NHTSA says, Give us a brake

ON DECEMBER 15, 2005, the National Highway Traffic Safety Administration (NHTSA) published in the Federal Register a Notice of Proposed Rulemaking (NPRM) to amend its air-brake standard to reduce the stopping distance of truck tractors by 20% to 30%.

If NHTSA finalizes the rule in March, as many in the industry anticipate, what will it mean?

ArvinMeritor and Meritor WABCO officials believe that depending on the percent reduction in the final rule — and they think it likely will be 30% — the stopping distance could be achieved by increasing the brake torque on just the steer axle. Larger front drum brakes or air disc brakes could accomplish the requirement for many typical vehicle combinations.

They believe that if stopping-distance reductions can be achieved with steer axle brake upgrade only, tractor trailer compatibility should not be impacted.

Paul Johnston, senior director of compression and braking systems for Meritor Wabco, expects to see changes in the front-axle steering and suspension as well as the ABS in order to implement either drum or disc brake solutions to meet more aggressive stopping distance reductions (30%). He says a more aggressive reduction in truck-tractor stopping distances may result in more attention to the trailer brake requirements.

NHTSA has requested additional comments regarding revisions to dynamometer test procedures and requirements that could possibly impact trailer brakes sometime after the new rule takes effect.

“For fleet customers as well as OEM customers, product changes to meet the new regulations will definitely be increasing brake performance, specifically on the steer axles,” he says. “These larger brakes or different brake technologies will have a cost implication to OEMs and fleets. However, there is potential for reducing the cost of ownership by increasing life and minimizing the maintenance costs required with these brakes, with a slight tradeoff of increasing the weights on steer and drive axles.”

Although NHTSA estimated last year that meeting the 30% standard would cost an additional $153 for larger S-cam drum brakes and $1308 for disc brakes, Johnston says it's too early to determine the cost implications because installation costs at the OEM level are “up in the air.”

“We're still working with OEMs on suspension and wheel-end changes,” he says. “We've seen projections (of) anywhere from $300 to $1000 installation-cost increases, but that is all very preliminary. Out in the field, in the area of disc brakes and some of the larger drum brakes, we're clearly seeing first lining life or first pad life in excess of 750,000 miles, which says the ongoing cost of the fleet is going to be relatively zero once we get these larger drum brakes or air disc brakes in the field.”

The background

On March 10, 1995, NHTSA published three final rules as a part of a comprehensive effort to improve the braking ability of medium and heavy vehicles (60 FR 13216 and 60 FR 13287). The major focus of that effort was to improve the directional stability and control of heavy vehicles during braking through ABS requirements. However, the 1995 effort also reinstated stopping-distance requirements for air-braked vehicles, and established different stopping distances for different types of heavy vehicles. Previous stopping-distance requirements for medium and heavy vehicles had been invalidated in 1978 by the United States Court of Appeals for the 9th Circuit because of issues with the reliability of ABS then in use.

The current stopping distance requirements under Federal Motor Vehicle Safety Standard No. 121, Air brake systems, as established under the 1995 final rule, are determined according to vehicle type. Under the loaded-60-mph stopping distance requirements of FMVSS No. 121, air-braked buses must comply with a stopping distance of 280 feet, air-braked single-unit trucks must comply with a stopping distance of 310 feet, and air-braked truck tractors must comply with a stopping distance requirement of 355 feet. Under the unloaded-60-mph stopping distance requirements of FMVSS No. 121, air-braked buses must comply with a stopping distance of 280 feet, and air-braked single-unit trucks and air-braked truck tractors must comply with a stopping distance requirement of 335 feet. Under the emergency brake-60 mph stopping distance requirements of FMVSS No. 121, air-braked buses and air-braked single-unit trucks must comply with a stopping distance of 613 feet, and air-braked truck tractors must comply with a stopping distance requirement of 720 feet.

For heavy truck tractors, the current stopping distance test at GVWR is conducted with the tractor coupled to an un-braked control trailer, with weight placed over the fifthwheel of the tractor, and a 4,500-pound load on the single axle of the trailer. This test method isolates the braking performance of the tractor so that only the performance of the tractor is evaluated. The performance of a tractor in an FMVSS No. 121 stopping distance test does not directly reflect the on-road performance of a tractor semi-trailer combination vehicle that has braking at all wheel positions.

Vehicles are tested at lightly loaded vehicle weight (LLVW). Emergency-brake-system performance is tested with a single failure in the service brake system of a part designed to contain compressed air or brake fluid.

Since the agency established the stability control and stopping-distance requirements for heavy vehicles almost 10 years ago, data indicate that the involvement of large trucks in fatal and injury-producing crashes has slightly declined while vehicle-miles-traveled (VMT) has increased.

