ABS is an anti-lock braking system. From the name, its purpose immediately becomes clear. But how does it work?
What is ABS for?
Every driver knows that during braking, sooner or later there may come a moment when the wheels stop turning and the car begins to skid. This situation is dangerous because the car becomes uncontrollable. Wheels that do not rotate, even if you turn the steering wheel, will not be able to change the trajectory of the car.
Wheel lock occurs when the braking force exceeds the coefficient of grip of the tire with the road. This moment occurs every time at different times and will come on ice much earlier than on dry pavement. Therefore, braking during ice (and even emergency!) Turns into a very difficult task.
To facilitate driving in difficult weather conditions, an anti-lock brake system has been developed.
How ABS works
The principle of operation of the anti-lock braking system is very simple - it is able to detect the blocking of one or more wheels and, when this occurs, “turns off” the brakes. This is the same as if you released the brake pedal. When the wheel starts spinning again, the ABS registers the start of rotation and "turns on" the brakes again...
The main "trick" of all these actions is that ABS disables and applies the brakes up to 30 times per second! During operation of the system, the brake pedal trembles under the foot, and on some vehicles, the chirping of operating valves is heard. At the same time, the wheels continue to rotate, the car does not lose control, and braking occurs with maximum efficiency.
ABS device
The anti-lock braking system incorporates a very modest number of large modules. These include wheel speed sensors, valve block and control unit. All.
Rotation sensors are used to determine the rotation of the wheel. If there is no rotation, but the car is moving, then the wheel is locked. The signal from the sensor comes to the control unit, and it turns on the corresponding valve. The valve closes the corresponding brake line, thereby disabling the brakes. Accordingly, when the wheel starts to rotate, the signal goes along the same chain, but the command from the control unit turns off the valve. The brake fluid supply resumes and braking continues.
Anti-lock braking systems are divided into three types:
1) Single-channel. The simplest ABS, capable of controlling blocking and braking only on all wheels at once. They are ineffective in cases where wheels of different sides drive on different surfaces (a classic situation: asphalt under the left wheels, and ice under the right wheels).
2) Dual channel. Work with two brake circuits separately. If the contours are distributed along the sides, then the rotation of the wheels will be controlled more efficiently than with single-channel ABS.
3) Multichannel. Each wheel is affected individually. These ABSs are the most effective because they are able to control any wheel exactly as needed at a given time. Braking will be excellent, even if there are completely different surfaces under all wheels.
The ABS control unit has a built-in self-diagnosis system. Polling sensors and determining the system's operability necessarily occurs after the ignition is turned on. At this time, a special indicator must be lit on the instrument panel. After a few seconds, it must also go out. If the indicator continues to glow, then there is a malfunction in the ABS. It is highly undesirable to operate a car with an inoperative anti-lock braking system - it is necessary to carry out diagnostics and repairs.
ABS Installation Diagrams. The braking dynamics of a car to a large extent depends on the installation scheme of the ABS elements on the car and the chosen control principle.
The following principles of wheel slip control are most common:
- individual regulation of the slip of each wheel separately (Individual Regelung) - IR;
- "low-threshold" regulation, i.e. regulation, which provides for the issuance of commands for releasing and braking both wheels of the axle simultaneously on the signal of the wheel sensor, which is in the worst grip conditions - "weak" wheel (Select Low) - SL;
- "high-threshold" regulation of the wheels of one axle, when the signal is given by the sensor of the "strong" wheel, i.e., located in the best grip conditions (Select High) - SH;
- modified individual regulation - Modifizierte Individual Regelung (MIR) is a compromise regulation between SL and IR. The meaning of MIR is that at first the regulation is carried out according to the “low threshold”, and then gradually there is a transition to individual regulation. MIR is useful when braking on ground with different traction under the left and right wheels, as well as when cornering and cross-sloping.
Individual control is optimal in terms of providing the best braking performance (minimum stopping distance). For this purpose, a speed sensor and a pressure modulator are placed on each wheel, and their parameters are regulated by a separate control channel in the electronic unit. Individual regulation makes it possible to obtain the optimal braking torque on each wheel in accordance with the traction conditions and, as a result, the minimum braking distance. However, if the wheels of the same axle are in different grip conditions, then the braking forces on them will also not be the same.
Swinging moment leading to buckling
In this case, a turning moment occurs, leading to a loss of stability. At the same time, the controllability of the car is maintained, since the wheels are not blocked and the margin of lateral stability remains sufficient. The scheme with individual regulation is the most complex and expensive.
