V90 L6-2.9L VIN 96 B6304S (1998)
Knock Sensor: Description and Operation
The function of the two knock sensors (KS) is to provide the engine control module (ECM) with signals to determine whether the engine is knocking.
The engine control module uses the knock sensor and camshaft position (CMP) sensor signals to identify the cylinder in which knock is present.
The engine management system incorporates two knock sensor, each of which consists of the following components:
^
housing
^
sleeve
^
piezo-electric crystal
^
contact strips
^
damping weight
^
washer
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nut.
Knocking occurs in the combustion chamber when the fuel/air mixture self-combusts. This can occur before or after the spark plug has produced an
ignition spark. In either case the mixture is ignited at two or more points in the combustion chamber.
This results in an extremely rapid combustion process, characterized by several flame fronts. Pressure increases rapidly and a metallic knocking noise is
heard.
Knock in a cylinder produces a certain type of vibration in the cylinder block. The mechanical stresses caused to the piezo-electric crystal in the knock
sensor causes the device to generate a voltage. This signal, with the signals from the camshaft position and engine speed sensors, is used by the engine
control module to identify which cylinder is knocking.
The knock sensors also detect some normal engine noise. Filtering, amplifying and processing the signal allows the engine control module to recognize
vibrations corresponding to engine knock.
If the knock sensors detect knock above a threshold value, ignition is retarded and the fuel/air mixture is enriched to eliminate knocking.
