The effect of viscosity index improver on the fuel economy of gasoline engine oil. The high frequency reciprocating tester was used to simulate the friction of the engine, and the lubrication performance of gasoline engine oil was investigated by measuring the friction factor. The smaller the friction factor of gasoline engine oil, the better the lubricating performance and the more conducive to improving fuel economy. The friction torque of gasoline engine oil was measured by engine drag test and compared with the friction torque of reference oil. The greater the torque difference (torque difference = the average value of the friction torque of the reference oil - the friction torque of the gasoline engine oil), the better the fuel economy of the gasoline engine oil. The friction coefficient of gasoline engine oil of 0W-20 viscosity grade prepared with polymethacrylate with smaller kinematic viscosity (kinematic viscosity at 100 ℃ of 890 mm2/s) and better shear stability (shear stability index 5) is higher than that of gasoline engine oil. Small, large torque difference, with better fuel economy. According to NEDC (New European Driving Cycle) simulation cycle test fuel consumption calculation, it can improve fuel economy by 0.28%. According to the "Passenger Vehicle Fuel Consumption Limits" issued by the Ministry of Industry and Information Technology: GB16578-2014 and "Passenger Vehicle Fuel Consumption Evaluation Methods and Indicators": GB27999-2014 mandatory standards, by 2020, all passenger vehicles will be The average fuel consumption of 100km must be reduced to 5.0L, so saving fuel and reducing fuel consumption is the general trend of the current automobile industry development. In order to reduce fuel consumption and improve fuel economy, in addition to improving the design of the engine, it is also an effective way to improve the lubrication state between the friction parts of the engine. Generally speaking, during the operation of the engine, the bearing parts are mainly in the state of elastic fluid lubrication, while the parts such as the valve train, piston and cylinder liner are mainly in the state of boundary lubrication and mixed lubrication. For fluid lubrication state, choosing low-viscosity gasoline engine oil can reduce friction loss; for boundary lubrication state, adding friction modifier to engine oil is a more effective method to reduce friction loss. For the mixed lubrication state, it is necessary to comprehensively consider the optimization of the viscosity characteristics and friction characteristics of gasoline engine oil. In order to improve the fuel economy of passenger cars, it is necessary to study the effect of gasoline engine oil components on fuel economy. As an additive that can improve the viscosity-temperature properties of lubricating oils, viscosity index improvers have been widely used in engine oils. Commonly used viscosity index improvers are hydrogenated styrene diene copolymer (HSD for short), olefin copolymer (OCP for short), polymethacrylate (PMA for short), hydrogenated styrene-isoprene copolymer (SDC) And polyisobutylene (PIB) etc. The overall performance of OCP and HSD is better, but HSD has better shear resistance than OCP, and is more commonly used in high-grade gasoline engine oil. PMA has the characteristics of improving the low temperature performance of gasoline engine oil and increasing the viscosity index, and is also widely used in high performance gasoline engine oil. Some studies have reported that gasoline oil formulated with PMA viscosity index improver helps to form a boundary oil film on the metal surface under high temperature and low speed conditions, thereby significantly reducing friction and improving the fuel economy of gasoline oil.