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Lesson 7 The BrakesThe brakes function by absorbing in friction the energy possessed by the moving car. In so doing they convert the energy into hear.function作动词，“起作用” 制动器通过摩擦的形式吸收运动车辆所具有的能量而起作用。并且将这些能量转化为热能。There are two types of brakes, the drum brake and the disc brake. drum brake鼓式制动器 disc brake盘式制动器有两种类型的制动器，即鼓式制动器和盘式制动器。Either or both types may be fitted. But where both types are used it is usual for the disc brakes to be fitted to the front wheels. 在一辆车上，可安装其中一种类型的制动器，也可同时安装两种类型的制动器。但在使用两种类型制动器的车上，盘式制动器通常安装在前轮。In both drum and disc brakes, a hydraulic system applies the brakes. The hydraulic system connects the brake pedal to the brake parts at each wheel.在鼓式和盘式两种制动系统中，都利用液压系统实现制动，液压系统将制动器踏板与每个车轮上的制动器构件连接起来。1 Drum BrakesThe drum brake consists of a pair of semicircular brake shoes mounted on a fixed back plate and situated inside a drum. 鼓式制动器含有一对（副）半圆形的制动蹄，制动蹄位于制动鼓内并安装固定于底板上。This drum is fixed to the road wheel and rotates with it .制动鼓与车轮固定连接，随车轮一起转动。 it 指road wheel One end of each shoe is on a pivot and a spring holds the other end in contact with the piston of a hydraulic cylinder.每个制动蹄的一端安装于枢轴上，而另一端在弹簧的作用下与液压缸内的活塞保持接触。 (In front brakes it is usual to use two hydraulic cylinders in order to equalize the pressures exerted by the shoes, as shown in Fig.7.1)（在前制动器内，通常用两个液压缸，以便均衡由两制动蹄产生的压力。（如图7.1所示） Each shoe is faced with material ,known as brake lining ,which produces high frictional resistance.brake lining制动衬垫（制动蹄摩擦片）每个制动蹄的表面都覆盖有制动衬垫，制动衬垫（制动蹄摩擦片）产生高的摩擦阻力。（每个制动蹄的表面都覆盖有产生高摩擦阻力的制动蹄摩擦片）。The hydraulic system comprises a master cylinder and the slave cylinders which are the cylinders on the road wheels. 液压系统包含一个制动主缸和多个位于车轮上的制动轮缸。The slave cylinders are connected to the master cylinder by tubing and the whole system is filled with hydraulic fluid .制动轮缸通过管道与制动主缸相连，并且整个系统都充满液压油。 A piston in the master cylinder is connected to the brake pedal, so that when the driver depresses the pedal the fluid is forced out to each slave cylinder and operates their pistons. 制动主缸中的一个活塞与制动踏板相联，所以当驾驶员踩下制动踏板时，迫使油液向外流到每一个制动轮缸，并使它们的活塞移动。 The fluid pushes the pistons out of their cylinders. They ，in turn, push against the inner ends of the brake shoes and force them against the drums in each wheel. We say that the brakes are on. 油液将活塞推出液压缸，接着，活塞又推动制动蹄的内端，并将制动蹄挤向位于车轮内的制动鼓。我们说这时制动产生（起作用）。This friction of the shoes against the drums, which are fixed to the road wheels, slows down or stops the car.制动蹄对固联于车轮的制动鼓产生的摩擦力，使汽车减速或停止。 As the brake pedal is allowed to come up, the hydraulic fluid returns to its original position, the pistons retract, and a spring attached to each brake shoe returns it also to its original position. 当允许制动踏板抬起时，液压油返回原处，活塞缩回，安装在每个制动蹄上的弹簧使制动蹄也返回原位。Free of the brake drum. Now we say that the brakes are off.(Fig.7.2)be on已经开始、产生、起作用 be off离开、取消、解除释放制动鼓，此时我们说制动解除。 （图72）The brakes may also be operated by mechanical linkages from the foot pedal and hand brake lever.mechanical linkage 机械连接制动器也可以用制动踏板和制动手柄的机械制动装置操纵。 Common practice is to operate both front and rear brakes hydraulically with a secondary mechanical system operating the rear brakes only from the hand lever. 通常惯例是前、后制动器均为液压操纵，同时仅仅利用手柄的辅助机械系统来操纵后制动器。One of the great advantages of hydraulic operation is that the system is self-balancing, which means that the same pressure is automatically produced at all four brakes, whereas mechanical linkages have to be very carefully adjusted for balance. 液压操纵的最大优点之一是系统的自动平衡（自动调节），这就意味着所有的四个制动器自动产生相等的压力，而机械传动装置必须经过非常仔细的调整才能达到平衡。