1, two-parameter control
ABS controlled by two parameters consists of speed sensor (speed radar), wheel speed sensor, control device (computer) and actuator.
Its working principle is that the vehicle speed and wheel speed signals are respectively input into the computer by the vehicle speed sensor and the wheel speed sensor, and the actual slip rate is calculated by the computer and compared with the ideal slip rate 15%-20%, and then the braking force of the brake is increased or decreased by the solenoid valve.
This kind of resistance sensor usually uses Doppler velocimetry radar. When the car is running, the Doppler radar antenna constantly emits electromagnetic waves to the ground at a certain frequency, and at the same time receives the reflected electromagnetic waves. By measuring the difference between automotive radar transmission and reception, the speed of the car can be accurately calculated. The wheel speed sensor is installed in the transmission housing and driven by the transmission output shaft. It is a pulse motor, and its frequency is directly proportional to the wheel speed.
The actuator consists of solenoid valve and relay. The solenoid valve adjusts the braking force to maintain the ideal slip rate.
This kind of ABS can ensure the ideal control of slip rate and has good anti-lock braking performance, but due to the addition of a speed measuring radar, the structure is more complicated and the cost is higher.
2. Single parameter control
The purpose is to control the angular deceleration of the wheel, control the braking force of the wheel and realize anti-lock braking. Its structure is mainly composed of wheel speed sensor, controller (computer) and solenoid valve. In order to accurately measure the wheel speed, there should be a gap of 1 mm between the sensor head and the wheel gear ring. In order to avoid the influence of water, mud and dust on the sensor, the sensor should be filled with butter before installation.
Solenoid valve is used for pressure adjustment of wheel brake. For a four-channel braking system, one wheel has a solenoid valve; Three-channel braking system, one for each front wheel and one for two rear wheels. The solenoid valve has three hydraulic holes, which are respectively connected with the master brake cylinder and the wheel brake cylinder, and can realize the pressure adjustment functions of boosting, maintaining and reducing pressure. The working principle is as follows.
1) When the booster solenoid valve does not work, the master cylinder interface is directly connected with each brake cylinder interface. Due to the force of the main spring, the oil inlet valve opens and the braking pressure increases.
2) Pressure maintenance When the pressure in the wheel brake cylinder increases to a certain value, the oil inlet valve is cut off and closed. The bracket is kept in the middle state, and the three holes are sealed with each other to maintain the braking pressure.
3) When the step-down solenoid valve works, the bracket overcomes the elasticity of two springs, opens the unloading meat, and reduces the pressure of the brake cylinder. Once the pressure is reduced, the solenoid valve is switched to the pressure holding state or the pressurization preparation state.
The main task of the control device ECU is to calculate, analyze, amplify and judge the signals sent back by the sensors of each wheel, and then the output stage outputs command signals to the solenoid valve to perform the task of brake pressure adjustment. The electronic control device consists of an input stage A, a controller B, an output stage C and a voltage stabilizing protection device D. ..
The electronic controller drives the solenoid valve at a frequency of 4- 10 1tz, which the driver cannot do.
This single-parameter control mode of ABS is widely used at present because of its simple structure and low cost.
Most Chrysler luxury cars in the United States are equipped with ABS with this single parameter control mode. It is equipped with wheel speed sensors on all four wheels of the car.
The wheel shaft is equipped with a gear ring with 45 teeth or 100 teeth, and the sensing head of the wheel speed sensor is installed at the top of the gear ring. When the wheel rotates, the sensor constantly generates a voltage signal, which is input into the computer, and compared with the ideal speed in RoM, the speed increase or deceleration of the wheel is calculated, and the command of boosting or depressurizing is sent to the solenoid valve to control the braking force of the cylinder.
3.3 classification of automobile ABS
Classification by structure
1 mechanical ABS
Mechanical ABS is characterized by compact structure and low price, but its control is not accurate enough.
This kind of ABS is used in cars and motorcycles, and the most famous one is produced by Green Company in England.
