Torsional Vibration and PSRU Design

stol wrote:
Today's multi-v belts -- the kind used to drive engine accessories on newer
cars -- are highly efficient and can handle huge amounts of power, up to
1000 hp.



Best of luck to ADK with his project.



Regards,



Gordon.




"cavelamb" wrote in message


Hmmmmm. If you are stating that a "serpentine belt", one that is a
about 1 inch wide and is used in most current vehicles will transmit
1000HP you might need to get another very stiff drink.
!!!!!!!!!!!!!!!!!!!!!!!!!!! G

Ben


Ben, no problem. Just have 3ft wide pulleys and run it at 10,000rpm.
Airplanes are all about compromises, right? 8*)

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Hi George,
Thank you very much for answering so many silly questions!

No problem, you're welcome.

I apologize for my crappy memory, but didn't we have a talk some
years ago after you broke your transmission by running on one rotor?

Dan

Jim,
Have you considered releasing some plans for the PSRU?

No.

How about your JN project? Are there pictures anywhere?

See Oct 98 Experimenter or Sept 04 Sport Aviation for cover shots
and articles (with two different paint schemes). EAA used it to
illustrate a lot of Sport Pilot articles. Dan Simonsen put it in one
of his fancy bookstore calendars. The best one was when a New York
financial magazine flew a photographer and his bigwig subject all the
way to Wetumpka, Alabama. They paid me $250 to dress the guy in my
leather jacket and get his picture taken standing by the airplane, all
for an article called "The Barnstormer of Wall Street". Compared to
New York prices, I'm sure they felt they were fleecing the rube. I
didn't mind. In Wetumpka, $250 was two month's hangar rent g

Dan

On 15 Apr 2006, Dan Horton wrote:

Yes Dan, and it eventually failed inflight as well, after almost 400
hours,and without warning. Fortunately, I was a mile high, and found a
nice road for landing. I have since changed to a Tracy Crook design
planetary PSRU- so far so good.

Great to hear from you again!

George, Sarasota Florida



I apologize for my crappy memory, but didn't we have a talk some
years ago after you broke your transmission by running on one rotor?

Dan




George Graham
RX-7 Powered Graham-EZ, N4449E
Homepage http://bfn.org/~ca266

Dan Horton wrote:
Gordon Arnaut wrote:

My understanding is that the springs in a clutch disk are under
preload, so the torque has to rise to a certain level before they will
compress.

Some clutch disks are indeed that way. No need to start at 0-0
when designing a clutch for an engine that makes, say, 150 or 200
ft-lbs of torque at idle. They only need to be soft enough to set
system F1 well below idle speed.


Dan, based on my studies, I don't think they are there to drop total
system resonance below idle speed. I think they serve another purpose.
I am pretty sure that the frequency of the driveline system is already
low. The engine/transmission is rubber mounted usually and the rear
axle is spring mounted and can rotate about the driveshaft axis. The
spring rate and compliance of both these elements factor into the
torsional stiffness of the system as a whole(i.e. total degrees of
deflection from the driveshaft perspective between engine and axle as a
result of torque inputs). I am pretty sure those elements will drop the
system frequency more than any clutch spring damper could hope to. Add
the fact that I think you would have to add the mass of the whole axle
assembly and its moment of inertia as well. Just my undertanding, but
reading various SAE papers it appears that the frequency of the
drivetrain is low enough that the problem they face is really low
frequency inputs like drivers jumping on and off the trhottle, which for
some reason they call tip-in and tip-out. The driveline reactions are
called shunt and shuffle and resonate evidently in the low hz range.

Regarding the torsional damper in the clutch , from Malloy's "Automobile
Engineers Reference" in the section "Clutches and Fluid Drives" there
are several passages that I believe are relevant and directly on topic.
In the "Requirements of Clutches" there is a paragraph on torsional
damping:

"Modern clutches, notwithstanding their own peculiar difficulties, are
also expected to incorporate some torsional-damping devices to eliminate
noise arising in the transmission. Suitable dampers could be placed in
many positions along the transmission, but it is generally considered
convienient for a variety of reasons to incorporate this feature within
the clutch itself"

and later in a few paragraphs titled "Transmission Noises" :

--Begin quote from Malloy ----

" The other major subject of complaint in a transmission system which
involves the clutch, although in this case as a means of providing a
cure, is that of transmission rattle.
The whole of the transmission can be regarded as a series of spring
mass systems, the spring element being provided by the torsional
deflection of various shafts, including those in the gearbox, and the
mass element by the inertia of the various gear wheels, etc.
Each of these units will have a natural frequency of vibration, and
if one or more should be excited by a disturbing force of an appropriate
frequency, then it may be set in vibration, and should the amplitude be
sufficient to take up the clearance between mating parts, noise may
ensue and some kind of torsional damping will be necessary. Two types
of damper are commonly in use, one being a seperate unit often attached
to the crankshaft, the other being a spring-cum friction unit in the
clutch driven plate. This latter unit can be tuned by the fitting of
different springs and varying the amount of friction. "

