It's ESP! Mercedes/Bosch system tames those slippery roads

ARJEPLOG, Sweden With claims of a system that may be five times more effective than antilock brakes (ABS) in preventing accidents, engineers at Mercedes-Benz AG and Robert Bosch GmbH introduce their innovative high-tech Electronic Stability Program (ESP) on frozen Lake Hornavan outside this small town near the Arctic Circle.

What the Mercedes/Bosch folks term as revolutionary may be too strong a description, but ESP definitely makes many giant steps forward in the evolution of vehicle safety. They have effectively turned the white-knuckle panic of traversing a slippery roadbed into something a whole lot closer to a Sunday drive.

Quite simply, a computer draws input from existing ABS (brake pressure sensors) and electronic traction control (wheel speed sensors) to data from additional sensors measuring steering angle, lateral-acceleration and yaw.

Steering sensors tell the computer where the driver wants to go, and if the vehicle strays from the driver's intentions, the computer can selectively activate the brakes or lower engine torque by reducing the throttle and even preventing a gearshift.

One of the most significant parts of the system is the aerospace-inspired yaw sensors "yaw is the tenedency for a vehicle to rotate on its vertical center axis," explain M-B engineers), which is the key to measuring understeer or oversteer. In understeer -- when a car is slow to respond to steering changes -- the ESP system increases brake pressure to the inside rear wheel. In oversteer -- when rear wheels try to swing around -- the system increases brake pressure to the outside front wheel.

Obviously the key to keeping out of trouble is being able to process a variety of inputs and take evasive action if necessary. Not only does the computer system process all the information, it does it quicker. In 40 milliseconds, the ESP computer has made its moves. The fastest a human can react, say M-B engineers, is about 300 milliseconds.

Admittedly, antilock brakes take a lot of worry out of waiting for loved ones caught out in the rain or snow. And driving any one of a growing number of cars with traction-control systems adds significant confidence that you can get out of your unplowed driveway and move on down the road well before the salt trucks have begun to sleepily crawl out of their yards.

But this is different. Significantly different.

To demonstrate, Mercedes folks dress journalists like a small herd of blue nylon-clad Pillsbury Dough Boys and send them onto the frozen lake with carte blanche to do what a right-minded driver could never consider: put a luxury auto into a tailspin without suffering the wrath of an insurance company, the car's owner or the writer's next of kin. Somewhat like a Disney theme park ride for those who are forever asking: What if I drove too fast on a wet road or glare ice and turned the wheel like this?

No doubt about it, the ESP computer won.

More specifically, Mercedes engineers set up a back-to-back test on a long straightaway on the ice-covered lake. Writers were asked to drive a pair of virtually identical 500 SLs must -- one with and one without ESP.

They made two passes with both cars; one at 38 mph (60 km/h) and another at 44 mph (70 km/h). Drivers had to suddenly avoid the funny little painted guy on a pole that dropped in front of the car (avoidance maneuver) and further down the road were asked to make a quick lane change.

The results need little explanation. In the non-ESP car traveling at 38 mph, 23% of the drivers went into a spin during the maneuvers. At 44 mph the number out of control jumped to 50%. (This driver managed a 540-degree spinout at 44 mph after over-confidently avoiding the little guy on the pole.)

Not one driver lost control in the ESP-equipped car.

And that data parallels tests at the Daimler-Benz driving simulator in Berlin. A Mercedes summary explains that a group of 80 customers were enlisted to "drive" down an imaginary road at 62 mph (100 km/h) spotted at four bends with black ice. Without ESP, 78% of the "drivers" lost control and there were three "accidents."

With ESP, there were no "spinouts" and no "accidents."

Back on Lake Hornavan, writers also were allowed to traverse a slalom and two circular courses carved out of the snow. Pushing the ESP system beyond its limits left more than one journalist buried in a snowbank and waiting for a tow, which proved out a warning offered by M-B director of electronic development Herman Gaus that ESP "could not overcome the laws of physics."

M-B offers ESP as standard equipment on the S 600 coupe as it debuts this month in Germany and it will be offered on other S 600 and SL 600 models "later in the year."

Mr. Gaus says the system will be standard on all 12-cyl. models and cost an estimated $1,200 as an option on 8-cyl. models, which already include standard ASR (traction control).

When later offered on 6-cyl. models, the added price will come closer to $2,300, which includes the cost of the ASR and ESP.

ESP likely will not be available until sometime next year for M-B customers in the U.S.

Other significant new components linked to the ESP system include an all-new five-speed fully electronic automatic transmission and new ME 1.0 engine electronics.