how ABS works

The ABS System


The theory behind anti-lock brakes is simple. A skidding
wheel (where the tire contact patch is sliding relative to the road)
has less traction than a non-skidding wheel. If you have been
stuck on ice, you know that if your wheels are spinning you have no traction.
This is because the contact patch is sliding relative to the ice (see Brakes: How Friction Works for
more). By keeping the wheels from skidding while you slow down, anti-lock brakes
benefit you in two ways: You'll stop faster, and you'll be able to steer while you stop.
There are four main components to an ABS system:

• Speed sensors
  
• Pump
  
• Valves
  
• Controller
  

Anti-lock brake pump and valves

­Speed Sensors
The anti-lock braking system
needs some way of knowing when a wheel is about to lock up. The speed sensors,
which are located at each wheel, or in some cases in the differential, provide this
information.
Valves
There is a valve in the brake line of
each brake controlled by the
ABS. On some systems, the valve has three positions:

• In position one, the valve is open; pressure from the master cylinder is passed
  right through to the brake.
  
• In position two, the valve blocks the line, isolating that
  brake from the master cylinder. This prevents the pressure from rising further
  should the driver push the brake pedal harder.
  
• In position three, the valve releases some of the pressure
  from the brake.
  

Pump
Since the valve is able to release pressure
from the brakes, there has to be some way to put that pressure back. That is
what the pump does; when a valve reduces the pressure in a line, the pump is
there to get the pressure back up.
Controller
The controller is a computer in the
car. It watches the speed sensors and controls the valves.
ABS at Work
There are many different variations and
control algorithms for ABS systems. We will discuss how one of the simpler
systems works.
The controller monitors the speed sensors at all times. It is looking for
decelerations in the wheel that are out of the ordinary. Right
before a wheel locks up, it will experience a rapid deceleration. If left
unchecked, the wheel would stop much more quickly than any car could. It might
take a car five seconds to stop from 60 mph (96.6 kph) under ideal conditions,
but a wheel that locks up could stop spinning in less than a second.
The ABS controller knows that such a rapid deceleration is impossible, so it
reduces the pressure to that brake until it sees an
acceleration, then it increases the pressure until it sees the deceleration
again. It can do this very quickly, before the tire can actually significantly change speed. The
result is that the tire slows down at the same rate as the car, with the brakes
keeping the tires very near the point at which they will start to lock up. This
gives the system maximum braking power.
When the ABS system is in operation you will feel a pulsing
in the brake pedal; this comes from the rapid opening and closing of the valves.
Some ABS systems can cycle up to 15 times per second.

Nice info napster. Mention the source or you will be infracted, read this carefully.

Hey I always wondered how ABS worked and now you have provided us with the information. Great going naps. :goodjob:

thanks for the info napster. has anyone had an experience where they felt greatful that their car had ABS?

Still didn't get a chance, as we have no ABS cars. But our next car will definitely have ABS.

source : www.auto.howstuffworks.com

yes, hummer_freak, recently the ABS in my car prevented me from rear ending a tempo. i was at 90-100 kmph & this idiotic tempo driver suddenly swerved into my lane (right lane). i pushed the pedal hard & also swerved a bit to the right & there was some space between my car & the divider. morover, there was some gravel on the road. i fould feel the pedal pulsating hard & the car came to a halt quickly & in a straight line.
without ABS, i would have either banged the tempo or the divider.

thats a good piece of info mate, thanks for sharing and also its source.

raj_5004 wrote:yes, hummer_freak, recently the ABS in my car prevernted me from rear ending a tempo. i was at 90-100 kmph & this idiotic tempo driver suddenly swerved into my lane (right lane). i pushed the pedal hard & also swerved a bit to the right & there was some space between my car & the divider. morover, there was some gravel on the road. i fould fell the pedal pulsating hard & the car came to a halt quickly & in a straight line.
without ABS, i would have either banged the tempo or the divider.

ok. thats nice. thanks for sharing your experience. my experience is just that i have a friend he's a great driver but loves to do all sorts of stupidity in his car. earlier he had a city. but now he has a corolla with ABS and now i feel much safe with him as the car never lets him take control. ;)

im_hummer_freak wrote:

raj_5004 wrote:yes, hummer_freak, recently the ABS in my car prevernted me from rear ending a tempo. i was at 90-100 kmph & this idiotic tempo driver suddenly swerved into my lane (right lane). i pushed the pedal hard & also swerved a bit to the right & there was some space between my car & the divider. morover, there was some gravel on the road. i fould fell the pedal pulsating hard & the car came to a halt quickly & in a straight line.
without ABS, i would have either banged the tempo or the divider.

ok. thats nice. thanks for sharing your experience. my experience is just that i have a friend he's a great driver but loves to do all sorts of stupidity in his car. earlier he had a city. but now he has a corolla with ABS and now i feel much safe with him as the car never lets him take control. ;)

so you were enjoying those skidds till now :lol: