Abstract: An ionic current detection apparatus for an internal combustion engine does not generate a false ionic current, and hence it does not generate a false knock component signal either, thereby avoiding an incorrect combustion determination or an incorrect knock determination. The apparatus detects an ionic current generated in spark plugs connected with secondary sides of a plurality of ignition coils, respectively, each of which generates a high ignition voltage immediately after firing of a corresponding combustion chamber. The ignition coils are arranged in such a manner that at least the directions of adjacent ignition coils do not coincide with one another. In addition, the ignition coils are fixed by a fixture, which has arrangement positions for the ignition coils predetermined according to the mounting directions thereof, in such a manner that the directions of adjacent ignition coils do not coincide with one another, the ignition coils being installed on the engine through the fixture.

Abstract: A combustion condition detecting apparatus for an internal combustion engine has a current distributor that distributes an ion current, a band pass filter which extracts a knock vibration component from a current distributor output, a knock determination section which outputs a knock pulse if the extracted knock vibration component is larger than a knock detection threshold value, a combustion determination section which outputs a combustion pulse when an current distributor output is larger than a combustion pulse threshold value, an ignition signal determination section which makes a determination on the basis of an ignition signal as to whether energization of an ignition coil for ignition in another cylinder is started, and an ion current limiting section which limits its ion current output to the current distributor during a predetermined time period after the start of energization of the ignition coil for ignition in the another cylinder.

Abstract: The present invention includes an engine diagnostic method and routine, wherein a method of using an ionization signal to perform an engine diagnostic routine includes the steps of detecting the ionization signal; integrating the ionization signal over a first sampling window to generate a first integration ionization value; detecting a peak of the ionization signal over said first sampling window to generate a first peak ionization value; integrating the ionization over a second sampling window to generate a second integration ionization value; detecting a peak of the ionization signal over a second sampling window to generate a second peak ionization value; and diagnosing the engine using said ionization signal.

Abstract: A control device for an internal combustion engine, including: an ion current detecting unit for detecting an ion current flowing between electrodes, via ions generated in a combustion chamber upon combustion, at a time when a voltage is applied to electrodes arranged in a combustion chamber of the internal combustion engine; a parameter extracting unit for extracting an ion current characteristics parameter correlating to an IMEP, from the ion current detected by the ion current detecting unit; an IMEP-related-information calculating unit for using the ion current characteristics parameter outputted from the parameter extracting unit, to calculate information relating to the IMEP of the internal combustion engine; and an internal combustion engine control unit for controlling operations of the internal combustion engine based on the output from the IMEP-related-information calculating unit.

Abstract: A plurality of ignition coils having a combustion detection capability, such as an ion sense capability or cylinder pressure detection capability, are connected to a common communication line. The combustion signals for the plurality of ignition coils is multiplexed on the common communication line. The combustion signal for each ignition coil/cylinder is applied to the common line combined with a respective sync signal such as a current flag signal or a respective electronic spark timing (EST) signal. The sync signals allow each ignition coil to determine when it can transmit its combustion signal.

Abstract: Ion current detection signal output section for outputting an ion current detection signal including a failure determination signal of an ignition operation is provided, and a failure determination as well as a combustion state can be performed based on this ion current detection signal.

Abstract: A misfire detection apparatus for an internal combustion engine is capable of detecting combustion when an ionic current generated upon combustion is superimposed on a leakage current, even if the ionic current does not contain an increased component. An ionic current detection part (1) detects an ionic current flowing between electrodes arranged in a combustion chamber of the internal combustion engine through ions generated upon combustion of an air fuel mixture therein by impressing a voltage on the electrodes. A tendency recognition part (4-7) recognizes a tendency of a change in the ionic current detected by the ionic current detection part. A threshold determination device (8) sets a threshold for an output of the tendency recognition part. A determination device (10) determines an occurrence of combustion or misfiring in the combustion chamber based on an output of the tendency recognition part and an output of the threshold determination device.

Abstract: A device and a method for controlling a drive unit of a vehicle. Starting from the position of an operating element, a power determining signal may be preselected. The actuator element is controlled as a function of a filtered power determining signal. The signal is filtered with a filter having at least one high-pass filter and one low-pass filter connected in parallel. The filtering is performed so that the filtered signal has at least one corresponding pulse in a transition to a modified signal.

