Aerospace and Electronic Systems Magazine April 2017 - 19
are attached to the rotor and interact with the electromagnetic field
generated by the stator to rotate the rotor.
Figure 2 also shows a BLDC drive and with the stator in solid
contact with the fan housing. The BLDC drive consists of transistors, resistors, capacitors, and integrated circuits (ICs) which control the current flow in the stator windings. The current flowing
through winding wires allows the stator to generate an electromagnetic field for the rotation of the rotor.
FAILURE ANALYSIS FOR FAN
Fan is used in cooling of EMA.
density can be correlated and predicted by using fan scaling laws,
assuming geometrically similar fans. These relationships make it
possible to compare the performance of a fan operating under a
wide range of altitudes, with the ambient pressure varying between
0.2 standard atmosphere (atm) to 1 atm.
THE TRADITIONAL DESIGN OF BLDC FAN
A typical brushless direct current electric motor (BLDC) fan was
selected for hardware analysis. Figure 2 presents the two core elements of a typical fan; i.e., the electric motor and blades. The
electric motor is disassembled into two parts: a stator and a rotor.
The blades are directly mounted on the rotor of the electric motor.
The rotor is supported by two ball bearings. Permanent magnets
Fault tree analysis (FTA) is used to construct the probability basis
for the ultra-high reliability requirement. The method utilized is
similar to that used in . An AND gate represents a combination
of independent events. Mathematically, in set theory terms, this is
equivalent to the intersection of the input event sets, and the probability of the AND gate output is given by (assuming A and B are
P ( A and B ) = P ( A & B ) = P ( A ) P ( B )
An OR gate, on the other hand, corresponds to set union:
P ( A or B ) = P ( A | B ) = P ( A ) + P ( B )
Typical BLDC drive, rotor, and stator (copper coil is stator windings).
IEEE A&E SYSTEMS MAGAZINE
One must first establish the reliability
requirement of the fan system. Based
on this, the required failure probability
for each component of the cooling fan
can be determined. Failure probability
determination offers cost-driven benefits because it provides the optimal
configuration and the optimal time for
replacement of fan components. The
optimal configuration and replacement
of fan components should be driven by
the above failure probability calculation
instead of simply based upon statistical