System operation abs. Everything about ABS. Types of anti-lock braking system

Hello dear guests and regular readers. The modern car is literally crammed with various. Moreover, few people understand their direct purpose, apart from airbags and seat belts. The name ABS, for our ears, has already become familiar, many motorists know that this system is on their cars, but not everyone understands how it works. So what does this acronym mean, what is this system for and how does it work?

ABS - (Anti-lock breaking system), or simply ABS, is an anti-lock braking system, the purpose of which is to prevent the wheels from locking when braking. For example, when, during braking, one or more wheels of the car are blocked and begin to slide on the road, the system will release the pressure in the brake line of the wheel, and it will start rotating again. And as long as the brake pedal is constantly and strongly depressed, the locking and unlocking process will continue as long as the braking process is in progress.

The ABS system appeared in the 80s of the last century and has since become an essential part of the vehicle's safety system. They install it not only on cars but also on trucks, and even on motorcycles.

What is ABS for?

As already mentioned, the ABS is designed to prevent the wheels from locking and to maintain the ability to drive the car during braking, even in emergency cases... The danger of wheel blocking is that during heavy braking, the slippery road, you can lose control over the car. In the absence of ABS, with an emergency pressing on the brake, inexperienced drivers will have locked steering wheels, and steering wheel turns, in either direction, will have no effect, the car will simply continue straight ahead until grip reappears.

This is exactly the task that ABS solves. The system continuously monitors the rotation of the wheels and, if necessary, unlocks them. This ensures constant traction with the road, which allows you to maneuver during stressful situations.

Often, together with ABS, EBD (brake force distribution system) is also installed. Imagine a situation where a car, on one side, hits a wet asphalt surface, and the other on a dry one. If it does not have an anti-lock braking system, then during emergency braking, one side will brake more efficiently than the other, which will lead to the car turning and going into an uncontrolled skid. This situation is most dangerous when cornering, when lateral force is already acting on the car. ABS system together with EBD, it will provide straight, safe and even braking on roads with uneven grip.

What the ABS system consists of and how it works.

During its existence, the system has undergone significant changes and improvements, but the principle of operation and the main functionality, in fact, has not changed. ABS consists of several acceleration sensors installed in the wheel hubs, pressure modulators that are built into the brake line, and an ECU (electronic control unit) that controls the signals from the valves and also receives them from the acceleration sensors.

It all works like this: each of the sensors located on the hubs measure the speed of the wheels. If the sensor receives information about a sharp deceleration, or even a stop, then a command is sent from the control unit to open the valve for a short time to reduce the pressure in the brake line, which will again force the wheels to rotate. This whole process of sensor control occurs very quickly, up to several tens of times per second. The driver can feel the work of the ABS by feeling weak vibrations on the brake pedal.

The system can have a different number of sensors and valves, based on this, and the ABS can be one-, two-, three- and four-channel. "Multiple port" is defined by the number of valves that control the pressure in the brake line. If each wheel has its own valve, then this is a four-channel ABS, if one for each front wheel and one for the entire rear axle, it is three-channel, for the valve on the axle - two-channel, and one-channel, if there is only one valve for the entire system. All modern cars are equipped with four-channel ABS, while the rest can be found only on old cars.

In addition to all the components described above, the anti-lock braking system can include a pump that restores the pressure in the brake line after a decrease due to the opening of the valves.

How to use ABS.

Probably, no driver will be able to press the brake pedal very often in order to dampen the speed and not lose control. The ABS system was created for this, it is capable of performing this action at intervals of up to fifteen times per second. It prevents the wheels from locking completely, which improves the vehicle's handling and roadholding.

Driving a car with ABS has its own characteristics. The braking effect, with this system, increases by itself. But it must be remembered that the car does not change its straight-line movement. Therefore, forget about smooth braking, on a car with ABS you need to "beat" the brakes. That is, during emergency braking, a lot of effort must be applied to the pedal. In addition, there is no need to brake with the engine, the ABS loves to work by itself. That is, during emergency braking, it is necessary to disconnect the engine from the transmission by pressing the brake and clutch pedals at the same time.

Cons of ABS.

One of the downsides is the human factor. Many car enthusiasts who have a vehicle with an anti-lock braking system begin to feel the illusion of complete safety and gradually lose concentration. As a result, vehicles with ABS are more likely to be involved in accidents than vehicles without ABS.

ABS really reduces braking distances on slippery roads. But if we talk about dry and even road surfaces, then here, on the contrary, braking distance may increase.

