V50 L5-2.4L VIN 39 B5244S7 (2005)
Variable Valve Timing Actuator: Description and Operation
Knock Control
Knock Control
Knock occurs in the combustion chamber when the fuel and air mixture self ignites. This can occur either before or after the spark plug has produced an
ignition spark. In both cases the gas in two or more places ignites in the combustion chamber.
This results in an extremely fast combustion process with flames from several directions. When these flames collide, the pressure in the cylinder
increases rapidly and there is a mechanical knocking sound.
If any of the cylinders knock there is a specific type of vibration in the cylinder block. These vibrations are transferred to the knock sensor (KS) which is
screwed into place in the cylinder block. The resulting mechanical stress in the piezo electrical material in the knock sensors generates a voltage. The
engine control module (ECM) can then determine which cylinder is knocking with the help of the camshaft position (CMP) sensor and the engine speed
(RPM) sensor.
The knock sensor (KS) also senses some normal engine sound. The control module is able to recognize the vibrations which correspond to knocking by
filtering, amplifying and using software to evaluate the signal.
If the knock sensor (KS) detects knocking in the engine above a certain threshold value, the ignition timing is first retarded and then the fuel/air mixture
is enriched to eliminate knocking.
