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Steady as she goes

TORONTO, Ont. - Stability systems are becoming a standard spec' on many types of trucks and there's pressure to legislate their use in some jurisdictions, including here in Canada. But Praxair Canada ...


TORONTO, Ont. –Stability systems are becoming a standard spec’ on many types of trucks and there’s pressure to legislate their use in some jurisdictions, including here in Canada. But Praxair Canada is one fleet that’s not waiting for government intervention. A brutal rollover in B. C. that claimed the life of one of its drivers was all the motivation the fleet needed to begin spec’ing stability systems on all new tractors and trailers.

The tanker fleet began tracking its rollovers in 2000 and noticed an increase over the next several years. Praxair’s tankers have a rollover threshold of just 0.23 Gs. That compares to a relatively high threshold of 1.3 G for passenger vehicles. A rollover typically costs Praxair between $125,000-$150,000. Even worse, there’s a high probability of a fatality when a rollover occurs.

In North America, Praxair now has 520 tractors and 125 trailers equipped with stability systems. In Canada, the number of rollovers experienced by Praxair has dropped from 45 in 2004 to only three in the first quarter of 07.The good news for drivers is that the systems have worked as advertised, and have dramatically reduced the number of rollovers. But have the systems created new headaches in the shop?

Not according to Praxair’s Tracy MacDonald, who insists that no additional maintenance has been required, except the need to recalibrate the sensors after a vehicle realignment.

There are several types of stability systems available. Tractor Roll Stability Systems (RSS) are useful in preventing rollovers, but don’t protect against a jackknife or other loss of control situations, explained Tom Weed, engineering supervisor, ESP and future systems with Bendix. Electronic Stability Programs (ESP) include additional sensors such as a steer angle sensor and yaw sensor which provide the added functionality of protecting against jackknifing and other slip-and-slide scenarios. Then there are trailer stability systems, which are fully-compatible with both types of tractor stability systems and are also effective on their own.

In an ideal world, every tractor-trailer combination would have both a tractor stability system and one on the trailer, MacDonald said.

The biggest responsibility for the technician who maintains this equipment, is to ensure the wiring is correct. Wires should be attached to hoses using approved clamps, not tie-wraps, noted Dave Engelbert, chief engineer, braking controls division with Haldex.

“Tie-wraps will cause you problems down the road,” he pointed out, explaining that they don’t allow enough room for the hoses to expand.

Recalibrating the sensors is simple, if you have the software provided by the manufacturer of the stability system you’re using, explained Weed. To calibrate the steer angle sensor of an ESP system, for instance, you just point the wheels straight ahead and click ‘Calibrate’ on your laptop.

Technicians are warned against swapping ECUs between trucks.

“With stability systems, you’re not able to swap ECUs from one vehicle to another,”Weed explained. “That’s because the ECU is tuned for that particular vehicle. Also, some ECUs are programmed with the VIN inside the ECU and if the VIN doesn’t match the VIN from the engine, the ECU will send a fault.”

Trailer stability systems are the only ones that can be retrofitted at this time. Tractor stability systems must be installed by the OEM. Trailer systems use the trailer’s existing ABS architecture, Engelbert explained. Additional components include: a lateral accelerometer; a brake apply; a port to connect to the air bags; and five pressure transducers. Haldex’s trailer stability system works with both air and spring suspensions.

While maintenance of a trailer stability system is fairly simple, Engelbert warned that a good understanding of ABS is required.

“If you haven’t gotten your head around ABS, you’re probably not ready for trailer roll stability,” he said, noting the ABS platform is the backbone of the trailer stability system. Other maintenance requirements involve lightly greasing connections and also taking care of the gladhands when they’re not in use. Oh, and don’t be dumping alcohol into those gladhands in the winter, he added.

Matthew Williams, manager fleet sales and service with Meritor Wabco, added that while a little grease is good, a lot of grease isn’t necessarily better.

When a truck equipped with a stability system is started up, a lamp on the dash should light up momentarily before turning back off. If it remains on, the system needs to be serviced, Williams explained. If the stability system suffers a failure, the ABS will continue to function. Troubleshooting a stability system is similar to troubleshooting ABS – blink codes are used to communicate a problem. As long as the technician is competent in working with ABS systems, stability systems should not pose a problem, the panel agreed. But Williams did warn that a technician should be equally well-versed in tractor and trailer maintenance.


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