Misfire detector

Abstract: In a misfire detector device for internal combustion engine, an ignition coil is provided to be on-off actuated by a primary current interruptor, circuit, each end of the ignition coil being connected to a spark plug installed in each cylinder of an internal combustion engine. A peak voltage detector circuit detects a peak voltage applied across the spark plug electrodes after an end of spark action of the spark plug. A peak voltage value distinction circuit recognizes a misfire when a voltage level exceeds a predetermined level which is detected by the peak voltage detector means after an end of spark action of the spark plug upon running the internal combustion engine at a high speed. A distinction circuit recognizes a variation of angles detected by the crank angle sensor so as to determine the misfire when the variation of angles exceeds a predetermined value upon running the internal combustion engine at a low speed.

Description: This invention relates to a misfire detector device for detecting a misfire in an internal combustion engine on the basis of a peak voltage appearing across the spark plug electrodes after the end of its spark discharge action. With the recent requirement of improved fuel efficiency and cleaner emissions from automobiles engines, it has been necessary to introduce a misfire detector device which is able to detect firing conditions in each cylinder of the internal combustion engine in order to effect a misfire prevention countermeasure. On misfire, ionized current is less likely to flow through a spark gap because of absence of ionized particles between the electrodes of the spark plug. With normal combustion, the ionized current is likely to flow through a spark gap because of presence of the ionized particles between the electrodes of the spark plug. Therefore, it is found that the spark plug voltage level applied across the spark plug increases after the end of spark action of the spark plug when the misfire occurs in the cylinder of the internal combustion engine, as compared to the case in which the normal combustion is continuously carried out. By making use of the increase of the spark plug voltage level (referred to as a peak voltage value distinction method), it is possible to detect the misfire in the cylinder of the internal combustion engine. A voltage appears across the spark plug electrodes after the end of the spark action due to an electrical energy stored in the secondary circuit of the ignition coil. A peak voltage after the end of the spark action is compared to a reference voltage level so as to distinguish the misfire from the normal combustion. This is because the voltage across the spark plug electrodes changes depending on an ion density existing mainly between the spark plug electrodes. For this purpose, a moulded conductor is provided around the cable connecting between the spark plug and the distributor to form a static capacitance so as to detect a voltage across the spark plug electrodes. The voltage is compared to a voltage value integrated in an integral circuit during a predetermined time period including the spark discharge duration period in order to determine the misfire in the cylinder. The moulded conductor, however, is not provided in each cylinder of the internal combustion engine. The voltage from the conductor probe serves as a signal corresponding to each cylinder in relation to the ignition timing of each cylinder. The voltage thus detected is uniquely determined as only one reference level irrespective of the different cylinders. However, it is found that the spark plug voltage appearing after the end of the spark action is different depending on not only the geometrical configuration of the electrode and the spark gap between the electrodes, but also swirl currents in the combustion chamber of each cylinder in which the spark plug is installed. In the misfire detector device in which a certain reference value is predetermined to detect the misfire irrespective of the conditions in the cylinder of the internal combustion engine, it is necessary to provide the reference value with a certain tolerance so as not inadvertently to indicate misfire on the basis of the detected level of the spark plug voltage in each cylinder of the internal combustion engine. US-A-5,226,394, and its equivalent DE-A-4,207,141, disclose a misfire detection circuit. In this circuit, a peak voltage detector is gated to obtain the peak value of the inductive discharge portion of the sparking voltage across the spark plug electrodes. The peak value is multiplied by a constant to obtain a comparative level. Misfire is detected if a gated portion of the sparking voltage covering the final capacitive discharge period exceeds the comparative level. EF-A-0,051,290 discloses an internal combustion engine analyser and is primarily concerned with diagnosing faults and displaying appropriate maintenance and repair instructions. The analyser detects the peak voltage of the initial firing pulse of the secondary voltage waveform. For use in diagnosis, an average peak voltage of the initial firing pulse for each cylinder is calculated, and an average for the engine is calculated. According to a first aspect of the present invention, there is provided misfire detector device for an internal combustion engine, comprising: an igniter having an ignition coil arranged to be on-off activated by a primary current interruptor circuit, the ignition coil being connected to respective spark plugs installed in each cylinder of an internal combustion engine; a peak voltage detector means arranged to detect the peak voltage across electrodes