Misfire detector using different methods for high and low engine speeds

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 appeared 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 automobile 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 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. However, upon running the internal combustion engine with a low speed range, the stepped-up level of the spark plug voltage reduces after the end of the spark action of the spark plug. For this reason, the misfire detection accuracy reduces. On the other hand, it is known that the crank angle varies depending on the occurrence of misfire. A crank angle variation distinction method has been developed to detect the misfire on the basis of variations of the crank angles. It is, however, difficult to accurately detect the misfire particularly upon running the internal combustion engine with a high speed range because the crank moves smoothly, and the crank angle substantially remains unchanged when a single misfire occurs in the respective cylinder of the internal combustion engine. Also, 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, each disclose a misfire detection circuit. A peak voltage detector is gated to obtain the peak value of the inductive portion of the sparkling 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 capacitive discharge period exceeds the comparative level. WO-A-11522 discloses a misfire detection circuit. Different diagnostic methods are selected according to where the engine is on a map of its current load and rotational speed. At low speed ranges the diagnostic method is based on the rotational speed of the engine. At high speed ranges the diagnostic method is based on the ignition current. US-A-5,201,293, and its equivalent EP-A-0,484,691, each disclose a misfire detection circuit capable of detecting combustion failures on the basis of faltering in the torque produced by the engine and of detecting ignition failures by monitoring the spark voltage electrically. Torque falter is not relied upon when the engine has a small load, but the documents say that electrical ignition failure recognition is efficient for engine operation at low loads and low speeds. According to the present invention, there is provided a misfire detector device for an internal combustion engine, comprising: an ignition coil arranged to be on-off activated by a primary current interruptor circuit, the ignition coil being for connection to a spark plug installed in a cylinder of an internal combustion engine; peak voltage detector means arranged to detect the peak voltage arising across the electrodes of the spark plug after the end of the spark action; peak voltage value distinction means arranged to recognise misfire by comparing the voltage level detected by the peak voltage detector means, after the end of the spark action, across a spark plug of a cylinder which is in a compression stroke with a voltage level arising, after the end of the stark action, across the spark plug of a cylinder when this cylinder is in an exhaust stroke, and to recognise misfire when a difference of the two voltage levels exceeds a predetermined value; crank angle sensor arranged to sense the angle of the crank shaft of the internal combustion engine; and crank angle variation distinction means arranged to recognise misfire on the basis of the variation of angles detected by the crank angle sensor; and means (ECU) arranged to indicate misfire on the basis of the peak voltage distinction means when the internal combustion engine is running in a high speed range and on the basis of the crank angle variation distinction means when the internal combustion engine is running in a low speed range. With the use of the peak voltage value distinction method which assures a high misfire detection accuracy within a high speed range and the crank angle variation distinction method which assures a high misfire detection accuracy within a low speed range, it is possible to accurately detect the misfire within an entire speed range of the internal combustion engine. Thus, embodiments of the invention as claimed can provide a misfire detector device for an internal combustion engine which is capable of accurately detecting misfire over a wide speed range of an internal combustion engine so as to contribute to cleaner emissions and improved fuel efficiency. By comparing the spark plug voltage level in which the spark effectively ignites the air-fuel mixture to the spark plug voltage level in which the spark is wasted uselessly in an exhaust stroke, it is possible to detect the difference of the two spark plug voltage levels to determine misfire. This makes it possible to accurately detect whether the misfire occurs with minimum data since a spark voltage waveform is analyzed under the circumstances in which variation of the spark voltage waveform remains significantly small irrespective of the running condition of the internal combustion engine. Advantageously, a dual-polarity type distributorless igniter is provided in which each end of the secondary circuit of the ignition coil is connected to a respective spark plug. In one embodiment, the peak value distinction means is arranged to compare the voltage level detected by the peak voltage detector means after the end of the spark action across a spark plug in a cylinder which is in a compression stroke with a voltage level detected, after the end of the spark action, across the same spark plug when its cylinder is in an exhaust stroke following the compression stroke and expansion strokes. By comparing the spark plug voltage level in which the spark effectively ignites the air-fuel mixture to the spark plug voltage level in which the spark is wasted uselessly in an exhaust stroke within the same cylinder, it is possible to compare the two spark plug voltage levels after the end of the spark action substantially under the same running conditions