汽车主减速器-外文翻译.docx

AUTOMOTIWE FINAL DRIVEFINAL DRIVEA final drive is that part of a power transmission system between the drive shaft and the differential. Its function is to change the direction of the power transmitted by the drive shaft through 90 degrees to the driving axles. At the same time. it provides a fixed reduction between the speed of the drive shaft and the axle driving the wheels.The reduction or gear ratio of the final drive is determined by dividing the number of teeth on the ring gear by the number of teeth on the pinion gear. In passenger vehicles, this speed reduction varies from about 3:1 to 5:1. In trucks it varies from about 5:1 to 11:1. To calculate rear axle ratio, count the number of teeth on each gear. Then divide the number of pinion teeth into the number of ring gear teeth. For example, if the pinion gear has 10 teeth and the ring gear has 30 (30 divided by 10), the rear axle ratio would be 3:1. Manufacturers install a rear axle ratio that provides a compromise between performance and economy. The average passenger car ratio is 3.50:1.The higher axle ratio, 4.11:1 for instance, would increase acceleration and pulling power but would decrease fuel economy. The engine would have to run at a higher rpm to maintain an equal cruising speed. The lower axle ratio. 3:1, would reduce acceleration and pulling power but would increase fuel mileage. The engine would run at a lower rpm while maintaining the same speed. The major components of the final drive include the pinion gear, connected to the drive shaft, and a bevel gear or ring gear that is bolted or riveted to the differential carrier. To maintain accurate and proper alignment and tooth contact, the ring gear and differential assembly are mounted in bearings. The bevel drive pinion is supported by two tapered roller bearings, mounted in the differential carrier. This pinion shaft is straddle mounted. meaning that a bearing is located on each side of the pinion shaft teeth. Oil seals prevent the loss of lubricant from the housing where the pinion shaft and axle shafts protrude. As a mechanic, you will encounter the final drive gears in the spiral bevel and hypoid design.Spiral Bevel Gear Spiral bevel gears have curved gear teeth with the pinion and ring gear on the same center line. This type of final drive is used extensively in truck and occasionally in older automobiles. This design allows for constant contact between the ring gear and pinion. It also necessitates the use of heavy grade lubricants. Hypoid Gear The hypoid gear final drive is an improvement or variation of the spiral bevel design and is commonly used in light and medium trucks and all domestic rear- wheel drive automobiles. Hypoid gears have replaced spiral bevel gears because they lower the hump in the floor of the vehicle and improve gear-meshing action. As you can see in figure 5-13, the pinion meshes with the ring gear below the center line and is at a slight angle (less than 90 degrees). Figure 5-13.Types of final drives. This angle and the use of heavier (larger) teeth permit an increased amount of power to be transmitted while the size of the ring gear and housing remain constant. The tooth design is similar to the spiral bevel but includes some of the characteristics of the worm gear. This permits the reduced drive angle. The hypoid gear teeth have a more pronounced curve and steeper angle, resulting in larger tooth areas and more teeth to be in contact at the same time. With more than one gear tooth in contact, a hypoid design increases gear life and reduces gear noise. The wiping action of the teeth causes heavy tooth pressure that requires the use of heavy grade lubricants.Double-Reduction