of respective ones of the spark plugs after the end of the spark action of the respective spark plug; a peak voltage averaging means arranged to determine, individually for each cylinder of the internal combustion engine, an average value of the peak voltages detected by the peak voltage detector means over a plurality of the sparkings of the respective spark plug; a reference value determining means arranged to determine, individually for each cylinder of the internal combustion engine, a reference value on the basis of the respective average value determined by the peak voltage averaging means; and a comparator means arranged to compare the peak voltage detected individually for each cylinder by the peak voltage detector means with the respective reference value determined individually for each cylinder by the reference value determining means, so as to detect misfires in each cylinder of the internal combustion engine. A misfire detector device for an internal combustion engine according to the present invention can be capable of detecting misfire substantially independently of the geometrical configuration cf the electrode, the spark gap between the electrodes and the swirl current in the combustion chamber of the cylinder in which the spark plug is installed. With a provision of the peak voltage detector means, the voltage across the spark plug is peak held in each cylinder of the internal combustion engine after the end of the spark action, and the average of the peak voltages is obtained in each cylinder of the internal combustion engine after the end of a plurality of the spark actions. In this instance, the peak voltage detector means may directly detect the peak voltage in the secondary circuit of the ignition coil in each cylinder of the internal combustion engine. Alternatively, the peak voltage detector means may detect the peak voltage in the primary circuit of the ignition coil in each cylinder of the internal combustion engine. Even when only a single sensor is provided as the peak voltage detector means, a voltage from the sensor may be used as the spark plug voltage detected in each cylinder of the internal combustion engine by timely dividing the voltage in synchronization with the ignition timing signals. The peak voltage in each cylinder may be detected to ensure the average of the peak voltage in each cylinder after the end of the spark action. On the basis of the average value of the peak voltage individually obtained in each cylinder, the average value multiplied by a constant number may be determined as a reference value in each cylinder, and the reference value compared to the peak voltage held after the end of the spark action. On the basis of such a comparison, it is possible to detect whether or not the misfire occurs in each cylinder of the internal combustion engine. In the case in which the misfire occurs consecutively only in a specified cylinder while carrying out a multitude of spark actions repeatedly, it is difficult to precisely detect the misfire only by comparing the reference value and the peak voltage because the voltage detected in the specified cylinder consecutively remains high. In this instance, the average value of the peak voltage in the specified cylinder remains exceedingly high compared to that of the peak voltage in the other cylinders of the internal combustion engine. Since the average value of the peak voltage detected in each cylinder is determined after the end of the spark action to present the reference value, it is possible to determine the reference value presented herein independent of the geometric configuration of the spark plug electrodes, the spark gap between the electrodes and the swirl current in each cylinder of the internal combustion engine. As a result of the reference value obtained being pertinent to each cylinder, it is possible to precisely detect the misfire by comparing the reference value to the peak voltage in each cylinder of the internal combustion engine. Preferably the misfire detector further comprises an average value averaging means arranged to derive average values of said average values of the peak voltages determined for a plurality of the cylinders excluding a specified cylinder, so as to obtain a comparative average value; and a comparator means arranged to individually compare said average value of the peak voltage determined for said specified cylinder with said comparative average value derived by the average value averaging means, so as to detect a misfire. According to a second aspect of the present invention, there is provided a misfire detector device for an internal combustion engine comprising: an igniter having an ignition coil arranged to be on-off activated by a primary current interruptor circuit, the ignition coil being connected to respective spark plugs installed in cylinders of an internal combustion engine; a peak voltage detector means arranged to detect the peak voltage across electrodes of respective ones of the spark plugs after the end of the spark action of the respective spark plug; a peak voltage averaging means arranged to determine individually for each cylinder of the internal combustion engine, an average value of the peak voltages detected by the peak voltage detector means over a plurality of sparkings of the respective spark plug; an average value averaging means arranged to derive an average value of said average values of the peak voltages determined for a plurality of the cylinder excluding a specified cylinder, so as to obtain a comparative average value; and a comparator means arranged to individually compare said average value of the peak voltage