The development of the ABS system dates back to the early 20th century. In the late 1970s, digital electronics technology and large-scale integrated circuits developed rapidly, laying a technical foundation for the practical development of ABS systems. Many companies have developed various forms of ABS systems. Since the mid-1980s, ABS systems have evolved toward cost-effectiveness. Some companies have simplified the structure and system optimization of ABS, and introduced economical ABS devices. Some companies have introduced rear-wheel ABS or four-wheel ABS systems for light trucks and passenger cars. These efforts have created conditions for the rapid spread of ABS. The ABS system is considered to be the most important technical achievement in terms of safety since the use of seat belts in automobiles.
One is classification by manufacturer, and the other is classification by control channel. The following mainly introduces the classification method by channel.
In ABS, the brake line capable of independently adjusting the brake pressure is called a control channel.
The control channel of ABS device is divided into four-channel type, three-channel type, two-channel type and one-channel type.
(1) Four-channel four-channel ABS has four wheel speed sensors. Each of the pipelines leading to the four wheel brake cylinders is provided with a brake pressure regulator device for independent control to form a four-channel control mode. . However, if the adhesion coefficients of the two wheels on the left and right of the car are significantly different (such as water or ice on the road surface), the ground braking force of the two wheels will differ greatly during braking, so a yaw moment will be generated, which will make the vehicle body to the brake The side with more power is off-track and cannot keep the car running in a predetermined direction, which will affect the stability of the car's braking direction. Therefore, when driving on some slippery roads such as icing or stagnant water, the driver should reduce the speed, and should not blindly believe in the ABS device.
(2) The three-channel three-channel ABS independently controls the two front wheels, and the two rear wheels are controlled together according to the principle of low selection (that is, the two wheels are controlled by one channel to ensure that the wheels with less adhesion do not lock up. Principle), also called hybrid control.
Performance characteristics: When the two rear wheels are controlled together according to the principle of low selection, the braking force of the left and right rear wheels can be guaranteed to be equal under various conditions. Limited to a low level of adhesion, so that the braking forces of the two rear wheels are always balanced, ensuring that the car has good directional stability when braking under various conditions.
Independent control of the two front wheels, mainly considering small cars, especially front-wheel-drive cars. The braking force of the front wheels accounts for a large proportion of the total braking of the car (up to about 70%). Front wheel adhesion. However, due to the imbalance of the braking force of the two front wheels, the stability of the car's driving direction is relatively small, and the resulting influence can be corrected by the driver's steering operation. Therefore, three-channel ABS is widely used in cars.
(3) Two-channel type Two-channel ABS is difficult to take into consideration aspects such as directional stability, steering control, and braking efficiency, and currently it is rarely used.
(4) One-channel one-channel ABS is often called single-channel ABS. It is to set a brake pressure regulator in the rear wheel brake manifold, and install a wheel speed sensor on the rear axle main reducer (also on the rear wheel). Install one each).
What is the role of the ABS system? The anti-lock braking system can improve the safety factor of the vehicle's emergency braking when driving. In other words, for cars without ABS, the car is prone to tire lock when emergency braking is applied in an emergency situation, that is, the steering wheel cannot be turned, so the risk factor will increase accordingly and it will easily cause serious consequences.
Single channel ABS generally controls the two rear wheels together according to the principle of low selection. A single-channel ABS cannot fully utilize the adhesion of the two rear wheels, so the braking distance may not necessarily be significantly shortened. In addition, the front wheel brakes are not controlled, and the front wheels still lock up when braking, so the steering ability is not improved, but the two rear wheels will not lock up when braking, which can significantly improve the braking. The directional stability at this time is a great advantage in terms of safety, at the same time simple structure, low cost and other advantages, so it is widely used in light trucks.
In summary, although the ABS device has a shorter braking distance, and the price of different types of ABS devices varies greatly due to their composition and other reasons, you should not only see the price when you buy a car, you should also see the installation What type of ABS device is it?
Limitations When the wheel is about to reach the next locking point, the pressure of the brake fluid causes the airbag to repeat its action, so it can be applied 60 to 120 times in one second, which is equivalent to constantly braking and relaxing, which is similar to a mechanical " Click the brake. " Therefore, the ABS anti-lock system can avoid losing control of the direction and wheel slippage during emergency braking, so that the wheel will not be locked during braking, and the tire will not be rubbed against the ground at one point, thereby increasing the friction and braking. The efficiency is over 90%, and at the same time, it can reduce the brake consumption and extend the service life of the brake drums, discs and tires twice. The anti-skid performance of ABS-equipped vehicles on dry asphalt roads, rainy days, and snowy days can reach 80% -90%, 10% -30%, and 15% -20%, respectively.
ABS system has its own limitations. It still cannot get rid of certain physical laws. In both cases, the ABS system cannot provide the shortest braking distance. One is to brake directly on the smooth main road by an experienced driver. Another situation is braking on loose gravel, loose soil or deep snow. In addition, usually on dry roads, the latest ABS systems can control the slip rate in the range of 5% -20%, but not all ABSs brake at the same rate or the same degree. Although the four-wheel anti-lock braking system enables the car to brake as short as possible, if the brake is applied too late to prevent it from stopping completely before colliding with an obstacle, the accident cannot be prevented .
