Enhanced networking in mobile working machines is clearly seen in a higher number of electronic control units per application and more intelligent sensors and actuators.
Modern passenger cars may contain up to eighty controlling units per vehicle in order to handle the various comfort functions such as height adjustment of seats. Safety-relevant applications as ABS or airbag can be cross-linked via the fieldbus. For applications in passenger cars the focus is set on the flexray fieldbus [www.flexray.com]. Flexray has a transmission rate of 10 Mbit/s, while CAN reaches 1 MBit/s in maximum. Flexray is designed to be used in safety-relevant applications, whereas the standard CAN-protocol is designed for non-safety systems.
What is the advantage of the CAN fieldbus? One point is the current low quantity costs and the second point is the wide choice of microcontroller components. The market offers a large number of microcontrollers with integrated CAN-controllers enabling a perfect adaption to the desired application. In mobile working machines the number of controlling units is significantly less than in passenger cars. Specific components in ASIC design are not profitable. Applications with flexray controllers are currently used in local network solutions and these controllers are expensive.
For safety-critical applications STW uses an extension of the standard CAN protocol, the CANopen Safety Protocol of CAN in Automation (CAN in Automation e.V., CiA 304). STW has adapted this protocol for use in safety-relevant applications up to SIL2 buth with standard CAN devices. The combination of this protocol with the SIL2 hardware ESX® was certified for STW with the acronym ECS (ESX® CAN Safety) protocol. This leaves clear advantages for a CAN fieldbus: low costs and a large variety of CAN components.
