JP2011007124A - Ignition device and ion current detection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ignition device reducing noise included in ion current.SOLUTION: The ignition device 10 includes a discharge electrode 24 electrically connected to a secondary coil 13 and keeping a secondary gap 29 with a stem 34, and a diode element 25 connected between the secondary coil 13 and the stem 34 and connected in parallel with the second gap 29 so as to make ion current flow from the secondary coil 13 side to the stem 34 side. Electricity is discharged at the secondary gap 29 by applying plug discharge voltage generated at the secondary coil 13 side on the discharge electrode 24, and electricity is discharged at a first gap 36 by applying discharge voltage based on the discharge on the stem 34.

Description

  The present invention relates to an ignition device having an ion current detection function and an ion current detection system.

  Conventionally, there has been known a spark plug in which a center electrode is held in a center through hole provided in an insulator and the insulator is held by a metal shell. A ground electrode is joined to the metal shell so as to face the center electrode. When a high voltage is applied between the center electrode and the ground electrode, a discharge occurs between the center electrode and the ground electrode, and the air-fuel mixture in the combustion chamber burns.

  At this time, the presence or absence of combustion in the combustion chamber can be determined by detecting the ionic current flowing through the spark plug. The ion current is a current that flows between the center electrode of the spark plug and the metal shell (ground electrode) due to the ions generated by the combustion of the air-fuel mixture in the combustion chamber.

  However, when a discharge voltage is applied to the center electrode, a high voltage is applied between the center electrode and the metal shell, and charges are accumulated in the insulator due to the high voltage. For this reason, the charge remaining on the insulator causes noise of the ionic current, and the detection accuracy of the ionic current is lowered.

  Therefore, Patent Document 1 proposes a spark plug in which a conductive film is formed on the surface of an insulator and the conductive film and the metal shell are electrically connected. Thereby, the electric charge accumulated in the insulator via the conductive film can be released to the metal shell.

JP 2000-68031 A

  However, in the above conventional technique, since the conductive film formed on the insulator is exposed to the combustion chamber, the conductive film is exposed to the combustion in the combustion chamber and the combustion is repeatedly performed, so that the conductive film becomes the insulator. There is a problem of peeling off. As a result, when a discharge voltage is applied to the center electrode, the charge is likely to remain in the insulator, and this charge causes noise of the ion current, and the detection accuracy of the ion current decreases.

  In view of the above points, an object of the present invention is to provide an ignition device and an ion current detection system that can reduce noise included in an ion current.

  In order to achieve the above object, according to the first aspect of the present invention, a current is supplied to the primary coil (12) of the ignition coil (11) and a current is supplied to the secondary coil (13) of the ignition coil (11). By inducing, a discharge is caused in the first gap (36) of the spark plug (30), and combustion ions generated in the first gap (36) when the fuel is burned by the discharge are detected as an ionic current. Thus, the ignition device includes an ion current detector (18) for detecting combustion and misfire of the engine, and the first gap (between the spark plug (30) and the secondary coil (13)). 36) is provided in series with a second gap (29), and a diode element (25) is connected in parallel to the second gap (29). The diode element (25) is connected to the secondary coil (13). ) Point from the side It is connected in parallel to the second gap (29) so that an ion current flows on the plug (30) side and the polarity is such that discharge occurs in the second gap (29) when the spark plug (30) is discharged. It is characterized by.

  According to this, since the voltage exceeding the dielectric breakdown voltage of the second gap (29) is applied to the spark plug (30), the voltage is applied to the spark plug (30) and then applied to the first gap (36). The time until discharge occurs is shorter than the time from when voltage is directly applied to the spark plug (30) until discharge occurs in the first gap (36). For this reason, since the time for which a voltage is applied to the spark plug (30) is also shortened, the amount of charge accumulated in the spark plug (30) can be reduced. Therefore, noise included in the ionic current can be reduced.

  In the second aspect of the present invention, a current is passed through the primary coil (12) of the ignition coil (11) to the secondary coil (13) side of the ignition coil (11) with respect to the spark plug (30). By generating a plug discharge voltage, a discharge is caused in the first gap (36) of the spark plug (30), and combustion ions generated in the first gap (36) when the fuel is burned by the discharge are generated. An ignition device having an ion current detector (18) for detecting combustion and misfire of an engine by detecting it as an ion current, which is electrically connected to the secondary coil (13) and ignited A discharge electrode (24) forming a second gap (29) between the plug (30), a secondary coil (13) and a secondary coil are connected between the secondary coil (13) and the spark plug (30). (13) Ignition plastic from the side A diode element (25) connected in parallel to the second gap (29) so that an ionic current flows on the (30) side, and the plug discharge voltage generated on the secondary coil (13) side is discharged A discharge occurs in the second gap (29) when applied to the electrode (24), and a discharge voltage based on this discharge is applied to the spark plug (30) so that a discharge occurs in the first gap (36). It is characterized by becoming.

