Anti-lock Braking System (ABS) is a system that allows a driver to slam the brakes as hard as they want without the wheels locking up and sending the car into a spin.
In an ABS system, there are the following components:
Speed sensors:
- The system needs this in order to tell if the wheels are about to lock up. They are usually located at the wheels.
Valves:
- There are valves in the brake lines of each brake. In some cases they have 3 positions:
- 1. Open - Pressure from the master cylinder is passed through the brake.
- 2. The valve blocks the line which isolates the master cylinder. (Stopping pressure from rising too high.)
- 3. Releases some pressure from the brake.
Pump:
- When pressure is released the pump helps build pressure back up.
Controller:
- If a wheel locks up, a signal is sent to the controller which will limit the brake force and activate ABS.
The basic principle of braking works like this:
- First, the brake pedal is depressed by the driver.
- The piston in the master cylinder gets pushed forward.
- This applies hydraulic pressure which is transferred by the brake lines.
- From there the brake fluid goes to the wheel cylinders which apply the brakes.
The way a master cylinder works is it converts non hydraulic pressure (e.g. from the drivers foot when the pedal is being depressed) into hydraulic pressure to be transferred into the wheel cylinders to apply the brakes.
In class we stripped a master cylinder down. We did this to see what was inside the master cylinder and check for scoring and marks in the cylinder itself.
We also used the honing tool to clean the inside of the cylinder if it was possible.
Brake calipers are very important in slowing/ stopping a car. This is because the calipers are the force pushing the brake pads onto the disc rotors which cause the friction that slows the car down.
There are two types of calipers out there e.g:
1. Floating calipers:
- This type moves with the rotation of the brake rotor. The caliper is pulled by the outer brake pad to ensure an even force by the brake pads.
2. Fixed Calipers:
- These do not move with the rotation and have pistons on both sides which make them the more effective option.
In class we took the caliper apart e.g. took the piston out and took measurements.
The brake booster uses vacuum from the engine to multiply the force in which you can apply to the brake pedal. This means that your foot won't hit the floor when you try brake hard.
You can test to see if the brake booster is working by switching the car off and pumping the brakes a few times. After 4-5 pumps the pedal should get hard and you won't be able to push on it anymore. This means that it is working.
Brake lines are very important in a braking system. This is because they transfer the brake fluid form the master cylinder to the brake calipers. So, if you don't have brake lines there's no way of getting the fluid from the master cylinder to the calipers.
In class we made our own brake lines to simulate replacing an existing damaged brake line. We used this machine.
Drum brakes work by a set of shoes or pads pushing up against a rotating drum shaped part known as a drum brake.
In a drum brake there is a wheel cylinder. When pressure builds up from the master cylinder, the pistons inside the cylinder push outwards onto the shoes.
The brake shoes are what cause the friction which causes the slowing force on the vehicle.
