Numerical and experimental study on the separation characteristics of microgroove rotary seals

The microgroove rotary seals used in the wet clutches of a vehicle operate in a mixed-lubrication state at low rotational speeds. When the speed increases to a certain value, the full-film hydrodynamic-lubrication state occurs in the sealing end face. The transition characteristics of the microgroove rotary seal in this operating state are called the separation characteristics and the critical speed is called the separation speed. In this paper, the separation characteristics of microgroove rotary seals are studied. First, a theoretical model considering the asperity contacts, the fluid lubrication with microgrooves and the axial motion dynamic characteristics of the seal is established. Then, the variation in the separation characteristics is studied systematically using the microgroove parameters, such as the number N_g of microgrooves, the groove width ratio δ_θ, the extent δ_r of the radial seal dam and the spiral angle β. The optimum ranges of the microgroove parameters are determined: N_g = 40-50, δ_θ = 0.65-0.75 and δ_r = 0.7-0.8 for radial grooves and N_g = 30-40, δ_θ = 0.5-0.7, δ_r = 0.7-0.8 and β = 12-17° for spiral grooves. Finally, the variations in the microgroove parameters of the separation characteristics are verified by several experiments. The experimental results are in good agreement with the simulation results.