Abstract: A knocking detection apparatus including: spark plugs disposed in cylinders of an internal combustion engine; an ion current detector for detecting ion currents flowing in the spark plugs; a time-frequency transformer for setting time intervals allowing one or more overlaps within a time from after ignition by the spark plugs to until the spark plug in the respective cylinder or in another cylinder next ignites and sampling ion currents in the respective time intervals to determine the time-frequency components of the ion current; a knocking detector for detecting knocking based on the time-frequency components; and a detection controller for inputting running status and controlling the time-frequency transformer and the knocking detector.

Abstract: A control device for an internal combustion engine, including: an ion current detecting unit for detecting an ion current flowing between electrodes, via ions generated in a combustion chamber upon combustion, at a time when a voltage is applied to electrodes arranged in a combustion chamber of the internal combustion engine; a parameter extracting unit for extracting an ion current characteristics parameter correlating to an IMEP, from the ion current detected by the ion current detecting unit; an IMEP-related-information calculating unit for using the ion current characteristics parameter outputted from the parameter extracting unit, to calculate information relating to the IMEP of the internal combustion engine; and an internal combustion engine control unit for controlling operations of the internal combustion engine based on the output from the IMEP-related-information calculating unit.

Abstract: A misfire detecting device for an internal combustion engine including an ion current detecting means for detecting ion currents generated between electrodes of spark plugs; an ion current judging means for judging whether or not the ion current exists at each ignition cycle based on the ion current signal; a misfire judging means judging when no ion current is judged to exist based on an ion current judgment signal; an ignition coil; an ignition coil signal judging means for judging whether or not the ignition coil signal generated in synchronism with an ignition timing exists; and a failure judging means for judging whether or not an failure of the ion current detecting means occurs based on a result from the ignition coil signal judging means when the ion current signal is not detected.

Abstract: A method is presented for positioning a measurement window in time for analysis of ionic current signals, detected at internal combustion engines via the electrodes of a spark plug, for an ignition system having an ignition transformer, e.g., a.c. ignition or in a capacitor ignition system or inductive transistor ignition or inductive coil ignition or inductive coil ignition having a limited spark duration, the ignition systems being combined with a measurement device for an ionic current at the secondary winding on the ground side, each spark plug being allocated one ignition transformer, and the detection of the end of a spark and the opening of the measurement window for the ionic current signal taking place as a function of the end of the spark.

Abstract: A method and apparatus for real-time measurement of combustion characteristics of each combustion event in each individual cylinder coupled with an ability to control the engine based upon the combustion characteristics are shown. The invention includes using selective sampling techniques and wavelet transforms to extract a critical signal feature from an ionization signal that is generated by an in-cylinder ion sensor, and then feeds that critical signal feature into an artificial neural network to determine a desired combustion characteristic of the combustion event. The desired combustion characteristic of the combustion event includes a location of peak pressure, an air/fuel ratio, or a percentage of mass-fraction burned, among others. The control system of the engine is then operable to control the engine based upon the combustion characteristic.

Abstract: A knock detection apparatus for an internal combustion engine is provided which accurately distinguishes knock from noise even when noise having a frequency component identical to a knock frequency component is superposed on an ion current signal.

Abstract: An electronic circuit and a method of generating an electrical discharge for an ionization detector system. The electronic circuit includes a transformer with a primary portion and a secondary portion. The circuit and method produce an electrical discharge across a set of electrodes. The discharge is stable over time and has relatively low peak currents associated therewith.

Abstract: A gasket embedding an ion sensor 5 used for sealing a cylinder head to a cylinder block of an engine which is intervened under pressure between the cylinder head and the cylinder block, the gasket having a detection function of the condition in a combustion chamber. The gasket comprises a metal sheet in which a bore seal is formed at a ring-like bead structure and of an insulation seal layer coating at least the upper surface and the lower surface of the metal sheet so as to include the bead structure. An ionic current detection electrode is formed so as to project into the combustion chamber from the insulation seal layer and further a lug projecting outside from the periphery of the insulation seal layer is served as an ionic current introduction electrode of the sensor.

Abstract: A misfire detection apparatus for an internal combustion engine is capable of accurately determining an occurrence of combustion or misfiring in each cylinder of the engine even when an ionic current superposed on a leakage current decreases monotonously to provide no period or range in which the ionic current increases. An ionic current detector 3 detects an ionic current signal corresponding to an ionic current generated when an air fuel mixture in each combustion chamber of the engine is combusted. A gradient detector 6, 7, 8 detects, after firing of the air fuel mixture, a first gradient of the ionic current signal at first detection intervals and a second gradient of the ionic current signal at second detection intervals longer than the first detection intervals. A determination of combustion or misfiring in each combustion chamber is made based on the first and second gradients.

