| With the introduction of the “dual carbon” policy and the upgrading of product performance,higher requirements have been placed on the friction performance of wheel bearings.Grease is widely used in automobiles,especially in wheel bearing lubrication,due to its rheological properties,long life and low cost.The friction loss can be reduced by developing high-efficiency grease and surface treatment of friction pairs.In this thesis,taking a certain MPV vehicle wheel hub bearing as the object,four kinds of greases were selected and diamond-like carbon(DLC)coatings with different parameters were prepared,and the lubrication mechanism of grease-DLC film synergistic lubrication on the friction properties of bearing steel GCr15 was studied through tribological tests.Then,The application effect on the wheel hub bearing was verified by the friction torque test and the vehicle sliding test.The main contents of this thesis are as follows:(1)By analyzing the formula of the grease,four kinds of grease were selected and the relevant physical and chemical properties were tested,and the performance difference of different formula greases was preliminarily evaluated.The DLC films doped with Ti element were prepared by the multi-functional magnetron sputtering coating technology with GCr15 steel as the substrate.By controlling the deposition time,sputtering power of the target and other process parameters,DLC films coating with different thicknesses and different contents of Ti doping were prepared.(2)In order to explore the effect of DLC film coatings of different greases and parameters on the friction properties of wheel hub bearing steel GCr15,the relevant tribological experiments were completed by using a reciprocating friction and wear testing machine with a noise acquisition system.The friction noise excited by the surface vibration of the friction pair is related to the wear characteristics.A timefrequency analysis method of friction noise was established based on empirical mode decomposition(EMD).Combined with the friction coefficient curve,the effect of grease-DLC film synergistic lubrication on friction performance was analyzed.The results show that the DLC film coating can improve the friction and wear properties of GCr15 steel,and has a good positive synergistic lubricating effect with the grease.Among the four grease samples tested,the grease with polyurea-based thickeners and ester-based base oils has the best friction reducing effect with DLC thin film coating.The friction properties of DLC films show a trend of increasing first and then that further increase in thickness will instead increase the residual stress of the DLC coating resulting in a decrease in performance and the Ti content has an effect on the content of Ti C nanocrystals in the thin-film carbon matrix.(3)The surface morphology of the test samples was analyzed by scanning electron microscopy(FESEM),and the synergistic lubrication mechanism was analyzed accordingly.The grease-DLC film is mainly adhesive wear and abrasive wear.Through the analysis of EDS results,it is found that the lubrication of grease-DLC film is accompanied by a certain amount of oxidative wear,and the content of surface oxygen is positively correlated with the friction reduction effect of the surface.This is because under grease lubrication,with the accumulation of reciprocating motion,the temperature of the contact area will increase locally,which will aggravate the oxidation reaction of the friction surface,and generate an oxide film on the surface of the friction pair.The polarity of the oxide film and the grease The groups and the like adsorb to each other to form a composite lubricating film to stably reduce friction.(4)Based on the above research,it was applied to the wheel hub bearing of an MPV model,and the bearing friction torque test and the vehicle sliding resistance test were carried out to verify the practical application effect of the improvement scheme on improving the friction performance and reducing the friction loss of the vehicle.The results show that the synergistic lubrication of the grease-DLC film has a good positive effect,which can reduce the friction torque of the wheel hub bearing by 31.6%,and reduce the sliding resistance of the whole vehicle by 6.9%. |
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