Two-speed gearbox

[RyanMech1]

Hello, I am designing a basic two-speed gearbox (high and Low) and was wondering if anyone new any good references or links in which I can find an exploded view or a general parts list of an existing model. I'm initially thinking of avoiding synchromesh and dogteeth as the gearbox does not need to shift while the vehicle is in motion, the operator will choose high or low before they begin product use. I am hoping that I can get by with spur gears. Any thoughts or advice (or criticism) would be greatly appreciated! Thanks, Ryan.

 

[MikeHalloran]

The operator _can_ choose to shift with the vehicle stopped.

Given the slightest familiarity with automobiles, the operator will probably _choose_ to shift on the fly, no matter what you might say in the product manual. If you have ever tried to change gears on a lathe without rotating something, you would do it, too.

A transmission with a sliding spur gear is certain to break off teeth when shifted on the fly. Constant mesh gears and dog clutches are _much_ stronger.



Mike Halloran
Pembroke Pines, FL, USA

 

[RyanMech1]

Thanks for the info although I must clarify a couple of things. Our "machine" has two attachments the operator must manually install before operation, one a high speed attachment and another a different low speed attachment, so there really isnt a need to shift on the fly as the gearbox is put into the proper gear before running the machine. We are running from the driveshaft and using its clutch to allow the operator to shift into neutral while it is in motion. Since their isnt a need to shift before machine is running I should be able to get away with spur gears, no??
Thanks, Ryan.

 

[cowski]

I can't answer your gear question, but a bit of advice if I may:

Don't design for what the operator is supposed to do, design for the worst case scenario of what the operator could possibly do.

ie if the operator isn't supposed to shift on the fly, design it so they absolutely can't. If your design could be shifted on the fly, make it strong enough to withstand that possibility.

 

[Allen]

Rayan,
For selecting gears there are some factors such as in/out shaft alignments, gear forces, ...
If the transmitted torque or speed is high then use helical gears.
Also note that you must select different bearings for different types of gears.

see :

http://www.engineersedge.com/gear_design.htm

And there are gear handbooks to download:

http://www.qtcgears.com/Q410/Q410Cat.htm

http://www.bostongear.com/products/open/theory.html

And an interesting collection:

http://gearlab.eng.ohio-state.edu/Pages/Gear_Collection/gear_collection.htm