Monitoring torque on a shaft.

[Ian Stirling]

I'm interested in measuring various parameters on a car - including
torque in the axle.
Is there a moderately simple way of doing this?
Breaking the shaft and sticking something in the middle is not an
option.
Is the best option to clean the shaft, and apply 4 strain guages, and
some means of measuring them and transferring the reading?

 

[Glenn Gundlach]

I'm interested in measuring various parameters on a car - including
torque in the axle.
Is there a moderately simple way of doing this?
Breaking the shaft and sticking something in the middle is not an
option.
Is the best option to clean the shaft, and apply 4 strain guages, and
some means of measuring them and transferring the reading?

Pet thought project of mine. I always pictured an optical or magnetic
reader at each end of the driveshaft and measure the position offset
under load. Let the DSP do the '0' load calibration while coasting. Of
course this assumes some twisting of the shaft under load. I thought
this would be good info to the transmission controller for smoother
shifts. I have NO idea if it's feasible so don't beat me up too bad.

GG

 

[John]

Pet thought project of mine. I always pictured an optical or magnetic
I would think that this would require knowing what the offset wold be
for different torque "settings"? That is, you would need to calibrate
the setup for your particular drive shaft size/material/mechanical
play, etc.

John

-- remove SPAMMENOT for e-mail responses --

 

[Boris Mohar]

I'm interested in measuring various parameters on a car - including
torque in the axle.
Is there a moderately simple way of doing this?
Breaking the shaft and sticking something in the middle is not an
option.
Is the best option to clean the shaft, and apply 4 strain guages, and
some means of measuring them and transferring the reading?

That is something the I would like to see in the drive shaft of my car as am
tuning it. Not an easy project. It is hell down there.



Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca

void _-void-_ in the obvious place

 

[Jim Thompson]

Pet thought project of mine. I always pictured an optical or magnetic
reader at each end of the driveshaft and measure the position offset
under load. Let the DSP do the '0' load calibration while coasting. Of
course this assumes some twisting of the shaft under load. I thought
this would be good info to the transmission controller for smoother
shifts. I have NO idea if it's feasible so don't beat me up too bad.

GG

Glenn, I had the same thought... wonder if there's enough "twist" to
read?

...Jim Thompson

 

[Adrian Jansen]

Pet thought project of mine. I always pictured an optical or magnetic
reader at each end of the driveshaft and measure the position offset
under load. Let the DSP do the '0' load calibration while coasting. Of
course this assumes some twisting of the shaft under load. I thought
this would be good info to the transmission controller for smoother
shifts. I have NO idea if it's feasible so don't beat me up too bad.

GG

Much easier to measure the reaction load on the springs/axle mounts. At
least you dont have to do it on a spinning object.


--
Regards,

Adrian Jansen adrianjansen at internode dot on dot net
Design Engineer J & K Micro Systems
Microcomputer solutions for industrial control
Note reply address is invalid, convert address above to machine form.

 

[Yukio YANO]

I'm interested in measuring various parameters on a car - including
torque in the axle.
Is there a moderately simple way of doing this?
Breaking the shaft and sticking something in the middle is not an
option.
Is the best option to clean the shaft, and apply 4 strain guages, and
some means of measuring them and transferring the reading?

Hook up a strain guage to the appropriate Engine Mount and Calibrate it
by measuring readings under load eg. accelerating up a long hill at
various speeds. No need to measure driveshaft, measure torque on the
entire powertrain!
Yukio YANO

 

[Tony]

That's a great suggestion!

Yukio Yano, demonstating great insight, wrote
"Hook up a strain guage to the appropriate Engine Mount and Calibrate
it
by measuring readings under load eg. accelerating up a long hill at
various speeds. No need to measure driveshaft, measure torque on the
entire powertrain! "

 

[John Larkin]

Pet thought project of mine. I always pictured an optical or magnetic
reader at each end of the driveshaft and measure the position offset
under load. Let the DSP do the '0' load calibration while coasting. Of
course this assumes some twisting of the shaft under load. I thought
this would be good info to the transmission controller for smoother
shifts. I have NO idea if it's feasible so don't beat me up too bad.

