Measuring and testing – Engine detonation – Specific type of detonation sensor
Reexamination Certificate
1998-12-14
2001-05-15
Noori, Max (Department: 2855)
Measuring and testing
Engine detonation
Specific type of detonation sensor
C123S429000
Reexamination Certificate
active
06230546
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method and an apparatus for detecting knocking during combustion in an internal combustion engine by evaluating an ionic current signal and electronically adjusting the ignition timing.
BACKGROUND INFORMATION
In the normal combustion of a fuel-air mixture in an internal combustion engine, the fuel-air mixture is ignited by an ignition spark and then burns in a controlled and progressive manner as the flame front advances through the compressed fuel-air mixture in the cylinder chamber. However, an undesired auto-ignition and uncontrolled explosion of the as-yet un-burned fuel-air mixture, commonly known as “knocking”, “pinging”, or “detonation”, can also occur. Such knocking is generally to be avoided because it causes intense pressure waves oscillating in the cylinder, which cause a vibration of the engine components and a resultant audible knocking noise. Ultimately, the intense knocking forces can damage or destroy the engine. Nonetheless, under at least some operating conditions, an engine can achieve its maximum power output and efficiency by operating directly at the limit or boundary of knocking conditions. Thus, an engine controller, such as the conventionally known electronic control unit (ECU), aims to operate the engine as close as possible to the knocking limit without actually causing knocking. If knocking does occur, then corrective measures are taken, for example the ignition timing is slowly retarded, i.e. adjusted in a direction toward the top dead-center position of the piston.
Knocking combustion is generally characterized by pressure oscillations having a frequency in the range from 5 to 20 kHz, taking place in a time interval following the maximum cylinder pressure, i.e. maximum compression. The knocking combustion can be detected by measuring and evaluating changes in the ionic current that flows within the cylinder combustion chamber. This ionic current can be sensed by a suitable sensor arranged in the cylinder, for example a spark plug may be used as an ionic current sensor. However, the ionic current signal already exhibits a first maximum signal level as well as oscillations of the ionic current at the time when the flame front advances and spreads through the fuel-air mixture in the cylinder. This maximum signal level and oscillations in the ionic current can be misevaluated to result in an erroneous detection of knocking when knocking has not actually occurred, because these signal oscillations are caused by turbulence in the cylinder and not by knocking.
Knock recognition methods using an evaluation of the ionic current signal are known in the prior art, but all suffer the disadvantage that they are very sensitive to interference and often result in false detections of knocking. A major cause of such problems in the prior art is that variations in the composition of the fuel, and especially with regard to any metallic components in the fuel, have a strong influence on the ionic current signal over time. Also, the overall signal level or amplitude of the ionic current signal is substantially increased or even multiplied several times, if even a relatively small amount of heavy metal impurities or other metallic components are present in the fuel. This can occur, for example, due to a contaminated production of the fuel or due to accidental fueling of the engine with leaded fuel. Since these variations in the fuel and resulting variations in the ionic current signal are not taken into account according to the prior art, the known methods and circuit arrangements can erroneously determine that knocking is occurring even when a proper combustion without knocking is actually taking place.
SUMMARY OF THE INVENTION
In view of the above it is an object of the invention to provide a method and a circuit arrangement for detecting and recognizing a knocking combustion condition by evaluating the ionic current signal, which effectively compensates for any variations in the fuel composition over time. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present description.
The above objects have been achieved in a method for detecting and recognizing a knocking combustion in an internal combustion engine, according to the invention, with the following features. During each combustion cycle in the engine, an ionic current is sensed in the combustion chamber to provide an ionic current signal, which is then detected during a specified time window, filtered through a band-pass filter, and integrated to provide a present integral value relating to the present combustion cycle. Variations in the ionic current signal, such as those caused by variations in the fuel composition, are compensated or corrected by applying a correction value derived from at least one prior integral value that was determined during a combustion cycle preceding the present combustion cycle in which the present integral value was determined. The resulting corrected present integral value is compared to a knocking threshold value, and if the corrected present integral value exceeds the knocking threshold value, then an output signal is released indicating that a knocking combustion has been detected. The correction of the signal can take place either before or after any one of the steps of time window sampling, band-pass filtering, and integrating the signal.
A key feature of the invention is that the correction value is derived from at least one of the preceding integral values of the ionic current signal, i.e. integral values that were determined in prior combustion cycles. This correction or compensation concept takes advantage of the fact that a change in the ionic current signal caused by a variation in the composition of the fuel takes place in a uniform stepwise manner over relatively long periods of time, i.e. over the course of many successive combustion cycles. This is generally the case when contaminated fuel or any fuel having a different composition is added to the fuel tank of the internal combustion engine, because the added fuel having a different composition first mixes with the previous fuel remaining in the fuel tank, while the previous fuel composition remaining in the fuel line is drawn to the engine. Then, the newly established mixed fuel composition will be drawn through the fuel line to the engine and remain substantially the same for a long period of time, i.e. until other fuel is added to the fuel tank and a new mixed fuel composition is established.
In view of the above, the time constant associated with a variation of the ionic current due to the change in fuel composition is many times slower, i.e. longer in duration, than the time constant associated with influences on the ionic current caused by knocking combustion. As a result, it is possible to account for and compensate the long time constant variations resulting from fuel composition variations, using a correction value derived from at least one prior integral value of the ionic current signal determined during a preceding combustion cycle. It is especially advantageous if the correction factor is derived from a time-weighted plurality of several prior integral values. In this manner, the slow variation of the ionic current signal over several combustion cycles can be compensated for, by “looking back” to the signal levels during plural preceding cycles.
According to a further feature of the invention, an integral mean value or average value is determined by integrating the prior ionic current signal without band-pass filtering, over a time interval that is longer than the time window specified for recognition of knocking. This integral average value is subtracted from the at least one prior integral value for determining the correction factor. In this manner it is possible to minimize a deviation of the integral value as a result of other short-duration variations of the ionic signal, for example resulting from ignition spark failures or “misses”, or resulting from kno
Bertelshofer Peter
Hohner Peter
Schenk Juergen
Wilstermann Hartung
Fasse W. F.
Fasse W. G.
Noori Max
Stevens Maurice
TEMIC Telefunken microelectronic GmbH
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