spark plug

Abstract

Spark plug, which includes: a tubular insulator (40) with a reduced diameter section (45) whose outer diameter narrows towards an upper end face of the spark plug (10) and an axial bore (41) extending from the upper end face to a rear end face of the spark plug (10) along an axis (O) of the spark plug (10); a central electrode (70) which is arranged in the axial bore (41); a tubular metal housing (20) arranged on an outer circumference of the insulator (40), wherein the metal housing (20) has a support section (27) on an inner circumference and a threaded section (26) on an outer circumference, wherein the support section (27) projects inwards in a radial direction of the metal housing (20) and holds the reduced diameter section (45) of the insulator (40) directly or by means of an annular seal (61) from the upper end side; a ground electrode (30) which is connected to the metal housing (20) and points to the center electrode (70) via a spark gap; a connection (53) which is located at the rear end face with respect to the threaded section (26); a detector electrode (52) provided on a section located above the upper end of a contact section (56) between the reduced-diameter section (45) and the support section (27) or the seal (61), in a space (55) formed between the outer circumference of the insulator (40) and the inner circumference of the metal housing (20), wherein the detector electrode (52) is an electrode for detecting an ion current; and a conductor (51) connecting the detector electrode (52) and the terminal (53), and wherein the detector electrode (52) and the conductor (51) are insulated from the center electrode (70), the metal housing (20) and the ground electrode (30), wherein the detector electrode (52) is provided on the insulator (40).

Description

Technical area

[0001] The present invention relates to a spark plug and, more particularly, to a spark plug capable of improving the detection accuracy of pre-ignition. Technical background

[0002] Known are a technique that distinguishes combustion conditions of an internal combustion engine by detecting an ion current generated when a flame appears between a center electrode and a ground electrode of a spark plug and reaches the center electrode and the ground electrode (Patent Documents 1 and 2), and a spark plug that detects the ion current with an electrode other than the ground electrode, which is provided and arranged close to the ground electrode (Patent Documents 3 and 4). Furthermore, a technique that adjusts or controls the ignition timing of the spark plug according to the detected internal combustion combustion conditions (Patent Document 5) is also known. According to these techniques, it is possible to accurately detect preignition that occurs when an overheated spark plug becomes a heat source, as well as preignition caused by self-ignition of carbon.The combustion state of internal combustion can be controlled according to the detection result.

[0003] Further prior art is known from DE 32 03 200 A1 and JP H04 - 148 070 A. List of cited publicationsPatent document Patent Document 1: Unexamined Japanese Patent Application Publication JP 2015 - 190 396 A Patent Document 2: Unexamined Japanese Patent Application Publication JP H04 - 133 281 A Patent Document 3: Unexamined Japanese Patent Application Publication JP H06 - 338 377 A Patent Document 4: Unexamined Japanese Patent Application Publication JP H09 - 260 023 A Patent Document 5: Unexamined Japanese Patent Application Publication JP 2014 - 109 196 A Summary of the inventionTechnical problem

[0004] However, the above techniques have the problem that they cannot accurately detect pre-ignition caused by a flame kernel occurring in the spark plug, which has been found by recent studies.

[0005] The present invention was developed to solve the above problem. Therefore, an object of the present invention is to provide a spark plug capable of improving the detection accuracy of pre-ignition caused by the flame kernel occurring in the spark plug. Solution to the problem and effects of the invention

[0006] To achieve the object, according to a spark plug according to claim 1, a tubular insulator having a reduced diameter portion whose outer diameter decreases toward a top end side of the spark plug is provided with an axial bore extending along an axis of the spark plug from the top end side toward a rear end side of the spark plug. A center electrode is arranged in the axial bore. A tubular metal shell positioned on an outer periphery of the insulator has a seating portion on an inner periphery thereof and a threaded portion on an outer periphery thereof. The seating portion protrudes inward in a radial direction of the metal shell and supports the reduced diameter portion of the insulator from the top end side directly or through an annular gasket. A ground electrode connected to the metal shell faces the center electrode via a spark gap.

[0007] A terminal is located at the rear end side with respect to the threaded portion. A detector electrode for detecting an ion current is provided at a portion located above an upper end of the contact portion between the reduced-diameter portion and the seating portion or gasket in a space formed between the outer periphery of the insulator and the inner periphery of the metal shell. The detector electrode and the terminal are connected by a conductor. The detector electrode and the conductor are insulated from the center electrode, the metal shell, and the ground electrode, and the detector electrode is provided on the insulator.

[0008] Since the detector electrode is provided in the space formed between the outer periphery of the insulator and the inner periphery of the metal shell, early detection of the flame kernel occurring inside the spark plug is possible. Therefore, it is possible to improve the detection accuracy of pre-ignition caused by the flame kernel occurring inside the spark plug.

[0009] According to a spark plug according to claim 2, a width in a direction orthogonal to an axial direction of the detector electrode is 0.5 mm or more. Since an area of ​​the detector electrode can be secured, detection sensitivity of the ion current can be ensured. Therefore, in addition to the effect of claim 1, an effect of preventing preignition from being detected incorrectly (that is, the detector electrode cannot detect preignition despite the fact that preignition occurs) can be achieved.

[0010] According to a spark plug according to claim 3, an upper end of the detector electrode is positioned below an upper end of the metal shell. Since this may make it difficult to detect the flame kernel occurring outside the space formed between the outer periphery of the insulator and the inner periphery of the metal shell, an effect of reliably and precisely detecting the flame kernel occurring in the space can be achieved in addition to the effect of claim 1 or 2.

[0011] According to a spark plug according to claim 4, an upper end of the detector electrode is positioned 6 mm or more away from an upper end of the insulator toward the rear end side. This can therefore reduce the tendency for electrical discharge to occur between the center electrode arranged in the axial bore of the insulator and the detector electrode. Thus, in addition to the effect of any one of claims 1 to 3, an effect of preventing spark wear of the detector electrode can be obtained.

[0012] According to a spark plug according to claim 5, an upper end of the detector electrode is positioned 3 mm or more away from the upper end of the contact portion toward the rear end side. Therefore, the upper end of the detector electrode can be placed in a region where the temperature increases slightly due to and according to the growth of the flame kernel.

[0013] As the temperature increases slightly, the ion current flows easily. Therefore, in addition to the effect of any one of claims 1 to 4, an effect of improving the detection accuracy of pre-ignition can be obtained.

