What can be reasons of gears braking on Dyno test? 5

[LKPTS]

Hi,

We are making 400cc Triple Cylinder 4 stroke Air cooled engine for Motorcycle and on Dyno tests we are facing the problem of Gears braking (tooth getting sheared off) Can any one from the same field give me possible reasons for this? What tests / checking we should perform? And possible solutions also?

Regards,

LK

 

[patprimmer]

Engine torque output exceeds torque capacity of gear box.

Regards

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[Tmoose]

Did it happen once, or repeatedly?
Was a Wrench or spare parts left in the gearbox?
Is it a new design gearbox, integral with the engine?

Analysis of the broken and surviving teeth and some new gear sets is an important step. There are several gearhandbooks that show different kinds of tooth failures and have discussions of causes.

Poor metallurgy is a little hard to detect, but magnetic particle inspection >should< show new gears to be flaw free, especially in the roots, and in the same areas where the teeth broke. hardness tests might be revealing.

 

[tbuelna]

Driveline dynamics. Make sure you're not operating the engine at the natural frequency of either the dyno or engine.

Also, if the gearbox is of original design, make sure that instantaneous torque loads through the gearbox do not exceed the allowable tooth bending loads experienced by the transmission gears. The magnitude of the sum of the instantaneous cranking torques in a 3 cylinder, 2-cycle engine can exceed the mean torque by several factors. And that instant torque spike load can be compounded by dynamic tooth loading effects if your gear mesh has a low contact ratio.

Of course, the most valuable engineering lesson you're going to learn from all of this is that engine development is always expensive. The mathematical relationship between horsepower and development cost is an exponential one.

 

[BrianPetersen]

1. Is there a sufficient vibration damper built into the clutch hub? Normally the gear on the backside of the clutch basket (which is driven by the crankshaft output gear) is linked to the clutch basket by a series of strong springs to absorb the crankshaft pulsations.

2. Is there a sufficient vibration damper on the output of the gearbox? Normally the sprocket carrier on the rear wheel is linked to the rear wheel itself by several rubber dampers, again to absorb shock loads and vibration.

Haven't had it happen myself (because I've always used OEM rear wheels) but some so-called "high performance" lightweight wheels don't have vibration dampers between the sprocket and the wheel, and they can smash up a gearbox.

 

[thundair]

I agree with tbuelna and BrianPetersen. In the past I have design and built a few gear boxes and the research for PSRU (power supply reduction unit) for piston aircraft shows without dampening the harmonics from the prop and the engine will destroy a gear box in very little time.

Cheers

I don't know anything but the people that do.

 

[MikeyP]

What Pat said plus...
bad materials
bad hardening process
misalignment (tip/root/edge contact
large pitch errors
backlash too small

I could go on...
You should probably consult a gear designer
IMHO vibration is usually a 2nd order effect, even if it is really bad.

M

--
Dr Michael F Platten

 

[dicer]

Who makes the gears? How are they made? Are they powder metalurgy?

 

[Tmoose]

I'd still like to hear/see the gear's side of the story.

http://www.practicingoilanalysis.com/Backup/200101/Gear3.jpg

http://www.practicingoilanalysis.com/Backup/200101/Gear1.jpg

http://www.practicingoilanalysis.com/Backup/200101/Gear4.jpg

http://materials.open.ac.uk/mem/images/images_fat/fat01r.jpg