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.  

In other words, the ABS system controls each wheel varyingly according to road conditions thereby preventing slipping of tires and maintaining maximum steering performance. In addition, the system controls each brake so as to adjust them to a state just before the car starts to slip.

The ABS system has a speed sensor on each wheel to analyze the rotation speed of the wheel and if one wheel is locked, only that wheel is pumped so as to provide all four wheels with the same gripping force.  

[Precautions]

However the ABS system is not all purpopse. If you step on your brakes full throttle with a faulty ABS system, there is danger of an accident.

Ofcourse, a faulty system will be indicated by a warning sign on the dashboard but a lack of awareness of the sign may easily lead to mistakes.

Even when not faulty, the ABS system does have its problems.

When not speeding, the braking distance of a car equipped with an ABS system may be longer than cars with regular brakes due to unecessary pumping.

The ABS system serves to reduce braking distance and enhance control of the vehicle in sudden stops and does not always gaurantee safe braking on slippery surfaces. It should therefore not be overly trusted.

Some drivers notice vibrations from the pedal and steering wheel when stepping on the pedals. This is due to the transfer of hydraulic vibration from the pumping action of the ABS system.

5. Brake Fluid

As the weight of vehicles has increased, the turning force during driving too has become very large. As too much force is required from the driver to stop the vehicle, hydraulic systems which use brake fluid as the operating medium are used to convert small forces to larger forces.

In terms of brake fluid standards, American standards inlcude FMVSS¹ 116- DOT² 3, DOT 4, DOT 5, DOT 5.1, as well as SAE-J1703, J1704, J1705, ISO-4025 while Japanese standards include JIS-K 2233 as well as their own car OEM standards. 

The Japanese JIS standard is based on the American DOT standard, with glycol ether used as base oil. JIS K 2233 type 3/4/5 were adjusted in accordance with DOT 3, DOT 4, DOT 5 and are classified as non-petroleum based brake fluid.  

Annotation. ¹ Federal Motor Vehicle Safety Standards
   ² DOT : Department of Transportation
​

There are 2 basic types of brake fluid ① Petroleum Base ② Non Petroleum Base
Petroleum base type brake fluid is typically not used in automobiles as non petroleum  base are typically used.

Therefore, FMVSS-116 Brake Fluid which abides by american government standards, is non petroleum base.

This standard is used as a globally certified spec while it also is the basis of OEM specs. The main items of the standard are summarized below.

Brake fluids are a mixture of additives such as viscosity adjusting agents, metal corrosion inhibitors, and pH adjusting agents. It is recommended that brake fluids be changed every 45,000 miles.

Characteristics of common braking fluids(US DOT classification)

Annotation ¹ 0% H2O,  ² 3.7% H2O, ³ viscosity standard@100℃ 1.5 cSt ↓

As a driver, it is a good idea to know the difference in specifications between each brake fluid in the above table.

Firstly, it is important to understand the chemical characteristics of each brake fluid. DOT 3, DOT 4, DOT 5.1 brake fluid are a mixture of glycol and glycol ether. DOT 5 is silicone based.

1) Boiling Point : Refer to above table

3) Color : Colors of products in the market
  • DOT 3  : Transparent, Pale Yellow, Blue & Crimson Red Color
  • DOT 4  : Transparent, Pale Yellow & Crimson Red Color
  • DOT 5.1 : Transparent, Pale Yellow & Blue Color
  • DOT 5  :  Purple & Violet
As seen above, the color of brake fluids should not be used as an absolute criterion in distinguishing types of brake fluids, as they are added for leakage check. It does not affect the quality of the product.