JP2019140005A - Spark plug - Google Patents

Abstract

To provide a spark plug capable of enhancing ignition and flame propagation even in ultra lean combustion and ultra high EGR combustion, and suitable for realizing ultra lean combustion and ultra high EGR combustion.SOLUTION: A spark plug suitable for ultra lean combustion and ultra high EGR combustion includes a housing 31 having a lower limit projecting into the combustion chamber, an insulator 32 placed on the inside of the housing 31, center electrodes (11, 12) placed on the inside of the insulator 32, and partially projecting into the combustion chamber from the lower end of the insulator 32, and ground electrodes (21, 22, 23) including an arm 21 having one end connected with the housing 31, extending downward from the housing 31, and bending to the medial axis O side of the center electrodes (11, 12), and a spark discharge expansion section 22 connected with the other end of the arm 21, having crown facing the medial axis O, and where the area in the direction perpendicular to the medial axis O becomes wider gradually downward from the crown.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a technique for realizing ultra lean combustion (super lean burn) and ultra high exhaust gas recirculation (ultra high EGR) combustion, and more particularly to an ignition plug suitable for ultra lean combustion and ultra high EGR combustion.

  In order to reduce carbon dioxide, which causes global warming, emitted from automobiles, it is important to improve the thermal efficiency of gasoline engines. In recent years, as a means for improving the thermal efficiency of a gasoline engine, development of technology for realizing ultra lean combustion and ultra high EGR combustion has been advanced. In order to stably realize ultra lean combustion and ultra high EGR combustion, a technique for promoting ignition and flame propagation is necessary.

  As a conventional spark plug, a spark that is formed by forming a vortex generating portion that separates the airflow in the vicinity of the ground electrode to generate a wake vortex downstream, and the center electrode and the ground electrode are deformed by the airflow flowing between both electrodes. Alternatively, a method for stabilizing the ignition by arranging the flame so as to enter the wake vortex has been proposed (see Patent Document 1).

  However, in the spark plug described in Patent Document 1, it is not considered to positively extend the discharge path generated between the center electrode and the ground electrode in a direction parallel to the center axis of the spark plug. For this reason, when the spark plug described in Patent Document 1 is applied to ultra lean combustion or ultra high EGR combustion, it is difficult to promote ignition and flame propagation.

JP 2017-147087 A

  In view of the above problems, the present invention can promote ignition and flame propagation even in ultra lean combustion and ultra high EGR combustion, and is an ignition plug suitable for stably realizing ultra lean combustion and ultra high EGR combustion. The purpose is to provide.

  In order to achieve the above object, one aspect of the present invention is to achieve the above object, and a preferred aspect of the present invention is to provide an air-fuel mixture having an excess air ratio of 1.5 or more in the combustion chamber, or an excess air A spark plug for igniting an air-fuel mixture having a rate of less than 1.5 and an EGR rate of 20% or more, (a) a housing whose lower end protrudes into the combustion chamber, and (b) a housing along the central axis of the housing An insulator disposed on the inside of the insulator, (c) a central electrode disposed on the inner side of the insulator along the central axis and partially protruding from the lower end of the insulator into the combustion chamber, and (d) one end of the housing Connected, extending downward from the housing, bent to the center axis side, connected to the other end of the arm, the center axis and the top face each other, and perpendicular to the center axis as it goes downward from the top Including a spark extension with a gradually increasing area. And summarized in that a spark plug and a pole. Here, the spark plug is also applicable when igniting an air-fuel mixture outside the range where the excess air ratio in the combustion chamber is 1.5 or more, or the excess air ratio is less than 1.5 and the EGR rate is 20% or more. Is possible.

  According to the present invention, it is possible to promote ignition and flame propagation even in ultra lean combustion and ultra high EGR combustion, and to provide a spark plug suitable for stably realizing ultra lean combustion and ultra high EGR combustion. be able to.

FIG. 1 is a schematic diagram illustrating an example of an internal combustion engine according to an embodiment of the present invention. 2A is a main part front view showing an example of a spark plug according to an embodiment of the present invention, FIG. 2B is a side view of FIG. 2A, and FIG. It is a top view of the ground electrode part of 2 (a). FIG. 3 is a schematic diagram illustrating an example of an ignition device according to an embodiment of the present invention. 4 (a) to 4 (c) are main part front views at the time of ignition of the spark plug according to the embodiment of the present invention. FIG. 5 is a schematic diagram showing a combustion trajectory on a turbulent combustion diagram. FIG. 6 is a main part front view of a spark plug according to a comparative example. FIG. 7A and FIG. 7B are graphs showing temporal changes in the accumulated heat generation amount when discharging by changing the excess air ratio by normal ignition using the spark plug according to the comparative example. . FIG. 8A to FIG. 8C are graphs showing temporal changes in the accumulated heat generation amount when the ignition plug according to the comparative example is used to discharge by changing the excess air ratio with strong ignition. . 9 (a) to 9 (d) show changes over time in the amount of heat generated when the spark plug according to the comparative example is discharged with strong ignition and strong tumble flow while changing the excess air ratio. It is a graph which shows. FIGS. 10 (a) to 10 (c) show temporal changes in the amount of accumulated heat generated when the ignition plug according to the embodiment is used to discharge with a strong ignition and a strong tumble flow while changing the excess air ratio. It is a graph which shows. FIG. 11A is a graph showing a discharge pattern at the time of discharge shown in FIGS. 10A and 10B, and FIG. 11B is a graph at the time of discharge shown in FIG. 10C. It is a graph showing a discharge pattern. 12A to 12D are graphs showing the direction of the tumble flow in the vicinity of the spark plug when the strong tumble flow is used. FIG. 13 (a) is a main part front view showing an example of a spark plug according to a modification of the embodiment of the present invention, FIG. 13 (b) is a side view of FIG. 13 (a), and FIG. ) Is a plan view of the ground electrode portion of FIG. FIG. 14 (a) is a front view of a main part showing an example of a spark plug according to a modification of the embodiment of the present invention, FIG. 14 (b) is a side view of FIG. 14 (a), and FIG. ) Is a plan view of the ground electrode portion of FIG. FIG. 15 (a) is a front view of a main part showing an example of a spark plug according to a modification of the embodiment of the present invention, FIG. 15 (b) is a side view of FIG. 15 (a), and FIG. ) Is a plan view of the ground electrode portion of FIG. FIG. 16A is a main part front view showing an example of a spark plug according to a modification of the embodiment of the present invention, and FIG. 16B is a side view of FIG. FIG. 17A and FIG. 17B are main part front views showing an example of a spark plug according to a modification of the embodiment of the present invention. FIG. 18 is a side view of an essential part showing an example of a spark plug according to a modification of the embodiment of the present invention. FIG. 19 is a main part side view showing an example of a spark plug according to a modification of the embodiment of the present invention. 20 (a) is a front view of a main part showing an example of a spark plug according to a modification of the embodiment of the present invention, FIG. 20 (b) is a side view of FIG. 20 (a), and FIG. ) Is a plan view of the ground electrode portion of FIG. FIG. 21A is a main part front view showing an example of a spark plug according to a modification of the embodiment of the present invention, FIG. 21B is a side view of FIG. 21A, and FIG. ) Is a plan view of the ground electrode portion of FIG. 22 (a) to 22 (c) are front views of essential parts during ignition of the spark plug shown in FIGS. 21 (a) to 21 (c). FIG. 23A is a main part front view showing an example of a spark plug according to a modification of the embodiment of the present invention, FIG. 23B is a side view of FIG. 23A, and FIG. ) Is a plan view of the ground electrode portion of FIG. 24A to 24C are cross-sectional views showing an example of the ground electrode portion.