The problem of repair and maintenance of ABS is also acute. For example, acceleration sensors. They get very dirty because they are in the closest proximity to rotating parts. Also, bearing play can disable them, or malfunction. It should only be noted that the system works almost without interruption for modern cars, and it can break down only through the fault of the very motorists, who neglect the safety rules.

And another problem associated with the ABS is that the sensors may not always react correctly to the situation on the road. For example, imagine climbing, losing halfway grip, and hitting the brake suddenly. The system may perceive this as wheel blocking, and even fully depressed gas pedal will not help keep the car on a slope. This situation rarely happens, but it may well be.

It will be more difficult to brake on ice, snow and sand with studded tires installed, since the system can neutralize the useful properties of the rubber.

Well, after all that has been said, it's safe to say that ABS significantly improves the vehicle's active safety. Today, a car is part of everyday life and, accordingly, manufacturers are trying to simplify its management as much as possible. That makes modern drivers less professional than those who were 30-40 years ago. A modern car should be as comfortable and safe as possible for novice car enthusiasts. And not without reason, since 2004, equipping with an ABS system has become mandatory in the countries of the European Union.

ABS is, of course, a useful thing, but you shouldn't put too much hope in electronics. It is better not to allow such cases on the road when the anti-lock braking system may turn on. Safe roads for you!

1. What is ABS?

ABS, or ABS, is an anti-lock braking system that prevents the wheels from locking when braking. If, during braking, one or more of the car's wheels are blocked and begin to slide on the surface, the ABS will release the pressure in the corresponding brake line and the wheel will start rotating again. If the brake pedal is constantly and strongly depressed, this process of locking and unlocking the wheel will continue continuously until the end of braking and can be carried out several times per second.

2. Why do you need ABS?

Even many of those who know what ABS is, sometimes mistakenly or not fully understand the main purpose of this system. The main mistake in the presentation of the ABS functionality is the belief that the anti-lock braking system is needed to reduce the braking distance of the car. However, in fact, its main purpose is to retain the ability to drive a vehicle during braking, even emergency.

On a car without ABS, during emergency braking by an inexperienced driver, the steering wheels will be locked - which means that turning the steering wheel in any direction will not have any effect on the vehicle's trajectory: it will continue to move straight until the front grip is restored. control wheels with a surface. ABS, on the other hand, solves this problem: by continuously controlling the rotation of the wheels and unlocking them if necessary, it ensures their rotation and thus maintains the necessary grip on the road surface, allowing you to brake and maneuver at the same time.

Another fundamentally important function of the ABS, directly derived from the above, is to provide safe, uniform and linear braking on surfaces with uneven traction. For example, if one side of the car hits a wet surface, slippery lane markings or ice, and the other is moving on relatively clean asphalt, emergency braking without ABS will cause one side to brake more efficiently than the other - and the car will immediately turn around and spin out of control. skidding. This is especially dangerous when driving in a corner, when lateral force is already acting on the car: the difference in wheel braking efficiency in this case easily disturbs the balance.

However, the statement about the usefulness of ABS for reducing the braking distance of a car is also true, but only partially. On surfaces with uniform and sufficient grip of the coated wheels, skid braking with locked wheels will be less effective than braking without locking the wheels, and the braking distance in the former case, as a rule, will be longer. In this case, the use of ABS really reduces the braking distance, preventing the wheels from sliding on the surface. However, on loose surfaces such as gravel, snow or sand, when braking without ABS, the locked wheels burrow inward, creating an additional barrier in front of them to shorten the braking distance. The work of the ABS in this case forces the wheels to rotate, preventing them from burying and thereby lengthening the braking distance of the car.

The anti-lock braking system and braking on clear ice on studded tires: a locked studded wheel "bites" into the ice, leaving furrows behind it, and works to its limit - and if ABS comes into play, the wheel rotates with short slippage, and the effectiveness of such braking will be lower. This fact is used by many "experienced" and "knowledgeable" drivers, who consider ABS to be a technological surplus that prevents them from "controlling" the car. However, despite the increase in the braking distance, the ABS retains its main advantage on ice: it makes it possible to maneuver and control the car, and not just wait for the outcome by pressing the brake pedal.

3. How does ABS work?

Over the years of its existence, ABS has undergone a noticeable evolution, but the basic principle and functional elements have been developed long ago. A typical ABS includes wheel speed sensors, control valves in the hydraulic brake line, and an electronic unit that receives information from the sensors and controls the valve operation.

