JP6199671B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug, and more particularly to a spark plug for use in an internal combustion engine for automobiles.

  For this type of spark plug, in addition to the main ground electrode that forms the main discharge gap in the plug axial direction with the center electrode, two sub grounds that form the sub discharge gap in the plug radial direction with the center electrode A so-called tripolar spark plug including an electrode is known (see, for example, Patent Document 1).

JP 2011-154965 A

  In this three-pole spark plug, the main ground electrode is disposed behind the center electrode, and the two sub ground electrodes are disposed on both the left and right sides of the center electrode. Above these ground electrodes, a bottomed cylindrical pocket gap is formed between the insulator and the housing. The pocket gap is opened on the tip end side in the plug axial direction, that is, on the combustion chamber side.

  According to this three-pole spark plug, the ground electrode is disposed behind the center electrode and on both the left and right sides, and the front is open without the ground electrode. When the air-fuel mixture in the combustion chamber enters the space surrounded by the three ground electrodes from this vacant space, the air-fuel mixture enters the pocket gap, and tends to stay out of the pocket. When this stagnation occurs, there is a problem that the air-fuel mixture in the pocket gap continues to receive heat and becomes high temperature, and preignition is likely to occur in the pocket gap. Particularly in recent years, spark ignition type internal combustion engines tend to have a high compression ratio and high supercharging, and the possibility of pre-ignition increases under such circumstances.

  Accordingly, the present invention has been made in view of the above circumstances, and an object thereof is to provide a spark plug that can suppress the occurrence of pre-ignition in a pocket gap.

According to one aspect of the invention,
A central electrode extending from the proximal side to the distal side along the plug axial direction;
A cylindrical insulator for holding the center electrode from the outer peripheral side;
A cylindrical housing for holding the insulator from the outer peripheral side;
A bottomed cylindrical pocket gap formed between the insulator and the housing and opened at the distal end side in the plug axial direction;
A main ground electrode that forms a main discharge gap in the plug axis direction between the central electrode and the center electrode;
A plurality of sub-ground electrodes that form a sub-discharge gap in the radial direction of the plug between the central electrode;
With
The main ground electrode includes a first main extension extending from the housing to the distal end side in the plug axial direction behind the center electrode, and extending forward from the first main extension, A second main extension to be formed,
The sub ground electrode is provided at least one on each of the left and right sides of the center electrode, and a first sub extension extending from the housing toward the distal end side in the plug axial direction on the side of the center electrode; A second sub-extension portion extending from the first sub-extension portion toward the center in the radial direction of the plug and forming the sub-discharge gap; and an upper surface of the second sub-extension portion facing the plug axial direction base end And
The second sub-extension part of at least one of the sub-ground electrodes has a rectangular cross-sectional shape, and the upper surface is formed of the plug shaft so as to form an atmospheric pressure lower than an internal pressure in a rear part of the pocket gap. spark plug, wherein the Ru Tei inclined rearward is provided to a virtual plane perpendicular to.
According to the second aspect of the present invention,
A central electrode extending from the proximal side to the distal side along the plug axial direction;
A cylindrical insulator for holding the center electrode from the outer peripheral side;
A cylindrical housing for holding the insulator from the outer peripheral side;
A bottomed cylindrical pocket gap formed between the insulator and the housing and opened at the distal end side in the plug axial direction;
A main ground electrode that forms a main discharge gap in the plug axis direction between the central electrode and the center electrode;
A plurality of sub-ground electrodes that form a sub-discharge gap in the radial direction of the plug between the central electrode;
With
The main ground electrode includes a first main extension extending from the housing to the distal end side in the plug axial direction behind the center electrode, and extending forward from the first main extension, A second main extension to be formed,
The sub ground electrode is provided at least one on each of the left and right sides of the center electrode, and a first sub extension extending from the housing toward the distal end side in the plug axial direction on the side of the center electrode; A second sub-extension part extending from the first sub-extension part toward the center in the radial direction of the plug and forming the sub-discharge gap;
The second sub-extension portion of at least one of the sub-ground electrodes has a substantially sectional shape of the second sub-extension portion so that an atmospheric pressure lower than the internal pressure in the rear portion of the pocket gap is formed. Mold shape
A spark plug is provided.

  According to this invention, the outstanding effect that generation | occurrence | production of the pre-ignition in a pocket clearance gap can be suppressed is exhibited.

