Trailer builders also agree on technology to meet NHTSA requirement by 2001

It wasn't an easy decision, and they took as long as they possibly could to consider all the angles and ramifications, but truck makers have finally chosen one of four competing and incompatible technologies to provide a federally mandated in-cab warning light for trailer ABS.

Meeting in Chicago last month, the Truck Manufacturers Assn. (TMA) endorsed a technology called PLC4TRUCKS as the industry's solution for providing a warning light system with interoperability across all tractor and trailer makes. The following day, TMA's counterpart among trailer builders, the Truck Trailer Manufacturers Assn. (TTMA), said it would not take a formal position on the ABS light issue. However, individual trailer makers meeting with TMA also agreed on PLC4TRUCKS as the industry's de facto standard. TMA and the trailer makers also agreed on how the signal would be carried from the trailer to the tractor over the standard J560 "7-pin" connector. In addition, both groups said that they expect the first warning light systems to be integrated into trailer and tractor ABS electronic control units (ECUs).

And so, apparently, ends the sometimes fierce debate over how the trucking industry would meet what on the surface seems like a simple rule requiring an in-tractor light that warns drivers of problems with trailer ABS. If all goes according to plan, the integrated circuit chips required for the system will be delivered to ABS manufacturers this fall for winter testing, and revised ABS components will be delivered to trailer makers for testing the following winter. That timetable should give trailer builders just enough time to meet the March 1, 2001, deadline for in-cab warning lights set by the National Highway Traffic Safety Administration (NHTSA).

Initially, NHTSA ordered trailer makers to provide in-cab warning lights by March 1, 1998, when its trailer ABS mandate took effect. However, industry suppliers pointed out that sending a fault signal from the trailer to the tractor was not a simple issue and would require development of new technology, so NHTSA pushed back the deadline to March 1, 2001.

Eventually, four systems from Air-Weigh, Grote Industries, PLC4TRUCKS, and Truck-Lite Co. emerged as competing but incompatible solutions. Fleets, represented by The Maintenance Council of ATA, as well as suppliers realized that everyone would have to agree on just one of those systems to ensure complete interoperability throughout the industry.

PLC4TRUCKS is the work of a consortium of industry suppliers specifically initiated by Freightliner Corp. to develop a solution for the in-cab warning light requirement. Consortium members currently include Meritor-WABCO, Cummins Engine Co., Wabash National, Eaton Corp., Allied Signal, Thermo King Corp., Phillips Industries, Qualcomm, Air-Weigh, Midland-Grau, HighwayMaster, Federal-Mogul, Kysor Medallion, Mack Trucks, and others. Intellon Corp. did the design work for the system and will manufacture the needed chips.

The basic technology behind the system is called power line carrier (PLC), which overlays a communications signal on an existing DC circuit without interfering with power transmission over that circuit. The signal itself is a variation of spread spectrum communications developed by Intellon for PLC. The communications protocol for the PLC4TRUCKS system would be the familiar J1587/J1708, which is the SAE data bus standard currently used on virtually all heavy-duty trucks.

As endorsed by TMA, PLC4TRUCKS would place a chip on the trailer, most likely integrated into the ABS ECU to keep costs low. Any malfunction signal would be transmitted as a J1587 message over the ignition-switched constant power "blue line" in the trailer's wiring harness. That blue line is already the industry standard for powering trailer ABS. A second chip on the tractor would receive the message and instruct the tractor's ABS to light the in-cab warning light.

Although the tractor chip could be integrated into the truck's main ECU, it's more likely that early versions will place it in the tractor's ABS control unit for reasons that illustrate both the initial limitations and future potential of the PLC4TRUCKS approach.

