Environmental Engineering Reference
In-Depth Information
1,000
800
600
D
ro_lim
D
so
i
400
D
ro
i
200
D
so_lim
D
ri
i
0
0
20
40
60
80
100
120
140
160
h
FCAS stack length (mm)
Figure 4.18 Variation of hybrid M/G diameters versus stack length
poles are used the aspect ratio trends to less than one and if more poles are used the
aspect ratio trends to values larger than 3/2 for drum type designs. Drum type
electric machine designs have radial flux from the rotor surface on its OD. Axial
type machines have axial flux emanating from side faces of the rotor. Even though
the hybrid propulsion M/G just elaborated on was pancake shaped, it was none-
theless a radial design.
Axial design machines were not considered here, although much the same
rationale applies, because in a powertrain the need to restrict axial movement of the
disc rotor becomes a major challenge. It would require some elaborate design to
restrain the crankshaft end play in an engine after it had been in service for some
years to guarantee that the crankshaft did not move axially more than 0.25 mm. If it
did, then a fair portion of the axial airgap would be intruded into, with possible
rotor impingement on the stator and subsequent damage to the machine.
The various types of electric machines used in hybrid propulsion are covered in
more detail in Chapter 5.
4.3 Sizing the power electronics
All of the electrical power directed to the hybrid propulsion M/G must pass through
the power electronics. It has been said that control electronics uses power to
