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  #31  
Old 06-25-2021, 01:34 PM
kreidljj kreidljj is offline
 
Join Date: Aug 2006
Posts: 46
Default Odd Failure Mode

I have 20+ years of electric motor design experience. This is not a failure mode that would typically happen on a belt loaded bearing system. The belt provides good radial loading in a single direction. This failure mode is very common on fan/pump type loads. On that type of a load the opposite drive end bearing can be allowed to roll around the housing unless there is something in place to prevent rotation. I never like to see a bearing race in an aluminum housing unless it is mechanically held from rotating. If you care for a few rules of thumb keep reading. Press fit the OD or the ID, never both - it eliminates the internal bearing clearances. Always provide some axial pre-load, it keeps the balls rolling instead of sliding. If you ever hear a motor that sounds like there is sand in the bearings, it very likely doesn’t have any axial pre-load. If the bearing will see light radial loading you need to lock the outer race to prevent rotation (avoid press fit OD and ID per above). One of the four races (inner or outer) needs to be allowed to float axially to compensate for thermal expansion. Right at the top of what is needed for a quite, long lasting motor is good bearing fits, with extraordinary quality control. Motor bearings today are designed for 40k hour life, with 80k possible, and 120k desired. This is a topic careers are made of, hard to hash out via a couple of lines of text. I have not even touched on grease, cleanliness, and thermal conditions…. Not sure if any of this is useful to the conversation, thanks for reading - Jason
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  #32  
Old 06-25-2021, 01:58 PM
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rv6ejguy rv6ejguy is offline
 
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Location: Calgary, Canada
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Default

Denso has figured all this out years ago in the automotive world with obviously good design and materials. They are one of the if not the largest suppliers of alternators in the world for good reason. Their products last a very long time in my experience.

Bearing failures at less than 200 hours points to something being done very wrong at PP. Denso can design or select a bearing that will have proper ball to race clearance when pressed into the housing and onto the shaft. This is exactly what is needed to make it as reliable as they are.
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Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 449.1 hrs. on the Hobbs,
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  #33  
Old 06-25-2021, 02:09 PM
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digidocs digidocs is offline
 
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Posts: 544
Default

Here is a photo of the replacement 70A housing I mentioned above.

It's interesting that it has a separate steel part that holds the rear bearing rather than using a simple recess machined into the aluminum. Perhaps they're on to something...
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  #34  
Old 06-25-2021, 02:45 PM
DanH's Avatar
DanH DanH is online now
 
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Default

Quote:
Originally Posted by kreidljj View Post
I have 20+ years of electric motor design experience. This is not a failure mode that would typically happen on a belt loaded bearing system. The belt provides good radial loading in a single direction. This failure mode is very common on fan/pump type loads. On that type of a load the opposite drive end bearing can be allowed to roll around the housing unless there is something in place to prevent rotation. I never like to see a bearing race in an aluminum housing unless it is mechanically held from rotating. If you care for a few rules of thumb keep reading. Press fit the OD or the ID, never both - it eliminates the internal bearing clearances. Always provide some axial pre-load, it keeps the balls rolling instead of sliding. If you ever hear a motor that sounds like there is sand in the bearings, it very likely doesn’t have any axial pre-load. If the bearing will see light radial loading you need to lock the outer race to prevent rotation (avoid press fit OD and ID per above). One of the four races (inner or outer) needs to be allowed to float axially to compensate for thermal expansion. Right at the top of what is needed for a quite, long lasting motor is good bearing fits, with extraordinary quality control. Motor bearings today are designed for 40k hour life, with 80k possible, and 120k desired. This is a topic careers are made of, hard to hash out via a couple of lines of text. I have not even touched on grease, cleanliness, and thermal conditions…. Not sure if any of this is useful to the conversation, thanks for reading - Jason
Very useful, and thank you for contributing.

Experience question please. In this case the OD of the brush end bearing and the ID of the aluminum case appear to be dimensioned the same (32mm). Elevated temperature thus results in a clearance. The outer race is assumed to rotate, and the clearance grows. Is there a quick 'n dirty fix you think might work?
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  #35  
Old 06-25-2021, 02:46 PM
BillL BillL is online now
 
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Location: Central IL
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Default What is the design function, precisely?

Quote:
Originally Posted by digidocs View Post
Here is a photo of the replacement 70A housing I mentioned above.

