Electric drive system technologies - Propulsion Systems for Hybrid Vehicles - page 243

Chapter 5
Electric drive system technologies

This chapter explores the four classes of electric machines having the most bearing
on hybrid propulsion systems: the brushless permanent magnet machine in its sur-
face permanent magnet (SPM) configuration; the interior permanent magnet (IPM)
synchronous machine in either inset or buried magnet configuration; the asynchro-
nous or cage rotor induction machine (IM); and lastly, the variable reluctance or
doubly salient machine (VRM).
There exists a mountain of topics, papers and training workshops dedicated to
the design and study of these four classes of machines. The purpose of this chapter is
to present a design perspective of these electric machines in the context of hybrid
vehicle propulsion. This is a topic that is still not as well defined, for example, as the
design of industrial electric machines. In this chapter, we focus attention on the
design characteristics of the four classes of electric machines of most interest for
hybrid propulsion. To amplify the reasons for these choices, consider the following
products now available in the market:

SPM (Honda Insight and Civic mild hybrids, FCX-V3 FCEV; Mannesmann
Sachs ISA)

●

IPM (Toyota Prius, Estima and Ford Motor Co. hybrid Escape) ●

IM (GM Silverado ISG, Continental ISAD, Delphi Automotive ISG ●

Valeo ISA)

VRM (Dana ISA) ●

These machines in current use are all of the drum design - that is, rotor flux is
radial across a cylindrical airgap, versus axial designs that have a distinct pancake
appearance with axial flux across an airgap that separates the disc-shaped stator(s)
and rotor(s). A plural connotation is used on axial machines because most will have
a single stator and twin rotor discs or vice versa.

5.1 Permanent magnets

Permanent magnet materials comprise various alloys of ferrous and non-ferrous
metals to achieve a strong ferromagnetic effect. Key attributes include high rema-
nence flux, B r , and high coercivity, H c , to yield the highest energy product, BH mx .