  According to this, since the discharge voltage exceeding the dielectric breakdown voltage of the second gap (29) is applied to the spark plug (30), the first gap (36) is applied after the discharge voltage is applied to the spark plug (30). ) Is shorter than the time from when the plug discharge voltage is directly applied to the spark plug (30) to when the first gap (36) is discharged. For this reason, since the time during which the discharge voltage is applied to the spark plug (30) is also shortened, the amount of charge accumulated in the spark plug (30) can be reduced. Therefore, noise included in the ionic current can be reduced.

  In the invention according to claim 3, the cylindrical metal shell (31), the insulator (32) held in the metal shell (31), and one end side (32a) of the insulator (32) are held. The center electrode (33), the stem (34) held on the other end side (32b) of the insulator (32) and electrically connected to the center electrode (33), and one end of the metal shell (31) The ignition coil (11) on the primary side with respect to a spark plug (30) having a ground electrode (35) opposed to the tip of the center electrode (33) through the first gap (36) A current is passed through the coil (12) to generate a plug discharge voltage on the secondary coil (13) side of the ignition coil (11), thereby causing a discharge in the first gap (36). Generated in the first gap (36) when the fuel burns An ignition device including an ion current detector (18) that detects combustion and misfire of an engine by detecting combustion ions as an ion current, and is electrically connected to the secondary coil (13). In addition, the discharge electrode (24) forming the second gap (29) between the stem (34) and the secondary coil (13) and the stem (34) are connected to the secondary side. A diode element (25) connected in parallel to the second gap (29) so that an ionic current flows from the coil (13) side to the stem (34) side, and is generated on the secondary coil (13) side When the plug discharge voltage is applied to the discharge electrode (24), a discharge occurs in the second gap (29), and a discharge voltage based on this discharge is applied to the stem (34) to thereby generate the first gap (36). ) Discharge to Characterized in that it is adapted to occur.

  According to this, since the discharge voltage exceeding the dielectric breakdown voltage of the second gap (29) is applied to the stem (34) of the spark plug (30), the discharge voltage is applied to the stem (34) after the discharge voltage is applied. The time until discharge occurs in one gap (36) is shorter than the time from when the plug discharge voltage is directly applied to the stem (34) until discharge occurs in the first gap (36). For this reason, since the time during which the discharge voltage is applied between the metal shell (31) and the center electrode (33) is also shortened, the insulator (32) between the metal shell (31) and the center electrode (33). It is possible to reduce the amount of charge accumulated in the. Therefore, noise included in the ionic current can be reduced.

  In invention of Claim 4, it forms as a hollow part (21) into which the other end side (32b) of an insulator (32) is inserted, and a dent of a part of the bottom part of a hole part (21), and a spark plug ( 30) a stem (34) is inserted, and a recess (23) in which a tip (24a) facing the stem (34) of the discharge electrode (24) is exposed from the bottom surface of the recess, and a hole (21) The other end side (32b) of the insulator (32) is in contact with a portion different from the portion where the concave portion (23) is formed in the bottom portion of the base, so that the gap between the discharge electrode (24) and the stem (34) is reached. And a step portion (28) that forms the second gap (29).

  According to this, the step portion (28) determines the position of the other end side (32b) of the insulator (32) in the hole portion (21) and the position of the stem (34) in the recess portion (23). The second gap (29) can be easily formed between the tip (24a) of (24) and the stem (34).

  The invention according to claim 5 is characterized in that the tip (24a) of the discharge electrode (24) is pointed. According to this, since the tip portion (24a) of the discharge electrode (24) is sharp, the electric field concentrates on the tip portion (24a), so that discharge easily occurs in the second gap (29). For this reason, the dielectric breakdown voltage of the second gap (29) becomes constant, and stable discharge can be caused in the second gap (29).

  Although the ignition device has been described above, the same can be said for the ion current detection system including the ion current detector (18). That is, in the invention according to claim 6, the ignition coil (11), the power source (50) connected to the primary coil (12) side of the ignition coil (11), and the secondary of the ignition coil (11) An ionic current detector (18) connected to one end of the side coil (13), and a spark plug (30) connected to the other end of the secondary coil (13). ) Is caused to flow through the primary coil (12) based on the power source (50) to induce a current in the secondary coil (13) of the ignition coil (11), whereby the first gap ( 36), and the combustion ions generated in the first gap (36) when the fuel is burned by the discharge are detected as ion currents by the ion current detector (18), so that the combustion of the engine And Io to detect misfire In the current detection system, a second gap (29) in series with the first gap (36) is provided between the spark plug (30) and the secondary coil (13), and the second gap ( 29) is connected in parallel with the diode element (25). The diode element (25) has an ionic current flowing from the secondary coil (13) side to the spark plug (30) side and the spark plug (30). The second gap (29) is connected in parallel so that the second gap (29) has a polarity that generates a discharge during discharge.

