Knock Sensor: Description and Operation

Knock Sensor:

PURPOSE
The knock signal is generated by the knock sensor. When engine knock is detected, the knock sensor develops a voltage which the APC ECU registers. The ECU then take appropriate action by adjusting boost pressure to reduce knock.

CONSTRUCTION
The knock sensor (C) consists of a housing (3) a piezoelectric crystal (4) mounted on a threaded sleeve (5) between two connector strips (6). One side of the assembly is fitted with a damping weight (7) and spring washer (8) secured by a nut (9).

OPERATION
Mounted on the engine block, the sensor is subjected to the vibrations generated by knock. The vibrations cause a small distortion on the surface of the piezoelectric crystal, which consequently generates a small voltage. This voltage is read by the APC ECU.

SIGNAL
The signal from the sensor is a continuous, but variable voltage. The frequency of the voltage is dependent on the amount of engine knock. The signal is fed into the APC ECU which computes it as a reference value.