1 shows a spark plug according to an embodiment of the present invention, wherein (A) is a front view when the spark plug is viewed from the front, and (B) is a side view when the spark plug is viewed from the left side (left side view). . It is an enlarged view of the front-end | tip part of a spark plug, (A) is a side view when a spark plug is seen from the right side (right side view), (B) is a front view, (C) is a left side view. It is a figure for demonstrating the effect of this embodiment, and is the III-III cross-section equivalent figure of FIG. 2 (B). It is a figure which shows the result of the numerical analysis simulation in the conventional 1 pole type spark plug. It is a graph which shows the test result which verified the effect of this embodiment. It is a graph which shows the result at the time of implementing the numerical analysis simulation similar to having shown in FIG. 4 about the ignition plug of this embodiment. It is an enlarged view of the front-end | tip part of the spark plug which concerns on 1st other embodiment, (A) is a right view, (B) is a front view, (C) is a left view. It is a graph which shows the test result similar to FIG. 5 in 1st other embodiment. It is an enlarged view of the front-end | tip part of the ignition plug which concerns on 2nd other embodiment, (A) is a right view, (B) is a front view, (C) is a left view. It is a figure which shows the cross-sectional shape of the 2nd sub extension part in 3rd other embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a spark plug 1 according to this embodiment in an attached state. (A) is a front view, (B) is a side view when the spark plug 1 is viewed from the left side to be described later. C represents a plug shaft that forms the central axis of the spark plug 1. In the front view of (A), the upper side (upper side in the plug axis C direction) of the figure is referred to as the base end side or upper side, and the lower side of the figure (lower side in the plug axis C direction) is referred to as the distal end side or lower side. The front side in the paper thickness direction is called the front side, the back side in the paper thickness direction in the figure is called the rear side, the left side of the figure is called the right side (indicated by R), and the right side of the figure is called the left side (indicated by L) ). It should be noted that the left and right sides of the figure and the left and right sides of the spark plug 1 are reversed.

  However, these terms “up”, “down”, “front”, “rear”, “left”, “right” are terms used to specify the direction and orientation only in the illustrated arrangement. It should be noted that the term is not necessarily used to specify the direction or direction in the actual use state.

  The spark plug 1 has a center electrode 2 extending from the base end side to the tip end side along the plug axis C direction, a cylindrical insulator 3 that holds the center electrode 2 from the outer periphery side, and an insulator 3 that is held from the outer periphery side. A cylindrical housing 4 is provided. The center electrode 2, the insulator 3 and the housing 4 are arranged coaxially with the plug shaft C.

  The housing 4 is formed in a substantially cylindrical shape by a metal material, and has a male screw 5 on its outer periphery. In the illustrated example, the housing 4 is screwed into a female screw hole 7 of a cylinder head 6 of a spark ignition type internal combustion engine (gasoline engine or the like). It has been. In this mounted state, the lower end surface 4A of the housing 4 is substantially at the same position in the plug axis C direction or height direction with respect to the lower surface 6A of the cylinder head 6.

  The insulator 3 is formed in a substantially cylindrical shape from, for example, a ceramic material such as alumina, and a tip portion thereof protrudes from the housing 4 toward the tip side in the plug axis C direction. The insulator 3 is inserted into the housing 4. The insulator 3 and the housing 4 are provided with projections 8 and 9, respectively, and the projections 8 and 9 are engaged to position the insulator 3 in the housing 4 in the plug axis C direction. A packing 10 is interposed in the engaging portion where the protrusions 8 and 9 engage with each other, and the engaging portion is hermetically sealed by the packing 10.

  As can be seen from the figure, a bottomed cylindrical pocket gap 11 is formed between the insulator 3 and the housing 4 and opened at the tip end side in the plug axis C direction. The pocket gap 11 is a triangular cross-section and a bottomed cylindrical gap that goes around the plug shaft C, and the upper end portion serving as the bottom of the pocket gap 11 is the engagement portion and packing between the protrusions 8 and 9 described above. 10 is closed or hermetically sealed. And the lower end part used as the entrance of the pocket clearance 11 is open | released by the combustion chamber 12 of the internal combustion engine.

  The center electrode 2 extends in the plug axis C direction over substantially the entire length of the spark plug 1. A base end (not shown) of the center electrode 2 is connected to a terminal attached to the insulator 3. Further, the illustrated distal end portion of the center electrode 2 protrudes from the insulator 3 toward the distal end side in the plug axis C direction. A tapered portion 13 having a diameter that decreases toward the distal end side in the plug axis C direction and a small-diameter and columnar central electrode tip 14 that extends from the tapered portion 13 toward the distal end side in the plug axis C direction are provided at the distal end portion of the center electrode 2. It has been. The taper portion 13 is made of, for example, a nickel alloy, and the center electrode tip 14 is made of, for example, an alloy material containing iridium, rhodium, or the like.

  As enlarged in FIG. 2, the spark plug 1 has a plug radius between the center electrode 2 and the main ground electrode 20 that forms the main discharge gap Y1 in the plug axis C direction with the center electrode 2. And a plurality of sub-ground electrodes 30 that form sub-discharge gaps Y2 in the direction. The plug radial direction means a direction extending perpendicularly to the plug axis C.

