From the car to the fully automated harvester, the CAN bus is the predominant communication technology in the mobile sector. Today, the increasing degree of automation requires more and more bandwidth. When it comes to the automation of safety-relevant functions, requirements like functional safety, hard real-time behaviour and expanded diagnostic capabilities show the limits of existing networking solutions. Hence, upgrading system architectures with complemental communication technologies becomes necessary. Technology transfers from industrial automation and the automotive industry can help to overcome the limitations of CAN networks in the area of mobile machines.
Growing Demands on Modern Bus Systems
In modern agricultural machines like tractors or fully automated harvesters, numerous CAN buses, such as an engine CAN or vehicle CAN, are used in order to enable communication within the control system. For this purpose – depending on the application – the CAN-based ISOBUS (ISO 11783) is additionally used in order to allow communication with implements such as trailers.
A modern CAN-based system including complex gateways often has an overall bandwidth of approx. 1-2 MBit/s, whilst future technologies will cause a data volume that is up to three orders of magnitude bigger than currently available.
Especially the automation functions in the area of drive, steering and working functions, also set strict requirements of functional safety, security and real-time capability. These three points particularly come to the fore if automation functions have to share the physical communication medium with other services, for example a steer-by-wire system that shares a network with the diagnosis system having cloud access. In this case, it must be ensured that in the event of problems in the diagnosis system, the automation function continues to have guaranteed bandwidth and latencies, so that the steering continues to reliably and safely work, despite an unwanted network load created by the diagnosis system.
Each possible solution has to ideally increase the bandwidth by an order of magnitude, i.e. make bandwidths of at least 10 to ideally 1,000 MBit/s available. CAN-FD, a further development of the classic CAN bus, that with a dynamic, time-limited bandwidth increase significantly improves the throughput of CAN by up to 12 MBit/s and a larger payload, offers a clear migration path from existing systems to higher bandwidths thanks to the technology relating to classic CAN. However, with an achievable average bandwidth of approx. 3-4 MBit/s it is not always suitable for IoT/Industry 4.0 or image-based applications such as Surround View.
A further solution could be completely based on Ethernet-standardized mechanisms of the IEEE.
Ethernet-based solutions offer many advantages: Ethernet is widespread, excellently standardized and there are already many products, technologies and tools by many suppliers that are based on Ethernet. However, there are also challenges to implementing a solution originally developed for use in an office environment in the area of mobile machines: they range from cabling and plug technology to functional safety, from determinism to integration into existing systems. In these areas, there are several current core developments such as new physical layers suitable for automotive or deterministic Ethernet expansions that solve these problems in the long term.
A more detailed article discussing several solutions with different complementary technologies can be downloaded as a PDF.