Audi A4

since 1994 release

Manual of the car

The detonation ignition arising in case the moment of ignition is determined with too big advancing harms the engine. An overheat, damages of bearings and pistons are its consequence.

On the other hand, the biggest exit of engine capacity happens when the moment of ignition is determined with the maximum advancing, i.e. the engine rigidly works at detonation border. Too numerous factors (quality of fuel, adjournment in combustion chambers and so forth) exert impact on this border of a detonation that it could be defined precisely in advance.

Therefore at traditional installation of ignition it is necessary to have big "distance of safety" or "an observation post" which establishes – if there is a detonation combustion – regulation of a detonation.

Function of adjustment of a detonation

Combustion in cylinders is controlled by a so-called sensor of a detonation which is screwed at the left on the engine block. Two sensors are installed in engines with a working volume of 1,8 l (at the left on the block) and in six-cylinder engines (on the right and at the left above on the block).

The sensor of a detonation "feels" when combustion in cylinders instead of usual uniform fluctuations gives a picture of uneven fluctuations. The sensor transfers this information to an electronic control unit.

There is a following: at receipt of a signal "detonation combustion at the last ignition" the cylinders following in line continue to receive the ignition moment calculated for them. But in that cylinder where the detonation was established, the moment of ignition moves approximately on 3 ° back. As it is noticed above, it occurs only in one cylinder. In others the ignition moment calculated originally remains.

If detonation combustion in this cylinder remained, then at the following working step the ignition moment moves on 3 ° back again. It can be carried out at most to 15 ° (a reference point the nominal moment of ignition is).

If in the corresponding cylinder ignition occurs again normally, then through short time the ignition moment moves towards an advancing again. It becomes approximately on 0,5 °, then the pause in several working steps follows while again there is no shift on 0,5 ° towards an advancing.

It proceeds until reach originally planned moment of ignition or so far the detonation sensor will not give a signal of detonation combustion again.

Detonation sensor

The piece of "pyezokeramika", material which we well know on gas pyezozazhigalka is inserted into this sensitive element. Mechanical forces (stretching, pressure) operating on a pyezokeramika will be transformed by it to voltage.

To make active a sensor, enough uneven fluctuations which are made by detonation combustion.