武汉理工大学汽车学院2017研究生专业英语试题及翻译答案

Translate the following English into Chinese：

The back axle

1、The final drive

Having dealt with the mechanical transmission system between the engine and output from the gearbox, we now turn to the three alternative final stages which are live axles, dead axles and axleless transmissions. A live axle is one that either rotates or houses shafts that rotate, while a dead axle is one that does neither, but simply carries at its ends the stub axles on which the wheels rotate.

The functions of turning the drive from the propeller shaft through 90°to distribute it to the two wheels, and of reducing the speed of rotation – thus increasing the torque – is performed by the gearing carried in the final drive unit, usually housed in the back axle. For relatively small reductions –up to about 7:1 –single-stage gearing is used; but for greater reductions, two or even three stages may be required, and the gearing for one or more of these stages may be housed in the wheel hubs. The terms single-, double- and triple-reduction axles are therefore used.

Generally, the first stage is either a bevel pinion and what is termed the crown wheel, or a worm and worm-wheel, both of which of course turn the drive through 90°. Worm drives have the advantages of silence, either a low drive line or a high ground clearance – according to whether the worm is underslung or overslung relative to the wheel – ease of providing for a through drive to a second axle in tandem with the first, and the fact that a high single-reduction ratio can be readily provided – even as high as 15:1.

Bevel and hypoid bevel final drives are, however, far more common because they are less costly to manufacture and have a higher efficiency – the sliding action of worm teeth generates a lot of heat, especially if the gear ratio is high, and makes heavy demands on the lubricant. A hypoid bevel gear is one in which the axes of the crown wheel and the pinion are not in the same plane, and in which therefore some sliding action takes place between the meshing teeth. The one advantage is that a low propeller drive line can be obtained, so that the floor, and therefore centre of gravity, of the vehicle can be kept down.

2、Single-reduction live axles

An elementary single-reduction live axle –with a differential –is illustrated diagrammatically in Fig. 1. It has a hollow casing A, which carries on its ends the road wheels B. The weight of the body and load is supported by the casing A through the springs which are attached to the body and to the axle in a manner which will be described later. The casing in turn is supported at its ends by the road wheels. It therefore acts as a beam and is subjected to a bending action as is shown in Fig. 2,

where the forces P are the supporting forces supplied by the road wheels, and the forces W are the body load, applied to the casing through the springs. The casing has to be stiff enough to withstand this bending action without undue flexure.

Supported in bearings in the casing A is a short shaft D integral with which is a bevel pinion E. The shaft D is coupled by means of a universal or flexible joint, outside the casing, to the propeller shaft and hence to the mainshaft of the gearbox. Inside the casing the bevel pinion E meshes with, and drives, a bevel wheel F which is fixed to a transverse shaft G. This shaft is supported in bearings HH in the casing and is bolted to the hubs of the road wheels B at its outer ends. Obviously, when the pinion shaft D is turned by the propeller shaft the drive is transmitted through the bevel wheel to the transverse shaft G and hence to the road wheels. The road wheels are kept in place on the casing A in the end direction by nuts J and shoulders K of the casing. Although a bevel gear drive is shown, the principle would have been similar –only the gear arrangement different – had a worm drive been used.

Fig. 1 Single-reduction axle

Fig. 2

3、Torque reaction

From Fig. 1, it can be seen that the propeller shaft applies to the shaft D a torque which, as it is transmitted through the bevel gearing, is increased in the same ratio as the speed is reduced. This increased torque is then transmitted through the shaft G to the road wheels. From Newton’s third law of motion, we know that action and

reaction must be equal and opposite, so not only will this torque tend to rotate the wheel, but also the reaction from the wheel will tend to rotate the shaft G in the opposite sense. Therefore, there will be a tendency for the pinion and its shaft D to swing bodily around the crown wheel, and this tendency will be reacted by the axle casing. Some means therefore must be introduced to prevent the axle casing from rotating in the opposite direction. This may be simply the leaf springs themselves, or additional links – torque-reaction or radius rods – may be used and will be essential if coil, instead of leaf, springs are employed.

Similarly, the axle casing will tend to rotate about the axis of the bevel pinion in a direction opposite to that of rotation of the propeller shaft. However, since the torque transmitted by the propeller shaft is less than that in the driveshafts, it can in most circumstances be reacted satisfactorily simply by the suspension springs.

4、Driving thrust

Again, according to Newton’s third law of motion, the driving thrust, or tractive effort, of the road wheels is reacted by the vehicle structure, the reaction being the inertia of the mass of the vehicle if it is accelerating, or rolling resistance of the other axle plus the wind resistance if it is not –the rolling resistance of the tyres of the driving axle involves of course purely local action and reaction. In effect, therefore, the driving axle has to push the carriage unit along, so it must be connected to the structure of the vehicle in such a way that this forward thrust can be transmitted from one to the other. This connection can be either the leaf springs or some other linkage for locating the axle relative to the carriage unit. The relevant members of this linkage are known as thrust members, or radius rods.

