Detailed analysis: CAN-BUS, the electronic system in the car

This article is a technical article. I will explain to you what the "CAN-BUS system" is and its functions.

For example: In the past, the circuit system of a car was a bit like household electricity. There must be electricity and plugs to supply electricity to electrical appliances. If anything did not work, it was either the appliance was broken or the plug was not supplying power. The fault was easy to determine, as it was either one or two. However, the numerous lines required would consume unnecessary electricity.

Detailed explanation: Controller Area Network (CAN) Nowadays, many automotive circuits use the "CAN-BUS system", which is a new control system that SAAB began to use in 1993. Currently, most European car models use CAN-BUS, and Japanese cars have also switched to the CAN-BUS system since 2002. TOYOTA and LEXUS car models launched after 2006 also use the CAN-BUS system.

Popularization in-depth analysis: What is special about CAN-BUS?

I will use the simplest words to make you understand. In the past, when you turned on the engine, you could see a series of lines, which transmitted various control signals. If you use faster lines as buses to transmit all signals, and add a signal filtering device to the corresponding components, the number of lines will be greatly reduced and the speed will be increased. However, the price of the added things and the reduced investment due to simplified lines must also be considered in the cost.

The computer system inside it becomes a loop similar to a small network. Each electrical appliance is a small computer. As long as there is a positive current and 2 to 3 signal lines, the entire car circuit can be controlled. For example, the electric window originally required a dozen wires to control it, but now it only needs 4 wires to control it. For example, if you want to lower the driving window glass, the button only needs to send a digital signal such as "1122". The small computer at the motor end can control the window to lower after receiving 1122. The signal line only sends a 1122 signal briefly and then has no power output. Therefore, when the electric window fails, if you do not use a special maintenance computer to check the fault, you will not know which part is faulty, because the signal line cannot measure the voltage, and there is no electricity to measure at the switch and motor end. Therefore, the fault diagnosis cannot find the problem without a special maintenance computer.

Taillight The system is the same. There is a small computer at the taillight that receives the signal. When it receives the signal, it will execute the action represented by the signal. For example, when you step on the brake, a signal of 3344 is sent. When the computer receives the signal of 3344, it will send power to the brake bulb to light up. When the brake is released, a signal of 4433 is sent, and the computer will control the brake bulb to turn off. However, when the bulb is not on, it may be that the bulb is burned out, or the small computer is broken, or the signal line is broken, or the brake pedal switch is faulty. If the computer is not plugged in, no one knows which link has a problem, because the wiring and working principle are completely different!

The engine water temperature switch combines three switches into a single water temperature switch to transmit signals. By sending the current water temperature signal to the computer, the computer can send three sets of signals to the water temperature gauge, fan computer, and engine injection system according to the situation for their respective operations. This saves the other two sets of sensors and lines.

Some cars have been changed from traditional wiring to CAN-BUS system, which saves 20 kg of wires alone. However, there may be 3 to 40 small microcomputers of various sizes in various places throughout the car. Although it reduces unnecessary power consumption and load, the only disadvantage is that the car cannot be repaired without a maintenance computer, and all the concepts and knowledge of electrical fault judgment must be relearned, otherwise the car cannot be repaired! This type of network wiring system can make the car have lower power consumption, and the computer can fully control the entire car system. The disadvantage is that the repairman must use a computer to communicate with the car, otherwise he will have no idea what is wrong with the car!

Basic judgment: If it is an individual small computer (network), you can use an ammeter to diagnose whether the positive and ground (negative) terminals are short-circuited or powered; if it is a signal line, you can only measure the resistance value; and the signal line itself is divided into high- speed (HS-CAN) and medium-speed (MS-CAN), you can only use an oscilloscope or a diagnostic computer to confirm whether the transmission rate is abnormal. The high-speed transmission rate is about 500KB per second, and the medium-speed transmission rate is about 125KB per second.

At present, the application of CAN-BUS bus in cars is becoming more and more popular, not only limited to high-end cars (such as Polo, Bora, Passat), but also more and more mid-range cars (such as Shanghai Volkswagen Touran) are equipped with CAN-BUS bus. However, it is not common to use this technology in small family cars in China. Chery is the first to apply this technology to the A5 model in China , which is also a breakthrough in the level of intelligence among independent brands.