Modeling, analysis and optimization of magnetic gearbox using FEM finite element method

Master thesis in the field of electricity-power orientation

Abstract

Gearboxes are essential and inseparable components of power transmission systems. These machines convert torque into speed and sometimes speed into torque. The use of mechanical gearboxes in these systems has been common since long ago as an interface between the power generation sector and the power consumption sector. With the expansion of the use of these gearboxes, the problems and disadvantages of these machines have appeared and prompted designers to look for a suitable alternative to the mechanical gearbox. Magnetic gearboxes do not have many of the problems that plagued mechanical gearboxes due to the lack of physical contact between the internal and external rotors. Problems such as the need for lubrication and greasing of wheels, noise, the need for wheel repairs and so on.

In this thesis, we have examined magnetic gearboxes and then by choosing a sample of these gearboxes, we have sought to make changes in the direction of optimization and commercialization of this machine. The changes that have been made in this thesis on the gearbox include investigating the effect of changing the number of pairs of poles and also investigating the effect of the type of magnet used on the torque behavior of the machine. It has been well observed that the increase in pole pairs has increased the torque output from the system. Keywords: magnetic gearbox, increase in pole pairs, volumetric torque density and two-dimensional finite element method Gearboxes are one of the members of the power transmission system, and the role of the gearbox in these systems is to convert speed and torque. The gearbox has the task of changing the torque (power) and the engine speed and making it as desired by the consumer. Initially, mechanical gearboxes were made to perform this task.

Mechanical gearboxes have wide applications in industrial machines and power transmission. Although these gearboxes have many and very important features and advantages and have an undeniable role in the industry, they also have inherent and undeniable disadvantages that have made it inevitable to look for a suitable replacement for these gearboxes. Problems and disadvantages such as friction caused by the contact action mechanism, losses related to energy transfer such as heat, multiple lubrications and revolutions, and noise and auditory noises caused by the physical contact of the input and output shafts. These disadvantages increase the maintenance cost of these gearboxes and reduce the useful life of these gearboxes. Magnetic gearboxes can be a suitable solution for this problem and a good alternative to mechanical gearboxes[1]. Magnetic gearboxes are a new technology that has emerged quickly. The torque transmission mechanism without physical contact is the most important feature and advantage of these gearboxes. In other words, this characteristic and inherent feature separates the mechanical contact of the input and output shaft from each other, and this in turn eliminates the subsequent problems such as the problem of lubrication and cooling. The absence of physical contact also results in a significant reduction in hearing noise, increased reliability and protection against overload at maximum efficiency[2]. Extensive studies have been conducted in relation to the expansion, improvement of performance and efficiency of magnetic gearboxes, and many different models and designs have been presented in line with this goal. But all these designs have something in common. In other words, they all have one common component, as you can see in Figure (1-1), the gearboxes consist of 3 main components: outer rotor, inner rotor and fixed pole parts, which inner and outer rotors are related to the high speed shaft and the low speed shaft, respectively.

The basis of these gearboxes is that with the rotation of the inner rotor, the field caused by the inner poles induces a current in the middle layer and creates a magnetic field in this layer. to be According to the lens law, this field opposes the field that creates it and a field is created in the opposite direction. The poles installed in the outer rotor are coupled with the poles formed in the middle layer and rotate, which is in the opposite direction to the rotation of the inner rotor. Due to the difference in the number of internal and external poles, the rotation speed of the external rotor is lower than that of the internal rotor [3]. Figure (1-2) shows the radial section of a magnetic gearbox.

Figure (1-1) Magnetic gearbox

Figure (1-2) Radial section of magnetic gearbox

The importance of examining magnetic gearboxes

From the past and with the invention of the steam engine, power transmission has always been one of the most important challenges facing designers and engineers. With the invention of gears and then mechanical gearboxes and the use of this new machine in the industry, the problems of using these devices have also appeared at the same time. The problems caused by the physical contact of the gears in these gearboxes.

With the advent of magnetic gearboxes and the lack of physical contact between the rotors, the biggest problem of mechanical gearboxes has been solved. These gearboxes were initially used for small purposes [1] and gradually with the advancement of technologies and the presence of chemical industries to produce better magnets, these gearboxes also entered heavy industries. In recent years, extensive studies have been conducted in the field of magnetic gearbox to increase output torque, increase efficiency and reduce torque fluctuations. A series of these works has been to prepare this new machine for replacement with mechanical gearboxes. Another field of research on magnetic gearboxes is trying to optimize this machine. As mentioned earlier, the main components of this machine are magnetic poles made of permanent magnets. Today, with the increase in the price of these permanent magnets and the exclusivity of the production of these materials for a few countries, the optimal use of these materials is necessary and inevitable.

So the necessity of research on magnetic gearboxes can be summarized in the following:

Increasing production torque

Increasing efficiency

Producing reliable and consistent torque

Optimization

Decreasing the finished price and commercializing the product

Applications of magnetic gearboxes

Chemical industries [1]

Wind power plants[4]

Medical applications[6]

Domestic, medical and humanoid robots[6],[12]

Use in military industries[7]

Use in Pumps and pumps

Usage in cars[8]

Aviation industry[9]

Ship propulsion

Aerospace industry[11]

Advantages of using magnetic gearbox

No physical contact between input and output shaft

No lubrication problem

No need Cooling

Low audible noises

Increased reliability

Protection against overload at maximum efficiency

Disadvantages of these gearboxes

Tossional stiffness[1] very low compared to mechanical gearboxes[5]

Hysteresis losses in the cores of both inner and outer rotors (gearbox bodies) and intermediate layer ferromagnetic parts[9]

Loss caused by eddy currents[2] induced in permanent rotor magnets and ferromagnetic parts of the gearbox

Aim, method and steps of the research

The purpose of this project is to investigate and simulate the magnetic gearbox using finite element analysis (FEM). In short, the goals and steps of this research can be stated as follows:

Study of available resources and information collection

Examination of different magnetic gearbox structures

Choosing the appropriate magnetic gearbox to carry out simulation steps

Two-dimensional simulation in finite element software

Validation of the simulated gearbox

Making suggested changes in the thesis and checking the results

Efforts to optimize the selective gearbox

The feature of this thesis is to present a new structure for gearbox designs in order to optimize the components of the gearbox, and to use the finite element method to check the proposed changes in the magnetic gearbox.

The structure of the thesis

In the second chapter, the relationship governing the magnetic gearbox including force, flux, torque and energy is discussed.

In the chapter Thirdly, examples of magnetic gearboxes are given along with the torque curves of each of these gearboxes.

In the fourth chapter, preliminary simulations have been performed to validate the model and the selected gearbox, then by making the proposed changes, we have done a comprehensive review on the behavior of the internal and external rotor torques.

In the fifth chapter, conclusions and suggestions are presented.