If a sensor installed on the wheel hub signals a sudden deceleration or complete stop, the control unit gives a command to open the valve for a short time in order to reduce the pressure in the brake line and make the wheel rotate. The process of polling the wheel sensors by the control unit and unlocking the wheels can be carried out several times per second - that is why the pedal “vibrates” when the ABS is activated. In addition to the three above-mentioned components, the ABS can include a pump, which is designed to quickly restore the pressure in the brake line after it has dropped due to the opening of the valve.

The ABS can have a different number of sensors and control valves: depending on their number, the so-called “four-channel”, “three-channel”, “two-channel” and “single-channel” ABS are distinguished. The number of "channels" is determined precisely by the number of control valves that can control the pressure in the brake line: if there are four of them, one individual for each of the wheels, then the system is four-channel, if three - one for each of the front wheels and one common for the rear the axis is three-channel, if there are two valves, one per axis is two-channel, and if there is one valve, then it is single-channel. Modern ABS, of course, are four-channel - the rest of the circuits are found on old cars.

It is worth noting that wheel rotation sensors react precisely to a sharp decrease in the speed of this rotation, and can also transmit information to the control unit about a large differential difference between the wheel rotation speeds on different axles or sides of the car. However, the work of the ABS takes into account the fact that the speed of rotation of the wheels on one axle can be uneven under normal conditions: for example, when turning, the wheels on the outside of the turn will rotate faster than on the inside.

4. Why has ABS become the standard for modern cars?

Given the above, the answer to this question is now obvious: ABS significantly improves the vehicle's active safety. The modern driver is much less specific and professional than half a century ago: if once upon a time high demands were made on the driver, forcing him to be able to do a lot, now the car has become a household item, and its control is made as accessible as possible for everyone. Respectively, modern car should be as comfortable and safe to drive as possible, even for a novice driver with minimal qualifications.

Well, the ABS, in particular, solves the problem of loss of control during emergency braking. The sudden appearance of an obstacle on the road makes a person instinctively hit the brakes. In case he entered a corner at too high a speed, the solution would be the same. Hooked on the side of the road - also braking ... In general, the natural reaction of a person to the occurrence of a dangerous or just an abnormal situation is a sharp press on the brake pedal, and only then - perhaps an attempt to correct this situation by driving. The ABS in this case significantly reduces the cost of this error. Therefore, it is not surprising that, for example, in the European Union, equipping a car with ABS became mandatory by law back in 2004.

5. What if my car does not have ABS?

If your car is not equipped with ABS, its work can be imitated by a simple technique, which is called quite obviously - "intermittent braking". Actually, it is precisely the possession of it that characterizes drivers with some experience: such a driver, having felt the wheels are blocked, overrides the natural instinctive desire to continue to press on the pedal harder, and reduces the effort on it and begins to brake intermittently, pressing the pedal with jerks. Such braking can be compared to the operation of a primitive single-channel ABS - only even an experienced driver is not able to provide such a frequency of "jolts" as in electronics. However, intermittent braking still provides the desired effect by keeping the wheels spinning when decelerating.

Today's new cars are equipped with a variety of systems that even novice drivers can handle with ease. One of the very first systems is the anti-lock braking system. The ABS system is installed even in basic configurations cars. This is an electromechanical unit that, in such complex traffic situations controls the braking of the vehicle, like a slippery, wet or icy road. In fact, this is the right hand of a driver, especially a beginner.

Correct braking without ABS

Every driver should be aware that it is not enough just to use the brake pedal in time. Since if you press the brake sharply at high speed, the wheels of the car are blocked, as a result of which there will be no coupling of the wheels with the road surface. The road surface can be different, therefore, the sliding speed of the wheels will be different. As a result, the vehicle is no longer steerable and can easily skid. If the owner of the car is inexperienced, then controlling the direction of the car may not be able to him.

The most important thing in such braking is to prevent the wheels from locking rigidly, causing the vehicle to skid. In order to avoid such cases, it is recommended to use the intermittent braking technique. To implement such correct braking, it is necessary to periodically press and release the brake pedal at short intervals, and in no case should the brake pedal be kept pressed until it stops completely. With such a simple braking technique, it is possible to control the vehicle regardless of the quality of the road surface.

However, it is necessary to take into account a simple human factor - the driver in an unforeseen situation is able to get confused and all the braking rules can simply fly out of his head. For vehicle control in similar emergency situations and an anti-lock braking system was developed.

What is the secret of ABS work

It is important to know on what principle the ABS works, because it has a close connection with the control system, which means that, accordingly, with the safety level of the driver and passenger. So, the main idea of ​​the system is that when the driver presses the brake pedal, instant control occurs, and also redistributes to the wheels braking force... Thereby, the vehicle is steerable in all conditions, and a speed reduction effect is achieved. However, one cannot rely solely on various additional systems because the driver needs to learn own car- the length of the stopping distance and behavior in emergency situations. It is recommended to test the ability of the car on specialized race tracks, in order to prevent awkward situations on the road in the future.