[0014] According to a spark plug according to claim 6, a first end portion of the ground electrode is connected to the metal shell, and a second end portion of the ground electrode intersects the axis of the spark plug and faces the center electrode. With respect to a fictitious plane, which is a plane including the axis of the spark plug and perpendicular to a plane including an axis extending from the first end portion toward the second end portion of the ground electrode and the axis of the spark plug, at least a part of the detector electrode is located on a first end portion side of the ground electrode. Since the flame kernel tends to occur in a region of the first end portion side with respect to the fictitious plane, by disposing at least a part of the detector electrode on this region, in addition to the effect of any one of claims 1 to 5, an effect of reducing the occurrence of the tendency for fault detection can be obtained. Brief description of the drawings Fig. 1 is a cross-sectional view of one side of a spark plug according to a first embodiment of the present invention. Fig. 2 is a left side view of the spark plug with a cut metal shell. Fig. 3 is a bottom view of the spark plug viewed from an axial direction. Fig. 4 is a block diagram showing an electrical configuration of an ignition device. Fig. 5 is a block diagram showing an electrical configuration of a control device. Fig. 6 is a flowchart showing a low speed pre-ignition avoidance operation. Fig. 7 is a block diagram showing an electrical configuration of an ignition device according to a modified example. Fig. 8A is a left side view of a cut metal shell spark plug according to a second embodiment. Fig. 8B is a left side view of a cut metal shell spark plug according to a third embodiment. Fig. 8C is a left side view of a cut metal shell spark plug according to a fourth embodiment. Fig. 8D is a left side view of a cut metal shell spark plug according to a fifth embodiment. Fig. 9A is a left side view of a cut metal shell type spark plug according to a sixth embodiment. Fig. 9B is a left side view of a cut metal shell spark plug according to a seventh embodiment. Fig. 9C is a left side view of a cut metal shell type spark plug according to an eighth embodiment. Fig. 9D is a left side view of a cut metal shell spark plug according to a ninth embodiment. Fig. 10A is a left side view of a cut metal shell type spark plug according to a tenth embodiment. Fig. Figure 10B is a right side view of the spark plug. Fig. 11 is a cross-sectional view of a spark plug according to an eleventh embodiment. Fig. 12A is a left side view of a cut metal shell type spark plug according to a twelfth embodiment. Fig. 12B is a right side view of the spark plug. Fig. Figure 13 is a drawing showing a relationship between an applied voltage to the spark plug and a failure detection rate. Fig. 14 is a drawing showing a relationship between a width of a detector electrode and the defect detection rate. Fig. 15 is a drawing showing a relationship between a distance from an upper end of an insulator to an upper end of the detector electrode in an axial direction and a frequency of internal ignition (or internal sparking). Fig. 16 is a drawing showing a relationship between a distance from an upper end of a contact portion to the upper end of the detector electrode in the axial direction and the defect detection rate. Fig. 17 is a drawing showing a relationship between a position in a circumferential direction of the detector electrode and the defect detection rate. Embodiments for carrying out the invention

[0015] With reference to the drawings, preferred embodiments of the present invention will be explained below. Fig. 1 is a cross-sectional view of a side of a spark plug 10, with an axis O of the spark plug 10 being a boundary, according to a first embodiment of the present invention. In Fig. 1, a lower side of the drawing is referred to as an upper end side (or a tip end side) of the spark plug 10, and an upper side of the drawing is referred to as a rear end side of the spark plug 10. As shown in Fig. 1, the spark plug 10 has a metal shell 20, a ground electrode 30, an insulator 40 and a center electrode 70.

[0016] The metal shell 20 is a substantially tubular member that is fixed to a screw hole of an internal combustion engine (not shown). The metal shell 20 is made of a metal material (e.g., low-carbon steel) with conductivity. The metal shell 20 includes, from its rear end side to its upper end side along the axis O, a sealed portion 21, a tool engagement portion 22, a bent portion 23, a seat portion 24, and a body portion 25, these portions being connected in this order. The body portion 25 is provided with a threaded portion 26 on an outer peripheral surface thereof.

[0017] The sealed portion 21 and the bent portion 23 are portions for sealing the insulator 40. The tool engagement portion 22 is a portion with which a tool such as a wrench engages when screwing the threaded portion 26 into the screw hole (not shown). The seat portion 24 is an annular portion located at a rear end side of the body portion 25 and protruding outward in a radial direction. An annular seal ring 60 is provided between the seat portion 24 and the body portion 25.

[0018] The seal ring 60 seals a gap between the screw hole and the threaded portion 26 by being sandwiched between the seat portion 24 and the internal combustion engine when the threaded portion 26 is screwed and inserted into the screw hole (not shown). A seating portion 27 is a portion protruding inward in the radial direction of the body portion 25. A gasket 61 is provided on an annular surface 28 on a rear end side of the seating portion 27. The gasket 61 is an annular plate member made of a metal material, such as a soft steel plate (or mild steel plate), which is softer than the metal material constituting the metal case 20.

[0019] The ground electrode 30 is a metal rod-shaped member (e.g., a nickel-based alloy rod-shaped member) connected to an upper end 29 of the metal shell 20. The ground electrode 30 is bent or curved toward the axis O so that it intersects the axis O. A first end portion 31 of the ground electrode 30 is connected to the metal shell 20, and a second end portion 32 intersects the axis O and points toward the center electrode 70.

[0020] The insulator 40 is a substantially tubular member made of alumina, etc., which exhibits excellent mechanical properties and high-temperature insulation performance. The insulator 40 is provided with an axial bore 41 extending through the insulator 40 along the axis O. The insulator 40 includes, from its rear end side to its upper end along the axis O, a rear portion 42, a bulging portion 43, a large-diameter portion 44, a reduced-diameter portion 45, and a small-diameter portion 47, these portions being connected in this order.

[0021] The insulator 40 is inserted into the metal shell 30, and the metal shell 20 is fixed to an outer periphery of the insulator 40. A rear end side of the rear portion 42 of the insulator 40 is exposed from the metal shell 20, and an upper end of the small-diameter portion 47 protrudes from the upper end 29 of the metal shell 20. The bulging portion 43 is a portion that bulges or protrudes outward in the radial direction from an upper end side of the rear portion 42. The bulging portion 43 is positioned on a radially inner side of the bent portion 23 of the metal shell 20.

[0022] The large-diameter portion 44 and the small-diameter portion 47 are each positioned on a radially inner side of the body portion 25. An outer diameter of the small-diameter portion 47 is smaller than an outer diameter of the large-diameter portion 44. The reduced-diameter portion 45, whose outer diameter becomes smaller toward its upper end side, is located at a boundary between the large-diameter portion 44 and the small-diameter portion 47. A diameter of an outer surface 46 of the reduced-diameter portion 45 becomes smaller toward the upper end side. The gasket 61 is arranged between the surface 28 on the rear end side of the seating portion 27 of the metal shell 20 and the outer surface 46 of the reduced-diameter portion 45 of the insulator 40.