  The main ground electrode 20 is generally disposed behind the center electrode 2 and has an overall L shape. The main ground electrode 20 extends from the housing 4 to the front end side in the plug axis C direction behind the center electrode 2, and extends forward from the first main extension 21 to the main discharge gap. And a second main extension 22 that forms Y1. The connecting portion 23 between the first main extending portion 21 and the second main extending portion 22 is curved in a round shape, but may not be curved or may be a right angle. The base end of the first main extension portion 21 is fixed or joined to the lower end surface 4A of the housing 4, and extends downward in a straight line parallel to the plug axis C direction. The second main extension portion 22 extends forward in a straight line shape perpendicular to the plug axis C direction, and a main ground electrode chip 24 is provided on the upper surface of the front end portion which is a free end portion thereof. Yes. The main ground electrode chip 24 is disposed coaxially with the plug axis C, is disposed directly below the center electrode chip 14, is opposed to the center electrode chip 14, and forms a main discharge gap Y <b> 1 with the center electrode chip 14. To do.

  In the present embodiment, one sub-ground electrode 30 is disposed on each of the left and right sides of the center electrode 2. That is, the spark plug 1 of the present embodiment is configured as a so-called tripolar spark plug including two sub ground electrodes 30 in addition to the main ground electrode 20. Hereinafter, the left sub-ground electrode 30 is referred to as the left sub-ground electrode 30L, the right sub-ground electrode 30 is referred to as the right sub-ground electrode 30R, and these are collectively referred to as the sub-ground electrode 30. Components of the left sub-ground electrode 30L are denoted by “L”, and components of the right sub-ground electrode 30R are denoted by “R”.

  The left sub-ground electrode 30L and the right sub-ground electrode 30R are symmetrical with respect to the plug axis C. First, the left sub-ground electrode 30L will be described. The left sub-ground electrode 30L is disposed on the left side of the center electrode 2 and has an overall L shape. The left sub-ground electrode 30L includes a first left sub-extension portion 31L extending from the housing 4 toward the distal end side in the plug axis C direction on the left side of the center electrode 2, and a plug radial direction from the first left sub-extension portion 31L. A second left sub-extending portion 32L that extends to the center side, that is, the right side and forms the left sub-discharge gap Y2.

  The connecting portion 33L between the first left sub-extending portion 31L and the second left sub-extending portion 32L is curved in a round shape, but may not be curved or may be a right angle. The base end of the first left sub-extending portion 31L is fixed or joined to the lower end surface 4A of the housing 4, and extends downward in a straight line parallel to the plug axis C direction. The second left sub-extending portion 32L extends perpendicularly to the plug axis C direction and linearly toward the right side, and the right end surface of the right end portion, which is the free end portion, is a center protruding from the insulator 3 The left sub-discharge gap Y2 is formed between the tapered portion 13 of the electrode 2 and the left side surface of the center electrode tip 14 facing each other.

  Similarly, the right sub-ground electrode 30R is disposed on the right side of the center electrode 2 and has an L shape as a whole. The right sub-ground electrode 30R includes a first right sub-extension portion 31R extending from the housing 4 to the front end side in the plug axis C direction on the right side of the center electrode 2, and a plug radial direction from the first right sub-extension portion 31R. It has a second right sub-extending portion 32R that extends to the center side, that is, the left side and forms the right sub-discharge gap Y2.

  The connecting portion 33R between the first right sub-extending portion 31R and the second right sub-extending portion 32R is curved in a round shape, but may not be curved or may be a right angle. The base end of the first right sub-extending portion 31R is fixed or joined to the lower end surface 4A of the housing 4, and extends downward in a straight line parallel to the plug axis C direction. The second right sub-extending portion 32R extends perpendicularly to the plug axis C direction and linearly toward the left side, and the left end surface of the left end portion which is a free end portion is a center protruding from the insulator 3 The right side sub-discharge gap Y2 is formed between the tapered portion 13 of the electrode 2 and the right side surface of the center electrode tip 14 facing each other.

  Here, when comparing the second left and right sub-extension portions 32L and 32R with the second main extension portion 22 of the main ground electrode 20, the second left and right sub-extension portions 32L and 32R are The second main extending portion 22 is located on the proximal side of the plug axis C direction, that is, on the upper side, and is located closer to the pocket gap 11. The second left sub-extending portion 32L and the second right sub-extending portion 32R are located at the same position in the plug axis C direction, but may be located at different positions. As can be seen from below, the second left and right sub-extending portions 32L, 32R and the second main extending portion 22 extend generally radially at 90 ° intervals about the plug axis C. Become.

