Difference and relation between chassis can and power can in electric vehicle vehicles

In the electronic architecture of intelligent electric vehicle, the communication network is like the nervous system of the vehicle.

With the popularity of domain control architecture and automatic driving, the importance of chassis CAN and power CAN as “functional twins” is becoming more and more prominent.

They not only undertake the most critical real-time control tasks of the vehicle, but also cooperate precisely through the gateway in the physical quarantine-this design philosophy perfectly illustrates the art of balancing “functional safety” and “system integration”.

When we discuss the handling stability or dynamic response speed of an electric vehicle, we are essentially evaluating the synergistic efficiency of the two high-speed CAN networks.

We will deeply analyze the duality of this core network: from the millisecond real-time difference to the design of fault quarantine, from the directional exchange of data flow to the deep coupling in the automatic driving scenario.

Understanding the wisdom of “collaboration in separation” is the key starting point to grasp the essence of modern automotive electronic architecture.

The chassis can (Controller Area Network) and the power can on the vehicle are two core high-speed communication networks in the automotive electronic architecture, which have significant differences in function, connected nodes, real-time requirements and safety quarantine, but also have close links, and work collaboratively through the gateway.

The following is a detailed explanation of their differences and connections:

The main difference

1. Core functions and purposes:

• Power CAN:It mainly serves the powertrain core system of the vehicle. The core task is to ensure that the engine/motor, gearbox and battery management system work together efficiently and safely to achieve the power output, energy management (fuel economy or electric energy efficiency) and emission control of the vehicle.
• Chassis CAN:It mainly serves the driving control and dynamic stability of the vehicle. The core task is to control the driving posture, steering and braking of the vehicle to ensure driving safety and maneuverability. Coordinated work involving undercarriage systems.
  2. Typical electronic control units connected:
• Anti-lock brake system/electronic stability program control module
• Electric power steering control unit
• Electronic parking brake control unit
• Adaptive suspension control unit
• Electronic Stability Control (if separate from ABS/ESP)
• Tire pressure monitoring system
• Four-wheel drive system control unit
• Engine control unit
• Transmission control unit
• Motor controller
• Battery management system
• Vehicle controller (some functions, especially power coordination)
• Electronic accelerator pedal
• Nergy management unit in hybrid power system
• Power CAN:
• Chassis CAN:
  3. Real-time requirements:
• Power CAN:usually has the highest real-time requirements. Engine ignition, fuel injection, gearbox shift and other instructions need to be executed accurately in a very short time (millisecond level), which is very sensitive to communication delay. The message cycle is usually very short (e.g. 5 ms, 10 ms).
• Chassis CAN:Real-time requirements are also high, but usually slightly lower than power CAN. For example, braking and steering commands also require fast response, but the cycle period of chassis control may be slightly longer (e.g. 10 ms, 20 ms, 50 ms) than timing requirement of precise control per engine revolution. However, systems such as ESP, which involve active safety, also have a very high update rate of key signals (wheel speed, yaw rate).
  4. Security and quarantine requirements:
• Power CAN:It carries the core driving function of the vehicle. The failure or congestion of the network may cause the vehicle to lose power, unable to drive, or even have potential safety hazards (such as sudden power interruption). Therefore, the requirements for reliability and fault quarantine are extremely high.
• Chassis CAN:It carries the control system (braking and steering) related to driving safety. The failure of the network directly affects the safety of driving, and may lead to serious consequences such as braking failure and steering failure. Safety and reliability requirements are also very high.
• Key:Both require high security and reliability, but quarantine, either physical or logical, is common practice. One of the main purposes of separating them is fault quarantine. Prevent the failure of a subsystem (such as an infotainment system) or network congestion from affecting a critical drive or safety system (power or chassis). Even if the same physical CAN-bus is used, strict logical quarantine and message filtering is performed by the gateway.
  5. Data content:
• Power CAN:mainly transmits engine speed, torque request/actual value, accelerator pedal position, transmission gear/mode, clutch status, battery power/voltage/current/temperature, motor status, fault code, etc.
• Chassis CAN:mainly transmits wheel speed signal, brake pedal position/pressure, steering angle/torque, body yaw rate/lateral acceleration, suspension height/damping status, parking brake status, tire pressure information, ESP activation status, etc.

Difference of technical features: priority and real-time

Because of the different importance of their functions, there are also significant differences in the technical characteristics of their network design.

1. Signal priority:In the CAN bus arbitration mechanism, the smaller the ID value, the higher the priority. Power CAN transmits the most core drive commands and high-voltage system status, and its messages are usually given the highest priority. Chassis CAN is concerned with braking and steering safety, which is also a high priority, but usually slightly lower or comparable to power CAN, to ensure that critical safety signals can be responded to in a timely manner.
2. Transmission rate (baud rate): Both belong to the high-speed CAN category. The typical baud rate of power CAN is 500kbps or even 1Mbps to meet the millisecond real-time requirements such as motor torque control. The chassis CAN also uses a high rate (e.g. 500kbps) to ensure very low latency transmission of signals such as braking, stability control, etc.
3. Security level:Both belong to the network domain with the highest security level in the vehicle. Any communication failure or signal delay may cause serious driving safety risks, so the reliability and robustness requirements are extremely high.

