ABS anti-lock braking system

The anti-lock braking system (ABS or ABV for automatic blocking preventer) is a system that is used in road traffic and is intended to increase road safety. The ABS is primarily effective in situations where emergency braking is necessary. Here the brake pressure of the individual wheels is regulated at intervals, this prevents the wheels from locking completely. ABS Provides considerable support to the driver, since the human ability to react is not sufficient to apply the correct braking force in a dangerous situation. However, ABS is able to control and regulate the braking behavior of each individual wheel correctly and optimally. This does not mean that the braking distance of a motor vehicle is shortened, on the contrary, it is actually the case that the braking distance is usually increased. However, the vehicle can be controlled almost completely by intermittent braking, since the wheels do not lock, which prevents the vehicle from skidding in the event of emergency braking.

The theory:

ABS is based on the knowledge that the maximum braking deceleration depends on the condition of the road. Due to the wheel slip, one can assume that with a distance of 1 meter, only 0.8 meters will be rolled off. If the maximum braking force is now exceeded, the transmittable braking force drops rapidly due to the locking wheels. In this case, the vehicle is only braked by the brake slip. The locking of the wheels creates a one-sided deflection of the tires, one speaks here of the so-called brake plates. The vehicle can hardly be controlled under these circumstances. To solve this problem, the ABS regulates the braking force on each wheel in such a way that optimal slip is ensured during the braking process.

The technique:

In current cars, only the 4-channel ABS is used. There are sensors on each of the four wheels that measure the current speed of the wheel. The information collected there is forwarded to an electronic control unit. This control unit then regulates the wheel brake cylinders of the individual wheels. The brake cylinders are each equipped with two electrovalves which can be opened and closed quickly. Two of the four valves are permanently open, but the other four are closed. For safety reasons there are pressure springs in the valves which keep the valves in this state even in the event of a power failure. If a wheel now tends to lock during braking, the open valve of the corresponding wheel is first closed and the brake pressure reached up to this point is kept constant. If the blockage is still too high despite the now closed valve, the previously closed valve is opened, which means that brake fluid is returned from the brake cylinder with the help of a small pump, causing the brake pressure to decrease. If the wheel speed increases again, the process starts again. This process is repeated up to 12 times per second, with motorcycles even up to 15 times. The ABS is only switched on from a speed of 6 km/h. The pulsation of the brake pedal, which is typical for ABS, is caused by the pressure fluctuations in the brake cylinder. The history: ABS originally came from aviation, as early as 1920 the French automobile and aircraft pioneer Gabriel Voisin used a hydraulic-based anti-lock system for the first time. Here, the wheels of aircraft were mechanically prevented from locking during landing and the aircraft thus staying safely on track. In 1928 Karl Wessel received the patent for a brake force regulator for automobiles, but this was never built and only existed on paper. It was not until 8 years later, namely in 1936, that Bosch received a patent for the so-called "device for preventing the wheels of a motor vehicle from locking.This pioneer of ABS consisted of around 1000 components and was therefore anything but unwieldy. With the breakthrough of digital technology, however, the number of parts could be reduced to around 140 pieces. Thanks to this fact, ABS was ready for series production.

Advantages and disadvantages of the anti-lock braking system

Advantages:

Even with emergency braking, the vehicle remains steerable
The vehicle has better braking behavior on wet roads and therefore a shorter braking distance
The wear of the tires is less because the braking force is distributed evenly and thus so-called brake plates are avoided.
Better controllability on different lanes thanks to yawing moment mitigation
The braking force can be regulated individually for each wheel

Disadvantages:

Longer braking distances may occur on loose surfaces (snow, gravel, sand, etc.).