The brake sector has never been a place for the faint of heart. The world's largest, most powerful automotive suppliers are entrenched in the segment, battling mercilessly for new business, new technology and, ultimately, survival. Yet, it appears the ranks of Robert Bosch GmbH, Delphi Corp., TRW Automotive, Continental Automotive Systems and Japan's Advics Co. Ltd. will face a new competitor with

Tom Murphy, Managing Editor

October 1, 2005

6 Min Read
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The brake sector has never been a place for the faint of heart.

The world's largest, most powerful automotive suppliers are entrenched in the segment, battling mercilessly for new business, new technology and, ultimately, survival.

Yet, it appears the ranks of Robert Bosch GmbH, Delphi Corp., TRW Automotive, Continental Automotive Systems and Japan's Advics Co. Ltd. will face a new competitor with unique technology that could revolutionize the sector.

SiemensVDO Automotive unveiled at last month's Frankfurt auto show its “wedge” brake concept, which is a completely electronic brake-by-wire system that eliminates components that have existed for decades: the vacuum booster, hydraulic lines, parking-brake assembly/cable, fluid reservoir, master cylinder and mechanical pedal.

SiemensVDO says with the wedge technology, it intends to dominate the brake market, which generates an estimated $30 billion (€25 billion) in global sales annually.

It is an ambitious order, given SiemensVDO is a nonplayer in the sector. The company currently makes only electric parking brakes and antilock brake controllers and motors.

The “wedge,” a term borrowed from the rudimentary wooden brake applied to stagecoach wheels before the arrival of the automobile, operates on a relatively simple principle.

When the brake pedal is depressed, the system sends an electronic signal to the four interconnected brake modules. The caliper at each wheel has two small motors, which respond instantaneously by turning a spindle, which then actuates a mechanism consisting of small wedges and bearings.

As the wedge-bearing mechanism moves, it applies pressure to both calipers, squeezing the brake disc based on the driver's input. It essentially functions as a high-tech door stop.

The power requirements for the system are minimal. Engineers say a traditional 12-volt battery can provide the necessary power.

Actually, the 12-volt system merely begins the braking event. The system is designed to “self-energize,” meaning the friction between the pad and the rotating disc actually pulls the wedge into the system, generating the force necessary to complete the braking event, says Karsten Hofmann, director-product marketing for SiemensVDO body and chassis electronics. The result is a highly efficient brake system.

In the event of a power failure, the backup would consist of an additional battery to drive the system. If the main brake controller fails, the driver's pedal would have a direct connection to each caliper to apply braking force. Plus, the system has built-in intelligence, with secondary backup on standby. There are up to five ways to give a command to the brake units, so a single failure will never cause a critical situation, SiemensVDO assures.

The system can save 0.78 cu.ft. (22L) of underhood packaging space and reduce weight by up to 42 lbs. (19 kg), Hofmann says. The electronic control unit for the foundation brake system also could govern the antilock brake and electronic stability control functions.

SiemensVDO expects to be in production with the system by 2009. If the concept lives up to the company's high expectations, the potential impact to the brake sector could be enormous.

The entrenched players have significant capacity to produce traditional components for hydraulically actuated disc and drum brakes, although all are hot on the development trail toward similar full or partially electronic brake-by-wire configurations.

“We will not be the only company in the future doing brakes like this,” Hofmann says. Already, the industry is migrating toward brake-by-wire by replacing some conventional hydraulic components with electromechanical ones.

In recent years, Bosch has supplied the Mercedes-Benz E-Class and SL with an electrohydraulic brake system (EHB), which relies on conventional foundation brakes at the wheel but eliminates the physical connection to the brake pedal.

A “brake operation unit” takes the place of a standard vacuum booster and master cylinder assembly, and a hydraulic modulator replaces the standard ABS and stability control unit. Mercedes has marketed the system as Sensotronic Brake Control.

However, a defect in the system led to a global recall of the vehicles in spring 2004. The auto maker says the feature remains standard today on the E-Class and SL, and that most of the problems were limited to heavily used taxi cabs.

The all-new Mercedes S-Class features a “hydraulic dual-circuit braking system” that is electronically controlled, but the company does not use the Sensotronic moniker in press materials.

Earlier this year, TRW Automotive Vice President Josef Pickenhahn told Ward's that future Mercedes vehicles will not employ the advanced sensor-brake control system, and that the episode cast a chill over brake-by-wire development in general.

Meanwhile, Siemens AG, the parent company of SiemensVDO Automotive, entered the brake-by-wire sector less than a year ago via its acquisition of a small German company named eStop GmbH.

Researchers from the German Aerospace Centre DLR near Munich had been attempting to apply the wedge principle to automotive applications and left the institute to form eStop in 2000.

In January, Siemens purchased eStop and recruited its principal, Bernd Gombert, to join SiemensVDO management to market the wedge brake. Gombert says he was skeptical of Bosch's EHB system years ago. “I said, ‘this is not an intelligent way to brake,’” Gombert tells journalists while explaining the wedge principles. “We should use the energy of the car to stop the car.”

Bosch admits its EHB volumes are down.

“In general, the cost-vs.-benefit ratio didn't materialize as everyone — Bosch and the OEMs — had anticipated,” Scott Dahl, marketing director for Chassis System Control at Bosch, tells Ward's. “I think you'll see continued decrease in EHB volumes for normal production vehicles.”

Still, Dahl defends the product. “EHB was a good product and is a good product,” he says. “We got a lot of education from that product, and there were no regrets bringing it to market.”

Bosch, like others in the sector, is working on full brake-by-wire concepts as well. “We have advanced products under development,” Dahl says. He expects the transition to electronic brake-by-wire to take at least 10 years. “I think you'll see that conventional brake systems will be around a long time,” he says.

Meanwhile, SiemensVDO is moving ahead with its wedge program, preparing for two years of summer and winter testing.

When production begins in four years, the supplier expects the system to be “cost neutral” with a conventional hydraulic system, Hofmann says, noting there are no regulatory hurdles for the system to clear.

SiemensVDO may have ambitious plans, but the company does not want to produce foundation brakes, says Chairman and CEO Wolfgang Dehen. Its focus centers entirely on electronic actuation.

Even the high-tech caliper could be sourced from another company. “We could buy the caliper,” Dehen says.

Migrating to brake-by-wire opens unlimited possibilities. An electronic pedal, for instance, can be safer because it eliminates hardware that can cause leg injuries in severe frontal collisions.

In addition, the pedal pulsation from ABS that some drivers dislike could be eliminated.

A joystick controlled by hand could actuate the brakes. And auto makers could program brake “feel” depending on the handling characteristics of certain vehicles, Hofmann says.

Eventually, a range of sensors could work in concert with brake-by-wire to detect dangerous situations and apply the brakes in advance of driver intervention, ushering in so-called autonomous braking.

“This system is a revolution,” Hofmann says at the show, adding SiemensVDO is ready to face the brake sector. “Otherwise, we would not be here. We would have buried this technology.”

About the Author(s)

Tom Murphy

Managing Editor, Informa/WardsAuto

Tom Murphy test drives cars throughout the year and focuses on powertrain and interior technology. He leads selection of the Wards 10 Best Engines, Wards 10 Best Interiors and Wards 10 Best UX competitions. Tom grills year-round, never leaves home without a guitar pick and aspires to own a Jaguar E-Type someday.

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