GG

That's commonly done. I've seen it on drive shafts for steamships and
jet engines, for instance. One shaft on the Joint Strike Fighter
transmits 32,000 horsepower to the lift fan, and it twists a *lot*.

Most shafts twist a good bit at full load. If they didn't, they'd be
by definition too expensive and heavy.

The pickups are often variable-reluctance magnetic things. They pick
up both speed and torque. You've got to watch out for vibration and
shaft runout.

You can get a bigger tube than the shaft, cut it into two lengths,
slide them over the shaft with a small gap, and pin the outer ends. At
the junction, each has a slotted optical mask or a plastic disk with
radial black stripes. Align the disks for zero light transmission at
zero torque, using a stationary led and photocell. Torque rotates the
disks relative to one another and lets light through, Moire' style.

John

 

[Anthony Fremont]

Glenn, I had the same thought... wonder if there's enough "twist" to
read?

Something like this perhaps.
http://www1.uspto.gov/web/patents/patog/week23/OG/html/1295-1/US06901815-20050607.html

I think the easiest way is to measure twist in the rear-end housing with
respect to the body (real wheel drive obviously). Tough with the
shocks/suspension doing their thing, but still should be doable. A
couple of those nifty pots with the pull strings that reel in and out
like a tape measure should let you easily measure the differential (pun
intended) twist and cancel out the common mode effects of the
suspension. Maybe I should file with the USPTO? ;-)

 

[John Popelish]

I'm interested in measuring various parameters on a car - including
torque in the axle.
Is there a moderately simple way of doing this?
Breaking the shaft and sticking something in the middle is not an
option.
Is the best option to clean the shaft, and apply 4 strain guages, and
some means of measuring them and transferring the reading?

Here are some options:
http://www.sensotec.com/torque_sensor_appnotes1.shtml

 

[Ross Herbert]

I'm interested in measuring various parameters on a car - including
torque in the axle.
Is there a moderately simple way of doing this?
Breaking the shaft and sticking something in the middle is not an
option.
Is the best option to clean the shaft, and apply 4 strain guages, and
some means of measuring them and transferring the reading?

This company seems to have achieved the goal.
http://www.mdi-sensor.com/

 

[Ian Stirling]

I would think that this would require knowing what the offset wold be
for different torque "settings"? That is, you would need to calibrate
the setup for your particular drive shaft size/material/mechanical
play, etc.

That's not horribly complex - putting it into 5th (or whatever), and
then pushing on it, to impart a known torque.
Several times, after moving the car, to eliminate systematic errors.

However, alas, my car is FWD, and I suspect the half-shafts have much
less torque induced bending - mainly due to the length - than
driveshafts.

 

[Ancient_Hacker]

You may find it difficult to find a spot on an engine mount where there
strain flows to mount a strain guage.

You could use the deflection of the engine on the mounts as a *rough*
indication of torque, but many cars have non-linear engine mounts--
they allow a lot of easy wiggle at idle, to isolate idle vibrations,
but under real torque the mounts have much more resistance per unit of
deflection.

..

 

[Ian Stirling]

I'm interested in measuring various parameters on a car - including
torque in the axle.
Is there a moderately simple way of doing this?
Breaking the shaft and sticking something in the middle is not an
option.
Is the best option to clean the shaft, and apply 4 strain guages, and
some means of measuring them and transferring the reading?

Many thanks everyone for the ideas.

Some more details of what I'm doing.
At the moment, I have an injector wire hooked, through a 100K resistor
to a laptop soundcard.
Works well. (It was initially a 100:1 divider, but I found I get vastly
lower noise (1lsb@8bit vs 80lsb) if I removed the ground wire.

This gives me RPM, and injector pulsewidth, and I can even see the other
injectors via crosstalk.

I'm now in the process of fitting two USB mice with hall sensors from a
1980s keyboard, to give nice simple quadrature inputs for wheel
rotations, to give tyre deflation warnings, not to mention dead
reckoning, and clutch wear.
Maybe even tyre wear, with GPS, though I doubt that.

 

[Jim Thompson]

On Fri, 10 Mar 2006 03:26:16 GMT, "Anthony Fremont"

[snip]

I think the easiest way is to measure twist in the rear-end housing with
respect to the body (real wheel drive obviously). Tough with the
shocks/suspension doing their thing, but still should be doable.

