What does a 'knock' sensor do? and how does it work?
- Thread starter Virdi
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Caporegime
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- 11 Mar 2005
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- Leafy Cheshire
in simple terms is a microphone bolted to the block and it listens for pre ignition. once it hears it, it tells the ecu and the ecu retards the ignition timing.
knock sensors need to be bolted on to the block at a specific torque thingy otherwise that can effect its sensitivity
knock sensors need to be bolted on to the block at a specific torque thingy otherwise that can effect its sensitivity
Soldato
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IIRC its to detect frequencies around 6400Hz which are inline with the shockwave attributed to detonation of the air fuel and leads to a breakdown of the boundary layer in the combustion chamber.
Most dont really work much past 5000rpm though due to the noise of the engine masting the noise.
Most dont really work much past 5000rpm though due to the noise of the engine masting the noise.
The fundamental frequency during a knock event depends a great deal on bore size (larger = lower frequency). Since you also get significant amounts of signal energy at the resonant frequency of the block in normal operation, the simple knock detector circuits you can find on the web that simply look at overall signal magnitude are pretty much worthless; an OEM ECU will apply a lot of filtering that is engine specific to achieve reliable operation.
