Dean Paige wrote:
At 4:47 PM -0700 10/1/01, Paige, Dean wrote:
>Without any doubt, yes the Hydraulic system does give that much mech
>advantage. Imagine trying to activate your disk brakes effectively w/o the
>advantage of hydraulics.
Okay. This brings up a great topic. Recently my dad and I were
engaged in a debate about this very subject, and I would LOVE to see
if I'm right about it!
It seems to me that in order for a hydraulic system to offer any
amplification of force or effect, there would have to be something
'magical' about the fluid itself. My contention is that strictly
speaking, a hydraulic system is NOTHING MORE than a way to transfer
motion. PERIOD. Allow me to analogize:
An example of a simple (and quite hypothetical) hydraulic 'system'
would be two IDENTICAL syringes joined nose-to-nose by a short tube.
One syringe is full of water and of course the plunger is backed all
the way out. The other syringe is empty and its plunger is all the
way 'in.' Assume that the tube between them contains only water as
well, no air. The syringe filled with water is the master, and the
empty syringe is the slave.
Now, the pivotal question is
when you push the master's plunger in
with 'x' amount of force, does the slave's plunger move out with
force that is EQUAL to 'x' or does it move out with force that is
GREATER than 'x'?
The answer can only be EQUAL to 'x.' At least that's my contention.
If it were otherwise, then we would have to believe in some sort of
perpetual motion and free energy, right? And the laws of
thermodynamics would be turned upside-down.
Of course, the question is complicated by the fact that master
cylinders and slave cylinders rarely (if ever) have the same bore and
stroke. Let me state right here and now that I realize fully that
hydraulic systems CAN offer some amplification of force and movement
when cylinder bore & stroke specs are dissimilar.
However, in the context of a car's clutch actuation system, we have
several other things going on that, while connected to the hydraulic
system, they should actually be considered separately from the
hydraulic system. Of course, I'm referring to the pedal itself and
the effective lever that operates the TO bearing.
The lever created by the clutch pedal on my TR6 is approximately 9
5/8" long. (a VERY rough measure, from the center of the pivot shaft
to the center of the foot pedal) The pushrod for the master is
located ROUGHLY 2 5/8" from the center of the pivot shaft. That
means that the length of the lever is 366% longer than the distance
from the fulcrum to the pushrod connection. I don't know how to
quantify the mechanical advantage that this creates, but I know it
creates A LOT.
Then on the other end of the system, we've got the drop arm and the
fork. The effective length of the drop arm is approximately 3 3/8"
(to the CENTER hole) and the effective length of the fork is about 2
7/16". The lever that the drop arm creates is 138% the length of the
lever created by the fork. Not nearly as much mechanical advantage
as at the pedal, but still there's some.
The differences in the bore & stroke specs for the relevant cylinders
shouldn't be totally overlooked, but it's my contention that they
contribute very little relative to the pedal arm, in particular.
Furthermore, (and drifting into a hypothetical) IF the bore & strokes
were identical, then it could be accurately said that the hydraulics
contribute ABSOLUTELY NO mechanical advantage whatsoever in that
particular system.
And this would support my notion that hydraulics is simply another
way to transfer motion.
Please correct me as necessary, and for those who are much more
schooled in physics and mathematics than I am (wouldn't take much,
you know) please expound where you feel it's necessary!
--
Pete Chadwell
1973 TR6
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