Page 327 - 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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Electrical systems 309

Figure 3.107 Vehicle horns

Figure 3.108 Ultrasonic reversing aid

fanfare horns illegal. Most horns draw a large current so are switched by
a relay.
The standard horn operates by simple electromagnetic switching. Current fl ow
Defi nition
causes an armature, which is attached to a tone disc, to be attracted to a stop.
A set of contacts is then opened. This disconnects the current, allowing the Hertz
armature and disc to return under spring tension. The whole process keeps One hertz (1 Hz) is one cycle or
repeating when the horn switch is on. The frequency of movement, and hence oscillation per second.
the tone, is arranged to lie between 1.8 and 3.5 kHz. This note gives good
penetration through traffi c noise.
Twin horn systems, which have a high and low tone horn, are often used. This
produces a more pleasing sound, but is still very audible in both town and higher
speed conditions.

3.4.3 Obstacle avoidance

The principle of radar as a reversing aid is illustrated in Fig. 3.108 . This technique
is in effect a range-fi nding system. The output can be audible and/or visual,
the former being perhaps more appropriate, as the driver is likely to be looking
backwards. The audible signal is a ‘pip pip pip’ type sound, the repetition