so as to ensure the accurate misfire detection. In another embodiment, the peak voltage value distinction means is arranged to compare the voltage level detected by the peak voltage detector means, after the end of the spark action, across a first spark plug in a cylinder which is in a compression stroke with a voltage level detected, after the end of the spark action, across a second spark plug in a cylinder which is in the exhaust stroke in synchronization with the compression stroke at the same time. By simultaneously establishing the spark plug voltage level in which the spark effectively ignites the air-fuel mixture to the spark plug voltage level in which the spark is wasted uselessly in an exhaust stroke, it is possible to compare the two spark plug voltage levels after the end of the spark action substantially under the same running conditions so as to ensure the accurate misfire detection. The crank angle variation distinction means may be arranged to recognise misfire when the variation of the angles detected by the frank angle sensor exceeds a predetermined value. Preferably, the peak voltage detector means is provided on the side of the primary circuit of the ignition coil. The invention as claimed will be further understood from the following description given by way of example only, when taken together with the accompanying drawings, in which: Fig. 1 is a schematic view of an ignition circuit of a dual-polarity type distributorless igniter device for an internal combustion engine in which a misfire detector device is incorporated according to a first embodiment of the invention; Fig. 2 is a view of spark plug voltage waveforms shown for the purpose of explaining an operation of the misfire detector device; Fig. 3 is a view similar to Fig. 2 according to a second embodiment of the invention; Fig. 4 is a schematic view of a distributor type ignition circuit for an internal combustion engine in which a misfire detector device is incorporated according to a third embodiment of the invention; and Fig. 5 is a view of spark plug voltage waveforms for the purpose of explaining an operation of the misfire detector device according to the third embodiment of the invention; Referring to Fig. 1 which shows a dual-polarity type distributorless igniter device 100 incorporated into a four-cylinder internal combustion engine (E). The igniter device 100 has two ignition coils 1, 2. To negative and positive spark plug voltage terminals 1a, 1b of the ignition coil 1, spark plugs 11, 12 are connected respectively which are installed in first and fourth cylinder H1, H4 of the internal combustion engine (E). To negative and positive spark plug voltage terminals 2a, 2b of the ignition coil 2, spark plugs 21, 22 are connected respectively which are installed in second and third cylinder H2, H3 of the internal combustion engine (E). Each primary circuit L1 of the ignition coils 1, 2 is connected to a vehicular power source V and a primary current interrupter means 4. Each secondary circuit L2 of the ignition coils 1, 2 is connected at one end 1a, 2a to the spark plugs 11, 21 by way of cables 11a, 11c, and connecting at the other end 1b, 2b to the spark plugs 12, 22 by way of cables 11b, 11d. In the proximity of each of the cables 11a ∼ 11d through which a spark plug voltage is applied across the spark plugs, a voltage divider probe 5 is placed. To the voltage divider probe 5, a spark plug voltage detector circuit 6 is connected to detect a spark voltage level applied across each of the spark plugs. To the spark plug voltage detector circuit 6, a peak value distinction circuit 7 is connected to determine in what cylinder a misfire occurs by comparing peak values of the spark voltage waveform appeared between the spark plug electrodes. The primary current interrupter means 4 has a switching element 41 and a signal generator,42 controlled by an engine control unit (ECU) which detects a crank angle and throttling degree, and on-off actuating the primary circuit of the ignition coils 1, 2 to appropriately correspond an ignition timing to an ignition advancement angle depending on the load and revolution speed of the internal combustion engine (E). The voltage divider probe 5 has high and low impedance elements 51, 52. The high impedance element 51 is placed around each of the cables 11a ∼ 11d between the secondary circuit L2 of the ignition coil and the spark plugs. The low impedance element 52 is connected from a common point Co of the cables 11a ∼ 11d to the ground. The high impedance element 51 acts as a conductor sensor arranged to form a 1pF static capacity between the conductor sensor and each of the cables 11a ∼ 11d. The low impedance element 52 serves as a 3000 pF capacitor to divide the spark plug voltage in the secondary circuit by the order of 1/3000. In parallel with the capacitor 52, 500 kΩ resistor 53 is connected to form a CR path. With the provision of the voltage divider probe 5, the maximum of 30000 V is reduced to the level of 10 V which is inputted to the spark plug voltage detector circuit 6. The spark plug voltage detector circuit 6 has a peak hold circuit 61 which is reset in synchronization with an output signal from the signal generator 42, and receives a sampling signal from the engine control unit (ECU) to detect a peak hold value at a certain elapse of time after a primary current interrupter signal is transmitted so as to detect a stepped-up voltage level across the spark plug electrodes after the end of the spark action of the spark plug. Upon determining the misfire, the peak value distinction circuit 7 compares a peak hold value P1 after the end of the spark action to a peak hold value P2 after the end of the spark action which is uselessly wasted in the exhaust stroke of the cylinder. Then the peak value distinction circuit 7 determines the misfire when the peak hold value P1 is greater than two times of the P2 (P1 > 2P2). Numeral 8 designates a crank