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Küçük güçlü daimi mıknatıslı doğru akım silecek motoru tasarımı ve gerçekleştirilmesi

Başlık çevirisi mevcut değil.

  1. Tez No: 75438
  2. Yazar: SERKAN ODABAŞI
  3. Danışmanlar: PROF. DR. NURDAN GÜZELBEYOĞLU
  4. Tez Türü: Yüksek Lisans
  5. Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1998
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Elektrik Mühendisliği Ana Bilim Dalı
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 98

Özet

Bu çalışmada, bir küçük güçlü daimi mıknatıslı doğru akım motorunun genel boyutlandırma yöntemleri tasarım kriterleri de dikkate alınarak çıkarılmış ve bir silecek motoruna uygulanmıştır. Çalışmanın ilk bölümünde daimi mıknatıslar incelenmiş, mıknatısların magnetik özelliklerine, çeşitlerine ve tarihi gelişimine yer verilmiştir. Diğer bölümlerde, daimi mıknatıslı doğru akım motorunun temel yapısı, motor ana yapısı, motor ana boyutları ve temel eşitlikler anlatılarak tasarım kriterleri detaylı olarak ortaya konulmuştur. Bu kriterler esas alınarak otomotiv sektöründe kullanılmak üzere bir daimi mıknatıslı doğru akım silecek motoru tasarımı yapılmıştır. Tasarım büyüklükleri, imalatı yapılan silecek motorunun sonuçlan ile karşılaştırılmıştır. Tasarım esnasında motorun mekanik zorlanmaları ve imalat esnasındaki montaj kolaylıkları da dikkate alınmıştır.

Özet (Çeviri)