There are still some features of the ABS. For example, when the driver decides to stop the movement of a car equipped with the ABS system, then when the brake pedal is pressed, a slight vibration is felt on the pedals, and an accompanying sound similar to a "ratchet" can be heard. Vibration and sound are a sign that the system is working. In the meantime, the sensors read the speed values ​​and the control unit monitors the pressure inside the brake cylinders. Thus, it does not allow wheel blocking, but slows down with quick jerks. Due to this, the speed of the car drops, and at the same time does not go into a skid, which allows you to drive the vehicle until the very stop. Even on slippery roads, with ABS, the driver only needs to keep the direction of the vehicle under control. This perfect and controlled braking is only possible thanks to the ABS system.

It should be emphasized next steps actions:

1. Release of pressure in the brake cylinder.
2. Maintain continuous cylinder pressure.
3. Increase the pressure to an appropriate level in the brake cylinder itself.

It is important to know that the valve body in the vehicle is mounted in the brake system in a row right after the main brake cylinder. As for the solenoid valve, this is a kind of valve that admits and blocks the flow of liquid substance to the brake cylinders themselves.

Monitoring, as well as the working processes of the vehicle braking system are carried out in accordance with the information that came to the ABS control unit from the speed sensors.

During the braking process, ABS decodes information from the wheel speed sensors, due to which the vehicle's speed decreases evenly. In the event of a stop of any wheel, the signal is instantly sent from the speed sensors to the control unit. Upon receipt of such a signal, the control module releases the blockage by activating the exhaust valve, which blocks the entry of liquid into the wheel brake cylinder. At this moment, the pump returns the liquid to the accumulator. When the wheel rpm increases to the permissible speed, the control unit will give the command to close the exhaust valve and open the intake valve. After that, the pump starts, which will build up pressure into the brake cylinder, as a result of which the wheel will continue to brake. These processes are carried out instantly, and last until the final stop of the vehicle.

The discussed essence of the ABS operation represents the newest four-channel system in which all wheels of the vehicle are monitored.

Other notable types

1. One-channel consists of a sensor located on rear axle, whose task is to distribute the braking force synchronously to four wheels. This kind of system has only one pair of valves, due to which, the pressure is varied simultaneously throughout the entire circuit.
2. Two-channel - it carries out paired control of the wheels, which are located on one side.
3. The three-channel consists of three speed sensors: one is mounted on the rear axle, and the rest are mounted on the front wheels separately. In the mentioned type of system, there are three pairs of valves (inlet and outlet). The action of this type of ABS is to individually control the front wheels and a pair of rear wheels.

Comparing different types of ABS, we can conclude that their difference is manifested only in a different number of valves themselves and speed control sensors. However, the essence of the system in the vehicle, as well as the order of the ongoing processes, is identical for all types of systems.

System implementation history

Engineers from leading automotive companies worked diligently to develop ABS in the first half of the 70s. Even the very first systems were quite successful, and already in that decade, similar systems began to be installed in mass-produced cars.

Initially, mechanical sensors were mounted on cars only on one axle, which sent data to the control module about the change in pressure in the brake circuits. Developers from Germany took this area one step further and began to use sensors without contacts, and this, in turn, catalyzed the transfer of information to the logic block. In addition, the number of false alarms has been reduced, and due to the fact that rubbing surfaces have been eliminated, wear has disappeared. The modern system works according to the same principle that was used in the first anti-lock braking systems.

Anti-lock braking system components

Hypothetically, the structure of the ABS is absolutely simple, and consists of the following devices:

• valve body
• speed sensors
• electronic control unit

The latter plays the role of the "intelligence" of the system (computer), so it is not difficult to imagine what role it plays. As for the speed control sensors and valve body, a deeper analysis is needed.

How the speed sensor works

The sensors that control the speed work on the principle of electromagnetic induction. A coil with a magnetic core is rigidly fixed in the drive axle gearbox. Also, a gear ring is fixed in the hub, which rotates in parallel with the wheel. Then this rotation changes the parameters of the magnetic field, which in response causes the appearance of a current. The strength of the electric current will increase in direct proportion to the speed of rotation of the wheels. Based on this force, in turn, a signal is generated and transmitted to the electronic control unit. The pulses are transmitted from four speed sensors, which are of two types: active and passive, and also differ in design.