  As can be seen from the arrangement of the ground electrodes 20, 30L, and 30R, the ground electrode is disposed only behind the center electrode 2 and on both the left and right sides, and is not disposed in front of the center electrode 2. Therefore, an open space 40 that makes it relatively easy to introduce the air-fuel mixture in the combustion chamber 12 is formed in front of the center electrode 2. Conversely, the space surrounded by the ground electrodes 20, 30L, 30R becomes a closed space 41 that makes it relatively difficult to introduce the air-fuel mixture in the combustion chamber 12 and discharge the air-fuel mixture once entered.

  On the other hand, the second left and right sub-extending portions 32L and 32R have upper surfaces 34L and 34R that face the proximal end side in the plug axis C direction, respectively. The present embodiment is characterized in that the upper surfaces 34L and 34R have inclined surfaces 50 inclined rearward with respect to a virtual plane P perpendicular to the plug axis C.

  That is, the left and right sub-ground electrodes 30L and 30R have a uniform rectangular cross section as shown, and this is the same for the second left and right sub-extending portions 32L and 32R. The rectangular cross section has a length in the front-rear direction that is longer than the length in the vertical direction. The second left and right sub-extending portions 32L and 32R are twisted about the center of the cross section at the base end portions connected to the connecting portions 33L and 33R. Thereby, the upper surfaces 34L and 34R of the second left and right sub-extending portions 32L and 32R are inclined so that the whole faces rearward. In other words, the upper surfaces 34L and 34R are all formed as a rearward inclined surface 50 whose rear end is lower than the front end. At this time, the inclination angle α of the upper surfaces 34L and 34R with respect to the virtual plane P is a predetermined positive value. That is, when the upper surfaces 34L and 34R are inclined or twisted to face rearward, the inclination angle α at that time has a positive value.

  Since the entire second left and right sub-extending portions 32L and 32R are twisted, the front surfaces 35L and 35R, the rear surfaces 36L and 36R, and the lower surfaces 37L and 37R other than the upper surfaces 34L and 34R are also relative to the positions before twisting. It is inclined by the inclination angle α.

  Next, the effect of this embodiment is demonstrated.

  FIG. 3 shows the tip of the spark plug 1 when viewed from the left side in the same manner as FIGS. 1B and 2C, and is a view corresponding to the III-III cross section of FIG. 2B. In general, there are air-fuel mixture flows in various directions in the combustion chamber 12, and one of them is the flow toward the spark plug 1 along the lower surface 6 </ b> A of the cylinder head 6 in the combustion chamber 12 as shown in the figure. There is an incoming flow G (eg a squish flow). On the other hand, the mounting direction of the spark plug 1 with respect to the cylinder head 6 is generally not controllable. In such a situation, as shown in the figure, the air-fuel mixture flow G is directed from the open space 40 of the spark plug 1 into the closed space 41 or from the front to the rear of the spark plug 1. And the subject of the present invention mentioned above tends to arise. In particular, since the flow G as shown tends to occur from the intake side toward the exhaust side, the problem of the present invention is likely to occur when the spark plug 1 is attached toward the intake side.

  That is, the air-fuel mixture flow G is unlikely to come out of the closed space 41, and is therefore deflected upward and easily stays in the pocket gap 11, particularly the rear portion 11 </ b> R. Further, as a cause of the stay, it is conceivable that the air-fuel mixture flow G hits the first main extension portion 21 of the main ground electrode 20 and is inhibited.

  FIG. 4 specifically shows the state of the stay. FIG. 4 shows the result of a numerical analysis simulation of the gas flow rate near the tip of the plug in a conventional unipolar plug having only the main ground electrode 20 and no sub-ground electrode 30. From this result, it can be seen that a low flow rate portion, stagnation or stagnation as shown in the circle a occurs in the rear portion 11R of the pocket gap 11, and gas exchange in the pocket gap 11 is not necessarily good. This is even more so with a three-pole plug as in this embodiment, even with a one-pole plug.

  When such a stagnation occurs, the air-fuel mixture continues to receive heat in the pocket gap 11 (particularly the rear portion 11R) and becomes high temperature, and preignition occurs in which the air-fuel mixture in the pocket gap 11 ignites before the original ignition timing. It becomes easy. Particularly in recent years, spark ignition type internal combustion engines tend to have a high compression ratio and high supercharging. Under such circumstances, the possibility of pre-ignition increases.

  However, according to the present embodiment, as shown in FIG. 3, the air-fuel mixture flow G causes the second left and right sub-extending portions 32L and 32R (only the second left sub-extending portion 32L is shown). When passing, the air-fuel mixture flow G can be split up and down as indicated by G1 and G2. The upper first flow G1 is a flow along the upper surfaces 34L and 34R of the second left and right sub-extending portions 32L and 32R, and the lower second flow G2 is the second left and right sides. This is a flow along the lower surfaces 37L and 37R of the sub-extending portions 32L and 32R.

