Little did anyone know the kind of products that would be developed as a result of the trucking industry’s move to electronically controlled braking systems. With the addition of a couple more sensors and some additional capability in the system’s computer, suppliers have brought us traction control, an array of electronic stability systems and, most recently, collision avoidance systems.

And now the National Highway Transportation Safety Administration (NHTSA) has announced new, shorter stopping distance regulations will be required for tractors beginning in August 2011. The new requirements do not affect existing vehicles. Only tractors built after the implementation date (or possibly August 2013, depending on the configuration and GVWR of the new tractor) will be required to meet the shorter stopping distances. The vehicle builder is responsible for making sure their products comply with the regulations. While single-trucks, buses and trailers are not included in this rule, ongoing research by NHTSA may impact future stopping distance requirements for air-braked vehicles other than tractors.

The new regulation, fortunately, has been expected by the industry and manufacturers are well prepared with a variety of products. ArvinMeritor, for example, has been working on reduced stopping distance product designs for over three years. As a result, its Q Plus product will meet the new requirements with an additional 10% margin, according to the manufacturer.

Today 15 x 4-in. brakes are common on steer axles. That might become 15 x 5-in. or even 16 ½ x 5-in. Drives may well need no change or possibly go to 16 ½ x 8 5/8-in.; all depending on the vehicle. Severe-duty vehicles may have to go to disc brakes all around.

While larger drum brakes will not necessarily be required to meet the new rule in all cases, moving to larger brakes will provide some advantages, including increased lining volume resulting in longer service intervals, lower operating temperatures, reduced fade and improved performance. Since existing product designs, or modifications of existing designs, will comply with the new regulations, drum brake service practices will see very little change. Technicians will not likely need to be re-trained, and your parts inventory practices will carry over to the new drum brake designs.
With their superior performance, air disc brakes, of course, could be utilized to meet the new regulations at a premium up-front cost. They also come with additional features. Fred Andersky, director of marketing for controls at Bendix Commercial Vehicle Systems, said, “I think of air discs not only in terms of stopping distances, but also in terms of better performance and their maintenance aspects. They provide a lot of potential value to fleets.” NHTSA estimates that the incremental cost for drum brakes on a typical three axle tractor would be $211, whereas the incremental cost to convert to disc brakes at all wheel positions would be $1,475.

Enhanced control
While the hardware portion of brake systems is not expected to undergo any radical changes in the near future, the electronic portion of the systems will quite likely continue to evolve. When NHTSA required the use of antilock braking systems on heavy trucks, design engineers gained control of the activation time of brakes on individual wheel ends. This brought with it the possibility of adding various stability systems since all depend on electronic control of brake actuation. While a number of systems have been introduced, two are currently of major importance, roll stability control (RSC) and electronic stability control (ESC) systems.

RSC systems counteract the tendency of a vehicle to tip over while cornering at high speed. The tires provide a sideways force at the road to turn the vehicle. The inertia of the vehicle, which tends to continue in a straight line, creates an opposing lateral force, effectively acting at the vehicle’s center of gravity. The vehicle will lean away from the curve, and, if the opposing lateral forces are great enough, the vehicle will roll over.

An RSC system automatically intervenes if a high rollover risk is detected while driving. If a rollover threat is occurring, the system tries to minimize the rollover risk by automatically reducing the throttle and if necessary, applying the engine and foundation brakes without action by the driver. RSC systems use drive axle, trailer axle and steer axle braking.
ESC systems address stability problems that result when a vehicle’s heading changes too quickly (spinning out) or not quickly enough (plowing out). With a combination-vehicle, a jackknife is caused by a driver over steering. The loss of traction can be caused by slippery roadway conditions or excessive speed in a curve or lane change. This can cause the tractor and trailer to move along separate paths. While ESC systems cannot increase the available traction, they can maximize the possibility of keeping the vehicle under control and on the road during extreme maneuvers. They do this by monitoring the driver’s natural reaction of steering in the intended direction in over steer and under steer situations, which, if uncorrected, lead to a running off the road, a rollover or a jackknife for combination units.

ESC systems are active systems that automatically take over when there is a high risk of rollover or directional instability. In currently available systems, the ECU constantly compares the vehicle’s actual movement to performance models using the wheel speed sensors, as well as lateral, yaw (rotational) and steering angle sensors. If the vehicle shows a tendency to leave an appropriate travel path, or if critical threshold values are approached, the system will intervene to assist the driver.

 For example, when a potential rollover risk is detected, an ESC system will reduce the throttle and apply the proper brake pressure to slow the vehicle below the rollover risk threshold. When a vehicle slide (over steer or under steer) is detected, the ESC system cuts the throttle and then selectively applies the appropriate individual brakes to produce a counter-force to better align the vehicle with the desirable path of travel.

A third system, designed for installation on trailers, is available that will intervene when a trailer is in danger of rolling over. For fleets that see an immediate need for stability controls in their operation, such a system could present a very cost-effective opportunity to apply stability technology to vehicles already in service, since a retrofit is possible.
According to Robert Sibley, director of trailer products at Meritor WABCO, trailer-based stability control is managed by the braking system’s electronic control unit (ECU), which contains an accelerometer that measures lateral movements of the vehicle. As the trailer rounds a curve or is involved in a sudden steering maneuver, the ECU is continually calculating the trailer’s roll stability threshold based on lateral acceleration and individual wheel speeds. Before a rollover is unavoidable, the system will selectively and automatically apply the trailer’s service brakes, slowing the vehicle to restore control to the driver.