determined for said specified cylinder with said comparative average value derived by the average value averaging means, so as to detect a misfire. With the provision of the comparative average value obtained by averaging the average value of the peak voltage in other cylinders except for a specified cylinder, the average value of the peak voltage in the specified cylinder is compared to comparative average value to distinguish the average of the average value in other cylinders from the average value in the cylinder in which the misfire occurs. This makes it possible to specify the cylinder in which the misfire occurs. Even in the case in which the misfire occurs consecutively in the specified cylinder, and rendering it difficult to accurately determine the average value, it is possible to specify the cylinder in which the misfire occurs by comparing the average value in the specified cylinder to the comparative average value obtained by averaging the average value of the peak voltage in other cylinders except for the specified cylinder. The invention will be further understood from the following description when taken together with the attached drawings, which are given by way of examples only, and in which: Fig. 1 is a schematic view of an ignition circuit for an internal combustion engine in which a misfire detector device is incorporated according to an embodiment of the invention; Fig. 2 is a block diagram of the misfire detector device incorporated according to the embodiment of the invention; and Fig. 3 is a view of peak voltage signals and an incidence distribution showing for the purpose of explaining how the misfire detector device works according to the embodiment of the invention. Fig. 1 shows an embodiment of the invention in which a misfire detector device 200 is incorporated into an internal combustion engine. The misfire detector device 200 has an ignition device 210, a misfire detection device 220 and a sensor device 250. In the ignition device 210, numeral 201 designates an ignition coil, numeral 202 a distributor, numeral 203 a spark plug installed in a respective cylinder, numeral 241 a switching transistor element, numeral 242 a signal generator. To each of the spark plugs, a high voltage is applied through a secondary coil 211 of the ignition coil 201 and the distributor 202 with a vehicular battery cell V1 as a power source. The sensor device 250 which detects a voltage across the spark plug electrodes has a high voltage side capacitor 251 and a low voltage side capacitor 252. The high voltage side capacitor 251 is provided by placing a conductor probe around a plug cable Pc connecting the secondary coil 211 to the distributor 202. The low voltage side capacitor 252 is connected in series with the high voltage side capacitor 251 so as to form a voltage divider circuit which divides the voltage across the spark plug electrodes according to the ratio of two capacitors 251, 252. In parallel with the capacitor 252, a resistor 253 is connected to form a RC path. The high voltage side capacitor 251 has 1 pF static capacity, while the low voltage side capacitor 252 has 3000 pF static capacity. This numerical arrangement divides the voltage across the spark plug electrodes by 1/3000 so as to reduce maximum 30000 V to the order of 10 V. Since the frequency component of a peak voltage is 10 kHz, the magnitude of the resistor is e.g. 500 kΩ to accurately detect the peak voltage with taking an impedance (approx. 5.3 kΩ) of the capacitor 252 into consideration. The misfire detector device 220 is comprised with a microcomputer as a main structure as shown in Fig. 2. The misfire detector device 220 has a peak voltage detector portion 221, a peak average calculation portion 222, a distinction level determining portion 223, an individual cylinder comparator portion 224, an average value averaging portion 225, a cylinder comparator portion 226, a misfire distinction portion 230 and other accessory device. When the peak hold circuit holds a detection signal from the sensor device 250 immediately after the end of the spark action of the spark plug, the peak voltage detector portion 221 detects the detection signal as a peak voltage after the end of the spark action, and dividing the peak voltage into four types of peak voltage signal in accordance with the number of cylinder on the basis of the time division corresponding to the timing signal in which the signal generator 242 sends to apply the spark discharge voltage across the spark plug electrodes in the cylinder of the internal combustion engine. The peak average calculation portion 222 individually calculates a peak voltage average value in each cylinder on the basis of the peak voltage signal divided by the peak voltage detector portion 221. In calculating the peak voltage average value in each cylinder of the internal combustion engine, it is calculated by in turn adding e.g. 1/20 of the peak voltage signals after the end of e.g. twenty times of the spark actions. Upon an entry of a newly added signal, the oldest signal is cancelled to obtain ever renewal peak voltage average value (method of running average). The distinction level determining portion 223 determines a distinction level in each cylinder on the basis of the peak voltage average value detected by the peak average calculation portion 222. The distinction level corresponds to the peak voltage average value multiplied by a constant number. The individual cylinder comparator portion 224 compares the peak voltage signal to the distinction level obtained by the distinction level determining portion 223, and producing a pulse signal according to the comparison result. In