Quote:
Originally Posted by JesseK
This used to be a good guide with an animated gif showing how the internal cyllinders work in the brake pump -- but it looks like they've changed it a bit in the couple of years since I've looked at it. I too had this question a few years ago:
http://auto.howstuffworks.com/anti-lock-brake.htm
It's "sorta" how it works. Instead of a speed sensor, some cars used to use a "slip" sensor that was a combination of a shaft encoder and accelerometer. Since then it's been proven to be easier and faster to use speed differentials to control the brake fluid pressure. |
Ok, so according to that article, the control system operates with a predetermined constant for the "maximum allowed deceleration" to prevent the wheels from slipping. But this "constant" is extremely dependent upon the coefficient of friction between the wheel and the ground, which changes depending on the surface of the road.
Based on my experience with ABS, this "constant" is smaller when driving on ice, than when driving on a dry road. But how does the control system know this?
Theoretically, this could be done with an accelerometer and encoders on the wheels. Is this the way it's done? The problem that might happen is that by the time the controller realizes the wheel speed is different than the car speed to start removing brake pressure, the wheels will already be slipping. Doesn't ABS prevent this situation completely?