Dog Clutch Calculations

[morris9791]

Dear Experts,

Is there a standard available for the design dog clutch teeth and calculating the strength of same? Any resources I can follow up?

Best Regards

Eddie

 

[tbuelna]

morris9791,

Dog clutch teeth are basically short, fat, cantilevered beams. You don't usually have a bending issue or a shear strength issue. So all you really need to worry about is surface contact fatigue and fretting. The contact condition under load is very similar to what you would have in a spline.

The most difficult variable to establish for your contact loading is load sharing among the teeth, if you have more than three teeth (with three teeth or less, the teeth should load share equally by definition). And also the effective contact area of each tooth pair can vary due to edge loading. Edge loading can be caused by deflections under load or torsional wind-up, or from manufacturing tolerance errors.

The only other thing you need to account for is how aggressive your driver is. If your driver is not a skilled shifter, you may want to alter things like tooth undercut, backlash spacing, and possibly adding helix to the top land surface.

One effective type of dog tooth geometry is the "Curvic" tooth form from Gleason. Unlike the more conventional straight flank tooth, the curvic tooth is self-centering and thus tends to load share more effectively.

Gleason's engineering has a design guide for curvic dog clutches.

Good luck.
Terry

 

[BrianPetersen]

The dog clutches that I'm familiar with are those in motorcycle transmissions. One consideration is the torque output of the engine; the other consideration is the impact loading that happens (more or less) in every gear change, including an allowance for "operator error".

There is generally some flexibility built into the clutch hub and the drive sprocket at the rear wheel to cushion this to some extent, and the slight slack in the drive chain adds some flexibility, too.

I've stripped the teeth off an engagement dog by first missing a shift at redline and then shifting the transmission into gear after the revs dropped too far (but road speed was still very high) ...

 

[morris9791]

Terry and Brian,

Thanks for the response! It appears we may have some problem wiht the compressive / contact stress on our current dog clutch.I think the tooth depth is too small for starters.
The curvic teeth is an interesting one, would greatly appreciate this information. Although I thought self centering was mainly associated planetary systems..

FYI, I have uploaded an interesting article downloaded from Timken regarding flexpin bearings which deals with the issue of load sharing in planetary systems.


Best Regards
Eddie