Abstract: A knock control apparatus normalizes a knock frequency magnitude and a background noise level to substantially the same levels in all the engine operating conditions in consideration of a variation in an ionic current level due to an environment, the number of revolutions per minute of the engine, an engine load, etc.

Abstract: An apparatus and method to detect abnormal combustion conditions for use as a feedback control of a lean burn reciprocating engine using ionization signals is presented. The system receives a succession of ionization signals for successive cycles of a running engine and processes a plurality of related ionization signals for signal stability. The ionization signals are checked to determine if an abnormal combustion condition such as knock or misfire has occurred. The variation of an ionization signal that changes with respect to an engine parameter over a combustion event of the lean burn reciprocating engine operating with an air to fuel ratio corresponding to a lambda (&lgr;) greater than 1.4 is measured and a floating bounded space is associated with the ionization signal. An indication that the abnormal combustion condition has been detected is provided if a portion of the ionization signal is within the floating bounded space.

Abstract: An apparatus for determining combustion condition of engine detects ion current flowing in a spark plug. The apparatus samples the ion current by carrying out A/D conversion at every constant time period. The apparatus stores a maximum value of A/D converted values as a peak hold value. The apparatus further detects and stores that the ion current traverses a reference voltage during the A/D conversion time period. The apparatus clears the peak hold value, if the ion current traverses the reference voltage. The apparatus determines the combustion condition based on the peak hold value which has not been cleared continuously over a predetermined number of times of the A/D conversion. It is possible to reduce influence of noise.

Abstract: In an ignition coil assembly of an ion sensing ignition system having an ignition coil output, a buffered ion-sense current source circuit is provided and includes a current sensing circuit, the current sensing circuit being disposed so as to be communicated with the ignition coil output and an active current source circuit, the active current source circuit being disposed so as to be communicated with the current sensing circuit and a current measuring device.

Abstract: An apparatus and method to detect and control the combustion quality of a lean burn reciprocating engine using ionization signals is presented. The system receives a succession of ionization signals for successive cycles of a running engine and processes a plurality of related ionization signals for signal stability. A start point and peak of the ionization signal is identified, using an initial current level for all of the signals. A geometric parameter is associated with the ionization signal that relates the start point to the peak. The geometric parameter is compared against a reference geometric parameter related to a desired combustion quality relating to a lambda greater than 1.4. A control parameter of the engine is adjusted such that an error difference between the geometric parameter and the reference geometric parameter is minimized. The ionization signals are checked to determine if an abnormal combustion condition such as knock or misfire has occurred.

Abstract: A knock detection apparatus for an internal combustion engine is provided which accurately distinguishes knock from noise even when noise having a frequency component identical to a knock frequency component is superposed on an ion current signal.

Abstract: An apparatus and method to detect abnormal combustion conditions for use as a feedback control of a lean burn reciprocating engine using ionization signals is presented. The system receives a succession of ionization signals for successive cycles of a running engine and processes a plurality of related ionization signals for signal stability. The ionization signals are checked to determine if an abnormal combustion condition such as knock or misfire has occurred. The variation of an ionization signal that changes with respect to an engine parameter over a combustion event of the lean burn reciprocating engine operating with an air to fuel ratio corresponding to a lambda (&lgr;) greater than 1.4 is measured and a floating bounded space is associated with the ionization signal. An indication that the abnormal combustion condition has been detected is provided if a portion of the ionization signal is within the floating bounded space.

Abstract: The present feature of the invention comprises a method and apparatus for determining cylinder ID. When a cylinder is compressed, the resistance increases across the spark plug gap. Thus, if a spark coil is only partially charged before activation of the spark, the air gap is not broken down and no ignition occurs in the cylinder in compression. The failure of a spark plug to spark is reflected in the ionization signal. In a preferred embodiment, the dwell time is selected so that the spark plug located in a cylinder that is not in compression will spark, while a spark plug in a cylinder that is in compression will not. The cylinder in compression will output an ionization signal with a shorter duration than a cylinder not in compression. In a preferred embodiment, two methods are used to calculate the duration of the spark, edge detection and integration.

