What is ABS (antilock braking system), rather, how the acronym stands for, now I know many drivers, and that's exactly what it blocks and what it's done, you know, just very curious. And this despite the fact that this system installs on most vehicles both imported and domestically produced.
ABS is directly connected with the braking system of the car, therefore, and with the safety of driver, passengers, and all others road users. Therefore, to know how it works, it will be useful for any driver. But first, to understand the working principle of ABS, you need to understand what it means “proper braking”.
To stop the car, not just timely press the brake pedal. After all, if during drive fast to brake sharply, then the wheels of the car locked and will not roll, but slide on the road. It may happen that under all of the tire surface will not be equally homogeneous, so the speed of the slide is different, and that's dangerous. The machine will no longer be manageable and will go into a skid, which, in the absence of skills of the driver, will be difficult to control. But a driverless car – this is a potential source of danger.
So the main thing in the braking – it does not give rigidly to lock the wheels and go to uncontrolled slide. For this there is a simple technique – intermittent braking. To run it, no need to hold the brake pedal constantly pressed down, and periodically release and re-press it (as would shaking). This seemingly simple action does not give the driver to lose control of the car, as they will not allow the tires to lose traction with the ground.
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But there is also the notorious human factor – the driver in an emergency situation, you may just get confused and forget about all the rules. Here for such cases and was invented ABS or otherwise – anti-lock braking system.
In simple explanation, the ABS system is an Electromechanical unit that controls the braking process of the vehicle in difficult road conditions (ice, wet road, etc.).
ABS – it is a good helper for the driver, especially a beginner, but you need to understand that it only helps in the control of the machine, and not running her, therefore, rely on “every” is not necessary. The driver must learn your car, its behavior on the road, in what cases and how works brake ABS, what is the stopping distance on different surfaces. Ideally, this should be checked on a dedicated circuit, to avoid further trouble on this road.
The First mechanisms, which resembled the principle of operation of the ABS appeared in the beginning of the last century, only they were intended for airplane chassis. Similar, but a car system, was developed by the ‘Bosch" of the patent for the invention which they received in 1936. However, really efficient device of this technology has been applied only to the 60-th years, when the first semiconductors and computers. And to create a prototype of a ABS, in addition to the ‘Bosch’, have sought and “GM”, “GE”, “Lincoln”, “Chrysler" etc.
A Full-fledged serial production of cars with “antiblikom” was started in 1992. It began to install on its products some of the major automakers. And since 2004, this system began to equip all cars descending from the conveyor of European plants.
Theoretically, the ABS design looks simple and includes the following elements:
The control Unit (BU), in fact, is a “brain” of the system (computer), and what functions it performs, is clear about, but the speed sensor and the hydraulic unit need to talk more.
In work-based sensorsspeed control is the effect of electromagnetic induction. Coil with a magnetic core movably mounted in the wheel hub (some models - reducer drive axle).
Installed In the hub of the ring gear rotating together with the wheel. Rotating the crown changes the magnetic field that causes a current. The magnitude of the current, respectively, depends on the speed of rotation of the wheel. And then, depending on its magnitude, a signal is generated which is transmitted to the control unit.
The Hydraulic unit includes:
There are three main phases of ABS operation:
First of all, it should be noted that the hydraulic unit in the car is embedded in the brake system in sequence, just behind the brake master cylinder. And solenoid valves are a kind of tap for opening and closing the access of fluid to the brake cylinders of the wheels.
Work and the control of the braking system of the vehicle shall in accordance with the data obtained by the control unit of the ABS speed sensors.
After the start of braking, the ABS reads the readings from the wheel sensors, and smoothly reduces the speed of the car. If any of the wheels stopped (beginning to slip), the speed sensor instantly sends a signal to the control unit. After receiving it, the control unit activates the exhaust valve, which blocks the access of fluid in the wheel brake cylinder, and the pump will immediately begin the selection of returning it to the accumulator, thereby removing the lock. After the wheel rotation exceeds the specified speed limit, “every” covering the exhaust and opening the inlet valve and activates the pump which starts to work in reverse, pumping pressure into the brake cylinder, thereby slowing down the wheel. All processes are instantaneous (4-10 iterations/sec.) and continue to stop the machine.
The above principle of operation of the ABS refers to the most perfect – 4-channel system, carrying out individual control of each wheel of the car, but there are other types of “Antiblock”.
Three-Channel ABS – this type of system contains three speed sensor: two mounted on the front wheels, third rear axle. Accordingly, the hydraulic unit contains three pairs of valves. The principle of operation of the ABS of this type is to separate the control of each of the front wheels and paired rear.
Dual-channel ABS – in such a system there is a pairwise control wheels located on one side.
Single-channel ABS – the sensor is mounted on the rear axle and distributes braking force to all 4 wheels at the same time. This system contains one pair of valves (intake and exhaust). The magnitude of the pressure changes equally throughout the circuit.
Comparing the types of “Antiblock”, it can be concluded that the difference between them is the number of sensors of speed control and, accordingly, valves, but, in General, the principle of operation of the ABS car, the order of processes that are similar for all types of systems.
Deciding to stop your vehicle equipped with an ABS system, the driver pressing the brake pedal, feels that it gently vibrates (the vibration may be accompanied by a distinctive sound resembling the sound of ‘ratchet’). This kind of report system that it has earned. Sensors read speed performance. The control unit controls the pressure in brake cylinders, not allowing the wheels to hard lock, with a quick “spurts” otorbaeva them. In the end, the car gradually slows down and is not skid and, therefore, remains manageable. Even if the road is slippery, the driver when such inhibition remains only to control the direction of movement of the machine to a complete stop. Thus, thanks to ABS, the perfect, and most importantly – controlled braking.
Of Course, the antilock considerably facilitates the life of the driver, simplifying and increasing the efficiency of the braking process. However, it has several disadvantages that should be known and considered in practice.
The Main disadvantage of ABS is that its effectiveness depends on the condition of the road.
If the road surface is a bumpy surface, the car braking distance will be longer than usual. The reason for this is that during braking the wheel periodically losing grip (bounces) and stops spinning. A stopwheel ABS regards as the lock, and stops the braking. But when restoring contact to the road specified program braking did not meet the optimal system has to re-adjust, and this takes time, which increases the stopping distance. To reduce this effect, reducing the speed of movement of the machine.
If the road surface is not uniform, with alternating portions, such as snow changes into ice, ice – asphalt, then again, ice, etc. In such a situation, getting on a slippery patch the ABS, evaluating coverage, adjusting the braking process, during the transition to asphalt “Antiblock” again have to be reconstructed as the selected braking force for slippery surface on the pavement is not effective, it leads to an increase in the length of the braking path.
With loose soil, the ABS is also not “friends”, in this case, the conventional braking system works much better as a locked wheel under braking burrows in the ground, forming on the way the slide preventing further move, accelerate and stop the car.
At low speed “every” generally disabled. Therefore, when driving on a slippery road going downhill, you need to be prepared for such an unpleasant time, and keep in good condition "handbrake", which can be used if necessary.
In conclusion we want to note that ABS is definitely a good addition to the brake system, allowing not to lose control of the car under braking. However, you should always remember that this system is not omnipotent, and in some situations can provide a disservice.
Article in other languages:
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Alin Trodden - author of the article, editor
"Hi, I'm Alin Trodden. I write texts, read books, and look for impressions. And I'm not bad at telling you about it. I am always happy to participate in interesting projects."
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