  Next, an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are affixed with the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness, and the like are different from the actual ones. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings. Further, the following embodiments exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is the material, shape, structure, and arrangement of components. Etc. are not specified as follows. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.

  In addition, the definition of the vertical direction in the following description is merely a definition for convenience of description, and does not limit the technical idea of the present invention. For example, if the object is observed by rotating 90 °, the upper and lower parts are read after being converted to the left and right, and if observed by rotating 180 °, the upper and lower parts are read in an inverted manner.

<Ignition plug>
The spark plug according to the embodiment of the present invention is applicable to super lean combustion (super lean burn) and ultra high EGR combustion. Super lean combustion refers to burning an ultra lean mixture rather than a stoichiometric mixture. In the present specification, for convenience of explanation, the region of the super lean combustion is, for example, an excess air ratio λ = about 1.5 or more, for example, an excess air ratio λ = 1.5 to 3.0. Note that the region of the super lean combustion may include a range where the excess air ratio λ is less than 1.5, or may include a range where the excess air ratio λ is greater than 3.0. The excess air ratio λ is a value obtained by dividing the mass of actually supplied air by the minimum air mass theoretically necessary. In ultra lean combustion, the cooling loss can be reduced by combustion at a lower temperature (about 2000 K) than the temperature (about 2600 K) of the conventional stoichiometric mixture (stoichiometric), and the thermal efficiency can be greatly improved. On the other hand, in ultra lean combustion, the stability of combustion decreases with the dilution of the air-fuel mixture, so a technique for promoting ignition and flame propagation is required.

  Exhaust gas recirculation (EGR) is a technique for reintake a part of exhaust gas after combustion in an internal combustion engine for the purpose of reducing nitrogen oxide (NOx) in the exhaust gas and improving fuel consumption. The region of ultra-high EGR combustion is, for example, an EGR rate of about 20% or more, for example, an EGR rate of about 20% to 70%. Note that the region of the ultra-high EGR combustion may include a range where the EGR rate is less than about 20%, and may include a range where the EGR rate is higher than about 70%. The EGR rate is a numerical value obtained by dividing the amount of exhaust gas (reflux gas) to be recirculated to the intake system by the amount of intake air (intake gas). Even if the excess air ratio λ is 1 or more and less than 1.5, in ultra-high EGR combustion using a mixture into which a large amount of EGR gas having an EGR rate of 20% or more is introduced, While the thermal efficiency can be greatly improved due to the low temperature combustion, the stability of the combustion decreases with the dilution of the air-fuel mixture. The spark plug according to the embodiment of the present invention ignites an air-fuel mixture having an excess air ratio λ of 1.5 or more in a combustion chamber or an air-fuel mixture having an air excess ratio λ of less than 1.5 and an EGR rate of 20% or more. It is suitable when doing. Note that the spark plug according to the embodiment of the present invention can also be used when an air-fuel mixture having an excess air ratio λ of less than 1.5 and an EGR ratio of less than 20% is ignited.

  A gasoline engine will be exemplarily described as an internal combustion engine according to an embodiment of the present invention. As shown in FIG. 1, the internal combustion engine according to the embodiment of the present invention is attached to a cylinder 3, a piston 4 disposed in the cylinder 3, a cylinder head 2 disposed on the cylinder 3, and the cylinder head 2. A spark plug 1 is provided. The piston 4 is disposed in the cylinder 3 so as to be movable in the vertical direction. A combustion chamber 5 is formed by a space surrounded by the inner wall of the cylinder head 2 and the inner wall of the cylinder 3. In the cylinder head 2, an intake port 8 communicating with the combustion chamber 5 and an intake valve 6 for opening and closing the intake port 8 are disposed. Further, an exhaust port 9 that communicates with the combustion chamber 5 and an exhaust valve 7 that opens and closes the exhaust port 9 are disposed in the cylinder head 2. The spark plug 1 is attached, for example, near the center of the cylinder head 2, and a part of the spark plug 1 projects into the combustion chamber 5. The internal combustion engine according to the embodiment of the present invention is provided as an external EGR system for realizing ultra-high EGR combustion, a passage that connects the intake port 8 and the exhaust port 9, and a passage, and the amount of recirculated gas is reduced. You may provide the EGR valve to adjust. Or the internal combustion engine which concerns on embodiment of this invention may be equipped with the internal EGR system for implement | achieving ultra-high EGR combustion.