Mechanical anti-lock device
2 mechatronics ABS
This is a widely used ABS, which is controlled by speed sensor, electronic controller and pressure regulator.
Good performance and high reliability.
2. Classification by control method.
According to different control methods, electronic ABS can be divided into the following two categories.
1 ABS with logic gate limit control
This method is technically mature. At present, almost all ABS widely used adopt logic gate limit.
Inspection method
2) Adopt modern control methods.
Due to technical and economic reasons, ABS using this control method is still in the research stage.
Reach the practical level
3 Classification by control channel
1) four-channel system
Each wheel is equipped with a speed sensor, one in the brake pipeline leading to each brake wheel cylinder.
A brake pressure regulating device and independent control of four wheels.
2) Three-channel system
Three-channel ABS independently controls the two front wheels and jointly controls the two rear wheels according to the principle of low selection.
The layout is conducive to driving stability. At present, most cars adopt this layout.
3) Dual channel system
The dual-channel system is mainly used for motorcycles, and independent control can be realized by installing sensors in the center of the front and rear wheels respectively.
Optimal control mode
4) Single channel system
Single-channel system generally controls two rear wheels according to the principle of low selection, and its main function is to improve the braking direction of the car.
Stability is widely used in light trucks and cars.
4. According to the structural relationship between the brake pressure regulating device and the brake master cylinder and brake booster, it is classified.
1) separated ABS
The characteristic of separated ABS is that the pressure regulating device of the brake master cylinder and the brake booster are separated in structure.
about
2) integral ABS
The integral ABS is characterized in that the pressure regulating device and the brake booster of the brake master cylinder are integrated.
At present, the compact ABS used by most cars is integral.
Chapter four: Common faults and analysis of automobile ABS.
4. 1.ABS fault diagnosis instruments and tools
In most anti-lock control systems, the fault code can be read according to the flashing of anti-lock warning (or LED of electronic control device) by bridging the corresponding terminals of the diagnostic seat string. Therefore, when reading the fault code, a suitable jumper is usually needed. Jumpers are wires with plug terminals at both ends, and some jumpers have safety tubes in the middle.
Fault codes are just a series of numbers representing fault conditions. In order to accurately understand the fault situation, we must check the fault situation represented by the fault code according to the maintenance manual. In addition, in order to correctly troubleshoot the system, you need to refer to the maintenance manual. Therefore, the maintenance manual is the most important tool in fault diagnosis and maintenance.
Multimeter is the basic test tool when checking the anti-lock control system. Because pointer multimeter can reflect the dynamic changes of electrical parameters, it is more suitable for circuit inspection of anti-lock braking control system. In addition, some special electrical parameter testers (such as multichannel oscilloscopes, etc. ) can be used to check the system more conveniently and deeply.
In most cars, the wiring harness plug of the electronic control device of the anti-lock control system is inaccessible, and the terminals in the quick plug are not marked, which makes it difficult to determine the terminals to be tested. Especially when the voltage is applied to some specific terminals, some electrical components in the system may be damaged if the wrong voltage is applied. In addition, if the system is tested directly from the terminal of the harness plug, the accuracy of the test results will not be affected, and the terminal may be deformed or damaged. Therefore, it is possible that the terminal number, the arrangement of the terminal number and the form of the plug in the wiring harness plug of various anti-lock control systems are different, so the junction box used is also different.
When testing the circuit of the anti-lock control system, remove the harness plug of the system from the electronic control device, and then connect the harness plug of the junction box with the harness plug of the system, so that the terminal number of the junction box corresponds to the terminal number of the system harness. By testing the terminal on the junction box, it is equivalent to finding the corresponding terminal in the system harness plug for testing.
