Internal-combustion engines – Combustion chamber means combined with air-fuel mixture...
Patent
1994-10-20
1995-06-06
Nelli, Raymond A.
Internal-combustion engines
Combustion chamber means combined with air-fuel mixture...
F02P 514
Patent
active
054213045
DESCRIPTION:
BRIEF SUMMARY
FIELD
The present invention relates to ignition control for an internal combustion engine, and more specifically to a knock control system and method for a spark ignition internal combustion engine.
BACKGROUND
In order to achieve optimized operation in a spark ignition internal combustion engine, it is necessary to vary the ignition timing or ignition point in accordance with the engine speed and load. For this purpose it is known practice to enter predetermined characteristic diagram values (sometimes referred to as characteristic map input) in a characteristic diagram (or characteristic map) of an electronic engine timing device in accordance with the load and speed such that the characteristic diagram values can be read out for each actual ignition point.
It is also known in the art to operate the internal combustion engine in the higher load range close beneath the knock limit in order to optimize fuel efficiency and low pollutant emission levels. However, care must be taken to ensure that the knock limit is not exceeded, since the risk of damage to the engine is great if the knock limit is exceeded too frequently. Since knock primarily occurs under wide-open-throttle operating conditions, it is therefore a direct constraint on engine performance. Further, since the position of the knock limit varies depending upon existing engine operating parameters, in particular fuel grade, temperature and air pressure, it is the known practice to control or regulate knocking on a short-term basis.
In accordance with the short-term knock control practice described above, when knocking combustion or knocking events occur, the predetermined characteristic diagram value taken from the characteristic diagram is reset one step at a time by a control stroke in the direction of retarded ignition through a relatively large retard correction value to a second adjusted diagram value for the actual ignition point. In the subsequent absence of any further pinging or knocking events, the retarded value for the actual ignition point is advanced, one control stroke at a time back to the original predetermined characteristic diagram value.
This short-term control or regulation is therefore related to the level of the predetermined characteristic diagram value entered in the characteristic diagram of the timing device for a particular engine. When the operating parameters are unfavorable, in particular when the fuel quality is poor, the knock limit may be relatively remote from the predetermined characteristic diagram value or map input. In this case, the knock control must be carried out with stepwise control strokes of an appropriate size and within a wide control band width. This has a disadvantageous effect on the control stability, since a relatively high number of knocking combustions, with sometimes violent and audible detonations, must be tolerated during the knock control period. This has an adverse effect on passenger comfort since knock produces unpleasant noise due to the sometimes audible detonations. In addition, such a protracted series of knocking combustions adversely affects the engine and the operation of the motor vehicle.
In the known practice, the short-term knock control starts with certain control strokes upon reaching an operating point of a particular speed and load. Upon leaving this operating point and reaching another operating point, the predetermined characteristic diagram value obtained from the characteristic diagram usually also changes in correspondence with the new operating point. The short-term control must then also re-adapt to these new conditions. When the transition conditions are unfavorable, a reactively high number of knocking combustions with sometimes violent detonations must be tolerated until the short-term control has re-adapted to the new operating point in the best possible manner.
Another problem with short-term knock control is that the first retard correction value has a fixed magnitude and cannot be automatically altered to account for changing operational conditions. For
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Gibtner Siegfried
Pfalzgraf Bernhard
Audi AG
Dulin Jacques M.
Nelli Raymond A.
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