this instance, it produces a high level signal according to the ignition timing while maintaining the peak voltage signal higher than the distinction level due to the misfire in each cylinder. The distinction level determining portion 223 produces a low level signal according to the ignition timing while maintaining the peak voltage signal lower than the distinction level due to the normal combustion in each cylinder. The average value averaging portion 225 further averages the peak voltage average value of each cylinder except a specified one in which the misfire is to be detected in order to obtain a comparative average value so as to compare the peak voltage average value of each cylinder with that of the specified cylinder. The comparative average value is determined by constant tines of an average of the peak voltage average value of each cylinder except the specified one in which the misfire is to be detected. The average value averaging portion 225 is independently activated once every 100 times of the spark actions in each cylinder by way of illustration. The cylinder comparator portion 226 compares the peak voltage average value of the specified cylinder with the comparative average value of other cylinders so as to a pulse signal according to the comparison result. When the peak voltage average value of the specified cylinder significantly exceeds an average of the peak voltage average value of other cylinders, it is assumed that the misfire consecutively occurs in the specified cylinder of the internal combustion engine. Therefore, the cylinder comparator portion 226 produces a high level pulse signal when the misfire is detected in the specified cylinder by the peak voltage signal divided by the peak voltage detector portion 221. The misfire distinction portion 230 determines in what cylinder the misfire occurs by the high level pulse signal produced from the individual cylinder comparator portion 224 or the cylinder comparator portion 226, and informing the operator of the misfire cylinder through a flicker lamp or the like. It is noted that the misfire cylinder may be informed by memorizing it on an engine computer. It is possible to specify the mifire cylinder because the timing of the pulse signal of the misfire distinction portion 230 corresponds to the respective cylinder of the internal combustion engine. With the structure thus described, the switching transistor element 241 is on-off actuated by the ignition timing signal produced from the signal generator 242 to draw a pulse-like primary current in the primary circuit of the ignition coil 201. The pulse-like primary current induces a high voltage in the secondary coil 211 so as to initiate the spark action across spark plug electrodes 203a, 203b. Following the initiation of the spark action, the inductive discharge accompanies. The duration of the spark action sustains by the time period corresponding to the revolution speed of the internal combustion engine, and ends with the decrease of an electrical energy stored in the ignition coil 201. After the end of the spark action, the voltage across the spark plug electrodes 203a, 203b rises, and culminates a maximum voltage (2∼3 kV at low speed, 5∼8 kV at high speed) by the energy stored in the ignition coil 201. In the misfire detector device 220, the detection voltage from the sensor device 250 is peak held after the end of the spark action, and the peak-held detection voltage is divided according to the ignition timing signal so as to form the peak voltage signal of each cylinder. By using the running average, the peak voltage average value is calculated in each cylinder so as to determine the distinction level in each cylinder on the basis of the peak voltage average value. The voltage across the spark plug electrodes 203a, 203b lengthens the discharge time period after the end of the spark action so as to present the low peak voltage due to small energy reserved in the ignition coil when the normal combustion occurs in the cylinder. Meanwhile, the voltage across the spark plug electrodes 203a, 203b shorten the discharge time period after the end of the spark action so as to present the high peak voltage due to greater energy reserved in the ignition coil when the misfire occurs in the cylinder. When the peak voltage signal is higher than the distinction level because of the misfire occurred in the cylinder, the individual cylinder comparator portion 224 produces the high level pulse signal in accordance with the ignition timing of the cylinder. Upon the normal combustion in the cylinder of the internal combustion engine, the individual cylinder comparator portion 224 produces the low level pulse signal in accordance with the ignition timing of the cylinder. Therefore, it is possible to specify in what cylinder the misfire occurs because the high level pulse signal from the misfire detector portion 230 is in accordance with the ignition timing of each cylinder. In the case in which the misfire consecutively occurs only in a specified cylinder during repeatedly carrying out a multitude of spark actions across the spark plug electrodes 203a, 203b, it may be difficult to compare the respective peak voltage signals because the high peak voltage signal is consecutively maintained. However, the peak voltage average value becomes exceedingly high in the cylinder in which the misfire occurs consecutively, as opposed against the peak voltage average value the other cylinders. This makes it possible to distinguish the peak voltage average value in the misfire cylinder from that of other cylinders. The cylinder comparator portion 226 produces the high level pulse signal to designate in what cylinder the misfire occurs. Fig. 3 shows an incidence distribution of the peak voltage signal concerning to the normal combustion and the misfire by broken lines and solid line respectively. In Fig. 3, the distinction level is designated by phantom lines a, b, c, d which in turn correspond to the cylinders H1 ∼ H4. According to the invention, it is possible to correctly (approx. 