The active type of sensor operates with a magnetic sleeve. The transmission of a binary signal is carried out by reading its label. Thanks to the rotational speed, there are no errors and, as a result, accurate pulse data.

The passive type uses a specific comb in the hub block. Thanks to such signals, the sensor is able to determine the rotational speed. It is important to take into account one drawback of this design - at low speed, inaccuracy may result.

Valve body

The valve body includes:

• a reservoir for storing brake fluid - a hydraulic accumulator;
• intake and exhaust solenoid valves, which regulate the pressure supplied to the brake cylinders of the vehicle. Each type of ABS differs in the number of valve pairs;
• thanks to the universal pump, the required pressure in the system is generated, as a result of which the brake fluid is supplied from the accumulator, and, when necessary, takes it back.

Some disadvantages of ABS

One of the biggest disadvantages of anti-lock braking systems is that their effectiveness depends on the quality and condition of the road surface. If the road surface is not good enough, the braking distance is much longer. This is due to the fact that from time to time the wheel loses contact or grip on the asphalt and stops rotating. ABS detects this kind of wheel stop as a blockage, and thus stops braking. At the moment of coupling the wheels to the asphalt, the programmed command does not agree with the one necessary in this case, and the system itself needs to rebuild again, which takes time and increases the braking distance. This effect can be minimized only by reducing the vehicle speed.

In the case of an uneven road surface, for example, snow - asphalt or ice - asphalt, getting on a wet or slippery road section, ABS evaluates the surface and adjusts the braking process for this road. At the same time, when the wheels hit the asphalt, the ABS is rebuilt again, due to which the length of the braking tupi again increases.

On dirt roads conventional braking systems perform much better and more reliably than anti-lock braking systems. Indeed, during normal braking, the locked wheel pushes the ground, creating a small hill, which does not allow the vehicle to move further. Thanks to this, the car stops very quickly.

Another flaw in the anti-lock braking system is that at low speeds, the system is completely disabled. In the case when the road is sloping and at the same time slippery, you need to remember that a reliable braking may be required. hand brake... Therefore, it must always be in working order.

Regular deactivation of the anti-lock braking system in cars is not provided. Sometimes drivers want to disable this system. To do this, pull the plug out of the block. It is also necessary to take into account that in new cars the redistribution of inter-axle braking forces depends on ABS. Therefore, by braking, the rear wheels are completely locked.

It is important to note that the ABS system is an excellent addition to the vehicle's braking system, thanks to which it is possible to control the vehicle in the most difficult and unusual situations. Despite this, it should not be forgotten that it is impossible to rely entirely on the machine. On the driver's side, too, you need to make great efforts to keep the situation under control.

Video

Anti-lock braking system (ABS) is an electro-hydraulic system active safety, which allows you to maintain controllability and stability of the vehicle when braking by preventing the wheels from locking. ABS is especially effective on road surfaces with a low coefficient of adhesion, as well as in bad weather (snow, ice, rain). Deciphering the abbreviation ABS - Antilock Brake System, which literally translates as "anti-lock braking system". Consider the principle of the system, its main components, generations, as well as the pros and cons of using.

Device and main components of the system

ABS system components

The anti-lock braking system includes:

• Wheel speed sensors. The sensors work on the basis of the Hall effect and are mounted on the hub of each wheel. They determine the wheel speed and transmit a signal to the ABS control unit.
• Control block. The main function of the electronic control unit (ECU) is to ensure the operation of the braking system in the most effective and stable range, at which the braking force will be maximum, and the wheels of the car will not be blocked. For this, the control unit continuously calculates the change in wheel speed (deceleration). Based on these indicators, control signals are generated for the actuators: the pump and the electromagnetic valves of the hydraulic unit.
• Hydraulic block. This ABS component is an actuator. The hydraulic unit includes solenoid valves (inlet and outlet), hydraulic accumulators, a cam pump with electric motor, damping chambers.

The solenoid valves control the braking process, each in its own circuit. For each working brake cylinder, a pair of valves is assumed (one inlet and one outlet). Hydraulic accumulators are designed to accelerate the release of pressure in the brake circuit. They are filled when the outlet valves are opened. Further, a cam pump is switched on, which pumps out brake fluid back to the brake master cylinder. It is for this reason that when the ABS system is operating, the driver feels jolts on the brake pedal. Damping chambers dampen fluid vibrations during system operation. Since the car has two hydraulic circuits for the brake system, two pressure accumulators and two damping chambers are usually integrated into the hydraulic unit.

