The application of CAN bus data in automobile digital technology is the starting point

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The application of CAN bus data in automobile digital technology is the starting point [Copy link]

In the development of modern automobile technology, more than 95% of cars have adopted the CAN bus protocol, and some entertainment systems have adopted Ethernet. Combined with the commercial application of 4G/5G , the original closed internal data closed loop of cars has been connected to the Internet. Our users can not only remotely unlock their cars, but also remotely control the cars. Even without keys, family members can still use the cars. As a mobile means of transportation, cars have become as simple as remotely controlling a TV under the new round of technology.

Tesla uses a variety of control methods such as RFID , NFC , Bluetooth, and remote control, which has become a gimmick that users are " proud of " . For this reason, a large number of users are obsessed with Tesla's high-tech. From the perspective of Tesla's unique innovation and application, it has really grasped the psychology of users. From the first large screen to the first RFID door unlocking, these technologies are eye-catching.

1. Technical Background

The automotive bus technology is used in today's mid-range and high-end cars. The automotive bus provides a unified data exchange channel for various complex electronic devices, controllers, measuring instruments, etc. inside the car. Some automotive experts believe that just like the introduction of integrated circuits in the 1970s and microprocessors in the 1980s, the introduction of data bus technology in the past 20 years will also be a milestone in the development of automotive electronic technology.

Since the 1990s , the number of components controlled by electronic control units (ECUs) in automobiles has increased, such as electronic fuel injection devices, anti-lock brakes, airbags, electric windows and doors, active suspensions, etc. With the widespread use of integrated circuits and single-chip microcomputers in automobiles, the number of ECUs in vehicles has increased. Therefore, a new concept , the concept of the Controller Area Network ( CAN ) on board, has emerged. CAN was first developed by the German company BOSCH to solve the data exchange between control and test instruments in modern automobiles. According to relevant ISO standards, the topology of CAN is a bus, so it is also called CAN bus.

The data volume of each frame in the CAN protocol does not exceed 8 bytes, and high real-time data is achieved by sending short frames multiple times; the error correction capability of the CAN bus is very strong, thereby improving the accuracy of the data; at the same time, the rate of the CAN bus can reach 1M bit/s , which is a real high-speed network, generally using 500Kbit/s , most commercial vehicles use 250bit/s , and there are 100250bit/s in the multi-channel CAN body control system .

There are many advantages of using CAN bus in automobiles:

(1) Low-cost twisted-pair cables are used to replace expensive wires in the vehicle body, greatly reducing the number of wires used; improving reliability , safety, and reducing costs.

(2) It has fast response time and high reliability, and is suitable for applications with high real-time requirements such as brakes and airbags; it serves as the interconnection basis for the control platform, information platform, and driving platform.

(3) CAN conversion chips ( generally NXP1040-1044 series ) can withstand high temperatures and high noise, and have low prices and open industrial standards.

In the design of new cars, CAN has become a must-use device. Mercedes-Benz, BMW, Volkswagen, Volvo, Toyota, Honda, Nissan and other cars all use CAN as a means of controller networking. When we cracked the entire BMW series in 2014 , BMW's ECU control unit on luxury models had more than 130 , and it was equipped with a multi-channel gateway to collect the car's CAN bus. For example, if you enter from the gateway, you generally cannot obtain its ECU data from the external OBD interface , and it is a multi-channel CAN .

As we all know, the core unit of a car is the engine. The operating parameters of the engine, such as engine speed, oil pressure, coolant temperature, etc., are closely related to car driving. The design method of traditional car instruments is: through sensors placed inside car parts (such as engines), mechanical signals are converted into electrical signals, such as voltage, current, and pulse signals, and then through D/A conversion or counters, the electrical signals are converted into visible pointer signals displayed on the analog instrument panel. With the development of automotive bus technology, many imported engines no longer directly provide sensor signals to the outside, but use CAN bus communication interface instead.

According to the OSI model defined by ISO ( International Organization for Standardization ) , the CAN protocol defines the physical layer and data link layer specifications, which greatly facilitates different automobile manufacturers to develop application layer protocols that meet their own needs. If you need to build a more complete system, you also need to choose a suitable application layer protocol based on CAN , such as CANopen , SAE J1939 , etc.　　　

The J1939 protocol is currently the most widely used application layer protocol in large vehicles (mainly diesel vehicles), and can reach a communication rate of 250Kbps . The J1939 protocol is maintained and promoted by the American SAE (Society of Automotive Engineer) . The J1939 protocol has the following characteristics:

(1) Based on the CAN2.0B protocol, the physical layer standard is compatible with the ISO11898 specification and uses CAN controllers and transceivers that comply with the specification . The communication rate can reach up to 250Kbps .

(2) Information is transmitted using PDU (Protocol Data Unit ) , and each PDU is equivalent to a frame in the CAN protocol. Since each CAN frame can transmit up to 8 bytes of data, the transmission of PDU has high real-time performance.

(3) Use the 29 -bit identifier of the CAN2.0B extended frame format to define the meaning of each PDU and the priority of the PDU .

(4) J1939 is a communication protocol used in automobiles. It specifies various parameters used in automobiles. The parameters are in accordance with ISO11992 standard.

2. Development of J1939 in China

Shenzhen Suruide Technology Co., Ltd., a supplier of China's National VI OBD emission online detection terminal equipment for heavy-duty diesel vehicles, has jointly defined the data for monitoring the National VI heavy-duty diesel vehicle OBD emission standards with China's China Automotive Technology and Research Center, the National Environmental Protection Administration, Metrology, Tsinghua University, etc., and designed and developed online monitoring terminals, realizing the J1939 gateway terminal H6S ( national standard ) series terminal products based on 4G networks , and realizing the data transmission requirements of GB17691 .

