Knock Sensor: Description and Operation

Knock Sensor:

PURPOSE
The knock sensor's piezoelectric element detects engine detonation. It sends a voltage signal to the Engine Control Module (ECM).

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

The signal is continuous, but variable in voltage. The frequency of the voltage is dependent on the amount of engine knock.

This "knock" signal is read by the ECM. When engine knock is detected, The ECM takes appropriate action by retarding the ignition timing and enriching the air/fuel mixture if necessary.

Knock Sensor:

CONSTRUCTION
The knock sensor is a piezo-electric crystal made of three elements: Titanium Oxide, Zirconium Oxide and Lead.

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.