  The second flow G2 is deflected obliquely downward along the lower surfaces 37L and 37R, whereby the flow velocity of the flow G2 decreases and the atmospheric pressure on the lower surfaces 37L and 37R increases.

  On the other hand, the first flow G1 once strikes the front surfaces 35L and 35R and is deflected obliquely upward, but thereafter is deflected obliquely downward along the upper surfaces 34L and 34R without substantially peeling. As a result, the upward flow toward the inside of the pocket gap 11 is reduced, and the flow velocity of the flow G1 increases and the atmospheric pressure on the upper surfaces 34L and 34R decreases. In particular, the atmospheric pressure on the upper surfaces 34L and 34R is lower than the internal pressure in the rear portion 11R of the pocket gap 11, and a pressure difference occurs between the two.

  Then, the air-fuel mixture in the pocket gap 11 (particularly the rear portion 11R) can be sucked out or discharged as indicated by F by the reduced atmospheric pressure on the upper surfaces 34L and 34R. And the retention of the air-fuel mixture in the pocket gap 11 can be suppressed, and the gas exchange in the pocket gap 11 can be promoted. As a result, it is possible to reliably suppress the occurrence of pre-ignition caused by the high temperature of the air-fuel mixture in the pocket gap 11.

  As described above, in the present embodiment, the plug shafts are formed such that the upper surfaces 34L, 34R of the second left and right sub-extending portions 32L, 32R form an atmospheric pressure lower than the internal pressure in the rear portion 11R of the pocket gap 11. An inclined surface 50 that is inclined backward with respect to a virtual plane P perpendicular to the C direction is formed.

  In the present embodiment, as described above, the second left and right sub-extending portions 32L and 32R are twisted and tilted backward to give the extending portions 32L and 32R a cross-sectional shape similar to the blade shape. As a result, the atmospheric pressure in the vicinity of the upper surfaces 34L and 34R is reduced, and the suction effect from the pocket gap 11 is obtained.

  In particular, in the present embodiment, the inclined surface 50 is provided on the second sub extension portions 32L and 32R of the sub ground electrodes 30L and 30R, which are closer to the pocket gap 11 than the second main extension portion 22 of the main ground electrode 20. Therefore, it is possible to obtain the above-described suction effect more effectively.

  FIG. 5 shows test results for verifying the effects of the present embodiment. In the figure, “three-pole plug embodiment” means the above-described three-pole spark plug according to this embodiment, and “three-pole plug conventional” means the three-pole spark plug according to this embodiment. This means a conventional three-pole spark plug in which the second sub-extending portions 32L and 32R are not twisted and the upper surfaces 34L and 34R are not inclined (that is, α = 0 °). “One-pole plug conventional” means a conventional one-pole spark plug in which the two sub-ground electrodes 30L and 30R are omitted from the three-pole spark plug of the present embodiment.

  During the test, a supercharged gasoline engine with a displacement of 2000 cc was used, and the engine was operated at a rotational speed of 2000 (rpm) and full load, and the ignition timing of the engine was gradually advanced for the purpose of raising the spark plug temperature. The probability of occurrence of self-ignition at the ignition timing (%) was obtained and the ease of occurrence of pre-ignition was evaluated. The inclination angle α in the three-pole plug of this embodiment is 30 (°).

  As is apparent from the figure, in the three-pole plug of this embodiment, the same autoignition occurrence probability occurs on the advance side and the plug high temperature side as compared with the conventional three-pole plug and one-pole plug. . Therefore, it was confirmed that the three-pole plug of this embodiment is very effective in suppressing pre-ignition.

  FIG. 6 shows the results when a numerical analysis simulation similar to that shown in FIG. 4 is performed on the spark plug of the present embodiment. In this case, the inclination angles α of the upper surfaces 34L, 34R of the second sub-extending portions 32L, 32R are changed stepwise in a range of + 90 ° to −90 °, and combustion is performed from the pocket gap 11 for each inclination angle α. The maximum gas flow velocity in the direction of the plug axis C toward the chamber 12 was examined. The flow rate of the gas flow in the combustion chamber 12 in the direction perpendicular to the plug axis C introduced into the spark plug was set to 16 (m / s) as in the simulation shown in FIG. In addition, the maximum gas flow velocity from the pocket gap 11 toward the combustion chamber 12 was examined at the inlet front end position B of the pocket gap 11 (see FIG. 4).

  As shown in FIG. 6, when the inclination angle α is set to a positive value larger than 0 °, compared with the case where the inclination angle α is 0 ° (in the case of a conventional three-pole spark plug), the combustion chamber is formed from the pocket gap 11. The maximum flow velocity of the gas toward 12 increases. From this, it can be seen that when the inclination angle α is set to a positive value, the suction effect of sucking out gas from the pocket gap 11 is obtained.