The basic aim of this work is to present design procedures for a small permanent magnet direct current commutator (PMDC) motor and apply it to a windscreen wiper motor. Electric machine design is a multi-disciplinary subject. It involves not only electromagnetic design but also selection of engineering materials, component specifications and production techniques. The complete study was carried out from research to implementation of the design into batch production for the industrial use. The design stage was scoped and limited to only small machines. In the second chapter the permanent magnets which are used in place of electromagnets in some electric machines to provide the excitation field are analysed. Classes of magnets and their characteristics are given and compared. The choice of a magnet material is mainly governed by the application requirements, which obviously include economic factors. General concepts of small PMDC commutator motor and design procedures are introduced in the third chapter. Main construction of the machine, size determining factors and magnet design are also defined. In the fourth chapter, according to design procedure a PMDC motor design problem for a windscreen wiper motor in automotive industry is demonstrated. The existing constraints were such as available laminations, standard frames and brushes. At every stage the factors affecting the design decision are discussed. The important points of mechanical parts which should be taken into account is the construction of wiper motor are explained fully. In the final chapter calculated and measured results are compared. Around the rated operation area negligible deviation was found where as the deviation at the no load and over load condition was to a great extend. The first permanent magnet excitation systems was applied to electrical machines as early as the nineteenth century. After the development of material technology especially the invention of Alnico in 1932, the use of magnet excitation increased drastically.The use of permanent magnets in construction of electrical machines has the following benefits; 1) No electrical energy is absorbed by the field excitation system and thus there are no excitation losses which means substantial increase in the efficiency. 2) Higher torque or output power per volume than when using electromagnetic excitation. 3) Better dynamic performance than motors with electromagnetic excitation (higher magnetic flux density in the airgap). 4) Simplification of construction and maintenance. 5) Reduction of costs for some type of machines. Cheap and simple d.c. commutator motors with barium or strontium ferrite permanent magnets mounted on the stator will probably still be used in the future in automobiles as heater motors, wiper motors, window lift motors etc. Magnet Dimensions The dimensions of a PM employed in an electromechanical device to furnish a specified value of air gap flux density may be estimated by making the following assumptions. The permeability of the iron parts in the rotor and stator yoke is assumed infinite. The effect of magnetic saturation of the iron parts can be taken into consideration by iteratively modifying the gap length.. The PM are assumed to be having a linear demagnetisation characteristic.. End effects are ignored.. All the magnetic flux lines produced by the magnet, less the leakage flux, cross the air - gap leakage is taken into account by a factor, K« Therefore; Bm. An, = Kg. Bg. Ag Where Bm and Am, Bg and Ag are the flux density and area of the magnet an air - gap respectively.. The magnetomotive force required to pass the flux lines in the soft iron parts of the magnetic circuit is taken into account by a factor Kr. Therefore; iim-Cm - JS.r.xlg.Gg XIVWhere Hg and £g are the air gap magnetic field and length, (HmQ magnet's magnetomotor force. According to sizing procedure which was introduced in chapter 3, the required magnetic flux density of magnet is estimated and correspondingly magnetic field intensity of magnet can be determined from the demagnetisation curve of the magnet material. (Bm, BU,) is the operating point of the magnet. Motor Configuration and Design Parameters The most common field excitation system in use today PMDC motor shown in fig 3.10 In this system, because the field flux is essentially constant the ratio between armature current and torque is fixed: Md = kM.Ia and the relationship between back - EMF voltage and shaft angular velocity is E = kfi.© These two equations form the fundamental basis for dc motor operation. As can be seen, this system allows for a very simple linear relationship between armature current, torque and velocity. The electrical expression for such a motor is as follows di U = kE.a)+L- +Ra.Ia dt Where U is the applied voltage and Ra is the armature resistance. Armature Designs The rotor and stator configuration of an iron-core motor is shown fig 3.2. The magnet structure in this example design is a segment of ferrite magnet material. The magnetic flux passes through rotor cross section. The rotor contains slots, into which wire is placed. The magnetic flux, therefore, must pass through a small air gap and over a low reluctance path to reach the opposite pole. The iron-core rotor structure has a high thermal capacity and can take overloads for extended periods of time without damage. Windscreen Wiper Motor Mechanical Structure The Windscreen wiper motor which is designed according to the procedure is a geared motor. xvGeared motor has an armature shaft with rolled-on or cut worm and worm wheel. The rolled worm type armature shaft has some advantages such as hardened surface and better surface roughness. That's why the rolled worm type armature preferred. The worm wheel is made of plastic. The plastic material is so important that it must withstand the torque on the over load without damage. The grease - filled gearbox is a alu-zinc die - casting. The motor has a sintered metal bush bearing on the motor side, and the gear side a ball bearing mounted in the bottom of the gearbox. The ball bearing assembly is done by on a special fixing segman to obtain a rigid shaft construction. In addition to this fixing and adjusting screw was also used for armature shaft end. Wiper Motor Rated Characteristics U = 13.5 V. nshaft = 40d/d. Ra = 0.472 Q P^ =40 W. AUb = 0.7 V. kE = 4.95 x 10“3 V/d/d la = 4.9 A. T] =0.62 kM = 47.31 x 10”3Nm/A. Results and Application The differences between the calculated and measured results for the performance of motor under continuous operation, especially at the points away from the rated load section, namely no load and over load moment points, are explained as follows; 1) The calculations are made assuming a constant loss moment at maximum load point, which in return showed a big variation from no load and over load values. 2) The demagnetisation curve of the permanent magnet segment used is the average of the curves given by the manufacturer, which may differ slightly from magnet to magnet. 3) The operating point on the both demagnetisation curve is certainly affected by the armature reaction which has not been taken into account in calculations. Application The linkage system, including arms and blades, is a complete unit with the motor. The motor performance and the design factors of other parts of the linkage system should be taken into consideration in a way that they affect each other mutually. Throughout the life test and short circuit test we found out the poor design of the arms and linkage have resulted in reduced life time and easy breakdown for the motor. XVITo overcome this problem, usually a motor with excess capability is being used in Turkish market, which is actually on unnecessary cost increase. To protect the wiper motors against misuse, it was decided to incorporate a protective current sensitive device, which has resetting capability as well. All the test run and found that the protection element did the job very properly. As a result this particular component should be used on every single motor. But we should never forget the initial source of the reduced life. In design stage a cost down from the point of labor was also taken into account and as a result 25 percent decrease because of size and single gear wheel adaptation and 50% decrease in assembly time was obtained. XVII

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