[snip]

Yep. With imaginary wheels it would be quite difficult ;-)

...Jim Thompson

 

[Iwo Mergler]

I'm interested in measuring various parameters on a car - including
torque in the axle.
Is there a moderately simple way of doing this?
Breaking the shaft and sticking something in the middle is not an
option.
Is the best option to clean the shaft, and apply 4 strain guages, and
some means of measuring them and transferring the reading?

What about fitting an accelerometer to the car? The torque is
linked to the acceleration via the mass of the car and the wheel
diameter - both roughly constant.

On a flat surface, anyway.

Regards,

Iwo

 

[Glen Walpert]

I'm interested in measuring various parameters on a car - including
torque in the axle.
Is there a moderately simple way of doing this?
Breaking the shaft and sticking something in the middle is not an
option.
Is the best option to clean the shaft, and apply 4 strain guages, and
some means of measuring them and transferring the reading?

I see the usual methods for measuring shaft torque have been covered
in this thread already, triggering a thought which I will toss out for
your entertainment, not suggesting this is a good idea to actually do:

In the early days of IC (Internal Combustion) engine development it
was not uncommon to measure Indicated Horsepower (IHP) in addition to
Brake Horsepower (BHP). BHP is what you get from measuring output
torque and speed regardless of the means of applying load, and IHP is
a measurement of power delivered to the top of the pistons. Engine
losses are IHP - BHP. IHP was measured with an Indicator, which
consisted of a small piston-spring assemply such that the position of
an attached pen is proportional to combustion chamber pressure. A
card holder was geard to the crankshaft, such that it moved
proportionally to the engine piston position. With the engine at
steady state on a dyno the pen is dropped onto the card and traces out
the pressure vs displacement curve; measuring the area within the plot
with a planimiter gives net work delivered to the piston, the top of
the curve is the power stroke and the bottom is the compression stroke
which gets subtracted. Intake and exhaust in a 4-stroke engine shows
up as a straight line which is neglected. Multiply by power strokes
per second to get IHP.

Needless to say the old mechanical Indicator does not work with modern
high speed engines, but the same thing can be and sometimes is done
with electronic pressure sensors and crank angle sensors. Engines
already have the crank angle sensor, and last time I looked pressure
sensors mounted on spark plugs were readily available. So you could
measure IHP, characterize your vehicle on a chasssis dyno, generate an
IHP and RPM look up table for BHP from the dyno test data, and
calculate shaft torque from there .

 

[Ian Stirling]

I see the usual methods for measuring shaft torque have been covered
in this thread already, triggering a thought which I will toss out for
your entertainment, not suggesting this is a good idea to actually do:

In the early days of IC (Internal Combustion) engine development it
was not uncommon to measure Indicated Horsepower (IHP) in addition to
Brake Horsepower (BHP). BHP is what you get from measuring output
torque and speed regardless of the means of applying load, and IHP is
a measurement of power delivered to the top of the pistons. Engine
losses are IHP - BHP. IHP was measured with an Indicator, which

<snip integration scheme>

Interesting - being able to measure the pressure in the cylinder would
also do interesting things - but alas not practical

I think I'll do some sums, and see what the torsional deflection in the
half-shafts is.

Integrating the engine mount forces would work - but I'd be looking at
~12 accurate linear position sensors, to nail down all the forces, not
to mention non-linearities, which would be hell.

 

[Glenn Gundlach]

That is something the I would like to see in the drive shaft of my car as am
tuning it. Not an easy project. It is hell down there.



Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca

Long ago I bought a Sears cruise control I wanted to use on a '77 VW
Dasher. The Sears was made for rear wheel drive but the Dasher was
front wheel. The speed detector was to attach a magnet to the drive
shaft and mount a pickup coil nearby. Since the driveshaft is 2-3 times
faster than the axle speed, I mounted 3 magnets at 120 degrees on the
flange of the final drive. It worked correctly. Point is while it is
hell down there, it is possible. It WOULD be interesting to work out
the mounts required for the pickup on the wheel/brake rotor.

DUH moment. Where are the factory sensors for the ABS? Could those
pulses be used as part of the project?

GG