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Manual Transmission Design

  1. Jun 5, 2008 #1
    Hi All,

    As a process of my project work, i have been asked to develop a manual transmission. I have to design gears (Crown, Planetary and Sun gears) to achieve a final reduction of 30.45, with first stage gear reduction & second stage reduction being 5.28 & 5.77 respectively.

    Can any one help me in solving this problem for gear designs ??? I have space constraints also, but I can take care of it, by controlling the number of teeth. I need to know how to start and where to start. Can any one guide me ??
  2. jcsd
  3. Jun 5, 2008 #2


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    The obvious place to start is with the full requirements of the gear box. You are giving a speed reduction requirement, but nothing else. What kind of power do you have to design for? That is going to go into your gear tooth selection, heavily. If you have a large power requirement, chances are that the tooth size will have to go up which may shoot you in the foot for your speed reduction since you are limited on space.

    Knowing the power will also give you a starting point for what kind of lubrication cooling you'll need.

    My recommendations would be:
    1) Collect ALL required design constraints. Cost, size, power, speed, etc... They will all have an affect on the other.

    2) Since this is your first design, start doing as much research as possible and then do some more. You have a lot to learn in this very specialized field so you need to educate yourself as much as possible.

    3) I would highly recommend that at some time you look at how it is going to be manufactured. You don't want to waste time designing components that you have no capability in producing either due to lack of machinery, talent or technical capabilities.
  4. Jun 5, 2008 #3
    I dunno much but a gear designing for a given power and rpm is easy to do, it is done is university syllabus, one can refer any handbook. Gear box is just more gears + space constraint.
  5. Jun 5, 2008 #4


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    ummm yeah. How about no. In undergrad the gear analysis done is very highly idealized. Looking at a certain number of teeth and some generalized numbers for tooth stresses is not the only thing to do. You have no clue to the complexities of a real gear train when it comes to the requirements for lubrication, bearings, interactions of those items on the selection of backlash as well as noise generation to name a few. Not to mention that you don't consider material requirements in terms of heat treating requirements, possible plating requirements, tooth profile, gear type...
  6. Jun 5, 2008 #5
    :redface:thats why i said i dunno:redface:

    But i dunno, lubrication, sound, bearings are all application specific. More than power requirement, the application must dominate these things. but then again, i m not even a novice in this field:shy:
  7. Jun 5, 2008 #6
    Hi all,
    Thanks for your replies and guiding me through. I have asked for Power requirements. As a process, they want me initially to work on only deciding the number of tooth on each gear, and the tooth profile & thickness of tooth, keping bearing loads, lubrications effects aside. So if I have power in my hand, how am I going to strat with ?? I am referring some undergraduate books, but nothing talks about a simple transmission design. If any one of you can guide me that would be very much helpful. Thanking you for your time.

  8. Jun 6, 2008 #7
    I wasn't aware manual trannies had planetary gear sets. The classic text "Mechanical Engineering Design" by Shigley & Mischke has a couple examples of what you want.
  9. Jun 9, 2008 #8

    Thanks for the reply. Insuctrial trucks, like fork lift trucks has a set of planetary gear with sun gear combination, which is used for a manual transmission. I am referring the Shiegly. If you are aware of any useful site, please do let me know.

    Thanks for everything.

  10. Jun 11, 2008 #9
    i think your lookin for someone to tell you the answer to what youre learning to work out. kinda defeats the object.

    if you dont know how something works or how somthing is done think of how it could work/could be done and narrow down your options to find the best way. think of the constraints of your design in terms of cost, weight, size, and function then all the ways of solving those constraints and just narrow down your options to find the best one in terms of cost, weight, size, and function.

    for your gearbox i would research gear design first, then contact gear suppliers and get a catalogue of gears. you can then narrow down your choice of gears by finding the cheapest, lightest, smallest, most funtional set of gears. infact your probably working within a budget, youve already said your working to a size constraint, and your probably working to functional requirements so just find the lightest set of gears for those constraints.

    so you know your cost, you know your size, you know your functions (at least you can work them out) so you only need to worry about weight.
  11. Jun 12, 2008 #10
    So I'm not sure if this is the info you want but I'll throw it out there.

    1. A manual transmission with a planetary gear set is highly unusual. In fact the only transmission like that I can think of was in the Model T!

    2. Gear ratios are easy it's just driven gear/drive gear (just count the number of teeth on each gear).

    3. If you are actually designing this like a real manual transmission you need to be aware that the gear ratio between the input shaft gear and the first gear on the cluster gear affects every other gear ratio except direct drive (which yours will not have.)

    I hope this helps, if not sorry, and if you think I could you more let me know.
  12. Sep 12, 2008 #11
    i'm so glad i've found this discussion..
    can anyone, design engineer help me to design a 5-speed manual transmission system..
    the engine delivers 80hp of power at 3000rpm to the transmission system..
    Can anyone guide me to start the design work..
    i'm still learning but i confused what should i consider and calculate first..
    the gear must base on AGMA as the standard..
    i am refering to shigley's book..
    thank you..
  13. Sep 12, 2008 #12


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    On a funny side-note (I thought it was funny), I was talking with some of the older engineers here, and most of the people here just say Shigleys. Just saying Shigleys implies the exact book that you're referring to. Maybe it's not really that funny, but I thought it was.
  14. Oct 23, 2010 #13
    I think that it is hard to do that project alone. And I think you should need some help of expert near your country. I hope that you can do that project. Hope to see some updates of that manual transmission design. :D
  15. Oct 23, 2010 #14
    Those ratios seem to be fairly specific. The lowest tooth count that I found that would satisfy all three ratio requirements in a single step per stage were 95:18 and 75:13.
  16. Oct 25, 2010 #15


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    This thread is two years old and the person you responded to hasn't been here in 2 years.
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