Magnetics Business & Technology - Summer 2012 - (Page 8)

FEATURE ARTICLE can be placed spatially remote from the torque originating pole pulse magnetized rare earths often demand a closed design chain pattern but still on the same rotor. There exist magnets with a si- starting with the material, taking into account the magnetization nusoidal working field to keep cogging torque and noise at a low process and ending up with the application itself. level in combination with trapezoidal commutation traces to supTo start with the material for pole oriented Ferrites, the orienply a commutation signal with small angular variations. Partially, tation and magnetization of the melt has to be known for each magnets even with two sensor traces for commutation and speed material compound quantitatively. This means, remanent polarcontrol in combination with the working ization and recoil permeability have to be field have been developed yet [1]. studied experimentally as a function of Magnets for water pump and fan systhe orienting field strength and melt temtems mainly consist of anisotropic Ferrites perature. Having these data, the molding whereas fuel pumps or other electric actuaand magnetizing process can be analyzed tors in automotive applications often deby magnetostatic FEM analysis. For each mand higher flux densities. Such magnets single finite element in the cavity of the are commonly made of isotropic NdFeB. mold, remanent polarization and recoil They usually have less complicated geompermeability are calculated from the local etries and always need an external pulse field strength under the assumption that magnetizing process. When even higher the magnetization vector is always paralflux densities are demanded, anisotropic lel to the magnetizing field. Substituting in SmFeN or anisotropic NdFeB can be used, Injection molded magnets for electrical machines each single finite element the virgin curve of the material by these new parameters which has made a leap forward in regard made of Ferrites or NdFeB. will result in a spatial distribution to temperature and external field staof magnetization and permeability. bility during the last years. Removing all other parts of the inNot to be separated from electrijection molding tool within the next cal machine applications are sensor step, provides a data base for the magnets, as many rotating systems manufactured pole oriented magnet. have an extra magnet placed on their The magnet’s application can then shaft. For commutation purposes, be assembled around that data base the background often is a lack of for doing the applications analysis space for a sensor close to the main itself, now with an adequate magnet or stray field of the rotor or that model [2]. the main field is too strong for the The average deviation between sensor. Magnets for commutation, calculations and measurements, (respeed detection or detection of anferring to the peak values of single gular position are made of Ferrites field components of the magnet) is whenever it is possible. The techaround 5 percent with the described nical principles of such sensor systems range from simply switching a Calculated distribution of the remanent polarization (T) of a pole method. Deviations may originate digital Hall sensor, the use of AMR oriented Ferrite magnet with three magnetic traces [1]. from materials batch variations or sensors for analog position signals varying injection molding parameup to the use of hall sensor arrays. ters. But the main impact that origiFor digital Hall sensor systems, (e.g. in automotive actuators for nates deviations is that flow and solidification effects are not beseat positioning or window lifting), fairly high spatial tolerances ing taken into account. in regard to pole positions are permitted. In contradiction to this, The treatment of magnetization of rare earth magnets differs motors for electronic power steering systems (EPS) demand the a bit from that of pole oriented magnets. For the materials, we highest quality in regard to noise and vibration free operation. need measured data of polarization in the first and second quadFor commutation signals this means that they have to be accurate rant of the hysteresis at room temperature. On the other hand a within a few 0.1°. coupled time transient analysis of the pulse coil with its feeding electrical circuit has to be performed. To calculate the resulting distribution of magnetization and permeability, a simple and Magnetic Design The ability to manufacture tailored field shapes, to combine commonly spread method is to use the time of the pulse maximultipurpose magnetic traces or to produce spatial field distribu- mum and assume that it determines the grade and orientation tions of highest accuracy are reasons for the economic success of of polarization by its current magnetic field strength [3]. Also, injection molded magnets. On the other hand, the design of the the approach of a magnetization parallel to the magnetic field related magnets is much more challenging when it is compared is commonly used. As time of the pulse maximum one can eito other kinds of magnets. Both pole oriented Ferrites as well as Article continues on pAge 20 8 Magnetics Business & Technology • Summer 2012 www.MagneticsMagazine.com http://www.MagneticsMagazine.com

Table of Contents for the Digital Edition of Magnetics Business & Technology - Summer 2012

Magnetics Business & Technology - Summer 2012
Editor's Choice
Injection Molded Magnets for Electrical Machines
The Process of Developing and Testing a New Transformer
Rare Earths & Corporate Social Responsibility
Research & Development
RE-use, RE-duce, RE-cycle, RE-place
Magnets • Materials • Measurement
Application • Component Developments
Industry News
Rare Earth Crisis Dissected: Securing the Future
Marketplace
Advertising Index
Spontaneous Thoughts: The End of Axial Pressing?

Magnetics Business & Technology - Summer 2012