When choosing an ABS scheme, they usually proceed from technical and economic feasibility. As studies have shown, they meet all the requirements, and therefore, belong to category 1 ABS with a control scheme (front wheels / rear wheels) IR / IR and MIR / IR, as well as other schemes (MIR / SL, SL / IR) if the SL principle used on an axle(s) providing no more than 50% of the total braking force. ABS using the SL principle on both axles of the vehicle (SL/SL) belongs to category 2. In ABS category 3, as a rule, the SL scheme is implemented.
Schematic diagram of the Bosch 2nd generation ABS system for a passenger car:
1 - sensor;
2 - signal lamp;
3 - control unit;
4 - modulator
The second-generation ABS system is built into the standard braking system and does not require changes in its design. The advantages of such systems lie in the simplicity and convenience of the layout on the vehicle.
The system contains a hydraulic unit located between the main brake and wheel cylinders, speed sensors mounted at the front wheels and the main gear, and an electronic control unit (ECU) installed in the passenger compartment or in the engine compartment of the vehicle. On all-wheel drive vehicles, a longitudinal deceleration sensor is added to the speed sensors. The hydraulic unit consists of a pump with an electric motor, a modulator with three solenoid valves, two accumulators with damping chambers.
The system uses a three-phase duty cycle. When braking without locking the wheels, the solenoid valve connects the wheel cylinder to the corresponding section of the master cylinder and the braking system operates normally. If the ECU detects a tendency to block the wheel, the solenoid valve is moved to a position where the wheel brake cylinder is disconnected from the master brake cylinder and, conversely, connected to the drain line. The fluid flows into the damping chamber, and then pumped into the brake master cylinder. The pressure in the wheel cylinder decreases. In the pressure holding phase, the solenoid valve is moved to a position in which all lines are disconnected from each other. The next phase of pressure build-up is carried out by moving the solenoid valve to its original position. The fluid from the brake master cylinder re-enters the wheel cylinder.
In the event of a pump failure, anti-lock braking is stopped, but the brake actuator remains functional.
What is ABS in a car, we will try to figure it out in the next 5 minutes while you read our article. It would seem ashamed not to know such a concept for a modern motorist, but our task is precisely to explain what is embarrassing to ask in our environment. The newfangled expression "anti-lock braking system" is synonymous with a modern braking device that leaves the possibility of maneuvering with the brake pedal pressed. What is the gain?
ABS system in the car - to be or not to be?
Let's analyze how the ABS system works in a car at the moment the brake pedal is pressed, compare it with a conventional system. When we see an obstacle in front of us, or rather, when it arises unexpectedly, and we are forced to abruptly try to stop, then the main difference between the anti-lock braking system and the usual one awaits us. Indeed, with a normal smooth stop, we will not feel the difference, the whole effect will be revealed in an emergency. So, we nervously clamp the brake accelerator with maximum force, and what happens at this moment?
In the usual case (without ABS), the car starts to stop due to the fact that the wheels are tightly clamped by the corresponding mechanisms and stop spinning, but the axle on which they are located also becomes not mobile, but stops. If at this moment you still need to go to the side at least a little to avoid a collision or move it along a tangent trajectory, then nothing will come of it. You will move along the path that is determined by the position of the wheels.
The ABS system does not block the wheels, and therefore, you are allowed to maneuver, it is not only more convenient, but also safer. Moreover, not only the ability to go around an obstacle is the safety of the presence of ABS.
What is ABS in a car and what do we win?
In the presence of anti-lock brakes, we gain not only the presence of moving wheels with the brake pedal depressed. As experienced motorists know, with blocked wheels, any road roughness, its inclination, the heterogeneity of the coating under different wheels, and even the difference in tread patterns become critical. What's the matter? In all cases, you face a terrible skid! And it is already unknown what would be better, to crash or reap the benefits of the uncontrolled behavior of a pile of iron weighing more than a ton.
The ABS system allows the wheels to maintain traction at the proper level and control the behavior of the car depending on the situation. This is due to induction sensors that determine the speed of the wheel, they also give the command to increase or decrease it. Also successfully applied in ABS and Hall sensors. In modern foreign cars, each wheel is equipped with a sensor, although earlier the device was single-channel, and one analysis algorithm and commands for action were applied to all wheels.
