Tests shedding light on ABS warning systems

by Tom Berg

This winter’s road testing of as many as 100 combination vehicles with the sometimes-controversial PLC4Trucks integrated circuit chip should help establish the reliability of the device, which is supposed to activate an in-cab warning light if a trailer’s anti-lock braking system malfunctions.

Winter testing should also calm fleet managers who are worried that the new device is not being tested thoroughly enough and that the industry will miss a federal deadline for the warning light.

The deadline of March 1, 2001 will cause ABS units in trucks running in the U.S. and Canada to incorporate the chip. Canada’s ABS regulations will mirror those in the U.S. by that time, and Canadian winter conditions that are often more severe than those in the south raise the stakes in the importance of the winter tests.

This winter’s evaluation of the devices in commercial trucks constitutes PLC4Trucks’ second season of testing, part of an understanding made when PLC4Trucks got the blessing of organized truck maintenance managers. But some managers wonder if it will be enough, and say they are frustrated that the multi-company PLC4Trucks consortium has not kept them informed of progress.

Meanwhile, engineers have not been able to suppress electrical interference from other on-board trailer devices, and those systems will have to “light the light” on their own (see sidebar).

The testing program and lack of information on it worries Jim Salas, a director of The Maintenance Council of the American Trucking Associations, which approved PLC4Trucks in June 1998.

“I have a little concern about the way it is going,” said Salas, who is manager of specifications and applications engineering at Ryder Transportation Services. “When we at TMC initially signed up for PLC4Trucks, it was with the understanding that we would have a two-winter, two-season exposure period in testing of the equipment. In fact, the PLC consortium has had some problems getting vehicles into road testing.”

Also, TMC directors didn’t get their first update on PLC4Trucks’ progress until Oct. 14, via a conference call with Paul Menig of Freightliner Corp., the consortium’s leader, during a board of directors meeting. They asked him to brief TMC members at each of the group’s meetings, starting at its annual meeting next March in Nashville, Tenn. Menig said he would.

“We as a fleet – we at Ryder – are real concerned about this,” Salas continued. “If PLC doesn’t get it done, that would give the federal government an out, which is, (requiring us to) put on a separate cable. We want to avoid that.”

The PLC4Trucks device will let motor carriers meet an upcoming requirement for the in-cab trailer ABS warning light by sending a coded signal over the existing connector cable between trailer and tractor. Fleet managers consider this “multiplexing” crucial because they do not want the expense of a second cable that would otherwise be needed.

Although several competing devices could also multiplex the cable and send the warning signal, the mostly unproven PLC4Trucks won the industry’s acceptance because it is a “generic” method that would avoid possible licensing fees. It also less costly than the other devices, Menig asserted.

On the winter testing issue, Menig said last season’s efforts included “a handful of ABS units at the test tracks of OEMs,” using prototypes. TMC members may have believed that commercial trucks would be tested last winter as well, but “that was a misunderstanding,” he said, “and that was my fault.”

Two hundred ABS units, with one unit on each tractor and trailer, is Menig’s goal for testing this winter. This equates to 50 tractor-trailers or fewer double- and triple-trailer combinations. But meaningful testing requires rigs to stay together; less-than-truckload carriers break up their doubles and triples constantly, so Menig hopes to get fleets run by retail stores to try to keep sets of tractors and trailers together for a test.

Many more ABS units with the PLC4Trucks chip will be fielded throughout the coming year, Menig said. Thus any problems induced by real-world operations in cold temperatures, snow, ice and salt spray should be uncovered.

But Rick Romer, engineering manager at Meritor Wabco Vehicle Control Systems, which makes ABS equipment, doubts that much will be learned. He wonders how many tractors and trailers with the equipment will stay hitched together so actual results will be recorded.

And most ABS units to be tested this winter will have temporary “daughter boards,” which include the circuitry for the warning light, not production units with integrated circuitry, he said.

The existing J560 trailer-to-tractor cable is still “the weak link,” Romer thinks. But he noted that cable makers have improved their products so they’ll be better able to carry out the additional duties, and fleet managers seem willing to pay more for them.

Meritor Wabco will, like other ABS suppliers, participate in the test and will continue laboratory testing involving vibration, extreme temperatures and other factors, so the equipment’s reliability can be established.

And PLC4Trucks is likely to become a standard of the Society of Automotive Engineers, said Romer, who heads an SAE task force dealing with power line carrier communications. Language has been drafted and the standard, given the designation J2497, will go out to SAE members for voting in February. n

Signal interference problem sidestepped

Although engineers have been trying for more than a year to eliminate electrical interference from other trailer-mounted devices, PLC4 Trucks’ critical warning signal continues to be “stepped on”, and the problem may not be solvable with current equipment. So makers of those products may have to provide their own ABS warning signal.

Trailer accessories like on-board scales, lift gates and interior dome lights use the auxiliary circuit of the seven-wire cable connecting the trailer with the tractor. Paul Menig, the Freightliner engineer who heads the multi-company PLC4Trucks consortium, said externally wired “notch filters” appear ineffective in separating signals from on-board scales and other devices.

Letting the trailer accessory furnish its own ABS signal appears “workable” to Martin Ambrose, president and CEO of Air Weigh. His company’s signaling system, which is also used by Hendrickson Suspension, is one of those competing technologies that lost out to PLC4Trucks. So Air Weigh is entirely capable of sending a trailer ABS malfunction signal to the tractor. On such vehicles, the PLC4Trucks chip would not have to be installed in ABS controllers.

The recommendation was initially made by Menig at a meeting between TMA members and ABS manufacturers at the SAE Truck and Bus meeting, and reiterated during a Nov. 30 teleconference. n

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