  As an outline of the operation (cycle) of the internal combustion engine according to the embodiment of the present invention, the piston 4 descends in the intake stroke, and a mixture of fuel and air is introduced into the combustion chamber 5 from the intake port 8 of the cylinder head 2. Is done. Next, in the compression stroke, the piston 4 rises and the air-fuel mixture introduced into the combustion chamber 5 is compressed. Next, in the combustion stroke, the compressed air-fuel mixture is ignited by the spark of the spark plug 1 and burns, and the combustion gas expands and the piston 4 is pushed down. Thereafter, in the exhaust stroke, the piston 4 rises due to inertia, and the combustion gas in the combustion chamber 5 is discharged to the exhaust port 9 of the cylinder head 2.

  The air-fuel mixture introduced into the combustion chamber 5 during the intake stroke forms a tumble flow in the combustion chamber 5. The tumble flow is a vertical vortex whose main flow is a flow swirling in a direction perpendicular to a horizontal vortex swirling around the central axis of the cylinder 3 (swirl flow). In ultra lean combustion, the stability of combustion decreases with the dilution of the air-fuel mixture, but the stability of combustion can be improved by enhancing the tumble flow (gas flow). In the embodiment of the present invention, the tumble flow in the vicinity of the spark plug 1 is controlled to a strong tumble flow having a flow rate of about 15 m / second to 50 m / second. The flow rate and direction of the tumble flow can be adjusted by the shape of the nozzle (adapter) attached to the intake port 8, the shape of the intake port 8, and the like. The flow rate and direction of the tumble flow can be measured with a microparticle image velocimeter (μPIV) or the like.

  The part which protrudes into the combustion chamber 5 of the lower part of the ignition plug 1 which concerns on embodiment of this invention is shown to Fig.2 (a)-FIG.2 (c). 2 (a) to 2 (c), for convenience of explanation, a direction parallel to the central axis O of the spark plug 1 according to the embodiment of the present invention is defined as a Z direction, and a direction orthogonal to the Z direction is defined as an X direction. The direction perpendicular to the Z direction and the X direction is defined as the Y direction. The X direction corresponds to the left-right direction in FIG. 1 and is a direction in which the intake port 8 and the exhaust port 9 of the cylinder head 2 are arranged. The direction of the spark plug 1 according to the embodiment of the present invention can be set as appropriate. The orientation of the spark plug 1 may be adjustable by attaching an actuator to the spark plug 1 according to the embodiment of the present invention and rotating the spark plug 1 around the central axis O.

  As shown in FIGS. 2A to 2C, the spark plug 1 according to the embodiment of the present invention includes a cylindrical housing 31 and a cylindrical insulator 32 arranged inside the housing 31. The center electrode (11, 12) disposed inside the insulator 32 and partially protruding into the combustion chamber 5, and the ground electrode (21, 22, 23) disposed opposite the center electrode (11, 12) ).

  The housing 31 is made of a conductive material and is fixed to the cylinder head 2 shown in FIG. The lower end of the housing 31 protrudes into the combustion chamber 5. The insulator 32 is disposed along the central axis O of the housing 31 (also referred to as the central axis O of the spark plug 1). The lower end of the insulator 32 protrudes into the combustion chamber 5 below the lower end of the housing 31.

  The center electrodes (11, 12) are positioned along the center axis O of the housing 31. The center electrode (11, 12) has a main body portion 12 protruding into the combustion chamber 5 from the lower end of the insulator 32 and a needle-like tip end portion 11 connected to the lower end of the main body portion 12. As a material of the main body 12, nickel (Ni), Ni alloy, or the like can be used. As the material of the tip portion 11, a noble metal such as platinum (Pt) or iridium (Ir), an alloy thereof, or the like can be used. The tip portion 11 is joined to the main body portion 12 by laser welding, resistance welding, or the like.

  As shown in FIGS. 2A to 2C, the ground electrodes (21, 22, 23) are connected to the arm portion 21 having one end connected to the lower end of the housing 31 and to the other end of the arm portion 21. The spark extension 22 and the needle-like protrusion 23 arranged on the spark extension 22 are provided. Ni, Ni alloy, or the like can be used as the material of the arm portion 21. The arm portion 21 is formed of, for example, a rectangular rod-like body, extends downward from the lower end of the housing 31 as shown in FIG. 2B, and bends (curves) in a shape close to an L shape on the center axis O side. doing. The width W1 of the arm portion 21 viewed from FIG. 2A is, for example, about 2 mm to 3 mm, and the width W2 of the arm portion 21 viewed from FIG. 2B is, for example, about 1 mm to 2 mm.

  Ni, Ni alloy, or the like can be used as the material for the spark extension 22. The material of the spark extension 22 may be the same material as the arm 21 or a different material. The spark extension 22 may be joined to the arm 21 by laser welding, resistance welding, or the like, or may be integrally formed in advance. Here, the case where the upper part of the side surface 222 of the spark extension part 22 is joined to the arm part 21 is illustrated, but the joining position of the spark extension part 22 and the arm part 21 is not particularly limited. The joining position of the spark extension 22 and the arm 21 is a position that does not hinder the flow of the tumble flow and the extension of the discharge path generated between the center electrode (11, 12) and the ground electrode (21, 22, 23). It is preferable to do.

  The spark extension portion 22 has a shape in which the central axis O and the top portion 221 face each other, and the area in the direction perpendicular to the central axis O gradually increases as it goes downward from the top portion 221. The spark extending portion 22 has a substantially conical shape (conical truncated cone shape with the top portion 221 as an upper base), and the side surface of the spark extending portion 22 is a conical surface (inclined surface) 222. As shown in FIG. 2B, the bottom surface 223 of the spark extension 22 is positioned below the lower end of the arm portion 21 at a position connected to the spark extension 22. The apex angle θ1 of the cone when the inclined surface 222 is extended is, for example, about 60 ° to 100 °. That is, the inclined surface 222 is inclined with respect to the central axis O of the spark plug 1 at an inclination angle (θ1 / 2) of about 30 ° to 50 °, for example. The diameter D1 of the bottom surface 223 of the spark extension 22 is, for example, about 4 mm to 10 mm, and can be set as appropriate within a range passing through a plug hole provided in the cylinder head 2. The height H1 of the spark extension 22 in the direction (axial direction) parallel to the center axis O of the spark plug 1 is, for example, about 3 mm to 6 mm.

