Wheel cylinder or slave cylinder assist the main cylinder in covering the pressure of the piston inside it and push the brake shoes attached to it. Some of the wheel cylinder having one piston and some having two pistons. The wheel cylinder having one piston will operate only one brake shoes and the two wheel cylinder are require to operate two brake shoes. In some wheel cylinder, both brake shoes are operated as they are having two piston in them. When brakes are applied the brake fluid enter into the cylinder through a brake pipe lines. It causes to force out the piston. This motion is transmitted to brake shoes causing them to expand against the running wheel drum to hold it tightly and stop it.
It is the most important part of the hydraulic braking system. It contains two main chambers.
- Fluid reservoir -which stores the brake fluid in it.
- Barrel -which is compressor and develops pressure in brake fluid.
- Reservoir : The reservoir also contains two parts. The larger part is called filter or intake port and the smaller portions is called bypass port through which the returned fluid from the system will enter into reservoir from barrel.
- Barrel :in the barrel of master cylinder the parts are :
- Primary cup.
- Secondary cup.
- Return springs.
- Retaining spring.
- Check valve.
When the brake pedal is applied the push rod will push the piston of master cylinder and the there by the pressure is applied on the hydraulic brakes fluid. The pressurized brake fluid will enter into system through check valves which does not allow the fluid to return back. This causes the pressure on the system and applying brakes at the wheel cylinder.
The hydraulic brakes are being operated in the Pascal’s law which states that “The pressure on any liquid is equally transmitted to all the direction at the same time “. In the same manner the pressure of brake pedal which is applied on the brake fluid in the master cylinder is transmitted to all the four wheels cylinder with equal pressure and at the same time. In this way the brake shoes which are attached to the wheels cylinder are expanded and thus the brakes are applied. The parts of hydraulic braking system one :
- Brake pedal .
- Pull and push rod.
- Master cylinder.
- Brake pipe lines.
- Wheel cylinder.
- Brake shoes.
When the brake pedal is applied the piston inside the master cylinder in pushed forward and it caused the pressurized brake fluid moves forward to all the four wheels cylinder at the same time with the same pressure. There at the wheel cylinder the brake shoes will be expanded with the developed pressure in the wheel cylinder. All the wheel cylinder will be operated at the same time according to pascal’s law. This is how the brakes are applied while releasing the brakes with contracting of the brake shoes with spring force the brake fluid in the wheel cylinder will try to go back to the master cylinder. As there is no pressure on the position of the master cylinder, the brake fluid push the check valve of master cylinder and the enter into the reservoir through the barrel and by pass valve of master cylinder.
Construction and working of mechanical brakes : these brakes are operated completely through mechanical links and lever. These are applied in two wheelers and these wheeler. These are also applied in four wheeler as parking or emergency brakes. In the wheels drum there are two brake shoes which are linked closely by a retracting spring. There will be a can between the two shoes. When brake pedal is applied, the can will rotate causing the brake shoes expand against the force of the returning spring. This causes the shoe to rub against rotating wheels drum and thereby stopping it. When brake pedal is released, the can inside wheel drum will come back to its position causing the brake shoes to come back with the presence of returning position and thus releasing brakes.
In this type of brakes, a brake drum is attached concentric to the axle hub whereas on the axle casing is mounted a back plate. In case of front axle, the brake plate are bolted to the steering knuckle. The back plate is made of pressed steel and is ribbed to increase rigidity and to provide support for the expanding brake shoes. These brakes are also known as internal expanding brakes.
The disc brake consist a cast iron disc bolted to the wheel hub and a stationary housing called calliper. The calliper is connected to some stationary part of vehicle, like axle casing or the stab axle and is cast in two parts, each part containing a piston. In between each piston and the disc, there is a friction pad held in position by retaining pins, spring plates etc. When the brakes are applied, hydraulically actuated piston move the friction pad into contact with the disc, applying equal and opposite forces on the later. On releasing brakes, the rubber sealing rings act as return springs and retract the pistons and the friction pads away from the disc.
- Disc brakes.
- Drum brakes.