However, because the number of registered large trucks has increased, the total number of crashes remains high. In 2002, 434,000 large trucks were involved in traffic crashes in the US; 4542 large trucks were involved in fatal crashes, resulting in 4897 fatalities (11% of all highway fatalities reported in 2002). Seventy-nine percent of the fatalities were occupants of another vehicle, 14% were truck occupants, and 7% were non-occupants.

Industry is supportive

Johnston says that over 35 supporting responses were given to the government before the deadline last April.

“In general, the industry is fully supportive of this move,” he says. “Unfortunately, there was no specific agreement as to magnitude of the reduction, but there was concurrence in the concerns over certain vehicle configurations. The 4×2 tractor has some special stopping-distance challenges, as well as some of the heavy-haul multi-drive and steer-axle vehicles.

“ArvinMeritor and Meritor Wabco fully supported the initiative. We provided specific feedback as to availability that our current technology — both drum and disc brakes — are in place to meet the requirements.”

Joe Kay, manager of engineering systems for the North American braking systems group of ArvinMeritor, says the daily overall performance is not going to change.

“This whole change may go unnoticed to drivers overall,” he says. “We believe we'll be able to maximize life and wear, improve them actually. And we'll try to minimize the cost of ownership overall.

“We'll have more brake torque capability. The capability will be there but the driver will not require it every time he's making a stop.”

He says on a typical 6×4 tractor, the brake performance will be increased by “adding either a high-performance cam brake and going to air disc brakes on front and cam brakes on the drive, or to all-wheel or disc brakes. Anytime we do that, we can gain in total torque. So with these multiple options available, we feel we can cover the regulations going forward with the high-performance brakes and all-wheel disc brakes. All the while, we're going to be balancing the overall system, and that includes the trailer braking. We don't want to upset the vehicle braking. We don't want to upset the balance between the tractor and trailer.”

He says that if the reduction is 30%, the stopping distance then is 249 feet. However, he says all vehicle and brake manufacturers use a 10% compliance margin, so realistically the target will be 224 feet.

He says that to determine the right brakes for fleets, the vehicle OEM will be consulted.

“They have overall ownership on it,” he says. “The brake providers will make sure the vehicle manufacturers have the right information, right data, and right product to supply their customers. There are different ways to go about this: analytical applications such as dynamometer data to run calculations, and there are also vehicle test tracks. ArvinMeritor and Meritor Wabco are working very closely with vehicle manufacturers. There are some additional factors we want to consider. Cost of ownership obviously is a big one for the fleets buying the vehicles — sensitivity to the safety. For example, fuel haulers or other riskier types of carriers might want to consider upgrading brakes to the fullest potential.”

Improved friction materials

Kay says ArvinMeritor and Meritor Wabco are proposing a 16.5×5 front brake, “which will get more efficient braking, which leads to higher output torque for a minimal amount of input torque. We're also looking at improved friction materials to try to optimize how the materials interact with the drum, and how they perform in the field.

“As friction increases in the system, the efficiency drops. This friction is specifically the rollers, cams, bushings, grease, and the whole effect of that system. If we can maintain a higher efficiency — less friction in the system — that will allow us to take the S-cam brake products down a bit further into higher axle ratings.”

Gary Ganaway, director of systems and product strategy for ArvinMeritor, says that braking capability will be “accentuated, so that in panic or emergency stops, the vehicle simply is able to stop in shorter distances. Those systems that are impacted include better brake life, whether we're talking about air disc brakes or larger, higher-performing drum brakes. There are minor concerns about tire wear. Simply saying that, proper alignment suddenly becomes more critical. The other concern is that due to higher braking loads going into tires, they could develop some irregular wear patterns. Another concern is load containment. The vehicle now can brake much more quickly, so the load transfers.”

He says there are two areas of concern with the front axle and suspension.

“With the vertical load, which comes into place as more load is transferred to the front axle, the natural or normal force causes a reaction straight up to the vehicle and perpendicular to the ground,” he says. “And now that we have more brake torque, it exerts torsion on the axle and wants to put it into a twist phenomenon.

“What do we do to mitigate that impact? We're working on a device that acts to absorb forces in the high-stress area. Depending on whether the axle is set forward or back, we can add this material, which acts very much like a cushion. As it comes in contact with the front suspension, it then absorbs a lot of the force that would normally want to twist the axle and suspension. We have designed these devices and they are being evaluated today by OEMs in North America.”

Johnston says NHTSA likely will take a two-tiered approach to enforcing the final rule. Three-axle tractors would have to comply in 2009, and specially configured tractors would have to comply in 2011.

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