  In particular, the maximum flow velocity becomes remarkably high in the range of 15 ° ≦ α ≦ 60 °, and it can be seen that a high suction effect is obtained in that range. Therefore, it is preferable to set the inclination angle α within the range. However, it is also possible to set the inclination angle α outside the range.

  In addition, since the suction effect from the pocket clearance 11 is obtained also at the entrance front end position B of the pocket clearance 11, it is considered that this suction effect extends not only to the rear portion 11R of the pocket clearance 11 but also to the whole. . The suction effect is considered to be highest at the rear portion 11R of the pocket gap 11 and gradually weaken as it reaches the front portion of the pocket gap 11. Further, it is considered that the suction effect is reliably obtained at both the left and right side portions of the pocket gap 11.

  On the other hand, as shown in FIG. 6, even when the inclination angle α is set to a negative value smaller than 0 °, the maximum flow velocity is larger than when the inclination angle α is 0 ° (in the case of the conventional tripolar spark plug). Will grow. For this reason, it is also preferable to set the inclination angle α to a negative value because gas exchange in the pocket gap 11 can be promoted. However, the effect in that case is less than when the inclination angle α is set to a positive value.

  Next, another embodiment will be described. The description of the same parts as those in the above-described embodiment (referred to as the basic embodiment) will be omitted, and the following description will focus on the differences.

  FIG. 7 shows a first other embodiment. In this embodiment, in particular, only the configuration of the right sub-ground electrode 30R shown in (A) is different from the basic embodiment, and the second right sub-extension portion is set so that the inclination angle α becomes a negative value smaller than 0 °. The upper surface 34R of 32R is inclined.

  More specifically, the right sub-ground electrode 30R has a uniform rectangular cross section, and the second right sub-extension portion 32R has a second left sub-extension portion approximately around the center of the cross section at the base end thereof. The upper surface 34R of the second right sub-extending portion 32R is inclined so as to face forward, by being twisted in the direction opposite to 32L. In other words, the upper surface 34R is a forward inclined surface 51 whose front end is lower than the rear end. The inclination angle α of the upper surface 34R with respect to the virtual plane P is a predetermined negative value.

  Since the entire second right sub-extending portion 32R is twisted, the front surface 35R, the rear surface 36R, and the lower surface 37R other than the upper surface 34R are also inclined by the inclination angle α with respect to the position before being twisted.

  The configuration of the second left sub-extending portion 32L is the same as that of the basic embodiment. Therefore, in the present embodiment, the left upper surface 34L having a positive inclination angle α and the right upper surface 34R having a negative inclination angle α are combined. The absolute values of the inclination angles α of the upper surfaces 34L and 34R may be the same or different.

  According to the first other embodiment, the upper surface 34L of the second left sub-extending portion 32L is still inclined at the positive inclination angle α, so that the upper surface 34L is used as described in the basic embodiment. Can achieve a good suction effect.

  Further, since the upper surface 34R of the second right sub-extending portion 32R is inclined at the negative inclination angle α, the atmospheric pressure on the upper surface 34R is higher than that when not inclined. However, 1) as described with reference to FIG. 6, the maximum flow velocity from the pocket gap 11 is higher even in the case of the negative inclination angle α than in the case of no inclination, and a certain gas exchange effect is obtained. 2) By increasing the atmospheric pressure, an indentation flow into the pocket gap 11 is generated, and this causes a circumferential circulation flow in the pocket gap 11 to promote the suction effect by the left upper surface 34L. 3) For each engine individual It is possible to obtain a certain pre-ignition suppression effect for reasons such as being able to cope with changes in the spark plug mounting direction.

  FIG. 8 shows the same test results as those in FIG. 5 in which the effect of the present embodiment was verified. In the drawing, “a three-pole plug first other embodiment” means the three-pole spark plug of the present embodiment. As can be seen from the figure, the spark plug of this embodiment is not as much as the basic embodiment, but the same autoignition occurrence probability is more advanced than the conventional three-pole plug and one-pole plug, and the plug is hot. Waking up on the side. Therefore, the spark plug of the present embodiment is also effective in suppressing pre-ignition.

  FIG. 9 shows a second other embodiment. In this embodiment, in particular, only the configuration of the right sub-ground electrode 30R shown in (A) is different from the basic embodiment, and the upper surface 34R of the second right sub-extending portion 32R is not inclined. That is, the inclination angle α of the upper surface 34R is zero. The second right sub-extending portion 32R is not twisted, its upper surface 34R and lower surface 37R are perpendicular to the plug axis C, and the front surface 35R and rear surface 36R are parallel to the plug axis C.