Final Drive In the final drives shown in figure 5-13, there is a single fixed gear reduction. This is the only gear reduction in most automobiles and light- and some medium-duty trucks between the drive shaft and the wheels.Double-reduction final drives are used for heavy- duty trucks. With this arrangement (fig. 5-14) it is not necessary to have a large ring gear to get the necessary gear reduction. The first gear reduction is obtained through a pinion and ring gear as the single fixed gear reduction final drive. Referring to figure 5-14, notice that the secondary pinion is mounted on the primary ring gear shaft. The second gear reduction is the result of the secondary pinion which is rigidly attached to the primary ring gear, driving a large helical gear which is attached to the differential case. Double-reduction final drives may be found on military design vehicles, such as the 5-ton truck. Many commercially designed vehicles of this size use a single- or double-reduction final drive with provisions for two speeds to be incorporated Figure 5-14.Double-reduction final driveTwo-Speed Final DriveThe two-speed or dual-ratio final drive is used to supplement the gearing of the other drive train components and is used in vehicles with a single drive axle (fig. 5-15). The operator can select the range or speed of this axle with a button on the shifting lever of the transmission or by a lever through linkageThe two-speed final drive doubles the number of gear ratios available for driving the vehicle under various load and road conditions. For example, a vehicle with a two-speed unit and a five-speed transmission, ten different forward speeds are available. This unit provides a gear ratio high enough to permit pulling a heavy load up steep grades and a low ratio to permit the vehicle to run at high speeds with a light load or no loadThe conventional spiral bevel pinion and ring gear drives the two-speed unit, but a planetary gear train is placed between the differential drive ring gear and the differential case. The internal gear of the planetary gear train is bolted rigidly to the bevel drive gear. A ring on which the planetary gears are pivoted is bolted to the differential case. A member, consisting of the sun gear and a dog clutch, slides on one of the axle shafts and is controlled through a button or lever accessible to the operatorWhen in high range, the sun gear meshes with the internal teeth on the ring carrying the planetary gears and disengages the dog clutch from the left bearing adjusting ring, which is rigidly held in the differential carrier. In this position, the planetary gear train is locked together. There is no relative motion between the differential case and the gears in the planetary drive train. The differential case is driven directly by the differential ring gear, the same as in the conventional single fixed gear final drive.When shifted into low range, the sun gear is slid out of mesh with the ring carrying the planetary gears. The dog clutch makes a rigid connection with the left bearing adjusting ring. Because the sun gear is integral with the dog clutch, it is also locked to the bearing adjusting rings and remains stationary. The internal gear rotates the planetary gears around the stationary sun gear, and the differential case is driven by the ring on which the planetary gears are pivoted. This action produces the gear reduction, or low speed, of the axleDIFFERENTIAL ACTIONThe rear wheels of a vehicle do not always turn at the same speed. When the vehicle is turning or when tire diameters differ slightly, the rear wheels must rotate at different speeds. If there were a solid connection between each