This paper mainly introduces the definition, structure and working principle analysis of automobile anti-lock braking system, and also introduces the composition and principle of electronic control part, wheel speed sensor and hydraulic control device of ABS system. And can analyze the control circuit.

Keywords: ABS system composition principle control circuit

I. Introduction

ABS (Anti-lock Brake System) is a kind of automobile safety control system, which has the advantages of anti-skid and anti-lock. Modern cars are equipped with a large number of anti-lock braking systems. ABS not only has the braking function of ordinary braking system, but also can prevent the wheel from locking, so that the car can still turn under braking conditions, ensure the stability of the braking direction of the car and prevent side slip and deviation. It is the most advanced braking device with the best braking effect in the car at present.

ABS system is mainly composed of sensors, electronic control devices and actuators.

Table1Functions of ABS System Components

component

function

sensor

vehicle speed sensor

Detect the vehicle speed and provide the ECU with the vehicle speed signal of slip rate control mode.

Wheel speed sensor

Detect wheel speed and provide wheel speed signal to ECU, and adopt various control methods.

Deceleration sensor

It is only used in the four-wheel drive control system to detect the deceleration of the car when braking and identify whether it is a slippery road such as ice and snow.

actuating mechanism

brake pressure regulator

Accept the instruction of ECU, and increase, maintain and reduce the pressure of braking system through the action of solenoid valve.

Fluid pump

Under the control of ECU, the control oil pressure is established in the control oil circuit of the variable displacement brake pressure regulator; In the process of adjusting the pressure of the circulating brake pressure regulator, the brake fluid flowing out of the wheel cylinder is pumped back to the master cylinder through the accumulator to prevent the brake pedal stroke from changing when ABS works.

ABS warning light

When ABS fails, EUC controls it to light up and give an alarm to the driver, and ECU controls it to flash and display the fault code.

European Currency Unit (European currency unit)

Receiving signals from sensors such as vehicle speed, wheel speed and deceleration, calculating vehicle speed, wheel speed, slip ratio, wheel deceleration and acceleration, and analyzing, judging and amplifying these signals, the output stage outputs control instructions to control the work of each actuator.

Second, the electronic control system

2. 1 sensor structure and working principle

(1) speed sensor

The gear ring and the wheel speed sensor are an assembly. When the gear ring rotates, the wheel speed sensor senses the AC signal and outputs it to the ABS computer to provide the wheel speed signal. Wheel speed sensors are usually installed on the differential, transmission output shaft and axle.

Installation position of wheel speed sensor on wheel

The wheel speed sensor consists of a sensor head and a gear ring.

(2) Lateral acceleration sensor

Some ABS systems are equipped with lateral acceleration sensors, which are generally called lateral acceleration switches because of the main switch contacts inside. The outline is shown in figure 1. When the lateral acceleration is lower than the limited value, the two contacts are closed and the two terminals of the plug form a loop through the inside of the switch. When the lateral acceleration exceeds the limit value in the process of high-speed sharp turn, a pair of contacts in the switch open under the action of their own inertia force, forming an open circuit inside the switch between the two ends of the plug. After this signal is input into ECU, the anti-lock braking control command can be corrected, thus effectively adjusting the hydraulic pressure of the left and right wheel cylinders and making ABS work more effectively. This device is widely used in more advanced cars and sports cars.

Figure 1

(3) deceleration sensor

At present, some four-wheel drive vehicles are also equipped with automobile deceleration sensors, also known as G sensors. Its function is to obtain the deceleration signal when the car is braking. Because the deceleration of the automobile is large when braking on the road surface with high adhesion coefficient and small when braking on the road surface with low adhesion coefficient, after the signal is sent to ECU, the road surface can be identified and the adhesion coefficient can be judged. When it is judged that the car is running on slippery roads such as snow and icy roads, corresponding control measures are taken to improve the braking performance.

The deceleration sensor includes photoelectric sensor, mercury sensor and differential transformer sensor.