  According to the second other embodiment, the upper surface 34L of the second left sub-extending portion 32L is still inclined at the positive inclination angle α, so that the upper surface 34L is used as described in the basic embodiment. An effective suction effect and a pre-ignition suppression effect.

  FIG. 10 shows a third other embodiment. This embodiment particularly relates to the cross-sectional shapes of the second left and right sub-extending portions 32L and 32R. Although the drawing shows various cross-sectional shapes of the second left sub-extending portion 32L, a similar cross-sectional shape that is symmetrical with respect to the plug axis C can also be applied to the second right sub-extending portion 32R. Will be understood. 10 is a cross-sectional view of the ignition plug as seen from the left side as shown in FIGS. 2 (C), 3, 7 (C), and 9 (C), and the left side of FIG. The right side of 10 is the plug rear. P indicates a virtual plane perpendicular to the plug axis C, but also indicates a reference position (reference height position) of the second left sub-extending portion 32L in the plug axis C direction. This also applies to FIGS.

  In the first embodiment shown in FIG. 10A, the cross-sectional shape of the second left sub-extending portion 32L is generally elliptical or bowl-shaped. The upper surface 34L is curved in an arch shape. The lower surface 37L is a plane that is substantially perpendicular to the plug axis C, but its front and rear end edges are formed in a rounded cross section. The front surface 35L and the rear surface 36L are planes parallel to the plug axis C.

  In the first embodiment, the rear half of the upper surface 34L behind the plug shaft C forms an inclined surface 52 that is inclined backward with respect to the virtual plane P. That is, the upper surface 34L has the inclined surface 52 in the latter half thereof. By having the inclined surface 52, it is possible to obtain the above-described suction effect and further the preignition suppression effect. In particular, since the trajectory length L1 along the upper surface 34L is longer than the trajectory length L2 along the lower surface 37L and the front and rear end edges thereof, the atmospheric pressure on the upper surface 34L can be reduced, and a suction effect can be obtained.

  In the second embodiment shown in FIG. 10B, the cross-sectional shape of the second left sub-extending portion 32L is generally an airfoil shape. The upper surface 34L is formed in an upwardly convex, slightly angular arch shape. The lower surface 37L is formed in a downwardly convex arch shape, but its protruding amount is smaller than that of the upper surface 34L. A front end edge (leading edge) LE and a rear end edge (trailing edge) TE are formed on the front surface 35L and the rear surface 36L. The height positions of the front edge LE and the rear edge TE are the same, but may be different. In particular, the height position of the rear edge TE may be lower than the height position of the front edge LE.

  In the second embodiment, portions of the upper surface 34L and the rear surface 36L from the maximum blade thickness position b to the rear end edge TE form an inclined surface 53 that is inclined rearward with respect to the virtual plane P. Also in this case, the upper surface 34L has the inclined surface 53 in the rear part from the maximum blade thickness position b. By having the inclined surface 53, the above-mentioned suction effect and preignition suppression effect can be obtained. In particular, the trajectory length L1 from the front end edge LE to the rear end edge TE via the upper surface 34L is longer than the trajectory length L2 from the front end edge LE to the rear end edge TE via the lower surface 37L. The pressure can be reduced and a suction effect can be obtained.

  In the third embodiment shown in FIG. 10C, the cross-sectional shape of the second left sub-extending portion 32L is generally bowl-shaped. The front and rear central portions of the upper surface 34L are planes perpendicular to the plug axis C, and the front and rear portions of the upper surface 34L are curved surfaces having a curvature radius R1. The lower surface 37L is a plane that is substantially perpendicular to the plug axis C, but its front and rear end edges are formed in a rounded cross-sectional shape with a radius of curvature R2 smaller than R1. The front surface 35L and the rear surface 36L are planes parallel to the plug axis C, but may be curved surfaces that smoothly connect the curved surfaces having the curvature radii R1 and R2.

  In the third embodiment, the curved surface having the radius of curvature R1 at the rear portion of the upper surface 34L forms an inclined surface 54 that is inclined rearward with respect to the virtual plane P. That is, the upper surface 34L has the inclined surface 54 at the rear part. By having this inclined surface 54, the above-mentioned suction effect and preignition suppression effect can be obtained. In particular, since the trajectory length L1 along the upper surface 34L is longer than the trajectory length L2 along the lower surface 37L and the front and rear end edges thereof, the atmospheric pressure on the upper surface 34L can be reduced, and a suction effect can be obtained.

