Safe At Any Speed
Unlike truck drivers, electronic control braking systems don't degrade in performance as the working day progresses.
STEVE STURGESS
SENIOR EDITOR
For several years now, Europe has enjoyed the benefits of skid control and rollover protection, along with protection from rear-end collisions. That's because a significant proportion of trucks there are electronically braked. Adding electronically controlled selective actuation of individual brakes around the tractor-trailer keeps the vehicle in lane on slippery surfaces, and upright when a combination of aggressive driving and high load might otherwise lead to a rollover.
Now Meritor WABCO has introduced to North America some of these stability benefits -- notably the rollover protection. And it's been done on conventional air braking systems by utilizing the intelligence built into its anti-lock braking controller.
The addition of an accelerometer to the ABS electronic control unit allows the system to detect an impending rollover. Unlike the earlier roll stability adviser introduced by Freightliner several years ago, the new Meritor WABCO Roll Stability Control System intervenes with three levels of braking to prevent a potential rollover.
This new introduction parallels some of the features of the European full electronic controls by cutting fuel and selectively applying first the truck engine brake and then drive-axle and trailer brakes.
At the same time, Meritor WABCO also has introduced a trailer stand-alone system. This is the Roll Stability Support, which senses trailer lateral accelerations and, if it detects an impending roll situation, applies trailer brakes.
These two closely parallel the European roll stability components of both the WABCO and the Knorr-Bremse/Bendix full electronic stability controls currently available as options on European trucks. Those systems, though, have additional features piggybacked on the control system that are enabled by the brake-by-wire electronics.
We were fortunate in having the opportunity to experience the full suite of stability options at the WABCO test center in Hanover, Germany. Following the European truck show there last fall, we saw and drove stability-enhanced Actros heavy trucks with the Mercedes-Benz Telligent braking systems.
Dr. Hartmut Marwitz, head of development for Mercedes-Benz trucks, said the driver is the weak link in the control system of any vehicle. A driver can process information at the rate of around 16 bit/sec where he must make a decision and take action. These speeds are slow in comparison with automatic systems like the new Meritor WABCO RSC and RSS introduction that can take information from sensors around the vehicle, compare with pre-set limits and then respond virtually instantaneously.
Automatic systems also don't degrade in performance through the working day like drivers do. Using these technologies, "allows Mercedes-Benz to reduce the number of accidents through the increase of information velocity," said Marwitz.
The proof was pretty convincing. We had demonstrations of several different technologies set up for driving and riding. One was a lane tracking system, another was full-on stability enhancement for rollover protection. Yet another was interactive cruise control with intelligent braking assistance. In combination, these systems — plus the all-round air disc brakes by Knorr — made the big Mercedes-Benz Actros an amazing piece of machinery.
The trucks were two-axle tractors with tri-axle trailers running super singles on three axles. All wheel positions featured the Knorr SB7 disc brakes.
The power of this braking setup is awesome, especially considering we were dealing with loaded trucks. On one occasion — misunderstanding an instruction — I was about to overshoot the staging area and I got hard on the binders. The deceleration was akin to a big-braked sport sedan's, and it was smooth as silk with absolutely no kickback or pull at the steering wheel.
Out on the test track we ran with the adaptive cruise engaged and an extra feature: the European-option Lane Tracker switched on. Drifting close to the edge marking immediately sounded the warning: a rumble-strip sound in the speaker up in the headliner on whichever side the truck was straying out of lane. It worked every time and it is, for sure, an attention-grabber.
A second truck on the track slowed in front of us and our adaptive cruise control kicked in, slowing the Actros down and matching its speed with the truck ahead, at the pre-set following distance. This was impressive, though not a new experience. A similar system is available in North America from Eaton Vorad. What was different was the leapfrogging of a car into the space between the trucks, causing my following Mercedes to back off. When the car driver then applied the brakes, the Actros followed suit, bringing the truck to a safe stop behind the car.
This automated braking is quite remarkable. In another demo, a small van sat parked on the track with us watching from the sidelines. The demo Actros came steaming in at a cruise-maintained 55 mph with the driver keeping his feet flat on the floor (one of the journalists was riding to observe). At an impossibly close distance, the observer reported, the Telligent braking system took over and performed the emergency stop, pulling up several feet short of the parked vehicle. As we observers noted, the deceleration and nose-down attitude of the Actros tractor caused so much vertical articulation between the tractor and the trailer that it lifted the lead trailer axle about a foot clear of the pavement during the stop.
This is but one feature among a whole suite of the aptly named Telligent braking and stability control system that is standard on the Actros. While we couldn't see it in action, since it requires a low friction surface, Telligent uses inputs from a steering sensor, a transverse acceleration sensor and a yaw rate sensor to tell if a truck is turning according to the driver's instruction. Any deviation from the path leads to individual wheel braking on the tractor and an application of the trailer brakes to correct either an over- or under-steer condition and keep the truck going in the desired direction. Film clips of trucks with the system enabled and disabled show a huge difference in transient maneuvers like a lane change at high speed. Events leading to dangerous instability and roll, jackknife or even a full-vehicle spin are simply eliminated.
The highlight of the day was not only seeing, but also riding in an Actros during a rollover incident. Fortunately the driver was experienced and also had the benefit of big outriggers on the unbaffled tank trailer. Again, the selective braking applied as the sensors warned of an impending rollover, slowed the truck and kept the trailer wheels on the ground. Riding in the truck during the controlled event was uneventful as the system took over. Interestingly, these systems penalize the driver for aggressive driving. The speed after such an interaction is less that it would be if the driver had proceeded at a non-rollover speed.
Testing the same truck with the rollover protection disabled proved interesting. When the combination went into the rollover, the trailer rolled outward onto the outrigger toward the passenger side. Without the outrigger, we'd have gone over -- but I didn't feel it. The lesson here is that a driver will only be aware of a rollover situation way past the point of no return.
With braking compatibility such a major issue in North America because of the huge numbers of older trailers still in service, it is fortunate that Meritor WABCO has introduced this anti-rollover component of the stability systems. With it, drivers can gain much of the safety benefits without the cost and complication of the European-style full ECBS implementation.
