CLAW-POLE ALTERNATOR AND AUTOMOTIVE ELECTRICAL SYSTEM

Size: px

Start display at page:

Download "CLAW-POLE ALTERNATOR AND AUTOMOTIVE ELECTRICAL SYSTEM"

Aron Allen
5 years ago
Views:

1 Chapter- 2 CLAW-POLE ALTERNATOR AND AUTOMOTIVE ELECTRICAL SYSTEM 2.1 Introduction The claw pole alternator is a special kind of synchronous machine. This chapter discusses the constructional features of the alternator which necessitate a 30 analysis. The types of load in automotive systems are also detailed with its power requirement. Even though this type of alternators is extensively made use of as generators in automobiles, the claw pole construction ts used in non conventional systems I also. 2.2 Constructional Details Stator The stator core ts laminated and consists of semi enclosed slots in which the three phase stator winding is placed. Fig. 2.1 shows the stator. The stator is clamped between two end brackets, the slip ring-end bracket and driveend bracket. 20

Fig. 2. 1 Stator 2.2.2 Rotor The claw pole rotor consists of rotor core and claw-pole wheels fitted to the rotor shaft. The rotor winding wound axially over a bobbin on the rotor core.

2 Fig Stator Rotor The claw pole rotor consists of rotor core and claw-pole wheels fitted to the rotor shaft. The rotor winding wound axially over a bobbin on the rotor core. The claw envelops the rotor core and the excitation winding. The peculiarity of this machine is that the field winding is composed of only one excitation coil enclosed by two pole wheels of claw poles. A claw pole rotor with 12 poles is shown in Fig fif. ".> '1;. ~ '~'...\.-..'7. ~., Fig. 2.2 Winding & claw assembly of a 12 pole rotor 21

Fig. 2.3 shows one pole wheel of the claw pole alternator. In fact the name of this alternator is derived from the rotor shape. Fig. 2.3 One pole wheel Each pole wheel will be of opposite polarity.

3 Fig. 2.3 shows one pole wheel of the claw pole alternator. In fact the name of this alternator is derived from the rotor shape. Fig. 2.3 One pole wheel Each pole wheel will be of opposite polarity. The polarity depends on the direction of exciting current in the rotor winding. So the claw shaped fingers of each half, mesh in the rorm of alternate north and south poles. The ratio of the length to diameter is selected to guarantee a maximum power lutput. As a result an alternator of large diameter and short length is obtained. This shape also allows heat dissipation. The magnetic flux produced due to excitation passes :hrough the pole core, left wheel and its fingers, then across :he air gap to its stationary stator core and winding and finally 22

4 completes the path by returning to the pole core through the right pole wheel. Each pole pair forms a separate flux path. All the twelve paths are in parallel and connected across a single mmf source. 2.3 Electrical Load in Vehicles Fig. 2.4 depicts a typical flow diagram representation of the power requirement of the vehicle loads. The electrical loads in an automobile come under one of the following categories. Permanent loads (ignition, fuel injection etc.) Long time loads (Lighting, entertainment devices). Short term loads (Turning signals, horn, stop lamp etc.) Seasonal loads (Air conditioner in summer, seat heater in winter etc.) The power requirement of the entire categories mentioned above is currently projected [ 1] as in Table 2. l, which total to about 2. 2 kw in summer. 23

