②To overcome the first problem, some kind of clutching arrangement is necessary. To overcome the second, the transmission needs to include a gearbox providing a range of different ratios of input to output speed, enabling the engine’s speed to be maintained within the useful range of torque output over a more or less wide range of vehicle speeds.
为了解决第一个问题，离合器装置是需要的。为了解决第二个问题，变速器要求包括能够提供不同输入和输出转速比的齿轮箱，从而使得能够提供有用转矩的发动机的转速范围可以大致满足车速要求。
③So important have these solutions become that transmission has in many minds come to mean that part of the system between the engine output and the gearbox output, neglecting the many complexities which exist between the gearbox output and the driven wheels.
这些部件如此重要，以至于很多人认为变速装置就是指从发动机输出到齿轮箱输出之间的系统，忽略了从齿轮箱输出到驱动轮之间很多部件。
Unit 10 The Differential 第十课差速器
Most cars have a standard, or unlimited-slip, differential. (A limited-slip differential costs more and is not necessary in most normal driving conditions. ) As mentioned, a differential must split power unequally when a car goes around a corner. Like the transmission, the differential has many gears and parts.
大多数汽车都有一个标准的或非防滑差速器。防滑差速器成本要高很多，而且大多数驾驶情况下并不需要。正如上述所言，当车辆转弯时，差速器必须要不均等的分配能量。像变速器一样，差速器也由许多齿轮和部件组成。 10.1 The Main Gears 10.1 主要齿轮
Suppose a shaft spins in one direction. You want that shaft to drive another shaft at an angle of 90°to the first shaft. You can do this by meshing two gears, each having teeth set at a 45° angle. There would be one gear on each shaft. Together, the two gears produce a 90°change in direction. Gears with teeth at such an angle are called bevel gears because they are beveled, or cut on an angle.
设想一根轴沿着一个方向旋转。如果你想让这根轴驱动和它夹角成90°的另一根轴，你可以通过两个纵倾角为45°的齿轮相互啮合实现。这样每个轴上都有一个齿轮，通过两个齿轮的啮合产生90 °的转向。拥有这样纵倾角的齿轮被称作锥齿轮，因为这样的齿轮城锥形或切成锥形的角度。
The bevel gears work well when one shaft must drive another. But in a final drive assembly, two axle shafts must be driven. (One shaft goes to each drive wheel.) Then one of the beveled gears must have a hole in its center through which the shaft extends. The large circular gear on the axle shafts is called the ring gear.
当一根轴驱动另一根轴时，锥齿轮工作正常。但对于主减速器总成，一根轴必须要驱动两根
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半轴。一根半轴驱动一个车轮。因此，锥齿轮中间有一个洞，使得半轴通过。半轴上较大的圆环齿轮被称作从动锥齿轮。
The final drive assembly also provides gear reduction so that the drive wheels spin more slowly than the drive shaft. The gear reduction varies, depending on engine size and power, engine torque, and vehicle size and weight. In general most final drives produce gear reduction ratios of about 2.50: 1 to 3. 50:1.
主减速器总成也要起到齿轮减速的作用，这是因为驱动轮的转速要比驱动轴慢很多。根据发动机的尺寸、功率、转矩、车身长度和重量的不同，齿轮减速有所不同。一般而言，大多数主减速器提供大约2.5到3.5的齿轮减速比。
Thus, the drive wheels turn at about one-third the speed of the drive shaft. (If the drive shaft spins at 3,000 rpm, the drive wheels turn at about l ,000 rpm.).To give the necessary reduction, the driving gear, in the final drive must be smaller than the driven gear, which is the ring gear. 因此，驱动轮的转速大约是驱动轴转速的1/3。如果驱动轴的转速为3000转/分，驱动轮的转速大约是1000转/分。为了提供必要的减速比，驱动轴上的驱动齿轮要比从动齿轮，也就是从动锥齿轮小。
Thus, the driving gear must make several turns for every single turn of the ring gear. The driving gear is called the pinion gear or pinion.
因此，从动锥齿轮每转一圈，驱动齿轮必须要转好几圈。驱动齿轮被称作主动锥齿轮。 The drive shaft turns the pinion. The pinion rotates the ring gear and axle shafts. If the teeth of the beveled gears are curved, the pinion meshes more easily and quietly with the larger ring gear. Now we can refer to the gears as spiral bevel gears.
驱动轴驱动主动锥齿轮。主动锥齿轮驱动从动锥齿轮和半轴。如果锥齿轮的齿是弯曲的，主动锥齿轮就可以更加容易和安静地和更大的从动锥齿轮啮合。我们称这种齿轮为螺旋锥齿轮。
Spiral bevel gears were used for many years. However, another arrangement allows the drive shaft and the floor pan to be lowered.
螺旋锥齿轮已经被使用很多年了。但是，另一种结构可以降低驱动轴和车身地板高度。 If the center line of the pinion were extended rearward, it would pass through the center of the ring gear. Half the ring gear would be above the centerline and half below it. The newer system places the pinion at a lower point on the ring gear. Thus, the center lines do not intersect. 如果主动锥齿轮的中心线向后延伸，它将通过从动锥齿轮的中心。从动锥齿轮一半位于中心线之上，一半位于中心线之下。新的系统将主动锥齿轮放置在从动锥齿轮偏下的位置，这样使得两者的中心线不会相交。
Since the drive shaft connects directly to the pinion, the drive shaft can be lowered. Front-engine, rear-wheel drive vehicles use this arrangement, which uses hypoid gears.
由于驱动轴和主动锥齿轮直接相连，这样也可以降低驱动轴的高度。发动机前置，后轮驱动的汽车使用准双曲面齿轮，采用这种布置。 10.2 The Differential System 10.2 差速系统
The final drive works fine as long as both drive wheels turn at the same speed. However, this system cannot provide different rates of speed for different wheels. As noted earlier, a differential system is needed to allow for speed differences. This gear system is the heart of the final drive assembly.
只要两个驱动轮的转速相同，主减速器运转正常。但是，这个系统无法给不同的车轮提供不同的转速。正如之前所言，此时需要一个差速系统来提供差速。这个差速系统就是主减速器
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