This chapter deals with automotive networks and the emerging requirements involved by the X-by-wire and X-tainment applications. The introduction of ECUs (Electronic Control Units) has been driven by new market (like navigation, multimedia, and safety). Furthermore, the automotive industry has to face a great challenge in its transition from mechanical engineering towards mechatronical products. Combining the concepts of networks and mechatronic modules makes it possible to reduce both the cabling and the number of connectors. To connect the ECUs, a variety of network technologies are already widespread. A review of the most widely-used automotive networks and emerging ones is given first. To fulfill the increasing demand of intra-car communications, a new technique based on power line communication (PLC) is proposed and reviewed in the second section. On the other hand, there are several infotainment applications (like mobile phones, laptop computers) pushing for the adoption of intra-car wireless communications. Some of the most common wireless technologies that have potential to be used in the automotive domain are considered and different experimentations are presented. Finally, the challenges of these wired or wireless alternative solutions to automotive networks are highlighted.
TopIntroduction
Fieldbuses are a family of automotive communication networks that have evolved as a response to the demand to reduce cabling costs in factory automation systems. Moving from a situation in which every controller has its own cables connecting the sensors to the controller to ECU sharing a bus, costs could be cut and flexibility could be increased. Pushing for this evolution of technology was the fact that the number of cables in the system increased as the number of sensors and actuators grew. Furthermore, the ECUs share their CPU power and knowledge with other controllers. Several fieldbus technologies, usually very specialised, were developed by different manufacturers to meet the demands of their application. The standardisation process stabilized not until the mid 90’s with CAN standardized in1993 by the International Standardisation Organisation (ISO) (Johansson, Törngren, & Nielsen, 2005).
Indeed, today’s vehicle networks are not just collections of discrete, point-to-point signal cables. They distribute the electronic systems according to their domain sharing networks. Replacing rigid mechanical components with dynamically configurable and even reconfigurable electronic elements triggers an almost organic, system wide level of integration. Furthermore, the amount of cables is drastically reduced by using these fieldbuses. As a result, the cost of advanced systems should plummet. Furthermore, highly reliable and fault-tolerant electronic control systems, X-by-wire systems do not depend on conventional mechanical or hydraulic mechanisms. They make vehicles lighter, cheaper, safer, and finally more fuel-efficient.
In (Len & Hefferman, 2001), the authors demonstrate the advantages of X-by-wire and embedded networks. For example, Leen and Hefferman write “X-by-wire steering systems under development will replace the steering column shaft with angle sensors and feedback motors. This removal will improve driver safety in collisions and allow new styling freedom. It will also simplify production of left- and right-hand models. It is natural to add advanced functions to such electronic systems. For example, consider systems that reduce steering-wheel feedback to the driver. In mechanical steering systems, the driver actually feels the vehicle losing control in unstable conditions and can react appropriately. These self diagnosing and configurable systems adapt easily to different vehicle platforms and make the diagnosis easier” (Len & Hefferman, 2001, p.90).
Figure 1 represents the future topology of embedded networks inside luxury cars. We can notice the different multiplexed networks which may need gateways to communicate between different application domains.
Figure 1. Network vehicle architecture (source: Automotive Systems Research Group, 2008)
Considering these large number of distributed ECUs, it makes the automotive system complex in many ways. Several different networks are used to address the different levels of communications requirements, including safety-critical, and fault-tolerant. High bandwidth becomes necessary to interconnect these systems with predictability. This last issue is a great challenge for car manufacturers. To reduce this complexity, without reducing safety, it is desirable to commit to a limited set of networks. However, it is not in the near future that the number of networks can be reduced to only one or two as such technology would provide the properties supporting the most demanding automotive systems. It would probably make it too expensive. Hence, it is more likely that a few network technologies will be used while providing timeliness and fault tolerance.
The next section gives an overview of networks used today in the automotives, identifying their strengths and possible drawbacks.
TopEvolution Of Automotive Networking Technology
The purpose of this section is to give a description of the most representative networks for different main domain of application. We will focus on the three most common vehicle networks, namely LIN, CAN and Flexray. These embedded networks have both increased the functionality and decreased the amount of wires. However, the usage of different wires for the different networks still has the disadvantage of heavy, complex and expensive.