Is it possible to do without the ABS system?
As you can see, ABS is smart enough to manage our braking force optimally, because the electronics are responsible for this. From here, by the way, the braking distance is shorter, thanks to the laws of physics, the system calculates the optimal dose of sliding and rest friction forces, ensures blocking in time and releases it in time so that you don’t even feel these transitions, but just keep the brake pedal almost to the floor. But these are all machinations of technological progress, but what about those who have an older car and have not yet been equipped with such “intelligence”?
Previously, they coped something like this: they put pressure on the brake, then released it, jerked the steering wheel in the direction of avoiding an obstacle, again clamped the pedal, etc., making the anti-blocking effect, roughly speaking, manually. But this is fraught with the same drifts, and therefore not all drivers successfully coped with emergency situations. And braking efficiency also suffered, the stopping distance is even longer and not always an adequate trajectory. So there was a chance to avoid an accident, but it was significantly less than with ABS on a modern car.
In an extreme situation, when we press the brake pedal with all our might, one or several wheels may be blocked, which leads to a significant deterioration in handling and an increase in braking distance. To prevent such blocking, cars are equipped with an ABS system, which we will discuss in this article.
For the first time, such anti-lock braking systems began to be used on cars back in the seventies of the last century. Many car manufacturers and subsequently car owners were able to evaluate the effectiveness of the active safety system, which made it possible to reduce the braking distance, increasing the safety of car operation at any time of the year.
If we talk about the benefits of using such anti-lock systems, then first of all we note the improvement in the safety of using a car. Thanks to this system, it is not only possible to reduce the braking distance, but also prevent the car from skidding, which is caused by wheel blocking.
In particular, such a system will be useful when operating a car in the winter season, when on a slippery road, with any inaccurate braking, the wheels can be blocked, and the car begins to slide forward. However, such a system ABS , having determined the blockage that has occurred, will reduce the intensity of braking, which will allow you to regain control of the car.
We also note the uniform wear of the wheels, which in turn reduces the cost to the car owner for the purchase of new tires. During the blocking of the wheels during braking, the projector can quickly wear out, and literally 3-5 such extreme braking will be enough to completely wear out the tires.
If we talk about the shortcomings of such systems, then it is necessary first of all to note the frequent failures of ABS sensors, which forces the car owner to change broken parts, which can lead to some increase in the cost of operating cars.
Anti-lock braking systems have become today the main element of the active safety of every modern car. Using data from sensors ABS course stabilization systems work, as well as a number of other active and passive safety systems, without which the operation of the car would be impossible. Automakers today are constantly improving their ABS systems, which are becoming more reliable, smarter and more functional.
The anti-lock braking system includes numerous sensors, hydraulic distributors with solenoid valves, a suction pump and a control unit that controls the operation of the brake system, preventing blocking of the entire axle or individual wheels.
In recent years, despite some simplification of such anti-lock systems, their effectiveness has increased, which is explained by the improvement of automation. If in the past most of the work was done by hydraulic systems, today the blocks and actuators are fully controlled by automation, which improves the quality of the work of such an anti-lock system.
The control unit constantly sends signals to the sensors, receiving the necessary information and makes the right decision to reduce the pressure in the brake system. Communication between sensors and control units is carried out via a special high-speed bus, while each wheel can have several individual sensors that provide the central computer with all the necessary data to adjust the operation of various vehicle systems.
The principle of operation of such an anti-lock braking system has not actually changed over the past few decades. When braking, a signal is sent from the control unit to the brake cylinders, after which the working fluid passes through the inlet channels. This brake fluid pressure is transmitted through solenoid valves to each wheel, which effectively slows the vehicle down. In the event that the control unit determines the danger of blocking the wheel, then the electromagnetic sensor receives a corresponding signal, it closes, which in turn prevents braking and blocking the wheels of the car.
Any even the easiest and simplest braking in a car equipped with an ABS system takes place under the control of automation. Depending on the intensity with which you press the brake pedal and the position of the wheels, the system decides whether to open or close the solenoid valves. Such systems using ABS sensors and solenoid valves are simple in design, so they are reliable and durable. Problems can only be caused by sensors, which are often damaged by anti-icing agents and require appropriate replacement.
At the moment when the ABS system works and dissolves the wheels, the car owner feels the pulsation of the brake pedal at that moment. This pulsation occurs when the solenoid valves open and close quickly to properly decelerate and prevent wheel lockup.
