Introduction to the working principle of automotive ECU

The ECU is the control center of the ABS system. Its essence is a miniature digital computer. It is generally an integral unit composed of two microprocessors and other necessary circuits that cannot be disassembled and repaired. The basic input signal of the electronic control unit is four wheels. The wheel speed signal sent by the sensor is: a control signal to the hydraulic control unit, a self-diagnosis signal outputted, and a signal output to the ABS fault indicator.

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1, ECU anti-lock control function

The electronic control unit has the function of continuously monitoring the speed signal of the four-wheel sensor. The electronic control unit continuously detects the pulse electrical signals from all four wheel sensors and processes them into a value proportional to the wheel speed. From these values, the electronic control unit can distinguish which wheel speed is fast and which wheel speed SLOW. The electronic control unit implements anti-lock brake control based on the speed of the four wheels. The electronic control unit uses the data from the sensor of the four wheels as the control basis. Once it is judged 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. Controlling the opening and closing of the oil passage on the sub-pump (wheel cylinder), the change of the oil pressure on the sub-pump adjusts the braking force on the wheel, so that the wheel does not completely lock the wheel due to the constant braking force. The frequency of on and off is generally 3 to 12 times per second.

Under normal circumstances, the anti-lock control adopts a three-channel mode, that is, the front wheel has two oil path controls respectively, and the electronic control unit can respectively perform anti-lock brake control on the left front wheel and the right front wheel respectively, and the rear wheel only has An oil circuit control. The electronic control unit can only centrally control the two rear wheels (once one rear wheel is about to lock, the electronic control unit simultaneously performs anti-lock control on the two rear wheels).

2, ECU fault protection control function

The ABS system electronic control unit has a fault protection control function. If the system malfunctions or is temporarily disturbed, the electronic control unit will automatically shut down the ABS system to allow the normal brake system to continue to work.

First, the electronic control unit can monitor its own work. Since there are two microprocessors in the electronic control unit, they receive and process the same input signal at the same time, and compare them with the internal signals of the electronic control unit and the generated external signals to see if they are the same. Thereby the electronic control unit itself is calibrated. 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 normal braking system work as usual. At this point, the repairman must check the ABS system (including the electronic control unit) to find out the cause of the failure.

The input signal from the wheel speed sensor is simultaneously sent to the two microprocessors in the electronic control unit, and after processing in their logic modules, the internal signal (wheel speed signal) and the external signal (signal to the hydraulic regulator) are output. Then, based on these two signals for comparison and proofreading. The internal signals generated by the logic block are sent to two different comparators (one comparator in each processor) where they are compared. If they are not identical, the electronic control unit will stop working. The external signal generated by the microprocessor is sent directly to the comparator, and the other routing hydraulic regulator control circuit is sent to the comparator through the feedback circuit. The external signal generated by the microprocessor is sent directly to the comparator and. By comparison with the comparator, if the external signal cannot be synchronized, the ABS system electronic control unit will turn off the anti-lock braking system.

The ABS system electronic control unit can not only monitor its own internal working process, but also monitor the operation of other components in the ABS system. It can send pulse check signals to the hydraulic regulator's circuit system and solenoid valve according to the program, and check whether the function is normal without any mechanical action. During the operation of the ABS system, the electronic control unit can also monitor and judge that the wheel speed signal sent by the wheel sensor is normal.

If the ABS system fails, such as brake fluid loss, hydraulic pressure drop or wheel speed signal disappears, the electronic control unit will automatically issue a command to let the normal brake system enter the work, and the ABS system stops working. The signal output generated by damage to a wheel speed sensor, as long as it is within acceptable limits, or the sensor emits a signal that exceeds the limit due to strong radio frequency interference, the electronic control unit may stop the ABS system depending on the situation. Work or let the ABS system continue to work.

It should be emphasized here that the amber (yellow) color ABS system fault indicator will not be extinguished at any time, indicating that the electronic control unit has stopped working on the ABS system or detected a system failure, and the driver or user must perform maintenance. If it can't be handled, it should be sent to the repair shop in time.

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