To expand the applications of polymer friction modifiers in low viscosity oils suitable for hybrid power systems, the tribological properties of five kinds of oil samples at different temperatures were studied, which were compounded with polymer friction modifiers Perfad XG 2500, molybdenum dialkyl dithiocarbamate (MoDTC), zinc dialkyl dithiophosphate (ZDDP). When Perfad XG 2500 is used alone, it forms a brush-like surface film at low temperatures, which can provide lower initial friction. With the rise in temperature, its antifriction effect decreases significantly, which is related to the desorption behavior of physical film. When Perfad XG 2500 is combined with MoDTC, it has the best synergistic antifriction effect, and the average friction coefficient is reduced by a maximum of 20.83% (90 °C). Its friction coefficients decrease significantly with the increase in temperature due to the dissociation process of MoDTC catalyzed by high temperature. However, there are many furrows on the worn surfaces, and the sharp features of the profiles are obvious. When Perfad XG 2500 is combined with ZDDP, it has the best synergistic anti-wear effect, and the total wear depth is reduced by 49.6%. Its worn surface is smooth and defect-free, with minimal residual strain. The friction coefficients are hardly affected by temperature, and the average friction coefficient is reduced by a maximum of 14.4% (30 °C). When Perfad XG 2500, MoDTC and ZDDP are used together, the average friction coefficient is reduced by up to 15.2% (30 °C). Its friction coefficient increases slightly with the rise in temperature. The reason for its moderate tribological performance may be related to the superficial competition of various additives.

Aimed to more truly and stably measure the fuel economy of a vehicle under different driving cycles, simultaneously reduce prime cost and short experimental period. An engine fuel economy test method and bench which could adapt to multiple cycle conditions was developed. The fuel economy test of a certain SUV under NEDC/WLTC was carried out, and the transient operating parameters of the engine were collected. The engine fuel economy test bench was established and accurately controlled according to transient parameters. The FEI of five different formulations of engine oils was tested. The results indicate that the actual bench parameters are in good agreement with the target transient parameters. Multiple FC measurements of baseline oil and multiple FEI measurements of high reference oil show that the engine bench has good repeatability. The data fluctuation degree of bench test is obviously smaller than that of vehicle test. The correlation coefficients of comprehensive FEI between bench test and vehicle test are 95.25% (NEDC) and 96.39% (WLTC). It means that the bench test can completely replace the vehicle test for fuel economy analysis. The FEI of No.3 oil which has the best fuel improvement are 1.888% (NEDC) and 1.248% (WLTC) respectively. Compared with the vehicle test, the engine bench testing can save 75% of the time. The fuel economy bench and test methods are also suitable for the verification of fuel economy improvement of other engine optimization measures under different driving cycles. The development period of engine technologies can be shortened, and the test cost can be reduced.