| The permanent magnet eddy-current coupling is a kind of mechanical power transmission device based on the permanent magnet driving technology.The eddycurrent is generated on the conductor plate by the non-rigid contact relative movement between the conductor plate and the permanent magnet disk.The electromagnetic torque generated by the interaction between the eddy-current and the air gap magnetic field realizes the electromechanical energy conversion of the soft coupling between the source and the load.Permanent magnet eddy-current coupling has the characteristics of simple structure,easy maintenance,energy saving and explosion protection,low demand,smooth operation,no contact connection,no environmental pollution,small vibration range and long service life.In coal mine production,permanent magnet eddy-current coupling is very suitable for applications requiring explosion-proof and harsh environmental conditions,so it has a good development prospects.At present,core technology of permanent magnet eddy-current coupling is still in the technical block state.As the relevant domestic research in the initial stage,the coupling products used in coal mine with independent intellectual property rights are rarely produced.Therefore,the research on the key technology of permanent magnet eddy-current coupling not only has important academic value,but also has important significance to improve the domestic permanent magnet drive technology and promote the safe and efficient production of coal industry in China.In this background,the analytical model,electromagnetic field,the mechanical characteristics and temperature field of the permanent magnet eddy-current coupling are studied by theoretical analysis,finite element method and experimental test combined with the current research situation at home and abroad.The research work is embodied in the following aspects.Study on the Method of Establishing Permanent Magnet Eddy-current Coupling Model.There are some shortcomings and limitations of the analytical model of permanent magnet eddy-current coupling based on the traditional two-dimensional linear layer theory.In order to establish an analytical model which can accurately describe the relationship between structural parameters and performance indicators,two analytical models are proposed based on methods of equivalent magnetic and energy and methods of separate variables respectively.Firstly,the expression of the relevant electromagnetic field quantity such as air gap magnetic flux is obtained by the equivalent magnetic circuit method in the case of permanent magnet equivalent magnetomotive force.Secondly,the eddy current generated by the variation of magnetic flux is calculated and analyzed by Faraday's law of electromagnetic induction.Finally,the analytical model of the coupling is derived from the relationship between the transmission torque and the eddy current loss established by the energy method.The second method is based on the reasonable physical model of the coupling,and the electromagnetic field problem of the coupling at a given boundary is from the Maxwell differential equation group,which is described by the introduced magnetic vector function.In this way,the electromagnetic field problem of the coupling is transformed into the boundary value problem for solving the Poisson equation or the Laplace equation.The partial differential equation is divided into several ordinary differential equations by using the separation variable method.The definite constant is determined by the given boundary condition,and the analytical solution of the magnetic vector function is obtained.On the basis of these,considering the influence of edge effect on the transformation of 2D model to 3D model,the transfer torque analytical model with Russell coefficient correction is established.In order to verify the correctness of the two analytical models established above and the need for subsequent research,the 40 KW permanent magnet eddy-current coupling drive test bed consisting of mechanical transmission system,detection system and control system is built.After the specific program developed,the simulation of the actual working conditions can be achieved.The comparison between the test data and the analytical model is used to complete the verification of the correctness of the theoretical analysis model,and the error size and the cause are analyzed.The results show that the simplification and assumption of the two modeling methods are reasonable,and the calculated theoretical values of the analytical model can well approximate the test curve.The analytical expression can clearly reflect the relationship between the structural parameters and the performance indexes of the permanent magnet eddy-current coupling,and the model establishment method can be proved as a powerful tool for theory research and initial design.Electromagnetic Field Finite Element Analysis of Permanent Magnet Eddy-current Coupling.In order to understand the distribution and variation of the electromagnetic field of permanent magnet eddy-current coupling,it can be analyzed by the finite element method.The finite element method and Ansoft Maxwell finite element software are used to furtherly study the numerical simulation of static electromagnetic field of permanent magnet eddy-current coupling.Considering the nonlinearity of the back yoke,a three-dimensional finite element model of 40 kW permanent magnet eddy-current coupling is established based on the actual structure size and material properties.In the 3D static electromagnetic field,the magnetic flux path of the coupling proves the correctness of the analysis of the main magnetic circuit and the leakage magnetic circuit in the equivalent magnetic circuit analytical model.The magnetic flux density distribution of the air gap magnetic field under the sector permanent magnet is discussed.The distribution of the axial component in the circumferential and radial directions at the surface of the copper plate is also analyzed.It is pointed out that the magnetic flux density at the air gap in the static field is periodically distributed in the circumferential direction.The circumferential component obtains the maximum value at the center of the magnet projection,obtains the minimum value at the interval of two magnets hm/2,the period is 2?