How the system works

ABS system diagram

The anti-lock braking system performs its work cyclically, with each cycle consisting of three phases:

1. Increased pressure (by the driver)... Braking occurs in normal mode, the pressure in the system is increased by pressing the brake pedal by the driver. The valve body inlet valves are open, the outlet valves are closed. If the speed of rotation of the wheel slows down too much and exceeds a certain value, then the ABS control unit moves the inlet valve to the "closed" position, the outlet is also closed. The system enters the next phase.
2. Hold pressure... At this stage, the ABS system, as it were, “cuts off” the braking process, and constant pressure is maintained in the “hydraulic block - wheel brake cylinder” circuit. Even if the driver presses the brake pedal further, the pressure will not increase. In this mode, braking occurs at the maximum braking force, that is, the most effective. The control unit continues to control the speed of rotation of the wheels, and if it decreases below the permissible threshold, that is, there is a threat of wheel blocking, a command will be sent to open the exhaust valve and release the pressure.
3. Pressure relief... In this phase, the outlet valve opens and the pressure drops sharply. First, the liquid enters the accumulator, then it is pumped out by the pump back to the GTZ. The inlet valve remains closed. After the speed of deceleration of the wheels returns to the permissible values, the exhaust valve closes. The inlet valve opens and the cycle starts over.

There is a fairly common misconception that ABS independently increases the pressure in the brake system. In fact, this is not the case when it comes to the ABS system in its pure form (without). The pressure in it increases solely due to the actions of the driver.

This cycle of the vehicle's anti-lock braking system is repeated until braking is complete, and can be repeated about 6 times per second. Note that ABS is triggered during emergency (sharp) braking. It is impossible to turn off the ABS system without interfering with the design of the car, since the suspension of its operation can lead to tragic consequences (therefore, it is not provided for by the automakers).

Note that ABS is integrated into a standard vehicle without structurally changing it. If the vehicle's anti-lock braking system is defective, the corresponding indicator (warning lamp) on the instrument panel will light up.

Generations of anti-lock braking systems

ABS malfunction indicator lamp

It took a huge number of engineers 14 years to create the ABS system. ABS has been produced since 1978 by Bosch.

The first generation of the system (1970) was named ABS-1. This electromechanical product was not reliable and durable due to the thousands of analog components that were used in the ECU. Although the main function of ABS was fulfilled, the product was not suitable for mass production.

Second generation (1978). Bosch ABS-2 was first installed as an option in Mercedes-Benz vehicles S-class, and after a while also in BMW 7-series limousines. The number of components was reduced to 140, and the mass of the hydraulic unit was 6.3 kg.

In subsequent generations of ABS, Bosch engineers focused on improving the system and reducing its size. So, in 1980, ABS-2E came out, in which the mass of the hydraulic unit was already 4.9 kg, and the number of components decreased to 40. In 1995, ABS 5.3 appeared with a hydraulic unit weighing 2.6 kg and 25 components. In 2003, ABS 8 comes out, in which 16 components, and the mass of the hydraulic unit has decreased to 1.6 kg. Since 2010, Bosch has been producing the 9th generation of the ABS system, which is distinguished by its compact dimensions and a hydraulic unit weighing only 1.1 kg.

Advantages and disadvantages of the system

ABS system on soft ground

Let's consider the main advantages of the ABS system:

• maintains controllability and stability of the vehicle during emergency braking, bad weather, etc .;
• in most cases, it reduces the length of the stopping distance;
• increases the efficiency of the braking process;
• provides better vehicle maneuverability on slippery road surfaces.

The anti-lock braking system also has disadvantages: its use increases the braking distance on soft soils (sand). On such surfaces, the wheels, on the contrary, must be blocked. In the latest generations of ABS, this defect has been practically eliminated: the system "learned" to determine the type of surface, and then implement a separate algorithm for a specific coating.

ABS... The words encrypted in this abbreviation are different: for example, in German Antiblockiersystem, in English Anti-lock Brake System, there is even a stable Russian-language phrase "anti-lock braking system", but they have the same translation and meaning. This is a system that prevents the wheels from locking during emergency braking and regulates the forces generated by the braking mechanisms. The main task of the triune system is to give the driver the ability to drive the car, maintain directional stability and provide the most effective deceleration during emergency braking.

Creation

The idea to create a system to prevent wheel locking dates back to before World War II. It was originally planned to use ABS in aviation. But the technologies and materials used at that time did not allow it to be implemented in mass production, and even more so on a production car. In 1964, Mercedes engineers, together with specialists from Teldix and Robert Bosch, got down to business. To begin with, we collected all the patents and reports over the past couple of decades, which mentioned the distribution of braking forces between the wheels.

