Table of Contents

Drum Brake : Components , Types and Working Principle

A drum brake is a brake that uses friction caused by a set of shoes or pads that press outward against a rotating cylinder-shaped part called a brake drum.

鼓制动器一词通常意味着制动系统，其中鞋子在鼓的内表面上按下。当鞋子在鼓外面按下时，通常称为扣子刹车。在两鞋之间捏合鼓（类似于传统的盘式制动器），有时被称为捏鼓制动器，尽管这种制动器相对较少。一个称为带刹车的相关类型使用柔性皮带或“带”包裹在鼓外面。

Drum brakes are primarily used at the rear axle of small and compact class vehicles.

FUNCTION

Drum brakes have been around for almost as long as the automobile itself and are still fitted today in a modified and more sophisticated form in modern cars. The term drum brake describes the design principle: namely, an enclosed cylindrical structure.

鼓制动组件

A drum brake comprises the following components:

1.背板：
Provides a solid base for other components in the drum brake attached to the axle sleeve.

2.制动鼓：
Bolted to the wheel hub and spins with the wheel. Often made of cast iron, and is resistant to heat and wear. This is what you see when you look at an assembled drum brake and is the component upon which braking force is applied to slow or stop the car.

3.轮缸：
Contains two pistons, one at each end of the cylinder, to operate the brake shoes. The cylinder applies pressure to the pistons, which pushes the brake shoes towards the drum, slowing or stopping the car. One cylinder is needed per wheel.

4. Brake shoe:
Pushes into the drum to create the friction necessary to slow or stop the car. Secured to the backing, but able to slide when pressure from the wheel cylinder is applied. It has a lining attached to it, made up of organic or metallic compounds. The lining is what actually comes in contact with the drum and wears away with use. Each brake contains two shoes. The primary shoe is closer to the front of the vehicle, while the secondary shoe is closer to the rear. Depending on the type and brand, the brake shoes may be interchangeable.

5. Automatic adjuster:
Keeps the brake shoes at a consistent distance away from the drum, even as the lining wears away.

6. Return springs:
当驾驶员放下刹车踏板时，将制动鞋从鼓上拉开。

The brake drum is fixed to the wheel and turns with it. On braking, the wheel cylinder forces the fixed brake shoes apart and presses them against the brake drum, thus slowing it down. When the brake is released, the return springs move the brake shoes back to their original position.

WORKING PRINCIPLE

When the driver steps on the brake pedal, the power is amplified by the brake booster (servo system) and changed into hydraulic pressure (oil-pressure) by the master cylinder. The pressure reaches the brakes on the wheels via tubing filled with brake oil (brake fluid). The delivered pressure pushes the pistons on the brakes of the four wheels. The pistons press the brake linings, which are friction materials, against the inside surfaces of the brake drums which rotate with the wheels. The linings are pressed on the rotating drums, which in turn decelerate the wheels, thereby slowing down and stopping the vehicle.

drum braking working — drum brake construction

鼓制动器类型

There are mainly three types – mechanical, hydraulic & pneumatic assisted Drum Brakes.

1. Mechanical:

在机械鼓式制动器系统如两个-wheeler & auto rickshaw, the brake shoes are actuated by a cam, which is attached to the brake linkage & pedal. When you press the brake pedal, the cam turns. Thus, it causes the brake shoes to expand outwards and rub against the drum.
The friction between the brake linings and the drum causes the drum to stop rotating, thereby the wheel to stop. When you release the brake pedal, the retracting springs bring the brake shoes back to their original position. This results in a gap between them and the drum and to again spin it freely.

2.液压：

The hydraulic Drum brake system such as in cars is a bit superior to a mechanical one. In this design, the hydraulic wheel cylinder replaces the cam. In the hydraulic system, instead of a cam, the wheel cylinder’s pistons push the brake shoes outwards. The brake shoes fit on the anchor plate or braking plate. It holds the brakes system parts together and on to the car’s axle. When you press the brake pedal, the oil in the brake master cylinder multiplies the hydraulic force sent to the wheel cylinders. Thus, it causes its pistons to push outwards. The pistons, in turn, cause the brake shoes to expand and rub against the drum. The friction between the brake linings and the drum causes the drum to stop rotating, thereby the wheel to stop.

3. Pneumatic assisted:

The third type – pneumatic assisted Drum-brake system; actuated by air-pressure, which works on the same principle of that of the mechanical Drum brake system. It is also operated by a bigger size cam or the ‘S’ shaped cam and is popularly known as the “S-Cam” brake system. However, high-pressure compressed air actuates a pneumatic piston which turns the cam. Mostly the medium to heavy commercial vehicles use this type of drum brake system.

基于原理

1. Leading/trailing shoe type drum brake

“Leading (or primary) shoe” is a term referring to the shoe that moves in the direction of rotation when it is being pressed against the drum. The other shoe is called the “trailing (secondary) shoe.” The leading shoe is pressed in the same direction as the rotation of the drums, and this rotation helps to press the shoes against the drum with greater pressure for stronger braking force. This is called the servo effect (self-boosting effect) which realizes the powerful braking forces of drum brakes.

Structurally, it has a wheel cylinder housing a piston with which hydraulic pressure is generated to push the two shoes against the drum’s inner surface.

这两种鞋子的功能以某种方式成为尾鞋或带领鞋子，具体取决于车辆是向前还是向后行驶。鼓制动器会产生一致的制动力，无论车辆向前还是向后行驶。这是因为鼓式制动器在任一方向上产生相同的制动力。通常，这种类型用于乘用车的后制动器。

2. Twin leading shoe type drum brake

This type of drum brake has two-wheel cylinders and two leading shoes. Each wheel cylinder presses on one shoe so that both shoes act as leading ones when the vehicle moves forward, providing superior braking force.
每个活塞都放在车轮缸中，朝一个方向移动，因此，当车辆倒转时，两种鞋子都充当拖曳的鞋子。这种类型主要用于小到中型卡车的前制动器。
The dual twin leading shoe type has pistons that displace in both directions, making it possible for both shoes to act as leading ones, regardless of the direction of travel. This type is mainly used for the rear brakes of small-to-mid-sized trucks.

3. Duo-servo type drum brake

The duo-servo type features a structure where two brake shoes, called the primary shoe and secondary shoe, are linked via an adjuster. Strong pressure from the servo effect (self-boosting effect) of the primary shoe is transmitted to the linked secondary shoe, thus generated a very large braking force.
This type is mainly used for parking brakes on passenger cars, the center brakes on trucks, and brakes on forklifts.

ADVANTAGES AND DISADVANTAGES

Advantages of Drum brake system:

1. Simple design and parts
2. Easy & cheaper to manufacture
3. Low maintenance cost
4. Comparatively longer life

Disadvantages of Drum Brake system:

1.与光盘相比，制动力低
2. Brakes ‘fade’ when applied for a prolonged time
3. The brake shoe lining made of asbestos is harmful to humans
4. When wet, the braking grip reduces considerably
5.非阿斯贝斯托衬里吸收水分，导致鼓制动器突然抓住。