When checking the hydraulic device of anti-lock control system, it is sometimes necessary to use a pressure gauge. When diagnosing the anti-lock braking control system, various test instruments can also be used, and some systems can only be diagnosed with special diagnostic terminal tester. Special diagnostic test instruments can be divided into two categories, one can replace the electronic control device of the system to check and simulate the working condition of the system. Such instruments include Bosch ABS diagnostic tester and Toyota ABS diagnostic tester. Another diagnostic tester needs two-way communication between the terminal control device of the system and the electronic control device of the system. It can not only read the fault code stored in the system electronic control device, but also convert the fault code into fault state and display it, which partially replaces the function of maintenance manual, and can also transmit control instructions to the system electronic control device to simulate the system. This test instrument includes SNAP-ON red box scanner, general TECH-L and ORB-LL of Clays, etc. These diagnostic test instruments are usually called decoders because they can read fault codes. The decoder can not only diagnose the fault of the anti-lock braking control system, but also diagnose and test other electronic control systems of automobiles by selecting the corresponding software.
4.2 General steps of fault diagnosis and elimination
When the warning light of the anti-lock control system lights up continuously, or if it feels that the anti-lock control system is not working normally, the system should be diagnosed and eliminated in time. In troubleshooting. In order to achieve good results, we should follow certain steps when diagnosing and troubleshooting. The general steps of troubleshooting are as follows:
1. Confirm the fault conditions and symptoms;
2. Visually inspect the system to see if there is brake fluid leakage, broken wires, loose plugs and low brake fluid level.
3. Read the fault code, which can be read directly by the decoder or by the warning light, and then find the fault situation represented by the fault code according to the maintenance manual.
4. According to the fault situation, use the necessary tools and instruments to conduct in-depth inspection of the fault location to confirm the fault location and cause;
5. Troubleshooting;
6. Clear the fault code;
7. Check whether the warning light is still on continuously. If the warning light is still on, it may be that there is still a fault in the system, or the fault has been eliminated and the fault code has not been cleared;
After the warning light is no longer on, carry out a road test to confirm whether the system is working again.
In the process of fault diagnosis and maintenance, it should be noted that not only different types of cars may be equipped with different anti-lock systems, but even the same type of cars may be equipped with different anti-lock control systems due to different production years.
Most of the failures of the anti-lock control system are caused by loose wiring plug or poor contact, open or short circuit of wires, open or short circuit of solenoid valve coil, open or short circuit of electric pump circuit, open or short circuit of wheel speed sensor electromagnetic wire, open or short circuit of internal relay, abnormal operation of brake switch, liquid level switch and pressure switch. In addition, the battery voltage is too low, the gap between the wheel speed sensor and the gear ring is too large or contaminated by mud, and the liquid level in the liquid storage room is too low, which will also affect the normal operation of the system.
4.3 Common Faults and Analysis
1 Fault symptom: When the user turns on the power supply, the ABS system does not self-check for 3 seconds, and the ABS indicator light does not light up. Fault analysis 1:ABS system has no power supply voltage. Elimination method: 1 Check whether the ABS wiring harness is connected with the 12v power supply on the vehicle; 2 Check whether the vehicle has a voltage of 12 volts. Fault analysis 2; The electronic control unit is damaged. Troubleshooting: replace ECU.
2 fault symptoms: the user turns on the power supply, ABS has 3 seconds of self-inspection, ANS works normally, but ABS indicator light does not light up. Fault analysis; Damage to the driving circuit of ABS indicator lamp: troubleshooting 1 short the connector between ABS harness and ECU 16 pin to ground. If the ABS indicator does not go out, replace the drive block. 2 If the ABS is still on after the replacement lamp is driven quickly, disconnect the connection between the ABS indicator lamp and the ABS wiring harness. Generally speaking, the ABS light will still be on when it is turned off. In this case, test the original car circuit.
3 Fault symptom: When parking, the ABS indicator light flashes 1 time. Fault analysis 1: the left front sensor is open or the sensor connector is in poor contact. Troubleshooting: Replace the sensor or eliminate poor contact. Fault analysis 2. The cable connecting the sensor at the end of 2ABS harness is open. Troubleshooting: Find the open point and reconnect it.
4 Fault symptom: When the vehicle is driving, the ABS indicator light flashes once. Fault analysis 1: the gap between the left front sensor and the gear ring is too large, and the wheel speed signal is insufficient. Troubleshooting: adjust the gap between the sensor and the gear ring < 0.7mm, check the output voltage of the sensor > > 0.3v Fault analysis 2 The gear ring of the left front wheel is unevenly installed or the gear ring is loose. Troubleshooting: Reinstall the ring gear.