Abstract: A method and apparatus for real-time measurement of combustion characteristics of each combustion event in each individual cylinder coupled with an ability to control the engine based upon the combustion characteristics are shown. The invention includes using selective sampling techniques and wavelet transforms to extract a critical signal feature from an ionization signal that is generated by an in-cylinder ion sensor, and then feeds that critical signal feature into an artificial neural network to determine a desired combustion characteristic of the combustion event. The desired combustion characteristic of the combustion event includes a location of peak pressure, an air/fuel ratio, or a percentage of mass-fraction burned, among others. The control system of the engine is then operable to control the engine based upon the combustion characteristic.

Abstract: This feature of the present invention comprises two embodiments of an integrated ionization detection circuit and ignition coil driver according to the present invention, an ASIC and a single electronic package. The apparatuses reduce the cost and complexity of an in-cylinder ionization detection system by combining like functionality into one ASIC or electronic module easing packaging constraints. In both embodiments, a current sink is used. The current sink removes noise in the form of voltage spikes. The voltage spikes are high voltage, but of short duration. The current sink prevents these spikes from turning on the IGBT. However, the current sink allows the IGBT command signal to pass. This feature of the present invention also comprises a switch whereby ionization current and coil primary current are multiplexed.

Abstract: This feature of the present invention comprises a method and apparatus that provides a regulated power supply for in-cylinder ionization detection by harvesting the excess ignition coil leakage and magnetizing energy immediately following the turn off of the ignition coil IGBT. It uses an additional energy storage capacitor which replaces a first capacitor as the primary energy storage device. Thus, this feature of the present invention uses a two step method for charging the ionization detection circuit, as opposed to just one stage. The second capacitor is charged first, typically up to 400 Volts DC, and is then used as a reservoir to charge the first capacitor.

Abstract: An ignition system has an ignition circuit and an ion current detecting circuit. The ignition circuit has an ignition coil that has relatively low inductance of about less than 10 henries (H) because it is used in conjunction with a separate energy accumulating coil, and a driving circuit for a multi-spark ignition sequence. The ion current detecting circuit detects a second harmonic component of engine knock. The components of the system are designed so that the resonance frequency of an ion current path substantially coincides with the second harmonic frequency component, so that the Q-value of the ion current path is greater than 1. As a result, it is possible to improve knock detecting accuracy.

Abstract: A knock control apparatus normalizes a knock frequency magnitude and a background noise level to substantially the same levels in all the engine operating conditions in consideration of a variation in an ionic current level due to an environment, the number of revolutions per minute of the engine, an engine load, etc.

Abstract: An impulse noise suppression circuit for an integrator-based ion current signal processing system includes a one-shot circuit activated by a trigger signal that is produced when a noise transient in a bandpass filtered ion current signal exceeds a predetermined threshold. The output pulse of the one-shot circuit is selected to have a pulse width configured to mask a substantial portion of the noise transient without masking the remaining filtered ion current signal during the remainder of a knock window in which knock is detected.

Abstract: A misfiring detection apparatus including a comparison unit 22 and a time counting unit 24 which accumulates periods of time during which the ion current flowing between the center electrode 10a and the ground electrode 10b of a spark plug 10 exceeds a predetermined current value; and an ECU 26 which judges that misfiring has occurred when a total of the accumulated periods is not greater than a predetermined value. The ion current is thus determined as a cumulative value of ion current generation periods. Therefore, even when the ion current contains a discharge noise component, the discharge noise component having a short duration accounts for only a small portion of the cumulative value, so that the influence of the discharge noise component on misfiring detection can be reduced. As a result, misfiring detection can be performed with improved accuracy.

Abstract: A firing or ignition state discrimination system for an internal combustion engines having a spark plug which produces spark discharge when supplied with discharge current from an ignition coil to ignite air-fuel mixture in the combustion chamber. In the system, ionic-current that flows during combustion of the air-fuel mixture is detected at a predetermined first timing and leakage current that flows across electrodes of the spark plug is detected at a predetermined second timing which is later than the predetermined first timing. The firing or ignition state of the engine is discriminated to one from among normal, misfiring, spark plug fouling, and failure in ignition system or in fuel supply system based on the detected ionic-current and leakage current and presence or absence of fuel cutoff to the engine. With this, it becomes possible to accurately discriminates the firing or ignition state of the spark plug and to inform the fact to the vehicle operator if desired.

