The CAN bus of the automobile power system is mainly related to automobile safety, and its real-time requirements are relatively high, so the transmission rate is relatively high, usually between 125kb / s-1Mb / s, and it must support periodic and real-time parameter transmission.
European car manufacturers basically adopt CAN bus standards such as ISO11898 for high-speed communication, and most of the vehicle power systems in the National Six OBD online monitoring use the J1939 protocol, which is widely used in trucks, buses, construction equipment, agricultural machinery and other industries High-speed communications in the field.
J1939 protocol and its characteristics
| Bus and protocol name |
|||
| characteristic |
CAN2.0/ISO11898 |
SAE J2284 |
SAE J1939 |
| Affiliation |
BOSCH / ISO |
SAE |
TMC-ATA |
| use |
Control diagnosis |
Control diagnosis |
Control diagnosis |
| medium |
Twisted pair |
Twisted pair |
Twisted pair |
| Bit coding |
NRZ-5 |
NRZ-5 |
NRZ-5 |
| Media access |
competition |
competition |
competition |
| Error detection |
CRC |
CRC |
CRC |
| Frame length |
11 or 29 |
11 or 29 |
29 place |
| Data length |
0-8 bytes |
0-8 bytes |
8 bytes |
| Bit rate |
1Mb/s |
500kb/s |
250kb/s |
| Bus length |
40m (typical) |
30m |
40m |
| Maximum number of nodes |
32 |
16 |
30 （STP） ： 10 （UDP） |
| cost |
in |
in |
in |
When the communication transmission rate between ECU (Electronic Control Units) of automobiles (sedans) is greater than 125kb / s and the highest is 1Mb / s, ISO11898 specifies the relevant characteristics of using the controller area network to construct digital information exchange.
J1939 is used for trucks and other trailers, buses, construction equipment and agricultural equipment. It is used to support real-time control functions and high-speed communication standards between electronic control units distributed at different positions of the vehicle. Its data transmission rate is 250kb / s . J1939 uses the controller area network protocol. Any ECU can send a message when the bus is idle. It uses the extended frame 29-bit identifier defined in the protocol to implement a complete network definition. The first three bits of the 29-bit identifier are used to determine the priority of messages during the arbitration process. For each type of message, the priority is programmable so that the original equipment manufacturer can adjust the network when needed.
In the National Six OBD online monitoring system, Su Ruide adopts this feature. The engine operating conditions collected from the J1939 data protocol include vehicle speed, atmospheric pressure, engine torque, friction torque, engine speed, fuel flow rate, and SCR upstream nitrogen. Oxide sensor output value, reactant remaining amount, intake air amount, SCR inlet and outlet temperature, DPF pressure difference, engine coolant temperature, mailbox liquid level percentage, positioning status, latitude and longitude, cumulative mileage, engine torque mode, accelerator pedal, fuel consumption, Data such as urea tank temperature, actual urea injection volume, and DPF exhaust temperature are sent to the data platform through the mobile 4G / 5G network and using the GB17691 network communication transmission protocol.
In the past, the purpose of using emission diagnosis was mainly to meet the OBD2 (On Board Diagnose), OBD3 or E-OBD standards, using ISO9141 and ISO14230, and Ford, GM and Chrysler of the United States using J1850. At present, more than 98% of automobile manufacturers adopt CAN bus diagnostic system, adopt ISO15765 communication standard as the communication standard of diagnostic system, and also meet E-OBD and OBD2 emission standards.
ISO15765 is suitable for the occasion where the vehicle diagnostic system is implemented on the CAN bus. The ISO15765 network service meets the requirements of the CAN-based vehicle network system, and is formulated in accordance with the content of the UEFA Champions League diagnostic services in ISO14230-3 and IOS15031-5. Therefore, ISO15765 is fully compatible with the services and parameters of the ISO14230 application layer, but it is not Limited to the occasions specified by these international standards. For example, the CAN protocol, which is also commonly used in elevators, medical, firefighting, industrial machinery, and power, realizes remote data transmission and control.
Commonly used will also be the network and protocol of the multimedia system. This will involve more in the development and application of in-car entertainment systems. There are generally three types of this protocol, namely low speed, high speed and wireless. The SAE classification is correspondingly: IDB-C (Intelligent Data Bus-CAN), IDB-M (Multimedia), and IDB-Wireless, the rate is between 250kb / s-100Mb / s. It includes voice system, car phone, stereo, car TV, car computer and GPS positioning and navigation system.
Low speed is used for remote communication, diagnosis and general information transmission. The characteristic is low cost. High speed is mainly used for real-time audio and video communication. The transmission medium is optical fiber. European automakers Daimler, BMW and Mercedes-Benz now mostly use MOST. MOST is a LAN (Local Area Network) interface network in the car. It is mainly used to connect car navigation systems and wireless devices. The data transmission speed is 24Mb / s.
With the rapid development of electronic technology and large-scale integrated circuits, network technology has been widely used in automobiles, so that the power, operational stability, and safety of automobiles have risen to a new height, injecting new developments into automotive technology. Vitality. The new generation of cars will include more controllers connected by multiple ECU control units to form domain controllers, gateways, intelligent gateways, etc. The advantage is that the parameters of the car can be customized through software, and the basic hardware is developed. The car has a greater degree of intelligence, networking and self-diagnosis functions. Taking full advantage of these characteristics, all two-way communication between the car and the network can be established in the subsequent car big data platform system, production tools and management, service tools And OTA upgrades.
