Performance Analysis And Experimental Study On Journal-thrust Floating Ring Hybrid Bearing With Independent Oil Supply

Externally pressurized hydrostatic/hydrodynamic bearings have become increasingly popular in many super high speed machines such as astronavigation, generators and high speed processing machine tool due to their remarkable characteristics in respect of low friction, high accuracy, long life, smooth operation, high fluid film stiffness, damping capacity etc. Hybrid bearings are also widely used in many vehicle components such as engine crankshaft, drive system, steering system and chassis. Adopting floating ring hybrid bearing is the effective method to increase the rotational speed of rotor-bearing system. Among most hybrid bearings in common use, the external restrictors are used and the oil is supplied both to the inner fluid film and the outer fluid film. Therefore the external restrictors are easy to be plugged and the inner and outer oil supply pressure can not be adjusted independently. The performance of rotor-bearing system can be controlled if the oil is supplied respectively to the inner fluid film and the outer fluid film independently. How to design the new structure bearing and how to build the model and analyze the influence of parameters on bearing characteristics is the base to improve the bearing performance.This paper presents a theoretical and experimental study concerning the static and dynamic performance of hybrid journal-thrust floating ring bearing with inner and outer fluid film independent oil supply. A new structure fluid lubricated floating ring hybrid bearing compensated by interior round pin restrictor is designed. The static and dynamic characteristics model of the journal-thrust floating ring hybrid bearing was established with finite element method (FEM) simulation. The influences of oil supply pressure, cavitations on bearing performance are analyzed. In order to verify the rationality of new structure and simulation model, the experimental rig with independently oil supply is established. This dissertation focuses on the following three aspects: (1) The structure design of journal-thrust floating ring hybrid bearing with independent oil supplyThe cylindrical hybrid bearings have no axial load carrying capacity and the conical bearing can support limited axial load due to conical angle. While the journal-thrust hybrid bearing combines the advantages of journal bearing and thrust bearing and can support great radial and axial loads at the same time. A new structure fluid lubricated hybrid bearing with independent oil supply is designed in order to adjust and improve the bearing dynamic performance. The new structure interior round pin restrictor which can reduce the restrictor pocket area and decrease friction power loss without increasing the bearing size and can avoid blockage effectively is studied in detail.(2) The static and dynamic performance simulation model and stability analysis of journal-thrust floating ring bearing with independent oil supplyBases on laminar current theory, the equations governing the flow of inner and outer fluid film in the journal-thrust floating ring bearing are established with FEM simulation. The variation regularity of static and dynamic performance with oil supply pressure, eccentricity and rotational speed are analyzed. It can be seen from the results that the static characteristics coefficients are not sensitive to oil supply pressure, but the dynamic characteristics parameters varies obviously with oil supply pressure.The stability is very important for the high speed rotational system. The dynamic simulation model for inner and outer fluid film is established separately considering the shaft mass and floating ring mass. The three dimension stability criterion is deduced using Routh-Hurwitz stability criterion. On the base of theoretically analysis, a set of oil supply feedback device is designed in order to control the stability of rotor-bearing system on line.The change of oil supply pressure will bring bubbles to the bearing pockets, especially in deep pockets. The dimensionless Reynolds equations of the variable density and viscosity with inertia term which govern the inner and outer film of this hybrid floating-ring bearing are developed. The static and dynamic characteristics coefficients with air rate 0 and 0.1 of this bearing are obtained under different eccentricity and rotational speed. It can be seen from the results that the performance varied obviously due to cavitations under small eccentricity. With the increase of eccentricity or rotational speed, the influences of cavitations weaken.(3) Experiment study of journal-thrust floating ring hybrid bearing Based on above theoretical analysis, the appropriate structure parameters of journal-thrust floating ring bearing are determined and a delicate test rig with independent oil supply is constructed. The pressure distribution, load carrying capability, friction moment, and volume flow rate are measured under different operating conditions. The stiffness and damping coefficients of the bearing are measured using impulse excitation method and compared with theoretical calculation results. So the validity of simulation model is verified. The journal-thrust floating ring hybrid bearing is applied to a certain turbine expansion unit and runs steadily over 38000 rpm.Numerical results and experimental results show that the journal-thrust floating ring bearing with independent oil supply has the advantages of low friction, high stability and easy being controlled. It can bear great axial load compared with conical bearing. Also it is possible to control the stability of high speed bearing on line with independent oil supply structure. Above all, the research fruits in this dissertation have important value to guide the design of floating ring bearing.