A. photoelectric deceleration sensor

When the car is driving at a constant speed, the transparent plate is stationary. When the car decelerates, the light-transmitting plate swings along the longitudinal axis of the car with the change of deceleration. The greater the deceleration, the higher the swing position of the light-transmitting plate. Because of the different positions of the light-transmitting plate, the light allowed by the light-emitting diode to be transmitted to the phototransistor is also different, so that the phototransistor forms two states: on and off. The combination of two light-emitting diodes and two phototransistors can divide the deceleration of the car into four grades, and this signal can be sent to the electronic controller to sense the road adhesion coefficient.

B. Mercury deceleration sensor

The basic structure of the mercury deceleration sensor is shown in the figure, which consists of a glass tube and mercury.

ON the road surface with low adhesion coefficient, the deceleration of the car is small, the mercury in the glass tube is basically motionless, and the switch is in the ON state in the glass tube. When braking on the road with high adhesion coefficient, the car slows down greatly, and the mercury moves forward in the glass tube due to inertia, which turns off the circuit switch in the glass tube. As shown in fig. 2, this signal can be sent to ECU to sense the road adhesion coefficient.

Figure 2

Mercury automobile deceleration sensor not only works in the forward direction, but also sends out deceleration signals in the backward direction.

C. differential variable pressure deceleration sensor

2.2 Structure and working principle of electronic control module (computer)

The electronic control part of ABS system can be divided into electronic controller (ECU), ABS control module and ABS computer, hereinafter referred to as ECU.

Basic structure of ECU

The ECU consists of the following basic circuits:

1) wheel speed sensor input amplifier circuit.

2) operation circuit.

3) Control circuit of solenoid valve.

4) regulated power supply, power supply monitoring circuit, fault feedback circuit and relay driving circuit.

The connection mode of each circuit is shown in Figure 3-5.

Figure 3

Figure 4

Figure 5

A) input amplifier circuit of wheel speed sensor

The wheel speed sensor installed on each wheel outputs an AC signal according to the wheel speed, and the AC signal is input into an amplifier circuit to amplify it into a rectangular wave, which is shaped and sent to an arithmetic circuit.

The number of wheel speed sensors in different ABS systems is different. When each wheel is equipped with a wheel speed sensor, four sensors are needed, and the input amplifier circuit also needs four sensors. When the wheel speed sensors are only installed on the left and right front wheels and the rear axle differential, only three sensors are needed, and the input amplifier circuit becomes three. However, one signal of the rear wheel should be sent to the arithmetic circuit as two signals of the left and right rear wheels.

B) arithmetic circuit

The arithmetic circuit is mainly used to calculate the linear speed, initial speed, slip rate, acceleration and deceleration of the wheel, and the control operation and monitoring operation of the opening of the solenoid valve.

The initial speed, slip rate and acceleration/deceleration operation circuit integrates the instantaneous wheel speed, calculates the initial speed, and then compares it with the instantaneous linear speed to get the slip rate and acceleration/deceleration. The electromagnetic valve opening control arithmetic circuit outputs decompression, pressure maintaining or pressurization signals to the electromagnetic valve control circuit according to the slip rate and acceleration and deceleration control signals.

C) solenoid valve control circuit

Receiving decompression, pressure maintaining or pressure increasing signals from the arithmetic circuit, and controlling the current flowing to the solenoid valve.

D) regulated power supply, power supply monitoring circuit, fault feedback circuit and relay driving circuit.

While the battery provides all 5V regulated voltage to the ECU, the above circuit monitors whether the voltages of 12V and 5V are within the specified range, and monitors the fault signals of the wheel speed sensor input amplifier, operation circuit and solenoid valve control circuit to control the solenoid valve motor and solenoid valve. When there is a fault signal, close the solenoid valve, stop the ABS work and return to the normal braking state. At the same time, the ABS warning light on the dashboard lights up to let the driver know that there is a fault.

