Dan Horton wrote:
Charles,
I said: I suspect that eliminating transmission noise (with selector
in neutral, clutch engaged, mainshaft spinning) is the purpose of the
654 ft-lbs/rad spring rate found at less than 3.5 degrees
displacement.

Got curious and ran numbers for a simple two element model. I used
what I think are reasonable guesses for the inertias, 0.07 slugs-ft^2
(crank, flywheel, and most of the clutch assembly), and 0.01 slug-ft^2
(transmission mainshaft and gearset). The connecting stiffness is of
course 654 ft-lbs/rad.

No joy. The above yields an F1 of 43.5 hz. That would make the
mainshaft rattle like hell at 1305 engine RPM with the selector in
neutral, so my guess about the purpose of the 654 spring rate does not
appear to be true. 654 isn't soft enough.

You got an idea about the 654 rate?

Dan


Two things. To get that spring rate(654), there would have to be
enough resistance in the transmission to absorb that level of torque. I
think that would be a pretty inefficient transmission. I doubt it. I
expect that in neutral, clutch engaged , idling you would have to be at
the lower limit of the spring since by definition you are at the lower
limit of torque, so look at the rates there. Once the shaft was
acclerated up to speed, the only torque that could be transmitted
through the springs would be the result of friction.

Second thing, dyno charts show the maximum torque the engine can provide
at a given rpm, doesn't mean that the engine has to produce that torque
at that rpm ( you do have a throttle right? the engine speed isn't
controlled solely by load). Every car is different, but I have heard
quotes of 25-30hp to cruise on the highway, so your 40ft lbs of torque
is almost enough at 3600 rpm for highway cruising, which means you could
see much lower torque values in high gear crusing at thirty miles an
hour. Finally, the torque on the dyno chart is the mean torque, not an
absolute ( the torque variations are how we got here in this
conversation) so I would expect it to have a range. But a definative
answer I can't give you, just my very unqualified thoughts. By the way,
I think I figured out why the auto engineers call it tip in and tip out.
Must be slang for TP in and TP out, the TP being throttle position.

Charles