Use Of Roller Bearings?
06-05-2004, 11:17 AM
#1
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Like the title says, is this plausible? they obviously cost more, but the reduced friction would be awesome!! Basically just replacing the rotor and main bearings with rlow friction roller bearings. Has anyone tried using them? they should be able to put up with abuse, I dont know. Just throwing an idea out there...any input?
06-05-2004, 05:46 PM
#3
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Originally Posted by onefastrx7turbo' date='Jun 5 2004, 08:17 AM
Like the title says, is this plausible? they obviously cost more, but the reduced friction would be awesome!! Basically just replacing the rotor and main bearings with rlow friction roller bearings. Has anyone tried using them? they should be able to put up with abuse, I dont know. Just throwing an idea out there...any input?
Roller bearings will take abuse, but for a rotary I would be interested to see if there were any gains to be had.
06-05-2004, 06:13 PM
#4
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i bet bearings have improved, but they used to use them on piston engines in the 20's and 30's and when you accelerate and decelerate at high rpms the bearing ***** will spin in the races and they wear out.
i'm sure there have been advances in the last 50 odd years though
i'm sure there have been advances in the last 50 odd years though
06-06-2004, 05:08 PM
#6
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I company makes stationary gears with ball bearing, but they are 100,000 yen for the set. I can't remember the name of the company, it is in a REV Speed though. I haven't seen ones made for the rotors, if you want them let me know Neil.
06-06-2004, 09:23 PM
#7
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Its WAY more friction. Think about it from a surface are point of view.
I know the Scoot 7 used them and they did not last very long. Think about it this way. If you have 100psi oil pressure on a liquid bearing you have that same pressure keeping the e-shaft aloft. With the right oil thats pretty damm relaible. PSI also has a direct relationship to engine rpm so as you need more support you get it. I have no idea why they used roller bearings on the Scoot. I would think it would be much easier to machine the e-shaft and cut the gear off a stat gear and modify it to fit tin the center housing. Also, roller bearings would need a much thinner oil to operated which would require you to clearence the rest of the engine to use that oil. Oh well.
My 2 cents
GregW
I know the Scoot 7 used them and they did not last very long. Think about it this way. If you have 100psi oil pressure on a liquid bearing you have that same pressure keeping the e-shaft aloft. With the right oil thats pretty damm relaible. PSI also has a direct relationship to engine rpm so as you need more support you get it. I have no idea why they used roller bearings on the Scoot. I would think it would be much easier to machine the e-shaft and cut the gear off a stat gear and modify it to fit tin the center housing. Also, roller bearings would need a much thinner oil to operated which would require you to clearence the rest of the engine to use that oil. Oh well.
My 2 cents
GregW
06-07-2004, 02:09 PM
#8
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Originally Posted by Jeff20B' date='Jun 6 2004, 12:05 AM
Roller bearings are good for constant RPM engines like compressors and etc. I've seen an ACVW crankshaft fitted with roller bearing connecting rods.
is that the same they use on 2 piece eccentric shafts?
06-07-2004, 02:39 PM
#9
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Well the server is flaking, so hopefully the third try will work.
Roller/ball bearings are not designed to take thrust, which is present even in rotary engines and especially present in pistons engines, running at various rpm but either way the process of igniting compressed air and gasses tends to put some thrust on the bearings which will quickly hammer roller bearings. Not to mention the impossibility of lubricating them.
In fact I believe that flat bearings are also referred to as "thrust" bearings, but don't quote me on that.
Roller/ball bearings are not designed to take thrust, which is present even in rotary engines and especially present in pistons engines, running at various rpm but either way the process of igniting compressed air and gasses tends to put some thrust on the bearings which will quickly hammer roller bearings. Not to mention the impossibility of lubricating them.
In fact I believe that flat bearings are also referred to as "thrust" bearings, but don't quote me on that.
06-07-2004, 10:29 PM
#10
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Roller bearings are only useful if you are relying on misting for lubrication, say as in many 2-cycle engines.
The pressure fed journal bearing is the ultimate in bearing design. The only friction is from the viscosity of the oil, and in a perfect world the two journals should never make contact, since they will be floating on a (mostly self-regenerating) pressure wedge of oil, or water, or air, or whatever is being used as a lubricant.
Roller bearings, on the other hand, don't have this pressure wedge of lubricant, so the rollers are always in hard contact with the races. You can't have 100% roller contact since there has to be some clearance, so at any given time only half (or less!) of the rollers are in use. They essentially run metal on metal, with the lubricant mainly for roller-cage contact.
As you can imagine, the forces are ENORMOUS compared to a journal bearing, since while on a journal bearing you have one riding on the other on a cushion of fluid, loads spread more or less evenly over half of the diameter, a roller bearing has the load on only a few discrete points (lines, actually).
If you are still jonesing for a roller, just consider a journal bearing to be the world's most ultimate "roller bearing". Rollers the size of molecules!
The pressure fed journal bearing is the ultimate in bearing design. The only friction is from the viscosity of the oil, and in a perfect world the two journals should never make contact, since they will be floating on a (mostly self-regenerating) pressure wedge of oil, or water, or air, or whatever is being used as a lubricant.
Roller bearings, on the other hand, don't have this pressure wedge of lubricant, so the rollers are always in hard contact with the races. You can't have 100% roller contact since there has to be some clearance, so at any given time only half (or less!) of the rollers are in use. They essentially run metal on metal, with the lubricant mainly for roller-cage contact.
As you can imagine, the forces are ENORMOUS compared to a journal bearing, since while on a journal bearing you have one riding on the other on a cushion of fluid, loads spread more or less evenly over half of the diameter, a roller bearing has the load on only a few discrete points (lines, actually).
If you are still jonesing for a roller, just consider a journal bearing to be the world's most ultimate "roller bearing". Rollers the size of molecules!