angle speed detector means which detects a crank angle and a rotational position of a crank shaft of the internal combustion engine (E). Numeral 9 designates a crank angle speed variation distinction circuit. The crank angle speed detector means has a toothed wheel 82 attached to a shaft 81 which moves in association with the crank shaft, and having a crank angle speed sensor 83 which detects a rotational position and an angular speed of the toothed wheel 82. The crank angle speed sensor 83 is made by utilizing a magnetic or photoelectronic element. The crank angle speed variation distinction circuit determines the misfire as follows: The misfire is determined when the difference of (Ri-Rh) exceeds a predetermined value. Where T360 is a time required for the crank shaft to move a single rotation measured by the crank angle speed sensor 83 at an upper dead point in each cylinder of the internal combustion engine (E), T90 is a time required to move a certain crank angle (e.g. 90 CA) after the end of the spark action in each cylinder of the internal combustion engine (E), R is T90/T360, Ri is R at the time of initially measuring T90/T360, Rh is an average value of R's obtained during a certain period of time after initially measuring T90/T360. To the engine control unit (ECU), output signals each from the crank angle speed variation distinction circuit 9 and the peak value distinction circuit 7 are fed. The engine control unit (ECU) determines the misfire on the basis of the output from the peak value distinction circuit 7 when running the internal combustion engine (E) in the high speed range, while the engine control unit (ECU) determines the misfire on the basis of the output from the crank angle speed variation distinction circuit 9 when running the internal combustion engine (E) in the low speed range. When running the internal combustion engine (E) in the intermediate speed range, the engine control unit (ECU) determines the misfire on the basis of the output from both or one of the crank angle speed variation distinction circuit 9 and the peak value distinction circuit 7 so as to inform an operator of the misfire to check or diagnose the internal combustion engine (E). In this instance, the peak value distinction circuit 7 compares the peak hold value P1 after the end of the spark action to the peak hold value P2 after the end of the spark action of the spark plug of which cylinder is in the exhaust stroke following the explosion stroke so as to determine the misfire when the peak hold value P1 is greater than two times of the peak hold value P2 (e.g. P1 > 2P2). With the structure thus far described, the signal generator 42 produces a pulse signal to on-off actuate each primary coil of the ignition coils 1, 2 so as to flow a pulse-like primary current in the primary circuit as shown at (1a) in Fig. 2. Across each of the spark plugs 11, 21, 22, 12 installed in the first ∼ fourth cylinders H1 ∼ H4, the spark plug voltage is applied as shown at (2a) in Fig. 2. The spark discharge voltage waveform (A) has a high and short voltage waveform portion (A1) due to capacitive discharge, and sustaining a gentle voltage waveform portion (A2) due to inductive discharge following the high voltage waveform portion (A1) to culminate a peak voltage portion (A3) near the end of the spark action of the spark plugs. A spark discharge waveform (B) appears after the end of the spark action of the spark plug of which cylinder is in the exhaust stroke, is substantially analogous to the spark discharge voltage waveform (A) except for the 1/2 scale. The the spark discharge voltage waveform (A) appears generally in synchronization with the spark discharge waveform (B), but the latter is initiated earlier than the former because of the low pressure of the cylinder. As shown at (3a) in Fig. 2, the voltage detector circuit 6 receives a peak hold reset signal, and totaling a voltage waveform appeared in the spark plug of the first cylinder H1 and an inverted voltage waveform appeared in the spark plug of the second cylinder H2. This makes it possible to appear a peak hold voltage waveform of the spark plug voltage stepped-up in the spark plug after the end of its spark action as shown at (4a) in Fig. 2. In the same manner, the voltage detector circuit 6 totals a voltage waveform appeared in the spark plug of the third cylinder H3 and an inverted voltage waveform appeared in the spark plug of the fourth cylinder H4 so as to produce a peak hold voltage waveform as shown at (5a) in Fig. 2. Each level of the peak hold voltage waveforms is detected by the sampling signal generated by the engine control unit (ECU) as shown at (6a) in Fig. 2. The peak value distinction circuit 7 compares the first totaled waveform (4a) and the second totaled waveform (5a) every other single unit wave so as to determine the misfire when one of the waveforms is higher than twice the other (e.g. level L). In a second embodiment of the invention, the spark plug voltages are simultaneously established in the two spark plugs connected to the same ignition coil. One is on the basis of the explosion stroke, and other is on the basis of the exhaust stroke. The peak value distinction circuit 7 compares the two spark plug voltage levels, and the polarity-opposed spark plug voltages are totaled. The peak value distinction circuit 7 determines the misfire when the peak hold value Po of the totaled voltage level exceeds a predetermined value. The voltage detector circuit 6 totals the voltages across the spark plugs each installed in the cylinders H1 ∼ H4 as shown at (7a) in Fig. 3. The totaled voltage is inverted in the negative side to detect the peak hold voltage as shown at (8a) in Fig. 3. In this instance, the peak value distinction circuit 7 compares the peak hold value to an integration of the peak hold value multiplied by a constant number (e.g. 2 to obtain the level L), and determines the misfire when the peak hold value exceeds