  The protrusion 23 has a cylindrical shape having a smaller diameter than the top 221 of the spark extension 22. The diameter of the protrusion 23 may be the same as the diameter of the top 221 of the spark extension 22. The height H2 of the protrusion 23 is about 0.5 mm to 1 mm. The protrusion 23 is joined to the spark extension 22 by laser welding, resistance welding, or the like. As the material of the protrusion 23, a noble metal such as Pt or Ir or an alloy thereof can be used. The discharge gap G1 between the protrusion 23 and the tip 11 is, for example, about 0.5 mm to 1.5 mm, and can be appropriately selected according to the output of the ignition coil. As the discharge gap G1 is larger, the spark (discharge path) generated between the protrusion 23 and the tip 11 is longer, so that flame propagation is easier, while the voltage applied between the discharge gap G1 is higher.

  As shown in FIG. 3, the ignition device using the spark plug 1 according to the embodiment of the present invention includes a plurality (10) of ignition coils 51, 52, 53 connected to the spark plug 1 via a distributor 43. , 54, 55, 56, 57, 58, 59, 60, and a control circuit 41 and a constant voltage source 42 connected to the ignition coils 51-60. Each of the ignition coils 51 to 60 includes a primary coil connected to the constant voltage source 42 and a secondary coil connected to the spark plug 1. The constant voltage source 42 supplies a constant voltage (for example, 12V) to the ignition coils 51-60. The control circuit 41 controls the operation of the ignition coils 51-60.

  According to the ignition device including the ignition plug 1 according to the embodiment of the present invention, the ignition energy is enhanced by using the plurality of ignition coils 51 to 60, so that even when a strong tumble flow is obtained in ultra lean combustion, Flame propagation can be promoted. Furthermore, a plurality of ignition coils 51 to 60 may be sequentially used to discharge a plurality of times at a predetermined interval within one cycle. For example, two sets of a plurality of ignition coils 51 to 60 are taken as a set, and discharge is performed five times within one cycle. By performing a plurality of discharges within one cycle, it is possible to stabilize ignition and flame propagation, and to suppress fluctuations in ignition and flame propagation for each cycle.

  Next, a method for igniting the air-fuel mixture using the spark plug 1 according to the embodiment of the present invention will be described. The position of the top dead center in the compression stroke is set to a crank angle θ = 0 °, and discharge is started at a crank angle θ = −40 °, for example. As shown to Fig.4 (a), a spark is generated by the discharge gap G1 between the front-end | tip part 11 of a center electrode (11,12) and the projection part 23 of a ground electrode (21,22,23) by discharge. Then, the discharge path S is formed in a substantially straight line at the shortest distance. By adjusting the direction of the spark plug 1 according to the embodiment of the present invention, the shape of the nozzle attached to the intake port 8, and the like, the direction of the tumble flow F in the discharge gap G1 is orthogonal to the central axis O of the spark plug 1. Control in the direction. In addition, the direction of the tumble flow F in the discharge gap G1 is not limited to this, and may be controlled in different directions so that the flow of the tumble flow F is not hindered. For example, the direction of the tumble flow F may be inclined with respect to the direction orthogonal to the central axis O of the spark plug 1 or may be opposite to the direction shown in FIG.

  Thereafter, the discharge is continued, and the discharge path S is deformed by the tumble flow F, and the discharge path S is extended downstream of the tumble flow F, as shown in FIG. When the discharge path S extends, the spark selects a path having a small electric resistance value, and therefore, the discharge point P at the root on the spark extension part 22 side of the discharge path S moves from the protrusion part 23 to the top part 221 of the spark extension part 22. Then, it moves from the top 221 to the inclined surface (conical surface) 222. When the discharge is further continued, the discharge point P on the spark extension portion 22 side of the discharge path S extends along the inclined surface (conical surface) 222 of the spark extension portion 22 and the inclined surface (conical surface) 222 of the spark extension portion 22. Toward the lower end side (the bottom surface 223 side of the spark extension 22). Here, in the vicinity of the stoichiometric mixture (stoichiometric) (for example, the excess air ratio λ = about 1.3), the initial flame nucleus is formed and propagates almost simultaneously with the dielectric breakdown, so that the discharge path can be extended only slightly. On the other hand, the inventors of the present invention have experimentally determined that during ultra lean combustion, the combustion mechanism is different from that in the vicinity of the theoretical mixture (stoichiometric), an initial flame zone is formed so as to surround the discharge path S, and the initial flame zone is immediately I found that it did not propagate. Therefore, this phenomenon is used to greatly extend the discharge path S before the initial flame zone propagates. This also has the effect of dispersing the initial flame zone in the premixed gas in the combustion chamber 5.

  Thereafter, as shown in FIG. 4C, the discharge point P on the spark extension portion 22 side of the discharge path S is at the lower end of the inclined surface (conical surface) 222 of the spark extension portion 22 (on the bottom surface 223 of the spark extension portion 22). When reaching the outer periphery), the discharge path S is stably maintained at this position. At this point, an initial flame zone is formed around the discharge path S, propagates, and ignites. In this way, the substantial discharge gap G2 in the direction (axial direction) parallel to the central axis O of the spark plug 1 can be made larger than the discharge gap G1 between the tip portion 11 and the protrusion 23.