  Thus, also when comprised as a system provided with the ion current detector (18), a voltage exceeding the dielectric breakdown voltage of the second gap (29) is applied to the spark plug (30). For this reason, the time from when the voltage is applied to the spark plug (30) until the discharge occurs in the first gap (36) is the time from when the voltage is directly applied to the spark plug (30) to the first gap (36). It can be made shorter than the time until discharge occurs. Accordingly, the time during which the voltage is applied to the spark plug (30) is also shortened, so that the amount of charge accumulated in the spark plug (30) can be reduced. Therefore, noise included in the ionic current can be reduced.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

1 is an overall cross-sectional view of an ignition device according to a first embodiment of the present invention. FIG. 2 is a partial cross-sectional view when the ignition device shown in FIG. 1 is attached to the ignition plug. FIG. 2 is an equivalent circuit diagram of an ignition system including the ignition device shown in FIG. 1. It is the figure which showed the circuit structure of the ion current detector. FIG. 5A is a diagram of the potential at the point X shown in FIG. 3, and FIG. 5B is a diagram of the potential at the point Y shown in FIG. (A) is when the second gap is not provided in the ignition device, (b) is when the second gap is provided in the ignition device, and (c) is Y when the second gap is larger than (b). It is the figure which showed the electric potential of a point, respectively. It is the figure which showed the waveform of the discharge voltage applied to a spark plug. It is the figure which showed the relationship between the length of a 2nd gap, and the amount of noise generation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. The ignition device shown in the present embodiment is, for example, a stick coil in which an ignition coil and an igniter are integrated.

  FIG. 1 is an overall cross-sectional view of an ignition device 10 according to the present embodiment. FIG. 2 is a partial cross-sectional view of the ignition plug 30 when the ignition device 10 is mounted. FIG. 3 is an equivalent circuit diagram of an ignition system (ion current detection system) including the ignition device 10 shown in FIG.

  Based on an ignition signal input from an engine ECU (not shown), the ignition device 10 causes a current to flow through the primary coil 12 of the ignition coil 11 shown in FIG. By generating a working voltage, the spark plug 30 is caused to discharge.

  In general, as shown in FIG. 2, the spark plug 30 includes a metal shell 31, an insulator 32, a center electrode 33, a stem 34, and a ground electrode 35. The insulator 32 is held in a cylindrical metal shell 31. Further, the insulator 32 has a through-hole penetrating, the center electrode 33 is held in the through-hole on one end side 32 a of the insulator 32, and the stem 34 is held in the through-hole on the other end side 32 b of the insulator 32. At the same time, it is electrically connected to the center electrode 33. The ground electrode 35 is welded to one end of the metal shell 31 and is opposed to the tip of the center electrode 33 through the first gap 36. Such a spark plug 30 is attached to each cylinder of the engine.

  On the other hand, as shown in FIG. 1, the ignition device 10 includes an ignition coil 11, an igniter 14, a case 15, and a holder 16.

  The ignition coil 11 includes a primary side coil 12 and a secondary side coil 13. Specifically, the secondary side coil 13 is wound around the outer periphery of the rod-shaped iron core, and the primary side coil 12 is wound around the outer periphery of the secondary side coil 13.

  As shown in FIG. 3, one end side of the primary coil 12 of the ignition coil 11 is connected to a power source 50 outside the ignition device 10, and the other end side is connected to the igniter 14. The power supply 50 is a vehicle battery. One end side of the secondary coil 13 of the ignition coil 11 is connected to the igniter 14, and the other end side is electrically connected to the discharge electrode 24 shown in FIG.

  The igniter 14 is an electronic component for causing a primary current to flow through the primary coil 12 of the ignition coil 11. Such an igniter 14 includes a switch unit 17 and an ion current detector 18 as shown in FIG.

  The switch unit 17 inputs an ignition signal from an engine ECU (not shown), and inputs a current based on the ignition signal to a switching element such as an IGBT provided in the switch unit 17 to drive the switching element. When the switching element is turned on, a primary current based on the power source 50 flows through the primary coil 12 of the ignition coil 11.

  The ion current detector 18 detects combustion ions generated in the first gap 36 when the fuel is burned by the discharge of the spark plug 30 as an ion current. The ion current detector 18 is connected to the secondary side coil 13 of the ignition coil 11, and an ion current flowing through the secondary side coil 13 is input thereto.