Safety protection circuit

The safety protection circuit of ECU has the function of displaying the fault state externally. When the system fails, first stop the ABS work and restore the normal braking state, so that the ABS alarm light on the dashboard lights up, prompting the whole system to be in a fault state. At present, the fault display method is usually displayed by the flashing of light emitting diode (LED) in ECU, the flashing of ABS alarm lamp on dashboard, or by special diagnostic device. When the ignition switch is turned off, the fault display disappears internally. If no fault is found when the ignition switch is turned on again, it is considered that the system is normal and ABS can be controlled normally. ABS system with special diagnostic instrument can memorize the fault content, and encode, display or eliminate the memorized fault according to the instruction of special diagnostic instrument.

1. Initial check when turning on the power.

When the ignition switch is turned on and the ECU power supply is turned on, the following items will be checked.

(1) microprocessor function check

(1) Let the monitor display an error message for the microprocessor to recognize.

② Check the data in the ROM area to make sure there is no change.

③ Input and output data to RAM area to judge whether it works normally.

④ Check whether the input of A/D conversion is normal.

⑤ Check whether the signal transmission between microprocessors is normal.

(2) solenoid valve action check

Make the solenoid valve act and judge whether it works normally.

(3) Function check of fault feedback circuit

The microprocessor is used to identify whether the fault feedback circuit works normally.

2. Check in automatic startup

Automatically start to check the important peripheral circuits. If the results are normal, ABS will start to work.

(1) solenoid valve function check

① Let the solenoid valve work and judge whether it is normal.

② Compare the on-off resistance of each solenoid valve to judge whether the solenoid valve works normally.

(2) Motor action inspection

Run the motor and judge whether the motor is normal.

(3) Signal confirmation of wheel speed sensor and input amplifier circuit.

Ensure that all wheel speed sensor signals can be input to the microprocessor.

3. Check regularly while driving

(1) 12V (24V for trucks) and 5V voltage monitoring.

Determine whether the supplied 12V voltage and 5V internal voltage are the specified voltage values. Monitor the voltage of 12V, consider the instantaneous voltage drop when ABS works and the instantaneous voltage drop when motor starts, and then analyze and identify it.

(2) Electromagnetic valve action monitoring

During the working process of ABS system, the solenoid valve must act, and the ECU monitors the working state of the solenoid valve at any time.

(3) Comparison and inspection of operation results in the operation circuit

There are usually two sets of operation circuits in ECU, which can perform operation and transmit data simultaneously. By comparing and monitoring each other's operation results, the reliability can be guaranteed and the abnormal situation can be found early.

In addition, various speed signals and input and output signals are also compared with each other in the operation circuit, and these results must be the same.

(4) microprocessor out-of-control inspection

The monitoring circuit judges whether the microprocessor works normally.

(5) Monitoring of pulse signal

The pulse frequency of the microprocessor clock signal cannot be reduced.

(6) Determine 6)ROM number

Calculate the sum of ROM data and confirm that the program works normally.

4. Self-diagnosis display

If the safety protection circuit detects an abnormal situation, it stops the work of the ABS system, returns to the original conventional braking mode (ABS is not used), and the ECU presents a fault state. At this time, the LED, ABS alarm lamp or special diagnostic device in the ECU sends out fault signals, and the ECU displays fault codes according to these signals.

When the car manufacturer, car model or ABS system are different, the fault code is also different.