FIG. 5 shows a combustion locus (indicated by a thin line) of the excess air ratio λ = 2.0 on the turbulent combustion diagram and a combustion locus (indicated by a thick line) in the case of the excess air ratio λ = 1.0. The vertical axis of FIG. 5 shows the turbulence intensity u '/ laminar burning velocity S _L, the horizontal axis represents the integral length scale l / flame zone thickness [delta]. “Ka” in FIG. 5 is a turbulent Karlovitz number and is represented by the following equation (1).

Ka = (l / δ) ^−1/2 (u ′ / S _L ) ^3/2 (1)

  The greater the Ka, the greater the effect of turbulence on the reaction (combustion). In FIG. 5, it is considered that the internal structure of the flame does not change in a region defined as a corrugated flamelet region where Ka <1. In a region defined as a thin reaction zone region where 100 ≧ Ka ≧ 1, it is considered that a part of the flame structure changes due to turbulent motion. In an area defined as a dispersion reaction zone area with Ka> 100, the influence of turbulent motion appears in the chemical reaction related to heat generation, and it is considered difficult to realize a flame.

  In the case of ultra lean combustion with an excess air ratio λ = 2.0, a spark discharge is started at a crank angle θ = −40 ° with the top dead center position in the compression stroke being set to a crank angle θ = 0 °, and surrounds the discharge path. The flame zone formed in this way is subjected to propagation inhibition by the stretch effect, and the number of flame zones and the dispersion area increase. Thereafter, Ka = 10 near the crank angle θ = −10 ° and flame propagation is started, and the crank angle (CA10) at which the combustion rate becomes 10% at the crank angle θ = −5 ° is reached. On the other hand, in the case of combustion of a theoretical air-fuel mixture with an excess air ratio λ = 1.0, flame propagation starts immediately after the start of discharge, heat generation starts, and CA10 is reached at a crank angle θ = −5 °. As described above, the spark discharge mechanism is greatly different between the ultra lean combustion with the excess air ratio λ = 2.0 and the combustion with the theoretical air-fuel mixture with the excess air ratio λ = 1.0.

  According to the spark plug 1 according to the embodiment of the present invention, the spark extending portion 22 has the central axis O and the top portion 221 facing each other, and the area in the direction perpendicular to the central axis O gradually increases as it goes downward from the top portion 221. Has a shape. For this reason, when the discharge path S extends to the downstream side of the tumble flow F by the tumble flow F in the combustion in the ultra-lean, ultra-high EGR, and high turbulent flow, the discharge point P of the discharge path S is changed to the spark extension portion. It can be moved downward along the 22 inclined surfaces (conical surfaces) 222. That is, in the embodiment of the present invention, the discharge point P of the discharge path S is positively extended in a direction (axial direction) parallel to the central axis O of the spark plug 1. At this time, the tumble flow is crushed in the compression stroke, so that many fine vortices of about 1 mm are formed in the vicinity of the spark plug 1. When the discharge point P on the spark extension portion 22 side of the discharge path S is extended in a direction parallel to the central axis O of the spark plug 1, the discharge point P can be extended across the fine vortex, and the central axis of the spark plug 1 can be extended. Compared with the case of extending in a direction orthogonal to O, the film can be stably extended. For this reason, the discharge path P can be stably extended by positively extending the discharge point P of the discharge path S in a direction (axial direction) parallel to the central axis O of the spark plug 1. The effective discharge gap G2 can be increased. Therefore, ignition and flame propagation can be promoted without increasing the voltage for starting discharge.

  Furthermore, when the tumble flow in the vicinity of the spark plug 1 is controlled to a strong tumble flow having a flow velocity of about 15 m / second to 50 m / second, the direction of the tumble flow in the vicinity of the spark plug 1 is in a range of 360 ° for each cycle. It has been found that it is likely to fluctuate greatly, and even within one cycle, it tends to fluctuate greatly within a range of 360 ° for each crank angle. Therefore, according to the spark plug 1 according to the embodiment of the present invention, even when the direction of the tumble flow F greatly fluctuates in the range of 360 ° by making the spark extension portion 22 have a substantially conical shape (conical frustum shape), Regardless of the direction of the tumble flow F, the discharge path S can be stably extended downward along the inclined surface (conical surface) 222 of the spark extension 22. Therefore, fluctuations in ignition and combustion for each cycle and each crank angle can be reduced, and the stability of ignition and combustion for each cycle and each crank angle can be improved.

<First embodiment>
An example of the spark plug 1 according to the embodiment of the present invention was produced, and a comparative example for comparison with the example was produced. The spark plug according to the comparative example includes a center electrode 101 and ground electrodes (102, 103) as shown in FIG. The ground electrodes (102, 103) do not have a spark extension, but have an L-shaped arm 102 and a protrusion 103 on the arm 102. In the spark plug according to the comparative example, as shown in FIG. 6, the discharge path S extends to the downstream side of the tumble flow F by the tumble flow F, but the discharge point on the protrusion 103 side of the discharge path S is at the protrusion 103. stay. A discharge test was performed using the spark plugs according to the manufactured Examples and Comparative Examples, and the temporal change in the integrated heat generation amount for each cycle was measured.

  7 (a) and 7 (b) show that the spark plug according to the comparative example is used, the engine output is 600 kPa, the normal ignition (one coil) is common, the excess air ratio λ is λ = 1, The change with time of the integrated heat generation amount when changed to λ = 1.6 is shown. In FIG. 7A, discharge is started at a crank angle θ = −12 °, and combustion is completed at a crank angle θ = 20 °. In FIG. 7B, it can be seen that there is a cycle in which combustion is incomplete, and combustion is more unstable than in the case of FIG.

  8 (a) to 8 (c) show that the ignition output according to the comparative example is used, the engine output is 600 kPa, the strong ignition (10 coils) and the normal tumble flow are common, and the excess air ratio λ Changes in accumulated heat generation when λ is changed to λ = 1.01, λ = 1.68, and λ = 1.87, respectively. As shown in FIGS. 8 (a) to 8 (c), by using strong ignition, combustion is stabilized more than in the cases of FIGS. 7 (a) and 7 (b), but the excess air ratio λ = It turns out that combustion becomes unstable when it becomes 1.87.

