As an additive, the viscosity index improver can improve the viscosity and temperature function of lubricating oil, so as to obtain a multistage starter oil with good starting function at low temperature and proper viscosity at high temperature.

Since fuel economy and emissions are considered in most vehicle oils, it is necessary to consider the balance between volatility and high and low temperature rheology. In order to meet the CCS requirements of SAE multistage oils, it is necessary to consider the balance between low viscosity base oils and viscosity index improvers at low temperatures. The lower the viscosity of the base oil, the greater the VII participation, the higher the CCS value, and the higher the evaporation loss. In addition to the kinematic viscosity requirements at 100 ℃, the selection of VII should also consider the minimum viscosity requirements of SAE at high temperature and high shear.

Different chemical categories of finger adhesives have different effects on CCS low temperature viscosity, viscosity index and high temperature and high shear viscosity. Therefore, the selection of different kinds and shear stability of viscosity index improver will greatly affect the proportion of each component in the oil, and greatly affect the production cost.

Viscosification ability is an important function of viscosity index improvers. The greater the viscosification ability of the viscosity index improver, the smaller the amount, the lower the cost of multistage oil. The viscosification ability is mainly related to the size of molecular weight of the viscosity index improver, the number of main chain carbon [-- CH2 --] on the molecule and its form in the base oil. The order of viscosification ability of commonly used viscosity index improvers is as follows: ethylene propylene copolymer > polyisobutene > styrene-butadiene copolymer > polymethacrylate. The viscosification ability of viscosity index improver VII of ethylene propylene copolymer is undoubtedly the strongest.

Viscosity stability is an important characteristic of gear oil during use. Especially like the gear oil with large span viscosity level of 75W/90, it is not without benefit to select the adhesive with good shear stability for the outstanding operation of the vehicle's transmission system and the protection of the gear.