  In the fourth embodiment shown in FIG. 10D, the cross-sectional shape of the second left sub-extending portion 32L is generally semicircular or truncated. The upper surface 34L is uniformly a curved surface having a curvature radius R1. The lower surface 37L is a plane that is substantially perpendicular to the plug axis C, but its front and rear end edges are formed in a rounded cross-sectional shape with a radius of curvature R2 smaller than R1. The front surface 35L and the rear surface 36L are curved surfaces that smoothly connect the curved surfaces having the curvature radii R1 and R2.

  In the fourth embodiment, the curved surface in the rear half of the upper surface 34L behind the plug axis C forms an inclined surface 55 that is inclined backward with respect to the virtual plane P. That is, the upper surface 34L has the inclined surface 55 in the latter half thereof. By having this inclined surface 55, the above-mentioned suction effect and preignition suppression effect can be obtained. In particular, since the trajectory length L1 along the upper surface 34L is longer than the trajectory length L2 along the lower surface 37L and the front and rear end edges thereof, the atmospheric pressure on the upper surface 34L can be reduced, and a suction effect can be obtained.

  The preferred embodiment of the present invention has been described in detail above, but various other embodiments of the present invention are conceivable. For example, two or more sub-ground electrodes 30L and 30R may be provided on at least one of the left and right sides of the center electrode 2. That is, a total of three or more sub-ground electrodes 30L and 30R may be provided. And at least one of them can be provided with an inclined surface.

  The cross-sectional shapes of the second sub-extending portions 32L and 32R can be other than those described above. For example, among the cross-sectional shapes as shown in FIG. 3, the front surface 35L and the rear surface 36L may be parallel to the plug axis C and may have a rhombic cross-sectional shape.

  The embodiment of the present invention is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

DESCRIPTION OF SYMBOLS 1 Spark plug 2 Center electrode 3 Insulator 4 Housing 11 Pocket clearance 11R Back part 20 Main ground electrode 21 First main extension part 22 Second main extension part 30L Left side sub ground electrode 30R Right side sub ground electrode 31L First Left-side sub-extension part 31R first right-side sub-extension part 32L second left-side sub-extension part 32R second right-side sub-extension part 34L, 34R upper surface 50, 51, 52, 53, 54, 55 inclined surface Y1 Main discharge gap Y2 Sub discharge gap C Plug axis P Virtual plane

Claims (2)

A central electrode extending from the proximal side to the distal side along the plug axial direction;
A cylindrical insulator for holding the center electrode from the outer peripheral side;
A cylindrical housing for holding the insulator from the outer peripheral side;
A bottomed cylindrical pocket gap formed between the insulator and the housing and opened at the distal end side in the plug axial direction;
A main ground electrode that forms a main discharge gap in the plug axis direction between the central electrode and the center electrode;
A plurality of sub-ground electrodes that form a sub-discharge gap in the radial direction of the plug between the central electrode;
With
The main ground electrode includes a first main extension extending from the housing to the distal end side in the plug axial direction behind the center electrode, and extending forward from the first main extension, A second main extension to be formed,
The sub ground electrode is provided at least one on each of the left and right sides of the center electrode, and a first sub extension extending from the housing toward the distal end side in the plug axial direction on the side of the center electrode; A second sub-extension portion extending from the first sub-extension portion toward the center in the radial direction of the plug and forming the sub-discharge gap; and an upper surface of the second sub-extension portion facing the plug axial direction base end And
The second sub-extension part of at least one of the sub-ground electrodes has a rectangular cross-sectional shape, and the upper surface is formed of the plug shaft so as to form an atmospheric pressure lower than an internal pressure in a rear part of the pocket gap. spark plug, wherein the Ru Tei inclined rearward with respect to a virtual plane perpendicular to.   A central electrode extending from the proximal side to the distal side along the plug axial direction;
  A cylindrical insulator for holding the center electrode from the outer peripheral side;
  A cylindrical housing for holding the insulator from the outer peripheral side;
  A bottomed cylindrical pocket gap formed between the insulator and the housing and opened at the distal end side in the plug axial direction;
  A main ground electrode that forms a main discharge gap in the plug axis direction between the central electrode and the center electrode;
  A plurality of sub-ground electrodes that form a sub-discharge gap in the radial direction of the plug between the central electrode;
  With
  The main ground electrode includes a first main extension extending from the housing to the distal end side in the plug axial direction behind the center electrode, and extending forward from the first main extension, A second main extension to be formed,
  The sub ground electrode is provided at least one on each of the left and right sides of the center electrode, and a first sub extension extending from the housing toward the distal end side in the plug axial direction on the side of the center electrode; A second sub-extension part extending from the first sub-extension part toward the center in the radial direction of the plug and forming the sub-discharge gap;
  The second sub-extension portion of at least one of the sub-ground electrodes has a substantially sectional shape of the second sub-extension portion so that an atmospheric pressure lower than the internal pressure in the rear portion of the pocket gap is formed. Mold shape
  A spark plug characterized by that.

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