Of course, if more pressure is put on one of the brakes than on the others there is a danger that the car will skid.当然，如果一个制动器上的压力比其他制动器大，那就有汽车制动测滑的危险The mechanical linkage on the rear brakes is a system of rods or cables connecting the handbrake lever to the brake-shoe mechanism, which work entirely independently of the hydraulic system.后制动器的机械传动装置是一套将制动手柄与制动蹄装置连接起来的杠系或缆绳，它们完全独立于液压系统而工作。Drum brakes are prone to a reduction in the braking effort, known as “fade”, caused by the overheating of the brake linings and the drum. 鼓式制动器的制动效能将会有减弱的趋势，或称为“制动热衰退”，它是由制动蹄摩擦片和制动鼓过热而引起的。 Fade can affect all or only some of the brakes at a time, but it is not permanent, and full efficiency returns as soon as the brakes have cooled down.制动衰退一次可影响全部或其中一部分制动器，但不是永久性的（长期的），一旦制动器冷却下来，又恢复到全部效能。 However, fading is unlikely to occur except after the brakes have been used repeatedly in slowing the car from a high speed or after braking continuously down a steep hill. be unlikely to 未必的，不太可能的然而，除了为使高速行驶的汽车减速而反复使用制动器，或者下陡坡连续制动外，制动（热）衰退是不太可能发生的。Descending such a hill, it would have been preferable to use engine braking by changing down into a lower gear.be preferable to最好是更可取的是下这样的陡坡，更好的办法是（变速器）挂上低档用发动机制动。Drum brakes can be made less prone to fade by improving the cooling arrangements, by arranging for more air to be deflected over them, for example.可通过改进冷却布置，如增加透气通风来减少鼓式制动器受制动热衰退的影响。 2 Disc BrakesThe disc brake consists of a steel disc with friction pads operated by slave hydraulic cylinders.盘式制动器由钢制圆盘和制动液压轮缸操纵的制动衬块构成。 The steel disc is attached to the road wheel and rotates with it. 钢制圆盘固定于车轮上并随车轮一起转动。Part of this steel disc is enclosed in a caliper. This caliper contains two friction pads，one on each side of the disc, and two hydraulic cylinders, one outside each pad. 钢盘的一部分装在制动钳内。制动钳有两个制动衬块（钢盘的每侧各一个）和两个液压轮缸（每个制动衬块的外侧各一个）。The pads are normally held apart by a spring, but when the driver depresses the brake pedal, pistons from the hydraulic cylinders force the pads against the sides of the disc. 制动衬块正常情况下由弹簧保持分离，但是当驾驶员踩下制动踏板时，液压缸内的活塞就将制动衬块压向钢盘的侧面。Because the disc is not enclosed all the way round, the heat generated when the brakes are applied is dissipated very much more quickly than it is from brake shoes which are entirely enclosed inside a drum.因为制动盘没有被完全包围，制动过程中所产生热的耗散，比从完全包围在制动鼓中的制动蹄上热的耗散更快得多。 This means that disc brakes are less prone to fade than drum brakes.(Fig.7.3)all the way round意为“全部”、“四周”这就意味着盘式制动器受制动衰退的影响比鼓式制动器更小。（图7.3）3 Anti-lock Brake System (ABS)The function of an anti-lock, or anti-skid, braking system is to prevent the wheels from locking under hard braking. 防抱死或防侧滑制动系统的功用是防止车轮在急剧制动中抱死。Maximum braking force is obtained just before the wheels lock and skid. 最大的制动力是正好在车轮抱死滑动之前得到的。Such anti-skid system ate useful on slippery surfaces, such as ice and snow, where the wheels may lock easily. 这种防滑系统在光滑的表面很有用，如在冰和雪上，在这种表面车轮容易抱死。Locked wheels are dangerous because the car needs a much longer distance to stop. 车轮抱死是危险的，因为这时需要更长的距离才能使汽车停止行驶。 Locked wheels also can cause the driver to lose control.车轮抱死也能导致驾驶员失去对汽车的控制。The system uses a sensor that knows when one wheel (or a pair of wheel) is skidding. (Fig.7.4) 系统使用了一个传感器，它能分辨（识别）一个车轮（或一副车轮）即将开始滑动的信息。The sensor sends a signal to a computer, which signals a modulator valve. 传感器将信号发送到计算机，计算机向调节器阀发出信号。The modulator connects into the hydraulic system and can momentarily release the brake pressure and prevent the wheels from locking.调节器联入到液压系统，并能瞬间（立刻）释放制动压力，防止车轮抱死。 (The pressure release is so fast that a driver is seldom aware of it.) （压力释放非常迅速，驾驶员很难觉察得到。）pressure is then reapplied until the sensor again senses