Abstract: A combustion condition detecting apparatus for an internal combustion engine has a current distributor that distributes an ion current, a band pass filter which extracts a knock vibration component from a current distributor output, a knock determination section which outputs a knock pulse if the extracted knock vibration component is larger than a knock detection threshold value, a combustion determination section which outputs a combustion pulse when an current distributor output is larger than a combustion pulse threshold value, an ignition signal determination section which makes a determination on the basis of an ignition signal as to whether energization of an ignition coil for ignition in another cylinder is started, and an ion current limiting section which limits its ion current output to the current distributor during a predetermined time period after the start of energization of the ignition coil for ignition in the another cylinder.

Abstract: A method and a device for analyzing a signal from an ion current sensor of an internal combustion engine. At least one torque quantity characterizing the torque produced by the internal combustion engine is determined on the basis of a signal from the ion current sensor.

Abstract: The arrangement for mounting a sparkplug of an internal combustion engine includes mounting the sparkplug so that all of the outside electrodes are arranged at an intake port side area and/or an exhaust port side area. Alternatively, in the case where at least one of the outside electrodes is located outside of the above-mentioned areas, no other remaining outside electrodes are arranged at a position that faces that outside electrode across the central electrode.

Abstract: In a method for detecting knocking combustion during the operation of an internal combustion engine with a device for measuring the ionic current, the raw ionic current signal or the evaluated value of the knocking intensity are normalized. This enables the value of the knocking intensity to be reliably compared with a threshold value. The normalization avoids the falsifying influence of large intensity fluctuations of the raw ionic current signal from one combustion cycle to the next without any relation to the true knocking intensity.

Abstract: A misfire detection apparatus for an internal combustion engine is capable of accurately determining an occurrence of combustion or misfiring in each cylinder of the engine even when an ionic current superposed on a leakage current decreases monotonously to provide no period or range in which the ionic current increases. An ionic current detector 3 detects an ionic current signal corresponding to an ionic current generated when an air fuel mixture in each combustion chamber of the engine is combusted. A gradient detector 6, 7, 8 detects, after firing of the air fuel mixture, a first gradient of the ionic current signal at first detection intervals and a second gradient of the ionic current signal at second detection intervals longer than the first detection intervals. A determination of combustion or misfiring in each combustion chamber is made based on the first and second gradients.

Abstract: A misfire detection apparatus for an internal combustion engine is capable of detecting combustion when an ionic current generated upon combustion is superimposed on a leakage current, even if the ionic current does not contain an increased component. An ionic current detection part (1) detects an ionic current flowing between electrodes arranged in a combustion chamber of the internal combustion engine through ions generated upon combustion of an air fuel mixture therein by impressing a voltage on the electrodes. A tendency recognition part (4-7) recognizes a tendency of a change in the ionic current detected by the ionic current detection part. A threshold determination device (8) sets a threshold for an output of the tendency recognition part. A determination device (10) determines an occurrence of combustion or misfiring in the combustion chamber based on an output of the tendency recognition part and an output of the threshold determination device.

Abstract: An ignition coil having ion sense capability with combustion and knock outputs features improved determination of when to open and close a combustion window during which a combustion signal indicative of the level of combustion is calculated. The system also includes a knock window during which a knock signal indicative of the level of knock is determined. A PWM combustion signal is multiplexed on the same physical line as a current flag signal, and, a PWM knock intensity signal is multiplexed on the same physical line as a knock window signal, which reduces system connections. Closed loop multicharge ignition is provided with combustion detection during multicharging to ensure the availability of knock detection, thereby providing a longer effective spark burn time while still allowing for knock detection.

Abstract: An apparatus for detecting a combustion condition, such as knock or misfire, includes an incremental integrator in proximity with an ignition coil and provides a stream of digital pulses to a remote control unit, such as an engine control unit. The incremental integrator includes an integration device, such as a capacitor, a threshold comparator, and a pulse generator. A charging current proportional to an ion current charges the capacitor to a preset level wherein the threshold comparator changes state, causing the pulse generator to generate a pulse. The pulse is provided to the control unit, which may include a counter for counting the stream of pulses. The generated pulse also is fed back to reset the integration device, for example discharge of the capacitor. The process is repeated during a condition window, such as a knock window or a combustion window. The count held in the counter of the control unit is indicative of the level of combustion or knock, as applicable.

