Armand et al,
Do you want to have a comfortable clutch (ease of push), need something
that is often used for speed shifting (slam, quick action at the top), or
some other purpose. I sort of lost track of what you were trying to
accomplish with a bigger (or was it smaller bored cylinder (master, not
slave??!?). I personally prefer a clutch that will engage and dis-engage
smoothly and without chatter. I can easily adjust the force and speed off
my left leg (yes Colin, I do shift with my left) to accommidate 99.9% of
the multitudinous variations of clutch, master, slave, lever, and fluids
that are known to me. I'm secretly hoping that this tread will move in the
direction of "I blew up a clutch so badly that....." or "I was actually
killed when my clutch exploded" or "I've been driving without a functional
clutch in my Tiger for 13 years and..." etc.
I think my monthly thing is soon to come- Chris in Trinidad
----------
> From: Bob Palmer <rpalmer@ames.ucsd.edu>
> To: Tom Hall <modtiger@engravers.com>
> Cc: tigers@autox.team.net
> Subject: Re: Hydraulic pressures
> Date: Sunday, January 24, 1999 9:42 PM
>
> At 01:33 PM 1/23/99 -0800, Tom Hall wrote:
> >At 10:16 AM 1/23/99 -0800, you wrote:
> >
> > It is important to recognize that the "brake hydraulic system" consists
of
> >both levers and cylinders. There are ratios for both at both ends which
> >end up actually transferring or applying the mechanical force applied
by
> >your foot to the brake friction material. The stock mechanical ratio of
> >the brake and clutch pedals are approximately 4.47:1. This means that
for
> >every 10 lbs you apply with your foot, about 44.7 lbs are applied to the
> >piston in the cylinder. The hydraulic ratios take it from there.
Remember
> >also that essentially no system pressure is produced until the receiving
> >cylinders move and the friction material contacts the discs and or
drums.
> >At this point the system develops a uniform hydraulic pressure
(ignoring
> >proportioning valves and similar devices). All of these ratios apply
all
> >the time to the total system dynamics. The booster is simply a device
> >which provides linear amplification of the system pressure.
> >
> > All of these components are potential variables but it is important to
> >know the change that will occur with substitution. Bob wanted to raise
the
> >clutch pedal so that it operated in a narrower range. His chance
reduced
> >the hydraulic ratio resulting in more slave movement at the price of
higher
> >pedal pressure. He could have also reduced the distance between the
pedal
> >pivot and the connection to the master cylinder with the same result, as
> >long as the mechanical components stayed within appropriate operating
ranges.
> >
> > Typical brake systems for race car applications are designed with a 6:1
> >mechanical ratio so you can see why the stock 4.47 ratio typically
> >requires boosting. Changing components is intriguing but it frequently
> >alters the total system dynamics such as front rear brake bias so be
> >prepared for some unexpected results until you've done some field
testing.
> >
>
> Tom,
>
> Thanks for pointing out (again) the importance of the mechanical part of
> the system. BTW, probably only an engineer would call 4.47
"approximately".
> Being a physicist, I'll just round that off to 4.5 thank you. Also, wrt
> your statement: "He could have also reduced the distance between the
pedal
> pivot and the connection to the master cylinder with the same result, as
> long as the mechanical components stayed within appropriate operating
> ranges." I believe you meant "increased the distance" so as to reduce the
> mechanical advantage.
>
> Now, I suppose it would be helpful if we could come up with an easy way
to
> remember which way the mechanical advantage works in a hydraulic system.
It
> seems pretty obvious with a mechanical lever. The longer the lever arm,
the
> farther we have to push, but the easier it is. With the master/slave
ratio
> its still the farther we have to push, the easier it is, and a smaller
> master bore requires more motion to accomplish the same motion of the
> slave. So smaller master bore equates to longer lever arm. Now
personally,
> I think in terms of force times area, which has to be equal at each end,
> but maybe that doesn't work for everyone. Or maybe we could think of the
> master cylinder as another foot pushing back and the bigger that foot,
the
> harder he has to push. Anything clicking here Armand?
>
> I think Armand's suggestion of changing the master cylinder, although to
a
> slightly smaller bore, might be a good alternative to a booster. Or, as
Tom
> alludes, you could increase the mechanical ratio at the pedal. The
downside
> to these ideas is that you increase the pedal travel required, so you can
> only go so far with this approach; but maybe enough to make it acceptable
> (e.g., 6:1)
>
> Have a nice evening,
>
> Bob
> Robert L. Palmer
> Dept. of AMES, Univ. of Calif., San Diego
> rpalmer@ames.ucsd.edu
> rpalmer@cts.com
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