Arresting Developments

Environmental interests and the automotive media work themselves into a lather almost daily about the “horsepower race” that's supposedly under way. It makes for good headlines, and if explosive sales of vehicles with ever-larger and more-bombastic engines are any indicator, it appears there is truth to the adage “horsepower sells.”

But there is a less-sexy race under way at the other end of the performance spectrum, the stopping part of the equation. Several auto makers and major suppliers are preparing new, high-performance brake systems that promise to advance the physics of reining in their accelerative beasts.

Unlike the hyper-expensive, carbon-ceramic braking systems recently launched by the likes of Porsche AG, Ferrari SpA and Mercedes-Benz, the new production-ready systems promise a vast improvement in braking performance for everyday vehicles.

The more unusual of two new braking systems is an innovative Delphi Corp. design that uses two brake rotors for each wheel. Delphi engineers and officials say the design has the potential to revolutionize passenger-vehicle braking dynamics.

The central components of Delphi's Maximum Torque Brake (MTB) system are two floating rotors where every production-vehicle disc-brake system to date has employed just one. Each rotor is clamped by a caliper just like a typical single-disc system, but there now are four friction surfaces to generate braking force, instead of two.

The effective doubling of friction-surface area allows the MTB system to generate 1.7 times more braking torque compared with a system using a single rotor of the same diameter, says Simon Hudson, testing and verification manager for the MTB system.

Delphi declines to name a customer for the system, saying only that MTB is “application ready with rotor sizes from 225 mm to 345 mm” (from 8.9 ins. to 13.6 ins., or essentially the entire disc-brake market), and it should appear on a production vehicle late next year.

Ward's has heard several OEMs mentioned as prospective early adopters — including Chrysler Group's Jeep and BMW AG.

Delphi says one of the system's best benefits is a marked reduction in the pedal effort necessary for a certain amount of stopping force. Hudson says this will give drivers the confidence to use more of the braking system's maximum capability.

Also apparent is the almost violent amount of decelerative force MTB can generate when the driver demands maximum braking. Delphi engineers decline to discuss the actual potential for reducing stopping distances because the dynamics of braking are specific for each vehicle (and tire) application. But the 1.7 times greater applied-torque figure — combined with MTB's ability to genuinely startle a driver with stopping power far beyond his experience — suggests the potential to demonstrably reduce stopping distances.

Hudson says Delphi has developed MTB systems for either the front axle or for both axles — but because most vehicles generate a disproportionate amount of the total deceleration with the front brakes, Delphi sees equipping a vehicle with the twin-disc arrangement on each front corner as being the most effective.

“It's most logical to fit the system for the front axle,” says Hudson. “Obviously we don't want to compete (on a cost basis) with any vehicle that has drums at the rear axle.” Although he says MTB can't compete with low-cost drum brakes that many lower-segment vehicles use, Delphi claims the system in many cases can offset what would appear to be inherently higher costs.

The company says MTB delivers certain cost efficiency because, if applied optimally, it can lead to parts-count reduction and the need for less hydraulic fluid and provides longer pad and disc life. And counter to one's intuitive conclusion about a system that doubles the number of heavy brake rotors at each corner, Hudson says the MTB system actually can cut unsprung mass if the potential component integration mentioned above is fully realized.

Volker Barth, Delphi's president of operations for Europe, the Middle East & Africa, tells Ward's, “Cost is our biggest enemy in everything we do. But OEs would like to spend more,” he says — particularly for components that can provide demonstrable benefits, a competitive edge, or lend a high-tech aura.

General Motors Corp., meanwhile, is spending more — and less — on a new braking system co-developed with Robert Bosch GmbH for GM's '05 fullsize pickups. GM says its light-duty Chevrolet Silverado and GMC Sierra will be equipped with an all-new braking system that also improves performance and is more pleasing to use.

The rub for GM engineers: Their 1-step-back-2-steps-forward solution requires a bit of explanation. At first blush, the uninitiated might be convinced GM actually is cutting back on the pickups' braking ability.

When GM's current pickups (internal designation: GMT800) were launched as '99 models, GM bragged they were the industry's first fullsize light-duty pickup trucks to come standard with 4-wheel disc brakes.

Until then, pickups — whose rear wheels typically don't contribute much to the act of slowing the truck — traditionally used less-powerful, less-costly drum brakes for the rear wheels. The new braking system for the '05 Silverado and Sierra returns to drum brakes for the rear wheels, but it is not a retrograde move.

GM engineers, along with co-developer Bosch, are leveraging their knowledge that pickups rarely use their rear brakes as hard as the fronts. They have taken the savings gleaned from the return to rear drum brakes and spent it on a serious upgrade of the trucks' front brakes and other braking-system components.

The new system, engineers say, will provide drivers with better feedback, require less pedal effort and deliver generally better overall response and “feel.”

Jully Burau, assistant chief engineer-fullsize trucks, says GM targeted the braking system because of J.D. Power and Associates initial-quality ratings and other consumer-clinic data that show customers believe there is plenty of room for improvement in the performance and feedback of pickup brakes. Issues most often cited include high brake-pedal effort, “mushy” feel from the pedal and the feeling the brakes don't generate enough stopping power.

Fixing those problems, says Ken Hamann, director-brakes and chassis control systems, led GM and Bosch to a host of solutions that reduce stopping distance and time and proffer more-responsive feedback to the driver.

The primary hardware upgrade for the '05 light-duty pickups is 1-in. (2.5-cm) larger-diameter front rotors and twin-piston calipers that are significantly larger and stiffer than the current twin-piston squeezers. Hamann says the larger rotor provides a 55-sq.-in. (355-sq.-cm) increase in rotor swept area, a tremendous aid in generating more stopping force.

The upgraded rotor/caliper components also deliver an important ancillary benefit, says Hamann. Their better stopping power means engineers could eliminate a booster previously necessary to comply with a federal safety standard that dictates the amount of allowable brake-pedal pressure in the event the braking system's power-assist is inoperable.

Hamann says the new brake system also includes a totally new master cylinder and booster that is stiffer and more efficient. That stiffness, combined with the extra beefiness found in the new calipers, helps to reduce the spongy feeling about which customers complain. By taking compliance out of these components, Hamann says drivers will “experience more confidence with the pedal.”

GM engineers, in fact, developed in the early 1990s a matrix to help quantify the sometimes esoteric subjective facets of brake-system feedback. Their Brake Feel Index (BFI) assigns a vehicle a single BFI score based on a composite of weighted variables that contribute to a customer's overall impression of the braking experience.

The new system, says Hamann, registers a 41% BFI improvement vs. the '04 brake system. Hamann adds that the new trucks' improved braking system will reduce stopping distance from 60 mph (97 km/h) by 85 ft. (26 m) and stopping time by 2 seconds. Meanwhile, the driver will not have to exert as much effort on the brake pedal, and the pedal will feel more responsive and deliver more of the confidence Hamann says is important to drivers, particularly when the pickup is heavily loaded.

But he knows the perception of returning to a less-sophisticated component is undeniable. That's why GM and Bosch engineers point to the improved performance and feel of the new system that takes advantage of pickups' unique braking behavior.

And why, Hamann says, he hopes pickup customers and auto critics try the new system before judging.

“They need to feel, touch and understand what we went through to make that call (to return to drum brakes),” he insists.