II-155
WSM Minor Change II Service Engineering Section
(7)Engine speed sensor
The engine speed sensor is a quick-response
proximity switch. When the teeth of a gear pass
close, the magnetic field inside the switch changes
and the variation is converted to pulses.
The number of pulses for "t" seconds is counted by
the microcomputer. The engine speed is then com-
puted in the following equation.
[rpm]
Such speed data is used for the starter's automatic
release system.
gear teeth:68
Fuel pump gear
0.7 ± 0.2 mm
2 x 60
68 x t
pulse
convert circuit
sensor chip
AB
N
A
B
+
-
V:
This sensor is composed of a sensor and a
rotor. The sensor has a coil wound up around
a magnet, and the rotor is of iron with teeth. As
the rotor turns, the magnetic flux varies at its
peaks and troughs according to the turning
speed. Such frequency-dependent change of
the magnetic force line generates an induced
electromotive force in the coil. The resulting
signal is fed to the controller to detect the turn-
ing speed.
Time for the rotor to move in one-tooth distance
V: Induced electromotive force
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