  FIG. 4 is a diagram showing a circuit configuration of the ion current detector 18. As shown in this figure, the ion current detector 18 is configured as a Zener diode 19 and a capacitor 20 connected in parallel. In FIG. 4, the Zener diode 19 and the capacitor 20 are drawn as a part of the configuration of the ion current detector 18, but circuits such as a resistance element and a signal amplifier circuit are actually included. In FIG. 4, these resistance elements are omitted.

  In such a configuration of the ion current detector 18, the ion current flows from the GND to the secondary coil 13 side of the ignition coil 11 through the capacitor 20 as indicated by the arrow path shown in FIG. 4. The ion current detected by the ion current detector 18 is used as an engine output signal for determining a combustion state such as normal combustion of the engine, misfiring, smoldering detection of a pre-ignition (early ignition) plug, etc. Is output. That is, the potential on the GND side of the capacitor 20 is output to the engine ECU as an ion output signal. Thus, the engine ECU determines the combustion state based on the ion output signal. The ion output signal is a signal processed by a signal amplification circuit or the like in the ion current detector 18.

  The case 15 is an external appearance part of the ignition device 10 and is made of resin. The case 15 has a hollow cylindrical shape, and has a hole 21 that is open on one end side of the case. The hole 21 is a portion into which the other end 32b of the insulator 32 is inserted. The diameter of the hole 21 is substantially the same as the diameter of the insulator 32.

  The case 15 incorporates the ignition coil 11 in the hole 21, and houses the igniter 14 on the other end side of the case 15. Further, a connector 22 is formed on the other end side of the case 15 so that wiring is connected.

  The holder 16 is for applying a voltage to the spark plug 30 and is insert-molded in the case 15 so as to be positioned between the hole 21 on one end side of the case 15 and the ignition coil 11.

  Such a holder 16 includes a recess 23, a discharge electrode 24, a diode element 25, and terminals 26 and 27.

  The concave portion 23 is a portion provided on one end side of the holder 16 and connected to the hole portion 21. In other words, the concave portion 23 is a portion formed as a partial depression at the bottom of the hole 21. The diameter of the recess 23 is substantially the same as the diameter of the stem 34 of the spark plug 30. The stem 34 of the spark plug 30 is inserted into the recess 23.

  Since the diameter of the hole 21 of the case 15 is the same as the diameter of the insulator 32 and is larger than the diameter of the recess 23, the diameter of the hole 21 and the diameter of the recess 23 are formed inside the hole 21. The end surface on the one end side of the holder 16 corresponding to the difference is exposed. The end surface of the holder 16 serves as a stepped portion 28 inside the hole 21. That is, the stepped portion 28 is a portion different from the portion where the concave portion 23 is formed in the bottom portion of the hole portion 21.

  The discharge electrode 24 is a rod-like electrode that is electrically connected to the secondary coil 13 of the ignition coil 11 and causes discharge between the ignition coil 11 and the stem 34 of the ignition plug 30. For this reason, the discharge electrode 24 is insert-molded in the holder 16 so as to be exposed from the bottom surface of the recess 23.

  Further, as shown in FIG. 2, the discharge electrode 24 faces the stem 34 with a predetermined interval H when the other end 32 b of the insulator 32 contacts the stepped portion 28. This predetermined interval H is referred to as a second gap 29. That is, the second gap 29 is formed between the discharge electrode 24 and the stem 34. The length of the second gap 29 is determined by the position of the stepped portion 28 that defines the insertion amount of the insulator 32 inserted into the hole 21 of the case 15 and the depth of the concave portion 23 of the holder 16.

  Thus, the stepped portion 28 in the hole 21 determines the position of the other end side 32 b of the insulator 32 in the hole 21 of the case 15 and the position of the stem 34 in the recess 23. Therefore, the second gap 29 can be easily formed between the distal end portion 24 a of the discharge electrode 24 and the stem 34. Further, the length of the second gap 29 can be adjusted by adjusting the formation position of the stepped portion 28.

  Further, the tip 24 a of the discharge electrode 24 facing the stem 34 is sharp. That is, the second gap 29 corresponds to the distance between the tip of the distal end portion 24 a of the discharge electrode 24 and the stem 34. The length of the second gap 29 is, for example, about 10 mm to 20 mm. The shape of the front end portion 24a of the discharge electrode 24 is, for example, a pyramid shape or a cone shape.

  The diode element 25 is for flowing an ionic current. The diode element 25 is connected between the secondary coil 13 and the stem 34 of the ignition coil 11 and is parallel to the second gap 29 so that an ion current flows from the secondary coil 13 side to the stem 34 side. It is connected to the. The diode element 25 is installed in such a polarity that discharge occurs in the second gap 29 when the spark plug 30 is discharged.

