SL roadster ready for EHB; Are consumers?

BOXBERG, Germany — DaimlerChrysler AG's Mercedes-Benz division is making a significant commitment to the concept of electro-hydraulic braking (EHB), the first step toward a completely dry “brake-by-wire” system.

The totally redesigned ’02 Mercedes SL roadster, which launches this summer in Germany, will be the first series-production car to feature 4-wheel EHB as standard equipment. “Series-production” yes, but volumes for the super-pricey roadster will not be high: worldwide production for the current-generation SL was 7,756 units in 2000 and 12,356 units in ’99.

But several more production vehicles equipped with EHB are preparing for launch, including the redesigned Mercedes E-Class, which likely will go into production in 2002. EHB also is expected to be standard for the E-Class.

Robert Bosch GmbH will supply the brake systems, and company executives say that by 2005, several other new vehicles will be equipped with EHB as well, most of them luxury or near-luxury cars. Competitor Continental Teves Inc. says it will launch its first EHB project in 2003.

Some of the vehicles equipped with Bosch systems will be global platforms, and one may operate with a 42-volt electrical system, says Gunther Plapp, senior vice president of braking systems at Bosch. A well-designed 14-volt system is adequate for EHB, though full-blown brake-by-wire systems lie further in the future, partly because they would require a high-grade and sophisticated 42-volt power supply, Mr. Plapp says.

The EHB control unit calculates the desired brake pressure for each wheel, working in concert with antilock brakes and stability control systems, which also happen to be Bosch products. Sophisticated distance and pressure sensors measure how hard the brakes have been applied.

Bosch says the benefits include lighter weight (no more brake booster), smoother braking, shorter stopping distances and the elimination of the pulsating pedal sensation common with antilock brakes.

A recent test drive of Bosch's EHB system at its test track near Boxberg confirms the lack of pedal pulsation, but it was hard to discern shorter stopping distances.

In fact, stopping seems too smooth. On wet tile, a heavy Mercedes-Benz S-Class felt like it enjoys less traction (sliding practically to the end of the skidpad) than two vehicles equipped with conventional brake systems (Audi A6 and Mercedes A-Class). Despite the “sliding” sensation, steering remained responsive, however.

Consumers who never warmed to the pulsations of ABS may be glad the sensation's been eliminated with EHB. Still, many drivers may need a re-education on the intricacies of “brake feel” with the arrival of EHB.

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