While both the tractor and trailer "speak" the same J1587 protocol, the physical J1708 data bus on the tractor is a twisted-pair network, while the trailer will use a single-wire DC circuit as its data bus. Some type of "bridge" will be necessary to connect the two data busses. If the chip is integrated into the existing tractor ABS control unit, it essentially provides such a bridge, although it would be limited. The tractor ABS would provide a hard wire to trip the in-cab warning light, as well as a twisted-pair data bus connection for capturing diagnostic information transmitted by the trailer ABS.

However, such an ABS-to-ABS system would not provide bi-direction communication over the current 7-pin connector for controlling or even monitoring other trailer accessories and systems. In its basic form, it will not be able to turn on backup lights or other trailer accessories that currently rely on the blue line for switched control from the tractor.

What PLC4TRUCKS does offer is the potential for bi-directional communications with the future development of hardware and software that can bridge the two different data busses, according to Guy Rini, chief engineer for electrical products at Mack Trucks, who also served on the TMA committee that endorsed the system.

"It gives us a platform that meets the minimum (light the light) requirement and allows for future migration that will open up whole new areas on trailers," he says. "As soon as you have communications (between the tractor and trailer), people will want to use it for everything from backup cameras to liftgates."

Developing that expanded system will be the truck makers' responsibility, Rini believes. It will probably involve moving the PLC4TRUCKS chip from the ABS to a separate "black box" or integrating it with the tractor's main ECU. Since J1708/J1587 was originally designed to carry diagnostic messages, the protocol would also have to be modified to handle control messages, which would involve working with an established SAE committee that administers the protocol's standards.

As endorsed by the truck makers, the PLC4TRUCKS solution does have one drawback involving communications over the blue line. Many existing trailers were spec'd with wiring harnesses that omitted the blue line because a fleet had no need for accessory power. In a doubles or triples combination, such a legacy trailer would block transmission of the fault code to the tractor. Dollies, which must also meet the trailer ABS requirements, pose the same problem.

While NHTSA rules seem to allow that legacy trailer exception to the in-cab light requirement, one important industry group, TMC, has issued a formal "recommended practice" that specifically calls for any warning-light system chosen to function with all legacy equipment.

"In the whole matrix of issues we looked at, the legacy issue was the most awkward," says Rini, who is also quite active in TMC. "All the different combinations possible in a doubles or triples configuration present a real mess. We decided that we had to meet the law and hope that TMC will revise its recommended practice, which is still just a proposal at this stage."

As for the three other competing technologies, William A. Leasure, executive director of TMA, says each had its own strengths. "It was a tough decision (choosing PLC4TRUCKS)," he says. "The committee met eight or nine times and really struggled with it."

The Truck-Lite system, called Smart-Lite, is most similar to the PLC4TRUCKS proposal. In fact, it uses an Intellon chip for its spread spectrum power line carrier communications. The major difference is that Truck-Lite chose a communications protocol called CEBus that is not currently used in trucking.

"We feel the CEBus protocol is more robust and less sensitive to (electromagnetic) noise interference than the J1708/1587 protocol," says Brad Van Riper, vp for research and development at Truck-Lite.

Unlike PLC4TRUCKS, Truck-Lite's system has already been field-tested on over 100 vehicles and an expanded bi-directional control communications version has also been run in a demonstration project sponsored by NHTSA, Van Riper points out.

The deciding factor for TMA, however, was SAE's existing standards body for J1587. "That gives us a standing committee to address any changes we might need for message content or structure," says TMC's Leasure. "There is no such body for CEBus."

However, Truck-Lite has applied for a patent for its system, which it believes would cover any system using PLC spread spectrum to communicate between a tractor and trailer, including PLC4TRUCKS. If the patent is granted, Truck-Lite would most likely expect licensing fees from PLC4TRUCKS. However, a spokesperson for Intellon, which supplies Truck-Lite's chip and which will also supply the PLC4TRUCKS chip, says they believe the technology is already in the public domain.

In addition, Truck-Lite's Smart-Plex system could be fitted with the PLC4TRUCKS chip and form the basis for the expanded bi-directional system that many foresee in the near future.