---end quote from Malloy ---

Again consider the lessons found in the Subaru clutch. The range
of torque capacity is 0 to 162 ft-lbs. A late 1980's EA81 was rated
73hp @4800 and 94 ft-lbs torque @ 2400. Don't know about idle speed
torque (anybody have a chart?), but let's guess 40 ft-lbs. So, we have
40 ft-lbs as we ease away from a stop, 94 ft-lbs in economy cruise, and
80 ft-lbs when pushing hard. Read carefully Gordon. All these numbers
are well within the range of 0 to 162. Actually they are all within
the single 1547 ft-lbs/rad spring rate found between 3.5 degrees and 6
degrees. Clearly engine torque has the springs in play at all times.


This would certainly be consistent with them damping transmission noise.
Regarding the rubber elements someone mentioned in their driveline,
"Automobile Engineers Reference" makes mention of these as well, saying
that they can provide similar damping to the clutch damper, and have the
added benefits of in some cases replacing the U-joint and the sliding
member in the driveshaft which is a real pain from an engineering
perspective.

To wrap it up, I am not claiming what these devices (clutch dampers) do
or don't do, just sharing what I have learned from my own reading. In
no automotive engineering text have I found them described as detuners
and your own empirical evidence suggests that in fact they are not.

Charles



Charles

Charles Vincent wrote:


I also forgot this quote from another source that might explain why the
spring rate is what you observe....

"In the case of idling noises the problem lies in the zero torque region
of the torsion characteristic of the clutch disk assembly. The problem
is alleviated if the torsional rigidity is low. Conversely, it is
necessary for the torsion characteristic of the clutch disk assembly to
be as rigid as possible to suppress the longitudinal vibrations caused
by tip-in and tip-out."

"Charles Vincent" wrote in message
et...
Dan Horton wrote:
Gordon Arnaut wrote:

My understanding is that the springs in a clutch disk are under
preload, so the torque has to rise to a certain level before they will
compress.

Some clutch disks are indeed that way. No need to start at 0-0
when designing a clutch for an engine that makes, say, 150 or 200
ft-lbs of torque at idle. They only need to be soft enough to set
system F1 well below idle speed.


Dan, based on my studies, I don't think they are there to drop total
system resonance below idle speed. I think they serve another purpose.
I am pretty sure that the frequency of the driveline system is already
low. The engine/transmission is rubber mounted usually and the rear
axle is spring mounted and can rotate about the driveshaft axis. The
spring rate and compliance of both these elements factor into the
torsional stiffness of the system as a whole(i.e. total degrees of
deflection from the driveshaft perspective between engine and axle as a
result of torque inputs). I am pretty sure those elements will drop the
system frequency more than any clutch spring damper could hope to. Add
the fact that I think you would have to add the mass of the whole axle
assembly and its moment of inertia as well. Just my undertanding, but
reading various SAE papers it appears that the frequency of the
drivetrain is low enough that the problem they face is really low
frequency inputs like drivers jumping on and off the trhottle, which for
some reason they call tip-in and tip-out. The driveline reactions are
called shunt and shuffle and resonate evidently in the low hz range.

Regarding the torsional damper in the clutch , from Malloy's "Automobile
Engineers Reference" in the section "Clutches and Fluid Drives" there
are several passages that I believe are relevant and directly on topic.
In the "Requirements of Clutches" there is a paragraph on torsional
damping:

"Modern clutches, notwithstanding their own peculiar difficulties, are
also expected to incorporate some torsional-damping devices to eliminate
noise arising in the transmission. Suitable dampers could be placed in
many positions along the transmission, but it is generally considered
convienient for a variety of reasons to incorporate this feature within
the clutch itself"

and later in a few paragraphs titled "Transmission Noises" :

--Begin quote from Malloy ----

" The other major subject of complaint in a transmission system which
involves the clutch, although in this case as a means of providing a
cure, is that of transmission rattle.
The whole of the transmission can be regarded as a series of spring
mass systems, the spring element being provided by the torsional
deflection of various shafts, including those in the gearbox, and the
mass element by the inertia of the various gear wheels, etc.
Each of these units will have a natural frequency of vibration, and
if one or more should be excited by a disturbing force of an appropriate
frequency, then it may be set in vibration, and should the amplitude be
sufficient to take up the clearance between mating parts, noise may
ensue and some kind of torsional damping will be necessary. Two types
of damper are commonly in use, one being a seperate unit often attached
to the crankshaft, the other being a spring-cum friction unit in the
clutch driven plate. This latter unit can be tuned by the fitting of
different springs and varying the amount of friction. "

