Types of Brakes

Automotive braking system isthe most important safety system on a car． It contains a group of mechanical, electronic and hydraulic components． Typically, each car has two completely independent brakes according to the different functions． One is service brake and the other is parking brake．

Service brake

Service brake is foot-operated by depressing the brake pedal to make a moving car slow down or stop during normal driving． It is also called foot brake which accomplishes through a hydraulic system．

Parking brake

Parking brake is used to keep an unattended car stationary and prevent the car from rolling down a hill． It is also called hand brake which is done by mechanical system such as a series of cables (see Fig.5-1).

Typically, the braking system consists of disk brakes on the front wheels and drum brakes on the rear wheels (see Fig.5-2). Some cars may have disk brakes on all wheels, but the principle is the same in any case．

Disk brake

Disk brake is comprised of a brake disk, brake pads and a brake caliper (see Fig.5-3).It works by causing two brake pads to press on either side of the brake disk that is rotating along with the wheel．

Brake disk is sometimes called disk rotor mounted on the wheel hub． The disk has highly machined surfaces where the brake pads contact it． Between the two sides of the brake disk are vents that help it cool down (see Fig.5-4).

Two brake pads are mounted in the brake caliper, one on each side of the brake disk． Each brake pad has a friction lining bonded on it． The friction linings are tough, very heat-resistant material (see Fig.5-5).

Brake caliper contains one or more pistons which transmit the brake force hydraulically to the disk． The most common type of the brake caliper on modern cars is the single-piston floating caliper (see Fig.5-6). It is self-centering and self-adjusting． The brake caliper is able to slide from side to side so it will move to the center each time the brakes are applied． Also, it is cheaper and more reliable．

Drum brake

Drum brake is comprised of two brake shoes, a wheel cylinder, an adjuster, an emergency brake mechanism, a back plate, a lot of return springs, and a brake drum as shown in Fig.5-7．

Brake shoes are curved pieces of metal with the friction linings riveted on them that are moved hydraulically against the brake drum to stop its rotation．

Wheel cylinder with a piston is a powerful mechanism, which exerthy draulic force on-to the brake shoes so they can contact the drum and stop the moving car with friction．

Adjuster is used to adjust the distance between the surface of the friction linings and the inside of brake drum．

Emergency brake mechanism is used in an emergency, also used as a parking brake to prevent a car from rolling． It is mechanical operated by a cable system, rather than a hydraulic one．

Back plate serves as the base for the brake shoes, the wheel cylinder, the adjuster and emergency brake mechanism． They are all mounted on the back plate．

Brake drum is a hollow round steel drum that rotates along with the wheel． The other drum brake components are located in the brake drum．

译文：

                              课文 制动系统类型

制动系统是汽车最重要的安全系统。它包括机械部件、电子部件和液压部件。通常，每辆汽车根据其不同的功能都有两个完全独立的制动器: 一个是行车行驶制动器，另一个是驻车制动器。

行车制动器

行车制动器是用脚来操作的，通过踩踏制动踏板，使正常行驶的汽车减速或停止行驶。行驶制动器也称为脚踏制动器，是通过液压系统来实现的。

驻车制动器

驻车制动器的作用是在汽车无人看管时，使汽车保持静止状态，防止汽车在坡路上溜车。它还被称为手拉制动器，是通过机械系统(如一系列制动拉索)来完成的(见图5-1).

一般来说，制动系统是由前轮的盘式制动器和后轮的鼓式制动器组成的(见图5-2)。有些车均采用盘式制动器，无论哪种情况，工作原理都是相同的。

盘式制动器

盘式制动器由制动盘、制动衬块和制动钳组成(见图5-3)。实现制动是通过使制动盘两侧的制动衬块夹住与车轮一起转动的制动盘。

制动盘有时称为盘形转子，安装在轮毅上。制动盘具有经加工获得的高精度表面，用来与制动村块接触。制动盘两侧之间带有通风孔，用于帮助制动盘迅速冷却(见图5-4)。

两个制动衬块安装在制动钳上，分别位于制动盘的两侧。每个制动衬块都有摩擦衬片粘在上面。摩擦衬片是用坚硬且耐热的材料制成的(见图5-5)。

制动钳有一个或多个活塞将制动力通过液压传递到制动盘上。在现代汽车上,最为常见的制动钳是单活塞浮动钳(见图5-6)。它是自动定中心和自动调节的。制动钳能够从一侧向另一侧滑动，所以每次施加制动时，它都会移动到中心处.而且单活塞浮动钳也更便宜、更可靠。

鼓式制动器

鼓式制动器是由两个制动蹄、制动轮缸、调节器、紧急制动装置、制动底板、复位弹簧和制动鼓组成，如图5-7所示。

制动蹄是曲形的金属块，其上有摩擦衬片，通过液压移动抵住制动鼓，使其停止转动。

一个活塞的轮缸是一个强大的机构，它的作用是将液压制动力施加到制动蹄上，使其与制动鼓接触，靠摩擦使行驶的汽车停车。

调节器用来调节摩擦衬片表面和制动鼓内测表面之间的距离。

紧急制动装置在紧急情况下使用，也可用来作为驻车制动防止溜车。它是通过制动拉索系统机械式运行而不是液压式运行。

制动底板作为制动蹄、轮缸、调节器和紧急制动装置的底座。它们都安装在底板上。

制动鼓是一个空心圆形钢制的鼓，随车轮同步转动，其他鼓式制动器的部件都安置在制动鼓内。