ECU is the control center of the ABS system. Its essence is a micro-digital computer. It is generally an integral unit composed of two microprocessors and other necessary circuits that cannot be resolved. The basic input signal of the electronic control unit is four wheels. The wheel speed signal sent by the sensor, the output signal is: the control signal to the hydraulic control unit, the output self-diagnosis signal and the signal output to the ABS fault indicator.
1. Anti-lock control function of ECU
The electronic control unit has the function of continuously monitoring the speed signals of four wheel sensors. The electronic control unit continuously detects the pulsed electrical signals from all four wheel sensors and processes and converts them into values ​​proportional to the wheel speed. From these values, the electronic control unit can distinguish which wheel speed is faster and which wheel speed slow. The electronic control unit implements anti-lock braking control based on the speed of the four wheels. The electronic control unit uses the data from the sensors of the four wheels as the basis of control. Once it is determined that the wheel is about to lock, it immediately enters the anti-lock control state, and outputs a pulse control voltage of 12V to the hydraulic regulator Control the on and off of the oil path on the cylinder (wheel cylinder), the change of the oil pressure on the cylinder adjusts the braking force on the wheel, so that the wheel will not completely block the wheel due to the always large braking force ( The frequency of on and off is generally 3 to 12 times per second).
Under normal circumstances, anti-lock control uses a three-channel method, that is, the front wheels have two oil channels to control, and the electronic control unit can separately perform anti-lock braking control on the left front wheel and the right front wheel. One oil circuit control. The electronic control unit can only centrally control the two rear wheels (once one of the rear wheels is about to be locked, the electronic control unit controls the two rear wheels at the same time).
2. ECU fault protection control function
The electronic control unit of the ABS system has a fault protection control function. If the system fails or is temporarily disturbed, the electronic control unit will automatically shut down the ABS system, allowing the normal braking system to continue to work.
First, the electronic control unit can monitor its own work. Because there are two microprocessors in the electronic control unit, they receive and process the same input signal at the same time, and compare the internal signal of the electronic control unit with the generated external signal to see if they are the same. Thus calibrating the electronic control unit itself. This calibration is continuous. If it cannot be synchronized, it means that the electronic control unit itself has a problem. It will automatically stop the anti-lock braking process and let the ordinary braking system work as usual. At this time, the repair personnel must check the ABS system (including the electronic control unit) to find out the cause of the failure in a timely manner.
The input signal from the wheel speed sensor is sent to two microprocessors in the electronic control unit at the same time. After being processed in their logic modules, the internal signal (wheel speed signal) and external signal (signal to the hydraulic regulator) are output. , And then compare and proofread based on these two signals. The internal signals generated by the logic module are sent to two different comparators (one for each processor), where they are compared, and if they are not the same, the electronic control unit will stop working. The external signal generated by the microprocessor is sent directly to the comparator all the way, and the other is sent to the comparator through the feedback circuit through the control circuit of the hydraulic regulator. The external signal generated by the microprocessor is directly sent to the comparator and. Comparing through the comparator, if the external signal cannot be synchronized, the electronic control unit of the ABS system will close the anti-lock braking system.
The electronic control unit of the ABS system can not only monitor its own internal working process, but also monitor the working conditions of other components in the ABS system. It can send pulse inspection signals to the circuit system of the hydraulic regulator and the solenoid valve according to the program, and complete the inspection of whether the function is normal without any mechanical action. During the operation of the ABS system, the electronic control unit can also monitor and determine whether the wheel speed signal sent by the wheel sensor is normal.
If the ABS system fails, such as loss of brake fluid, reduction of hydraulic pressure, or disappearance of the wheel speed signal, the electronic control unit will automatically issue a command to let the ordinary brake system work, and the ABS system stops working. For the signal output of a wheel speed sensor damage, as long as it is within an acceptable limit, or the sensor emits a signal beyond the limit due to strong radio high-frequency interference, the electronic control unit may stop the ABS system according to the situation. Work or let the ABS system continue to work.
It should be emphasized here that at any time, the amber (yellow) ABS system fault indicator light is on, which means that the electronic control unit has stopped the ABS system or has detected a system fault. The driver or user must perform maintenance. If it cannot be handled, it should be sent to the repair shop in time.
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