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""Hitting the Brakes" is an important and enjoyable book. Cars are fascinating, and the opportunity to see how a significant safety system, antilock brakes, became part of them should interest anyone curious to learn how the cars we drive came to be as they are. But this book is more than an enjoyable history. It fundamentally rethinks how we understand engineering and the knowledge that engineers create. It will challenge philosophers to better understand knowledge and historians to better understand the development of knowledge. "Hitting the Brakes" is at once a social history of engineering communities, a philosophical thesis about engineering knowledge, and a great story."--Davis Baird, author of "Thing Knowledge: A Philosophy of Scientific Instruments"

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Hitting the BRAKES

Duke University Press

Contents

Preface...............................................................................................................xvAcknowledgments.......................................................................................................1one Design and the Knowledge Community...............................................................................23two A Genealogy of Knowledge Communities and Their Artifacts.........................................................37three The British Road Research Laboratory: Constructing the Questions...............................................63four The Track and the Lab: Brake Testing from Dynamometers to Simulations...........................................85five From Things Back to Ideas: Constructing Theories of Vehicle Dynamics............................................103six Learning from Failure: Antilock Systems Emerge in the United States..............................................117seven Eines ist sicher! Successful Antilock Systems in West Germany..................................................137eight Public Proprietary Knowledge? Knowledge Communities between the Private and Public Sectors.....................157epilogue ABS and Risk Compensation...................................................................................167Notes.................................................................................................................187Bibliography..........................................................................................................201

Chapter One

In 13 August 2000 an anonymous author with the screen name "Starrion" posted a review of the 2000 Mercury Sable on the website Epinions.com. Starrion told the following story:

I was on Rt 24 headed for Walnut Creek, California. And I'm approaching my exit. It's a beautiful day in the San Francisco area, I've got the sunroof open, going 75, the local radio station playing, and all is well. I know I need to drop a lane, and when an opening appears behind a smart-looking silver Grand Am, I take it. I have only a few feet to spare. Just as I enter the lane, a cloud comes up from the road, the Grand Am's brake lights come on, and she panic-stops. Just as I put my foot to the floor, I see a tire twenty feet in the air-complete with aluminum hub-come bounding over the Pontiac headed right for me. I brake ever harder and the Sable stops flat. No control loss, pointed straight and I out-stopped the Grand Am. The tire lands about a foot from my passenger side door and rebounds into panicking traffic behind me. It was so close that chips of rubber landed in my car through the sunroof. As I started off, I noticed a Jeep Cherokee sans rear-mounted spare about a half a mile up. As I made my exit, I was very glad I had clean underwear in my suitcase.

How was this ordinary family sedan able to avoid this hazard and come to an uneventful stop? Starrion's answer came in the next line of the post: "The Sable LS has great brakes. Better than any other rental car I've driven. This car had ABS or else I wouldn't be writing this. I highly recommend it. Extra highly." While there are many reasons for the differences in the ways various cars handle, in this case, the car's behavior is typical of cars with antilock braking systems, or ABS. When Starrion slammed on the brakes, the Mercury Sable went into an antilock mode. Its computer compared the angular speeds (i.e., the speed of rotation) of all four wheels. The computer also compared the angular velocity of the wheel to the linear velocity of the car. If the computer determined that one or more wheels were decelerating more quickly than the vehicle, the computer could send an electrical signal to the hydraulic system controlling the brakes. That signal would tell the brake caliper (at the wheel that was decelerating too quickly) to pulse, reducing the braking pressure on that wheel. This computerized system is able to apply and release the brakes dozens of times per second, much faster than adrenaline-infused Starrion could pump the brakes. Once the rate of deceleration of that wheel was back in line with the vehicle speed, the brake would revert back to normal operation, even though the wheel sensors would continue to monitor the rate of deceleration for further problems. The result of this active monitoring and modulation of the automobile's brakes meant that the car never started to skid, and as a result Starrion avoided the crash.

Skidding is dangerous for two reasons: a driver cannot steer a skidding car effectively, and a skidding car can take longer to stop. Although it may seem counterintuitive that a car with locked wheels stops less quickly, under most conditions sliding wheels encounter less resistance than rolling wheels. This is also the reason a skidding car often spins; the wheels with the lower sliding resistance move faster than the wheels with the higher rolling resistance. As a result, if the rear wheels start to skid, as they commonly do on a pickup, which usually carries less weight on the rear axle, the vehicle will spin 180 degrees to face the oncoming traffic. No amount of steering correction or countersteering can overcome the friction differential because the direction in which the wheels are pointing does not matter when wheels are sliding, only when they are rolling. Because of the car's ABS, Starrion avoided skidding and therefore maintained directional control, making possible the emergency lane change and quick stop. In this scenario, the proper use of antilock brakes allowed the driver to avoid losing control, to change lanes under emergency braking conditions, and to stop as quickly as possible. The antilock braking system is a well-designed invention for several reasons. Once invented, it appears obvious. What it does and how it does it are easy to understand, at least superficially. Its function is socially desirable; in principle all drivers prefer not to lose control of their vehicles and to be able to stop quickly. An antilock braking system is fundamentally a technology of control, often represented as a triumph of engineering over dangerous road conditions and unpredictable drivers. In early advertisements, ABS was often presented as a great idea whose time had finally come. Skidding had been a problem on cars for decades. The fact that antilock systems only begin to proliferate in the 1980s points to a difference between ABS as an idea and ABS as a functional, real-world product. From an engineering perspective, ABS is a complex, electronically controlled, mechanical system. At its heart, it is a measuring apparatus, but not one which exists in a clean, temperature-controlled laboratory. Instead, ABS has to send electrical signals along the bottom of automobiles, which vibrate, get wet, dirty, and salty, operate in temperature extremes, and operate at speeds from 0 to over 100 miles per hour. An antilock system has to interface with but not interfere with several other electrical systems. If ABS fails, the braking system itself must continue to work normally. Making ABS meet these real-world conditions proved to be far more difficult than simply dreaming up the idea. A functional ABS required newly invented components, from sensors to computers, circuits to valves, and new understandings of how drivers behave and how other parts of the automobile function....