posted on June 08, 2011 19:56
|Here are the parts assembled together. You can see that the thrust collar covers both sides of the thrust bearing. A film of oil goes between the two parts on both sides in order to handle thrust loads in both directions. The spacer keeps the journal bearings located properly. This is a newer method as opposed to older turbos that use C-clips on each side of the journal bearings to keep them in place.
The other most common type of bearing system used for turbos is the ball bearing system. Ball bearings are a specific type of rolling-element bearing and they work on the principle of the rolling element supporting the load. In a ball bearing, the balls are the rolling element (duh). The most common type of ball bearing used in turbos was pioneered by Garrett and uses what is known as a cartridge bearing. The cartridge bearing consists of two rows of angular contact ball bearings in one assembly to handle both radial and thrust loads. The balls go between a set of inner races and an outer race. This design of bearing system has been used to win pretty much every WRC and LeMans race since the 1990s. As more racing series have gone turbo, more and more racers use ball bearings turbos. Besides the WRC cars and Audi R18 and Peugeot 908 LeMans prototypes, British Touring Car and World Touring Car racers this year are powered by Garrett Motorsports ball bearing turbos.
|Some generic ball bearings.
||A section view representative of the ball bearing cartridge.
|Two examples of ball bearing cartridges used in turbos.
So the ball bearing system is superior to the journal bearing system as proven in motorsports, but why? In a phrase, power loss. Let's go back and have a look at the journal bearing system and how it works. For a journal bearing system to work, it has to keep a film of oil between all the spinning parts so that none of them contact each other. This requires a significant volume of oil flow through which all the parts have to spin. Next, there’s the fluid dynamics principle called the no-slip condition. This states that the fluid in contact with a surface does not slide past it.
The film of oil between the shaft and journal bearings is only fractions of a millimeter thick. One side of the film moves with the shaft while the other side stays put with the journal bearing due to the no-slip condition. Imagine this; you have a flat surface with a film of oil only a fraction of a millimeter thick on top. Put a flat plate on top of the oil and move it at 200mph over the flat surface. That’s what the oil sees between the shaft of a turbo and the journal bearing. Shearing the oil like that requires a lot of power!
Thursday, June 09, 2011 11:29 PM
Thx for the great info KD, always an interesting read :-)
Friday, June 10, 2011 8:24 AM
Awesome read! Granted some of the terminology is interchangeable with an amateur porn film ;)
Friday, June 10, 2011 8:53 AM
^^^ KD is no amateur..... ;-)
Friday, June 10, 2011 9:35 AM
Nice read Khiem. This is why compressor surge is so damaging to journal bearing turbos, since the loads exceed what the oil film can support and there is direct part to part contact at a most inopportune time, correct?
Wes: I wonder if someone's measured Peter North's radial and thrust loads...
Friday, June 10, 2011 9:36 AM
KD, an awesome balance of tech, fluid dynamics and the trademark MotoIQ irreverance. Great insight on a subject that escaped me. I got pissed offf with turbos when they made the beauty of F1 quiet.
Lately after driving so many awesome turbo'd cars on track (leatest was a TechArt Porsche @700hp+, as well as the phenomenal Turbo Panamerica) it's time to drop the rock . . .
Friday, June 10, 2011 10:06 AM
Wes/mxpop, I've found that knowledge on thrust loading and shaft motion is important. Proper lubrication is also critical for durability.... just sayin
Steve, yup, compressor surge creates really big pressure spikes which in turn creates really big changes in thrust loading. It's pretty much like whacking the shaft with a hammer. In the picture of the thrust bearing, you can see little pads on it which supports the loading. The three little holes are the oil feeds for the three pads. So compressor surge will overload the oil film and you'll get metal-to-metal contact between the thrust bearing and collar. The more it happens, the more those pads wear away and the thrust bearing losses its capacity to handle loads. And then your turbo blows up.
Friday, June 10, 2011 10:27 AM
I was beginning to wonder when the URL of this site was going to change to driftIQ.com. Thanks for the refreshing non-drift related article. I will send all who ask about BB turbos here.
