Gordan and Hans,
I want to thank you guys for bringing this subject up. I thought about it a lot
in the last 12 hours. A fixed ratio has some other bad effects. It is possible
to overload the traction drive HP wise by zinging the engine up with little or
no load such as a fine pitch or fixed pitch prop or on a dyno with
no load what so ever. This is because of the rotational inertia of the
turbine is added to the rotational inertia of the compressor and both are spinning
at 20 times engine RPM.

Another bad effect it has is it limits the range of ratios possible between
box and engine. One must always think of not exceeding the turbine red
line of about 120,000 RPM at max engine RPM so that severly limits the
choice of ratios used.

So I have decided to put in a one way clutch. This now means you could use
a ratio of as little as 1:10 and get power out of the turbine at 60,000 RPM
(if it were available) while the engine is running at 6000 RPM. In fact the
coupling will not lock up until the traction box output RPM exceeds the engine RPM.
I now understand and believe this feature is essential.
I will upload a drawing shortly.

I was concerned about the traction drive overload on acceleration too,
but then thought about the rotrex application, they drive a compressor
with their traction drive.  Have you calculated the torque loads?  Of
course you are right about adding the turbine inertia as well, but the
turbine should be putting in some torque in too.  You will lose some
responsiveness with a sprag clutch preventing the engine from driving
the turbine/compressor assembly, but it is a reasonable choice.  It
would be good to datalog the RPM differences across the one-way (sprag)
clutch at various loads, RPM's etc to see if it really is a problem.
One concern that pops into my non-engineer mind, is will the sudden
engagment of the clutch create to much of a load on the
turbine/compressor assembly?   It may be gentler to not have a clutch.
Without the clutch, the engine will have some more inertial load and
will spool up slower until the exhaust energy takes over the inertial
load of the turbine/compressor and reduction drive.

I don't see how a one way clutch will expand your choice of ratios.
Care to elaborate?  As I see it you probably want to pick your ratio so
that at cruise RPM you are in the sweet spot of the compressor chart,
for best efficiency, and not exceeding the compressor RPM limits at max
engine RPM.  I think you want big pieces, larger turbines and
compressors for efficiency reasons.  This is uncharted territory of
course, will require trial and error fitment.
Hans

Lets say we had a 20:1 fixed ratio. 10:1 in the box and 2:1 in the belt. No clutch.
That would limit max engine RPM to 6000 RPM. With clutch the engine will
over run the box at anything over 120,000 turbine RPM red line and 6000 engine RPM.
We can limit turbine RPM with a waste gate or larger compressor.
No matter the ratio with clutch the engine will never force the
turbocharger to exceed what ever RPM it wants to do.

Lets say we had a 20:1 fixed ratio. 10:1 in the box and 2:1 in the belt. No clutch.
That would limit max engine RPM to 6000 RPM. With clutch the engine will
over run the box at anything over 120,000 turbine RPM red line and 6000 engine RPM.
We can limit turbine RPM with a waste gate or largef compressor.
No matter the ratio with clutch the engine will never force the
turbocharger to exceed what ever RPM it wants to do.
Paul Lamar

Right, I understand the math Paul, my question is more like, shouldn't
things be sized/geared so that that the turbine is "pushing" the engine
at anything but a low RPM?   In other words, if you do not have the
ratio set so that you are extracting torque out of the turbine at
higher RPM, then there is no turbo compounding happening anyway.
Therefore the clutch is of no use to prevent over speeding.  I can see
its use in preventing overtorqueing of the traction drive at low RPM
where the engine is torquing the turbine.  But if the clutch is moving
at anything approaching even cruise power, then you are not getting
power out of the turbine.

You know a turbo over speeding and too much boost is a big problem with
higher power turbo rotaries, you have created the ultimate turbo
control, just tie it to the engine.

Hans


Suppose the turbine puts out max HP at 60,000 RPM and we want
to cruise the engine at 5000 RPM. The optimum  over all ratio is then
12 to one fixed. At 7000 RPM take off the turbine RPM would
be 84,000 RPM with a fixed ratio and no clutch. No problem.

Suppose the turbine generated max HP at 100,000 RPM and we
wanted to cruise the engine at 5000 RPM. Then the optimum over all
ratio would be 20:1. At 7000 RPM take off the  engine RPM
would then be 140,000 RPM  (too high.) with a fixed ratio
and no clutch. Big problem.

We want the flexibility of setting the over all ratio to almost
anything with out over speeding the turbo charger at 7000 RPM
take off. The HP peak on the turbine could be anywhere
from 50,000 to 120,000 RPM.

Paul Lamar ...No rotor no motor.

BTW please one subject per heading.
Things get too confusing way too fast.

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