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Excellent read. Thank you SonofJoe.
Understanding HTHS
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Originally Posted By: Shannow
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Re the 150C, that's the sort of temperature that is seen in the big end bearings, even IF the sump is tooling along at 100C.
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I would think a turbo would also be an area where the oil is much hotter than in the sump?
...
Re the 150C, that's the sort of temperature that is seen in the big end bearings, even IF the sump is tooling along at 100C.
...
I would think a turbo would also be an area where the oil is much hotter than in the sump?
Originally Posted By: Virtus_Probi
Originally Posted By: Shannow
...
Re the 150C, that's the sort of temperature that is seen in the big end bearings, even IF the sump is tooling along at 100C.
...
I would think a turbo would also be an area where the oil is much hotter than in the sump?
Oil in a turbo can exceed 350 C. Page 59: https://www.atc-europe.org/public/Docume...%20Benefits.pdf
Originally Posted By: Shannow
...
Re the 150C, that's the sort of temperature that is seen in the big end bearings, even IF the sump is tooling along at 100C.
...
I would think a turbo would also be an area where the oil is much hotter than in the sump?
Oil in a turbo can exceed 350 C. Page 59: https://www.atc-europe.org/public/Docume...%20Benefits.pdf
Originally Posted By: Virtus_Probi
Originally Posted By: Shannow
...
Re the 150C, that's the sort of temperature that is seen in the big end bearings, even IF the sump is tooling along at 100C.
...
I would think a turbo would also be an area where the oil is much hotter than in the sump?
Discussion was HTHS...which is about big ends
Originally Posted By: Shannow
...
Re the 150C, that's the sort of temperature that is seen in the big end bearings, even IF the sump is tooling along at 100C.
...
I would think a turbo would also be an area where the oil is much hotter than in the sump?
Discussion was HTHS...which is about big ends
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Yep … wrong HTHS and those big ends can get cranky
Originally Posted By: Shannow
Discussion was HTHS...which is about big ends
To be fair, the turbo shaft bearings would also be a high temp/shear environment with how hot and fast it spins right? However, I’m not sure if that’s an area where you’d want a high HTHS oil due to its effect on turbo response.
Discussion was HTHS...which is about big ends
To be fair, the turbo shaft bearings would also be a high temp/shear environment with how hot and fast it spins right? However, I’m not sure if that’s an area where you’d want a high HTHS oil due to its effect on turbo response.
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Originally Posted By: 1JZ_E46
Originally Posted By: Shannow
Discussion was HTHS...which is about big ends
To be fair, the turbo shaft bearings would also be a high temp/shear environment with how hot and fast it spins right? However, I’m not sure if that’s an area where you’d want a high HTHS oil due to its effect on turbo response.
While I agree with you that the turbo bearings would be high temp for sure, I'm not sure about the high shear part in relation to what Shannow is stating. The big ends on the rods are being slammed by the force of combustion occurring above them, this creates an area of extremely high pressure, whilst simultaneously rotation is occurring. This is the area of high shear.
Originally Posted By: Shannow
Discussion was HTHS...which is about big ends
To be fair, the turbo shaft bearings would also be a high temp/shear environment with how hot and fast it spins right? However, I’m not sure if that’s an area where you’d want a high HTHS oil due to its effect on turbo response.
While I agree with you that the turbo bearings would be high temp for sure, I'm not sure about the high shear part in relation to what Shannow is stating. The big ends on the rods are being slammed by the force of combustion occurring above them, this creates an area of extremely high pressure, whilst simultaneously rotation is occurring. This is the area of high shear.
200,000 rpm is possible on turbo. Call that rpm1. Bearing diameter of r1 (inches) and bearing clearance of c1 (inches).
Tangential velocity of bearing surface (inches/sec): 2*pi/60*rpm1*r1
Shear rate (1/sec): 2*pi/60*rpm1*r1/c1
Ratio of that shear rate to shear rate in another bearing, with its variables ending in “2”, after simplifying, is:
(rpm1*r1/c1)/(rpm2*r2/c2)
With equal clearances, r2 twice as big as r1, and rpm1 of 200k rpm and rpm2 of 7500 rpm, shear rate of oil in turbo bearing is 13.3 times as large as in the other bearing. The effect of a force increasing the eccentricity ratio is to decrease the clearance at the location of minimum oil filtm thickness, increasing the shear rate there and decreasing it 180 degrees from there.
