Automotive Electrical and Electronic Systems Classroom Manual Fifth Edition Update by John F. Kershaw
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Automotive Electrical and Electronic Systems Classroom Manual Fifth Edition Update by John F. Kershaw

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02.10.2022 Views

Charging System Operation 153Figure 8-12. Exploded view of the parts of the completerotor assembly. (DaimlerChrysler Corporation)Figure 8-11. The magnetic field of the rotor is createdby current through the rotor winding. (Reprinted bypermission of Robert Bosch GmbH)residual magnetism is not strong enough to induceany voltage across the conductors. Current producesthe magnetic field of the rotor through therotor winding, which is a coil of wire betweenthe two pole pieces (Figure 8-11). This is also calledthe excitation winding, or the field winding.Varying the amount of field current through therotor winding varies the strength of the magneticfield, which affects the voltage output of the ACgenerator. A soft iron core is mounted inside therotor-winding (Figure 8-12). One pole piece isattached to either end of the core; when field currenttravels through the winding, the iron core is magnetized,and the pole pieces take on the magneticpolarity of the end of the core to which they areattached. Current is supplied to the winding throughsliprings and brushes.The combination of a soft iron rotor core andsteel rotor halves provides better localization andpermeability of the magnetic field. The rotor polepieces, winding, core, and sliprings are pressedonto a shaft. The ends of this shaft are supported bybearings in the AC generator housing. Outside thehousing, a drive pulley is attached to the shaft, asshown in Figure 8-13. A belt, driven by the enginecrankshaft-pulley, passes around the drive pulleyto turn the AC generator shaft and rotor assembly.StatorThe three AC generator conductors are woundonto a cylindrical, laminated core. The laminationprevents unwanted eddy currents from formingin the core. The assembled piece is called aFigure 8-13. AC generator (alternator) and drive pulley.(DaimlerChrysler Corporation)stator (Figure 8-14). The word stator comesfrom the word “stationary” because it does notrotate, as does the commutator conductor of a DCgenerator. Each conductor, called a stator winding,is formed into a number of coils spacedevenly around the core. There are as many coilconductors as there are pairs of N-S rotor poles.Figure 8-15 shows an incomplete stator with onlyone of its conductors installed: There are sevencoils in the conductor, so the matching rotorwould have seven pairs of N-S poles, for a totalof fourteen poles. There are two ways to connectthe three-stator windings.HousingThe AC generator housing, or frame, is made oftwo pieces of cast aluminum (Figure 8-16).Aluminum is lightweight and non-magnetic andconducts heat well. One housing piece holds abearing for the end of the rotor shaft where the

Figure 8-14.An AC generator (alternator) stator.Figure 8-15. A stator with only one conductor installed.(Delphi Automotive Systems)Figure 8-16. AC generator (alternator) housingencloses the rotor and stator.154

Figure 8-14.

An AC generator (alternator) stator.

Figure 8-15. A stator with only one conductor installed.

(Delphi Automotive Systems)

Figure 8-16. AC generator (alternator) housing

encloses the rotor and stator.

154

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