Brakes: Drum Brakes - Part2

In the previous article, we talked about the basic concepts that are related with brakes and terminology that is defined to understand brakes and its features. The previous blog can be found at: http://themechunicorn.blogspot.in/2014/04/brakes-general-part1.html
Now, in this part, we will start discussing about the components and construction of different braking systems, we will start with the simplest friction based drum brakes for vehicle and will continue towards disk brakes, aircraft drag brakes, jake brakes and will end towards electromagnetic brakes. This differentiation will be based on categories depending upon the vehicle i.e. we will first take brake systems used in cars, then aircrafts and then other vehicles.

The two images above show a basic drum-brake assembly for cars and motorcycle. These are the most common braking system till now for vehicles but are now being replaced by disc brakes at a very fast rate, the reason for this migration is quite simple, high brake fade, low peak force, less brake power when compared to disc brakes and less durability. The drum brakes work on a very simple principle of friction. The drum-brake assembly include the following:

1) Brake Drum - It is the brake cover that gets attached to the wheel while also serving as the friction surface for the brake system, the inner side of the brake drum is lined with frictional surface having a friction coefficient (µ) of anything between 0.4 to .45 while depending upon application, the µ might gets increases as high as 0.66. Brake drum also connects with the tire and is subjected to high torque when braking action is required.

2) Brake Shoe - It is the component that is attached with the brake lining material of the inner assembly and the actuation occurs here itself, the hydraulic slave cylinder is connected to both the brake shoes and when brakes are actuated, the slave cylinder pushes the brake shoe towards the brake drum and the shoe returning springs bring it back after actuation is completed.

3) Shoe Adjustment: It is the component through which you can set the initial position of the brake shoe! It is used to control the pedal play as well as to control the peak force, but increasing the initial value of shoe might result in reduced durability due to increased drag and more brake power.

4) Hydraulic Slave Cylinder: It is the actuator unit of the drum brakes, apart from hydraulic actuators like hydraulic cylinders, various drum brake designs also use mechanical actuation which is still commonly seen in motorcycles. Through a hydraulic pipe it is directly connected with the master hydraulic cylinder which in turn is connected with the brake pedal! As hydraulic systems are based on Pascal's law, the rest of the actuation method is nothing but a series of clever engineering architecture.

The brake power is directly related to the surface area of the brake pads or brake lining material in contact with the inner brake lining of the brake drum. Now, a days the application of drum brakes have been reduced considerably and are usually used as secondary braking system like the parking brakes while newer disk brakes have taken the place as primary braking system in the cars.

Thus, with this we conclude the information related to drum brakes, in next series of article, we will talk about other types of brakes and their constructions. Also, we will also bring in all the equations related to drum brakes and their designs in upcoming articles so that entrepreneuring designers can use the resources for designing their own drum brake systems and innovate!