Possible regulations
Late last year NHTSA published a report of a study it conducted to examine the performance of electronic stability control (ESC) systems, and roll stability control (RSC) systems for heavy-truck tractor-semitrailers. The findings of the study indicate that stability control systems provide substantial safety benefits for tractor-semitrailers. Assuming that all existing five-axle tractor-semitrailers operating on U.S. roads were fitted with RSC, the expected annual rollover safety benefit is a reduction of almost 3,500 crashes and over 100 fatalities. Alternatively, assuming that all existing five-axle vehicles were fitted with ESC, the expected annual combined rollover and directional (yaw) instability safety benefit is a reduction of over 4,500 crashes and more than 125 fatalities. ESC addresses both rollover and yaw instability crashes and is more effective in reducing the likelihood of rollover crashes over RSC. Bottom line? The net annual expected benefit for an ESC system was found to be greater than for RSC by NHTSA.

Such findings suggest the possible direction NHTSA might take regarding mandates. Stability systems are already required on new trucks manufactured in Europe, and WABCO just received approval for its trailer system. NHTSA is currently considering regulations relative to stability technology for Class 6, 7, and 8 air-braked combination vehicles. U.S. manufacturers are expecting to see NHTSA publish a Notice of Proposed Rule Making on the topic sometime yet this year.

In the market?
Currently, Bendix manufactured stability systems are standard fare, without the option of deletion, on all Volvo and Mack trucks. Other truck OEMs offer stability systems supplied by either Bendix or Meritor WABCO as options that can be deleted for credit.

SmartTrac, the name given to the family of stability control systems offered by Meritor WABCO, is comprised of three distinct products. Its Roll Stability Control system provides rollover protection with relatively few components and minimum maintenance requirements at an affordable price. It continually monitors conditions that can lead to a rollover and can automatically de-throttle the engine and apply the engine brake, as well as both drive and trailer axle foundation brakes, to reduce tractor-trailer speed when lateral acceleration limits are about to be exceeded.

The company’s full stability offering, which it calls Electronic Stability Control, combines Roll Stability Control with the added capability of yaw or rotational control. The system can reduce the risk of vehicle instability in a slippery curve or while taking an evasive action, preventing jackknife and drift-out conditions through select braking of the tractor and application of the trailer brakes. If loss of stability is detected, tractor-trailer speed is reduced through automatic engine control and application of the engine brake, tractor and trailer foundation brakes.

RSSplus is Meritor WABCO’s trailer-only system that integrates with the trailer’s anti-lock braking system and calculates the trailer’s roll stability threshold based on load and measures actual lateral acceleration and individual wheel speeds. If conditions indicate that a rollover may occur, the system automatically reduces engine torque and engages the engine retarder while automatically applying drive axle and trailer brakes. The product is designed for retrofitting in a fleet shop.
Alan Korn, director of vehicle dynamics and control at Meritor WABCO, said, “While it’s difficult to retrofit a tractor-based system, it’s much easier to do it on a trailer-based system. We have a retrofit program that’s up and running right now. A number of trailer repair facilities are currently trained and set up around the country, and we are currently looking to expand to other locations. The Roll Stability Support system is compatible with both spring and air suspensions.”
Bendix ESP technology is a full stability system, offering both roll and yaw stability to help provide loss of control and rollover mitigation. This ABS-based truck stability system is capable of recognizing and assisting in under steer and over steer loss-of-control driving events, as well as in loss of traction situations.

The Bendix TABS-6 Advanced system is the supplier’s trailer stability system. It’s a solution that delivers rollover mitigation in a simple package. This system will intervene automatically when detecting conditions that may lead to a trailer rollover—typically before the driver realizes an intervention is needed. The system, a two-sensor/one-modulator configuration, provides quick stability performance and is simple to both install and maintain.

Collision avoidance
Bendix and Meritor have both joined Eaton with collision avoidance products, which are another example of automatic control of the truck’s brake system.

When a truck with the Bendix Wingman ACB is running with cruise control turned on, it will not only maintain the cruise control speed, but also a time-based following distance behind the vehicle it is following. When not in cruise control, the system will provide following distance alerts to warn if following distance between the truck and forward vehicle is closing. The system uses a forward-looking radar sensor mounted to sense the lead vehicle.

OnGuard, the name of Meritor’s system, is a forward-looking, radar-based collision safety system for heavy trucks and tractors. It’s designed to detect objects in a vehicle’s path and automatically control the throttle, engine retarder and service brakes when it senses an impending collision without immediate action from the driver. Unlike passive collision, it initiates braking, helping the driver control the truck and potentially shorten the stopping distance.

Information flow
All of these systems generate information, but for successful implementation require that drivers be told how they operate. They provide data that fleets can use to help tailor driver training programs. Bendix’s Andersky said, “Drivers learn the best way to avoid issues is to drive a bit safer that they might have been. In that way the system will not intervene and no data will be recorded that might come back to bite them.”

Drivers also need to understand that these systems have upper limits. You can over-drive them. Andersky said, “Going into a 25 MPH curve at 55 MPH spells disaster. The system will intervene, but the laws of physics are going to take over.”
While a move to any stability system is a move in the right direction for any trucking operation, fleets must understand that they all depend on the braking system to work properly. Meritor’s Korn said, “All stability system performance is predicated on the fact that we’re going to have good maintenance. They all rely on the brake system generating torque. If your brakes are out of adjustment, the system is never going to perform as good as it could. It’s critical that proper maintenance be performed on foundation brakes, when people reline they use quality linings.”  FE