Anti-Lock Braking System Tips
Modern anti-lock braking systems are durable and reliable components that do not require any special maintenance. It is only necessary from time to time to check the performance of the sensors in the wheels and, if necessary, replace them.
Do not overheat the control units or fill them with water.
In the event that you need to weld metal in a car or you need to connect to the car's on-board electrical system, the ABS wiring must be disconnected.
Monitor the condition of the contacts on the generator, which will prevent short circuits and failure of sensors.
Avoid connecting your vehicle's battery to another vehicle.
Do not separate the electrical connectors of the sensors when the ignition is on and the engine is running.
In the event that malfunctions of the ABS system are noted, the corresponding control lamp will light up on the dashboard. The car in this case will brake effectively, but with excessive force on the brake pedals, the wheels will be blocked, which can lead to skidding. Therefore, if any malfunctions of the ABS are noted, it is necessary to take this into account and brake smoothly and carefully, and if possible, contact the appropriate service stations as soon as possible for repair work.
The technical equipment of modern cars is so diverse that it never ceases to please with a variety of useful and convenient options, and many motorists will no longer be surprised by the presence of such frills that you had only dreamed about before.
One of the systems that are equipped with machines equipped with the latest technology is the ABS anti-lock braking system. It has appeared on the automotive market for a long time, but for many Russian motorists ABS is still a novelty.
The anti-lock braking system is installed on the car as an additional equipment, the task of which is to prevent the wheels from blocking during heavy braking. Thanks to ABS, when you press the brake pedal hard, the car will not skid on dry pavement or on wet roads.
And yet, what is abs in a car? This system is a complex electronic device that includes a central unit and speed sensors installed on each wheel. At the moment the brake is applied, they determine the speed at which each wheel rotates. Then cunning electronics remove excess pressure from the brake line into a special hydraulic accumulator.
In this case, the rotation of the wheel begins to recover, as the brake pads are released. If the pressure is still high enough, the process described above is repeated again until it returns to normal.
Purpose of ABS
The anti-lock braking system, in its principle of operation, imitates the actions of an experienced motorist who uses intermittent braking on a slippery road so that the car does not skid. And here the question arises: why do we need an electronic system when the driver himself can perform these actions? Cars that do not have ABS are difficult to control under heavy braking, and in many situations it is simply impossible to do without it.
The anti-lock braking system is automatically activated 15-20 times per second, so that the braking distance in the event of emergency braking is minimal. A person is not physically capable of working at such a speed.
Perhaps the main advantage of ABS is that the driver, even with strong braking, can make the car obey the steering wheel. When this device is absent, during braking, the car will slide uncontrollably along a straight path, despite all the efforts of the driver to align the movement of personal vehicles using steering wheel turns.
When you turn on the ABS in the cabin, you can hear a soft crack, indicating the functioning of the executive unit, and feel slight and frequent jolts in the brake pedal. For those motorists who have not previously dealt with such a system, it will take some time to get used to this innovation.
The anti-lock braking system of the car has proven itself well, but, nevertheless, it could not do without a certain number of dissatisfied motorists who claim that no electronics can replace an experienced driver, because he will orient himself much better in a difficult situation on the road and take the right actions.
ABS does not interfere with the braking process at all, but serves as an indispensable assistant in preventing an irreparable traffic situation. Thanks to the anti-lock braking system, the uncontrollable mountain of iron, which the car turns into under heavy braking, begins to obey the steering wheel and is able to perform at least some maneuvers.
Tasks performed by ABS
Thus, the anti-lock braking system performs a number of very important tasks:
- ensures safety during braking, both for the driver himself and for his passengers;
- shortens the braking distance on slippery or wet road surfaces;
- prevents the drive wheels from locking up during heavy braking, which makes it possible to maneuver and avoid the obstacle that has arisen.
In some cases, the use of ABS is not justified. So, moving down a steep descent in conditions of heavy snow or mud swamp, the inclusion of an anti-lock braking system can lead to sad consequences. Due to gravity, the car rolls down, while the ABS does not allow the wheels to lock up, in connection with this, the car, although slowly, still continues to move forward even with the brake pedal fully depressed.
Despite the fact that such situations are extremely rare, all modern SUVs are equipped with additional sensors that determine the degree of slope of the road track. If the descent is too steep, the anti-lock system becomes inactive.
Video
The principle of operation of the ABS system is clearly shown in this video:
