Are Fleets Ready For Trailer ABS?

Feb. 1, 1998
With the NHTSA deadline only weeks away, some OEMs and operators have still not fully factored trailer ABS into their plansThe March 1, 1998, deadline for NHTSA's trailer-ABS mandate is not expected to be met as smoothly as last year's tractor ABS deadline. This is troublesome because the second phase of the mandate will impact more pieces of equipment than the tractor part.The mandate -- which will

With the NHTSA deadline only weeks away, some OEMs and operators have still not fully factored trailer ABS into their plans

The March 1, 1998, deadline for NHTSA's trailer-ABS mandate is not expected to be met as smoothly as last year's tractor ABS deadline. This is troublesome because the second phase of the mandate will impact more pieces of equipment than the tractor part.

The mandate -- which will increase safety by preventing hazardous trailer swings that result from trailer brake lockups -- calls for a minimum requirement of a two-sensor/one-module configuration (2S/1M) on trailers and dollies. More sensing and modulation are available at a higher cost, however. In addition to preventing lockups, top-end 4S/2M and 4S/4M systems can eliminate tire flatspotting on tandem axles and provide economical performance for multi-axle applications.

In spite of these benefits, however, fleet interest in trailer ABS is not nearly as strong as that generated by tractor ABS when it first came on the market. Many operators, in fact, haven't even factored ABS into their trailer buying decisions. Trailer makers report that only 5-6% of new trailers coming off the lines are equipped with ABS.

Reactions to trailer ABS range from a total misunderstanding of powering basics by fleets whose businesses depend on the workings of electrical accessories aboard trailers to outright ambivalence by even some of the more savvy carriers.

Some of the same fleet managers who were enthusiastic about tractor ABS are ignoring its counterpart for the trailer, which may turn out to be a shortsighted approach. Drivers often prefer trailer ABS to tractor ABS because it compensates for the lack of trailer "brake feel." While a good driver can sense the reaction of a non-ABS tractor when the service brakes are tapped, the same does not hold true for trailers. If the brakes lock up on a non-ABS trailer and the vehicle begins to swing, the driver has only seconds to respond. By the time he realizes what is happening, it's often impossible to correct the situation.

In addition, some vocational operators still believe that their needs for auxiliary trailer power will continue to be met through the J560 connector. The J560 will not be a feasible source of such power in many instances, however. In fact, the ABS regulation mandates ignition-switched constant power. Supplying this power through the auxiliary circuit of the J560 connector is part of a "convention" that was agreed to by OEMs and fleets with the help of The Maintenance Council of ATA as a way of meeting the ABS regulation with minimal or no change to the J560 coupler.

Unfortunately, more than a few fleets will be unable to follow the convention. While operators can pull auxiliary power from the ABS power supply when trailers are parked, the ability to tap this source for auxiliary power when trailers are moving is very limited. In reality, some of the fleets that depend on trailer accessories when rigs are moving will need a second (modified ISO 3731) electrical connector to supply the power.

Determination of fleet needs for auxiliary power must be made in advance with help from suppliers. For example, some fleets currently use pin 7 to power something that must be switched "off" from the cab during vehicle operation. If pin 7 is to carry a signal to turn on trailer backup lamps, the ABS convention cannot be followed without either making a change to something other than pin 7 as the constant power source, or changing the ancillary equipment's power source to something other than pin 7.

Carriers must also understand that if they elect to use a second electrical connector for ABS purposes, it doubles the total number of inter-vehicle cables on a tractor semi-trailer to two; a set of doubles goes from two or three to six; and a set of triples goes from three or five to ten.

Another disturbing fact is that, unlike tractor OEMs, the level of competency for ABS installation is not uniform among trailer makers. The biggest trailer makers, which manufacture the majority of standard van and platform trailers, are clearly prepared to make high-quality ABS installations.

But the same cannot be said about the smallest members of the trailer-OEM community. There are hundreds of smaller trailer makers that produce relatively large numbers of non-standardized specialty trailers, many of which contain auxiliary equipment that is powered by electricity. It seems that some of these builders are not devoting engineering effort to ABS matters. This is evident from trailer-ABS suppliers' anecdotal reports about smaller trailer makers that are still negotiating over ABS prices. If trailer makers have not yet settled on price, they probably haven't gotten around to engineering the systems into their vehicles.

In contrast, tractor makers found they had no choice but to apply engineering resources in advance of the mandate deadline to assure top-quality ABS installations. This ensures that the systems work when new vehicles leave the plant, as well as continue to function in a trouble-free manner as vehicles put on the miles. For example, tractor OEMs found that unless properly routed, ABS leads can snag on moving undercarriage parts and be torn away, and connectors can fail months after vehicles enter service.

Tractor makers ensure ABS is working by performing dynamometer tests of new vehicles. While new trailers could be mated to yard tractors and hauled around to perform brake tests, this would be a cumbersome ABS-testing procedure in high-production facilities.

Consequently, as the larger trailer makers ramp up for quantity production of ABS-equipped trailers, they will be testing ABS as soon as new undercarriage assemblies come off the bogie line. Power supplies will be hooked up to energize the ABS, verifying that the requisite 9.5-14V DC is being supplied to ECUs. As part of the ABS electrical hardware/installation test, trailer makers will raise finished trailers off the ground and spin the wheels to be sure that the ABS warning lamp and ECU blink-code systems operate correctly, although it's also possible to use diagnostic tools to check ABS functionality.

To help gain the highest percentage of successful installations, the Truck Trailer Manufacturers Assn. (TTMA) and ABS suppliers have taken some pre-emptive steps.

TTMA established a performance requirement for supplying at least 9V at the trailer ABS ECU (Recommended Practice No. 97-97, released October 10, 1997). According to ABS makers, a minimum of 8.5V is needed to fire off the systems. The RP also sets the standard for electrical pin-out assignments, a five-conductor connector to join the ABS electronic control unit and the trailer wiring harness.

Under the new RP, Packard Electrical Systems' Weather Pack 15324197 will be used on all makes of trailer ABS. This ensures uniform hookups for J560 stoplamp power, the J560 antilock lamp, modified ISO 3731 trailer ABS malfunction signal to tractor (optional), trailer-mounted ABS malfunction lamp, and J560 ground. ABS wiring is standardized for simplified hookups in much the same way that bogie assemblies are prewired and preplumbed.

In anticipation of the trailer-ABS deadline, suppliers have made a number of technical modifications to ECUs to meet NHTSA regulations, including a change in lamp sequencing. During initial power-up, the trailer warning lamp had originally remained on until the trailer was moved. Now, the light flashes on and off as part of a diagnostic check. There is also a new circuit to suppress the trailer-mounted lamp when the stop lamp is powered.

In addition, TTMA wanted high-side-driven lamp commonality. This meant additional system changes, such as positive power from the ECU for the high-mounted trailer side ABS lamp; and a ground signal from the trailer ABS ECU via the 7-way connector for the low-side-driven in-cab ABS warning lamp.

In an effort to simplify installation, especially for the smaller trailer makers, ABS suppliers have reduced the number of parts and made the systems self-configuring. Meritor WABCO, for example, has reduced the number of parts on its Easy Stop 2100 Basic and Easy Stop 4300 units. And in a move to reduce overall cost and maintenance, the 4300 now needs only a single ECU, rather than two.

According to Denny Sandberg, director of electrical products for Meritor WABCO, installation has also been simplified because the ECUs in the Meritor systems are shipped preconfigured for 2S/1M installation and automatically reconfigure to the type of system that is specified.

AlliedSignal Truck Brake Systems has long touted the benefits of a highly responsive two-sensor, one-modulator approach to trailer ABS. Jim McClelland, managing director, electronic control systems, explains that the company's system is basically that -- and not a more complex system adapted to 2S/1M application.

The AlliedSignal/Bendix system has simplified components and self-contained LED diagnostics. The trailer modulator/controller contains a digital microprocessor-based ECU, as well as solenoid and standard R-12 relay valves to maintain brake balance, timing, and response.

For the first quarter of 1998, McClelland notes, the Bendix system will have a self-draining function built into the ABS modulator. "Any moisture that condenses or is poured into the trailer service gladhand will automatically be drained from the relay valve."

Midland-Grau's 2S/1M single-valve product, dubbed Mod-1 FFABS (Modular 1, Full Function ABS), provides service- and spring-brake control, as well as antilock functions. It is programmed with SLH (Select Low High) algorithms that are said to provide stopping distance performance comparable to costlier 2S/2M systems, but without additional valving or wiring. The design permits "drop in" installation, is available in either service-brake or parking-brake priorities, and can be expanded for full-trailer or application-specific requirements.

According to Duane Stocksdale, Midland-Grau's OEM market product group manager, the company is using plastic overmolding on all connectors to prevent water from getting in and causing wiring problems. "The system is made with variable-length sensor leads to facilitate application changes with minimum changes to the product itself," says Stocksdale. "This feature also minimizes potential reliability issues related to wheel wash, where sensor connections are near the wheel ends."

Eaton Truck Components Operations-Americas recently began marketing the Bosch A-18 trailer antilock brake. A two- or four-port valve option makes the A-18 a totally self-configuring system. It can be set up as 2S/1M, 2S/2M, or 4S/2M. Modular design permits easy removal of the ECU in the event of a valve failure, allowing the substantially more expensive ECU to be reused.

The A-18 features a new diagnostic plug that mounts on the side of the trailer. Troubleshooting can be initiated by inserting a screwdriver or coin into the diagnostic plug slot. However, fleets can also use the MPSI Pro-Link 9000 hand-held tool or a PC-based system for troubleshooting, explains Evan Hughes, ABS market development manager.

But even with all this system work, installation problems can still lead to trouble codes or improper functioning of trailer ABS. If this happens, fleets should contact their ABS suppliers promptly for corrective action.

At its spring meeting in Nashville, The Maintenance Council's trailer, and body and chassis study groups will take a joint look at the situation. A technical session on trailer ABS will demonstrate how mixed systems in tractor-trailer units can be diagnosed in the event of malfunctions. TMC will use the opportunity to take a closer look at installation techniques for the different makes of trailer antilock being installed.

This concern is right on target. It's clear that some trailer makers and fleets have underestimated the impact this aspect of NHTSA's antilock mandate will have on trailer production and operations.

Nearly one year ago, NHTSA's mandate that all new tractors be equipped with ABS went into effect. Since March 1, 1997, tractor OEMs have installed ABS on about 150,000 heavy-duty tractors. The impact of this equipment change cannot be underestimated: As the population of tractors with antilock brakes increases, it's expected that tractor jackknifing due to overbraking will decrease. In contrast to the situation facing the industry as the trailer-ABS deadline nears, the deadline for Phase One of NHTSA's antilock mandate came and went without a ripple.

What accounts for the difference? Most would agree that the level of advance planning by ABS manufacturers, fleets, and tractor OEMs is the primary reason the tractor ABS mandate was implemented so seamlessly.

ABS makers applied RF- and EMR-proof electronics to the new-generation systems, allowing ABS valves to respond rapidly and accurately to signals from the wheel sensors. The new controls not only eliminated the unreliability that had plagued the old analog ABS, but conserved air pressure.

In the late 1980s, far-sighted carriers embraced the improved technology. Intrigued by the ability of tractor ABS to help drivers maintain vehicle stability during hard-braking conditions, they spec'd it into new units. Word spread that tractor ABS really worked, enabling drivers to turn potential accidents into close calls. At the same time, shop personnel began to feel comfortable diagnosing and servicing the electronic systems.

Confidence in tractor ABS was boosted by NHTSA's two-year, 40-million-mile reliability evaluation in the early 1990s, which demonstrated that Bendix, Bosch, Midland-Grau, and Meritor WABCO antilocks were economical to maintain. The evaluation's final report persuaded many fence-sitters to heed the agency's recommendation to voluntarily spec ABS on 10% of their new power. By the time the implementation date of the tractor-ABS mandate was announced in 1996, ABS prebuying was on the rise.

Perhaps the most crucial part of tractor-ABS planning was the accumulation of installation expertise. Freightliner Corp. was certainly out front in promoting and installing ABS, but all eight tractor OEMs were diligent in applying engineering resources. They determined how to correctly install these systems in a variety of tractor models in production-line environments.

About the Author

Stewart Siegel

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