[0023] Ring members 62 and 63 and a filler 64, such as talc, positioned between these ring members 62 and 63 are provided between an outer periphery of the rear portion 42 of the insulator 40 and an inner periphery of the tool engagement portion 22 of the metal shell 20. When the sealed portion 21 of the metal shell 20 is sealed in the radially inward direction toward the insulator 40, the insulator 40 is pressed by the ring members 62 and 63 and the filler 64 toward the surface 28 of the seating portion 27 of the metal shell 20. When the gasket 61 is sandwiched between the surface 28 on the rear end side of the seating portion 27 and the outer surface 46 of the reduced-diameter portion 45, the gasket 61 is thereby plastically deformed. The seal 61 hermetically seals a gap between the support section 27 and the reduced diameter section 45.

[0024] The spark plug 10 is provided on the insulator 40 with a conductor 51 and a detector electrode 52 for detecting an ion current. In the present embodiment, the conductor 51 is embedded in the insulator 40. The insulator 40 has a groove 48 on its outer periphery extending from the rear portion 42 to the small-diameter portion 47, and the conductor 51 is arranged on a bottom of the groove 48. The conductor 51 connects a terminal 53 provided on the outer periphery of the rear portion 42 at a rear end side with respect to the metal shell 20 and the detector electrode 52 provided on an outer periphery of the small-diameter portion 47. The detector electrode 52 is arranged between the outer periphery of the insulator 40 and an inner periphery of the metal shell 20. The terminal 53 is a portion to which an external wiring (not shown) is connected.

[0025] The conductor 51 and the detector electrode 52 are formed with a noble metal such as platinum, which has heat resistance and low resistivity. In the present embodiment, the conductor 51 and the detector electrode 52 are formed in the groove 48 by firing or printing a metal paste containing the noble metal and / or silver, etc. The conductor 51 is covered with an insulating member 54 embedded in the groove 48, and then the conductor 51 is insulated from the metal case 20. In the present embodiment, the insulating member 54 is formed by curing a thermostable inorganic adhesive.

[0026] Since the conductor 51 is formed integrally with a surface (the groove 48) of the insulator 40, an increase in the outer diameters of the metal shell 20 and the spark plug 10 can be prevented, compared to the case where the conductor 51 is arranged between the insulator 40 and the metal shell 20 or the case where the conductor 51 is embedded in the metal shell 20. Furthermore, since the conductor 51 provided on the insulator 40 is covered with the insulating member 54, a short circuit between the conductor 51 and the metal shell 20 can be prevented while ensuring the durability of the conductor 51.

[0027] The center electrode 70 is a rod-shaped electrode formed by embedding a core superior to a metal electrode base material (e.g., an electrode base material made of a nickel-based alloy) in the electrode base material having a bottomed tubular shape. The core is made of copper or an alloy with copper as the main component. The center electrode 70 is held in and by the axial bore 41 of the insulator 40 and is arranged along the axis O. An upper end of the center electrode 70 protrudes from the axial bore 41 and faces the ground electrode 30 via a spark gap.

[0028] A terminal metal housing 80 is a rod-shaped member to which a high-voltage cable (not shown) is connected. The terminal metal housing 80 is made of a metal material (e.g., low-carbon steel) with conductive properties. An upper end of the terminal metal housing 80 is positioned in the axial bore 41 of the insulator 40. A conductive glass seal 65 is provided between the terminal metal housing 80 and the center electrode 70. The center electrode 70 and the terminal metal housing 80 are electrically connected by the glass seal 65.

[0029] The spark plug 10 is manufactured, for example, in the following manner. The insulator 40, which is provided with the conductor 51, the detector electrode 52, and the terminal 53, is formed, and the center electrode 70 is inserted into the axial bore 41 of the insulator 40. The center electrode 70 is fixed so that the upper end of the center electrode 70 protrudes from the axial bore 41 and is exposed to the outside. The terminal metal shell 80 is inserted into the axial bore 41 of the insulator 40, and an electrical connection is established between the terminal metal shell 80 and the center electrode 70. After mounting the metal shell 20, to which the ground electrode 30 has been previously connected, on the outer periphery of the insulator 40, by bending or curving the ground electrode 30 so that it faces the center electrode 70 in the direction of the axis O, the spark plug 10 having the spark gap between the center electrode 70 and the ground electrode 30 is obtained.

[0030] Next, the detector electrode 52 is Fig. 2 and Fig. 3 explained. Fig. 2 is a left side view of the spark plug 10 with cut metal shell 20 (seen from the first end portion 31 of the ground electrode 30 toward the insulator 40). In Fig. 2 are the metal housing 20 and a rear end side (in Fig. 2 an upper side) in the direction of the axis O of the insulator 40 is not shown. Fig. 3 is a bottom view of the spark plug 10 as seen from the axial direction O.

[0031] As in Fig. 2, the detector electrode 52 is formed on the small diameter portion 47 of the insulator 40 to have a rectilinear shape along the axis O. The detector electrode 52 is located above (in Fig. 2 below) of the upper end of a contact portion 56 between the outer surface 46 of the reduced diameter portion 45 and the seal 61 in a space 55 formed between the outer periphery of the insulator 40 and the inner periphery of the metal shell 20.

[0032] The inventors have found that with respect to low-speed preignition (LSPI) occurring in a heavy load and low-speed condition of the internal combustion engine at high compression and / or high charge, its fire or spark source tends to occur in the space 55. When the detector electrode 52 is disposed in the space 55 and a potential difference exists between the detector electrode 52 and the metal shell 20, when a flame kernel occurs in the space 55, the ion current flows to the detector electrode 52. By detecting this ion current, early detection of the LSPI, which indicates the occurrence of the flame kernel in the space 55, can be possible. Therefore, it is possible to improve the detection accuracy of the preignition caused by the flame kernel occurring in the spark plug 10.

[0033] The detector electrode 52 is arranged such that its upper end 52a is positioned in the direction of the axis O between the upper end of the contact portion 56 and an upper end 49 of the insulator 40. Furthermore, the detector electrode 52 is arranged such that its rear end 52b is positioned above (in the direction of the axis O) Fig. 2 below) of the upper end of the contact portion 56 with the seal 61. This ensures insulation of the rear end 52b of the detector electrode 52 from the seal 61.

[0034] In the present embodiment, the detector electrode 52 is arranged so that the upper end 52a in the direction of the axis O is below (in Fig. 2 above) of the upper end 29 of the metal casing 20 in the direction of the axis O. This arrangement may make it difficult to detect the occurrence of the flame kernel outside the space 55 (occurring above the upper end 29 of the metal casing 20). Consequently, it is possible to strictly distinguish between the flame kernel occurring outside the space 55 and the flame kernel occurring in the space 55. The flame kernel occurring in the space 55 can therefore be reliably and precisely detected.

[0035] It is preferable that a width W in a direction orthogonal to the direction of the axis O of the detector electrode 52 be 0.5 mm or more. Since an area of ​​the detector electrode 52 is secured, error detection is prevented by suppressing noise.