Working principle of ECU

ECU is the control center of ABS system. Its essence is a micro digital computer, which is generally an integral unit composed of two microprocessors and other necessary circuits. The basic input signal of the computer is the wheel speed signal sent by four wheel speed sensors, and the output signals are: the control signal of the hydraulic control unit, the output self-diagnosis signal and the output signal of the ABS fault indicator lamp, as shown in the figure:

1.Anti-lock control function of ECU

The electronic control module (computer) has the function of continuously monitoring the speed signals of four wheel speed sensors. The computer continuously detects the pulse electrical signals from all four wheel speed sensors, and processes and converts them into values proportional to the wheel speed. From these values, the computer can distinguish which wheel is faster and which wheel is slower. The computer implements anti-lock braking control according to the rotation speed of four wheels. The computer takes the data of four wheel sensors as the control basis. Once it is judged that the wheel is about to lock up, it will immediately enter the anti-lock control state, and output the pulse control voltage with the amplitude of 12V to the hydraulic regulator to control the on-off of the oil circuit on the wheel cylinder. The change of the oil pressure on the wheel cylinder can adjust the braking force on the wheel, so that the wheel will not be completely locked all the time because of the large braking force (the on-off frequency is generally 3- 12 times/second).

2.2 Fault protection control function. European Currency Unit (European currency unit)

First, computers can monitor their own work. Because there are two microprocessors in the computer, they receive and process the same input signal at the same time, and compare the internal signal of the computer with the external signal generated by the related state of the system to see if they are the same, so as to calibrate the computer itself. This calibration is continuous. If you can't synchronize, there is something wrong with the computer itself. It will automatically stop the anti-lock braking process and make the ordinary braking system work as usual. At this point, the repairman must test the ABS system (including the computer) to find out the cause of the failure in time.

Fig. 6 is a brief description of computer internal monitoring of ABS system. The input signal from wheel speed sensor ① is sent to two microprocessors ② and ③ in the computer at the same time. Internal signal ⑤ (wheel speed signal) and external signal ⑤ (hydraulic regulator signal) are processed in logic module ④ and then output, and then the two signals are compared and checked. The internal signal ⑤ generated by the logic module ⑤ is sent to two different comparators ⑤ and ⑧ (each processor has a comparator), where they are compared. If they are different, the computer will stop working. The external signal ⑥ generated by the microprocessor ② is directly sent to the comparator ⑥, and the other route is sent to the comparator ⑨ through the feedback circuit ⑨. The external signal generated by microprocessor ③ is directly sent to comparators ⑦ and ⑧. Compared with the comparator, if the external signals are not synchronized, the ABS computer will turn off the anti-lock braking system.

Figure 6

The computer of ABS system can not only monitor its internal working process, but also monitor the working conditions of other components in ABS system. It can send pulse inspection signals to the circuit system and solenoid valve of hydraulic regulator according to the program, and complete normal function inspection without any mechanical action. In the working process of ABS system, the computer can also monitor and judge whether the wheel speed signal sent by the wheel speed sensor is normal.

When the ABS system fails, such as the loss of brake fluid, the decrease of hydraulic pressure or the disappearance of wheel speed signal, the computer will automatically issue instructions to make the ordinary brake system work, while the ABS system will stop working. As long as the signal output generated by the wheel speed sensor is within the acceptable range, or the sensor sends out signals beyond the range due to strong radio high-frequency interference, the computer may stop the ABS system or let the ABS system continue to work according to the situation.

What I want to emphasize here is that the amber (yellow) ABS system fault indicator lights up at any time, indicating that the computer has stopped the work of the ABS system or detected a system fault, and the driver or user must carry out maintenance. If it can't be handled, it should be sent to the repair shop in time.

2.3 ABS fault indicator light

When the following abnormal phenomena are found, the ABS control computer will light the ABS fault indicator:

(1) The function of the oil pump motor exceeds a certain time.

② The vehicle has been driving for more than 30 seconds and forgot to release the parking brake.

③ No sensor signal was received from any of the four wheels.

④ The solenoid valve acts for more than a certain time, or it is detected that the solenoid valve is open.

⑤ The engine has started running, or the vehicle has started, and the output signal of the solenoid valve has not been received.

⑥ When the ignition switch is turned on in the first gear, the ABS fault indicator will light up. If there is no abnormality, the ABS fault indicator will go out after the engine is started.