axle and the differential case, the tires would tend to slide, squeal, and wear whenever the operator turned the steering wheel of the vehicle. A differential is designed to prevent this problem. Driving Straight AheadWhen a vehicle is driving straight ahead, the ring gear, the differential case, the differential pinion gears, and the differential side gears turn as a unit. The two differential pinion gears do NOT rotate on the pinion shaft, because they exert equal force on the side gears. As a result, the side gears turn at the same speed as the ring gear, causing both rear wheels to turn at the same speed. Turning CornersWhen the vehicle begins to round a curve, the differential pinion gears rotate on the pinion shaft. This occurs because the pinion gears must walk around the slower turning differential side gear. Therefore, the pinion gears carry additional rotary motion to the faster turning outer wheel on the turn.Differential speed is considered to be 100 percent. The rotating action of the pinion gears carries 90 percent of this speed to the slowing mover inner wheel and sends 110 percent of the speed to the faster rotating outer wheel. This action allows the vehicle to make the turn without sliding or squealing the wheels. Figure 5-15.Two speed final drive汽车主减速器主减速器主减速器是在传动轴和差速器之间的一个动力传动系统的组成部分。它的作用是通过90°传动轴改变传给驱动轴的动力传递方向。同时，它提供了一个固定的减速，该值介于传动轴和驱动轮轴的速度之间。主减速器的减速和齿轮传动比取决于环形齿轮齿数和小齿轮齿数。客车的减速在3:1到5:1之间，卡车是在5:1到11:1之间。计算后轴传动比要数每个齿轮上的齿数。然后把小齿轮的齿数插入环形齿轮的齿数。例如，如果小齿轮有10齿，齿圈有30(30除以10)，后轴比率将3:1。生产厂家在安装后轴传动比时要考虑到性能和费用之间的协调。客车平均的比率是3.50:1更高轴比，例如4。11:1，将增加加速度和动力但会降低燃油经济性。发动机将不得不突然进攻一个更高转速保持一个能与之匹敌的速度。较低级轴比如3:1，将减少加速度和拉动力但是将会增加燃油里程。发动机将突然进攻一个降低转速而维持同一速度。主减速器的主要元件包括连接到传动轴上的小齿轮，和一个被啰嗦或是铆钉固定在差速器壳上的斜齿轮或者是圆柱齿轮。为了保持轮齿之间准确，正确的接触，齿圈，差动总成被安装在一定的方位。主动小锥齿轮由二对圆锥滚子轴承支撑，安装在差速器上。这个小齿轮轴跨式组合安装。意味着那是一个能被定位在每个小齿轮齿侧的轴齿。油封是为了防止润滑剂，小齿轮轴，轴凸出的部分泄漏弧齿锥齿轮具有弯曲的轮齿的弧齿锥齿轮同小齿轮，齿圈在同一中心线。这种主减速器形式被广阔使用在卡车上，偶尔用在年长的汽车上。这个设计允许环形齿和小齿轮之间建立不断地联系。它也因此有必要用高等级滑润剂。双曲面齿轮双曲面齿轮减速器是一个改进或变异的盘旋斜角设计，常用在轻型和中型卡车以及所有国内的四轮驱动汽车上。双曲面齿轮已经取代了弧齿锥齿轮，因为他们降低了汽车底板上的凸起，改善轮齿啮合行动。正如你看到的在5-13图中，小齿轮轴线在中心线的下方，在一个轻微角度(少于90°)。这个角度和用的重（大）的轮齿可以保证被传递的功率增加同时保持环形齿的大小和容积不变。这种齿型设计类似盘旋斜角然而包括一些蜗轮的特征。这个保证驱动器角的减小。双曲线齿轮轮齿有一个更显著的弯曲和陡峭的角，导致了在大齿轮轮齿地区更多的轮齿在同时接触。在不止一个轮齿在同时接触的情况下，一个双曲线设计能够增加齿轮的寿命和减少齿轮噪音。轮齿的纵向滑动会引起很大的压力，所以要使用高等级的润滑油。双级主减速器在图5-13所示的主减速器中，有一个独立的固定减速齿轮。这个独一无二的减速齿轮常用在大多数汽车和轻型和中型卡车的传动轴和车轮之间。双极主减速器被用在重型卡车上。有了这种安排（图：5-14）我们就没必要用一个大直径的环形齿轮来使其获得必要的齿轮减速。第一级齿轮减速是通过一个小齿轮，齿圈作为单固定齿轮减速来实现的主减速器。提到图5-14，我们注意到那个次要小齿轮被安装在主环形齿轮轴上。第二级齿轮减速是通过被安装在主环形齿轮轴上的次要小齿轮驱动被附属在差动器里面的一个大的螺旋齿轮实现的。双级主减速可在军用汽车上发现，例如5吨卡车上。许多这种尺寸的商用汽车设计使用单级或双级主减速器同规定的双速结合在一起。双速主减速器双速或者是两传动比的主减速器常常被用来补充另一个传动元件的齿轮，常用在单驱动轴的汽车上。（图5-15）操作者选择这个轴的范围或者是速度可以通过一个按键安装在传输的变速杆上或者是一个连锁的杠杆。双速减速器拥有两个齿轮比来驱动汽车以适用多种多样的负荷和道路状况。例如，一辆汽车有一个双速单元，一个五速传输，那么就有十种不同的前进速度可供使用。这个单元提供一个足够高的齿轮齿数比来保证拉重负荷徒级行驶，和一个低的比率以允许车辆在轻载或者是空载的情况下以高速来运行。常规螺旋小伞齿轮，齿圈驱动双速单位，但一个行星齿轮系被放置在差速器传动齿轮和差速器壳之间。内齿轮行星齿轮系被用螺丝定在硬性斜角传动齿轮。有一个环，在这个环上行星齿轮是回转的，这个环被钉在差速器壳上。一个成员，它的组成包括太阳轮 和一个爪形离合器，滑动在其中的一个半轴上，通过一个按键或者是连接到操作者那里的杠杆被控制。当在高的范围，相啮合的太阳齿轮同在环上的内齿携带行星齿轮，从左边的调整环上脱离接触爪形离合器，这个环硬性固定在差速器壳上。在这个位置上，星系齿轮系被锁在一起。在差速器壳和在行星传动轴里的齿轮之间没有相对运动。差速器壳由差速器环齿轮直接驱动，在常规的单级主减速器也是同样的。当在转换到低的范围，太阳齿轮从啮合的状态滑离，和环一起驱动行星齿轮。爪形离合器和左边的调整环构成了一个刚性连接。因为太阳轮也是爪形离合器的一部分，它业被锁在调整环上，保持静止。内齿轮使行星齿轮绕着静止的太阳轮旋转。差动器壳通过行星齿轮被安装在枢轴上的环来驱动。这个动作将产生齿轮减速或者是低速的轴。不同动作一辆汽车的后轮不是总是用同一种速度在行驶。当汽车在转弯或者是当轮胎直径不同时，汽车的后轮们必须以不同的速度运转。如果在每个轴和差速器壳之间都有一个固体连接，那么轮胎将倾向于滑动、发出尖锐的噪声、以及每当操作者转动方向盘的时候磨损。一个差速器就被设计用来防止这样的问题。直线行驶当汽车在直线行驶是，齿圈，差速器壳，差速器小齿轮和差速器边缘齿轮像一个单元一样运转。两个差速器小齿轮不在一个小齿轮轴上运转，因为他们施加相等的力量到变齿轮上。结果，两半轴齿轮与环形齿轮同一速度运转，导致两个车轮用同一速度运转。转弯当车辆按曲线行驶，差动齿轮旋转在小齿轮轴。发生这种情况四因为小齿轮齿轮必须绕这慢转差速器侧齿轮旋转。因此，在转弯时，小齿轮会带动差速器旋转运动来使外转向轮运动速度快。差动的速度被认为是百分之百。小齿轮的旋转运动将会把百分之九十的这个速度带该运动缓慢的内轮，把百分之一百一的速度传递给运动较快的外轮。这个动作会使汽车在转弯的时候无滑动或者是这轮无噪声。