Non-Newtonian oil’s viscosity as a function of shear rate looks like what Shannow showed. Increasing shear rate, starting on the lower plateau may not decrease the viscosity (if it stays on that plateau. I think I’ve seen in a paper years ago that at even higher shear rates, another lower plateau was found, showing a total of 3 plateaus.
Tangential velocity of bearing surface (inches/sec): 2*pi/60*rpm1*r1
Shear rate (1/sec): 2*pi/60*rpm1*r1/c1
Ratio of that shear rate to shear rate in another bearing, with its variables ending in “2”, after simplifying, is:
(rpm1*r1/c1)/(rpm2*r2/c2)
With equal clearances, r2 twice as big as r1, and rpm1 of 200k rpm and rpm2 of 7500 rpm, shear rate of oil in turbo bearing is 13.3 times as large as in the other bearing. The effect of a force increasing the eccentricity ratio is to decrease the clearance at the location of minimum oil filtm thickness, increasing the shear rate there and decreasing it 180 degrees from there.
Non-Newtonian oil’s viscosity as a function of shear rate looks like what Shannow showed. Increasing shear rate, starting on the lower plateau may not decrease the viscosity (if it stays on that plateau. I think I’ve seen in a paper years ago that at even higher shear rates, another lower plateau was found, showing a total of 3 plateaus.
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Originally Posted By: JAG
200,000 rpm is possible on turbo. Call that rpm1. Bearing diameter of r1 (inches) and bearing clearance of c1 (inches).
Tangential velocity of bearing surface (inches/sec): 2*pi/60*rpm1*r1
Shear rate (1/sec): 2*pi/60*rpm1*r1/c1
Ratio of that shear rate to shear rate in another bearing, with its variables ending in “2”, after simplifying, is:
(rpm1*r1/c1)/(rpm2*r2/c2)
With equal clearances, r2 twice as big as r1, and rpm1 of 200k rpm and rpm2 of 7500 rpm, shear rate of oil in turbo bearing is 13.3 times as large as in the other bearing. The effect of a force increasing the eccentricity ratio is to decrease the clearance at the location of minimum oil filtm thickness, increasing the shear rate there and decreasing it 180 degrees from there.
Non-Newtonian oil’s viscosity as a function of shear rate looks like what Shannow showed. Increasing shear rate, starting on the lower plateau may not decrease the viscosity (if it stays on that plateau. I think I’ve seen in a paper years ago that at even higher shear rates, another lower plateau was found, showing a total of 3 plateaus.
The bolded and underlined part is what I was driving at, in particular the point of decreased clearance where we know that there is an acceptable minimum HTHS for a given bearing width and clearance that will, if exceeded, result in the journal contacting the bearing surface. The turbo bearings, while having an overall higher sheer rate to a comparable journal bearing, do not have to deal with the eccentricity issue, as you've touched on.
We have observed with various OEM's in the quest for thinner lubricants, widening their bearings to compensate. Honda is one example of that. Have we also seen similar changes in turbo design? That's intended as a legitimate question, as I haven't seen it mentioned but perhaps we have?
200,000 rpm is possible on turbo. Call that rpm1. Bearing diameter of r1 (inches) and bearing clearance of c1 (inches).
Tangential velocity of bearing surface (inches/sec): 2*pi/60*rpm1*r1
Shear rate (1/sec): 2*pi/60*rpm1*r1/c1
Ratio of that shear rate to shear rate in another bearing, with its variables ending in “2”, after simplifying, is:
(rpm1*r1/c1)/(rpm2*r2/c2)
With equal clearances, r2 twice as big as r1, and rpm1 of 200k rpm and rpm2 of 7500 rpm, shear rate of oil in turbo bearing is 13.3 times as large as in the other bearing. The effect of a force increasing the eccentricity ratio is to decrease the clearance at the location of minimum oil filtm thickness, increasing the shear rate there and decreasing it 180 degrees from there.
Non-Newtonian oil’s viscosity as a function of shear rate looks like what Shannow showed. Increasing shear rate, starting on the lower plateau may not decrease the viscosity (if it stays on that plateau. I think I’ve seen in a paper years ago that at even higher shear rates, another lower plateau was found, showing a total of 3 plateaus.
The bolded and underlined part is what I was driving at, in particular the point of decreased clearance where we know that there is an acceptable minimum HTHS for a given bearing width and clearance that will, if exceeded, result in the journal contacting the bearing surface. The turbo bearings, while having an overall higher sheer rate to a comparable journal bearing, do not have to deal with the eccentricity issue, as you've touched on.