The main elements of any ABS: the control unit and the actuator of the hydraulic unit (1), wheel speed sensors (2). The hydraulic unit regulates the pressure in the brake system circuits using a hydraulic accumulator, an electric hydraulic pump reverse and electro-hydraulic control valves. The diagram shows a four-channel ABS, which is able to regulate the pressure separately in each of the four brake lines.
yellow - data cables;
red - brake circuit of the front right and left rear wheels;
blue - brake circuit of the front left and rear right wheels

All modern systems have four wheel speed sensors and four pairs of valves - two for each brake circuit or channel. Such systems are called 4-channel systems. They allow you to individually adjust the braking force at each wheel, achieving the most effective deceleration.

Studies have yielded results, for example, helped to determine the functional diagram of the ABS. Sensors (then only on the front axle) measured the rotational speed of each wheel. These measurements were recorded and compared by the control unit and, if necessary, gave corrections to the actuator to correct the pressure in any circuit of the brake system. It worked out pretty smoothly on paper. But in real situations, ABS did not work clearly, reacted with delays to a change in the grip of the wheels, and was not famous for its reliability.

Back in 1936, Bosch registered a patent for a “mechanism that prevents the wheels of motorized Vehicle". But it was only with the introduction of electronics that engineers were able to develop an anti-lock braking system (ABS 1) suitable for use on a car.

One of the first significant steps towards mass production was the replacement in 1967 of mechanical sensors on wheels with contactless ones, using the principle of electromagnetic induction. The advantages are obvious: they do not wear out, are resistant to mechanical stress, and there are no false alarms. It was with such sensors that Mercedes presented the first ABS c in 1970 to the public. electronic control for cars, trucks and buses. The sensors transmitted signals to the unit, which controlled the hydraulic module installed between the main brake cylinder and calipers.

In 1978, Mercedes-Benz was the world's first automaker to introduce ABS on the production S-Klasse. The option added 2217 marks to the price of the car. A little later, the same ABS 2 was tried on by the BMW 7-series. And today more than two-thirds of all new cars in the world are equipped with anti-lock brakes.

The principle of the first ABS is embedded in the most modern system. Sensors monitor the speed of rotation of each wheel, the control unit compares the readings and issues commands to the solenoid valves of the hydraulic module, which regulate the pressure in the brake system, - a pair (inlet and outlet) for each circuit. During emergency braking, the valves operate at a frequency of several tens of times per second (15-20 Hz, depending on the system) - it is their chirping that we hear when the wheels are locked-unlocked. In this case, the pressure in one or several circuits at once rises and is immediately released, and the pads, accordingly, compress and release the disc, providing the very intermittent braking.

The first systems were based on analog technology, which often gave errors, the wiring diagrams themselves were complex and cumbersome. And the level of development of "digital" was then incomparably low - the first microprocessors, which appeared in the early 1970s, were not suitable for controlling the anti-lock braking system. Only 5 years later, Bosch made a fully digital control unit. The electronic filling became almost an order of magnitude more compact - the ABS 1 unit consisted of about 1000 components, and only 140 were in the "brains" of the second generation system. In addition, ABS began to work almost flawlessly and several times faster - the electronics processed data from the wheel sensors in milliseconds and sent command impulses to the hydronic module.

In the mid-1990s, anti-lock brakes braking systems began to be installed on motorcycles. They prevented blocking front wheel and the rider's flight through the steering wheel. The top diagram shows the ABS advantage when braking the average motorcyclist on dry pavement from a speed of 100 km / h.

Many modern motorcycle systems work even if the driver only pressed the rear or front brake.

The further evolution of anti-lock braking systems went in two directions - the improvement of hydraulics and electronics. For example, consider the development of ABS from Bosch, which is not only the ancestor of the anti-lock braking system, but also the main supplier for most car manufacturers, including Russian ones.

The most powerful supplier of ABS components is Bosch, which supplies accessories for most of the models. Bendix Corporation works for Chrysler and Jeep, Continental Automotiv Systems for Ford, GM, Chrysler. Infiniti and Lexus use parts from Nippondenso, while their fellow countrymen Mazda and Honda use Sumitomo. And also Aisin Advics, Delphi, Hitachi, ITT Automotive, Mando Corporation, Nissin Kogyo, Teves, TRW and WABCO are engaged in the development and production of ABS components.