[0036] It is preferable that the upper end 52a extends downwards (in the direction of the axis O of the detector electrode 52) 6 mm or more away from the upper end 49 of the insulator 40. Fig. 2 upward) in the direction of the axis O. That is, by setting a distance D1 between the upper end 52a of the detector electrode 52 and the upper end 49 of the insulator 40 in the direction of the axis O to 6 mm or more, occurrence of electric discharge due to a potential difference between the center electrode 70 and the detector electrode 52 can be suppressed. Since spark wear of the detector electrode 52 caused by the electric discharge can be suppressed, durability can be improved.

[0037] It is preferable that the upper end 52a in the direction of the axis O of the detector electrode 52 is 3 mm or more away from the upper end of the contact portion 56 toward the upper end side (in Fig. 2 toward the lower side) in the direction of the axis O. That is, by setting a distance D2 between the upper end of the contact portion 56 and the upper end 52a of the detector electrode 52 in the direction of the axis O to 3 mm or more, the detector electrode 52 can be arranged in a region where a surface temperature of the small-diameter portion 47 slightly rises due to and according to the growth of the flame kernel. As the surface temperature slightly increases, the ion current flows easily. Therefore, it is possible to improve the detection accuracy of pre-ignition.

[0038] It is preferred that the upper end 52a of the detector electrode 52 is above (in Fig. 2 below) a position of half (1 / 2) the length L in the direction of the axis O of the small-diameter portion 47 of the insulator 40 (a length L from the upper end of the contact portion 56 to the upper end 49 of the insulator 40 in the direction of the axis O). This is because an area (a length) of the detector electrode 52 that detects the ion current is secured, and detection sensitivity is ensured.

[0039] As in Fig. 3, at least a part of the detector electrode 52 is located in the space 55 on the side of the first end portion 31 of the ground electrode 30 with respect to a fictitious plane 58, which is a plane comprising the axis O and perpendicular to a plane (a plane extending in Fig. 3 right-and-left extending plane) including an axis 57 extending from the first end portion 31 toward the second end portion 32 of the ground electrode 30 and the axis O. Since an origin (the flame kernel) of the LSPI tends to occur in a region of the first end portion 31 side with respect to the fictitious plane 58 in the space 55, the above arrangement of the detector electrode 52 facilitates the detection of the LSPI compared to a case where the detector electrode 52 is located in a region of the second end portion 32 side of the ground electrode 30 with respect to the fictitious plane 58.

[0040] Next, a control device designed to avoid low speed pre-ignition (LSPI) is described based on Fig. 4 to 6 explained. Fig. 4 is a block diagram showing an electrical configuration of an ignition device 90. Fig. 5 is a block diagram showing an electrical configuration of the control device. Fig. Figure 6 is a flowchart showing an LSPI avoidance operation.

[0041] As in Fig. As shown in Fig. 4, the spark plug 10 is mounted on a cylinder head so that its upper end protrudes into a combustion chamber 99 of an internal combustion engine 98. An engine control unit (ECU) 91 is a logic operation circuit including CPU, ROM, RAM, etc., and outputs an ignition command signal for the spark plug 10 to a driver circuit 92.

[0042] When a primary current of a primary coil 94 connected to a battery 93 is interrupted by the driver circuit 92, a high voltage is generated at a secondary coil 95. The high voltage is applied to the central electrode 70 (see Fig. 1) and the ground electrode 30 of the spark plug 10, and a spark discharge occurs between the center electrode 70 and the ground electrode 30, igniting an air-fuel mixture in the combustion chamber 99. A voltage change of the secondary coil 95 is detected by a first detection circuit 96.

[0043] The battery 93 provides a potential difference between the terminal 53 and the metal housing 20 (see Fig. 1) of the spark plug 10. When the flame kernel occurs due to the LSPI and between the detector electrode 52 (see Fig. 1) and the metal housing 20, which is provided with the potential difference, increases, the ion current flows between them. A voltage drop at terminal 53 during the flow of the ion current is detected by a second detection circuit 97.

[0044] As in Fig. As shown in Fig. 5, the first detection circuit 96 and the second detection circuit 97 output their detection results to the ECU 91. In the case of the internal combustion engine 98 in which pre-ignition does not occur, the second detection circuit 97 detects the voltage drop after the first detection circuit 96 detects the voltage change. When pre-ignition occurs in the internal combustion engine 98, the second detection circuit 97 detects the voltage drop before the first detection circuit 96 detects the voltage change. The ECU 91 detects or determines the presence or absence of pre-ignition by comparing the detection result of the first detection circuit 96 and the detection result of the second detection circuit 97.

[0045] An air mass meter 100 measures an air flow into the combustion chamber 99 (see Fig. 4) the amount of air drawn from an intake pipe (not shown) and outputs its measurement result to the ECU 91. A throttle sensor 101 detects an opening degree of a throttle valve (not shown) and outputs its detection result to the ECU 91. The opening degree of the throttle valve is adjusted according to an operating amount of an accelerator pedal (not shown), and by this throttle valve opening adjustment, the amount of air drawn into the combustion chamber 99 is controlled.

[0046] A crank angle sensor 102 detects a speed of the internal combustion engine 98 (see Fig. 4) and outputs its detection result to the ECU 91. An exhaust gas temperature sensor 103 is a sensor installed in the intake pipe (not shown) connected to the combustion chamber 99. The exhaust gas temperature sensor 103 detects an exhaust gas temperature and outputs its detection result to the ECU 91. A fuel injection valve 104 is a device that injects an amount of fuel corresponding to the amount of air drawn into the combustion chamber 99 into the combustion chamber 99. The ECU 91 detects or determines an operating condition of the internal combustion engine 98 based on the detection results of the air mass sensor 100, the throttle sensor 101, the crank angle sensor 102, and others, and calculates a basic fuel injection amount and a basic ignition timing of the spark plug 10.

[0047] Here, if LSPI (low-speed ignition advance) occurs continuously or frequently during operation of the internal combustion engine 98, it causes severe knocking, and the internal combustion engine 98 may suffer serious damage. Furthermore, if LSPI occurs under heavy load and low-speed conditions of the internal combustion engine 98, it poses a problem that it becomes difficult to raise the torque of the internal combustion engine 98.

[0048] To prevent the occurrence of LSPI, the ECU 91 therefore carries out, as shown in Fig. 6, executes the LSPI avoidance operation. This operation is performed repeatedly (e.g., at an interval of 0.2 ms) by the ECU 91 when the ECU 91 is energized. The ECU 91 avoids the LSPI by adjusting or controlling the fuel injection valve 104 and the driver circuit 92.

[0049] When executing the LSPI avoidance operation, the ECU 91 determines whether or not LSPI occurs by comparing the detection result of the first detection circuit 96 and the detection result of the second detection circuit 97 (at S1). If LSPI does not occur (S1: NO), this LSPI avoidance operation is terminated. If LSPI occurs as a result of the operation at S1, the ECU 91 determines whether or not the exhaust temperature is greater than or equal to a predetermined value based on the detection result of the exhaust temperature sensor 103 (at S2).