5 I Loads d g;sttllt v.tich..-eon oonilull.lei Manata/gBlelctor e,er P'(l(U:& T 1, t Loads v.tich a-em for I Jrdavrl paioa. Blitery Ef1!1W store T t Lra&,, v.tich ae on I for aid paioa. lgitim "}f.jw 8fdllc fuel JX.IT1P w. Bemaic gasoline lrjedim N ErvneMEnvinet "}f.jow Ca"rado W Sde ITBker lcll1l6 4Weach lnstn.mer IB"S llfl1l8 2Neach i.-- i.-- Lioen;e pae l s) 10Weach i.-- TIJ'll sig,a lcll1l6 21Weach Sklplarrp; Weach lrmior larrp '!JN Por.er-wndolM, 150W r-1' i.--- r-1' i.--- Foglanp; fb/tleach Eladq:> larrp Weach Wpels &L.OOW St.arq rrotorfoc passeiger cas fm...30cxmi Pa'ld!l118111JS 3... each ead 11111B, kma' bean 55Weach eadlarrfs, bean a>weach Tal ISl'fllS 5Weach "8ldleheae' :!J... a>w 14-- i.--,.,.,. 8edric raclakrfa'l 200W BlcMer rrotorfoc arrl'or ooolirl! i.--- PON eated rear wmow 120W i.--- R!a' wrxiowv.iper f'ijw tms & fanfares <MI each Eledric aliema f!ijn V\eshWpe 5)6tenlfor headlarrp; ft1n Clpelle lgter 100W Auloliary dmll) larp; 55Weach bake li{ie 21Weach In desel vetides p PlQSfor starlill 100il/ each Fig. 2.4 Power requirements of loads in vehicles 24

6 Table 2.1 Electrical Loads, Type of load Peak Electro-mechanical valves (6 cylinders at 6000 rpm 2400 Water pump 300 Engine Cooling fan 800 Power steering (all-electric) 1000 eated windshield 2500 Catalytic Converter 3000 Active suspension Communications, navigation& entertainment 100 TOTAL Power, W Average Summer Winter Applications of Claw pole Topology Claw pole structure offers high pole number excitation with very simple field coil and pole system. So, the construction 1s recommended for low power electrical machines with high number of poles. The canned motors used in timers [43] and automobile alternators come under this category. The claw pole machines with permanent magnets for 25

7 providing excitation and machines which make use of claw pole structures on ac side also have been reported. But the use was limited to small size and/ or low speed because excessive eddy currents will be induced in solid steel used for construction of claw poles. Production of the 3D geometry with laminations is also difficult. The introduction of soft magnetic material using compacted iron powder (SMC) has opened up the possibility of obtaining 3D complex geometries. These materials are magnetically isotropic and eddy current loss is much lower than in laminated steels. A permanent magnet machine with claw pole topology in the armature employing SMC as the material is discussed in [44], [45]. The use of claw poles in the construction of linear pulse motor was reported in 1980's [46]. Claw pole permanent magnet stepping motor [ 47] has been used m office automation equipments such as printers or facsimile machines to control the rotor position and speed simultaneously. Lundell type claw pole alternators running at rpm and 1200 z rated at 14.3 kva have been designed [7] for the solar power generation plant on board NASA's space station, Freedom. An overloaded alternator is 26

8 reported to be used as a source of electric energy to a catalytic reactor in initial stage of operation. A motor with claw pole topology for automotive application was given by Felicetti and Rameshol [48]. A claw pole motor was suggested (49) as an alternative for de motor or universal motor in combination with step down gear box, used for power hand tool application. Claw pole machines are used in EV traction where the electrical machine is used to adjust the acceleration of the piston in the combustion engine in order to improve the combustion process[ 50]. igh speed claw pole synchronous machine is reported [51] to be built in the power range of kw as generators in hybrid vehicles and MAGLEV trains as well as helium compressor drives. A claw pole type eddy current coupling used as variable speed drive system for 'low power application is explained in [52]. Universal motor with claw pole structure in the stator is presented in [53] for application in hand tools and domestic appliances. A split phase claw pole induction machine with soft magnetic composite material for stator is proposed in [54]. 27

9 2.5 Conclusion The topological aspects of the alternator are reviewed in this chapter together with a review of the power requirement in the automobiles. Other applications of the claw pole topology are also briefed. Today's power hungry automotive functions give emphasis to efficiency, quality and reliability of the power source. 28

AC MOTOR TYPES. DESCRIBE how torque is produced in a single-phase AC motor. EXPLAIN why an AC synchronous motor does not have starting torque.

AC MOTOR TYPES. DESCRIBE how torque is produced in a single-phase AC motor. EXPLAIN why an AC synchronous motor does not have starting torque. Various types of AC motors are used for specific applications. By matching the type of motor to the appropriate application, increased equipment performance can be obtained. EO 1.5 EO 1.6 EO 1.7 EO 1.8