33pop Vitek Hajek 2 New

8/13/2019 33pop Vitek Hajek 2 New

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automotive, alternator, claw-pole

design, finite element method, measurement

Ondej VTEK*, Vtzslav HJEK*

DESIGN AND ANALYSIS OF AN AUTOMOTIVE ALTERNATOR

The article deals with design of the heavy-duty claw-pole automotive alternator. This type of al-

ternator should operate under unfriendly condition, e.g. in agricultural applications. Described devel-opment is supported by Ministry of Industry and Trade in frame of the project FI-IM4/194. Requiredparameters were evaluated and analytic design of magnetic circuit was performed in cooperation withMagneton a.s. Krom company. A laboratory sample was also manufactured in this stage of theproject solution. The 3D finite element method model was created simultaneously using the ANSYSprogram. The model was used to verify the magnetic flux density distribution and it will be used foroptimization in following stage of the project.

1. INTRODUCTION

The alternator is a common equipment of the all today automobiles. Their are usednot only on small cars but also in agricultural engineering, structural engineering,

stationary generators, etc. They are produced in a variety of power and voltage levelsand generally are always examined from many points of view, such as reliability, effi-ciency, dimensions, weight and costs. Special attention is paid to whole service life ofalternator.

The method of analytic calculation of claw-pole alternator is based on common de-sign method of synchronous machines with salient poles. However, magnetic circuitgeometry is more complex due to claw-pole arrangement (Fig. 1, left) and the leakageflux calculation becomes especially complicated. There is not unique solution of alterna-tor design and it is necessary to estimate some parameters entering to calculation. Thisestimation was based on experience with previous verified alternator constructions.Design procedure includes several steps shown in block diagram in Fig.1, right.

Designed alternator should attain following nominal parameters: voltage 14 V, cur-rent 42 A, speed 6000 rpm, min. speed for accumulator charging initiation 1300 rpm.

__________*Brno University of Technology, UVEE, Technick 8, 612 00 BRNO, [email protected]

Prace Naukowe Instytutu Maszyn, Napdw i Pomiarw ElektrycznychNr 62 Politechniki Wrocawskiej Nr 62

Studia i Materiay Nr 28 2008


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Fig. 1. Sketch of magnetic circuit of the alternator (left) and design procedure block diagram (right)

2. FEM MODEL OF THE ALTERNATOR

The alternator design procedure described above should be considered as the initialsolution only and therefore verification and optimization of magnetic circuit is advis-able. The magnetic flux flows throw the claw-poles and rotor yoke in z-direction (direc-

tion of alternator axis, Fig. 1, left) therefore the 2D FEM analysis is not sufficient andthe magnetic saturation of each part of the magnetic circuit is necessary to verify by the3D model. Cutaway view of the automotive alternator is shown in Fig. 2. The magneticcircuit geometric structure was built using Autodesk Inventor and it was imported toANSYS environment (Fig. 2, right).

The mesh generation was the most time consumption part of the model creation.Mesh layout and quality has significant influence to calculation accuracy. Unfortu-nately, the number of finite elements is limited by current computing power. Finite ele-ments representation of the alternator magnetic circuit is shown in Fig. 3. There arethree elements in radial direction between stator and rotor (in the air gap). The totalnumber of elements is approximately 1.2 million.


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Fig. 2. Cutaway view of designed alternator (left) and its magnetic circuit (right)

Fig. 3. Finite element mesh of the alternator model

Electromagnetic field of the alternator was solved using the general magnetic scalarpotential strategy. The stationary field was excited by rotor coil. Calculation was per-formed for various values of excitation current. The obtained results correspond to 1 Aof excitation current and the total magnetomotive force of 435 Ampere-turns. This lower

value was chosen because the nominal excitation current 4.3 A causes oversaturation ofmagnetic circuit under no-load condition and then the critical parts of magnetic circuitsare not clear visible.


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Fig. 4. Magnetic flux density distribution: in the whole magnetic circuit (left) and part of the stator (right)

The magnetic flux density distribution in the alternator core is presented in Fig. 4.The uniform level of magnetic saturation in the whole magnetic circuit is usually re-quired, but it is seen that the magnetic flux density in the claw-poles roots is signifi-cantly higher in comparison with other magnetic circuit areas and components (Fig. 5).Improvement of claw-pole design is therefore advisable. On the other side, increasingthe cross-section area of the claw-pole root causes reduction of exciting winding space.Optimization will be consequently performed in the next stage of project solution. Themagnetic flux density in the air gap is shown in Fig. 5 (right). Visible teeth and claw-poles contact areas confirm the suitable mesh layout.

Fig. 5. Magnetic flux density distribution in the rotor (left) and air gap (right)


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3. CONCLUSION

The analytic design method of the claw-pole alternator was developed in cooperationwith Magneton a.s. Krom company. The automotive alternator of nominal voltage14 V and current 42 A was calculated and manufactured. The 3D FEM model was cre-ated and some results were discussed in previous chapter. The FEM model was used toverify the analytic design results and to check the saturation level of the alternator mag-netic circuit. The claw-poles roots tend to be oversaturated and optimization of theseareas is therefore advisable. Unfortunately, the measurements results are not availableup to now and may not be compared with theoretical results. Modification of the alterna-tor magnetic circuit based on prospective optimization results will be included in designof an alternator prototype which will be introduced in following stage of the projectsolution.

REFERENCES

[1] DDEK, L., DDKOV, J., Elektromagnetismus, VUTIUM Publishing, Brno, 1998, 229 pages,ISBN 80-214-1106-6.

[2] PETROV, G.N.,Elektrick stroje 2, Praha: Academia, 1982, 732 pages, ISBN 21-055-82.[3] CIGNEK, L., Stavba elektrickch stroj, SNTL PRAHA, 1958.[4] HJEK, V., Vpoet rozptylovch vodivost drpkovho rotoru automobilovho alterntoru, TES

1987.[5] HSEK, R., Vpoet drpkovho tfzovho alterntoru, DP, Ostrava 1997.[6] ANSYS Inc.,ANSYS Release 11.0 Documentation , 2007.

This paper has been supported by FI-IM4/194, GA102/06/1320 and MSM0021630516.

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