Except for 74 kW motors
Detonation combustion, which occurs when the ignition timing is moved too far in the "spark advance" direction, is harmful to the engine. The consequences are overheating, damage to bearings and pistons. But the engine operates at maximum power if the "spark advance" is set as far as possible, that is, if the engine operates on the edge of detonation. This detonation limit is determined by many factors (fuel quality, deposits on the walls of combustion chambers, etc.), so it is impossible to fix it precisely. Therefore, usually a larger "safety interval" is needed for ignition regulation. Or "clock", which determines whether detonation combustion takes place - detonation regulation.
Operating principle of knock control
Combustion in the cylinders is controlled by the so-called knock sensor, which is located on the left side of the cylinder block in models with 4- and 5-cylinder engines. Models with 6-cylinder engines are equipped with two sensors, one on the right and one on the left at the top of the cylinder block. The knock sensor "feels" if uneven oscillations occur in the cylinder during combustion instead of the usual uniform ones. It transmits this information further to the control unit. The following happens there: when the signal "knock combustion at the last ignition" is received, the following cylinders with normal combustion receive a spark, as before, at the previously calculated ignition moment. But for the cylinder in which detonation was detected, the ignition moment shifts by approximately 3°. And this happens, it should be noted, only for this single cylinder. All the others operate in the previous mode.
If detonation combustion in the specified cylinder still persists, then during the next working stroke the ignition timing is shifted by another 3°. And so it is possible to adjust up to a maximum of 15° (calculated from the standard ignition timing). If combustion now proceeds normally in the corresponding cylinder, then after a certain time the ignition timing is again advanced in the direction of "early ignition". The adjustment is made by 0.5°, then there is a pause of many working cycles before the adjustment is made again by another 0.5° in the direction of "early ignition". This process continues until the originally planned ignition timing is reached or until the sensor again reports knocking combustion.
Knock Sensor
This sensor contains a piece of piezoelectric ceramic, a material we are familiar with from lighters (produces a spark). Mechanical forces (stretching, compression), acting on the piezoceramics are converted by it into electrical voltage. Uneven oscillations arising from detonation combustion are sufficient to activate the sensor.
Important: The tightening torque of the knock sensor must be exactly 20 Nm.