The ABS system has two fault indicators, one is a red brake fault indicator, and the other is an amber or yellow ABS fault indicator, as shown in Figure 7. When the ignition switch is turned on, the red indicator light and the amber indicator light will light up almost at the same time, the red indicator light will light up for a short time, and the amber indicator light will light up for a long time (about 3s); After the engine is started, the accumulator should build up the system pressure, and the two lights will light up again for more than ten seconds. When parking brake, the red indicator light should also light up. If the light does not light up under the above circumstances, it means that the fault indicator lamp itself or the line is faulty.

Figure 7

The red indicator light is always on, indicating that the brake fluid is insufficient or the pressure in the accumulator is insufficient (below 14MPa). At this time, the ordinary brake system and ABS system can not work normally; The amber ABS fault indicator is always on, indicating that the electronic control unit has found that the ABS system is faulty.

Third, the hydraulic control system

3.3 Working principle of circulating brake pressure regulator

This brake pressure regulator connects a solenoid valve in series between the master brake cylinder and the wheel cylinder to directly control the brake pressure of the wheel cylinder. The pressure regulating system is characterized in that the brake pressure oil circuit is communicated with the ABS control pressure oil circuit, as shown in Figure 8. The function of the accumulator in the figure is to temporarily store the brake fluid flowing through the solenoid valve from the wheel cylinder during decompression. Oil return hydraulic pump, also known as recirculation pump, is used to pump the brake fluid flowing into the accumulator from the brake wheel cylinder back to the master cylinder during decompression. The working principle of the system is detailed as follows.

Figure 8

1. Normal braking state

During normal braking, the ABS system does not work, no current passes through the solenoid, and the solenoid valve is in the "supercharged" position. At this time, the states of the master cylinder and the wheel cylinder are as shown in Figure 9. Brake fluid from the master cylinder directly enters the wheel cylinder, and the wheel cylinder pressure increases or decreases with the master cylinder pressure. At this time, the oil return hydraulic pump does not work.

Figure 9

2. Pressure maintenance state

When the speed sensor sends out the locking danger signal, the electronic control unit inputs a small holding current (about 1/2 of the maximum working current) to the electromagnetic coil, and the electromagnetic valve is in the "holding pressure" position, as shown in Figure 10. At this time, the master cylinder, the wheel cylinder and the oil return hole are isolated and sealed from each other, and the braking pressure in the wheel cylinder remains constant.

Figure 10

3. Decompression state

If the wheel still tends to lock up after the electronic control unit sends out the "pressure maintaining" command, the electronic control unit will input the maximum working current to the electromagnetic coil to make the electromagnetic valve in the "decompression" position. At this time, the solenoid valve will connect the wheel cylinder with the oil return passage or the liquid storage chamber, and the brake fluid in the wheel cylinder will flow into the liquid storage chamber through the solenoid valve, and the pressure of the wheel cylinder will drop, as shown in figure 1 1.

Figure 1 1

4. Pressurized state

When the pressure drops and the rear wheel speed is too fast, the electric control unit cuts off the current to the solenoid valve, the master cylinder and the wheel cylinder are reconnected, and the high-pressure brake fluid in the master cylinder re-enters the wheel cylinder (see figure), which increases the braking pressure. When braking, repeat the above process until the braking is released.

3.2 Working principle of variable displacement brake pressure regulator

As shown in Figure 12, it is the basic schematic diagram of the variable displacement brake pressure regulator. It is mainly composed of solenoid valve, control piston, hydraulic pump and accumulator. Its basic working principle is as follows.

Figure 12

During normal braking, no current flows in the electromagnetic coil 6. The solenoid valve 7 connects the working chamber of the control piston 14 with the oil return pipeline, and the control piston is pushed to the far left under the action of a strong spring. The push rod at the top of the piston opens the check valve 13 and connects the brake master cylinder 2 and the brake pipeline of the wheel cylinder 10. Brake fluid from the master cylinder directly enters the wheel cylinder, and the wheel cylinder pressure changes with the master cylinder pressure. This state is the normal braking state before or after ABS works. As shown above.

