Introduction to High Temperature High Shear(HTHS)

1.The full name of HTHS is: High Temperature High Shear

This parameter is the apparent viscosity of the oil obtained by the capillary viscosity test at 150 °C, that is, the dynamic viscosity.

It is tested under the conditions of simulating the working temperature of the internal combustion engine cylinder and high-speed shearing, reflecting the lubrication between the cylinder liner and the piston ring and the fuel economy of the lubricating oil.

The test standard is 150 degrees and the apparent viscosity at a shear rate of 10^6. This working condition is the working condition of the crankshaft bearing. This is the parameter that was determined after the crankshaft bearing was damaged after the use of multi-grade oil at that time.

Because there is a large positive pressure (compressive stress, non-shearing stress) between the cam and the ejector rod, between the piston and the cylinder, and between the shaft and the bearing bush, the oil film will be squeezed, and HTHS is reflected in the piston and the bearing. The adhesion of lubricating oil between cylinders and between shafts and bearing bushes is related to the oily or polar agent added to the lubricating oil. Many people call it oil film strength, and understand it as oil film strength which is very vivid and accurate.

2.The difference between 100 degree viscosity and HTHS

100 degrees corresponds to the engine water temperature, and this kinematic viscosity reflects the fluidity and flow resistance of the lubricating oil when the engine is running.

The viscosity of 100-degree lubricating oil is the kinematic viscosity, which indicates the thickness of the oil film that this lubricating oil can form. HTHS is the characteristic that the lubricating oil film can maintain the integrity of the oil film under high temperature and high shear conditions.

Simply put:

100 degree viscosity—indicates the thickness of the oil film;

HTHS—-indicates oil film strength under high temperature and high shear conditions. Therefore, HTHS is an index indicating the viscosity stability of lubricating oil under high temperature and high shear, which reflects the lubricating ability of lubricating oil under high temperature and high shear conditions.

3.About the relationship between oil viscosity and wear resistance

Some people think that the oil viscosity will cause damage to the engine when it is diluted. This is actually based on the problem of HTHS. If the HTHS is sufficient, there will be no problem of damage.

From the perspective of anti-wear, it is not only the oil film that plays a role, but also the additive formula of the engine oil. The anti-wear additive system inside plays a key role, because wear is the most extreme boundary friction that occurs during the working process. Under the circumstance, at this time, the oil film between the friction pairs no longer exists, and it cannot play an anti-wear effect. Additional chemistries are required for anti-wear effects, such as zinc, molybdenum and phosphorous.

The mixture of combustion and work can reach more than 500 degrees. When the mixture is ignited to do work and the piston moves downward, can the residual oil film on the upper part of the cylinder wall still exist? After the temperature exceeds the flash point of the oil, the oil has been vaporized and burned. In the next exhaust stroke, when the piston moves upward, the oil film no longer exists, and the chemical film formed on the cylinder wall by the anti-wear additives inside the oil can also play a role in anti-wear protection. In addition, whether it is the compression stroke or the power stroke, the pressure on the piston near the top dead center is the largest. Because the crankshaft works in a ring shape, most of the time the connecting rod is due to the angle of inclination. The shear pressure on the cylinder wall is extremely high. If high-speed shearing motion is added, serious boundary friction will occur at this time, and the oil film will rupture. It is not the oil film but the chemical film that protects. The additive formula of the engine oil used in many cars is not good enough, so it is more obvious that the cylinder barrel is ground into a big one and a small one.


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