# Sprag clutch



## Woodsmith (Jun 5, 2008)

I just found this tractor over run clutch on Ebay.

That could be remachined to fit the male end in the female spline of a large pump motor and the transmission primary shaft into the female end.

Instant coupler with a freewheel.


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## dreamer (Feb 28, 2009)

Well, the tractor PTO clutch on ebay has no specs on torque or RPM ranges, so that is really useless.

I like this idea a lot. I had not thought about the connection to the transmission, but had thought about coupling multiple motors together using Sprag clutches -- a high efficiency AC motor like the HPGC AC-50 direct to the transmission for cruising, but Sprag-backed by a high-torque DC motor for added torque during acceleration. The Sprag would reduce the drag of having the DC motor hard-coupled to the AC-50.

The Renold sprag clutches look promising, with torque specs up into the thousands of Nm or ft/lbs. But the RPM ranges for the overrunning clutches that have the torque necessary -- upwards of 200Nm -- are relatively low. A difference of only 1000rpm might be enough for shifting and it might not. Have you found prices for an appropriate Renold coupling model ?

I had previously found this inexpensive Sprag bearing, but its torque is too limited, I thought.

http://www.vxb.com/page/bearings/PROD/One-Way-Bearings/Kit8183


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## dreamer (Feb 28, 2009)

I wonder. Could using the Sprag input clutch from an auto tranny car on a manual tranny as the electric motor coupling be a great solution ?

http://cgi.ebay.com/ebaymotors/RECO...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories


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## Woodsmith (Jun 5, 2008)

An automotive sprag would suggest a suitable torque/power/speed capacity and I know that the early Saabs had them. Gearbox sprags would need some sort of sealed housing to keep lubricants in though.

The tractor sprag could be assessed for capacity through a chat with a manufacturer and possibly comparison with those from Renolds. At least they are designed for a harsh environment and to be low cost for replacement.
I have a Renolds trade outlet near me so I may pop in and see what the costs are for a suitable one.
If they are costly and the tractor one are usable then that could be a cheaper way to go depending on resplining costs.

It is making think harder about not keeping the clutch flywheel assembly if this is a good option.
Cost wise I will take into account that I would still need to make an adaptor for the flywheel or direct drive anyway so the overall cost of the sprag may be still be competititve.


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## dreamer (Feb 28, 2009)

It occurs to me that a Sprag clutch removes the possibility of regenerative breaking, but that is only a concern if planning an AC or Sepex motor. If using just a series DC motor, a Sprag sounds pretty good.

Just letting up on the accelerator should be enough to allow a smooth shift, right ? It sounds so simple, there must be something wrong with this idea.


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## Woodsmith (Jun 5, 2008)

dreamer said:


> It occurs to me that a Sprag clutch removes the possibility of regenerative breaking, but that is only a concern if planning an AC or Sepex motor. If using just a series DC motor, a Sprag sounds pretty good.
> 
> Just letting up on the accelerator should be enough to allow a smooth shift, right ? It sounds so simple, there must be something wrong with this idea.


Yes, these were my thoughts. No good for regen but not that many use regen yet.

The reason I posted is because it sounds so simple something must be wrong with the idea. I just can't think what.


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## dreamer (Feb 28, 2009)

*Re: High Torque Sprag (one-way) clutch*



Woodsmith said:


> Yes, these were my thoughts. No good for regen but not that many use regen yet.
> 
> The reason I posted is because it sounds so simple something must be wrong with the idea. I just can't think what.


Maybe people aren't familiar with therm "Sprag" ? Maybe changing the title of the thread to "High Torque Sprag (one-way) Clutch" you'd get more feedback.


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## Dave Koller (Nov 15, 2008)

Woodsmith said:


> Yes, these were my thoughts. No good for regen but not that many use regen yet.
> 
> The reason I posted is because it sounds so simple something must be wrong with the idea. I just can't think what.


Well you got my attention - neat idea but like you say what is the "wrong " side... your llink explained a lot... no let's hear from all those "experts" out there lol


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## BWH (Sep 26, 2008)

I'm not an expert, but the idea intrigued me so I looked around a bit.

The biggest downside I've found for sprag clutches in automotive use is that it does not allow engine braking on downhill runs leading to brake system failure. That's not a big deal for EVs though since there is no engine braking anyway. 

The most common failure appears to be a failure to lock up, although they will turn into grenades if the torque rating is exceeded. 



> http://www.maxwellpropulsion.com/PDF/mps_psru_update.pdf
> the most likely source of the sprag clutch failure is a misalignment problem... There is no way to ensure that a sprag clutch will lock up before it spins free.
> By design, all the sprags must engage together to achieve the full torque rating. Misalignment of even 0.002 inches may cause only a portion of the sprags to initiate the engagement. Up to a point, the clutch is self-centering, since the cage will force the remaining sprags to engage and bring things into alignment, however, this is not a long term solution. If the sprags on one side of the clutch engage first, the cage transmits the force to engage the remaining sprags. When this occurs over and over, the cage fatigues and the life of the clutch is reduced considerably.


I got a few leads from this site: http://www.eng-tips.com/viewthread.cfm?qid=184403&page=7

http://www.epilogics.com/md/100600.htm
*Rated Torque* 500 ft-lb.........678 N-m 
*Max Torque* 1,250 ft-lb..........1,695 N-m 
*Max Overrun Speed* 12,000 rpm

http://www.formsprag.com/PDF/P-956-FC_pg014-047.pdf
Or you could look through this catalog. ​


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## Birdman Jack (Feb 28, 2010)

Dave Koller said:


> Well you got my attention - neat idea but like you say what is the "wrong " side... your llink explained a lot... no let's hear from all those "experts" out there lol


I have used a lot of these in the plant maintenance I do at different plants. We always laser align them. On most of the machinery we put them on there can be no vibration what so ever. Most of the motors have vibration monitors electrically monitored just for this reason. If they go out at all they are toast. I have not bought any but they are not cheap from what I understand.


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