Research On The Measurement Technology Of Oil Film Thickness Based On The Method Of Capacitance

Tribology is an applied science studying the friction, lubrication and wear of the relative motion. In the research of the elastohydrodynamic lubrication state of contact friction pair, one of the significant criterions of lubricating state is characterized by the thickness of lubricating oil film which also determinates the lubricating state between the surfaces of different mechanical components. In the thesis, the capacitance method is employed to measure the capacitance of oil films between the friction pairs, and the relationships of the capacitances verse the revolving speed, load, roughness of the disk, and viscosity of the oil are shown using the characteristic curves.The original machine system of testing contact friction is improved in follow-ing aspects to optimize the capacity of resisting disturbance. Firstly, PTFE material is introduced to insulate both the upper and lower samples from the outside environment thoroughly. Secondly, a specialized permalloy is used to shield the influence of external electromagnetic field and waves on the instrument of the resistance-capacitance characteristic parameters. At last, the high-voltage components and the shell of machine are electronically connected to the earth, which can eliminate the disturbance of the external noise and the static electricity from human body and the metal shell. With relatively low load and low revolving speed, the experiments in the condition of fixed load-vibrational-revolving-speed and fixed revolving speed-vibrational load are carried out. The main conclusions are displayed as follows:Specifically, with certain load, the capacitance of the oil film decreases while increasing the revolving speed. In the different ranges of the revolving speeds, the oil film has different peak values of the capacitance and exhibits different lubricating state because of the variation of the revolving speed; in a certain range of the revolving speed, the capacitance slightly increases while increasing the load; a fter the load increases above a certain value, the capacitance varies little over the increase of load, and the characteristic curve tend to be flat. In the work, the influence of the viscosity and roughness on the capacitance is further investigated under a fixed load. In the condition of a low revolving speed, the viscosity significantly affect the capacitance; while the high revolving speed has relatively small influence over the capacitance. Also, the roughness affects the capacitance. Less rough disk leads to more stable lubricating oil film with a smaller capacitance.