douglasye

The chatter marks worsen the seal between chambers and this phenomenon still exists.Curtiss-Wright believed the chatter marks were the result of high speed bouncing of the apex seal as it passed over the reinforcing ribs of the rotor housing. Daimler-Benz believed that the leading apex seal would push oil, carbon, fuel, and combustion byproducts past its edge. As the build up accumulated and the resistance became higher, the leading apex seal would then lift over the obstruction and off of the working surface.
But which one is correct or is there another reason?

nycgps

iTrader: (1)

both.

but that was quite some years ago. Like around 1960s ?

Tons of stuff has changed since then, material, worksmanship, science.

epitrochoid

Here's a patent for a modified trochoid shape that supposidely prevents chatter...I'm not sure how similar this is to technology used today

http://www.google.com/patents?vid=US...id#PRA1-PA5,M1

(starts at column 1 line 62)

TeamRX8

iTrader: (25)

sounds like you need to take a trip with Sherman and Mr. Peabody in the Way Back machine ...

rotarygod

It was caused by apex seals bouncing off of the housings at high rpms. The issue gets worse the heavier the seals are. The material they are made out of and amount of oil lubiration on them has an affect on it too.

douglasye

thx. So it means that modified trochoid can prevent chatter permanently? In Curtiss-Wright 's theory, what's the reinforcing ribs of the rotor housing and what's their method to prevent the chatter? Is it the biggest reason of chatter when the apex seals bounce off the housings at high rpms? Some theory said that it's becuse the contact force variation by the changing sliding coefficient of friction.

StealthTL

iTrader: (1)

Looks like someone read a book....

S

j9fd3s

well ive never heard the competing ideas, but slide something across the table, try a few things, when the friction gets too high, it doesnt slide, it skips. after that its like ruts in a dirt road....

r0tor

iTrader: (1)

theres also a engine vibration matching the natural frequency of the seal theory

otherside

Quite a good example...

douglasye

thx j9fd3s
But can anyone give more details about the seal theory of a engine vibration matching the natural frequency or its file link?

douglasye

Does it mean the natural frequency of the seal should avoid the engine vibration?
But how to measure the engine vibration and what if the frequency of the seal is caused by the roughness of the rotary surface?

Nubo

It's the Devil's fingernails.

rotarygod

I have never heard of a natural resonance causing it.

r0tor

iTrader: (1)

the theory goes that its possible for engine vibrations to match the resonance (or natural) frequency of the seal - which would amplify the normally tiny movements of the seal from vibrations... i doubt it has much merit, but was mentioned as a possible theory for chatter marks in the Rotary Engines book by Yamamoto

douglasye

many people say the bouncing seals cause the matter marks when the seals are pushed by high gas pressure and the spring push the seals back to the housing surface. But can this reason explain the regular chatter marks' frequency? Can we calculate the frequency of the bouncing?

r0tor

iTrader: (1)

theres also a resonance frequency associated with any spring-mass system... which the seals would be modeled as - if you have the spring rate and seal weight its pretty easy to calculate

calculating the frequency causing the chatter marks by just looking at the chatter marks is next to impossible unless you know the rpm at which the marks are being caused

olddragger

iTrader: (3)

how about mechanical and thermo disruption? Sealing is of course is a very important thing. In that we share with recips. So trueness of bore or rotary housing in our case, the rotary housing surface (peaks and valleys), ring (or seal) tensio can add to the chatter marks or in the case of recips the scuff marks on the cylinder wall. For example truing the bore on a recip Ls-1 using thermo coupled torque plates can net 25hp by that alone. I wish we had a way to do that with the rotory and the housing on our engines.
Good question for discussion.
olddragger

Nubo

You might be able to look at it in the same manner of how waves form on open water. They start out as tiny ripples, barely noticeable. But once those features form, they are self-reinforcing. And gradually you end up with 30-foot waves

corners

Kinda like a washboarded gravel road.

rotarygod

That's actually a pretty accurate analogy.

Soravia

Holy thread revive. A 2019 paper says this vibration is compounded by the angle of the brush (Apex seal) relative to the surface it's riding on. Leading angle (against the rotation motion) causes more while trailing causes almost zero bouncing or vibration.
So solution is to make the Apex seal ride on the housing in trailing angle. BUT that will make the rotors directional in their application.
Currently the Apex rides on side housing in varying angles. Some as much as perpendicular, some more in trailing manner, some in leading manner.