the level L. According the embodiments of the invention as claimed, the spark plug voltage levels are compared which are appeared simultaneously or before and after the ignition timing by effectively utilizing the characteristics of the dual-polarity type distributorless igniter device 100. Upon detecting the misfire, this makes it possible to obviate experimental test data which correspond the spark plug voltage level to the running conditions of the internal combustion engine (E). Fig. 4 shows a third embodiment of the invention in which a distributor type ignition device is incorporated into the four-cylinder internal combustion engine (E). In this instance, the corresponding reference numerals in Fig. 4 are identical to those in Fig. 1. Numeral 3 designates a single-polarity type ignition coil, numeral 31 a distributor, and numeral 53 a voltage divider circuit which divides a voltage in a primary circuit of the ignition coil 3 by resistors 54, 55. Numeral 62 is a peak value detector circuit which detects the voltage of the voltage divider circuit 53, and maintains the peak hold of the detected voltage depending on the signal from the signal generator 42. Numeral 71 is a misfire distinction circuit which detects the misfire by comparing the reference level with the peak hold value maintained by the peak value detector circuit. As shown in the third embodiment of the invention, the single-polarity type ignition coil 3 is used in the ignition device with the distributor 31 attached. A voltage across electrodes of a spark plug 10 is determined by detecting a voltage across the primary circuit of the ignition coil 3. As a result, a stable zero voltage of the voltage divider circuit 53 is obtained so that the misfire distinction circuit readily determines the misfire by comparing the peak value of the peak value detector circuit 62 with the reference level. Referring to Fig. 5 in which the misfire is detected by the peak value detector means according to a third embodiment of the invention, it is observed that the voltage across the spark plug electrodes can be determined by detecting the voltage across the primary circuit of the ignition coils 1, 2 in the ignition device (DLI). In this instance, the voltage detector circuit 6 detects in the primary circuit the total sum of the voltage level appeared in the spark plug of which cylinder is in the explosion stroke, and the voltage level appeared in the spark plug of which cylinder is in the exhaust stroke. The former voltage level significantly changes depending on whether or not the misfire occurs as opposed against the latter voltage which is maintained stable. Therefore, whether or not the misfire occurs is readily determined depending on the voltage level across the primary circuit of the ignition coils 1, 2. 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 ignition coil (1,2;3;201) arranged to be on-off activated by a primary current interruptor circuit (4;241,242), the ignition coil being for connection to a spark plug (11,12,21,22;203) installed in a cylinder of an internal combustion engine (E) ; peak voltage detector means (6,62,221) arranged to detect the peak voltage arising across the electrodes of the spark plug after the end of the spark action; peak voltage value distinction means (7,71,220) arranged to recognise misfire by comparing the voltage level detected by the peak voltage detector means (6), after the end of the spark action, across a spark plug of a cylinder which is in a compression stroke with a voltage level arising, after the end of the spark action, across the spark plug of a cylinder when this cylinder is in an exhaust stroke, and to recognise misfire when a difference of the two voltage levels exceeds a predetermined value; crank angle sensor (8) arranged to sense the angle of the crank shaft of the internal combustion engine; and crank angle variation distinction means (9) arranged to recognise misfire on the basis of the variation of angles detected by the crank angle sensor; and means (ECU) arranged to indicate misfire on the basis of the peak voltage distinction means when the internal combustion engine is running in a high speed range and on the basis of the crank angle variation distinction means when the internal combustion engine is running in a low speed range. A misfire detector device according to claim 1, wherein a dual-polarity type distributorless igniter (100) is provided in which each end of the secondary circuit (L2) of the ignition coil (1,2) is connected to a respective spark plug (11,21,12,22). A misfire detector device according to claim 1 or 2, wherein the peak value distinction means is arranged to compare the voltage level detected by the peak voltage detector means after the end of the spark action across a spark plug in a cylinder which is in a compression stroke with a voltage level detected, after the end of the spark action, across the same spark plug when its cylinder is in an exhaust stroke following the compression stroke and expansion strokes. A misfire detector device according to claim 1 or 2, wherein the peak voltage value distinction means (62) is arranged to compare the voltage level detected by the peak voltage detector means, after the end of the spark action, across a first spark plug in a cylinder which is in a compression stroke with a voltage level detected, after the end of the spark action, across a second spark plug in a cylinder which is in the exhaust stroke in synchronization with said compression stroke. A misfire detector device according to any one of the preceding claims, wherein the crank angle variation distinction means (9) is arranged to recognise misfire when the variation of angles detected by the crank angle sensor exceeds a predetermined value. A misfire detector device according to any one of the preceding claims, wherein said peak voltage detector means is provided on the 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