EV 고효율 BLDC 모터 코어 성형해석에 관한 연구

Abstract

ABSTRACT

A Study on the Moulding Analysis of High Efficiency BLDC Motor Core to EV

Choi Ji Hyun Advisor : Prof. Cha Yong-hun, Ph.D. Department of Mechanical Engineering, Graduate School of Chosun University

The necessity of EV has expanded and interest in it has been increasing while environmental restrictions has been stricter due to energy and environmental issues such as reinforced standards of discharged gas, depletion of fossil fuel, and global warming. EV is an area which is expected to occupy 10% of the entire automobile markets in 10 years. If EV is mass-produced 10 years later, companies which advance first into the markets will have advantages and dominated the market in advance. EV motor, home electronic and industrial motor manufacturers are rushing into development of 10kw100kw BLDC motor, an EV driving motor. As BLDC motor doesn't have brushes, it has more advantages such as less electric and mechanical noise, high-speed, high reliability, and no need of maintenance in comparison with DC and AC motors. So, although the BLDC motor is expensive, its life and efficiency is superior, there have been a number of studies on it. The BLDC motor uses a permanent magnet. Today, a rare-earth permanent magnet has become a fundamental element as its coverage is very wide. With the development of electronic industries and increase of motor output, DC motors with brush is being replaced by brushless motors and ferrite magnet is being replaced by neodymium sintered magnet as a built-in magnet. A rare-earth permanent magnet id necessarily used for development of high-performance motor needed by better performance and light-weight. BLDC Core mostly uses a ferrite magnet as a permanent magnet, but torque per cubic volume is small. To overcome this disadvantage, a rare-earth magnet is used, but it demands higher cost, 60% of the expenses of motor manufacturing. As there is a limitation in reserves of rare-earth metal worldwide, the crystal size of neodymium sintered magnet was decreased to 5μm through 1.1μm in order to improve coercivity and to curtail the amount used of dysprosium. This study manufactured BLDC motor core as an EV driving motor system and modelled the BLDC core and improved BLDC core using CATIA V5 R18, a three-dimensional design program. Then it analysed transient heat transfer with Ansys Workbench R13, evaluated health of spare parts according to thermal behaviors and achieved an optimal design of the EV motor. A core was molded and sampled through powdered compressed molding to measure density and hardness. Therefore, the results are presented as follows:

1. A less-weight optimal modelling was performed with a use of CATIA and the weight of the core was decreased from 1.15kg to 0.99kg.

2. A transient heat transfer with a use of Ansys Workbench R13 and the changes in temperature distribution of the near the BLDC rotor was larger than the around the BLDC core. In addition, based on these analysis results the transient heat transfer of many 3D models was performed. BLDC core drawing works of less-weight optimal modelling were completed through a evaluated health of spare parts according to thermal behaviors.

3. Five species of molded A-type and B-type were randomly extracted for density test and the two samples were almost same in molding density, 7.2g/cm. It was near to 7.2g/cm7.5g/cm, mean densities of rare-earth permanent magnet, which indicates that powder compacting ability is good.

4. Five species of molded A-type and B-type were randomly extracted for hardness test. A-type was Hv=586.4, B-type was Hv=578.6. It was near to 560650 mean hardness of rare-earth permanent magnet, which indicates that mechanical properties is good.

As indicated in this study, if the developed BLDC core is applied for industrial fields, it is suggested that the production cost will be reduced to more than 5% and motor manufacturing time can be decreased to more than 5%. Through decreasing 2% of motor weight, BLDC motor can be light-weight and production procedures can be simplified. If the entire tendency of thermal behavior of the BLDC core is analysed, the results can be helpful to engineers who design motors in industrial fields, and to high-efficiency motor production according to future distribution of EV.

Key Words : EV, BLDC core, rare-earth Permanent magnet, Powder moulding, Moulding density, optimal modelling, Finite element method, transient heat transfer, Convection