  9 (a) to 9 (d) use an ignition plug according to a comparative example, and the engine output is 600 kPa, strong ignition (10 coils), and strong tumble flow (30 m / sec) by an adapter are common. And the time variation of the accumulated heat generation amount when the excess air ratio λ is changed to λ = 1, λ = 1.60, λ = 1.89, and λ = 1.99, respectively. As shown in FIGS. 9 (d) to 9 (d), combustion is more stable than in the cases of FIGS. 8 (a) to 8 (c) by using strong ignition and strong tumble flow. It can be seen that combustion becomes unstable when the excess ratio λ = 1.99.

  10 (a) and 10 (b) use the spark plug according to the embodiment and share the engine output of 800 kPa, strong ignition (10 coils), and strong tumble flow (30 m / sec) by the adapter. And the time variation of the integrated heat generation amount when the excess air ratio λ is changed to λ = 1.95 and λ = 2.07, respectively. In the discharge shown in FIGS. 10 (a) and 10 (b), as shown in FIG. 11 (a), 10 coils were collectively used and discharged once in one cycle. As shown in FIGS. 10 (a) and 10 (b), according to the spark plug according to the example, stable combustion could be realized even when the excess air ratio λ = 1.95 and λ = 2.07. I understand.

  FIG. 10 (c) shows an excess air ratio using an ignition plug according to an embodiment of the present invention, with an engine output of 600 kPa, strong ignition (10 coils), and a strong tumble flow (30 m / sec) by an adapter. The time change of the integrated heat generation amount when λ = 2.06 is shown. In the discharge shown in FIG. 10 (c), as shown in FIG. 11 (b), five sets of two using 10 coils are used and the discharge interval is 0.2 milliseconds within 5 cycles. The discharge was repeated. As shown in FIG. 10 (c), stable combustion can be realized even with an excess air ratio λ = 2.06, and moreover, in each cycle than in the case of discharging once in one cycle shown in FIG. 10 (b). It can be seen that the fluctuation was reduced.

<Second embodiment>
When the top dead center position is the crank angle θ = 0 ° and the tumble flow in the vicinity of the spark plug at the crank angle θ = −40 ° to −10 ° is controlled to a strong tumble flow of about 15 m / sec, the vicinity of the spark plug The direction of tumble flow was measured using μPIV. The measurement results are shown in FIGS. 12 (a) to 12 (d). The numbers along the circumference in FIGS. 12A to 12D indicate the azimuth (unit: [°]) viewed from the position of the spark plug, and the azimuth toward the exhaust port side is 0 °. The direction toward the intake port side is 180 °. Moreover, the direction of the arrow in FIGS. 12A to 12D indicates the direction of the tumble flow, and the length of the arrow indicates the frequency of the direction of the tumble flow.

  As shown in FIG. 12A, the direction of the tumble flow at the crank angle θ = −40 ° is concentrated around 0 °. As shown in FIG. 12B, the direction of the tumble flow at the crank angle θ = −30 ° is widely dispersed in the range of about 0 ° to 120 °. As shown in FIG. 12 (c), the direction of the tumble flow at the crank angle θ = −20 ° increases with a frequency of about 120 ° to 150 °, and is dispersed in a wider range. As shown in FIG. 12 (d), the direction of the tumble flow at the crank angle θ = −10 ° increases in the frequency of about 120 ° to 180 ° and is dispersed over the entire range of 0 ° to 360 °. Thus, even within one cycle, the direction of the tumble flow varies greatly in the range of 360 ° at a crank angle θ = −40 ° to −10 °.

<Modification>
In the embodiment of the present invention, the substantially conical ground electrodes (21, 22, 23) illustrated in FIGS. 2A to 2C are illustrated, but the shape of the ground electrode is not limited thereto. For example, as shown in FIGS. 13A to 13C, the side surface of the spark extension 22 of the ground electrode (21, 22, 23) may have two inclined surfaces 222a, 222b. . The two inclined surfaces 222a and 222b are provided to face each other in the X direction. For example, the length L1 in the X direction of the spark extension 22 is about 5 mm to 10 mm, the width W3 in the Y direction is about 2 mm to 3 mm, and the curvature radius R of the two inclined surfaces 222a and 222b is 1 mm to 1.mm. It is about 5 mm. Even when the ground electrodes (21, 22, 23) shown in FIGS. 13 (a) to 13 (c) are provided, the discharge path generated in the discharge gap between the tip 11 and the protrusion 23 is a tumble flow. When extending downstream, the discharge point on the protrusion 23 side of the discharge path can be moved downward along one of the two inclined surfaces 222a and 222b.

  Moreover, as shown to Fig.14 (a)-FIG.14 (c), the spark extension part 22 of the ground electrode (21,22,23) may have one inclined surface 222b. When the ground electrodes (21, 22, 23) shown in FIGS. 14 (a) to 14 (c) are provided, the discharge path generated in the discharge gap between the tip 11 and the protrusion 23 is downstream of the tumble flow. When extending to the side, the discharge point on the protrusion 23 side of the discharge path can be moved downward along the inclined surface 222b.

  Further, as shown in FIGS. 15A to 15C, the spark extension 22 of the ground electrode (21, 22, 23) may have a substantially pyramid shape (pyramidal frustum shape). The spark extension 22 has four inclined surfaces 222e, 222f, 222g, and 222h. When the ground electrodes (21, 22, 23) shown in FIGS. 15 (a) to 15 (c) are provided, the discharge path generated in the discharge gap between the tip 11 and the protrusion 23 is caused to flow in a tumble flow. When extending downstream, the spark extension 22 can be moved downward along two boundaries (ridges) of the four inclined surfaces 222e, 222f, 222g, and 222h. 15A to 15C exemplify a quadrangular pyramid shape, but the present invention is not limited to this, and a triangular pyramid shape (triangular frustum shape) or a polygonal pyramid shape having more than a pentagonal pyramid (polygonal frustum shape) ).

