Toyota COMPUTER-CONTROLLED SYSTEM

ELECTRONIC CONTROL SYSTEM - Knock Senso
r
KNOCK SENSO R
The knock sensor is mounted on the cylinder
block and detects knocking in the engine
.
Low
- Frequency - Hig h
ELECTRICAL CIRCUITRY
OHP 3
7
Engine EC U
OHP 3 7
When engine knocking occurs, the Engine ECU
uses the KNK signal to retard the ignition timing
in order to prevent the knocking .
This sensor contains a piezoelectric element
which generates a voltage when it becomes
deformed as a result of cylinder block vibration
due to knocking .
Diaphrag m
AM l
Piezoelectric element
OHP 3 7
Since the engine knocks at a frequency of
approximately 7 kHz, the voltage output by the
knock sensor is at its highest level at about that
frequency .
There are two types of knock sensor . One type
generates high voltages over a narrow range of
vibration frequencies, while the other type
generates high voltages over a wide range of
vibration frequencies .
OHP 3 7
REFERENCE
The Engine ECU judges whether the engine is
knocking by measuring whether the KNK
signal voltage has peaked above a certain
voltage level or not . When the Engine ECU
judges that the engine is knocking, it retards
the ignition timing . When the knocking stops,
the ignition timing is advanced again after a
predetermined period of time .
Strong
Ignition
Weak
Ignitio n
KNK SIGNAL
Time -
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