[0050] When the exhaust gas temperature is greater than or equal to the specified value as a result of the operation at S2 (S2: Yes), the fuel injection amount into the combustion chamber 99 from the fuel injection valve 104 is increased (at S3), and this LSPI prevention operation is terminated. As the fuel injection amount is increased, the temperature of the combustion chamber 99 decreases due to latent heat of vaporization by increasing the fuel amount and the combustion speed decreases due to the increase in fuel, thereby preventing LSPI.

[0051] When the exhaust gas temperature is lower than the specified value as a result of the operation at S2 (S2: No), the ignition timing of the spark plug 10 is retarded (at S4) to avoid LSPI by controlling an operation of the driver circuit 92, and this LSPI avoidance operation is terminated. Since the ECU 91 can properly control the ignition timing of the spark plug 10 and an air-fuel ratio by executing the LSPI avoidance operation, damage to the internal combustion engine 98 can be prevented while ensuring the torque of the internal combustion engine 98. Consequently, the reliability of the internal combustion engine 98 can be enhanced. Furthermore, since LSPI occurring under the heavy load and low speed condition can be avoided, an improvement in the efficiency of the internal combustion engine can be promoted by the high compression and / or high boost.

[0052] Next, another ignition device 105 is designed based on Fig. 7 explained. Fig. Fig. 7 is a block diagram showing an electrical configuration of the ignition device 105 according to a modified example. The same element or component as that of the ignition device 90 ( Fig. 4) is designated by the same reference symbol and its explanation is omitted.

[0053] In the ignition device 105, the center electrode 70 (see Fig. 1) and terminal 53 of the spark plug 10 are connected through a capacitor that prevents the penetration of a discharge current. A detection circuit 106 detects a voltage generated at the secondary coil 95 and the ion current, and outputs their detection results to the ECU 91. According to the ignition device 105, the ECU 91 detects or determines the presence or absence of pre-ignition based on the detection results of the detection circuit 106 by comparing a time at which the voltage is generated at the secondary coil 95 and a time at which the ion current is generated.

[0054] Next, spark plugs according to second to tenth embodiments are described with reference to Fig. 8A to 10B. The same element or component as that of the first embodiment is denoted by the same reference numeral, and its explanation is omitted. Fig. 8A is a left side view of a spark plug 110 with cut metal shell 20 according to a second embodiment. Fig. 8B is a left side view of a spark plug 120 with cut metal shell 20 according to a third embodiment. Fig. 8C is a left side view of a spark plug 130 with cut metal shell 20 according to a fourth embodiment. Fig. 8D is a left side view of a spark plug 140 with cut metal shell 20 according to a fifth embodiment.

[0055] Fig. 9A is a left side view of a spark plug 150 with cut metal shell 20 according to a sixth embodiment. Fig. 9B is a left side view of a spark plug 160 with cut metal shell 20 according to a seventh embodiment. Fig. 9C is a left side view of a spark plug 170 with cut metal shell 20 according to an eighth embodiment. Fig. 9D is a left side view of a spark plug 180 with a cut metal shell 20 according to a ninth embodiment. In Fig. 8A to 9D, the metal housing 20 and the rear end side in the direction of the axis of the insulator 40 are not shown.

[0056] At the Fig. The spark plug 110 according to the second embodiment shown in FIG. 8A includes a detector electrode 111 positioned at the small-diameter portion 47 of the insulator 40, a rectilinear first portion 112 extending in the axial direction, and a circular second portion 113 formed at an upper end in the axial direction of the first portion 112. The first portion 112 is connected to the conductor 51 (see Fig. 1) covered by the insulating member 54. The second portion 113 is positioned substantially at the center in the axial direction of the small-diameter portion 47. The second portion 113 is formed such that its width in a direction orthogonal to the axial direction is larger than that of the first portion 112, and the second portion 113 is also shaped into a circle whose outer edge has a small curvature. This can therefore reduce the tendency for electrical discharge to occur between the detector electrode 111 and the center electrode 70. The durability of the detector electrode 111 can thus be improved.

[0057] At the Fig. In the spark plug 120 according to the third embodiment shown in FIG. 8B, a detector electrode 121 located at the small-diameter portion 47 includes a third portion 122 provided at the first portion 112 positioned below the second portion 113 in the axial direction. The third portion 122 is formed into a circle whose width in a direction orthogonal to the axial direction is larger than that of the first portion 112. Since the detector electrode 121 includes the third portion 122, it is possible to increase the detection sensitivity in addition to the function and effect obtained by the second embodiment.

[0058] At the Fig. In the spark plug 130 according to the fourth embodiment shown in FIG. 8C, a detector electrode 131 is formed into a band shape or a belt shape that surrounds the outer periphery at a rear end side of the small-diameter portion 47 over the entire circumference of the small-diameter portion 47. Since heat dissipation or radiation performance of the small-diameter portion 47 can be improved by the detector electrode 131, heat resistance of the spark plug 130 can be improved.

[0059] At the Fig. The spark plug 140 according to the fifth embodiment shown in FIG. 8D includes a detection electrode 141 located at the small-diameter portion 47, a first portion 142 that bends and extends in the axial direction, a circular second portion 143 formed at an upper end in the axial direction of the first portion 142, and a third portion 144 provided at the first portion 142 and positioned below the second portion 143 in the axial direction. The second portion 143 is formed such that its width in a direction orthogonal to the axial direction is larger than that of the first portion 142, and the second portion 143 is also shaped into a circle with a small curvature.Since positions of the second portion 143 and the third portion 144 are different in a circumferential direction of the small diameter portion 47 by the bent first portion 142, in addition to the function and effect obtained by the third embodiment, a detection region (or detection range) of the flame kernel can be enlarged in the circumferential direction.

[0060] At the Fig. In the spark plug 150 according to the sixth embodiment shown in FIG. 9A, a detection electrode 151 includes a rectilinear first portion 152 extending in the axial direction and a rectangular second portion 153 formed at an upper end in the axial direction of the first portion 152. The second portion 153 is formed so that its upper end is positioned substantially at the center in the axial direction of the small-diameter portion 47. The second portion 153 is further formed so that its width in a direction orthogonal to the axial direction is larger than that of the first portion 152. Therefore, even if electrical discharge occurs between the second portion 153 and the center electrode 70 and a part of the second portion 153 wears, a portion of the second portion 153 can be secured. This can improve durability.

[0061] At the Fig. In the spark plug 160 according to the seventh embodiment shown in FIG. 9B, a detector electrode 161 includes a rectilinear first portion 162 extending in the axial direction and a second portion 163 formed at an upper end in the axial direction of the first portion 162. The second portion 163 is formed into a trapezoid whose width becomes narrower toward an upper end side in a direction orthogonal to the axial direction. In this case, too, it is possible to achieve the same function and effect as in the sixth embodiment.

