Automobile ABS（Anti-lock Brake System）

Even 10 years ago, the ABS System (Anti-lock Braking System or Anti-skid Braking System) sticker on the side of a car or window conveyed a sense of pride.

The ABS system (Anti-Lock Brake System) has now become a basic option and is considered to be revolutionary automotive brake technology, making significant contributions to saftey.

Since its development for aircrafts in the 1970s, Chrysler and ford have applied this technology to cars which has spurred its development.

1. Types of brakes

There are two types of car brakes, ①Hand Brake and ②Foot Brake.

Hand Brake is also called a parking brake.  Generally, when the level is manually pulled a wire will lock the left and right rear wheels (in FF vehicles, the front wheels will be locked) which prevents the wheels of the car from being pushed.

The slowing down or stopping of a vehicle  all occur due to the pressing of a disk on an axle, or a drum.

2. Brake Mechanism

In passenger cars, as shown below, the front wheels are slowed down by pressing brake pads with resin against round metal discs on both sides, or by disc formed brakes.  

In the rear wheels, a drum shaped brake shoe pushes againt a the inside wall of a drum on both sides.

3. Skidding of an automobile

You've probably seen a car coming to a sudden halt whilst making screeching sounds. 

A sudden stop will prevent the tires from rotating but the vehicle will not stop immediately due to inertia, as shown below.

The vehicle will slip along the road without the rotation of tires, as if skiing, despite the friction.

When this occurs, only one side of the tire will rub against the road, leaving a black tire mark. This is called the lock phenomenon. 

What happens in the event a locked tire? The first and biggest problem is that the course of the vehicle cannot be controlled with the handles. 

In order to control the angle of the front tires and the direction of the vehicle with the handles, the tires must be roatating. If the tires are locked, the handles will not be able to control the direction of the vehicle.

Thus, regardless of the driver's will, the vehicle rotates or slips, increasing the risk of accidents.

The second problem is that the braking distance increases.

		Friction
		Maximum static friction force
		Periodic friction force section
		Warm friction zone
		Initiate braking
		The moment the tire begins to slip
		Friction
		Time

4. ABS method

If the wheels slip, the most effective braking method is to repeatedly step on and off the brakes and to step on the brake pedal until just before the tires lock, which will result in maintenance of maximum grip force.  

However, the speed at which the driver steps on the pedal is too slow to have any effect.

The ABS brake system will execute such repetitive movements 10 times per second.

The system will continually repeat these movements to prevent the wheels from locking, movements that cannot be mimiced by a human being.