Acentric Chain Tension

[BenjaminL]

Hi Guys,

For our new design I`m working on an acentric chain tensioner integrated in the Diff mount.

From what I`ve seen in many of these type of tensioners - the internal plate with the acentric hole is attached to the diff mount only by tightening the outer part of the mount on this plate - which means the only thing keeping it (the plate)from moving, is the friction between the mount and the plate. If friction is the issue and I`m not missing some kind of invisible spline? how do you calculate the closing pressure for the diff mount over the plate?

Hope I managed to pass through my question correctly. I`ll try to upload a photo in case this in not as clear as I intended it to be.

Thanks for your help

Ben

[BenjaminL]

Hi Guys,

For our new design I`m working on an acentric chain tensioner integrated in the Diff mount.

From what I`ve seen in many of these type of tensioners - the internal plate with the acentric hole is attached to the diff mount only by tightening the outer part of the mount on this plate - which means the only thing keeping it (the plate)from moving, is the friction between the mount and the plate. If friction is the issue and I`m not missing some kind of invisible spline? how do you calculate the closing pressure for the diff mount over the plate?

Hope I managed to pass through my question correctly. I`ll try to upload a photo in case this in not as clear as I intended it to be.

Thanks for your help

Ben

[Jay Lawrence]

Hi,

Not sure about the ins and outs of the eccentric design (never used one), but as for the pressure between the plates: you know how many bolts you're using, you can specify a bolt torque, and you know the kind of bolts you're using. Therefore you can work out the compressive force that you achieve by putting the bolts into tension when you tighten them (tightening torque translated through the inclined plane of the bolt).

[Rex Chan]

We tension our chain with turn-buckles between the diff assembly and the engine. We run a spool, but still have driveline bearings in plates like any diff design (I think). The whole assembly is pivoted at the top (off the rear bulkhead), and the turnbuckles react the forces back to the engine/lower engine mounts.

MUR 2011: Driveline/Spool/Rectifier/ (http://www.facebook.com/photo.php?fbid=10150400732188036&set=a.10150400731033036.361642.559588035&type=3)

In the picture you can't see how the turnbuckles work, but it does show the pivot (the 2 alum plates between the steel tabs, welded to the square section bulkhead. The guy who designed it puts the forces back into the engine by reacting it into the engine mounts, very close to the actual engine block.

The advantages of this design (to me at least), is the reduction in machining, and less stuff (mass, complexity).

[kcapitano]

Hi Benjamin

If I remember correctly, Stuttgart's eccentric chain tensioners that I saw at Michigan in 2011 did use a spline profile. My team uses turnbuckles very similiar to Rex Chan's picture, except the assembly pivots around the lower frame mounts. Hopefully that helps you out a bit.

[Kirk Feldkamp]

Rex: Your rectifier works (stays cool) sitting right there? I've never had good luck with motorcycle rectifiers in any location other than in clean airflow with the fins oriented along the direction of the airflow.

[Hector]

I designed diff mounts that used nothing but friction to constrain the diff in the longitudinal direction. Ran them for 2 years and never a slip. It's totally doable.

Don't make the same mistake we made the first time we designed accentric mounts: you need fine resolution in adjustment. The difference between a super-tight chain and a too-loose chain was about 1.25 mm. I recommend adjustment resolution in the half mm range.

[mattd27]

Our drivetrain guy in 2010 designed an eccentric mount with a vernier scaled adjustment. 45 holes on one side 40 on the other. Allowed for 0.14mm displacment resolution.

The system worked brilliantly and is still in use.


Diff Render (http://www.facebook.com/media/set/?set=a.404564583276.177920.320933128276&type=3#!/photo.php?fbid=438624368276&set=a.404564583276.177920.320933128276&type=3&theater)


Matt

[JRod]

Monash Motorsport '08 arrangement was similar to Matt's picture. It was difficult to tension, but once it was done, you were damn sure it would stay that way. I loved it.

[Rex Chan]

Kirk: I've never actually measured how hot it gets. But I've accidentally touched it at least once, and it is quite hot.

In terms of "working", I think it does. We're happy with how our electrical system charges, and haven't blamed any performance issues on the rectifier.

When you say "never had good luck", what problems did you attribute to an overheating rectifier? Our battery volts (how I judge how well the system is working/charging) is stable running all the engine electrics, fuel pump (Delphi 6A), and water pump (EWP115 10A). It's only when we turn the fan on (Pacet 10A) that the volts drop, which I take to mean that the battery is being drained/alternator overwhelmed.

Do you think we might get more current out of our charging system if the rectifier was cooler?

[Boffin]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by mattd27:
The system worked brilliantly and is still in use.
</div></BLOCKQUOTE>Well, the vernier system works great, except for when some dofus (me) lines the holes up wrong during rebuilding.

[BenjaminL]

Thanks Guys for all the info and Photos.

I`ve attached a few pics I found over the net for several tensioners of this sort. Non of them has a spline or anything similar to it that holds the plate other then friction. ( correct me if I`m worng).

http://www.mad-engineer.com/en...attachment/img_0385/ (http://www.mad-engineer.com/engineering/fsae/diff-brackets/attachment/img_0385/)
http://i1158.photobucket.com/a...enlevit/IMG_4057.jpg (http://i1158.photobucket.com/albums/p607/benlevit/IMG_4057.jpg)


Hector - can you tell a bit more about the material you used? did you have the inner plates and diff mounts made of different material ? and did you do some analysis for the closing pressure of the mounts over the inner plates?

Boffin - can you tell us how much this system weighs? looks a bit heavy...