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My 2011 Audi A4 B8 has cruise control and although not adaptive, it does engage the brakes if I set a cruising speed well below my current speed or if the car picks up speed during descents.

The car has ABS, ESP and I think also EBD. As far as I know, the brake pressure is only created mechanically by the driver pushing the pedal, and amplified by the brake booster. The pressure is then handled by the aforementioned systems. How is it then, that the car can brake on its own without me touching the pedal?

DavidRecallsMonica
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Erik
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2 Answers2

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The abs system can provide the function to engage the brakes.

Solar Mike
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The original ABS systems only modulated pedal pressure. Some systems only worked on two of four wheels.

"Better" or later systems could modulate all four wheels. Even more developed was the ability to modulate each wheel independently.

Modern systems have an electric pump, which pressurizes a reservoir. Sometimes you can hear them whine for a few seconds on startup (modern Honda Civic comes to mind).

These systems can compensate for "too much" as well as "not enough" pedal pressure. Through sophisticated electronics, they can possibly even do a variety of other tasks:

  • Retard cruise control or steep slope descents
  • Emergency braking triggered by proximity radar
  • Traction control to redirect torque across a differential away from the slipping wheel
  • Dynamic handling assist that can figure out which wheel to drag in a corner and help steer/pivot or prevent spinout.
  • Automated parallel parking assist
  • Launch control

These are just a few off the top of my head. I'm certain there are several more, and more to come.

While you won't find Lauch Control in all but hyper sports cars, some Volvos have Dynamic Stability Control (they may call it something slightly different).

I'm not current with BMW and Mercedes offerings, but I do know that they offer a menu of features beyond "anti-lock braking" on the higher-end [more expensive] vehicles.

Even my lowly 2018 Toyota Sienna van (don't get me wrong; I love it) has emergency braking, traction control, and some other high end features which are effected with the ABS "pump".

SteveRacer
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