  That is, as shown in FIG. 3, as a circuit configuration in the ignition device 10 and the ignition system, a second gap 29 in series with the first gap 36 is provided between the ignition plug 30 and the secondary coil 13. Further, a diode element 25 is connected in parallel to the second gap 29. The diode element 25 is connected to the second gap 29 so that the ion current flows from the secondary coil 13 side to the spark plug 30 side and has a polarity that causes the second gap 29 to discharge when the spark plug 30 is discharged. Connected in parallel.

  Thus, from the viewpoint of an equivalent circuit, the first gap 36 of the spark plug 30 and the second gap 29 of the ignition device 10 are located in series, and the diode element 25 is connected in parallel to the second gap 29. Actually, the parallel connection means that one end of the diode element 25 is electrically connected to the discharge electrode 24 and the other end of the diode element 25 is electrically connected to the stem 34 of the spark plug 30 as described above. It corresponds to that.

  In the present embodiment, when a discharge occurs in the first gap 36 of the spark plug 30, the spark plug 30 side of the diode element 25 has a negative voltage, so the ion element is detected from the ion current detector 18 for detecting the ionic current. The voltage applied to 25 must be a positive voltage. Therefore, as shown in FIG. 3, the anode of the diode element 25 is electrically connected to the secondary coil 13 of the ignition coil 11, and the cathode is electrically connected to the stem 34 of the ignition plug 30.

  One of the terminals 26 and 27 is for electrically connecting the anode of the diode element 25 and the discharge electrode 24, and the other is for electrically connecting the diode element 25, the cathode and the stem 34. is there. The diode element 25 and the terminals 26 and 27 are connected by a conductive wire.

  Each of the terminals 26 and 27 has a ring shape, for example. The one terminal 26 is insert-molded in the holder 16 so that the inner wall surface of the ring contacts the discharge electrode 24. The other terminal 27 is insert-molded in the holder 16 so that the inner wall surface of the ring is exposed on the wall surface of the recess 23 and the stem 34 inserted into the recess 23 is in contact with the stem 34. Yes.

  The above is the overall configuration of the ignition device 10 according to the present embodiment, and the overall configuration of the ignition system.

  Next, the ignition operation and the ion current detection operation in the ignition device 10 will be described with reference to the drawings. 5A is a diagram of the potential at the point X shown in FIG. 3, and FIG. 5B is a diagram of the potential at the point Y shown in FIG. The potential at point X is the potential between the secondary coil 13 and the discharge electrode 24, and the potential at point Y is the potential of the stem 34 of the ignition coil 11. Hereinafter, the voltage at point X is referred to as plug discharge voltage, and the voltage at point Y is referred to as discharge voltage.

  In the voltage diagrams shown in FIG. 5, the horizontal axis indicates time, and the vertical axis indicates negative voltage. The following operations are performed for each cylinder of the engine.

  As a general operation of the ignition device 10 and the ignition system, the first gap of the spark plug 30 is obtained by causing a current to flow through the primary coil 12 of the ignition coil 11 and inducing a current through the secondary coil 13 of the ignition coil 11. 36 is caused to discharge. Further, the combustion current generated in the first gap 36 when the fuel is burned by the discharge of the spark plug 30 is detected by the ion current detector 18 as an ion current, thereby detecting engine combustion and misfire. Become.

  In the present embodiment, the plug discharge voltage generated on the secondary coil 13 side is applied to the discharge electrode 24 to cause a discharge in the second gap 29, and the discharge voltage based on this discharge is applied to the stem 34. As a result, discharge occurs in the first gap 36. These plug discharge voltage and discharge voltage are negative voltages.

  Specifically, first, for example, a high-level ignition signal is input to the ignition device 10 from the engine ECU. The ignition signal is input to the switch unit 17 of the igniter 14, and the IGBT is turned on. As a result, a primary current flows through the primary coil 12 of the ignition coil 11 and magnetic energy is stored in the ignition coil 11.

  Further, since there is a stray capacitance between the point X and the engine, the ion current due to the primary current flowing through the primary coil 12 is generated in the ion current detector 18 by the spark plug 30 and the diode element 25. The secondary side coil 13, the capacitor 20, GND, and the route through the engine flow.

  The timing when the ignition signal falls from the high level to the low level is the ignition timing. That is, by suddenly interrupting the primary current flowing through the primary coil 12, the magnetic energy stored in the ignition coil 11 flows from the secondary coil 13 into the discharge electrode 24 as a discharge current. As a result, as shown in FIG. 5A, the potential at the point X rises, and when the potential exceeds the dielectric breakdown voltage of the second gap 29, discharge occurs in the second gap 29.

  Due to the discharge occurring in the second gap 29, a discharge voltage based on the discharge is applied to the stem 34 of the spark plug 30. In this case, as shown in FIG. 5B, a discharge voltage exceeding the breakdown voltage of the second gap 29 is suddenly applied to the spark plug 30. That is, a high voltage is applied to the stem 34 of the spark plug 30 from the beginning instead of a voltage that gradually increases as shown in FIG.