It's interesting that it has a separate steel part that holds the rear bearing rather than using a simple recess machined into the aluminum. Perhaps they're on to something...
How does this work? Does it press onto the outer race then get assembled? It appears to have an internal screw? Is the SRE inner race pressed onto the rotor?
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  #36  
Old 06-25-2021, 04:09 PM
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rv6ejguy rv6ejguy is offline
 
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By using a steel bearing capture, they can keep the thermal expansion rate the same as the steel bearing. Could get away with a lighter press fit than in an aluminum housing.
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Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 449.1 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
https://www.youtube.com/channel/UCiy...g2GvQfelECCGoQ


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  #37  
Old 06-25-2021, 04:13 PM
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digidocs digidocs is offline
 
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Quote:
Originally Posted by BillL View Post
How does this work? Does it press onto the outer race then get assembled? It appears to have an internal screw? Is the SRE inner race pressed onto the rotor?
Bill,

The steel part is permanently attached to the aluminum SRE frame, and I don't think the screw is intended to be removed.

I haven't tried installing this housing, but the rear bearing appears to be a press fit on the rotor shaft. I think the steel part is intended to press/slide? over the bearing OD when the housing is installed.
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  #38  
Old 06-25-2021, 06:09 PM
scsmith scsmith is offline
 
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Location: Ashland, OR
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Default

Quote:
Originally Posted by kreidljj View Post
I have 20+ years of electric motor design experience. This is not a failure mode that would typically happen on a belt loaded bearing system. The belt provides good radial loading in a single direction. This failure mode is very common on fan/pump type loads. On that type of a load the opposite drive end bearing can be allowed to roll around the housing unless there is something in place to prevent rotation. I never like to see a bearing race in an aluminum housing unless it is mechanically held from rotating. If you care for a few rules of thumb keep reading. Press fit the OD or the ID, never both - it eliminates the internal bearing clearances. Always provide some axial pre-load, it keeps the balls rolling instead of sliding. If you ever hear a motor that sounds like there is sand in the bearings, it very likely doesn’t have any axial pre-load. If the bearing will see light radial loading you need to lock the outer race to prevent rotation (avoid press fit OD and ID per above). One of the four races (inner or outer) needs to be allowed to float axially to compensate for thermal expansion. Right at the top of what is needed for a quite, long lasting motor is good bearing fits, with extraordinary quality control. Motor bearings today are designed for 40k hour life, with 80k possible, and 120k desired. This is a topic careers are made of, hard to hash out via a couple of lines of text. I have not even touched on grease, cleanliness, and thermal conditions…. Not sure if any of this is useful to the conversation, thanks for reading - Jason
Thanks for this! Always learning. Imparo Ancora.
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  #39  
Old 06-25-2021, 08:24 PM
kreidljj kreidljj is offline
 
Join Date: Aug 2006
Posts: 46
Default Check this - then

Quote:
Originally Posted by DanH View Post
Very useful, and thank you for contributing.

Experience question please. In this case the OD of the brush end bearing and the ID of the aluminum case appear to be dimensioned the same (32mm). Elevated temperature thus results in a clearance. The outer race is assumed to rotate, and the clearance grows. Is there a quick 'n dirty fix you think might work?
Since this failure mode is not typical for this loading I would first try to find out what the cause is. So, to me step one would be to sweep the speed range of the alternator to look for a resonance, off hand I think this is a potential cause. The bandage to apply is something called a tolerance ring. You would of course need to open up the housing to make room, but they work. I experimented extensively with them, but they only made production a few times due to cost. Be careful when installing the bearing because you can not press on the balls, said another way you may not transfer any pressing loads from the inner race to the outer race via the balls. Much like men, these are very fragile components and while they may appear ok at first you HAVE damaged them and shortened the life of the bearing by pressing on them. - Jason
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  #40  
Old 06-25-2021, 09:35 PM
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rv6ejguy rv6ejguy is offline
 
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You could also use a bolted bearing capture for the outer race as some alternators use and thread the center shaft to capture the inner race with a small bolt and washer. I used this method on my belt idler. Nothing has spun on the aluminum shaft or housing. I did replace a crappy offshore bearing at around 50 hours with a German one which has gone around 400 more with no issues now.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 449.1 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
https://www.youtube.com/channel/UCiy...g2GvQfelECCGoQ


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