中存在的问题,从而提出了适应彼此生产过程、相同的序号的算法。他们俩在改变的情况下,会有很多问题。在这些系统中,常见的损伤是,磨损的齿轮2 - 4。在这项研究中,对齿轮轴的差速进行了检查。小型巴士是柴油车辆驱动后桥的，载客能力的有15人。最高的发动机为每分钟4000转，功率为90匹，当发动机转速达到每分钟1600转时，输出最大扭距力为205顿米。它有手操作的传动箱系统(5前面,1后部)。而导致的破坏和起动小巴停在红绿灯处。这个差速器、输入轴携带的有小齿轮轴断了。已经进行了很多不同的研究来确定类型和可能的原因损坏的地方。这些是:研究确定了轴的材料;实验确定了研究微观结构;研究相关的断裂表面。有一个更近的照片和断裂区骨折的表面。2 实验过程在标本中提取的轴在受到各种试验包括硬度测试、金相和扫描电镜以及化学成分的测定。所有的测试都是在室温条件下进行的。2.1 化工和冶金分析化学分析裂隙微分材料进行了用分光计。材料的化学成分是表1规定的数值。化学成分表明,该材料是一种低合金钢板8620类型。淬硬钢是非常低的,因为对低碳的比例。因此,通过增加表面积碳比例的操作会使表面面积会变硬,高度耐用,及内部变的越加的坚硬。这是这种钢是受到普遍采用的机械部分做扭转和弯曲。高阻表面上是获得耐力值和高疲劳,可获得压残余应力使表面更加困难5 - 7。在那些的合金元素分布主要取决于炭素钢的复合，化学和碳化依赖于每个元素。镍溶于铁素体中后形成碳化物比铁有更少的趋势。硅结合是有限的程度与氧气存在于非金属夹杂物在钢形成溶于铁素体,但除此之外。大部分的锰添加到碳素钢溶于铁素体。铬,它有一个趋势比铁稍微要强的元素,它的划分于铁素体和碳化物合金阶段。铬的分布依赖于碳量的百分比，如果其他更强的元素,如钛和铜都没有。钨、钼结合碳形成碳化物，如果有充足的碳的百分比，现在和如果其他更强的元素,如钛和铜都没有。锰和镍的在低温下回形成共熔体。初步的微结构检测失败的微分资料被显示在图5。可以看出,该材料具有的一种混合结构,其中一些铁氧体存在或许由于缓慢降温和高硅含量。高硅含量在这种类型的钢提高热处理敏感性进行改进的屈服强度和最大应力,没有任何减少延性9 如果不能倒置的显微结构由淬火马氏体,减少了疲劳极限是观察到的现象。在一些领域与碳相图5(a)。有渗碳结构钢过渡边界在图5(b)和(c)显示核基质附着区,无需渗碳结构钢矩阵。从图片5可以看出该材料是一种有铁素体存在的混合结构。这种高硅含量的钢可以改善钢热处理时易受损的状态，同时也可以在没有任何延展性减小的情况下改善屈服和最大应力。如果显微结构的不能够通过淬火使马氏体得到转换，也会较少它的疲劳界限。在图片5a中显示的是碳含量阶段,图片5b中显示的都是渗碳剂的过度界限，图片c中显示的都是在没有渗碳剂的模型。2.2 硬度测试硬度测量是执行的一种 MetTest-HT 型计算机集成硬度计。载荷 1471:中等硬度值的内部地区获得 43 个错误。取得了微硬度的测量方法来确定硬度值的机会沿截面由于硬化由于渗碳结构钢表面积。维氏硬度测量的结果 4.903 载荷作用下的 N 是说明表 2。2.3 检测断裂在本章中直接地给出了观察和扫描电镜(SEM)片与断裂表面。裂纹开始因为一个可能的问题引起的底部轴切口完全被打破。裂纹开始在外层,在经过若干时间它不断超越本中心只有很小一部分离开了。和这部分断了静态的突然开始在飞行器在红绿灯处。为特征的疲劳断裂,有两个地区断裂表面。这些是光滑的表面由裂纹扩展和粗糙的表面由突然断裂。这两个区域可以被清晰地看到整个问题作为图4中。疲劳裂纹扩展的区域包括了80%以上的断面。轴功向下弯曲、扭转和轴力的影响取决于反复使用一个地方。在断裂层的表面上一个快尖锐的切片。因为这个原因,所以断定了该区域的应力集中系数值。Kt = 2.4价值(弯刀和张力)和Kt = 1.9%的价值(扭力)已获得根据计算的结果。这些都是相当高的价值为区域暴露在联合加载中。这些观察和分析表明,该块断了的影响下,以较低的公称应力和扭转应力集中10所聚集的媒介。扫描电镜显示,这也发生在断裂韧性的方式(图6)。有一些切变裂痕在裂纹扩展区,这是一种胶塑性剪切变形。图7显示贝壳状裂纹扩展的一个标志。任何两线之间的距离是近133纳米。3结论在这项研究中分析了出现故障的差速器小齿轮轴，这个小齿轮轴是 AISI8620 的经过渗碳，淬火和回火的热处理程序的低渗碳钢。通过力学性能，微观结构特性，化学结构组成以及金属断面的显微结构观察以确定组件可能断裂的原因。以下部分是本次试验的结论：经过疲劳程序在组合挠度，转矩和轴向力变大时，断裂的区域发生在应力集中较高的地方，断裂的裂纹一开始可能是在材料的临界状态位置，该断裂在发生一定程度的延展。通过在关键部位减少压应力集中能够很容易的避免以后可能出现的故障。参考文献1. 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