×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Gear Ratios and Efficiency

Gear Ratios and Efficiency

Gear Ratios and Efficiency

(OP)
Assuming that we have a gear ratio g < 1 from the driving to the driven gear in terms of the number of teeth.  Say g = 0.01 and assume the gear train efficiency e is 0.8.

To me, this means that the effective output torque, Tout, will be reduced so that

Tout = e x Tin/gr .

Also, if one uses energy conservation

 [Tout x Omega_out] / [Tin x Omega_in] = e,

this also tells me that the effective speed at the shaft will reduce.  

This is where I get confused.  Motors have a inversely proportional torque-speed relationship.  Doesn't this say that if the effective torque reduces, then the effective speed increases?  

TIA

Klaus

RE: Gear Ratios and Efficiency

(OP)
I must be missing something in the above equations. Does a reduction in efficiency translate to both a reduction in output torque and speed or just output torque alone?

i.e

Tout = e x Tin/gr    and
Vout = gr*Vin

=> Tout x Vout  = e x Tin x Vin

Is this valid?

TIA

Klaus

RE: Gear Ratios and Efficiency

The average tooth speed changeth not.

with a gear.

Cheers

Greg Locock

RE: Gear Ratios and Efficiency

...unless the gear is made of something verrrrrry stretchy, right?

RE: Gear Ratios and Efficiency

(OP)
So are we saying the a reduction in drive train efficiency translates to a reduction in output torque ONLY?

TIA

RE: Gear Ratios and Efficiency

Yes. Unless you have rubber gears.

Cheers

Greg Locock

RE: Gear Ratios and Efficiency

(OP)
Thank you Greg.

Klaus

RE: Gear Ratios and Efficiency

It might be helpful to look at the lost torque more carefully:

Tout * Omegaout = (Tin - Tfriction)* Omegain

If your goal is to apply a specific output torque, then you need to use more input power than you would expect if you didn't take friction (and other losses) into account.

Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources