Audi 80/Avant (B4)

since 1991-1995 release

Repair and operation of the car

Except engines of 66 kW

The detonation combustion arising if the moment of ignition was too far moved towards "an ignition advancing", harms to the engine. The overheat, damage of bearings and pistons are a consequence of it.

But the engine works with the maximum power if "early ignition" that is if the engine works at a detonation side is established as much as possible. This border of a detonation is caused by many factors (quality of fuel, adjournment on walls of combustion chambers, etc.) so it cannot be recorded precisely. Therefore usually "the safety interval" is necessary for regulation of ignition bigger. Or "sentry" who defines, whether takes place detonation combustion – regulation on a detonation.

The principle of action of regulation on a detonation

Combustion in cylinders is controlled by the so-called sensor of detonation combustion which is located at models with 4-and 5-cylinder engines at the left on the block of cylinders. Models with 6-cylinder engines are supplied with two sensors on the right and at the left above on the block of cylinders. The sensor of detonation combustion "feels" if at combustion in the cylinder there are uneven fluctuations instead of the usual uniform. He transfers this information further to the control unit.

There is a following: with receipt of a signal "the detonating combustion at the last ignition" the following cylinders with normal combustion receive a spark still at the ignition moment calculated earlier. But at that cylinder in which the detonation was installed, the moment of ignition is displaced approximately on 3 °. And it occurs, it is necessary to notice, only at this only cylinder. All others work as before.

If detonation combustion in the specified cylinder still remains, at the following working step the moment of ignition is displaced for 3 °. Also it is so possible to regulate to at most 15 ° (calculated from the standard moment of ignition).

If in the corresponding cylinder now combustion proceeds normally, after a while the ignition moment again moves in the direction of "early ignition". Adjustment happens on 0,5 °, the break during many working steps before there is a repeated adjustment for 0,5 ° in the direction of "early ignition" follows then.

This process proceeds until initially planned moment of ignition or so far a sensor again is reached will not report about detonation combustion.

Sensor of detonation combustion

The slice of a pyezokeramika, material with which we are familiar on lighters is inserted into this sensor (gives out a spark). The mechanical forces (stretching, compression) influencing a pyezokeramika are transformed by it to voltage. – arising because of detonation combustion – it is enough uneven fluctuations for activation of a sensor. Important: the moment of an inhaling of the sensor of detonation combustion has to make precisely 20 N • m.