  As a result, a discharge voltage is applied to the first gap 36 of the spark plug 30, and when the discharge voltage exceeds the dielectric breakdown voltage of the first gap 36, the fuel is ignited and combustion occurs in the combustion chamber. As described above, since the distal end portion 24a of the discharge electrode 24 is sharp, an electric field concentrates on the distal end portion 24a, and discharge is likely to occur in the second gap 29. For this reason, the dielectric breakdown voltage of the second gap 29 becomes constant, and stable discharge can be caused in the second gap 29.

  When ignition is performed, flame ions of fuel and combustion ions of thermal dissociation ions of NO are generated in the combustion chamber of the engine. At this time, current flows through the spark plug 30, the diode element 25, the secondary coil 13, and the Zener diode 19, and a potential difference is generated between both ends of the Zener diode 19, so that the capacitor 20 is charged.

  During the charging period of the capacitor 20, a current (arc current) indicated by a path indicated by an arrow in FIG. 4 flows. When charging of the capacitor 20 is completed, a current due to coil residual magnetism (coil residual magnetic current) flows. The period after the coil residual magnetic current flows is a misfire monitoring period in the engine ECU.

  That is, during the misfire monitoring period, if the magnetic energy stored in the ignition coil 11 is lost, the flow of the coil residual magnetic current in the secondary coil 13 stops, but at this time, the capacitor 20 is charged. Therefore, a potential difference is generated between both ends of the capacitor 20. For this reason, the capacitor 20 serves as an ion power source for ion detection, and an ion current flows along the path of the arrow in FIG. 4 through the ions generated in the gap of the spark plug 30. The voltage of the ion power source (the voltage on the high side of the capacitor 20) is opposite in polarity to the plug discharge voltage.

  When normal combustion occurs in the engine, an ionic current indicating normal combustion flows during the misfire monitoring period. Therefore, the engine ECU can determine that normal combustion has been performed in the engine by making a determination using a threshold value for the ion output signal input during the misfire monitoring period.

  Further, when the fuel is misfired without burning, combustion does not occur in the combustion chamber, so that combustion ions are not generated. Therefore, current due to combustion ions does not flow in the path indicated by the arrow in FIG. Therefore, the engine ECU can detect misfire by determining that the ion output signal at the time of misfire becomes flat during the misfire monitoring period using the threshold value.

  It is also possible to detect preignition that occurs by igniting the fuel earlier than the ignition timing. Since preignition occurs earlier than normal combustion, it is also possible to detect preignition by detecting the ion current flowing in the path indicated by the arrow in FIG. 4 during the preignition monitoring period earlier than the misfire monitoring period. .

  Next, the role of the second gap 29 provided in the ignition device 10 will be described with reference to FIGS.

  6A shows a case where the second gap 29 is not provided in the ignition device 10, FIG. 6B shows a case where the second gap 29 is provided in the ignition device 10, and FIG. The potential at the point Y when the second gap 29 is larger than b) is shown.

  As shown in FIG. 6A, when the second gap 29 is not provided in the ignition device 10, the potential at the point Y gradually increases. For this reason, since a high voltage is continuously applied between the metal shell 31 and the center electrode 33 of the spark plug 30, electric charges are charged in the insulator 32 between the metal shell 31 and the center electrode 33 while the high voltage is applied. Will continue to accumulate. Here, T is the time during which the voltage is applied to the insulator 32.

  On the other hand, as shown in FIG. 6B, when the ignition device 10 is provided with the middle (for example, about 5 mm) second gap 29, as described above, after the discharge that has occurred in the second gap 29. Since the discharge voltage is applied to the spark plug 30, the time T during which the voltage is applied to the insulator 32 is shorter than when the second gap 29 shown in FIG. 6A is not provided. That is, the time T from when the discharge voltage is applied to the stem 34 until the first gap 36 is discharged is the time T from when the plug discharge voltage is directly applied to the stem 34 until the first gap 36 is discharged. Shorter than.

  Furthermore, as shown in FIG. 6C, when the ignition device 10 is provided with a large (for example, about 10 mm to 20 mm) second gap 29, the ignition plug 30 has a length corresponding to the length of the second gap 29. Since a discharge voltage exceeding the dielectric breakdown voltage is applied, the time T during which the voltage is applied to the insulator 32 is further shorter than that shown in FIG.

  Thus, by increasing the length of the second gap 29, the time T of the discharge voltage applied to the spark plug 30 is shortened.

