Investigation On Actively Controlled Hydrodynamic Bearing

As the key supporting components for rotor-bearing system, hydrodynamic oil film bearing have much important effect on the stability of rotor-bearing system. With development of rotor-bearing system capacity, high speed, high precision and heavy loading, better performance oil film bearing are needed to meet present rotational equipment requirement. It is a hot research area to improve fluid film bearing performance. In this thesis, a new active controllable oil film bearing is put forward in order to improve the bearing performance. By making use of the giant magnetostrictive actuators (GMA), the location of oil film bearing can be actively controlled and vibration of the rotor-bearing system can also be restrained dynamically. This doctoral project is mainly on the investigation of this newly developed bearing with GMA and the main works have been done are as follows:Based on the design of present GMA used in the position allocation and sonar excitation, etc., the special GMA for oil film bearing is designed. Its structure is simpler. Working condition, needed excitation and amplitude adjustment range for oil film bearing are also considered in the design of this GMA. Besides, static displacement-force model and dynamic mechanical-magnetic coupling model for GMA are established. A simple lever rig is built up to measure static extension of GMA. The static tests have been done under different magnetic field and pre-loading force. The test results are consistent with the GMA static displacement-force model. It is also measured in the test that the GMA can extend several tens of micrometers, which is at the same order of the clearance of oil film bearing. Dynamic tests of GMA have also been done under different excitation frequency of current using the material test rig. The special GMA has good dynamic response when exciting current frequency attains 800Hz, which can almost meet the requirement of restraining vibration of rotor-bearing system with oil film bearing. These primary researches show that the designed GMA is fit to control oil film clearance and also have potential to restrain vibration of rotational machine supported with oil film bearing.Application of GMA in thrust bearing is investigated in order to verify the capacity of GMA to adjust oil film clearance and solve the problem that some pads in thrust bearing have excessive temperature due to inhomogeneous loads on pads. A numerical calculation program is developed to analyze the sensitive relationship among oil film clearance, the maximum temperature and the load on a pad. The results indicate that the load on a pad can be changed and temperature rise can be adjusted by controlling oil film clearance at the supporting place of the pad. Based on this, an active controllable hydrodynamic thrust bearing is put forward by using GMA to adjust oil film clearance. A thrust bearing test rig has been built up and experiments were done to verify the performance of the thrust bearing.The dynamics of Jeffcott rotor system model supported by active controllable journal bearing is analyzed. A numerical calculation program for journal bearing-rotor system is developed considering the mechanical-magnetic coupling model of GMA and excitation from the bearing. The nonlinear oil film force database is used to calculate oil-film forces of hydrodynamic journal bearing in this program. The shaft vibration signal is taken as the feedback signal to control the excitation current on GMA. Runge-kutta integral method is adopted to calculate the journal center loci. Calculated results show that phase difference and control gain have important effect on unbalance vibration and stability of the system. It also shows that appropriate phase difference and control gain can greatly reduce unbalance vibration and whirl vibration. It can improve the stability of the system. Results also imply that there is an optimal phase difference value which can minimize the unbalance vibration for a certain control gain.The developed controllable journal bearing rig with GMA is built up. Its test control system is given. As a preliminary rig to verify the controllable journal bearing performance, one end of the rotor is supported by a controllable hydrodynamic bearing and the other end by a radial ball bearing. Besides, electricity spindle and converter are used to drive the rotor-bearing test rig to meet the test requirement at different speed. Washer spring is used to add GMA with preloading according to the driven requirement of GMA. It also can assure that hydrodynamic bearing sleeve is always contacted with GMA and has two moving degree of freedom.The auto-centering tests of the controllable bearing are done and results are firstly presented. The shaft center can be adjusted to the same position under different loads and speeds by changing GMA's magnetic field. The results show that controllable hydrodynamic bearing has good auto-centering function.Tests on the vibration compression function of the bearing also have been done and introduced. The test results indicate that the unbalance vibration can be restrained obviously. These tests imply that controllable journal hydrodynamic bearing with GMA has very good potential to improve the stability and rotational accuracy of rotor-bearing system.