Tham khảo tài liệu 'lubricants and lubrication part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 198 I 9 Lubricants for Internal Combustion Engines Physical and Chemical Testing The physicochemical properties of an engine oil can be determined in the laboratory with standard test methods Chapter 19 . This characterization mainly focuses on rheological test values and the previously shown SAE classification system. Various viscosity tests are used to determine exact low- and high-temperature viscosities . The viscosity thus determined is a characteristic of the engine oil at a defined engine state. At low temperatures -10 to -40 C a MRV mini rotary viscometer with a low shear gradient is used to determine the apparent viscosity and thus the oil s flowability in the area of the oil pump. In addition maximum viscosity as the threshold of viscosity is determined in five graduated steps. The dynamic CCS cold cranking simulator viscosity which is determined at -10 to -40 C with a high shear gradient is also an apparent viscosity which represents the tribological conditions at the crankshaft during cold starts. The maximum values laid-down in SAE J 300 guarantee reliable oil circulation during the start-up phase. The rheological characteristics at higher thermal loads which occur during full-throttle operation are described by the dynamic viscosity at 150 C and a shear rate of 106 s-1 or HTHS high-temperature high-shear . The corresponding threshold values also guarantee an adequate lube film even in these conditions. Apart from the rheological characteristics the Noack evaporation test described in Chapter 19 to test the volatility of base oils and additives as well as foaming tendency and air release can be characterized with simple methods. Furthermore the compatibility of high-additive oils with seal materials is tested on standard reference elastomers in static swelling and subsequent elongation tests . The viscosity loss resulting from mechanical load is described in Section . Engine Testing Because realistic engine oil tests cannot
