1
Introduction
1.1 Scope
The term axial flux permanent magnet (AFPM) machine in this book relates
only to permanent magnet (PM) machines with disc type rotors. Other AFPM
machine topologies, e.g. transverse flux machines, have not been considered.
In principle, the electromagnetic design of AFPM machines is similar to its
radial flux PM (RFPM) counterparts with cylindrical rotors. However, the
mechanical design, thermal analysis and assembly process are more complex.
1.2 Features
The AFPM machine, also called the disc-type machine, is an attractive alter-
native to the cylindrical RFPM machine due to its pancake shape, compact
construction and high power density. AFPM motors are particularly suitable
for electrical vehicles, pumps, fans, valve control, centrifuges, machine tools,
robots and industrial equipment. The large diameter rotor with its high mo-
ment of inertia can be utilised as a flywheel. AFPM machines can also operate
as small to medium power generators. Since a large number of poles can be
accommodated, these machines are ideal for low speed applications, as for
example, electromechanical traction drives, hoists or wind generators.
The unique disc-type profile of the rotor and stator of AFPM machines
makes it possible to generate diverse and interchangeable designs. AFPM
machines can be designed as single air gap or multiple air gaps machines, with
slotted, slotless or even totally ironless armature. Low power AFPM machines
are frequently designed as machines with slotless windings and surface PMs.
As the output power of the AFPM machines increases, the contact surface
between the rotor and the shaft in proportion to the power becomes smaller.
Careful attention must be given to the design of the rotor-shaft mechanical
joint as this is usually the cause of failures of disc type machines.