Machine Drivetrain Efficiencies 2

[jerryv]

Machine Drivetrain Efficiencies

What is best way to determine the sum of machine drivetrain efficiencies?

Example:
20 hp motor driving a gearbox (98% efficient), which drives a timing belt (89% efficient) which drives a roller chain(89% efficient). What is total efficiency of the drive system?

See attached file.

 

[vpl]

Somewhere I have some formulae (formulas?) on calculationg efficiencies -- if I have an opportunity and nobody else answers, I'll look them up.

However, until then, at least a rough estimation could be obtained through the "square root - sum of the squares" method: [√]([η]_g² + [η]_t² + [η]_c²)

where the subscripts refer to the gearbox, the timing belt, and the rolling chain, respectively.

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[PeterCharles]

Isn't it just 0.98*0.89*0.89 ???

And I can't see how "square root - sum of the squares" would work with the figures quoted, as you appear to end up with a number greater than 1 ???

 

[DesignerGuy16]

Multiplication as Peter says is the key.
98% of 100% is 98%
89% of 98% is 87.2%
89% of 87.2% is 77.6%
etc, etc.

You don't magically make up for lower efficiency with a higher efficiency, it still lowers the overall, just not as much.

James Spisich
Design Engineer, CSWP

 

[vpl]

PeterCharles & JSpisich

You're right -- that's what I get for giving an off-the-cuff answer. The SRSS doesn't work for percentages.



Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.