5 Fault phenomenon: When the car is at rest or driving, the ABS indicator light blinks slowly 1 time. Fault analysis 1 the left front wheel solenoid valve package is open. Elimination method: replace the wire package or ECU.
6 when using ABS braking, the vehicle leans to the right or the ABS effect is not good. Fault analysis 1 is generally caused by the unbalanced braking force on both sides of the front wheel of the vehicle during braking. Troubleshooting: This phenomenon should be that there is some air in the brake pipeline, which leads to the imbalance of braking force in the brake pipeline. Vent the air from the brake pipe. Fault analysis 2 There is a certain blockage in the internal aperture of 2ABS hydraulic adjustment. Elimination method; Clearly adjust its internal aperture or replace the regulator. Fault analysis 3: It is possible that the lack of power supply voltage on the vehicle leads to the lack of electromagnetic force in the solenoid valve package, thus affecting the normal work of the regulator. Troubleshooting: Check whether the power supply voltage is within the normal range.
7 failure phenomenon; The left front wheel locks when braking. Fault analysis 1ABS hydraulic regulator The internal pressure relief hole of the left front wheel is completely blocked. Elimination method: adjust its internal aperture or replace the regulator. Fault analysis 2: Wrong connection of brake pipeline. Troubleshooting: Adjust the brake line. Fault analysis 3: It may be that the ABS motor has failed. Elimination method; Replace ABS motor
8 fault phenomenon: the braking force is weak when braking. Fault analysis 1: There is air in the brake pipeline or the brake cylinder can't get enough oil pressure. Exclusion method: 1, empty. 2. Check whether there is brake fluid in the brake cylinder. If there is no brake fluid, please check and adjust whether there is brake fluid at the corresponding oil outlet. If not, please continue to check and adjust whether there is brake fluid at the corresponding oil inlet. If not, please check the brake master cylinder. Fault analysis 2: The sensor may have insufficient signal. Elimination method: find the corresponding sensor and simplify its adjustment to the standard range. Fault analysis 3: check whether the braking force of the original car is qualified.
Fault phenomenon: When the vehicle is braked by ABS, the vehicle may be locked. Fault analysis: this phenomenon should be an internal fault of ABS regulator. Troubleshooting: Replace the hydraulic regulator.
Chapter 5: Introduction of typical ABS vehicles.
5. The basic structure and working principle of1Mercedes-Benz YL6120H bus ABS.
Basic structure of 1ABS
The ABS of Mercedes-Benz YBL6 120H bus is a kind of ABS attached to two axles.
The four-channel control system of automobile pneumatic braking system is shown in figure 1.
The system mainly consists of four wheel speed sensors and gear ring, 1 electronic controller and four pressure control valves.
2 ABS working principle
The sensor generates an induced voltage through the gear ring, and the voltage frequency varies with
When the wheel speed changes, the electronic controller sends a signal from the sensor.
Interest rate, and after confirming that the trend wheel is locked, press.
The force control valve outputs a pulse signal, and the pressure control valve outputs a pulse signal according to the input pulse.
The pulse signal controls the braking pressure, which can be maintained, increased or decreased.
The number has decreased. When the electronic controller of ABS issues a decompression instruction,
The corresponding pressure control valve passes the compressed air in the wheel brake cylinder through pressure.
The air outlet of the force control valve is discharged into the air. The brake pressure is correspondingly reduced,
The speed of the wheel starts to increase, and then it is maintained by alternating pulses.
Pressure/increasing pressure ",the brake pressure increases again until the wheel again.
Stick to death. This enables the vehicle to "brake" under braking conditions.
The repetitive action of "release" is similar to the "point" manually adopted by the driver.
Brake ",but its frequency is much faster than manual, its frequency is about every
6 ~ 10 times per minute.
