PARK RIDGE, Ill. Four of the biggest names in the automotive industry announced this past week that they will form a consortium to back development of a safety-critical bus standard that will compete with a separate effort recently backed by German carmaker Audi AG.
BMW, DaimlerChrysler, Motorola and Philips Semiconductors will standardize the design of an advanced automotive communication system, to be called FlexRay, that will support a time-triggered network architecture. With their move, the FlexRay proponents effectively rejected the Time-Triggered Protocol (TTP), recently backed by Audi for safety-critical systems. The companies had engaged in research on TTP.
"That Audi announcement was disappointing; it does muddy the water," said Jim Trent, operations manager for Motorola's Advanced Vehicle Systems Group. "Our goal was to make FlexRay a number-one industry standard, and it still is our goal. So we need to work with Audi a little bit."
Indeed, both sides spoke of the need for a unified standard. A time-triggering architecture is considered key to reliable operation of such safety-critical systems as drive-by-wire, adaptive cruise control, collision avoidance and active suspension. "The automotive market needs a bus that will allow all those systems to play together," said Trent. "We need a high-end protocol for chassis applications, particularly steering and braking, and we want it to be accepted by the whole community."
"We are having some discussions with Audi, and GM General Motors has talked to the consortium as well," said Anton Schwab, manager of electronic engineering for body, chassis, powertrain and safety for BMW and a member of the consortium. Schwab said he is not aware of any discussions with Ford.
Walter Streit, senior engineer responsible for bus systems and airbags at Audi, confirmed that his company will give FlexRay an airing. "We spoke to them, and our target is to have one standard. We have some dates to see what FlexRay can do. At the moment we have opened the door so that the different parties can come together."
Streit added, however, that "TTP meets our requirements. We will see what FlexRay has to offer, but our first priority is the safety of our customers." He said that Audi will not use multiple safety buses in its vehicles; the company believes "there has to be one standard."
TTP was developed at the Technical University of Vienna and is licensed by TTTech AG (Vienna, Austria) and promoted through the TTP Forum. The FlexRay consortium has established a Web site at www.flexray-group.com.
Automakers have been pushing harder for the development of a safety-critical bus for the past two years because of the looming prospect of drive-by-wire systems, which include steer-by-wire, brake-by-wire, and throttle-by-wire. Such systems let automakers eliminate heavy mechanical linkages, and they offer the possibility of creating smarter, more efficient components that can be connected to a network bus.
Automakers and electronics vendors know, however, that a reliable, fault-tolerant bus is needed for such applications. Controller area network (CAN) buses, which are typically used for powertrain and other automotive controls, are not considered reliable enough for drive-by-wire.
"The issue with CAN is that it is only event-based, so there is always the possibility that a message won't get through," said Paul Hansen, publisher of The Hansen Report on Automotive Electronics. "For important applications, you need time-triggered architectures because as time rolls along, you always have a slot for important messages."
Engineers say CAN also lacks the speed needed for safety-critical applications. "CAN tops out at 1 Mbit/second, and that's not good enough to handle the expected data rates of upcoming systems based on drive-by-wire," said Brian Brewster, strategic marketing manager for Philips' automotive business line (Eindhoven, Netherlands).
Time-triggered architectures are fault-tolerant, enabling the electrical bus and controllers to continue operating in the presence of a failed sensor, short-circuit, transient software glitch or other problem. That keeps safety-critical systems up and running.
FlexRay is said to offer the fault tolerance and determinism needed for safety-critical applications, and it provides higher speed than CAN buses. Based in part on the Byteflight system, FlexRay owes its determinism to an architecture that uses flexible time-division media-access (FTDMA) time slots for data. The system targets a maximum of 64 nodes and operates at data rates up to 10 Mbits/second. It also employs an independent bus guardian, which eliminates the potential of the "babbling idiot mode," in which a faulty sensor transmits a stream of meaningless data and locks up the controller.
Development of the FlexRay protocol is being driven by BMW and DaimlerChrysler; Motorola and Philips are implementing the design in silicon.
Philips, which is responsible for the physical layer, will make the transceiver module, which will comprise the transmitter, receiver and bus guardian. The group said the module will be the first in the automotive industry capable of supporting a data rate of 5 Mbits/s or higher.
Motorola, for its part, will design the datalink controller and processor for the system.
Members of the consortium say the FlexRay technology will sample by 2002 or 2003.
Motorola's Trent said FlexRay combines some of the best features of TTP and ByteFlight. "From the dynamic point of view, it's very similar to ByteFlight, which is event-driven," he said. "But like TTP, it also has time slots, and that's the part that makes it fail-safe."
One key area in which TTP and FlexRay diverge is speed. TTP typically runs at 2 Mbits/s over copper wire; FlexRay runs at up to 10 Mbits/s.
But TTTech may be on the verge of shifting that spec in TTP's favor. The company last week said it developed TTP chips with Austria Mikro Systeme International AG that will run at up to 25 Mbits/s.
Another distinction is that TTP has to be licensed from TTTech, and FlexRay is expected to be put into the public domain.
TTTech executives claimed to be unperturbed by Motorola's allegiance to the FlexRay consortium. "Motorola's intention to back FlexRay will not change TTTech's good relationship with Motorola with regard to TTP," said Georg Kopetz, a director of TTTech and the son of TTP developer Hermann Kopetz.
Stefan Poledna, chief executive officer of TTTech, acknowledged that, "clearly, the solution from DaimlerChrysler and BMW is competition. We will see which will be adopted in volume."
Poledna said TTTech had not had an opportunity to determine whether FlexRay infringes any TTTech patents.
Some tier-one automotive vendors say they plan to be ready no matter which technology emerges as a standard. Delphi Automotive Systems, for example, is developing by-wire systems that could be used in conjunction with TTP or FlexRay.
"Right now, there's not a standard, so we know we need to understand both," said Brian Murray, manager of systems safety engineering for Delphi Steering Systems (Saginaw, Mich). "We think there's going to be a convergence . . . into a single standard. "But until that happens, we need to be ready to support both."
Additional reporting by Patrick Mannion.