  FIG. 7 shows the waveform of the discharge voltage applied to the spark plug 30. As described above, when a discharge voltage is applied to the spark plug 30 through the second gap 29, the plug discharge voltage is not directly applied to the ignition coil 11 from the secondary coil 13, and the hatched lines shown in FIG. No voltage is applied during the time indicated by the area.

  For this reason, in the ignition coil 11, no charge corresponding to the area indicated by the oblique lines shown in FIG. 7 remains in the insulator 32. As shown in FIG. 6, as the length of the second gap 29 increases, that is, as the time T decreases, the area of the hatched area increases, and therefore the amount of charge remaining in the insulator 32 decreases. .

  FIG. 8 is a diagram showing the relationship between the length of the second gap 29 and the amount of noise generated. As the length of the second gap 29 increases, the area of the region indicated by the oblique lines shown in FIG. 7 increases and the time T decreases, so the amount of charge remaining in the insulator 32 decreases. Therefore, as shown in FIG. 8, the amount of noise generated in the ionic current decreases as the length of the second gap 29 increases.

  As described above, the second gap 29 serves to prevent the charge from remaining in the insulator 32 of the spark plug 30.

  As described above, in the present embodiment, the second gap 29 is provided between the discharge electrode 24 of the ignition device 10 and the stem 34 of the spark plug 30, and after the discharge is caused in the second gap 29, the ignition is performed. The discharge 30 is caused to occur in the first gap 36 of the plug 30.

  According to this, since the plug discharge voltage is not directly applied from the secondary coil 13 of the ignition coil 11 to the spark plug 30, but a discharge voltage exceeding the dielectric breakdown voltage of the second gap 29 is applied. The time during which the discharge voltage is applied can be made shorter than when the plug discharge voltage is directly applied to the plug 30. For this reason, since the time during which the discharge voltage is applied to the spark plug 30 is also shortened, the amount of charge accumulated in the spark plug 30 can be reduced. That is, since the time during which the discharge voltage is applied between the metal shell 31 and the center electrode 33 is shortened, the amount of electric charge remaining on the insulator 32 between the metal shell 31 and the center electrode 33 can be reduced. it can. Therefore, noise included in the ionic current can be reduced.

  The plug leg length to which the insulator 32 is exposed to the combustion chamber is usually the length of the insulator 32 between the central electrode 33 exposed from the insulator 32 and the metal shell 31. When a conductive film is formed on the insulator 32 as in the prior art, the above plug leg length is the length of the insulator 32 from the center electrode 33 to the conductive film. The plug leg length becomes shorter than when the film is not formed. For this reason, the so-called rust resistance in which carbon generated with combustion of the air-fuel mixture adheres to the surface of the insulator 32 is deteriorated. However, in this embodiment, since the conductive film is not necessary for the insulator of the spark plug 30, the plug leg length can be ensured, and as a result, the sag resistance of the spark plug 30 is not lowered.

  Further, when a conductive film such as silver paste is formed on the insulator 32 of the spark plug 30 as in the prior art, the uniformity of the surface roughness of the silver paste is not good. The reliability of the seal will deteriorate. However, in this embodiment, since the conductive film is not necessary for the insulator 32 of the spark plug 30, the surface roughness of the surface of the insulator 32 can be secured, and as a result, the reliability of the seal between the insulator 32 and the metal shell 31 is ensured. Can be secured.

  That is, by using the ignition device 10 according to the present embodiment, it is not necessary to treat the spark plug 30 so that no electric charge remains in the insulator 32. Therefore, the conventionally used spark plug 30 can be used as it is.

(Other embodiments)
In the first embodiment, as the ignition device 10, a stick coil in which the ignition coil 11, the igniter 14, the discharge electrode 24, and the diode element 25 are integrated in the case 15 is shown. An example is shown. That is, the ignition device 10 is not provided with the ignition coil 11 or the igniter 14, and it is sufficient that at least the discharge electrode 24 and the diode element 25 are provided.

  In the first embodiment, the structure in which the holder 16 in which the discharge electrode 24 is insert-molded is housed in the case 15 is shown. However, even if the holder 16 separate from the case 15 is not prepared, the discharge electrode 24, the diode element 25, and the like may be directly insert-molded into the case 15.

  In the first embodiment, the tip 24a of the discharge electrode 24 is pointed, but this shows an example of the shape of the tip 24a. Therefore, you may use the discharge electrode 24 in which the front-end | tip part 24a is not sharp.

