Is a reduction gearbox efficiency the same for forward and backdriven? 2

[medo79]

Dear All,
Is the reduction gearbox efficiency is the same in both forward and backdriven directions? If No, is there a relation to calculate a backdriven effecifiency from forward efficiency?

 

[tbuelna]

medo79,

What type of gearbox? A high ratio reduction worm gear set will not backdrive, so its backdriven efficiency would be zero, right?

Other gear meshes, such as a simple spur mesh, would likely have similar efficiencies when driven in either direction.

Good luck.
Terry

 

[medo79]

What about Harmonic drive and planatery gearbox?

 

[Windward]

Here is a good answer to your question, from Earle Buckingham's Analytical Mechanics of Gears (Dover:1949). See the example in Chapter 18 pp. 407-8, which calculates the efficiency of a spur gear set, first as a reduction drive, then as a step-up drive:

"...the efficiency of the step-up drive is a little higher than that of the same gears used for a reduction drive, primarily because of its greater recess action. When the amount of approach and recess are equal, there will be no difference. When the recess action of the driver on a reduction drive is greater than the approach action, then the corresponding step-up drive will be less efficient than the reduction drive."

As Buckingham explains in this chapter, as the degrees of approach and recess action change, the friction factors change. That is what determines the efficiency of the gearset, everything else remaining constant - diametral pitch, pressure angle, number of teeth, pitch line velocity, etc.

Of course, approach on a reduction drive is recess if it is used as a step-up drive.

However, it is well known that a gearset designed for reduction should not be used in reverse, as a step-up drive. It will be noisier and less efficient, and I suppose that it won't last as long.

I also suppose that a gearbox designed for step-up should not be used for reduction.

In a good design, the teeth are modified to suit the service, either reduction or step-up. They work best only in the direction intended. I hope the experts in this forum, of which I am not one, will give us some details.

 

[medo79]

what does approach and recess in gear mean?

 

[israelkk]

If you ask this question you are far behind and need to educate yourself using good books such as Dudley's book and the book mentioned above about gear design before continuing.

 

[medo79]

Many thanks, I found the book, and I know now what approach and recess mean.