[0062] At the Fig. In the spark plug 170 according to the eighth embodiment shown in FIG. 9C, a linear detector electrode 171 extending in the axial direction toward a top end side rotates or bends in the axial direction of the small-diameter portion 47 substantially at the center toward a rear end side in the axial direction. Since the detector electrode 171 extends in the axial direction and also in a circumferential direction of the small-diameter portion 47, a detection region (or detection range) of the flame kernel can be enlarged in the circumferential direction.

[0063] At the Fig. In the spark plug 180 according to the ninth embodiment shown in FIG. 9D, a detector electrode 181 is formed into a grid shape (or a lattice shape) at a rear end side of the small-diameter portion 47. Since the detector electrode 181 extends in the axial direction and also in the circumferential direction of the small-diameter portion 47, a detection region (or detection range) of the flame kernel can be enlarged in the circumferential direction.

[0064] Fig. 10A is a left side view of a spark plug 190 with cut metal shell 20 according to a tenth embodiment. Fig. 10B is a right side view of the spark plug 190. In Fig. 10A and Fig. 10B, the metal housing 20 and the rear end side in the direction of the axis of the insulator 40 are not shown. In Fig. 10B, the ground electrode 30 is also not shown.

[0065] At the Fig. The spark plug 190 according to the tenth embodiment shown in FIG. 10A includes a detector electrode 191 located at the small-diameter portion 47, a rectilinear first portion 112 extending in the axial direction, a second portion 192 formed at an upper end in the axial direction of the first portion 112, and a third portion 193 provided at the first portion 112 positioned below the second portion 192 in the axial direction. As shown in FIG. Fig. As shown in Fig. 10B, the second portion 192 and the third portion 193 are each formed into a ring shape that surrounds the outer periphery of the small-diameter portion 47 over the entire circumference of the small-diameter portion 47. Since the second portion 192 and the third portion 193 are provided, a detection region (or detection range) of the flame kernel can be enlarged in the circumferential direction.

[0066] Next, Fig. 11 explains an eleventh embodiment. In the first to tenth embodiments, a case where one detector electrode is provided was explained above. In contrast, in the eleventh embodiment, a plurality of detector electrodes are provided. The same element or component as in the first embodiment is denoted by the same reference numeral, and its explanation will be omitted. Fig. Fig. 11 is a cross-sectional view, including the axis O, of a spark plug 200 according to the eleventh embodiment. Fig. 11, a lower side of the drawing is referred to as an upper end side (or a tip end side) of the spark plug 200, and an upper side of the drawing is referred to as a rear end side of the spark plug 200. As shown in Fig. As shown in Figure 11, the spark plug 200 includes the metal shell 20, the ground electrode 30, an insulator 210, and the center electrode 70.

[0067] In addition to the conductor 51 and the detector electrode 52, the insulator 210 is provided with another conductor 212 and another detector electrode 213 for detecting the ion current. The insulator 210 has a groove 211 on its outer periphery extending from the rear portion 42 to the small-diameter portion 47, and the conductor 212 is placed on a bottom of the groove 211.

[0068] The conductor 212 connects a terminal 214 provided on the outer periphery of the rear portion 42 at a rear end side with respect to the metal shell 20, and the detector electrode 213 provided on the outer periphery of the small-diameter portion 47. The detector electrode 213 is arranged between the outer periphery of the insulator 40 and the inner periphery of the metal shell 20. The terminal 214 is a portion to which an external wiring (not shown) is connected.

[0069] The conductor 212 and the detector electrode 213 are formed with a noble metal such as platinum, which has heat resistance and low resistivity. In the present embodiment, the conductor 212 and the detector electrode 213 are formed in the groove 211 by firing or printing a metal paste containing the noble metal and / or silver, etc. The conductor 212 is covered with an insulating member 215 embedded in the groove 211, and then the conductor 212 is insulated from the metal case 20. In the present embodiment, the insulating member 215 is formed by curing a thermostable inorganic adhesive. The detector electrode 52 and the detector electrode 213 are insulated from each other.

[0070] In the present embodiment, the conductor 212 and the detector electrode 213 are arranged on a side opposite the conductor 51 and the detector electrode 52, respectively, with respect to the axis O. However, the arrangement of the conductor and the detector electrode is not limited to this arrangement. As long as at least a part of each of the detector electrodes 52 and 213 is located within the space 55, the detector electrodes 52 and 213 can be arbitrarily arranged within this area.

[0071] In the spark plug 200, since the detector electrodes 52 and 213, which are insulated from each other, are arranged in the space 55, when a potential difference exists between the detector electrode 52 and the metal shell 20 and between the detector electrode 213 and the metal shell 20, the occurrence of the ion current caused by the flame kernel can be detected in the space 55. Since the spark plug 200 has the plurality of detector electrodes 52 and 213, by detecting whether the ion current flows to the detector electrode 52 or the ion current flows to the detector electrode 213, a position where the flame kernel occurs can be located or determined. Instead of specifying a potential difference between the detector electrode 52 and the metal shell 20 and between the detector electrode 213 and the metal shell 20, the ion current can also be detected by specifying a potential difference between the detector electrodes 52 and 213.

[0072] Next, Fig. 12A and Fig. 12B illustrates a twelfth embodiment. The same element or component as in the first embodiment is denoted by the same reference numeral, and its explanation is omitted. Fig. 12A is a left side view of a spark plug 220 with a cut metal shell 20 according to the twelfth embodiment (as viewed from the first end portion 31 of the ground electrode 30 toward the insulator 40). Fig. 12B is a right side view of the spark plug 220. In Fig. 12A and Fig. 12B, the metal housing 20 and the rear end side in the direction of the axis O of the insulator 40 are not shown.

[0073] The spark plug 220, as used in Fig. 12A and Fig. 12B, detector electrodes 221 and 225 are arranged on both sides of the small diameter portion 47 of the insulator 210 with respect to the axis O. The detector electrodes 221 and 225 are insulated from each other. The detector electrode 221 includes a rectilinear first portion extending in the direction of the axis O, a second portion 223 extending in the circumferential direction of the small diameter portion 47 from an upper end toward the axis O of the first portion 222, and a third portion 224 extending in the circumferential direction from the first portion 222 positioned below the second portion 223 in the direction of the axis O, with a distance or a space from the second portion 223.

