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"keystone" taper on clutch spline

"keystone" taper on clutch spline

"keystone" taper on clutch spline

I am trying to specify a "keystone" taper on a cylindrical spline, i.e. to have the male and female splines be cylindrical in cross-section, but to have the tooth thickness on the male, and space width on the female, increase linearly along the axis. The application is a female selector which slides on an input shaft and can mate with male teeth on either a high- or low-speed gear. The "keystone" profile keeps the selector in positive engagement with the spline on the gear and prevents it from creeping or jumping out of engagement. I have seen pictorial representations in textbooks such as Nunney's "Light and Heavy Vehicle Technology". However, I am wondering is there a specification for this kind of spline or at least for the rate of taper? We have used crowned splines in the past but not this.

RE: "keystone" taper on clutch spline

The selector you describe typically uses 'face dogs' on gears' axial faces. Search on 'dog clutch' and variants.

Mike Halloran
Pembroke Pines, FL, USA

RE: "keystone" taper on clutch spline

Ah. You seem to be talking about an SAE 'square' spline with keystoned ends having back-taper like a dog clutch tooth typically has on its load carrying faces.

I've never seen anything quite like that in practice, so I'm not aware of a standard for it.

Mike Halloran
Pembroke Pines, FL, USA

RE: "keystone" taper on clutch spline

That design will introduce a lot of backlash. It seems to me that it would cause more problems than it would solve. Perhaps that is why I have never seen it.

RE: "keystone" taper on clutch spline

While this arrangement looks like it might work in theory, in practice it will likely have some serious limitations. The most obvious limitation is that after you cut the required "keystone" profile into both sides of the mating spline flanks, there will be little material left in the tooth root sections to handle the shear stresses. There is also the issue of how will you accurately produce the "keystone" profile on the internal spline teeth.

If you want a face-type coupling that provides better precision than the common dog ring clutch, you might consider a curvic coupling with teeth that have a negative pressure angle (around 2-4deg).

You could also apply some helix angle to your spline teeth to promote an axial force in one driving direction.

RE: "keystone" taper on clutch spline

PJM - that looks exactly like what we are looking for! Do you have a source for the photo? And possibly even a reference for the standard (if any) to which they were manufactured or alternatively a reference to the manufacturer of the gears?

tbuelna - unfortunately a helical arrangement is out because in reverse it will drive the clutch out of engagement. I think shear weakness of the keystone wouldn't be too much of a problem with adequate design, a minimal taper angle and coarse tooth pitch, but obviously this would be a part of the design process. We are, in fact, also thinking of curvic couplings with negative angle, as you suggest, which we have used elsewhere in the driveline, but this may raise space claim and also strength issues and might require a fairly substantial redesign.

RE: "keystone" taper on clutch spline


My Thoughts are.

How about an internal major dia slight press fit spline. AGMA class 4.

I agree with Terry keystone appears to be a nightmare to fabricate.
I believe the RPM's will be limited, in it's application.

all looks good on paper. how is your experience with these type of splines.


RE: "keystone" taper on clutch spline

Here's a video showing the machine that both the back-taper and end rounding/chamfering are machined on. Both are continuous rolling operations.


RE: "keystone" taper on clutch spline

Great Job Gearcutter

RE: "keystone" taper on clutch spline

Thanks Gearcutter, that's very good info.

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