We have observed with various OEM's in the quest for thinner lubricants, widening their bearings to compensate. Honda is one example of that. Have we also seen similar changes in turbo design? That's intended as a legitimate question, as I haven't seen it mentioned but perhaps we have?
I think it was the lady who works for GM, who is on video presenting Dexos Gen-2 specification, that said that most turbo designs are not fully compatible with xW-20 oils. I think she then said that turbo manufacturers are in the process of designing them for such oils. Turbo shafts experience axial thrust and if the oil is too thin, it will not provide adequate protection. I bet one of the changes that are necessary is to increase the surface area involved in that thrust. Have any manufacturers sold any engines with turbos and specified xW-20 yet?
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Originally Posted By: JAG
I think it was the lady who works for GM, who is on video presenting Dexos Gen-2 specification, that said that most turbo designs are not fully compatible with xW-20 oils. I think she then said that turbo manufacturers are in the process of designing them for such oils. Turbo shafts experience axial thrust and if the oil is too thin, it will not provide adequate protection. I bet one of the changes that are necessary is to increase the surface area involved in that thrust. Have any manufacturers sold any engines with turbos and specified xW-20 yet?
That sounds compelling, but doesn't Honda recommend 0w-20 for the 1.5L turbo DI Civic?
I think it was the lady who works for GM, who is on video presenting Dexos Gen-2 specification, that said that most turbo designs are not fully compatible with xW-20 oils. I think she then said that turbo manufacturers are in the process of designing them for such oils. Turbo shafts experience axial thrust and if the oil is too thin, it will not provide adequate protection. I bet one of the changes that are necessary is to increase the surface area involved in that thrust. Have any manufacturers sold any engines with turbos and specified xW-20 yet?
That sounds compelling, but doesn't Honda recommend 0w-20 for the 1.5L turbo DI Civic?
Overkill, I looked it up and yes, that engine calls for 0W-20. Let’s hope the turbo design is a good match for the oil. There have been too many screw ups in the auto industry for me to have blind faith that all will be well and that the specified oil is the best choice.
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Originally Posted By: JAG
Overkill, I looked it up and yes, that engine calls for 0W-20. Let’s hope the turbo design is a good match for the oil. There have been too many screw ups in the auto industry for me to have blind faith that all will be well and that the specified oil is the best choice.
I share your concern
Overkill, I looked it up and yes, that engine calls for 0W-20. Let’s hope the turbo design is a good match for the oil. There have been too many screw ups in the auto industry for me to have blind faith that all will be well and that the specified oil is the best choice.
I share your concern
Didn't think of the thrust...that's a hard one without going full roller and the random failures that introduces.
Make the thrust bigger, and there goes the responsiveness.
(The big diesel gensets at work have a standalone turbo reservoir, sits there soot free).
Make the thrust bigger, and there goes the responsiveness.
(The big diesel gensets at work have a standalone turbo reservoir, sits there soot free).
There are all kinds of turbocharger bearing designs (search the 'net), but many are journal/sleeve type so I'd think there is hydrodynamic lubrication going on there. Considering how fast the turbo shaft spins (up to 300K) I'd say there's lots of oil hydrodynamic shearing going on.
http://www.turbos.bwauto.com/products/turbochargerBearingSystem.aspx
http://www.turbos.bwauto.com/products/turbochargerBearingSystem.aspx
Thanks for that link Zee. One part of the bearing description caught my attention. From the Radial Bearing System paragraph;
“Besides the lubricating function, the oil film in the bearing clearances also has a damping function, which contributes to the stability of the shaft and turbine wheel assembly.”
Now I am not a engineer nor that mechanically inclined but I understand the damping effect as another term for stabilizing the bearing/turbo shaft from vibration or that sort. Correct me if I’m wrong here.
With that said, it seems to me a 30wt oil would perform better in this regard than would a 20wt. I have nothing against thin oil but when turbos come into play and the manufacturer recommends 0w20 as we see with Honda etc, I do scratch my head and wonder. This especially after Ford changed to 5w30 for some of their EcoBoost engines.
Please correct or educate me if I’m off the mark here. Great discussion.
“Besides the lubricating function, the oil film in the bearing clearances also has a damping function, which contributes to the stability of the shaft and turbine wheel assembly.”
