Power assist brake design - Page 2

rdorman · #21 (**permalink**) 01-29-2004, 12:20 PM

I seem to recall something about vacuum assist windows!

My work sheet takes into account all the factors you listed and then some! But I have nothing on power brakes. Begining to think that I never will! Oh well. The brakes on our cars, if done properly work so well that who needs them anyways!

Rick

trularin · #22 (**permalink**) 01-29-2004, 04:02 PM

Barnsnake · #23 (**permalink**) 01-29-2004, 10:26 PM

I don't believe you should look at the brake booster as an "amplifier" of pedal pressure. When you press the petal you are telling the diaphragm how "far" to move, not how much pressure to exert. The influence of the springs in the assembly will make the pedal effort increase with the distance moved, thus creating "feel".

The total force available will always be the area of the diaphragm times the maximum pressure differential across it. When the diaphragm "catches up" with the pedal piston it will reduce the pressure differential to maintain that "position". If you press the pedal so far that it cannot "catch up", it exerts the maximum possible pressure. Pressing the pedal an extra amount from that point will not increase the pressure on the cylinder unless you have "bottomed" the pedal shaft into the cylinder shaft.

It works much like a power steering assist. You tell it what direction to move and how far to go. It catches up and recreates an equilibrium at that position.

rdorman · #24 (**permalink**) 01-30-2004, 06:17 AM

So there is no physical connection between the brake peddle and the master cylinder push rod?
Thanks
Rick

strictlypersonl · #25 (**permalink**) 01-30-2004, 04:39 PM

Quote:

Originally posted by rdorman

So there is no physical connection between the brake peddle and the master cylinder push rod?
Thanks
Rick

Only through the spring that creates the resistance to the vacuum valve. Of course if there's no vacuum, the pedal pushrod eventually makes contact (through the floating vacuum valve) with the master cylinder pushrod.

Karel289 · #26 (**permalink**) 01-31-2004, 05:21 AM

Hi,
I made a spread sheet for the brakes calculations, the units are European, but you can make a conversion.
I did for a Dual M/C setup and for a tandem M/C.
You can find on my web pace under brakes.
If you like I can send you the spread sheet.

http://www.donostia.demon.nl

I hope this will help you!!
Regards,
Karel289

rdorman · #27 (**permalink**) 02-02-2004, 10:11 AM

Another brake spreadsheet! Please do send one. I would like to compare notes.
Thanks
Rick
rfdorman@aep.com