Gear Question 5

[DJM123]

Hi:

I am building a custom crankcase to build a 4 cylinder 2stroke engine ... I want to have two seperate crankshafts "geared together" on both ends of the crankshaft ... so the load is shared over two cranks instead of one long crank ...

I need some help selecting the proper "spur???" gear to do this job. It can have a maximum diameter of 6.5" and min of 6.25" and I need the face width to be as small as possible. Each engine makes approx 300ftlbs of torque at 8000RPM (500hp).

I need the geartrain to be both efficient and "durable" ...

Any help you can offer would be appreciated.

Thanks.

Dave

 

[MikeHalloran]

It's time to sign up for engineering school.

... or rent someone who already went through it.



Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

DJM123,

You'll get the best efficiency from spur gears. And to keep the face width to a minimum, you'll naturally want to use as large a pitch diameter as possible. However, a 6" PD spur gear at 8K rpm would have a PLV of over 12K FPM, which is higher than normally preferred due to dynamic tooth loads.

You can get a good gear text and design your own gears. But in your post you require both minimum size and "durability". If you have little or no experience designing gears, the safest approach is to design your gears with very large margins. Otherwise, they are likely to fail very rapidly, costing you much time and money. But using large margins won't produce minimum size gears.

However, if you do as MikeHalloran suggest and pay a qualified gear design consultant to design your gears for you, the gears will perform properly first time out and will meet your requirements for minimum size and durability. A good gear designer should be able to develop your gear set geometry with all the necessary tweeks, plus give you guidance on materials, heat treatment, grinding, etc., in 1 or 2 days at most. It is money well spent, since his consulting fee will be less money than making a replacement set of gears.

Plus, the benefit of having your gears professionally designed is that it will allow you to focus all of your time and money fixing the endless problems you will encounter in the rest of your engine.

Good luck with your project.
Terry

 

[flash3780]

Dave,
Spur gears are efficient, but tend to be noisy. Helical gears are a bit more lossy, and you have to deal with thrust loads, but they are quieter and smoother. Automobiles these days use helical transmission gears. Camshaft-crankshaft connections are usually made by chains or belts. The cam-crank gears that I've seen are often spur gears - specifically in the Ford 300 CID 6-cylinder truck engine.
If you're looking for an off-the-shelf solution, check Boston Gear. Their catalog has got a great engineering section.

http://www.bostongear.com/litportal/pdfs/P-1930-BGlo.pdf

Good luck!

-Chris

 

[MikeyP]

Remember to consider the peak torque of the combustion pulses in your gear sizing calcs - not just the mean delivered torque.

M

--
Dr Michael F Platten