/p,and the radial component obtains the maximum value at the center of the magnet projection.The reluctance of the air gap layer is larger,and the magnetic flux density at the copper plate is negatively correlated with the thickness of the air gap.In the 3D transient electromagnetic field,the variation of the air gap flux density is simulated and the whole distribution of the induced eddy-current of the copper plate is obtained.The relationship between the value of the eddy current and the relative speed is discussed.The distribution of eddy-current is found along the circumferential and radial distributions.The simulation results show that the number of eddy-current regions is equal to the number of permanent magnets,and the eddy-currents in the adjacent regions are opposite.The current value of the central area is small,but the current reaches the maximum surrounded by the outer edge of the two adjacent current pool stack.In addition to its own rotational motion,the eddy-current will follow the direction of rotation of the active disk in the same direction.The eddy-current is positively correlated with the slip.By comparing the distribution of magnetic flux density and eddy-current,it is found that the outer circumference of the outer circumference of the eddy-current has the most significant change in the magnetic flux density,and the central region with smaller eddy-current is the position where the magnetic flux density does not change.This phenomenon is consistent with the law described by Faraday's law of electromagnetic induction.Study on Mechanical Characteristics and Influencing Factors of Permanent Magnet Eddy-current Coupling.The relationship between the output speed and the transmission torque is characterized by the mechanical properties measured by the experiment.Based on the sufficient and necessary conditions for the stable operation of the transmission system,the matching of the coupling with the constant torque load,the linear load and the parabolic load is discussed respectively.The stable working range of the three types of loads is determined.The thickness of the copper plate,the length of the air gap,the number of magnetic poles,the thickness of the permanent magnet,the radial length and the conductivity are taken as the influencing factors by using the method of FEA and experimental study to analyze the influence of the mechanical properties such as eddy current loss,maximum transmission torque and speed range(constant torque load)on the coupling.The results of the influencing factors show that the number of poles(p?12),the conductivity,the thickness of the permanent magnet and the radial length are positively correlated with the transmission torque.But the number of poles(p?12),copper plate thickness and air gap length are inversely proportional.In addition to the constant torque load matching,the increase in the number of magnetic pole will reduce the stable operation of the adjustable speed range,the reduce of the conductivity will increase the adjustable speed range.Based on the conclusion that the air gap length significantly affects the mechanical properties of the coupling,the principle of changing the air gap to realize speed control function is described.A set of adjusting mechanism for controlling the air gap during the operation of the coupling is designed by the servo motor to control the worm gear,the screw and the sleeve to transmit the axial slip and the gear rack to synchronize the adjustment.In order to solve the problem that the low pump operation efficiency caused by the traditional valve control method and the wasted power,the feasibility of the application of the air gap adjustable permanent magnet eddy-current coupling in the pump load speed control is analyzed to achieve the energy saving effect and speed control function.Study on Permanent Magnet Eddy-current Coupling with A Slotted Conductor Used in Coal Mine.It is stated that the eddy-current of the radial path in the slotless conductor plays a major role in torque transmission.In order to furtherly improve the transmission performance,a new permanent magnet eddy-current coupling's structure is proposed,in which the conductor plate is slotted and the yoke is filled in the slot.The analytical model of the coupling with a slotted conductor is analyzed and calculated by using the separation variable method to obtain the analytical expression of the magnetic field,eddy-current and transmission torque.The results of the analytical expression are compared with the finite element simulation results,which proves that the change rule is consistent,the coincidence degree is high and the error is small.The validity of the analytical model is verified.Compared with the analysis results without slot,the magnetic induction intensity,the eddy-current distribution and the mechanical properties of the air gap magnetic field are discussed.The results show that the magnetic induction of the surface position of the yoke is obviously increased,and the magnetic field between the air gap and the copper spoke is strengthened.After the conductor plate is slotted,the eddy-current flows more concentrated on the radial path,and the eddy-current in the central region is reduced.This new structure of the coupling obtains the greater transmission torque than the structure without slot.The influence of the slot Q on the maximum transmission torque and the optimal value of the ratio of the spoke arc to the slot pitch are furtherly analyzed.The simulation results show that the increase in the number of slots in the total area of the spoke will cause the coupling to transmit a greater torque.In addition,when the output speed is constant and the ratio of spoke arc to slot pitch is ? = 0.77,the transmission torque reaches the maximum value.When ? <0.77,the transmission torque increases monotonically with ?,and the transmission torque decreases with it when ? > 0.77.Study on Temperature Field of Permanent Magnet Eddy-current Coupling.The eddy-current loss that must occur during the operation of the coupling can cause the temperature to rise,which can lead to the decrease of the magnetization of the permanent magnet,the decrease of the mechanical strength of the material,the thermal deformation of the structural member and the increase of the manufacturing cost.Based on the theory of heat transfer,the thermal energy transfer between the components of the permanent magnet eddy-current coupling is described in the case of neglecting the heat radiation.The physical model of the temperature field of coupling is established in ANSYS Workbench finite element analysis software,and the boundary conditions are determined.According to the definition of heat flux,the eddy-current loss of copper plate is used as heat source,and the effective thermal conductivity is introduced to describe the heat exchange capacity of air in air gap.The convective heat transfer characteristics of the rotating disc are measured by the method of naphthalene sublimation and the comparison of heat and mass.The surface heat dissipation coefficient of the inner and outer circumferences of the rotating disc is determined by fluid similarity theory.The temperature distribution of the coupling under normal operating conditions is analyzed.It is pointed out that the temperature distribution of the permanent magnet plate is not uniform,the temperature of the center of the magnet is higher and the temperature of the outer edge diameter of the disk is lower.The influence of the air gap,the thickness of the copper plate and the thickness of the permanent magnet on the temperature rise of the permanent magnet under the finite element model is discussed.The error results between the measured data and the experimental data are analyzed.The simulation results are corrected by the coefficient of temperature coefficient of Br.The corrected simulation results are in good agreement with the measured data.The research shows that the temperature of the coupling in the overload condition is very fast.After about 45 s NdFe B permanent magnet's temperature reaches Curie temperature,the temperature of the back yoke reaches 96.4? at 60 s.The design of the permanent magnet eddy-current coupling needs to take into account the adverse effects of the temperature rise factor,while ensuring that the performance requirements are met. |
PDF Full Text Request