Adding a torque sensor to a steering column

I want to retrofit a torque sensor to a steering column. The car runs hydraulic assist, not electric, and will remain hydraulic. Anyone have any clever ideas or parts sources?

"Hydraulic" starts to look really weird if you read it too many times.

Seems like a pressure sensor would give you the information you seek.  Would give you the wrong units for torque, but should parallel the amount of torque.

Why?

I'd look for one from a newer car to retrofit, it's basically a rotary load cell. Any car with direct-drive EPS has one somewhere.

Just be aware that it will add a small amount of play to the column.

I can probably convert. Pressure sensor, I like that. It would have to have a pretty high range, though.

Why? Because I have a traction control system that wants input from a torque sensor, and no torque sensor

I realize I might be able to steal one from a car with EPS. Any suggestions as to what that car might be? It's inside the rack on an ND Miata so I can't use that one even though I have a stack of ND racks.

Aren't there some hydraulic power steering pumps with built-in torque sensors?  Just trying to think outside the box.

Hm.  I would think there would be a lot of extraneous noise in a hydraulic pressure sensor from the pump, variances in output at different RPMs, etc.  Then again, I guess you don't feel them in the wheel, so maybe they're all high enough frequency you can filter them out?

There's an "AvE" video on youtube where he buys a cheap load-cell torque sensor from Harbor Freight, takes it apart to show how itw orks, and then tests it to destruction.  It's interesting, as GameboyRMH says it's basically a load cell, but it's wrapped around the shaft.  Applying torque twists the shaft, which results in minutely stretching one resistor, and that's something you can measure with a sensitive-enough amplifier.  In principle one should be able to do the same thing with a steering column, although I have no idea how difficult it is to do the actual attachment.

I'm not familiar with the EPS on a Miata, however I did custom build diagnostic equipment for the EPS used on the RX-8.  The RX-8 had a  non-contact differential transformer torque sensor.  The output of the sensor has two sine waves and depending on the torque applied through the sensor the sine wave will change and the difference between the waves is what was measured.  Needless to say this is a very hard system successfully mimic.  Anyway this signal was used by the  EPS controller, I'm not sure what the traction control was expecting.

I'm not sure if the traction control module you speak of is native to the Miata or is something out of another car that you're adapting to one of your creations.  As I recall there are at least three types of non-contact torque sensors used by various manufactures.  Each one outputs a different type of signal.

Where was this sensor mounted, Doc?

Familiarity of the EPS on the Miata is not necessary, as it is no longer there. We can modify the torque sensor signal to our heart's content, we just need something to feed into the box.

The thingy circled is the torque sensor on an RX-8.  It will have a  three  pin connector on it.

EDIT...

Schematic of sensor and how it is connected.

Not sure if it would work on a steering column, but the question made me think of the wireless drive shaft transducers.  Maybe they make something suitable?

You can use a strain gauge stuck to the outside of the steering column shaft 45* from the shaft axis. You would probably have to filter the signal with a small capacitor or within the software to smooth it out.  And it will probably take some trial and error to find the right strain gauge, amp, and filtering to make it work well. That said, I think it would be the easiest and "cleanest" install. Remember to leave a service loop of wire to not stress the electrical components. I wish I could be more specific but it's been a few years since I played with strain gauges.

I don't know those systems well, but it seems odd that it's taking in torque and not just steering angle? 

We have a steering angle sensor already. This is an OE TC system, not a simplified aftermarket one. You'd be amazed at what inputs this car uses for odd things.

freetors said:

You can use a strain gauge stuck to the outside of the steering column shaft 45* from the shaft axis. You would probably have to filter the signal with a small capacitor or within the software to smooth it out.  And it will probably take some trial and error to find the right strain gauge, amp, and filtering to make it work well. That said, I think it would be the easiest and "cleanest" install. Remember to leave a service loop of wire to not stress the electrical components. I wish I could be more specific but it's been a few years since I played with strain gauges.

You would need an ultrasensitive strain gauge fitted very precisely to the column, and you'd have huge problems filtering out noise from ambient temperature and warmth from the driver's hands, since the column will only flex microscopically. You need a flexible piece in the column to make measuring steering force practical, which the OEM torque sensors and old-fashioned rotary valves have in them.

Keith Tanner said:

We have a steering angle sensor already. This is an OE TC system, not a simplified aftermarket one. You'd be amazed at what inputs this car uses for odd things.

I figured with you that base was already covered, just checking!

Any more details on the system itself or is it secret? With steering torque and all the accelerometers onboard(+wheel speed + throttle position +etc) you can probably get a good idea of "intent" of an input. 

John Block over at Auto-ware could help you with parts and data collection  and or dialogues what ever you need.

He used to be on here but i don't recall his screen name.  I have a bunch of his programs and they really did help me racing program.

http://www.auto-ware.com/

accordionfolder said:

Keith Tanner said:

We have a steering angle sensor already. This is an OE TC system, not a simplified aftermarket one. You'd be amazed at what inputs this car uses for odd things.

I figured with you that base was already covered, just checking!

Any more details on the system itself or is it secret? With steering torque and all the accelerometers onboard(+wheel speed + throttle position +etc) you can probably get a good idea of "intent" of an input. 

I'm trying to see what we need to keep the traction control system happy on the V8-powered ND. It's had the stock EPAS removed and replaced with a hydraulic rack. We can simulate the EPAS output with software, but we need all the inputs to generate the correct messages. Right now, it's throwing errors under certain conditions and I think it's related to torque. The EPAS does output a torque signal as well as steering angle.

Corvette and Mustang used a valve mounted in the steering linkage (track rod)  to control the assist cylinder. I believe it could called a follower circuit. Some boats use a similar valve to hydraulically assist the steering.

Raetech has a clamp on style that i have used at work but they are not cheap and you need the data acquisition to back it up.

https://www.raetech.com/Instrumentation/Steering_Torque_Sensor.php

PMRacing said:

Raetech has a clamp on style that i have used at work but they are not cheap and you need the data acquisition to back it up.

https://www.raetech.com/Instrumentation/Steering_Torque_Sensor.php

Impressive. That's basically the ultra-high-tech hypothetical column-shaft-attached sensor I mentioned earlier. I can understand why the price is "you have to ask."