Ethernet in Steer-by-wire Applications

Abstract: A Controller Area Network (CAN) is a multi-master serial data communication bus designed primarily for the automotive industry. It is reliable and cost-effective and features error detection and fault confinement capabilities. CAN has been widely used in other applications, such as onboard trains, ships, construction vehicles, and aircraft. CAN has even been applied within the industrial automation segment in a range of devices such as programmable controllers, industrial robots, digital and analog I/O modules, sensors, etc. Despite its robustness and other positive features, the CAN bus has limitations in form of limited maximum data rate and maximum bus length. Also the CAN network topology is rigidly fixed which is a severe limiting factor in some of its application cases, therefore several industrial actors are evaluating alternatives to CAN. Ethernet is one of the potential candidates to replace CAN. It is a widespread and well knowntechnology, easily accessible, and many off-the-shelf solutions are available. It can support extended networks and offers wide possibilities in terms of network topology thanks to active switches. It features very high bandwidth, which has increased systematically from 10 Mbps to 100 Gbps year after year, always preserving backward compatibility to the maximum possible extent. The purpose of this thesis project is to investigate the possibility of replacing the CAN bus with Ethernet according to the following requirements: Standard off-the-shelf components and software stacks No modification of the network node application software, i.e. messages formatted accordingto CAN protocols must be transferred by means of Ethernet. A main issue is that CAN is time deterministic; it is always possible to predict the maximum latency in a message transfer. On the other hand Ethernet is still considered unreliable for time-critical applications, although the advent of Ethernet switches has minimized this non-deterministic behavior. A unique approach to this issue is offered as a result of the work done by Time Critical Networks, a newly started Swedish company. Their tool makes it possible to calculate the maximum forwarding time of a frame in an Ethernet network. This tool may make it possible to validate the use of Ethernet for time-critical applications. CPAC Systems, a company in the Volvo group which develops and manufactures steer-by-wire systems based on the CAN technology, wishes to verify whether Ethernet could now be considered as a solution to complement or replace CAN, thus overcoming CAN’s limitations. This verification is the goal of this master thesis project. The work was carried out through three different phase: First we performed a theoretical evaluation by modeling the Ethernet network using Time Critical Network’s tools. Next we verified the results by implementing the modeled CAN/Ethernet network that was previously modeled. Finally, we validated the solution by directly testing the modeled CAN/Ethernet in combination with CPAC System’s steer-by-wire technology. The results obtained show that Ethernet in combination with Time Critical Network’s modeling tool, when it comes to time-determinism, can be a complement and/or an alternative to the CAN bus.