When decompression is needed, when the electric control unit 9 inputs a large current to the electromagnetic coil 6, the plunger 8 in the electromagnetic valve moves to the right against the spring force under the action of electromagnetic force. Connect the accumulator 3 with the working chamber pipeline of the control piston 14 as shown in figure 13. Brake fluid enters the working chamber of the control piston to push the piston to move to the right, the check valve 13 closes, and the passage between the master cylinder 2 and the wheel cylinder 10 is cut off. At the same time, because the control piston moves to the right, the volume on the wheel cylinder side increases and the braking pressure decreases.

Figure 13

When the electric control unit 9 inputs a small current to the electromagnetic coil 6, the plunger 8 moves to the position where the accumulator, the oil return pipe and the control piston working chamber pipeline are mutually closed under the action of the spring force because the electromagnetic force of the electromagnetic coil is reduced, as shown in Figure 14. At this time, the hydraulic pressure on the left side of the control piston remains unchanged, and the control piston is kept in a certain position under the action of hydraulic pressure and strong spring elasticity. At this time, the one-way valve 13 is still in the closed state, the wheel cylinder side volume remains unchanged, and the braking pressure remains constant.

Figure 14

When pressurization is required, the electric control unit 9 cuts off the current in the electromagnetic coil 6, and the plunger 8 returns to the initial position at the left end. As shown in figure 12, the working chamber of the control piston is connected with the oil return pipe, and the hydraulic pressure on the left side of the control piston is released. When the control piston moves to the leftmost position, the check valve opens, and the wheel cylinder pressure will increase with the increase of the master cylinder pressure.

3.3 Structure of Brake Pressure Regulator

The pressure regulator assembly (also called ABS brake actuator and ABS hydraulic control assembly) is formed by adding an ABS brake pressure regulator on the basis of the hydraulic device of the common brake system. The hydraulic devices of common brake systems generally include brake booster, dual-cavity brake master cylinder, liquid storage chamber, brake wheel cylinder and dual hydraulic pipelines. The ABS brake pressure regulator is installed between the master brake cylinder and the wheel cylinder. If it is installed with the brake master cylinder, it is called an integral brake pressure regulator, otherwise it is called a separate brake pressure regulator.

ABS brake pressure regulator usually includes electric pump, accumulator, main control valve, electromagnetic control valve and some control switches besides the hydraulic components of ordinary brake system. In essence, ABS controls the hydraulic pressure on the wheel cylinder through the electromagnetic control of the control valve on the valve body, which makes it rapidly increase or decrease, thus realizing the anti-lock braking function. ABS brake pressure regulator assembly can be basically divided into three categories: integral type, in which the brake master cylinder and hydraulic assembly are integrated, as shown in Figure15; Separated, the brake master cylinder and the hydraulic assembly are independent assemblies, as shown in figure 16; Vacuum type, which only controls the rear wheel, adopts vacuum hydraulic control, as shown in figure 17.

Figure 15

Figure 16

Figure 17

3.4 Structure and working principle of solenoid valve

Electromagnetic control valve is an important part of hydraulic regulator, which controls the braking force of each wheel of ABS system. There is one or two electromagnetic valves in ABS system, and several pairs of electromagnetic control valves control the braking of front and rear wheels respectively. Commonly used solenoid valves are three-position three-way valve and two-position two-way valve.