[0074] The detector electrode 225 includes a linear first portion 226 extending in the axis O direction, a second portion 227 extending in the circumferential direction of the small-diameter portion 47 from an upper end toward the axis O of the first portion 226, and a third portion 228 extending in the circumferential direction from the first portion 226 positioned below the second portion 227 in the axis O direction, with a distance or space provided from the second portion 227. Since the detector electrodes 221 and 225 extend in the axial direction and also in the circumferential direction of the small-diameter portion 47, a detection region (or detection range) of the flame kernel can be enlarged in the circumferential direction. IMPLEMENTATION

[0075] The present invention is further illustrated by the following implementation. However, the present invention is not limited to the following implementation. (Implementation 1)

[0076] Experimenters mounted the spark plug (see Fig. 2) with the linear detector electrode explained in the first embodiment, and a pressure sensor on a turbocharged internal combustion engine (displacement 1.6 l). Regarding the detector electrode of the spark plug, its axially upper end is positioned at the center of the small-diameter portion of the insulator, and its width W in a direction orthogonal to the axial direction is 1 mm. The detector electrode is further arranged on the small-diameter portion of the insulator facing the first end portion of the ground electrode.

[0077] The experimenters ignited and burned an air-fuel mixture supplied to the internal combustion engine with the spark plug. The experimenters detected the ion current by applying a potential difference between the detector electrode and the metal casing of the spark plug through the ignition device explained in the first embodiment (see Fig. 4) and detected the occurrence and growth of the flame kernel (hereinafter referred to as "plug LSPI") occurring in the space between the insulator and the metal shell of the spark plug. Using the pressure sensor, the experimenters detected the ignition and combustion of the air-fuel mixture by the spark plug and the plug LSPI.

[0078] By comparing a detection result of the pressure sensor and a detection result of the spark plug, the experimenters determine a failure detection rate (a ratio of the number of undetectable time points of the plug LSPI by the spark plug to 100 detectable time points of the plug LSPI by the pressure sensor), which indicates a ratio of the number of time points at which the spark plug could not detect the plug LSPI despite the fact that the pressure sensor detected the plug LSPI.

[0079] Fig. Figure 13 is a diagram illustrating the relationship between the applied voltage across the spark plug (a potential difference between the detector electrode and the metal shell) and the fault detection rate. A plus in the applied voltage indicates that the polarity of the detector electrode is "+," whereas a minus in the applied voltage indicates that the polarity of the detector electrode is "-." As can be seen from Fig. As can be seen from Figure 13, by setting the polarity of the detector electrode at “+” and setting the applied voltage at +50V or more, it is possible to substantially eliminate or avoid the fault detection of the candle LSPI. (Implementation 2)

[0080] The experimenters detected the candle LSPI in the same way as in implementation 1, except that the width W (see Fig. 2) the spark plug's detector electrode was changed. The applied voltage (the potential difference between the detector electrode and the metal housing) was +50V. Fig. Figure 14 is a graph showing a relationship between the width of the detector electrode and the defect detection rate. Fig. As can be seen from Figure 14, by setting the width of the detector electrode to 0.5 mm or more, the defect detection rate of the candle LSPI can be reduced to 10% or less. The experimenters concluded that the defect detection rate was reduced because the influence of noise, etc., could be eliminated. (Implementation 3)

[0081] The experimenters detected the candle LSPI in the same way as in implementation 1, except that the distance D1 (see Fig. 2) was changed in the axial direction from the upper end of the insulator to the upper end of the spark plug's detector electrode. The applied voltage (the potential difference between the detector electrode and the metal housing) was +50V. Fig. Figure 15 is a diagram illustrating a relationship between the distance D1 from the upper end of the insulator to the upper end of the detector electrode in the axial direction and a frequency of internal ignition (or internal sparking) (electric discharge between the center electrode and the detector electrode). As can be seen from Fig. As can be seen from Figure 15, by setting the distance D1 to 6 mm or more, the plug LSPI can be detected while preventing the occurrence of internal ignition. This is because the electrical discharge between the center electrode and the detector electrode can be prevented and the detection sensitivity of the plug LSPI can be increased. (Implementation 4)

[0082] The experimenters detected the candle LSPI in the same way as in implementation 1, except that the distance D2 (see Fig. 2) from the upper end of the contact section between the insulator and the gasket to the upper end of the spark plug's detector electrode in the axial direction. The applied voltage (the potential difference between the detector electrode and the metal shell) was +50V. Fig. Figure 16 is a diagram showing a relationship between the distance D2 from the upper end of the contact portion to the upper end of the detector electrode in the axial direction and the defect detection rate. As can be seen from Fig. As can be seen in Figure 16, by setting the distance D2 to 3 mm or more, the defect detection rate of the candle LSPI can be reduced to 10% or less. The experimenters concluded that the defect detection rate was reduced because the detector electrode could be placed in a region where the temperature rises slightly due to and according to the growth of the flame kernel and the ion current flows easily by setting the distance D2 to 3 mm or more. (Implementation 5)

[0083] The experimenters detected the spark plug LSPI in the same way as in Implementation 1, except that the circumferential position of the spark plug's detector electrode relative to the ground electrode was changed. The applied voltage (the potential difference between the detector electrode and the metal housing) was +50 V. Fig. Figure 17 is a drawing showing a relationship between the position in the circumferential direction of the detector electrode and the defect detection rate. Fig. 17, a center indicates the axis O, and a side axis indicates a position of the axis (57, see Fig. 3) extending from the first end portion 31 to the second end portion 32 of the ground electrode 30. A vertical axis indicates the fictitious plane (58, see Fig. 3), which includes the axis O.

[0084] As from Fig. 17, by arranging the detector electrode with respect to the fictitious plane (the vertical axis) (with respect to the center of Fig.17 on a left side) on the first end portion 31 side of the ground electrode 30, the fault detection rate of the plug LSPI can be reduced to 10% or less. The experimenters concluded that the fault detection rate was reduced because the frequency of occurrence of the plug LSPI with respect to the fictitious plane in the space between the insulator and the metal shell on the first end portion side of the ground electrode is high.

[0085] Although the present invention has been explained based on the above embodiments, the present invention is not limited to the above embodiments, and the present invention can be modified within the technical ideas of the present invention. For example, although the shape and size of the detector electrode are exemplified in the above embodiments, these shapes and sizes can be arbitrarily determined.

[0086] In the above embodiments, a case was explained where the upper end 49 of the insulators 40 and 210 protrudes toward the upper end side in the direction of the axis O relative to the upper end 29 of the metal shell 20. However, a position of the upper end 49 of the insulators 40 and 210 is not necessarily limited to this. Of course, the upper end 49 of the insulators 40 and 210 may be positioned below the upper end 29 of the metal shell 20 in the direction of the axis O. Even in this case, it is possible to realize the same function and effect as in the above embodiments.

[0087] In the above embodiments, a case was explained in which the gasket 61 is provided between the inner periphery (the seating portion 27) of the metal shell 20 and the outer periphery (the reduced diameter portion 45) of the insulators 40 and 210, and the metal shell 20 holds the insulators 40 and 210 through the gasket 61. However, the holding of the insulators 40 and 210 is not necessarily limited to this. Of course, the gasket 61 may be removed, and the inner periphery (the seating portion 27) of the metal shell 20 and the outer periphery (the reduced diameter portion 45) of the insulators 40 and 210 contact each other, then the metal shell 20 can hold the insulators 40 and 210 through this contact portion. Even in this case, it is possible to realize the same function and effect as in the above embodiments.