答案：

后桥

1、主减速器

学习过介于发动机和变速器输出之间的传动系统之后, 我们现在开始学习传动系统的最后一个阶段，它有三种可替换的形式，即断开式车桥、整体式车桥以及无轴传动。断开式车桥的轴或者轴壳旋转，而整体式车桥的轴和轴壳都不旋转，只是在其末端承载着使车轮在其上转动的短轴。

位于后桥桥壳上的主减速器的功能是将传动轴传递的动力的方向改变90度再分配给两个车轮，同时它的齿轮起到减速增距的作用。当减速比较低（大约低于7：1）时，使用单级齿轮传动。但是当减速比较大时，通常需要两级甚至三级齿轮传动。这些齿轮有时被装配在轮毂上，因此可能会使用一根、两根甚至三根减速轴。

通常，第一级传动使用的是一组锥齿轮和冠轮，或者是一组蜗轮蜗杆，这两者都是将动力的传递方向改变90度。无论离地间隙的高低（根据蜗杆相对位于车轮上方还是下方来判断），蜗轮蜗杆传动都具有噪音低的优点，且便于第一轴与第二轴直接传动，并能够轻而易举地提供高达15：1的单级减速比。

然而，锥齿轮与准双曲面锥齿轮传动更为常见，因其制造成本较低并且具有更高的效率。蜗轮蜗杆啮合齿之间的相对滑动会产生大量的热量，特别是传动比较大的时候，这也使得它对润滑剂的要求很高。准双曲面锥齿轮是一种冠轮和小齿轮的轴线异面的锥齿轮，因此它的齿轮啮合时会发生一定的滑动。它的一个优点是可以降低传动系的高度，从而降低车辆的底板和重心。

2、具有单级减速器的断开式车桥

基本的具有单级主减速器和差速器的断开式车桥概略地描述如图1，它具有空心桥壳A，其尾端连接车轮B。车身和负载的质量通过车身与车轴之间的弹簧以某种方式（稍后会介绍）传递到桥壳A，桥壳的尾端又由车轮支撑。因此桥壳起到了一个梁的作用，其所受的弯曲作用力如图2所示。图中P是由车轮提供的支持力，W是由弹簧传递至桥壳上的车身与负载的重力。桥壳必须具有足够的刚度来承受弯曲作用力，以防止过度的弯曲变形。

桥壳内的轴承中有短轴D，它与锥齿轮E是一体的。在桥壳外部，短轴D通过万向节与传动轴相接，从而与变速器的主轴相连。在桥壳内部，主动锥齿轮E 与固定在横轴G上的从动锥齿轮F相啮合，并且驱动F。横轴G支撑于桥壳内部的轴承组H-H之间，其两端用螺栓固定在车轮B的轮毂外端。当主动锥齿轮轴D 被传动轴带动时，驱动力通过锥齿轮传递到横轴G，从而传递到车轮上。在桥壳A的末端，车轮通过螺母J与桥壳挡肩K轴向定位并固定在桥壳A上。虽然此处只给出了锥齿轮传动的示意图，但是使用蜗杆传动的原理与此类似，只是齿轮布置不同而已。

3、反转力矩

由图1可知，传动轴作用于短轴D一个力矩，由于此力矩通过锥齿轮向后传递，所以该力矩会以速度减小的比率增加。增加的转矩通过横轴G传递给车轮。根据牛顿第三运动定律，我们知道作用力与反作用的是大小相等方向相反的。所以转矩不但会驱动车轮转动，来自车轮的反作用力也会以相反的方向阻碍半轴的转动。因此主动锥齿轮和短轴D受力后整体会产生围绕冠轮摆动的趋势，这

种趋势将由桥壳反应出来。所以应当采取一些方法来防止桥壳向相反的方向转动。可能会通过使用钢板弹簧来实现上述需求，或者附加一些连杆如反向力矩杆和纵向推力杆。如果使用螺旋弹簧而不是钢板弹簧，就必须使用附加连杆了。

同样，桥壳也会有以与传动轴转向相反的方向相对于主动锥齿轮转动的趋势。然而，由于传动轴传递的转矩小于驱动轴的转矩，因此在大部分情况下，这些反作用力完全可以被悬架弹簧所吸收。

4、驱动力

同样，根据牛顿第三定律，驱动力或者说车轮的牵引力受到汽车结构的影响。当汽车加速行驶时，反作用力变为车辆的质量惯量；当汽车非加速行驶时，它变为其他轴上的滚动阻力和空气阻力。驱动轴上的轮胎的滚动阻力当然包括纯粹的局部作用力与反作用力。因此，驱动桥实际上需要推动承载单元，所以它必须通过某种方式与车辆相连。通过这种方式，向前的推力才能够从一个单元传递到另外一个单元。这种连接可以是钢板弹簧或者其他的一些用于定位与承载单元相关的轴的连接件。这些部件被称作推力构件或推力杆。