Now I am not a engineer nor that mechanically inclined but I understand the damping effect as another term for stabilizing the bearing/turbo shaft from vibration or that sort. Correct me if I’m wrong here.
With that said, it seems to me a 30wt oil would perform better in this regard than would a 20wt. I have nothing against thin oil but when turbos come into play and the manufacturer recommends 0w20 as we see with Honda etc, I do scratch my head and wonder. This especially after Ford changed to 5w30 for some of their EcoBoost engines.
Please correct or educate me if I’m off the mark here. Great discussion.
Originally Posted By: PimTac
... it seems to me a 30wt oil would perform better in this regard than would a 20wt. I have nothing against thin oil but when turbos come into play and the manufacturer recommends 0w20 as we see with Honda etc, I do scratch my head and wonder. ...
Possibly, but keep in mind that the viscosity difference between a 20 and a 30 is not as huge as people seem to imagine---not a 2:3 ratio or worse. Any system that has serious trouble with a 20 would be borderline at best with a 30 weight.
... it seems to me a 30wt oil would perform better in this regard than would a 20wt. I have nothing against thin oil but when turbos come into play and the manufacturer recommends 0w20 as we see with Honda etc, I do scratch my head and wonder. ...
Possibly, but keep in mind that the viscosity difference between a 20 and a 30 is not as huge as people seem to imagine---not a 2:3 ratio or worse. Any system that has serious trouble with a 20 would be borderline at best with a 30 weight.
Originally Posted By: PimTac
“Besides the lubricating function, the oil film in the bearing clearances also has a damping function, which contributes to the stability of the shaft and turbine wheel assembly.”
Now I am not a engineer nor that mechanically inclined but I understand the damping effect as another term for stabilizing the bearing/turbo shaft from vibration or that sort. Correct me if I’m wrong here.
Stability/damping, not quite the right terms, it's oil film "stiffness"....here's a (typical) map of what happens with high speed turbomachinery.
Bottom axis is Somerfeld number (r/c)^2 * u * N /P
(r=radius, c= clearance, u is viscosity N is speed, and P is load on projected area).
The 45% lines are the lines that a simple machine would follow speeding up and down.
So for a given machine, an increase in u by (say) 10% would increase So by 10% and possibly push into the unstable region
Although slightly different, you know that sound that small electric motors make when they are on the way out ? - that's instability called "whirl"...in hydrodynamic bearings it's one of the shaft's natural frequencies interacting with the bearing stiffness...
I had one Generator bearing that you could watch the Fourier transform. 30um 1x vibration, and a noisy 1/4 times. Over the course of half an hour, it would be 6, 0, 12, 0, 6, 25, 75, 150. Drop the vicosity, by lowering operating temperature by 5 degrees and the 1/x would settle down again...maybe not come back for days.
Operation in the unstable range isn't automatically high vibration, but it can snap between to states with little provocation.
“Besides the lubricating function, the oil film in the bearing clearances also has a damping function, which contributes to the stability of the shaft and turbine wheel assembly.”
Now I am not a engineer nor that mechanically inclined but I understand the damping effect as another term for stabilizing the bearing/turbo shaft from vibration or that sort. Correct me if I’m wrong here.
Stability/damping, not quite the right terms, it's oil film "stiffness"....here's a (typical) map of what happens with high speed turbomachinery.
Bottom axis is Somerfeld number (r/c)^2 * u * N /P
(r=radius, c= clearance, u is viscosity N is speed, and P is load on projected area).
The 45% lines are the lines that a simple machine would follow speeding up and down.
So for a given machine, an increase in u by (say) 10% would increase So by 10% and possibly push into the unstable region
Although slightly different, you know that sound that small electric motors make when they are on the way out ? - that's instability called "whirl"...in hydrodynamic bearings it's one of the shaft's natural frequencies interacting with the bearing stiffness...
I had one Generator bearing that you could watch the Fourier transform. 30um 1x vibration, and a noisy 1/4 times. Over the course of half an hour, it would be 6, 0, 12, 0, 6, 25, 75, 150. Drop the vicosity, by lowering operating temperature by 5 degrees and the 1/x would settle down again...maybe not come back for days.
Operation in the unstable range isn't automatically high vibration, but it can snap between to states with little provocation.
Thanks Shannow. In another paper I read yesterday, it said that since no turbo is perfectly balanced, its rotor will gyrate and the oil film helps damp that motion. Higher viscosity increases the damping. Is that captured in the stability vs speed and Sommefield number, or is it a totally separate phenomena?
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