The schematic diagram of the internal structure of the three-position three-way solenoid valve is shown in Figure 18, which is mainly composed of valve body, oil inlet valve, pressure relief valve, one-way valve, spring, nonmagnetic support ring and electromagnetic coil. Both ends of the sliding support 6 are guided by the nonmagnetic support ring 3. The main spring 13 and the auxiliary spring 12 are arranged oppositely, but the elastic force of the main spring is greater than that of the auxiliary spring. In order to close the oil inlet valve 5 and open the pressure relief valve 4, the sliding support has a movement process of about 0.25mm, and the nonmagnetic support ring is pressed into the valve body, which can force the magnetic flux to pass through the support and the working air gap A when passing through the coil, thus ensuring the stability of the electromagnetic characteristics of the magnetic circuit. The check valve 8 is arranged in parallel with the oil inlet valve 5, and its function is that when the brake is released, the check valve opens, and an extra and larger oil outlet channel is added from the wheel cylinder to the master cylinder, so that the pressure of the wheel cylinder is rapidly reduced, and the wheel brake can be released even if the main spring is broken or the bracket is stuck.

Figure 18

The working process of the solenoid valve is as follows: when there is no current in the solenoid coil, because the force of the main spring is greater than that of the auxiliary spring, the oil inlet valve is opened, the pressure reducing valve is closed, and the brake master cylinder is connected with the oil circuit of the wheel cylinder, so the wheel cylinder pressure can be increased under the working condition of the ABS system without ABS participation.

When the maximum working current 1/2 (holding current) is input to the electromagnetic coil, the electromagnetic force moves the bracket downward for a certain distance and closes the oil inlet valve. Because the electromagnetic force is not enough to overcome the elastic force of the two springs, the bracket remains in the middle position and the pressure relief valve is still closed.

At this time, the three channels are sealed with each other, and the wheel cylinder pressure keeps a certain value. When the electric control unit inputs the maximum working current to the electromagnetic coil, the electromagnetic force overcomes the elasticity of the main spring and the auxiliary spring, so that the bracket continues to move down and the pressure relief valve is opened. At this time, the wheel cylinder is communicated with the oil return pipe through the pressure relief valve, and the brake in the wheel cylinder flows into the oil return pipe to reduce the pressure.

As shown in figure 19, it is the internal structure of a normally open two-position two-way solenoid valve. When no current passes through the electromagnetic coil 3, under the action of the return spring 7, the iron core 12 is pushed to the position where the limit rod 9 collides with the buffer washer 1 1. At this time, the ejector pin 10 connected with the iron core does not push the ball valve 6 against the valve seat 5, and the oil inlet A of the solenoid valve is communicated with the oil outlet B, and the solenoid valve is in an open state. When a certain current passes through the electromagnetic coil, the iron core overcomes the spring force under the action of electromagnetic attraction and drives the ejector pin to move to the right together, and the ejector pin pushes the ball against the valve seat, so that the passage between the oil inlet and the oil outlet of the solenoid valve is closed, and the solenoid valve is in a closed state. The function of the pressure limiting valve 4 is to limit the maximum pressure of the solenoid valve, so as not to damage the solenoid valve due to excessive pressure.

Figure 19

Fourth, summary.

By writing this paper, I know more about ABS system, especially the electronic control part. ABS system is to make full use of the adhesion coefficient between the tire and the ground, so that each braking can produce as much braking force as possible without locking, improve the braking ability of the car, and improve the maneuverability and stability. When writing a paper, I also consulted a lot of ABS-related knowledge. In fact, it has the same function and principle as ASR (Automobile Anti-skid Electronic Control System), and many of them are related. By consulting books, I have broadened my horizons and added some new knowledge to me who is about to graduate.

References:

[1] Yang Qingbiao. Principle and maintenance points of automobile electronic control braking system. Beijing: Machinery Industry Press, 2006.

[2] Handan North School. How to maintain abdominal muscles? ASR and SRS system of automobile. Beijing Machinery Industry Press 2007

[3]-bear. Automobile ABS. ASR and ESP maintenance diagram. Beijing: Electronic Industry Press, 2006.

Zou changgeng. Structure principle and fault diagnosis of modern automobile electronic control system (Ⅱ) —— Body and chassis.

Beijing: beijing institute of technology press, 2006.

Dong and Luo. Automobile detection and diagnosis technology. Beijing: Machinery Industry Press, 2007.

You'd better write it yourself. Please refer to this.