Electronic Design

Fault Tolerant Networks Are Critical For Drive-By-Wire Control In Cars

New x-by-wire systems (steer-by-wire and brake-by-wire) being developed by vehicle manufacturers and their suppliers require fault tolerance. There's no fail-safe state to which these systems can default, unlike the anti-lock braking system (ABS), for example. In ABS, a fail-safe default is to not intervene in the braking as initiated by the driver. Automotive fault-tolerant systems must be functional under all possible fault conditions.

One of the subsystems that needs built-in fault tolerance is the communication network. Unfortunately, today's in-vehicle networks don't meet this requirement. The body and comfort modules are connected to a CAN bus, which is complemented by the LIN bus for control of peripheral devices.

Higher-speed vehicle control systems such as powertrain and transmission controls are networked today using CAN and J1850. Even though two-wire CAN continues to be functional even if one of its wires is cut or shorted to ground or the battery, the timing behavior of a CAN bus can become unpredictable under such fault conditions. A new protocol is needed to overcome these shortcomings.

Although there are major technical challenges to developing such a fault-tolerant automotive network protocol, they pale in comparison to getting overall acceptance of a common standard. But it can be done, as the CAN bus exemplifies.

The more users that a protocol has, the higher the benefit to its users—better tool support, more components to select from, lower cost due to higher production volume, and more cycles of learning. Economists call this effect "network externalities." Key to setting a standard is having the technical elements, including the specifications, products, tools available, and public commitment by a sufficient number of industry partners to achieve critical mass. Once past this hurdle, network externalities will make the standard a self-runner.

Motorola is currently backing two emerging open standards for in-vehicle networking—FlexRay for highly dependable automotive networks, and LIN for automotive body electronics. Providing silicon that supports these standards and publicly demonstrating a commitment toward them will shorten the time that it takes to achieve widespread market adoption. Motorola has teamed up with BMW, DaimlerChrysler, and Philips to drive the FlexRay standard. This will encourage the industry to a standard early on, avoiding years of supporting multiple networking protocols.

Active standards and protocol development include LIN, AMIC, MOST, CAN, OSEK, FlexRay, Bluetooth, IDB, 42V, Byteflight, Linux, Java, and DSI for connecting the new waves of electronics to the vehicle. By working closely together with vehicle manufacturers and subsuppliers, hardware and software can be developed early on to optimize and verify specifications.

TAGS: Automotive
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