Automotive Electronics and Vehicle Network Technology Chengdu Panfeng Technology

With the rapid development of automobile technology and the extensive application of electronic technology and control technology in automobiles, more and more electronic control modules are used in automobiles. From the original few blocks to the current dozens of blocks, it is obvious that the traditional data transmission method can no longer meet the requirements for data transmission between modules. A new type of data transmission network is used in the control system of new cars. The English abbreviation is (r). Its purpose is to speed up the data transmission of the car control system and simplify the car control system. New Volkswagen passenger cars adopt this kind of local network control system.
1. The composition and working principle of the data transmission system
The data transmission system changes the traditional multi-line transmission system into a two-line (bus) transmission system (as shown in the figure). In this way, no matter how many control modules there are in a car or how large its information capacity is, each control module only needs to lead out two wires and connect them to two nodes. These two wires are called data buses. The data bus is also called a data bus because information is transmitted through vehicles traveling on the highway.
.Composition of data transmission system
Each control unit in the data transmission system contains a controller and a transceiver. Each control unit is connected via two data buses. Data transmission terminals are installed at both ends of the data bus. It is not difficult to see that the data transmission system consists of the following four parts:
⑴Controller
The function of the controller is to receive the data processing data sent by the microprocessor in the control unit and transmit it to the transceiver. At the same time, the controller also receives the data processing data received by the transceiver and passes it to the microprocessor.
⑵ Transceiver
The transceiver is a combination of a transmitter and a receiver. It converts the data provided by the controller into electrical signals and sends them out through the data bus. At the same time, it also receives the bus data and transmits the data to controller.
⑶Data transmission terminal
The data transmission terminal is actually a resistor. Its function is to protect the data from being reflected back to the terminal to generate reflected waves.
⑷Data bus
The data bus is a bidirectional data line that transmits data. It is divided into high-order data lines and low-order data lines. In order to prevent external electromagnetic wave interference and outward radiation, data buses are usually intertwined. The sum of the potentials on these two wires is constant. If the voltage on one wire is then the voltage on the other wire is .
.The working principle of the data transmission system
The control unit provides the controller with the data that needs to be sent. This data is composed of binary numbers, which means that the circuit is connected or disconnected. That is to say, the number of bits can represent a kind of state. The number of bits can represent a kind of state. And so on. The largest data is a bit. The amount of information it can represent is equal to the power of times. Examples of using numbers to express temperature information are shown in the table.
In order to avoid conflicts when multiple messages are transmitted, the data bus only allows one data to be transmitted at the same time. The order of data transmission is determined by the priority level of the data. Data with higher priority level is sent first, and the priority level of the data is represented by the binary bit value. When multiple control units send data at the same time, the bit numbers representing the priority levels are compared one by one on the data transmission line from left to right. If a control unit sends a low potential (represented by ) and detects a high potential that is about to be received (represented by ), then the control unit stops sending and changes to the receiving state. If a control unit sends a high potential (represented by ) At the same time, another control unit sends out a low potential (indicated by ), and the data transmission line will reflect a high potential (indicated by ). For example, the data to be sent by the engine control unit is and the data to be sent by the automatic transmission control unit is.
So how will the data transmission line transmit this data? First of all, the first digits on the data transmission line are also reflected as the second digits of the three data. The automatic transmission control unit is ready to send out?? Therefore, the automatic transmission control unit sends a low potential (indicated by) and receives a high potential ( Indicated by Switch to receiving state for data transmission line transmission.
By comparing the status fields of the three data, it can be determined that the control unit has the highest priority and can take over control of the data bus. This priority ensures that it continues to send data until the transmission is completed. After the control unit finishes sending data, because the engine control unit has a higher priority than the automatic transmission control unit, the order of sending the data bus is: first send the control unit data, then send the engine control unit data, and finally send the automatic transmission control unit data.
2. Overhaul of the data transmission system of Volkswagen passenger cars
. Composition of the data transmission system of Volkswagen passenger cars
The data transmission system of Volkswagen passenger cars consists of comfort control bus, power control bus It is composed of bus, vehicle network control and gateway.
⑴ Comfort control bus
The comfort control bus system consists of the vehicle network control unit, the diagnostic interface of the data bus, the electronic control system control unit, the air conditioning control unit, the central control unit of the comfort system, the driver's side It consists of a door control unit, a front passenger door control unit, a left and right rear door control unit, a radio and navigation control unit. Its data transfer rate is lower than that of the power control system, which transmits data at a faster rate.
⑵ Power data bus
The data transmission system consists of the vehicle network control unit, the diagnostic interface of the data bus, the instrument panel control unit and the engine control unit, the automatic transmission control unit, the control unit, the airbag control unit, the steering Auxiliary control unit and other components.
⑶ Vehicle network control system
The vehicle network system monitors various signals of the vehicle through the control unit and controls actuators such as fuel pump relays and interior lights based on set programs.
⑷Gateway
A gateway is a computer that is connected to multiple data buses with different data transmission rates at the same time and plays the role of translation when transmitting data. That is to say, the gateway converts the formats of data at different rates into data that meets network requirements and puts it on the network. The gateway computer of Volkswagen passenger cars is installed together with the instrument computer.
. Maintenance of the bus system of Volkswagen passenger cars
The system faults of Volkswagen passenger cars can be detected and diagnosed using the latest version of the type detector. Now the power data bus system is taken as an example to illustrate.
The power data bus system of Volkswagen passenger cars connects each control unit one by one. The data that the bus system needs to transmit include the data group of the engine control unit, the data group of the automatic transmission control unit, and the data group of the control unit.
Fault query: Use the , type detector to enter the , , address respectively to perform self-diagnosis on the engine, and automatic transmission control unit, and then enter the function code to query whether the three electronic control units store the fault code of the data transmission system. Power data bus fault See the code table.
Faults in the data bus system are mostly caused by short circuits, open circuits, or mixing of high-order data lines and low-order data lines. You can use an oscilloscope to check and eliminate them. When checking the data transmission terminal resistance, turn off the ignition switch, unplug the engine control unit, and use a multimeter to measure the resistance between needles. This is the resistance value of the data transmission terminal. If it does not meet the requirements, replace the engine control unit.