Except 74 kW motors
Knocking combustion that occurs if the ignition timing has been moved too far to the side «ignition timing», damages the engine. The consequence of this is overheating, damage to bearings and pistons. But the engine runs at maximum power if set to as high as possible «early ignition», that is, if the engine is running on the verge of detonation. This detonation limit is determined by many factors (fuel quality, deposits on the walls of combustion chambers, etc.), so it cannot be fixed exactly. Therefore, it is usually necessary to control the ignition more «safety interval». Or «hourly», which determines whether knock combustion occurs - knock control.
How knock control works
Combustion in the cylinders is controlled by a so-called knock sensor, which is located on models with 4- and 5-cylinder engines on the left side of the cylinder block. Models with 6-cylinder engines are equipped with two sensors on the right and left at the top of the cylinder block. knock sensor «feels», if, during combustion, uneven oscillations occur in the cylinder instead of the usual uniform ones. This information is passed on to the control unit. The following happens there: with the arrival of a signal «detonating combustion at last ignition» the following cylinders with normal combustion still receive the spark at the previously calculated ignition point. But for the cylinder in which detonation was installed, the ignition timing is shifted by about 3°. And this happens, it should be noted, only for this single cylinder. All others work as before.
If knocking is still present in the indicated cylinder, the ignition timing is shifted by another 3°during the next power cycle. And so it can be adjusted up to a maximum of 15° (calculated from the standard ignition moment). If the combustion in the corresponding cylinder now proceeds normally, then after a while the ignition timing again moves in the direction «early ignition». The adjustment is made by 0.5°, followed by a pause for many working cycles before being adjusted again by another 0.5°in the direction «early ignition». This process continues until the originally scheduled ignition timing is reached or until the sensor again reports knocking.
Knock sensor
Inserted into this sensor is a piece of piezoceramic, a material we are familiar with from lighters (gives out a spark). Mechanical forces (stretching, compression), acting on the piezoceramics are converted by it into electrical voltage. The uneven vibrations resulting from detonation combustion are sufficient to activate the sensor.
Important: The tightening torque of the knock sensor must be exactly 20 Nm.
Visitor comments