Abstract: An ignition coil having ion sense capability with combustion and knock outputs features improved determination of when to open and close a combustion window during which a combustion signal indicative of the level of combustion is calculated. The system also includes a knock window during which a knock signal indicative of the level of knock is determined. A PWM combustion signal is multiplexed on the same physical line as a current flag signal, and, a PWM knock intensity signal is multiplexed on the same physical line as a knock window signal, which reduces system connections. Closed loop multicharge ignition is provided with combustion detection during multicharging to ensure the availability of knock detection, thereby providing a longer effective spark burn time while still allowing for knock detection.

Abstract: An impulse noise suppression circuit for an integrator-based ion current signal processing system includes a one-shot circuit activated by a trigger signal that is produced when a noise transient in a bandpass filtered ion current signal exceeds a predetermined threshold. The output pulse of the one-shot circuit is selected to have a pulse width configured to mask a substantial portion of the noise transient without masking the remaining filtered ion current signal during the remainder of a knock window in which knock is detected.

Abstract: A method and a device are described for evaluating a signal from an ionic current sensor of an internal combustion engine. Based on a signal from the ion current sensor, at least one quantity characterizing the combustion in the internal combustion engine is determined. At least one quantity characterizing a combustion start and/or a combustion quality is determined by conditioning the signal.

Abstract: A motorcycle including a two-cylinder engine. The engine includes a housing, first and second cylinders having first and second combustion chambers, respectively, and first and second pistons reciprocating in the first and second chambers, respectively. The motorcycle further includes a spark generating circuit including a spark plug having a spark gap exposed to the first combustion chamber, an ion sensing circuit including the spark plug and being operable to generate an ion signal indicative of an ion current generated across the spark gap, and an analysis module coupled to the ion signal circuit. The analysis module is operable to receive the ion signal and to analyze the ion signal to determine whether a no-combustion event occurs in the first cylinder. The analysis module may be further operable to determine if the spark generating circuit has an intermittent connection.

Abstract: An ignition device for an internal combustion engine comprising: an ignition coil comprising a primary winding and a secondary winding, the ignition coil generating an igniting high voltage in the secondary winding by turning off a primary current flowing in the primary winding; an ignition switching unit; a spark plug connected to an igniting high voltage generation end of the secondary winding; a reverse current prevention unit series-connected on a current-conduction path of the discharge current connecting the secondary winding to the spark plug; a voltage application unit connected to an other end of the secondary winding opposite to the igniting high voltage generation end; an ionic current detection unit; and an ionic current detection switching unit series-connected on a current-conduction path of the ionic current-detecting voltage connecting the voltage application unit to the other end.

Abstract: A misfire detecting device for an internal combustion engine including an ion current detecting means for detecting ion currents generated between electrodes of spark plugs; an ion current judging means for judging whether or not the ion current exists at each ignition cycle based on the ion current signal; a misfire judging means judging when no ion current is judged to exist based on an ion current judgment signal; an ignition coil; an ignition coil signal judging means for judging whether or not the ignition coil signal generated in synchronism with an ignition timing exists; and a failure judging means for judging whether or not an failure of the ion current detecting means occurs based on a result from the ignition coil signal judging means when the ion current signal is not detected.

Abstract: An apparatus for determining combustion condition of engine detects ion current flowing in a spark plug. The apparatus samples the ion current by carrying out A/D conversion at every constant time period. The apparatus stores a maximum value of A/D converted values as a peak hold value. The apparatus further detects and stores that the ion current traverses a reference voltage during the A/D conversion time period. The apparatus clears the peak hold value, if the ion current traverses the reference voltage. The apparatus determines the combustion condition based on the peak hold value which has not been cleared continuously over a predetermined number of times of the A/D conversion. It is possible to reduce influence of noise.

Abstract: A method for determining the air/fuel ratio in an internal combustion engine combustion chamber having at least two ignition plugs spaced apart from one another. Ion-current measurement is carried out during successive operating cycles, wherein a first ignition plug is operated as an ion-current sensor and does not release ignition energy. The time of arrival at the first ignition plug of a flame front formed at the ignition point of a second ignition plug, is detected. The detected time of arrival of the flame front, the ignition point and the ignition-plug spacing are used to determine the speed of the flame and, from this, the air/fuel ratio is determined as a function of the speed and/or load of the internal combustion engine.

Abstract: A combustion state detection apparatus for an internal combustion engine has a detection period limit section, which limits a detection period of an ion current processed in misfire detection section or knock detection section.