Have you ever had to go around a sudden obstacle and brake at the same time? Surely … What is anti-lock braking system for? ABS (ABS - Anti-lock Brake System).
The first production car to be fitted with ABS was the 1979 Mercedes S-Class. The system was offered as an option for a long time and only in 1992 it entered the list of standard equipment. In the early 1980s, ABS was available as an option on the BMW 7 Series.
Have you ever had to go around a sudden obstacle and brake at the same time? Surely yes. It would seem that this is difficult - pressed the brake, turned the steering wheel and corrected the trajectory. However, everything is relatively simple up to a certain point. If, during emergency braking, you press the brake pedal harder than necessary, the wheels may lock and …
Further, there are two possible scenarios for the development of events. Both are due to the presence or absence of anti-lock braking system ABS (ABS - Anti-lock Brake System) … If the car is archaic, has its pedigree from the mid-seventies of the last century, or rolled off the assembly line of one of the domestic car factories, then, no matter how diligently you turn the steering wheel, the vehicle will not change its trajectory. The fact is that the locked wheels, sliding, deprive the driver of the opportunity to maneuver - having fallen into a skid, the car will go stupidly in a straight line, as if the steering wheel was chopped off. Only an experienced pilot will be able to coolly unlock the wheels by momentarily releasing the brake pedal. And then, using impulse braking, regain control and dampen the speed. The second option is for a car equipped with ABS. The driver is only required to press the brake pedal harder and work calmly at the steering wheel. Do you feel the difference?
In the ABS, to determine the rotation speed, induction frequency sensors and sensors operating on Hall effect … Each new generation of wheel speed sensors is getting smaller, more accurate and more reliable. At first, only one sensor was installed, which was mounted on the rear axle gearbox or gearbox. Later, two more were added to it - on the front wheels. And only the latest versions of the ABS provide for the installation of sensors on each wheel, respectively, with individual modulators. By the way, the most ancient and primitive single-channel ABS acted on all braking mechanisms at once.
Another negative effect of blocking is an increase in stopping distance. The point here is that the static friction force is usually greater than the sliding friction force. Therefore, to stop the car as quickly as possible, it is necessary to generate such an amount of pressure in the brake lines so that the wheels rotate on the verge of blocking during braking. There is such an important indicator as relative slippage. Depending on the degree of braking of the wheel, it can vary from zero (the wheel rolls without slipping) to 100% (the wheel is completely locked). It has been experimentally established that the maximum braking efficiency is achieved with 15–20% slippage - that is, in the case when the rotation speed of the braked wheel is 15–20% lower than the speed of a free-wheeling wheel at a constant vehicle speed. Looking ahead, let's say that the electronics maintains exactly this value during braking, periodically blocking and unlocking the wheels.
The task of ABS is to regulate the speed of rotation of the wheels by changing the pressure in the lines of the brake system. To control the angular velocity, you need to know its magnitude and how it changes over time. Each wheel is equipped with a sensor that emits electrical impulses with a frequency proportional to the wheel speed. This information goes to the ABS control unit.
If, during braking, the angular speed of the wheel approaches zero, the electronic brain will immediately decide to “release” it. The hydraulic modulator, with the help of an electrovalve, will release the pressure from the line and redirect the "excess" portion of the brake fluid to the accumulator. The pressure will decrease until the wheel, again "grasping" the surface, spins up to a certain speed. Further, ABS will again sharply increase the pressure in the line and slow down the wheel. The cycle will continue until the car stops or the driver releases the pedal pressure to a position where ABS is not needed.
Many will say: "Little wisdom!" You can intermittently brake yourself. And it's true: in many cases, this method of deceleration on vehicles not equipped with ABS allows you to bypass a sudden obstacle during emergency braking. When the wheels are locked - you brake, as soon as "released" - you get the opportunity to correct the direction of travel. Naturally, in this situation, the braking distance will increase significantly, but the driver will be able to bypass the obstacle and extinguish the skid with the preemptive action of the steering wheel.
Unfortunately, no award-winning racer is capable of delivering "portion" braking at the rate that ABS does. The system (depending on the version) manages to lock and unlock the wheels about 15 times per second. In addition, the driver simultaneously acts on all the brakes (this is how the first ABS systems worked), while modern 4-channel anti-lock braking systems monitor the rotational speed and adjust the braking force for each wheel separately.
with control unit (black).
In most modern cars, ABS works in conjunction with EBD (Electronic Brake Distribution), a brake force distribution system that doses the intensity of the braking to each wheel. With EBD, you can safely brake in the corner and on the "mixed". The electronics, by the difference in rotational speeds, will understand that the wheels have hit areas with a dissimilar surface, and will reduce the braking forces on the wheels, which have better grip. By the way, the intensity of deceleration in this case will decrease and will be determined by the friction force of the wheel (s), which has the worst grip.
It is worth noting that for maximum deceleration efficiency, the brake pedal on cars with ABS must be pressed into the floor as much as possible. However, the latter does not have to be done by those drivers whose cars are equipped with the Brake Assist system, which itself creates excess pressure in the brake line, "braking" for a weak or indecisive person. With standard decelerations, it does not interfere. However, a sharp pressing (blow) on the Brake Assist pedal is regarded as a signal for emergency braking and takes effect.
But not everything is so smooth. ABS, like any other system, has disadvantages. For example, a simple "antiblock" can lose the usual brakes on snow, ice or sand, negate the advantages of studded rubber. Indeed, on ice, the spikes provide the greatest deceleration only with the maximum relative slippage, when they, like claws, dig into the ice and furrow it. The trick is that ABS, trying to release the wheels, does not allow the studs to work and thereby increases the braking distance. The same happens on unpaved roads (sand, gravel, clay) and snow-covered surfaces.
Cars with ABS in this case have a longer braking distance, because the permanently unlocking wheels do not create a "plow effect". But it is precisely on such surfaces that the locked wheels have the maximum braking efficiency - due to the fact that they rake in front of them "rollers" of soil or snow. This is why you need to remember that on an icy, snowy or unpaved surface, the braking distance of a vehicle without ABS may be shorter.
The ABS can put a small pig on an uneven road. If, during braking, one wheel hovers for a moment in the air and is blocked, the deceived electronics will begin to save you from skidding and immediately reduce the pressure in the other lines. When cornering, the car will unpleasantly wag its "tail", and the braking distance will increase. In principle, no one is insured against such accidental breaks, but it must be remembered that a good suspension is the key to adequate ABS operation.
In case of any malfunction in the system, a warning lamp on the dashboard comes on. In this case, there is only one piece of advice - run to the service.
Progress gives birth to more and more advanced systems. Operating with a large number of indications, they are able to adapt to the type of road surface and brake according to one of the previously laid down effective algorithms. Of course, electronics cannot be perceived as a panacea for all ills, but statistics are stubborn things: a competently tuned ABS with all vehicle systems in good condition on dry and wet surfaces, on average, helps to save up to 20% of the braking distance and leaves the driver a chance to maneuver. Needless to say, life and health can depend on these precious meters?
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