H6S can be used for automotive remote digital instruments, automotive J1939 gateways, and core units of automotive multi-function electronic controls. It has passed rigorous reliability tests and actual product verification and has been put into mass production.

The terminal's various indicators have reached the advanced level of the National VI Standard (the most stringent international standard). In addition to supporting SAE J1939 firmware, it can also support SAE 14229 and ISO15765 standards to achieve data collection and remote transmission of automotive instruments. Internationally, it has passed the interconnection test with the J1939 engines of the United States, Germany, and Italy, and obtained an international pass.

The system consists of 11 network nodes, with J1939 network as the backbone, integrating the network essence of modern automotive technology. Including LINbus , 4G (wireless TCP/IP network), RS232 , embedded Ethernet, CANFD and other latest technologies. The power unit data of the car is directly realized through embedded hardware digital simulation technology. It includes:

( 1 ) Engine ECM simulation unit: ( Node 1)

It can realize the bus simulation function of the (actual) engine, generate 10~20 kinds of electronic control parameters of the engine, and simulate the actual operation state of the automobile engine. It is suitable for automobile EMC requirements.

( 2 ) NMT/ body electronic control unit (node 2 )

It can realize the network management function and diagnostic record function specified in J1939/81 , send out alarm control information, and has 16 photoelectric isolation output interfaces ( 50V/500mA ), 8 digital signal (sensor) input interfaces and 4 analog sensor interfaces. The control function can be modified by on-site programming. It is suitable for various automotive EMC development requirements.

( 3 ) Retarder simulation unit: (Node 3 )

The driving interface of the electromagnetic retarder can be controlled according to the vehicle's operating status and speed.

( 4 ) ABS simulation unit: (Node 4 )

The ABS braking force and activation time are controlled according to the comprehensive parameters of the vehicle network .

( 5 ) AMT simulation unit: (Node 5 )

The communication between the gearbox and the engine ECM can be simulated according to the design parameters .

( 6 ) Asymmetric bridge (node 6 )

It can realize asymmetric bridging of traffic between high-speed network (power system) and low-speed network (instrument information electrical control system) to ensure the safety of bus load rate and electrical safety.

( 7 ) LIN BUS Gateway (Node 7 )

Realize the interconnection of LIN-BUS sensors, electrical control systems and CAN-BUS systems, and comply with the J1939 protocol.

( 8 ) J1939MFM (node 8 )

J1939 multifunctional automobile comprehensive parameter instrument (automobile information center) can realize real-time display of 14 kinds of automobile operating parameters (Chinese LCD ), programmable 300~5000Km historical vehicle condition record and has fault alarm information display function, which is suitable for automobile EMC requirements.

( 9 ) J1939 Automotive Remote Instrumentation (Node 9 )

Realize J1939 bus-type automobile instrument. Can be adapted to a variety of domestic or imported automobile instrument assemblies.

( 10 ) J1939 to Ethernet SAE14229 to J1939 (Gateway Node 10 )

It can be connected to the J1939 network via Ethernet or a general-purpose computer , perform statistical analysis on the bus load rate, and open an API interface.

( 11 ) J1939 real-time operation parameter recording (node 11 )

Access to the J1939 network can record 200,000 operating parameters for real-time analysis of the operating conditions of each ECU unit. It can also test the operating parameters in an actual running car and access the Internet network environmental protection online monitoring server through the 4G network . It has strong anti-electronic interference capabilities and is suitable for automotive EMC and National VI requirements.

The network system has been working continuously for more than 10,000 hours under 12 nodes (with a maximum bus load rate of 30% ) in accordance with the physical layer, link layer and network reference layer of J1939 . The productization test of MFM/J1939 multi-function gateway and bus-type digital automotive instrument test have been completed in accordance with the J1939/71 vehicle application layer standard .

3. Technology Outlook

The future car is an intelligent network computing platform. The car network runs through every unit of the vehicle, that is, the control system, information system, driving system and sensor execution system are all interconnected by the control area network CAN-BUS . Mastering the application layer network standards and developing embedded software are key technologies.

Connecting the control network and information network in the car, such as the remote detection system for fault information, the automatic recording system for vehicle conditions, and the real-time driving information display system (intelligent digital instrument), with the embedded Internet (supporting 4G and 5G ) , so that each car has an independent web page and can manage the entire life cycle of the car, will be the key core technology of the future automotive computing platform.

The difficulty of this technology lies in the matching of the vehicle model library. It is necessary to understand the different data formats and status of each vehicle under the CAN bus. In the actual operation and management process, we need to know how the vehicle is used, whether it has oil / electricity, whether the car belongs to Zhang San or Li Si, how many times the brakes are applied, whether the tire pressure is normal, where it has been, how many kilometers it runs every day, and other information. These will constitute a model and portrait of the vehicle's use, which will help companies provide effective actual data information.

There are not many domestic companies that support multi-car multi-data matching. Some do it for show, while others do it for practical applications. To engage in development in this field, you need to understand not only cars, but also CAN , automotive electronics, networks, platforms, and controls. There are very few in China, including China Automotive Technology and Research Center, Suruide, and Hikvision, and abroad, there are Tesla, Victor, Bosch, etc.

huo_hu

Even fighter jets use canbus

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huo_hu posted on 2020-2-13 00:42 Canbus is used even in fighter jets

Well, you are right. Most of the aerospace, medical, elevator, industrial control, heavy machinery, etc. use CANBUS.