---end quote from Malloy ---

Again consider the lessons found in the Subaru clutch. The range
of torque capacity is 0 to 162 ft-lbs. A late 1980's EA81 was rated
73hp @4800 and 94 ft-lbs torque @ 2400. Don't know about idle speed
torque (anybody have a chart?), but let's guess 40 ft-lbs. So, we have
40 ft-lbs as we ease away from a stop, 94 ft-lbs in economy cruise, and
80 ft-lbs when pushing hard. Read carefully Gordon. All these numbers
are well within the range of 0 to 162. Actually they are all within
the single 1547 ft-lbs/rad spring rate found between 3.5 degrees and 6
degrees. Clearly engine torque has the springs in play at all times.


This would certainly be consistent with them damping transmission noise.
Regarding the rubber elements someone mentioned in their driveline,
"Automobile Engineers Reference" makes mention of these as well, saying
that they can provide similar damping to the clutch damper, and have the
added benefits of in some cases replacing the U-joint and the sliding
member in the driveshaft which is a real pain from an engineering
perspective.

To wrap it up, I am not claiming what these devices (clutch dampers) do
or don't do, just sharing what I have learned from my own reading. In
no automotive engineering text have I found them described as detuners
and your own empirical evidence suggests that in fact they are not.

Charles



Charles

Another way to look at this might just be to say that the clutch springs
isolate (or decouple) the engine assembly from the driveline assembly (which
could be the psru and prop, the automobile's driveline, or some other
equipment).

On that basis; it would be reasonable to hypothesize that, so long as the
complete engine and clutch assembly is used without and modification, the
engine can be treated as a "black box" unit.

That would drastically reduce the work necessary to design and test the
psru.

Additionally; any theoretical resonance between the engine and psru in the
idle range would be mitigated by the progressive rate, and somewhat
uni-directional, nature of the clutch springs.

I am deferring to Dan for further observations.

Peter

P.S.: This really does not fully address the issue of the pusher
configuration which originated in an earlier thread. The disturbed air from
the wings, tail, andor fuselage could still cause a resonance in the prop
and/or psru which could destroy one or both.

Dan, based on my studies, I don't think they (clutch springs) are
there to drop total
system resonance below idle speed......I am pretty sure that the
frequency of the driveline system is already low.

Good argument. Consider me corrected, with a caveat. I think
you're right about driveline frequency already being low, even if there
were no clutch. The caveat? The clutch springs are one of the
stiffnesses in that system, and contribute to that low frequency. Take
them out, frequency goes up. Design them in, frequency goes down.

This clutch data is for a FWD car. No driveshaft, no long skinny
billet axles, no axle housing on a flexible mount. The clutch spring
rate of 1547 ft-lbs/rad is very soft. (For comparison, the little
rubber Centaflex CF12 I used in the Suzuki drive was 1991 ft-lbs/rad.)


System stiffnesses are additive like resistors;

1 / (1/K1 + 1/K2 + 1/K3 + 1Kx...) = K combined

Just for fun let's assume a simplified system with either two or
three connecting stiffnesses. Assume the drive axles are very soft
(1500 ft-lbs/rad) and the transmission shafts are equally soft. With
no clutch springs in the system, combined stiffness would be 750
ft-lbs/rad. Add a set of 1500 ft-lb/rad clutch springs, and overall
stiffness goes to 500 ft-lbs/rad.

Now assume drive axles and transmission shafts at 5000 ft-lbs/rad.
Without the clutch springs, stiffness is 2500. With the clutch, 938.

The point? Even in the company of other soft elements, the
addition of another makes a significant difference. If the addition is
a lot softer than the other elements, it makes a huge difference.

transmission rattle.....some kind of torsional damping will be
necessary. Two types
of damper are commonly in use, one being a seperate unit often attached
to the crankshaft, the other being a spring-cum friction unit in the
clutch driven plate. This latter unit can be tuned by the fitting of
different springs and varying the amount of friction. "

Lemme tell a little story. After testing a viscous disk damper
running in parallel with a soft element and finding out how well it
worked, I got the idea that perhaps I should obtain a patent. Before
spending money on an attorney, I did some searches in the patent
database. Turned out that Eaton had already patented a clutch for HD
truck (big rig) applications with a serious viscous damper in parallel
with the clutch springs. There were lots of friction damped clutches
too. I didn't pursue the patent on my "invention".

Note the use of the term "damper" in the quoted text. Are you sure
the text wasn't speaking of something a bit larger than our light duty
clutches? Not much sign of a frictional damper in the Subaru clutch.

