написано что такое и насколько важно свойство HTHS.
The kinematic way of measuring viscosity of a fluid is very simple indeed. Take a steel ball and measure the time it takes to fall under the force of gravity through a column of (in our case) oil. The longer it takes the more viscous or thicker the oil.
50 years ago when all we had was single grade mineral oils (Okay there was also Castor oil, a natural ester, but that was used primarily for racing applications), you could reliably compare the kinematic viscosities of different brands of oil and if they had the same 100C kinematic viscosity spec' they would have the same "operating viscosity" in an engine. Operating viscosity is the flow rate of the oil at the normal operating temperature of the oil in an engine. The best proxy for the operating viscosity is oil pressure as determined by an oil pressure gauge. The higher the oil pressure reading (it actually measures back pressure) the higher the viscosity of the oil.
But with the move to multi-grade oils due to the use of polymer thickeners, that all changed. These viscosity improvers do dramatically increase the kinematic viscosity of an oil but not linearly when compared to the operational viscosity in an engine. Take for example a 10W-30 oil, which is a 10wt oil with the addition of sufficient polymer thickeners to bring it's 100C viscosity up to that of a 30wt oil. The problem is, a 10W-30 with the same 100C viscosity as a straight 30wt oil will still have a lower operational viscosity (lower oil pressure) because of the temporary shear (compression) of the polymers in the bearings of an engine. Consiquently to compensate for this affect the 10W-30 must have a sufficiently higher 100C viscosity that the non polymer containing straight 30wt oil to maintain the same operating viscosity. Of course we are just talking about temporary shear and nor permanent shear which was another problem of the early multi-grade oils.
What's different about the high temperature/high stress (HTHS) at 150C viscosity spec', other than being a much more expensive measure of viscosity, is that does incorporate the effect of shear since the measure is taken under preasure. This measure of viscosity correlates more directly with the viscosity of oil flowing through the bearings of an engine.
The introduction of synthetic oils allowed for the viscosity index (VI), a measure of an oils resistance to thinning with increased temperature, to rise significantly without the addition of polymer thickeners or much less of their use.
Naturally high VI syn oils have lower kinematic viscosities compared to mineral oils to maintain a given operating viscosity.
Today, we have PCMO's and HDEO's with every combination imaginable of base oil, GP II through GP V, and with all kinds and qualities of viscosity improvers. Consiquently trying to predict what the actual operational viscosity will be from the lowly kinematic 100C viscosity spec' is near impossible. There are 10 cSt at 100C oils that have higher operational viscosities than 14 cSt oils. The answer is the very accurate HTHS vis spec. Dispite the fact that the viscosity measure is
taken at 150C it still correlates almost uncannily precisely with the operational viscosity of an engine at 100C and at operational viscosities even lower than that.
That's one reason why fuel economy correlates with the HTHS vis' of an oil and not the kinematic 100C spec':
http://www.bobistheoilguy.com/forums/ubbth...9041&page=2The SAE have been criticised for not incorporating the more accurate HTHS vis measure into the SAE grading system. For the 20wt grade we have a minimum HTHS vis of 2.6 cP but no maximum. Same for the 30wt grade which must be greater than 2.9 cP with no maximum, same for the 40wt grade, and nothing at all for 50wts and heavier.
http://books.google.com/books?id=Fu-99Mc...p;q&f=falseIn the tradition of BITOG I've personally compared almost a dozen oils so far. The bottom line is this. Oils with the same HTHS vis have the same operational viscosity regardless of their 100C k'vis spec's. Oils with the higher HTHS vis spec' are indeed heavier than oils with lower HTHS vis spec's at normal operating temp's, again regardless of their 100C k'vis spec's.
A couple of popular examples;
RL 5W-20 ( 100C vis 9.1 cSt,HTHS vis 3.3 cP) is heavier than M1 5W-30 (100C vis 11.3 cSt,HTHS 3.09 cP) and PP 5W-30 (100C vis 10.3 cSt,HTHS 3.1 cP). Both M1 and PP have the same operational viscosity.
GC (100C vis 12.2 cSt,HTHS 3.5-3.6 cP) is lighter than RL 5W-30 (100C vis 10.6 cSt, HTHS 3.8 cP) which is slightly heavier than M1 0W-40 (100C 14 cSt, HTHS 3.7 cP).
For those wanting to replicate my experience and
to make the comparison accurately, in addition to an oil pressure gauge you must have a oil temp gauge and tachometer. The oil comparisons must be made at the same engine rpm and oil temperature. Again what you're measuring is oil pressure (back pressure to be more precise) which is a proxy for the operational viscosity of the oil at that temperature.
So what's good about the 100C k'vis spec'?
Well it's a very inexpensive measure of viscosity so at the very least it gives you a ball park measure.
It's also fine when comparing oils with exactly the same chemistry and VII composition although that is hard to know at times.
It's still a necessary spec' along with the 40C k'vis spec' for determining the viscosity index of an oil.
And from a practical view point it's still a VOA reference point for UOA; ie., to determining viscosity loss. You are comparing the oil against it's virginal self.
There are an awful lot of myths associated with the HTHS viscosity measure and it's significance.
Everything from it being somewhat esoteric and not really applicable to daily street use applications that don't see temp's much if ever above 100C. That it's some sort of reserve capacity of an oil and therefore the higher the number the better. To a very critical element of an oil's specification to deal with parts of an engine that get incredably hot regardless of how cool the sump bulk oil temp's may be.
The truth is that it's an accurate measure of an oil's viscosity under stress (pressure) at 150C.
It's a very useful spec' for possibly hot running engines and as such it's an engine lubrication spec' by many manufacturers.
It's a determining factor in the fuel efficiency of an oil.
But probably it's most practical use is as a comparative determinate of an oil operational viscosity.
Cheers
Peter M
в нашей стране другие реалии и есть паленое масло. Я тут тоже пытался писать про hths и про дизельное масло и тд и тп 