  Moreover, as shown to Fig.16 (a), the spark extension part 22 of a ground electrode (21,22,23) may have the convex-shaped (saddle-shaped) inclined surface 222 on the outer side. Moreover, as shown in FIG.16 (b), the spark extension part 22 of a ground electrode (21,22,23) may have the convex inclined surface 222 inside. Even when the ground electrode (21, 22, 23) shown in FIG. 16 (a) or FIG. 16 (b) is provided, the discharge path generated in the discharge gap between the tip 11 and the protrusion 23 is a tumble flow. When extending to the downstream side, the discharge point on the projection 23 side of the discharge path can be moved downward along the inclined surface 222 of the spark extension 22.

  Also, as shown in FIGS. 17A to 17C, the lower end (the bottom surface 223 of the spark extension 22) of the inclined surface (conical surface) 222 of the spark extension 22 of the ground electrode (21, 22, 23). May be rounded (chamfered) and have a curvature. When the inclined surface (conical surface) 222 and the bottom surface 223 of the spark extension 22 form an acute angle, the lower end of the inclined surface (conical surface) 222 is likely to be locally high temperature under high speed and high load operation conditions. On the other hand, since the lower end of the inclined surface (conical surface) 222 of the spark extending portion 22 has a curvature, the lower end of the inclined surface (conical surface) 222 of the spark extending portion 22 is even under high-speed and high-load operation conditions. Locally high temperature can be suppressed, and hot surface ignition can be suppressed. Further, by increasing the diameter of the arm portion 21 of the ground electrode (21, 22, 23), the heat generated in the spark extension portion 22 can easily escape through the arm portion 21, thereby increasing the temperature of the spark extension portion 22. Can be suppressed. The inclined surfaces 222a and 222b shown in FIGS. 13A to 13C, the inclined surfaces 222b shown in FIGS. 14A to 14C, and FIGS. 15A to 15C. The inclined surfaces 222e, 222f, 222g, and 222h shown in FIG. 16 and the lower ends of the inclined surfaces 222 shown in FIGS. 16A and 16B may also have a curvature.

  As shown in FIG. 18, the ground electrode (21 a, 21 b, 22, 23) may have a plurality of (two) arm portions 21 a, 21 b connected to the spark extension 22. The plurality of arm portions 21a and 21b are arranged so as to face each other in the X direction, for example. Thereby, the heat which generate | occur | produced in the spark extension | expansion part 22 can be released via several arm part 21a, 21b. Therefore, even under high-speed and high-load operation conditions, the lower end of the inclined surface (conical surface) 222 of the spark extension 22 can be prevented from locally becoming high temperature, and hot surface ignition can be suppressed. In addition, although the case where it has two arm parts 21a and 21b was illustrated in FIG. 18, you may have three or more arm parts connected to the spark extension part 22. FIG. For example, the three arms may be arranged at equal intervals so as to be separated by 120 ° around the center axis O of the spark plug 1. Further, the four arm portions may be arranged at equal intervals so as to be separated by 90 ° around the center axis O of the spark plug 1.

  In addition, as shown in FIG. 19, the joining position of the spark extension 22 and the arm 21 of the ground electrode (21, 22, 23) may be the lower end of the inclined surface (conical surface) 222 of the spark extension 22. Good. Thereby, the heat generated at the lower end of the inclined surface (conical surface) 222 of the spark extension 22 can be easily released via the arm 21. Therefore, even under high-speed and high-load operation conditions, the lower end of the inclined surface (conical surface) 222 of the spark extension 22 can be prevented from locally becoming high temperature, and hot surface ignition can be suppressed.

  Moreover, as shown to Fig.20 (a)-FIG.20 (c), the ground electrode (21, 22) does not need to have a protrusion part. The spark extension 22 of the ground electrode (21, 22) has a conical shape. In this case, when the discharge path generated in the discharge gap between the tip 11 and the top (vertex) 221 of the spark extension 22 is extended downstream of the tumble flow, the discharge on the top (vertex) 221 side of the discharge path The point moves downward along the inclined surface (conical surface) 222 of the spark extension 22 and stabilizes at the lower end of the inclined surface (conical surface) 222 of the spark extension 22. Note that the shape of the spark extension 22 when the ground electrode (21, 22) does not have a protrusion is not limited to this. For example, the spark extension 22 of the ground electrode (21, 22) may have a truncated cone shape as shown in FIGS. 2 (a) to 2 (c), or may have a pyramid shape.

  Further, as shown in FIGS. 21A to 21C, the spark extension 22 of the ground electrode (21, 22, 23) may be disposed below the end of the arm 21. . The spark extension 22 has a substantially conical shape (conical frustum shape) and has an inclined surface (conical surface) 222 that is inclined with respect to the central axis O of the spark plug 1. The top 221 of the spark extension 22 is joined to the lower surface of the end of the arm 21 by laser welding, resistance welding, or the like.

  In this case, as shown in FIG. 22A, discharge starts at the discharge gap G1 between the tip 11 and the protrusion 23, and the discharge path S is formed in a substantially linear shape. Thereafter, when the discharge path S is extended to the downstream side of the tumble flow F by the tumble flow F, after the discharge point P of the discharge path S moves to the side surface of the arm portion 21, as shown in FIG. The discharge path S further extends, and the discharge point P of the discharge path S moves to the inclined surface (conical surface) 222 of the spark extension 22. Thereafter, the discharge point P of the discharge path S moves downward along the inclined surface (conical surface) 222, and the discharge path S reaches the outer periphery of the bottom surface 223 of the spark extension 22 as shown in FIG. Reach and stabilize. According to the ground electrodes (21, 22, 23) shown in FIG. 21 (a) to FIG. 21 (c), the spark extension 22 is disposed below the end of the arm 21. The substantial discharge gap G2 can be increased below the lower end of the end portion of the portion 21.

