I don't think so Mike. You cannot switch pressure off. You must
allow fluid to escape to a low pressure reservoir. The reason
this is so is because of deflection in the hyd lines and
the brake calipers. The wheel must unlock.
Read my book on Race Car Braking Systems
published about 30 years ago by Steve Smith Autosports.
May be out of print. Steve Smith himself was a student
of mine.

http://www.ssapubl.com/

Paul Lamar

I looked closer at the diagram and article you attached, and realized I had
(yet again) stuck foot firmly in mouth. This synthetic leather is tastier
than Nike's, at least.

My understanding from the article is that the fluid pressure from the locked
wheel brake line is bled off into a reservoir in the ABS unit itself, and
then introduced back into the system by a small pump over time (in non-ABS
operation). The sudden cutoff of flow from MC to WC is what causes the
typical vibration, as the MC side sees no pressure relief, correct?

In large aircraft, the antiskid is a per-axle thing, with the fluid pressure
switched from WC to a return to reservior line until the wheel starts
turning again. Doing the gear swing and check with a cordless drill and
pressure tester is a fun way to spend an afternoon :)

Mike Harrington

There is another point I failed to make in my last message.
It takes less pressure to keep a wheel locked than it does
to lock it in the first place. That means the pressure must
go WAY down in the lines. Bleeding off fluid is the only
way to achieve this. 

The reason for this is the sliding coefficient of friction for a tire is 
lower than the the coefficient just prior to locking. That is
one of the rationale for ABS in the first place. The other is you
cannot steer a locked up tire.

BTW When we were supplying test equipment to the LA County Sheriffs 
Department for testing police cars the highly skilled test drivers were 
complaining that they could not stop as fast with the then new anti 
lock systems. The stopping distance data we were seeing confirmed 
those results. They were still trying to modulate the force on the 
brake pedal. I explained that they had to stand on the brake pedal with
both feet to stop short with ABS :-)

Paul Lamar
 
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