Skid-Control Works, Silly Maneuvers Don't
ESP stability and skid-control test gets a little icy.
Steve Sturgess
Senior Editor
The flat light from the gray sky made the snowfield completely featureless. It was impossible to distinguish between the packed white surface and the snowbanks bulldozed around the edge of the driving course. So, sure enough, while checking out the safety benefits of the Bendix ESP skid-control system, I slammed into the biggest bank. Way in. They had to get the big 6x6 to drag the International 9400 out.
The irony was that we were testing a stability and skid-control system designed to prevent such eventualities. And it does. But it doesn't stop snow-blind trucking journalists from going headfirst into a bank out of plain stupidity.
But there I was, thigh-deep in snow, having my picture taken for posterity in Houghton, Mich., last February. I was there with a group at the Keweenaw Research Center, a vehicle test center way north in the Upper Peninsula, where Bendix and others do their cold-climate testing.
It was Part II of a demonstration of the ESP stability-control system that will start to appear early next year. The first installment was at the Transportation Research Center in East Liberty, Ohio, last summer. There, on high friction surfaces, the engineers allowed us to drive trucks fitted with the stability-control system. The object was to demonstrate the system's rollover avoidance capabilities. This time we were on ice and snow to learn of its low-friction surface benefits: the capacity to maintain tractor-trailer control on incredibly slippery surfaces.
In the first case, we had experienced the ESP system's ability to keep a truck firmly planted on the ground — even when a driver entered a corner too fast, or performed a sudden lane change. At the Houghton track we were driving on a constant 600-foot radius ice circle, doing lane-changes on packed snow and attempting a slalom course on a skating rink. All of these are seemingly impossible, but with the application of appropriate sensors and a few additional valves to a fully featured ABS brake system, the impossible becomes easily achievable.
The ESP System
ESP is Electronic Safety Program and is the extremely elegant stability solution Bendix has designed to suit the North American trucking environment. It is based on the electronic braking system technology developed by Bendix' new parent, Knorr Bremse of Germany. In Europe, full electronically controlled braking systems — ECBS, or brake by wire — have fully taken over on truck tractors. The reasons have nothing to do with performance, but entirely to do with cost and complexity. European air brake systems had become so complex that if you dropped a wrench between the frame rails, it would never hit the ground. ECBS actually saved money.
Over here, the reverse is true. FMVSS121 brake systems are simple, inexpensive and they work. So there's no incentive to swap to ECBS. Unless it would be to pick up the stability control benefits that come from actuating the brakes individually by electronics.
But braking systems over here already have electronics and electronic actuators by virtue of the antilock braking systems (ABS). Why not, reasoned the Bendix engineers, take the best of the Knorr braking system and overlay it on top of an ABS architecture?
And that's exactly what they have done, going straight to a thoroughly workable stability control system that delivers everything a North American truck operator could want from a stability control braking system without the need to redesign the whole thing.
In fact, the ESP system is simple and relatively inexpensive, requiring only five additional sensors, a couple of air valves and a more powerful electronic controller. What's even more clever, they've been able to use the software — the algorithms developed to make the Euro system function so well — and plug them straight into the North American system.
What Is Stability Control?
Simply put, stability control is using sensors on the vehicle to anticipate potential accident situations and respond to them faster than a driver can, using the vehicle brakes to forestall an accident. In a rollover on high-friction surfaces, a lateral acceleration sensor predicts that the cornering force will cause the vehicle to tip, so braking is applied to reduce speed. On low-friction surfaces, the system looks at where the driver wants to turn the truck, it looks at its rotation rate through a yaw sensor, and if it determines the truck is not going where the driver is pointing it, it applies selective braking to the front or rear of individual tractor wheels and to the trailer to get the truck back onto the desired trajectory.
With ABS, the truck has modulator valves in the system that can apply the brakes. With traction control, it has the ability to limit engine power. Put a yaw sensor and lateral accelerometer in a box on the frames rail and a steering angle sensor on the steering column, and you've got all the elements to make stability and skid control happen. Add the more powerful controller and the very complex control software and it's a done deal.
So what does this mean to the driver?
On Thin Ice
The previous report on the system verified that rollover protection works — at least up the the limits of physics. If you are going way too fast, you're going to have the accident, whatever technology is on the truck. And the same applies to driving on ice. But what ESP allows you to do is little short of incredible.
The most amazing demo was the 600-foot circle. We were driving bobtail tractors — more unstable and more difficult to control in low friction circumstances than a tractor-trailer. On the constant circle we drove both with and without the ESP system engaged. With it enabled, I found I could drive the tight circle with the pedal to the metal at around 25 mph with almost no correction at the wheel. And we are talking about driving on polished ice at around 32 degrees F — the most slippery you could imagine. In fact, when getting out of the truck, it was a real challenge not to fall flat on my rear end.
The system takes over throttle, pulling it back as the truck starts to get out of shape, selectively braking the inside rear brakes in an understeer (front end plowing out) and braking the outside front in an oversteer (rear end stepping out).
Trying the same circle without the assistance required extreme care balancing throttle with opposite lock or additional lock, desperately balancing the tractor in a semi-controlled steady state slide. And it was a shade faster than the stability controlled situation. However, bear in mind this was a test track with wide run-off areas. You could never do this — nor want to — on a public highway. There's too much else to hit and there's no predictability where you'll find the traction and where you'll find the ice like there is on a carefully tended winter test track.
On the snowfield, we were trying those fast lane changes, replicating the sort of situation where a car suddenly appears out of a side road and you have to change lanes to avoid it, then get back in lane as soon as possible. With the stability control working, selective braking kept the tractor stable and steerable. Without it, the tractor would make the first lane change, but I had to be really fast to catch the rear end. But with major excursions, the tractor would get far enough out of lane that as it snapped back, there was just too much angular momentum to be able to catch it a second time and the truck would just go around.
The same happened on the skating rink, except it was hard to generate any sideways friction, and without the stability control, the truck just wanted to plow straight ahead through anything in the way.
Anyone who read my earlier report knows I am a believer in stability control. I have been ever since the first systems rolled out on high performance sedans nearly a decade ago. Their application to tractor-trailers seems just such a natural progression, considering the potential for rollover and jackknife these vehicles present. The fact that the systems work is demonstrable. And the ESP solution engineered by Bendix brings some additional benefits that give operators and drivers the tools to address the cause of most single vehicle truck accidents.
Given that truck driving is one of the top 10 most dangerous professions, Bendix should be encouraged and congratulated for bringing the system to market.
Starting early next year, it is for the fleets to look long and hard at the accident statistics in their operations and make a decision about whether ESP is right for them.
And it may be that drivers, too, should look at what could be a lifesaver for them, and opt to work for fleets that put safety systems like ESP onto their equipment to keep good drivers safe and whole.