.. Actually they are all within the single 1547 ft-lbs/rad spring rate found between 3.5 degrees and 6 degrees.
This would certainly be consistent with them damping transmission
noise.

I'm guessing that it is not the 1547 ft-lbs/rad spring rate. 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.
There is no other logical explanation for the dual rate, since the
lowest torque output from the engine is more than 40 ft-lbs. Remember,
with the transmission engaged you have a system that includes
driveshafts, axles, etc. With the transmission in neutral you have an
entirely different truncated system; crank, flywheel, clutch and the
tranny mainshaft. If somebody here has a late 80's Subaru mainshaft
with gears, we could do a bifilar, get an inertia, and calculate
natural frequency for the truncated system.

I'm thinking out loud here, nothing more. Before today I've put
very little thought into automotive drivelines.

Regarding the rubber elements someone mentioned in their driveline,
"Automobile Engineers Reference" makes mention of these as well, saying
that they can provide similar damping to the clutch damper

Rubber elements do have a damping value, although it is very, very
small. We got the actual value from Lovejoy when we were doing the
modeling, but logic alone tells you it ain't much. If it had much
damping value, it would melt g

Dan

Dan, based on my studies, I don't think they (clutch springs) are
there to drop total
system resonance below idle speed......I am pretty sure that the
frequency of the driveline system is already low.

Good argument. Consider me corrected, with a caveat. I think
you're right about driveline frequency already being low, even if there
were no clutch. The caveat? The clutch springs are one of the
stiffnesses in that system, and contribute to that low frequency. Take
them out, frequency goes up. Design them in, frequency goes down.

This clutch data is for a FWD car. No driveshaft, no long skinny
billet axles, no axle housing on a flexible mount. The clutch spring
rate of 1547 ft-lbs/rad is very soft. (For comparison, the little
rubber Centaflex CF12 I used in the Suzuki drive was 1991 ft-lbs/rad.)


System stiffnesses are additive like resistors;

1 / (1/K1 + 1/K2 + 1/K3 + 1Kx...) = K combined

Just for fun let's assume a simplified system with either two or
three connecting stiffnesses. Assume the drive axles are very soft
(1500 ft-lbs/rad) and the transmission shafts are equally soft. With
no clutch springs in the system, combined stiffness would be 750
ft-lbs/rad. Add a set of 1500 ft-lb/rad clutch springs, and overall
stiffness goes to 500 ft-lbs/rad.

Now assume drive axles and transmission shafts at 5000 ft-lbs/rad.
Without the clutch springs, stiffness is 2500. With the clutch, 938.

The point? Even in the company of other soft elements, the
addition of another makes a significant difference. If the addition is
a lot softer than the other elements, it makes a huge difference.

transmission rattle.....some kind of torsional damping will be
necessary. Two types
of damper are commonly in use, one being a seperate unit often attached
to the crankshaft, the other being a spring-cum friction unit in the
clutch driven plate. This latter unit can be tuned by the fitting of
different springs and varying the amount of friction. "

Lemme tell a little story. After testing a viscous disk damper
running in parallel with a soft element and finding out how well it
worked, I got the idea that perhaps I should obtain a patent. Before
spending money on an attorney, I did some searches in the patent
database. Turned out that Eaton had already patented a clutch for HD
truck (big rig) applications with a serious viscous damper in parallel
with the clutch springs. There were lots of friction damped clutches
too. I didn't pursue the patent on my "invention".

Note the use of the term "damper" in the quoted text. Are you sure
the text wasn't speaking of something a bit larger than our light duty
clutches? Not much sign of a frictional damper in the Subaru clutch.

.. Actually they are all within the single 1547 ft-lbs/rad spring rate found between 3.5 degrees and 6 degrees.
This would certainly be consistent with them damping transmission
noise.

I'm guessing that it is not the 1547 ft-lbs/rad spring rate. 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.
There is no other logical explanation for the dual rate, since the
lowest torque output from the engine is more than 40 ft-lbs. Remember,
with the transmission engaged you have a system that includes
driveshafts, axles, etc. With the transmission in neutral you have an
entirely different truncated system; crank, flywheel, clutch and the
tranny mainshaft. If somebody here has a late 80's Subaru mainshaft
with gears, we could do a bifilar, get an inertia, and calculate
natural frequency for the truncated system.

I'm thinking out loud here, nothing more. Before today I've put
very little thought into automotive drivelines.

Regarding the rubber elements someone mentioned in their driveline,
"Automobile Engineers Reference" makes mention of these as well, saying
that they can provide similar damping to the clutch damper

Rubber elements do have a damping value, although it is very, very
small. We got the actual value from Lovejoy when we were doing the
modeling, but logic alone tells you it ain't much. If it had much
damping value, it would melt g

Dan

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