  In addition, even when the spark extension 22 of the ground electrode (21, 22, 23) is disposed below the arm 21, the spark extension 22 of various shapes can be employed. For example, as shown in FIGS. 23A to 23C, the spark extension 22 of the ground electrode (21, 22, 23) may have two inclined surfaces 222g and 222h. The two inclined surfaces 222g and 222h are provided to face each other in the X-axis direction. Even when the ground electrodes (21, 22, 23) shown in FIGS. 23 (a) to 23 (c) are provided, the discharge path generated in the discharge gap between the tip 11 and the protrusion 23 is a tumble flow. When extending downstream, the discharge point on the protrusion 23 side of the discharge path is moved from the protrusion 23 to one of the two inclined surfaces 222 g and 222 h via the side surface of the arm 21. It can be moved downward along one of the inclined surfaces 222g and 222h. In addition, when the spark extension part 22 is arrange | positioned under the arm part 21, the shape of the spark extension part 22 is shown in Fig.14 (a)-FIG.14 (c), FIG.15 (a)-figure. The shape shown in FIG. 15 (c), the shape shown in FIG. 16 (a), the shape shown in FIG. 16 (b), the shape shown in FIG. 17 (a) and FIG. .

  FIG. 24A shows a cross-sectional shape obtained by cutting the spark extension 22 and the protrusion 23 of the ground electrode (21, 22, 23) shown in FIGS. 2A to 2C in the X direction. Show. As shown in FIG. 24A, the spark extension 22 has, for example, a trapezoidal cross-sectional shape. As shown in FIG. 24 (b), the concave portion 224 may be provided on the bottom surface side of the spark extending portion 22 so that the inside of the cone is hollow. High lean combustion and high EGR combustion are greatly affected by the cooling loss of the spark plug, but by making the inside of the cone of the spark extension 22 hollow, the heat capacity of the ground electrodes (21, 22, 23) is reduced, and the cooling loss is reduced. Can be reduced.

  Similarly, the spark extension 22 of the ground electrode (21, 22, 23) shown in FIGS. 21 (a) to 2 (c) has a spark extension as in the cross-sectional shape shown in FIG. 24 (c). The shape which provided the recessed part 224 in the bottom face side of 22, and hollowed the cone inside may be sufficient. Note that the spark extension 22 has the shape shown in FIGS. 13 (a) to 13 (c), the shape shown in FIGS. 14 (a) to 14 (c), and FIGS. 15 (a) to 15 (c). ), The shape shown in FIGS. 16 (a) and 16 (b), the shape shown in FIGS. 17 (a) and 17 (b), and FIGS. 20 (a) to 20 (c). Even in the case of the shown shape, the shape shown in FIGS. 23A to 23C, etc., it is also possible to provide a recess on the bottom surface of the spark extension 22 and a cavity on the inside of the spark extension 22. Good.

(Other embodiments)
As mentioned above, although this invention was described by embodiment, it should not be understood that the statement and drawing which form a part of this indication limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art. It goes without saying that the present invention includes various embodiments not described herein. The technical scope of the present invention is determined only by the invention specifying matters according to the scope of claims reasonable from the above description.

DESCRIPTION OF SYMBOLS 1 ... Spark plug 2 ... Cylinder head 3 ... Cylinder 4 ... Piston 5 ... Combustion chamber 6 ... Intake valve 7 ... Exhaust valve 8 ... Intake port 11 ... Exhaust port 11 ... End part 12 ... Main-body part 21, 21a, 21b ... Arm part 22 ... Spark extension 23 ... Projection 31 ... Housing 32 ... Insulator 41 ... Control circuit 42 ... Constant voltage source 43 ... Distributor 51, 52, 53, 54, 55, 56, 57, 58, 59, 60 ... Ignition coil 221: Top portions 222, 222a, 222b, 222e, 222f, 222g, 222h ... Inclined surface 223 ... Bottom surface

Claims (11)

An ignition plug for igniting an air-fuel mixture having an excess air ratio of 1.5 or more in a combustion chamber, or an air-fuel mixture having an excess air ratio of less than 1.5 and an exhaust gas recirculation rate of 20% or more,
A housing whose lower end protrudes into the combustion chamber;
An insulator disposed inside the housing along a central axis of the housing;
A central electrode disposed inside the insulator along the central axis and partially protruding from the lower end of the insulator into the combustion chamber;
One end is connected to the housing, extends downward from the housing, is bent to the central axis side, is connected to the other end of the arm part, the central axis is opposite to the top, and from the top A ground electrode including a spark extension having a shape in which the area in the direction perpendicular to the central axis gradually increases as it goes downward;
A spark plug comprising:   When the discharge path generated in the discharge gap between the center electrode and the ground electrode is extended downstream of the tumble flow by the tumble flow in the discharge gap, the discharge point on the ground electrode side of the discharge path is The spark plug according to claim 1, wherein the spark plug is moved downward by the spark extension portion.   The spark plug according to claim 2, wherein the flow rate of the tumble flow is 15 m / sec to 50 m / sec.   The spark plug according to any one of claims 1 to 3, wherein the spark extension has a conical or pyramidal conical surface. The spark extension has a truncated cone shape or a truncated pyramid shape,
The spark plug according to any one of claims 1 to 3, wherein the ground electrode further includes a protrusion disposed on the spark extension and facing the center electrode.   The spark plug according to any one of claims 1 to 3, wherein the spark extension portion is disposed below the other end of the arm portion.   The spark plug according to any one of claims 1 to 6, wherein a bottom surface of the spark extension portion is positioned below a lower end of the arm portion.   The spark plug according to any one of claims 1 to 7, wherein an outer peripheral portion of a bottom surface of the spark extension portion has a curvature.   The spark plug according to any one of claims 1 to 8, wherein a cavity is provided inside the spark extension portion.   The spark plug according to claim 1, wherein the ground electrode includes a plurality of the arm portions connected to the spark extension portion. The spark plug according to any one of claims 1 to 10, wherein discharge is repeatedly performed within one cycle by a plurality of ignition coils.

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