The system developed by Air-Weigh also uses power line carrier communications, but does not use spread spectrum to carry the signal or J1587 as its message protocol. It does, however, provide two-way control communications between a tractor and trailer for a limited number of accessories or sensors.

Air-Weigh's main business is on-board scales, which use the blue line for both power and communicating weight information to the driver. With trailer ABS taking over the blue line, the company needed to come up with a solution to replace it, says CEO Martin Ambros. "We couldn't wait until 2001, so we developed Wire-Link based on the same technology we use on the scale."

Essentially, Wire-Link is a standalone system that will "light the light" and also provide control communications for up to four trailer accessories or sensors, replacing and expanding the blue line capabilities lost to the trailer ABS. It can also operate over a turn-signal or stop-lamp circuit if the blue line isn't available, making it compatible with all legacy trailers.

Hendrickson Vehicle Control Systems, which was looking for a way to add control functions to trailer suspensions, also decided it couldn't wait, and has signed an agreement to market the Air-Weigh system to equipment manufacturers under the name Control-Link.

TMA's concerns with Wire-Link were the relatively narrow bandwidth of its PLC technology compared to spread spectrum, as well as its lack of J1587/J1708 structure.

"We could add the (PLC4TRUCKS) chip to our system for J1587 data, but there are no systems on trailers yet that use that protocol, so why add the cost?" asks Ambros. That might happen in the future, especially if a need develops quickly for the expanded bi-directional communications, but for now, Wire-Link offers immediate accessory control for fleets that need it.

The strength of Grote's system -- and its weakness, in the eyes of TMA -- is its simplicity. Using yet another flavor of PLC, the basic or System 1 version of Grote's Ultra-Plex simply provides an in-cab warning light. Although it could be packaged in a standalone configuration, Ultra-Plex would generally be installed as chips integrated in tractor and trailer ABS ECUs, and by almost all accounts would be the lowest cost proposal. Communicating over the turn-signal circuit, it also sidesteps the problem of legacy trailers without blue lines.

"Our research showed that most fleets were interested in meeting the 2001 light requirement," says marketing manager Dominic Grote. "The fleets told us that two-way communications would be nice, but only if it's free." In fact, the company's research found that less than 5% of existing trailers currently use any form of two-way communications.

As envisioned by Grote, a second phase of Ultra-Plex would add two switchable functions for trailer accessories, while a third phase expands capabilities even further and provides compatibility with both J1587 and the newer J1939 protocol through a special gateway.

While cost makes it attractive, the main drawback to the basic Grote system is that "it's limited because it just lights the light," says TMA's Leasure.

Expanding it to other functions would also be difficult, adds Rini. "It works on the turn-signal wire," he points out. "If you wanted to use it for messaging or control, you'd have to run a turn-signal wire to each component. Using the blue constant power line was the key to our decision."

At presstime, Grote was still evaluating TMA's choice of PLC4TRUCKS and the implications for the future of its Ultra-Plex system. "Grote is a main industry supplier of vehicle lighting and wiring harnesses," says Dominic Grote. "We've said right from the beginning that no matter what system was chosen, we'll be participating in developing the technology."

While good arguments can be made for all four systems, the time for weighing pros and cons has run out. "We don't want to drive the standard one way or another," says Rick Youngblood, ABS market development manager for Eaton's Automation Products Group. "But that 2001 deadline is pretty close, and we have to have a standard if we're going to have universal compatibility -- especially if we're going to bake it into the ABS."

There are no absolute certainties in this world, but TMA's decision, and support for that decision from trailer builders, clearly puts all but irresistible momentum behind the emergence of PLC4TRUCKS as that standard for an in-cab warning light. There are a number of important bridges to be crossed before PLC4TRUCKS also becomes the standard for advanced bi-directional communications between tractors and trailers, but once the basic technology finds its way into every new tractor and trailer, it's hard to see it being displaced by another approach.