Modern vehicles have tremendous amounts of electronics and computer hardware that make them operate properly. The core of this virtual network is the Controller Area Network (CAN) that handles data flow between different electronic control units (ECUs). This article compares the importance, function and influence of the CAN bus systems in the automotive world.
What is a CAN Bus System?
In 1986, Bosch released the CAN bus (short for controller area network bus), a vehicle bus standard that was far more resilient to noise and capable of communicating between the microcontrollers and devices on a vehicle without having to do so through a host computer – instead, allowing different components of the vehicle to share information between themselves, so that everything from engine management to in-car entertainment can function together.
The world of automotive designs was forever altered with the development of the CAN bus system. The CAN bus drastically reduced the sheer number of wires needed within vehicles compared with the predecessor – point-to-point – wiring systems. In point-to-point systems, each component of the vehicle had to have a direct wire running to every other component that it might need to communicate with. Not only did this add weight to the vehicle, it made troubleshooting and repairs more difficult. With the CAN bus, all the devices needing to communicate could be connected to a two-wire system.
How Does the CAN Bus System Work?
Two-wire differential signalling is used, with the vehicle’s two CAN wires, typically known as CAN high and CAN low. Here’s how CAN works (for a more detailed description of CAN, see here): When an ECU uses the CAN bus to transmit data to the rest of the network, a voltage is supplied to one wire of the CAN bus through the sending ECU (let’s call this Pin 1) and another voltage is supplied to the other wire through another pin on the sending ECU (let’s call this Pin 2). The voltages sent to the wires follow the same pattern as in the voltage-divider circuit above. They are in opposite directions, and so the difference between the voltages on both wires is the important value: this is the pulse sent down the CAN bus to the rest of the network. By using this differential voltage signalling method, the CAN bus is highly immune to electrical interference: even in the very electrically noisy environment of an engine bay, data should still be received reliably.
These links connect each ECU to the other ECUs on the network through the two wires. Every ECU on the CAN bus listens with the other three lines of its connector to what’s going on on the CAN bus, and every ECU can transmit data that it wants to broadcast on to the bus. That’s where those three wires beyond the two used for connecting to the ECUs come into play. To transmit data via the bus, an ECU sends a message that states which function it wants to execute. In addition to its identifier, the message has another field that lets each ECU on the CAN bus know the priority of the incoming data, depending on the type of message. Budd normally has two message types: some types are real-time data, which have the highest possible priority. Data that requires immediate and undelayed transmission of brake signals and similar information will not be postponed by lower-priority messages.
The CAN bus system, for example, is based on a multi-master architecture, meaning that any of the ECUs can start communication at any time. This decentralised design is better suited to the safety-critical nature of automotive control systems, because it removes the single point of failure that could cause the whole network to cease functioning.
Types of CAN Bus Systems
Different bus systems exists which are applicable to vehicles intended for different purposes. In general, the CAN bus system functionalities are classified according to different levels based on the required data transfer rates and whether the communication is safety-related. The two most commonly used designs are:
High-Speed CAN: refers to a CAN bus that operates at speeds of up to 1Mb/s. High-speed CAN is used for critical systems, where communication speed is important for real-time control of the operation. Some examples of high-speed CAN use are in engine control, transmission control, ABS (Anti-lock Braking System), etc. When a vehicle is moving at a high speed, a delay in the data transmission made by a high-speed CAN bus will not result in serious malfunction of the system, especially when it comes to safety-critical systems.
Low‑Speed CAN (or Fault‑Tolerant CAN): Low‑speed CAN can run at speeds of up to 125 kbps, and is used for controlled systems that aren’t safety-critical, such as window controls, seat adjustment and lighting. When part of a fault‑tolerant CAN system, it can still communicate if one of the bus wires breaks; it just slowed down. This means that, if five out of 10 failed, there would still be a functioning CAN network. This redundancy is crucial for things such as your vehicle’s comfort and convenience features.
The Role of CAN Bus in Modern Vehicles
The CAN bus represents the central nervous system of the car, connecting the series of EMC and ECUs that manage the functions the car needs to perform. For instance, the ECU that controls the engine will talk to the TCU for transmission to determine gear shifts (the engine load and vehicle speed affect the optimal gear to be in) at a rate of 500 times per second. In the same vein, the module controlling the ABS will speak to the module managing the traction control for vehicle stability while braking.
One of these networks – which integral to the car, not optional extras – is the so-called controller area network (CAN) bus. It works beyond the drivetrain and occupant-safety systems into infotainment and telematics systems to provide real-time traffic information, car-navigation systems, and remote diagnostics (ie, sensing the performance data in a car and sending it to a cloud-based service to be analysed).
Benefits of the CAN Bus System
The adoption of CAN bus systems has brought numerous benefits to the automotive industry:
Reduced Wiring Complexity: Because individual computers can be assigned unique IDs on the same common communication network, there is no longer a need for a separate wire lead running between every device. Using the CAN bus, an entire farm of computers can be connected by just a few pairs of wires, reducing weight, respecting space and simplifying the construction of the entire vehicle.
Improved Reliability: The differential signalling and multi-master architecture make it much more reliable than other automotive networks, even in the noisy automotive environment. The system is less vulnerable to electrical interference and will continue to work if one ECU fails.
Scalability: The CAN bus system is designed to be very scalable, meaning that it is applicable to vehicles of all sizes and complexity. For example, it can be used in a compact supermini as well as a mighty heavy goods vehicle hauling a triple trailer.
Cost-Effectiveness: The CAN bus has few components, and – using a principle known as ‘daisychaining’ – relatively little wiring, saving material costs and reducing the labour needed for wiring and assembly.
Challenges and Future Developments
However, CAN bus does have some drawbacks. The more intelligent and connected vehicles become, and the more capability they gain, the more data must be transmitted within the vehicle. To address this challenge, communication protocols have advanced (and will continue to do so): firstly, to CAN FD (Flexible Data-rate), and then to Ethernet-based systems.
Yet the CAN bus will not ride off into the sunset any time soon. Like any technology that actually works, development of derivatives continues apace and it will likely co-exist with newer technologies in years to come. The CAN bus maintains its status as an essential component of automotive communication, providing a cost-effective and reliable solution for many of the important functions of a motor vehicle. Autos will become increasingly capable of driving themselves, but they will still need can.
Conclusion
The CAN bus system is a technology that has revolutionised the whole automotive industry because it allowed different electronic systems to share and communicate over the same network, allowing easier sharing of messages in the vehicle. As a result, the CAN bus system has revolutionised the modern car, making life on board safer and more fun. Just as it has done for years, it will continue playing a central role in the exponential advancement of vehicle communication.