Which Layout is Best for a Double Reduction Speed Reducer?

[hanson]

Hi all!
I am going to design a double reduction speed reducer. using spur gears.
There are a few basic layout that I can choose.
And which layout would be the best?

Below is my consideration:

All the design have the same number of bearings, so I think that the efficiency of the bearing is not a key.

I can't see any big difference between design 1 and design 3 except that design 3 can save more space. In terms of efficieny, they should be the same, isn't it? Also, the axis of input an output shaft are aligned differently in design 1 &3, that should have some drastic difference, right? But what? I am not quite sure.

Comparing design 1 and design 2, the main difference is that design 2 utilized an additional pair of gear. That reduce the load on driving gears and hence a longer life could be achieved, right? In terms of efficieny, the intuitive feeling tells me that the efficiency of having an additional inefficient (not 100% efficiency) gears would be reduced. But I work out some analogue and find that the efficieny should be the same due to the reduced load on each pair of gears. Am I correct?

So what do you think about the disadvantages and advantages of each design?

By the way, the speed reducer is going to be used in a tractor.

 

[FredGarvin]

It looks to me like option 2 will require 7, not 6 bearings. You will need a bearing to support the output shaft on box #2 which is one I think you may not have considered.

All things being equal, there are some other factors to gearbox efficiency than the number of bearings. Gear flexure is something you need to contend with as well as heat build up and alignment issues in the end application.

So let's get some preliminary design criteria here...What speeds are we talking about (input and output)? What kind of horsepower does the box need to accommodate? What lubrication scheme are you considering? What kind of service will it have, i.e. continuous, intermittant? Could the box be exposed to rapid loading or reversing? What is the environment the box will be operating in? I could keep going, but I think this gets the big questions out of the way.

All in all, from the surface, the smaller gearbox will usually be beneficial because it usually means lower cost of materials and manufacture.

Let's get some of the preliminary stuff out of the way then we can decide which is the better route to take.

 

[hanson]

Thx FredGarvin!
The input speed is 2000rpm and the output speed is in the range of 290 to 295rpm. The speed reducer is to transmit 12kW. Regarding the environment, I just know that the reducer is going to be installed in a tractor, and moderate shock will be encountered.

What do you think about the axis of input and output?
Design 3 is the only design having the input an oupt shaft being on the same axis. Is this preferrable? If yes, design 3 is absoultely better than design 1?

Also, you've mentioned the heat issues, any peferred design that make the heat issues better?

About the lubrication, I have not got a contrete scheme yet since that will be dealt with later.

 

[FredGarvin]

So that guy's pretty slow speed which is good. The shock will simply have to be dealt with in the bearing selection and the tooth profile.

I would think that since this is going into a tractor that option 3 would make the most sense. It takes the least amount of room and would be easier to adapt to the tractor. Plus, I would think that a straight run on the drive shaft would also be beneficial for mounting purposes.

As far as the heat loads go, you'll just have to make sure you size your sump and pump to be able to handle the flow that you need. Since you won't get much air cooling to take advantage of you might need to do what cars that do a lot of hauling do, which is to have a small heat exchanger up by the engine's radiator to help cool the transmission fluid.

 

[NMLL]

Hello FredGarvin, I want to know what are the advantages and disadvantages of using design 1?

 

[FredGarvin]

It's tough to say what advantages you'd get from #1 without having a specific layout of where it is going to be installed. Do you require a shaft configuration like that to accommodate your set up? I will say that the box to contain the gearing would be less complicated than that of option 3. With the split shaft on option 3 there will have to be two bearings in between the two small shafts which would make the housing a bit more than just a square box.

As far as disadvantages, the one I see is size, which, for the tractor application stated could be an issue. They have the same gear sets and the same amount of bearings.

I think it's impossible to say which one would be better as far as heat dissipation/lubrication and the other tangibles that one needs to look at. I guess the only other thing that I would be concerned about would be to make sure that the bearing loadings would be similar in both cases.

 

[Danger]

Just my 2 cents: are you dead-set upon using spurs? It just seems to me that herringbones might be more efficient in this application.

 

[mustufahaider]

Two Stage Gear Reducer Design

Hi FredGravin

I m Mustufa Haider Abidi from B.Tech(Mechanical), Jamia Millia Islamia , New Delhi. India.
My final year project is to design a 2 stage gear reducer using CAD. So please help me as you already design this.

Please reply me as soon as possible.

 

[Danger]

Welcome to PF, Mustafa.
Fred is off for his weekly nap, so you probably won't get a response for a while. We're on the other side of the planet, so our circadian rythyms are a bit off from yours. (ie: It's just after midnight here, and I'm about to turn in.)

 

[mustufahaider]

Welcome to PF, Mustafa.
Fred is off for his weekly nap, so you probably won't get a response for a while. We're on the other side of the planet, so our circadian rythyms are a bit off from yours. (ie: It's just after midnight here, and I'm about to turn in.)

Oh Thats Fine

 

[FredGarvin]

Welcome to PF, Mustafa.
Fred is off for his weekly nap, so you probably won't get a response for a while. We're on the other side of the planet, so our circadian rythyms are a bit off from yours. (ie: It's just after midnight here, and I'm about to turn in.)

My weekly nap is indeed what it feels like.

Mustufa,
Welcome to PF. If you have specific questions, please ask. Otherwise it is very difficult to help you. We do not simply do your work for you here. We will help you but you need to do the work and put forth the effort.

 

[mustufahaider]

no i m not saying u to do my work. I already develop programs using C++ to design Gear,Shaft,Key & Bearing but now i don't know how to import it in any CAD software like CATIA/Pro-E. So if u have any idea please tell me.
tc

 

[FredGarvin]

no i m not saying u to do my work. I already develop programs using C++ to design Gear,Shaft,Key & Bearing but now i don't know how to import it in any CAD software like CATIA/Pro-E. So if u have any idea please tell me.
tc

It sounds to me that you need a CAD jockey and a designer. Having code in C++ will not take care of detailed design work. Has your code done anything with tolerances required? Simply shooting out numbers is only the first step in detailed design.

I would be interested in seeing what your code is telling you for gears, bearings and such.


For applications like this these things are mostly already tabulated and well known.
i would suggest picking up a copy of Machinery's Handbook for starters.

 

[P.Ramesh]

Hi Guys!
If you want to do the gear design yourself, do it for your good for your knowledge sake. Or If anybody wants a quicker readymade results of a gearbox design with the results and also exporting 3d models (result) to CATIA / PRO-E /UG NX, better to download Demoversion of KISSSOFT which is used for total machine design of elements like from key to gears.