Clutch options (Curvic/Hirth?)
7

Question

Clutch options (Curvic/Hirth?)

Davidlinsk (Aeronautics)

(OP)

28 Dec 20 08:39

Hello,
I am currently designing a rotating system. Simplified, it is essentially an electric motor driving some load (the load is connected to a separate shaft). The electric motor, after some ramp up sequence, has to disengage for the load and completely pull it back (while the load continues rotating). Also, the dimensions are quite small, the driven shaft has a 10 mm diameter. I estimate that the load reaches a peak of around 5 Nm from mass inertia for around 10k RPM.

I need some kind of clutch solution so that I can easily disengage from the load, without risking pulling the load with the e-motor.
I had thought to use a curvic or hirth design, but most manufacturers don't make them this small for 1 or 2 units and it's quite difficult to find proper information on the design of these (I had searched the forum and got some results, but not enough to produce a reliable design).

My question is- does anyone have some design tools or guidelines for these types of couplings or knows a supplier who manufactures them at these sizes? or alternatively, are there other clutch options that anyone knows of that may fit my requirements? I have very limited experience with this type of thing, unfortunately.

Thank you!

desertfox (Mechanical) · Answer 1 · 2020-12-28 10:34:24

Hi

Hard to visualise your situation however what about a spragg clutch https://www.renold.com/company/latest-news/couplin...

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

DAVIDSTECKER (Mechanical) · Answer 2 · 2020-12-28 15:25:39

Hillard also makes over-running, one way clutches.
Really easy to design around.

hendersdc (Mechanical) · Answer 3 · 2020-12-28 19:33:29

From your description it is hard to say if you really need a clutch or just a shaft coupling that is easy to disengage. You might consider looking into magnetic shaft couplings.

TugboatEng (Marine/Ocean) · Answer 4 · 2020-12-28 21:47:20

Ogura has a more complete line of electric clutches even in very low torque ranges:

https://ogura-clutch.com/

DAVIDSTECKER (Mechanical) · Answer 5 · 2020-12-28 22:48:47

You may want to look in to car starter motors for design ideas also.
GM uses a sliding pinion gear on a splined shaft activated by a shifting fork and a solenoid.

TugboatEng (Marine/Ocean) · Answer 6 · 2020-12-28 23:05:25

Colloquially, we call that a Bendix drive. There are two types, a pre-engaged and inertia type. They each have advantages though I have never experienced an advantage of the inertia type.

Davidlinsk (Aeronautics) · Answer 7 · 2020-12-29 09:37:07

Thanks for all your replies!

So I guess it was unclear to me what constitutes a "clutch". My meaning was indeed a coupling that can be disengaged during operation.

It seems that a Bendix or Magnetic couplings are the way to go.

Some questions regarding the Bendix: I had actually thought of a similar mechanism using a "pre-engaged" male spline (DIN 5480) on the driven shaft, and a female on the driving shaft. Where, when needed, the female side would pull back and the splines would disengage. I was thinking that perhaps there is too much contact surface, and the splines would get stuck to each-other. Does anyone have experience with this? what kind of gear shape would be the best for this "sliding operation"? Also, is there a rule of thumb to how rapid the sliding operation would have to be?

If anyone has design material to share on these (at least on the Bendix, since the Magnetic coupling is COTS), or some known manufacturers of magnetic couplings, that would be great. I'm Googling all of this in any case, but anything I can learn from the experience that you guys have would be the best.

Thanks again!

DAVIDSTECKER (Mechanical) · Answer 8 · 2020-12-29 14:45:35

The spiral clutch style may be something to look at.
If you screw down the drive shaft key you can open up the bore and keyway to allow it to slide.
I've done that many times but for much lower speeds.
For spline shaft specifications I'd take my cue from the hydraulic pumps and motors since it is very popular and many shop already have the broach tooling.

Davidlinsk (Aeronautics) · Answer 9 · 2021-01-09 17:25:52

Thank you everyone for all the help!
With your advice, I ended up using an overruning clutch with an involute splined connection, and of course some disengagement mechanism.

TugboatEng (Marine/Ocean) · Answer 10 · 2021-01-09 19:14:42

Lubricating splines at high RPMs can be problematic. If it's not in an oil bath, seals to contain the lubricant are a must as are shear stable greases.

Davidlinsk (Aeronautics) · Answer 11 · 2021-01-10 09:03:22

Lubrication is a bit of a problem here. This is essentially a one-off kind of thing, and it's impossible to use a bath here unfortunately.
The splines are engaged for a period of about 10 seconds and then the female side is completely disengaged and then pulls back a significant distance.
How would you lubricate something like this?

I had thought to use copper plating to reduce friction, but otherwise I thought to have it dry running.

Thanks

TugboatEng (Marine/Ocean) · Answer 12 · 2021-01-10 19:30:17

Dana/Spicer have a nylon coating they apply to splines for automotive driveshafts: https://patents.google.com/patent/US5903965A/en

Otherwise, there are MoS2 coatings that require a light sand blast and then are sprayed, dipped, brushed on. I can't give specifics as I've only heard of them.

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