Engine Detonation Knock Signal KNK Knock Sensor

The knock sensor is a piezoelectric device mounted to the cylinder block which generates a voltage whenever it is exposed to vibration. When engine detonation occurs, vibration of the cylinder block causes the sensor to generate a voltage signal. The sensor signal varies in amplitude depending on the intensity of knock.

Typically, detonation vibration occurs in the 7KHz range (7 thousand cycles per second). Knock sensor and ECU designs take advantage of this fact.

There are two different types of knock sensors used on Toyota engines. The mass type sensor produces a voltage output over a wide input frequency range; however, its signal output is greatest at a vibration frequency of approximately 7KHz. With this type of sensor, the eCu uses a filter circuit to distinguish between background noise and actual engine knock.

The resonance type sensor is tuned into a very narrow frequency band and only produces a significant signal voltage when exposed to vibrations in the 7KHz range. The ECU requires less complicated filter circuitry with this type of sensor.

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