Study On Design Theory For Hybrid Bearings Based On Hydraulic Servo Cotrol

With the development of the modern mechanical equipment to large-scale, high speed, high precision, heavy load, etc. liquid lubrication hybrid bearings become more and more widely be used. On the entrance to hydrostatic oil recesses, the throttleers are used as regulate elements, and the throttleers play an important role in the static and dynamic performance of the hybrid bearings. For the bearing performance and the oil film rigidity of the fix throttleer are not very good and the dynamic characteristics of the variable throttleer is poor, The paper creatively puts forward to a kind of hybrid bearings with new type of throttle----based on the hydraulic servo control system. The hybrid bearing changes the way of fixed throttle and variable throttle to throttle by need. The main works and results are as follows:①By analyzing the composition and work principle of the hydraulic servo control system of the hybrid bearings, the Reynolds equation of the mechanical properties of the hybrid bearings were established. Finite difference method is adopted to solve the static performance of the hybrid bearings with different throttle ways and hydraulic servo control, MATLAB software was used to calculate the pressure field of the oil film. Analytical models for the static performance of the hybrid bearings were established to realize the analytic calculation. FLUENT software was applied to analyze and solve the static performance of the hybrid bearings. According to the comparative analysis of three methods above, all the methods can effectively solve the pressure field and static performance of the hybrid bearings, and compared with hydrostatic bearings with four oil recesses, the hybrid bearings with three oil recesses and the ladder hybrid bearings with three oil recesses have higher bearing capacity and oil film rigidity, and the hybrid bearing controlled by the hydraulic servo system has higher bearing capacity and oil film rigidity.②The mathematical model of the temperature field of the hybrid bearing was established, the energy equation was discreted and iterative calculated. Then the temperature field distribution of the several forms hybrid bearings respectively were calculated by numerical calculation and FLUENT. The examples show that the results of two methods are close to each other and agree with the actual operating conditions.③The formation mechanism of oil film rigidity and damping of hybrid bearing were analysed, and eight dynamic characteristics coefficients were put forward and the solving methods of the dynamic characteristics coefficients were discussed ---- finite difference method and drawing analytic method, and the coefficients of the hydrostatic bearings and the hybrid bearings were solved based on different throttle ways and different cavity shapes. The results of the two methods are close to each other, the ladder hybrid bearings with three oil recesses have higher oil film rigidity and damping coefficients and could greatly improve the performance of the bearings. Besides, the mathematical model of spindle axes locus with external disturbance was built, the movement equation of the spindle axes locus was derived when dynamic load was exerted to the spindle. Examples show that the axes will move when external disturbance is exerted to the constant load spindle, axes can come back to the original balance location after the disturbance was eliminated.④In order to deeply study the throttle mechanism of the hydrostatic bearing, the analytic equation of the bearing performance and the oil film rigidity for different throttle methods such as capillary, holes,film feedback, slide valve feedback throttle were established, and the bearing performance and oil film rigidity of the bearings with the throttle methods mentioned above were verified through experiment. According to the lack of study of dynamic performance of the bearings in different throttle ways, the dynamic transfer functions of the hydrostatic bearings throttled by throttle methods mentioned above were derived through the flow balance equations and the linearlization method, and the dynamic characteristics block diagrams were gained. The simulation results show that the dynamic characteristics of the hydrostatic bearing throttled by fixed throttle is better than variable throttle, the dynamic response of the hydrostatic bearings in variable throttle is slowly and the dynamic overshoot is large, which provided the important theory basic for the study of hydraulic servo control throttle method.⑤In order to generally analyze the dynamic characteristics of the hybrid bearings controlled by hydraulic servo system. Firstly, the mathematical models of the dynamic characteristics of the single degree of freedom hydraulic servo-controlled hydrostatic bearings were established. Seconedly, the dynamic characteristics block diagram for the two degrees of freedom hybrid bearing is derived by combinating the linear method with the method of dynamic characteristics of coefficients. lastly, the solution methods of the dynamic characteristics of spindle rotor system for several degrees of freedom cross-coupled such as radial bearings and spindles were quested, a series of simulation analysis were obtained. The simulation results show that the hydrostatic bearing and the hybrid bearing controled by hydraulic servo system have a more satisfactory dynamic characteristics.The study methods and the results of the new type throttle theory in the thesis provide important reference and theoretical value for the new hybrid bearings of the fields such as high speed and high precision, heavy load. It is a quest for the theory innovation of the liquid lubricant bearings, It will play an important role in the design theory of bearing.