Gear vs Chain efficiency

[AshleyJean]

We are working on a high mileage car with a 1HP engine. Yes, a 1HP engine. We are thinking about cutting a large diameter plastic gear on our CNC that will be driven by our small engine. We have some ideas that we like about this. Our question is, are simple spur gears as efficient as a chain or flat belt drive. Our ration is about 14:1. Any help in this matter would be great.
Thanks

 

[GearmanPE]

Gears are very efficent, with a lubricated gear tooth loss less than 1%.

For a practical car drive, you probably need a steel gear with oil lubrication. Due to the high strength of hardened steel, the gear can be quite small and this keeps the size and cost down when comparied to plastic.

The only chain drives, in modern automotive hitory, were the Invo-chain used in some early GM front wheel drives. Didn't stand the test of time.

 

[mirekp]

Gears are efficient, but if you want to guarantee the high efficiency, it is necessary to use steel gearing with lubrication, with high accuracy grade and so on. Maybe should be fine in this case to use the toothed belt, but the right choice is strongly dependent also on the machine design.

Here are some common parameters of transmission choices:

Spur Gearing (steel)
transmission ratio optimum: 2-8
transmission ratio extreme: 20
efficiency: 97-99%
weight/power [kg/kW]: 1.8-0.4

Chain transmission
transmission ratio optimum: 1-6
transmission ratio extreme: 10
efficiency: 97-98%
weight/power [kg/kW]: 10-6

Toothed belt
transmission ratio optimum: 1-8
transmission ratio extreme: 14
efficiency: 96-98%
weight/power [kg/kW]: 4-0.8

Flat belt
transmission ratio optimum: 1-5
transmission ratio extreme: 20
efficiency: 96-98%
weight/power [kg/kW]: 6-1.5

http://www.mitcalc.com

Mirek

 

[Tmoose]

>>Invo-chain ..........Didn't stand the test of time.<<

Hummers use them.

http://thehummerclubinc.com/Tech/tcase/Transfercase.jpg

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If vintage Jeeps used gears, and modern Jeeps use chain, which one has time chosen?

http://www.skidmore.edu/~pdwyer/amc/

eagle/80eagle2_954738.htm

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Mercedes

http://www.4x4abc.com/ML320/

txcut.html

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If driving the front half of a Hummer seems like part-time work, My 1980 Yamaha 850 has its original primary (crankshaft > transmission) chain. 42,000 miles.

http://www.yamaha-triples.org/

I think that HyVo chain primary drive is pretty typical on Japanese inline 4 cylinder motorcycles.

 

[Tmoose]

The gear efficiency ratings are terribly deceiving especially with splash or re-circulating lube when the revs go up, and with many gear meshes, like in a planetary or epicyclic gearbox. (4) 97% efficient gear meshes in series make an 89% efficient machine.

In the last 3 years we have had bouts with 2 large name brand industrial gearboxes that ran at least 5O DEG F hotter than we were &quot;promised.&quot; That darned 97% - 98% efficiency figure kept being tossed our way.
A 50 HP rated gearbox with 1/4 HP coming out the output shaft, but using about 6 HP to tear up its oil is NOT 98% efficient. Its more like 5% efficient. All our spindle testing is a operating speed, but not cutting metal. I'm guessing even at full working load it would still lose something like 6 HP to oil pumping/shear, and the efficiency would be more like 85 to 90%.

And, then, when they finally sent THEIR test data, OUR high temps were declared normal. Just last week We received factory permission to run 4X the recommended oil flow in in a desparate effort to help cool the danged thing down. Both are now researching &quot;minimal&quot; spray lubrication as a means to quickly chop the temp back down.
Too late for us.

 

[EnglishMuffin]

Tmoose: Yes - I have long been of the opinion that minimal lubrication of gears should work, and have done designs with mist-lube which were successful. (It also seems to work quite well for hand held electric drills!) If you look in gear textbooks, they often give recommendations for the oil flow rate needed - with the further comment that most of the flow is to carry the heat away. But in fact, most of the heat is generated by the oil in the first place - a sort of chicken and egg thing. By analogy with ball bearings, which like gears are elastohyrodynamically lubricated, it should be possible to get some reliability with marginal lubrication, although even with bearings it tends to be the case that for the greatest reliability, full flow lubrication is often used, provided the heat can be dealt with. The heat generation can be minimized, and efficiency maximized, by minimizing the peak slide roll ratio for each gear mesh.

 

[MattRR]

One of the primary advantages of non-involute gears is that it is possible to dramatically reduce sliding losses in gear meshes. I am so tired, of the so called gear &quot;experts&quot;, who keep insisting involute meshes are always so efficient. I won't even talk to them anymore. Involute gears are very efficient in certain applications under certain conditions - for example turbomachinery, which has high oil film thickness, where the gears are not oversupplied with oil, and the oil has low viscosity. There are many industrial applications though where oil visocities must be high, where oil films are low, and resulting mesh losses are high (greater than 1% per mesh).

 

[EnglishMuffin]

MattRR:
Which particular non-involute types are you referring to ? Wildhaber-Novikov types perhaps ? You must be involved in very demanding applications to make it worthwhile to consider non-involute types from a cost standpoint, as things currently stand. But I have always been puzzled as to why non-involute types have not made many inroads in this country (USA).

 

[MattRR]

EnglishMuffin,
I was not referring to Novikov gears, although I do believe Novikov gears do have unrecognized advantages. For Novikov gears, I would recommend contacting Dr. Stepan Lunin, his contact information is at

http://www.zakgear.com.

I was referring to S type gears, and derivatives of S gears. Researchers at University of Ljubjana in Slovenia have made dramatic advances in recent years. I do not see increased cost for non-involute gears. Actually, if they are conformal, manufacturing costs can be reduced if case hardening can be eliminated, and through hardening to Rc50 is used instead.