100 %) distinguish the misfire from the normal combustion because the distinction level is determined individually depending on the cylinders H1 ∼ H4. In the prior art in which the distinction level is predetermined uniquely to the internal combustion engine, it is only possible to detect the misfire by the probability of approx. 50 % because it is necessary to arrange the distinction level as shown at (Po) in Fig. 3. As apparent from the foregoing description, the misfire distinction level is individually determined depending on the cylinders, it is possible to make each of the distinction levels pertain to the geometrical configuration of the electrode, the spark gap and swirl current in each cylinder. As a result, it is possible to precisely detect whether or not the misfire occurs by comparing the respective distinction level (reference value) to the peak voltage in each cylinder of the internal combustion engine. It is noted that resistors may be used in a primary circuit 212 to form a voltage divider probe so as to detect the voltage across the spark plug electrodes 203a, 203b instead of the sensor device 250 although the sensor device 250 is provided in the secondary coil 211 of the ignition coil 201 in the embodiment of the invention. While the invention has been described with reference to the specific embodiments, it is understood that this description is not to be construed in a limiting sense in as much as various modifications and additions to the specific embodiments may be made by skilled artisan without departing from the scope of the invention as claimed.

Claims: A misfire detector device for an internal combustion engine, comprising: an igniter (210) having an ignition coil (201) arranged to be on-off activated by a primary current interruptor circuit (241,242), the ignition coil being connected to respective spark plugs (203) installed in each cylinder of an internal combustion engine; a peak voltage detector means (221) arranged to detect the peak voltage across electrodes of respective ones of the spark plugs after the end of the spark action of the respective spark plug; a peak voltage averaging means (222) arranged to determine, individually for each cylinder of the internal combustion engine, an average value of the peak voltages detected by the peak voltage detector means over a plurality of the sparkings of the respective spark plug; a reference value determining means (223) arranged to determine, individually for each cylinder of the internal combustion engine, a reference value on the basis of the respective average value determined by the peak voltage averaging means; and a comparator means (224) arranged to compare the peak voltage detected individually for each cylinder by the peak voltage detector means with the respective reference value determined individually for each cylinder by the reference value determining means, so as to detect misfires in each cylinder of the internal combustion engine. A misfire detector device for an internal combustion engine comprising: an igniter (210) having an ignition coil (201) arranged to be on-off activated by a primary current interruptor circuit (241,242), the ignition coil being connected to respective spark plugs (203) installed in cylinders of an internal combustion engine; a peak voltage detector means (221) arranged to detect the peak voltage across electrodes of respective ones of the spark plugs after the end of the spark action of the respective spark plug; a peak voltage averaging means (222) arranged to determine individually for each cylinder of the internal combustion engine, an average value of the peak voltages detected by the peak voltage detector means over a plurality of sparkings of the respective spark plug; an average value averaging means (225) arranged to derive an average value of said average values of the peak voltages determined for a plurality of the cylinder excluding a specified cylinder, so as to obtain a comparative average value; and a comparator means (226) arranged to individually compare said average value of the peak voltage determined for said specified cylinder with said comparative average value derived by the average value averaging means, so as to detect a misfire. A misfire detector device according to claim 1 and further comprising: an average value averaging means (225) arranged to derive average values of said average values of the peak voltages determined for a plurality of the cylinders excluding a specified cylinder, so as to obtain a comparative average value; and a comparator means (226) arranged to individually compare said average value of the peak voltage determined for said specified cylinder with said comparative average value derived by the average value averaging means, so as to detect a misfire. A misfire detector device according to any one of the preceding claims, wherein said peak voltage detector means is provided in a side of the primary circuit of the ignition coil.

Inventors: ITO YASUO, MIYATA SHIGERU, ITO, YASUO, MIYATA, SHIGERU, Ito, Yasuo, c/o NGK SPARK PLUG CO., LTD., MIYATA, SHIGERU, C/O NGK SPARK PLUG CO., LTD.
Applicants: NGK SPARK PLUG CO, NGK SPARK PLUG CO., LTD
Application year: 1993
Main classification: F02P17
IPC codes: G01M15, F02P17, F02P15