Page 324 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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306 Automobile mechanical and electrical systems

Figure 3.102 Wiper motor and linkage

Figure 3.103 Motor brushes and armature

or some form of electronic control, to allow two-speed operation. In three-
brush motors, the normal speed operates through two brushes placed in the
usual positions opposite to each other. For a fast speed, the third brush is
placed closer to the earth brush. This reduces the number of armature windings
Key fact
between them, which reduces resistance, hence increasing current and therefore
Wiper motors or the circuit must speed ( Fig. 3.103 ).
have short-circuit protection to
protect the motor in the event of Wiper motors or the associated circuit must have some kind of short-circuit
stalling. protection. This is to protect the motor in the event of stalling, if the wiper blade
is frozen to the screen for example. A thermal trip of some type is often used, or
a current sensing circuit in the wiper ECU if fi tted.
A windscreen washer system consists of a simple d.c. permanent magnet motor
( Fig. 3.104 ), which drives a centrifugal water pump. The water, preferably with
a cleaning additive, is directed onto an appropriate part of the screen by two or
more jets. A non-return valve is often fi tted in the line to the jets to prevent water
siphoning back to the tank. This also allows ‘instant’ operation when the washer
button is pressed. The washer circuit is normally linked in to the wiper circuit,