[0088] In the above embodiments, a case was explained where the detector electrode is provided on the insulators 40 and 210. However, a position where the detector electrode is provided is not necessarily limited thereto, as long as the detector electrode is located in the space 55 formed between the insulators 40 and 210 and the metal shell 20. Of course, the detector electrode may be provided on the inner periphery of the metal shell 20, or the detector electrode may be provided with the detector electrode not in contact with both the metal shell 20 and the insulators 40 and 210.

[0089] In the above embodiments, a case was explained where the conductors 51 and 212 and the terminals 53 and 214 are formed by firing or printing the metal paste. However, a method for forming the conductors 51 and 212 and the terminals 53 and 214 is not necessarily limited thereto. Instead of the metal paste, the conductors 51 and 212 may of course be formed by metal wire, and the terminals 53 and 214 may be formed by metal sheet.

[0090] In the above embodiments, a case was explained where the conductors 51 and 212 and the terminals 53 and 214 are formed on the surface of the insulators 40 and 210. However, an arrangement of the conductors 51 and 212 and the terminals 53 and 214 is not necessarily limited to this, as long as the conductor is insulated from the center electrode 70, the metal shell 20, and the ground electrode 30. Of course, to ensure insulation, the conductor is covered and, for example, embedded in the metal shell 20 or arranged between the metal shell 20 and the insulators 40 and 210.

[0091] In the above embodiments, a case was explained where the upper end in the axis O direction of the detector electrode is located below the upper end 29 of the metal shell 20 in the axis O direction. However, a position of the upper end in the axis O direction of the detector electrode is not necessarily limited to this. Of course, the upper end of the detector electrode in the axis O direction may protrude toward the upper end side in the axis O direction with respect to the upper end 29 of the metal shell 20. In this case, depending on a length and an area of ​​a protruding part of the detector electrode from the upper end 29 of the metal shell 20, it is possible to detect not only the occurrence of the flame kernel in the space 55 formed between the insulator 40 and the metal shell 20 but also the occurrence of the flame kernel outside the space 55.

[0092] In the eleventh embodiment, a case where two detector electrodes 52 and 213 are provided was explained. However, the number of detector electrodes is not necessarily limited to this. Of course, one or more detector electrodes may be provided as needed.

[0093] In the above embodiments, a case was explained in which the second end portion 32 side of the ground electrode 30, whose first end portion 31 is connected to the metal shell 20, is bent or curved. However, a shape of the ground electrode 30 is not necessarily limited to this. Of course, a straight ground electrode may be used instead of the bent ground electrode 30. In this case, the upper end side of the metal shell 20 extends in the direction of the axis O and the first end portion of the straight ground electrode is connected to the metal shell 20, then the second end portion of the ground electrode faces the center electrode 70.

[0094] In the above embodiments, a case was explained where the ground electrode 30 is arranged so that the second end portion 32 of the ground electrode 30 intersects the axis O of the center electrode 70. However, an arrangement of the ground electrode 30 is not necessarily limited to this, and a positional relationship between the center electrode 70 and the ground electrode 30 can be determined accordingly. As the positional relationship between the center electrode 70 and the ground electrode 30, for example, the ground electrode 30 may be arranged so that a side surface of the center electrode 70 and the second end portion 32 of the ground electrode 30 face each other, or the ground electrode 30 may be arranged so that the axis 57 of the ground electrode 30 intersects the axis O obliquely. EXPLANATION OF REFERENCE SYMBOLS 10, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 220 Spark Plug, 20 metal housings, 26 threaded section, 27 edition section, 30 ground electrode, 31 first final section, 32 second end section, 40, 210 insulator, 41 axial bore, 45 section of reduced diameter, 51, 212 ladder, 52, 111, 121, 131, 141, 151, 161, 171, 181, 191, 213, 221, 225 detector electrode, 52a upper end, 53, 214 connection, 55 rooms, 56 contact section, 57 axle, 58 fictitious level, 61 seal, 70 center electrode, W width, O axis

Claims

[1] Spark plug, which includes: a tubular insulator (40) having a reduced diameter portion (45) whose outer diameter becomes narrower toward an upper end side of the spark plug (10), and an axial bore (41) extending from the upper end side toward a rear end side of the spark plug (10) along an axis (O) of the spark plug (10); a center electrode (70) disposed in the axial bore (41); a tubular metal casing (20) arranged on an outer periphery of the insulator (40), the metal casing (20) having a support portion (27) on an inner periphery thereof and a threaded portion (26) on an outer periphery thereof, the support portion (27) projecting inward in a radial direction of the metal casing (20) and holding the reduced diameter portion (45) of the insulator (40) directly or through an annular gasket (61) from the upper end side; a ground electrode (30) connected to the metal housing (20) and pointing to the center electrode (70) via a spark gap; a connector (53) located on the rear end side with respect to the threaded portion (26); a detector electrode (52) provided at a portion located above the upper end of a contact portion (56) between the reduced diameter portion (45) and the seating portion (27) or the seal (61), in a space (55) formed between the outer periphery of the insulator (40) and the inner periphery of the metal casing (20), the detector electrode (52) being an electrode for detecting an ion current; and a conductor (51) connecting the detector electrode (52) and the terminal (53), and wherein the detector electrode (52) and the conductor (51) are insulated from the center electrode (70), the metal housing (20) and the ground electrode (30), wherein the detector electrode (52) is provided on the insulator (40). [2] The spark plug according to claim 1, wherein: a width (W) in a direction orthogonal to an axial direction of the detector electrode (52) is 0.5 mm or more. [3] The spark plug according to claim 1 or 2, wherein: an upper end (52a) of the detector electrode (52) is positioned on the rear end side with respect to an upper end (29) of the metal shell (20). [4] A spark plug according to any one of the preceding claims 1 to 3, wherein: an upper end (52a) of the detector electrode (52) is positioned 6 mm or more away from an upper end (49) of the insulator (40) toward the rear end side. [5] The spark plug according to any one of the preceding claims 1 to 4, wherein: an upper end (52a) of the detector electrode (52) is positioned 3 mm or more away from the upper end of the contact portion (56) toward the upper end side. [6] Spark plug according to one of the preceding claims 1 to 5, wherein: a first end portion (31) of the ground electrode (30) is connected to the metal housing (20) and a second end portion (32) of the ground electrode (30) intersects the axis (O) of the spark plug (10) and points towards the center electrode (70), and at least a part of the detector electrode (52) is located on the side of a first end portion (31) of the ground electrode (30) with respect to a fictitious plane (58), which is a plane that includes the axis (O) of the spark plug (10) and is perpendicular to a plane that includes an axis (57) that extends from the first end portion (31) towards the second end portion (32) of the ground electrode (30) and includes the axis (O) of the spark plug (10).

Images