Friday, June 10, 2011 10:54 AM
^^ What Eric Hsu said, completely, including the thanks.
Friday, June 10, 2011 12:51 PM
"A pro-cyclist can only do 1000W in an all-out sprint" with EPO :)>
I think we MIGHT be seeing more ball-bearing turbos, if it means peak torque can be found much earlier and fatten the torque curve to achieve better mpg at the right production cost of course! The flip side of that is that they'll probably use a longer stroke with higher compression pistons and just utilize a journal bearing turbo that's less expensive and still expected to last 100k+ at stock power levels. As to your point about the oil Khiem, the domestic and asian manufacturers will probably make everybody use the more expensive euro blends to overcome some of the weight/viscosity issues and pass that cost on to the public.
Friday, June 10, 2011 1:14 PM
I'm a total ignorant about turbos, not gonna lie....so this for me it's "somewhat" easy to digest. Thanks for the info Khiem.
But I still love N/A simplicity and power,less stuff that can break :)
Friday, June 10, 2011 1:17 PM
Actually I do have a dumb fucking question I'm sure you guys could answer.
It's known that needle bearings in many application are much stronger than ball-bearings....why not just replace the ball-bearings with the needle ones?
Once again, I apologize in advance if this question is too dumb.
Friday, June 10, 2011 1:58 PM
Needle bearings are not as good at super high speeds.
Friday, June 10, 2011 3:59 PM
Any comment on ceramic versus steel ball bearings? I have only heard of Turbonetics offering ceramic to consumers. Does the cost not outweight the benifit? Is the benifit negligible?
Friday, June 10, 2011 4:40 PM
Some of the larger Garrett aftermarket ball bearing turbos use ceramic ball bearings. The Borg Warner EFRs use ceramic BB. The advantage of the ceramic BBs are reduced friction, greater durability, and I think reduced inertia also. The Garrett Dual Boost turbo used in the Ford Powerstroke has ceramic ball bearings.
Saturday, June 11, 2011 2:25 AM
Good to know, seems there are more out there than I thought :)
Saturday, June 11, 2011 7:29 AM
I was talking to an "un-named" engineer (don't want to get him in trouble, lol) that works in the turbo industry, and he was telling me that the response on the ball bearing turbo's are fudged a bit as compared to the journal bearing turbos (at least in Garrett's case) due to them having different turbine wheels for the same sized turbo. Not sure if this is correct, or if he was just bitter, but I could see the marketing advantage of ball bearing turbos over their journal bearing counterparts.
Saturday, June 11, 2011 10:00 AM
@2_Liter, I'm going to be blunt, it doesn't sound like the guy you talked to has a very fundamental understanding of turbos. First off, what has been 'fudged'? I have never seen any claim from any of the major turbo manufacturers (Garrett, Borg Warner, MHI, IHI, Holset) saying that a ball bearing turbo will responed X percent faster across the board.
Why not? Because there are so many variables. Looking at just a ball bearing system: overall size of ball bearing, size of balls, number of balls, ball material used (steel, ceramic), retainer material (polymide, alloy), material of the inner and outer races. Looking at the journal bearing system: size of journal bearings, clearances, thrust bearing size (270/360 degree, size/number/shape of pads), thrust collar size/mass, volume of oil feed to the system.
Then throw in oil viscosity and the temperature of the oil. It's just a fact that ball bearings have less friction than journal bearings which in turn improves turbo response. See if any journal bearing turbo will do this: http://youtu.be/DbUN9eSjbqE
Saturday, June 11, 2011 12:08 PM
Lol, I was just relaying what I was told because it pertained to the topic. It is not my theory at all. The guy has been in the industry a long time, but he could also have a chip on his shoulder. Who knows, ha ha.
Saturday, June 11, 2011 12:19 PM
I know, that's why I said, "the guy you talked to" :)
Saturday, June 11, 2011 2:17 PM
Ahh, lol. I just wanted to clarify that it wasn't me.
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