DESCRIPTION OF SYMBOLS 10 Ignition device 11 Ignition coil 12 Primary side coil 13 Secondary side coil 18 Ion current detector 24 Discharge electrode 25 Diode element 29 Second gap 30 Spark plug 31 Main metal fitting 32 Insulator 32a One end side 32b of insulator The other end 33 Central electrode 34 Stem 35 Ground electrode 36 First gap

Claims (6)

A current is passed through the primary coil (12) of the ignition coil (11) to induce a current in the secondary coil (13) of the ignition coil (11), whereby the first gap (36) of the spark plug (30) is obtained. ), And detects the combustion and misfire of the engine by detecting the combustion ions generated in the first gap (36) when the fuel is burned by the discharge as an ionic current. An ignition device comprising a current detector (18),
A second gap (29) in series with the first gap (36) is provided between the spark plug (30) and the secondary coil (13), and further, the second gap (29) A diode element (25) is connected in parallel,
The diode element (25) discharges into the second gap (29) when the ion current flows from the secondary coil (13) side to the spark plug (30) side and the spark plug (30) is discharged. The ignition device is connected in parallel to the second gap (29) so as to have a polarity that causes the With respect to the spark plug (30), a current is passed through the primary coil (12) of the ignition coil (11) to generate a plug discharge voltage on the secondary coil (13) side of the ignition coil (11). And causing the first gap (36) of the spark plug (30) to discharge,
Ignition equipped with an ion current detector (18) that detects combustion and misfire of the engine by detecting combustion ions generated in the first gap (36) as an ion current when the fuel is burned by the discharge. A device,
A discharge electrode (24) electrically connected to the secondary coil (13) and forming a second gap (29) with the spark plug (30);
The secondary coil (13) is connected between the spark plug (30) and the ion current flows from the secondary coil (13) side to the spark plug (30) side. A diode element (25) connected in parallel to the second gap (29),
When the plug discharge voltage generated on the secondary coil (13) side is applied to the discharge electrode (24), a discharge occurs in the second gap (29), and the discharge voltage based on the discharge is An ignition device characterized in that discharge is generated in the first gap (36) when applied to the ignition plug (30). A cylindrical metal shell (31), an insulator (32) held in the metal shell (31), and a center electrode (33) held on one end side (32a) of the insulator (32) The stem (34) held on the other end (32b) of the insulator (32) and electrically connected to the center electrode (33) is welded to one end of the metal shell (31). The primary coil (12) of the ignition coil (11) with respect to the spark plug (30) having the ground electrode (35) facing the tip of the center electrode (33) through the first gap (36). ) To cause a discharge in the first gap (36) by generating a plug discharge voltage on the secondary coil (13) side of the ignition coil (11),
Ignition equipped with an ion current detector (18) that detects combustion and misfire of the engine by detecting combustion ions generated in the first gap (36) as an ion current when the fuel is burned by the discharge. A device,
A discharge electrode (24) electrically connected to the secondary coil (13) and forming a second gap (29) with the stem (34);
The second coil is connected between the secondary coil (13) and the stem (34) and the ion current flows from the secondary coil (13) side to the stem (34) side. A diode element (25) connected in parallel to the gap (29),
When the plug discharge voltage generated on the secondary coil (13) side is applied to the discharge electrode (24), a discharge occurs in the second gap (29), and the discharge voltage based on the discharge is An ignition device characterized in that a discharge occurs in the first gap (36) when applied to the stem (34). A hole (21) into which the other end side (32b) of the insulator (32) is inserted;
The stem (34) of the spark plug (30) is inserted into the bottom of the hole (21), and the stem (34) of the discharge electrode (24) is inserted from the bottom of the recess. ) And a recessed portion (23) in which the tip portion (24a) facing the surface is exposed,
The other end side (32b) of the insulator (32) comes into contact with a portion different from the portion where the concave portion (23) is formed in the bottom portion of the hole portion (21), thereby the discharge electrode (24). The ignition device according to claim 3, further comprising a step portion (28) that forms the second gap (29) between the first gap and the stem (34).   The ignition device according to claim 3 or 4, characterized in that the tip (24a) of the discharge electrode (24) is pointed. An ignition coil (11), a power source (50) connected to the primary coil (12) side of the ignition coil (11), and one end side of the secondary coil (13) of the ignition coil (11) An ion current detector (18) connected, and a spark plug (30) connected to the other end of the secondary coil (13),
A current based on the power source (50) is passed through the primary coil (12) of the ignition coil (11) to induce a current in the secondary coil (13) of the ignition coil (11). 30) is caused to discharge in the first gap (36), and when the fuel is burned by the discharge, combustion ions generated in the first gap (36) are used as an ion current to detect the ion current detector (18). ) To detect the combustion and misfire of the engine,
A second gap (29) in series with the first gap (36) is provided between the spark plug (30) and the secondary coil (13), and further, the second gap (29) A diode element (25) is connected in parallel,
The diode element (25) discharges into the second gap (29) when the ion current flows from the secondary coil (13) side to the spark plug (30) side and the spark plug (30) is discharged. The ion current detection system is connected in parallel to the second gap (29) so as to have a polarity in which the above occurs.

Images