Main contact

1. Both of them belong to the high-speed vehicle network:the chassis CAN and the power CAN are usually high-speed CAN, which follow the ISO 11898 -2 standard. The physical layer uses twisted pair, and the baud rate is usually 500kbps (the most common) or 1Mbps. They are distinguished from body comfort CAN (125kbps) and infotainment CAN (possibly based on CAN FD, FlexRay, Automotive Ethernet, etc.).
2. Interconnect via Gateway:

• This is the core link between the two. Modern cars have one or more central gateway modules.
• The gateway acts as a router, firewall, and protocol converter between different network domains (power domain, chassis domain, body domain, infotainment domain, etc.).
• The power CAN and chassis CAN are physically separate buses, but are logically connected via gateway. The gateway allows the necessary information to be securely and controllably exchanged between the two networks.
  3. Information interaction and system collaboration:
• Chassis-> Power:
• Power- > Chassis:
• Brake pedal signal:tells the driver of the power system that he is decelerating and may need to stop injecting fuel (fuel vehicles) or activate regenerative braking (electric vehicles).
• Wheel speed signal/ESP activation signal: When ESP detects wheel slip, it requests the powertrain (engine/motor) to reduce torque output (torque intervention) to help stabilize the vehicle.
• Steering angle/torque: used for advanced functions such as adjusting the engine response characteristics according to the steering state.
• Actual torque of engine/motor: ESP and traction control system need to know the actual torque on the current driving wheel to judge whether it is slipping.
• Transmission Gear/Mode: Affects control strategies for systems such as ESP and Hill Assist.
• Driving state (Ready state, etc.): inform the chassis system whether the vehicle can be driven, and affect the behavior of EPB, Autohold and other systems.
• Regenerative braking status/intensity: affects the pressure distribution of the braking system (coordinated hydraulic and motor braking).
• As a whole, the powertrain and chassis systems need to work closely together to achieve complex functions. This collaboration relies on the gateway to pass critical information between the two:
• Vehicle controller:as the “brain” of vehicle control, it is usually connected to the power CAN or part of the gateway, and needs to integrate key information from the power CAN and chassis CAN to make the highest level of coordination decisions (such as energy management strategy, driving mode switching).
  4. Jointly support advanced driver assistance systems and autonomous driving:
• The realization of ADAS and automatic driving functions (such as adaptive cruise, automatic emergency braking, lane keeping and automatic parking) requires the acquisition of the ability of both the power system (controlling acceleration and deceleration) and the chassis system (controlling steering and braking). The gateway must efficiently and reliably transfer a large amount of sensor data and control commands between the power CAN and the chassis CAN.

• Difference:“how to move” the power can tube (drive, energy), “how to control” the chassis can tube (direction, stop). They are connected to different core systems and have high real-time requirements, but the power CAN usually has the highest requirements. Physical or logical quarantine is standard practice.
• Connections:They are high-speed backbones connected by a “secure bridge” of central gateways. In order to drive safely and efficiently, the vehicle must rely on the gateway to exchange key information between the two (such as brake signal to the power system to reduce torque, wheel speed signal to the power system for anti-skid), so as to achieve the deep coordination of power and control.

This separate and collaborative design is the key to the functional safety, reliable communication and complex system integration of modern automotive electronic and electrical architecture.

The “separate cooperation” mode of chassis CAN and power CAN is undergoing a historic transformation.

With the popularity of vehicle-cloud integration and Gigabit Ethernet backbone network, these two classic networks will gradually evolve into virtual channels within domain controllers. But their core design philosophies, “secure quarantine” and “precision collaboration,” will still have a profound impact on the next generation of electronic architecture.

Application cases in electric vehicle.

Modern passenger cars, especially intelligent electric vehicle, have a clear distinction between power and chassis domains in their network architecture, and the relevant cases are very typical.

Vehicle network system of pure electric passenger vehicle: In a patent design of pure electric vehicle communication system, the vehicle network is clearly divided into four CAN buses, of which power CAN (EVCAN) and chassis CAN (CH CAN) are the core.

Power CAN (EVCAN) case: key components such as motor controller (MCU), battery management system (BMS), vehicle control unit (VCU) and electric air conditioning compressor (EAC) are connected to the bus. It is responsible for the core driving instructions and energy management of the vehicle, so it is designed as a bus with the highest signal priority and the highest transmission rate in the vehicle network. For example, the VCU sends a torque request to the MCU through the bus, and the BMS monitors and reports the battery status in real time.

Chassis CAN (CH CAN) case: Electronic Stability Program (ESP), brake-by-wire system (such as iBooster), electric power steering (EPS) and advanced driver assistance system (ADAS) control unit (ACU) are integrated on the bus. It is mainly responsible for vehicle braking, stability, steering and other dynamic control, because it involves driving safety, its network signal priority is also very high. For example, ESP obtains wheel speed, yaw rate and other signals through the bus, and interacts with steering and braking systems in milliseconds to maintain body stability.

In the future, three trends deserve attention:

1. Functional integration:the intelligent driving domain controller will take over some chassis control (such as automatic emergency steering)
2. Latency challenge:L4 autopilot requires cross-network response speed to exceed 1ms threshold
3. Safety redundancy:Dual gateway architecture becomes the standard of high-end vehicles
   This change is not to eliminate differences, but to push the coordination of power and chassis control to a new height through more powerful central computing power. Understanding the duality of today’s CAN network is the preparation for the full evolution of tomorrow’s “car brain”.

The design of “cooperation in separation” of the “functional twins” of chassis CAN and power CAN is not a simple functional division, but a profound philosophy of safety and efficiency.

It ensures that the core “motion” and “control” of the vehicle can achieve millisecond-level precise coordination under the premise of extreme reliability. For drivers, behind every smooth acceleration and every stable cornering are countless silent dialogues between the two networks through the “safety bridge” of the gateway.

Looking forward to the future, with the evolution of domain centralized architecture to central computing platform, the boundaries of physical bus may be blurred, but the core principles of “secure quarantine” and “functional synergy” will only be strengthened and reconstructed. Understanding the duality of today’s CAN network not only gives us insight into the intelligent core of current vehicles, but also provides us with a key perspective to grasp the evolution of the next generation of “software-defined vehicles”.