
Auxiliaries
477
where: T = torque to move one wiper arm, F = force of one blade onto the
screen, µ
max
= max. dry coefcient of friction (e.g. 2.5), f
s
= multiplier for joint
friction (e.g. 1.15), f
t
= tolerance factor (e.g. 1.12), l = wiper arm length, ω
a
=
max angular velocity of arm, ω
m
= mean angular velocity of motor crank, e =
efciency of the motor gear unit (e.g. 0.8), R
h
= motor winding resistance – hot,
R
c
= motor winding resistance – cold.
11.4.2 PM Motor – electronic speed control
The automotive industry uses PM motors because they are economical to
produce and provide good performance. A simple current limiting resistor or a
voltage ...