A complete analysis of the CAN bus of the Bora Automotive

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A complete analysis of the CAN bus of the Bora Automotive [Copy link]

The Bora car uses two CAN buses, namely the drive system CAN bus and the body system CAN bus, which can fully meet the ISO definition. The drive system CAN bus has a communication rate of 500kbps and is called the high-speed CAN. Its connection objects are the control units of the vehicle power and transmission mechanism, etc. The vehicle engine control unit, automatic transmission control unit, ABS control unit, airbag control unit, etc. The body system CAN bus has a communication rate of 100kbps and is called the low-speed CAN or comfort system CAN. Its connection objects are the central controller, 4 door controllers, etc. In addition, another important feature of the Bora car is that the concept of network management is introduced in the CAN of the body system. This is very suitable for event-triggered data communication.

The high-speed CAN used for the drive system and the low-speed CAN used for the body system are two independent buses, but from the perspective of resource sharing, it is best to have a connecting bridge between them so that the body system can also obtain information from the drive system. Of course, from a traditional perspective, it seems that the problem can be solved by simply adding a few wires.

However, in actual development, adding even one signal pin to the existing controller hardware will lead to hardware redesign, which is often not allowed by cost and schedule. In order to obtain the information of the other party's system without any hardware changes, the Bora car uses a gateway - J533 to complete this task. The gateway of the Bora car is "parasitic" in the instrument cluster.

Typical control units related to the drive system on Baolai cars include the electronic fuel injection system, automatic transmission system, anti-lock braking system (ABS), airbag system, etc.

Since the real-time requirements of each control unit are different due to the different data update rates and control cycles, in order to meet the real-time requirements of each subsystem, the public data is shared, such as engine speed, wheel speed, accelerator pedal position, etc. For example, if the 4-cylinder gasoline engine of the Bora car runs at 4000r/min, the time interval between two injections controlled by the electronic control unit is 6ms, of which the injection duration is 30 degrees of crankshaft angle (1ms), and a series of processes such as speed measurement, oil quantity measurement, A/D conversion, working condition calculation, and actuator control must be completed within the remaining 5ms. This means that data transmission and reception must be completed within 1ms to meet the real-time requirements of gasoline engine electronic control. This requires that its data exchange network is based on a priority competition mode and has an extremely high communication rate. The CAN bus used in the Bora car is designed to meet these requirements.

In addition to the drive system, the body system CAN is also a major controller area network. Its main connection objects are: central controller, 4 door controllers, memory modules and other components. The control objects of the body system are mainly the centralized locks on the 4 doors, windows, trunk locks, rearview mirrors and interior ceiling lights. In the case of remote control function, it also includes the reception and processing of remote control signals and the control of other anti-theft systems.