So, soon after the appearance of the compact digital filling, the control unit moved to the hydronic module. This not only made life easier for car assemblers and assemblers, but also reduced the cost of the system. The next generation ABS 5, which has become not only lighter and faster, has received more advanced mechanics, including a block of solenoid valves that are new in design. Now the anti-lock braking system has made it possible to implement additional functions, in particular, the EBD (Electronic Brake Distribution) program, which doses the braking force for each wheel separately, the TSC program ( Traction control system), which combats slip, and a program that controls lateral dynamics - ESP (Electronic Stability Program). The implementation of these functions required engine management - for example, when the electronics detects slipping or cross-slip, it automatically reduces the fuel supply.

Mechanical wheel sensors have been replaced by inductive sensors. Their principle of operation is simple: when the vehicle is moving, an electric current is induced in the sensor coil. Its frequency is directly proportional to the speed of rotation of the wheel. Over time, they began to measure not only the speed of rotation, but also the direction. Now, on some models, sensors are built into wheel bearings.

Modern systems are built on a modular basis. For example, the ninth generation supports many functions that increase comfort and safety - the electronics are able to prevent the car from rolling back when starting uphill, regulate the speed of descent from the mountain (implemented on crossovers and SUVs) and even automatically stop the car urgently (you can read more about such systems). Moreover, the automaker purchases the set that he needs for a particular car. And the ABS developer assembles a unit for him from the corresponding electronic and hydraulic modules. In addition, this arrangement made it possible to produce systems for cars at a lower cost and more expensive. For example, Bosch offers units with more complex mechanics for premium models. So, instead of a two-piston return pump, a six-piston one is installed in the hydraulic module. It very quickly reduces the pressure in the circuit, which is why there are almost no vibrations on the brake pedal.

Simplified scheme of operation of a hydraulic unit as part of an ABS. For simplicity, the diagram shows the operation of a single wheel system. In a four-channel system, there are four such circuits per wheel.

And what about in practice?

We recently ran a test to demonstrate the benefits of anti-lock braking systems. Obstacle avoidance with braking was performed on a vehicle with and without ABS. The tires on the experimental Logans were the same - Barum Brilliantis 185/70 R14. For greater persuasiveness, a slippery coating was simulated - plastic moistened with soapy water. It was necessary to enter the “gateway” at a speed of 40 km / h and immediately start an emergency ( swipe on the brake pedal - the driver was "frightened") braking with a simultaneous lane change.

Vehicle without anti-lock braking system

with the wheels turned inside out, without changing the trajectory, he knocked down the obstacle and continued to move on. The culprit is sliding friction in contact patches, locked wheels do not perceive lateral forces as appropriate, therefore, it is impossible to drive a car at this moment. I used intermittent braking, as taught in special courses, the effect on this type of coverage is practically zero. Attempts to find the moment when the blocking began and to apply search steering (searching for the angle of rotation of the wheels when the car stops responding to the steering wheel) also failed.

Logan with ABS

with a much more effective deceleration, it allowed even beginners to easily and without straining get away from the obstacle the first time. The braking distance with ABS for this surface was on average 1.5 times shorter than that of Logan, which was not equipped with an anti-lock braking system. What's the trick? In intermittent braking with short-term blockings - ABS manages to brake-release each wheel 15 times in a second. While the wheel is rolling for a fraction of a second, you have the ability to set the direction (at this moment, the resting friction in the contact patches). At the same time, for each type of coating (it is established empirically during design and refinement), the most optimal degree of wheel slip (15-20%) is maintained, at which deceleration is most effective. In addition, ABS doses the braking force to each wheel separately, preventing skidding.

Why didn't intermittent braking help in a car without ABS? Unlike ABS, I can lock-unlock the wheels a maximum of three to four times per second - I act a priori slower. The degree of slippage is not optimal for me, therefore, the braking is less effective. Unlike ABS, I act on all wheels at once with the pedal, and this can cause drift or skid, because under the wheels there can be dissimilar surfaces, or the load along the axles and sides can be changed. You can learn to change the trajectory with this method of braking slightly, but training is needed. The same is true for "tracking" braking. The conclusion is unambiguous - with ABS, the car is safer.

However, not everything is as cloudless as it might seem at first glance. In some cases ABS can increase the stopping distance, for example, on ice and a number of unstable surfaces (loose ground, rolling gravel road, or hard ground covered with dust, sand or snow). Worn out shock absorbers and an unscrupulous suspension setting can also add fuel to the fire ... If at least one wheel breaks off the road for a long time during braking and locks up, the system, thinking that it has hit the ice, releases it, and at the same time reduces the pressure in the hydraulic lines of the remaining wheels. In this case, the system understands that the wheels hit dissimilar surfaces and thus seeks to maintain directional stability. In addition, the very adequacy of the ABS setting on some modern models raises many questions. Next time we'll talk about how to deal with these nuances.