In braking without ABS, the pressure in the brake pump can only increase with the pressure on the brake pedal, and the wheel speed of the wheel is different from that of the car.
The vehicle speed will decrease mechanically accordingly, and the wheels will eventually lock up.
5.2 ABS structure principle of FAW Jetta car
At present, domestic Jetta cars are all front-wheel drive. The car adopts MK20-I electronic anti-lock braking system of famous SABS/ITT company. 1995 was introduced to the United States, and 1996 was introduced to the European market. China FAW-Volkswagen used it for the first time to assemble this product on the Jetta city car mass-produced in 1999. MK20- 1, as a new generation of ABS electronic control braking anti-lock system device, adopts a series of advanced designs and technologies, adopts modular structure design, and integrates motor, hydraulic detection unit and electronic control unit. The control software written in C language is enhanced in the electronic control unit in a modular way. The hydraulic valve body adopts compound hole technology, and the solenoid valve coil is integrated in the electronic controller, which saves the connecting line between the solenoid valve coil and the controller. The high-power integrated circuit is used to directly drive the solenoid valve and the pump motor, which saves the relay device and the controller has a fault storage device.
ABS structure of 1 Jetta car
ABS system is mainly composed of hydraulic transmission system, wheel speed sensor and controller. It adopts a hydraulic diagonal loop braking system, and the front cavity of the master cylinder is communicated with the braking loop connecting the right front wheel and the left rear wheel. The rear cavity of the brake master cylinder is communicated with the brake circuit connecting the left front wheel and the right rear wheel, and the two brake circuits are diagonally arranged. This hydraulic braking system for conductor circuit can ensure that the braking effect can still reach 50% when a certain circuit fails.
vehicle speed sensor
The wheel speed sensor is mainly composed of a gear ring and a sensor, and the sensor is mainly composed of a permanent magnet and an induction coil to generate an induction signal. The wheel speed sensor is mainly used to monitor the movement state of wheels. When the wheel is locked, the deceleration and slip rate of the wheel increase sharply. At this time, the sensor transmits the sensed information to the electronic controller. If the values of deceleration and slip rate reduced by the electronic controller exceed the determined critical value, the electronic controller will send instructions to the solenoid valve of the actuator, and the actuator will quickly reduce or stop increasing the wheel pressure to avoid locking and achieve the purpose of anti-lock.
Electronic control unit (ECU)
The electronic control unit is a microcomputer, which is the control center of ABS system. The electronic control unit converts the pulse signal generated by the sensor into a square wave with the same frequency after being amplified by the shaping amplifier circuit, and then calculates the acceleration and deceleration. The calculation result is transmitted to the logic controller and compared with the stored given limit value. If it reaches the limit value, it will send out a control command pulse, which will be amplified by the power amplifier to control the solenoid valve in the hydraulic regulator. The system is equipped with a lower limit speed controller. When the vehicle speed drops to a certain pulse speed, it will automatically interrupt the ABS work and go to.
Hydraulic regulator
MK20- 1 ABS hydraulic regulator is mainly composed of low-pressure liquid storage pipe, electric liquid return pump, solenoid valve and valve body. The hydraulic regulator has four pairs of solenoid valves, namely, four liquid inlet solenoid valves and four liquid outlet solenoid valves. A liquid inlet valve and a liquid outlet valve are respectively arranged in the hydraulic pipeline leading to each wheel brake. The liquid inlet valve is a two-position double normally open solenoid valve, and the liquid outlet valve is a two-position double normally closed solenoid valve.
The working principle of 2.2. ABS system
During automobile braking, the wheel speed sensor continuously transmits the rotating speed signals of four wheels to the electronic braking unit (ABSECU) of ABS anti-lock braking system. ABSECU calculates the reference speed according to the speed signal and certain logic, and then calculates the reference slip rate of the wheel according to the reference speed and wheel angle. When the acceleration/deceleration speed and the reference slip rate of the wheel exceed their control limits, ABSECU sends instructions to the hydraulic regulator to control the braking change and keep the reference slip rate of the wheel within the ideal range.