During braking, ABS can quickly determine the locked state of the wheel according to the speed signal from each wheel speed sensor. Close the normally open input solenoid valve on the wheel to start the locking, so that the braking force does not change. If it is locked, the normally-closed output solenoid valve is opened. The brake pressure on this wheel is quickly moved down due to the pipeline leading to the brake fluid storage tank, which prevents the wheel from being completely locked due to excessive braking force. When the braking state is always at the best point (slip ratio S is 20%), the braking effect is the best and the driving is the safest.
The brake fluid in the cavity in front of the master cylinder is dynamic pressure brake fluid, which pushes the reaction sleeve to the right, which in turn pushes the booster piston to move the brake pedal push rod to the right. Therefore, when the ABS is working, the driver can feel the vibration of the foot pedal and hear some noise.
After the car decelerates, once the ABS computer detects that the wheel lock state disappears, it will close the main control valve, so that the system will work in the normal braking state. If the pressure of the accumulator drops below the safety extreme, the red brake fault indicator and the amber ABS fault indicator are on. In this case, the driver needs to apply a deep pedal braking method with a large force to effectively brake the front and rear wheels.
In ABS, a speed sensor is placed on each wheel, and the signal about the speed of each wheel is input to the electronic control device. The electronic control device monitors and determines the movement state of each wheel according to the signal input from each wheel rotation sensor and forms a corresponding control instruction. The hydraulic solenoid valves are not energized and closed in all places, and the electric pump is not energized. The brake lines from the master cylinder to the brake wheel cylinders are in communication, and the brake cylinders to the reservoir are in communication. The brake lines are closed, and the brake pressure of each brake wheel cylinder will change with the output pressure of the brake master cylinder. The braking process at this time is exactly the same as that of the conventional braking system.
During the braking process, the electronic control device determines that the wheels tend to lock up according to the wheel speed signal input by the wheel speed sensor, and the ABS enters the anti-lock braking pressure adjustment process. For example, when the electronic control device determines that the front right wheel is about to lock up, the electronic control device energizes the liquid inlet solenoid valve that controls the brake pressure of the right front wheel, turns the right forward liquid solenoid valve into a closed state, and brakes the master cylinder output. The brake fluid no longer enters the right front brake wheel cylinder, the electronic control device de-energizes both the right forward liquid solenoid valve and the liquid discharge solenoid valve, turns the liquid inlet solenoid valve into an open state, and turns the liquid discharge solenoid valve into a closed state. State, at the same time, the electric pump is also energized, and the brake fluid is delivered to the brake wheel cylinder. The brake fluid output by the brake master cylinder and the brake fluid pumped by the electric pump both pass through the right forward fluid solenoid valve in the open state. Entering the right front brake wheel cylinder, the braking pressure of the right front brake wheel cylinder is rapidly increased, and the right front wheel starts to decelerate again.
ABS keeps the braking pressure of the wheels tending to lock to cycle through the process of maintaining-decreasing-increasing, and the slip rate of the wheels tending to lock is controlled in the vicinity of the peak adhesion coefficient slip rate. There are a pair of solenoid valves for the liquid inlet and outlet for each brake wheel cylinder, which can be controlled by the electronic control device. Therefore, the brake pressure of each brake wheel cylinder can be adjusted independently, so that four wheels No brake lockup occurred.
Although the structural forms and working processes of various ABSs are not completely the same, they prevent the controlled wheels from braking by adaptively adjusting the braking pressure of the wheels that tend to lock. This kind of ABS is the same in the following aspects.
(1) ABS only adjusts the anti-lock brake pressure on the wheels that tend to be locked during braking only after the speed of the car exceeds a certain speed (such as 5km / h or 8km / h). When the car speed is reduced to a certain level, ABS will automatically stop the anti-lock brake pressure adjustment. After that, the braking process of ABS-equipped cars will be the same as that of the conventional braking system. Dead hold the car brakes. This is because when the speed of the car is very low, the effect of the brake lock on the brake performance of the car is very small, and to make the car brake and stop as soon as possible, the wheel brake must be locked.
(2) During the braking process, ABS will only adjust the braking pressure of the wheels that are going to be locked when the controlled wheels are going to be locked. When the controlled wheels are not going to be locked, The braking process is exactly the same as that of the conventional braking system.
(3) ABS has a self-diagnostic function, which can monitor the working condition of the system. Once it finds a fault that affects the normal operation of the system, it will automatically turn off the ABS, light the ABS warning light, and send a warning signal to the driver. The car's braking system can still be braked just like a conventional braking system.
① Give full play to the effectiveness of the brake and shorten the braking time and distance.
② It can effectively prevent the vehicle from sliding and tailing during emergency braking, and has good driving stability.
③ It can steer during emergency braking and has good steering maneuverability.
④It can avoid the severe friction between the tire and the ground, and reduce the wear of the tire.
ABS warning light
ABS warning lights monitor the anti-lock braking system. This warning light will stay on for four seconds when the ignition is turned ON.
If the ABS warning light is on, the brake system should be overhauled as soon as possible to restore the function of the anti-lock brake system. If the ignition switch is turned ON and the ABS warning light does not turn on, repair the lamp as soon as possible.
If both the brake warning light and the ABS warning light are on, the anti-lock braking system (ABS) and electronic braking force distribution system (EBD) will lose their function. The anti-lock braking system must be repaired immediately.