JP2010238377A - Spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug capable of restraining heated-surface ignition due to overheating of a grounding electrode, and realizing stable ignitability to fuel-air mixture even in case of an internal combustion engine with strong in-cylinder air stream existing in a combustion chamber. <P>SOLUTION: In the spark plug 1 setting in protrusion a tip part 32 of a housing 30 exposed to an inside of the combustion chamber 400 so as to cover a tip part 21 of an insulator 20 in nearly ring-shaped and making at least a part of the outer periphery face a rectifying means for rectifying the in-cylinder air flowing in the combustion chamber 400 and guiding it in a desired direction, a tip 310 of the grounding electrode 31 opposed to a central electrode 10 arranged on a center axis C/L is to be decentered toward a base-end side of the housing 30 with a given angle of eccentricity θ<SB>OFS</SB>against the center axis C/L, and at the same time, the rectifying means is to make an outer periphery face of the tip part 32 of the housing 30 a part of a slanted face of a circular cone with one point on a linear line connecting a tip 101 of the central electrode 10 and the tip 310 of the grounding electrode 31 as a virtual vertex P. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a spark plug used for ignition of an internal combustion engine, and is particularly suitable for a supercharged mixed combustion engine in which a strong in-cylinder airflow is generated in a combustion chamber.

Conventionally, for ignition of an internal combustion engine such as an automobile engine, a center electrode formed in a long axis, a substantially cylindrical insulator covering the outer periphery thereof, a substantially cylindrical housing covering the insulator, A grounding electrode that extends and provides a predetermined discharge gap with respect to the center electrode and is opposed to the center electrode, and generates a spark discharge between the center electrode and the ground electrode by applying a high voltage to ignite. Spark plugs to perform are widely used.
In recent years, higher output and smaller size of internal combustion engines have progressed, the valve occupation area in the combustion chamber has increased, and the space for mounting the spark plug tends to be reduced. In addition, in order to improve the mixing state of the fuel injected into the combustion chamber and compressed air and to further reduce fuel consumption, the in-cylinder airflow generated in the combustion chamber such as tumble vortices tends to be strengthened. The temperature in the combustion chamber tends to increase with vaporization.
However, if the thickness of the insulator that secures electrical insulation between the center electrode and the housing is reduced due to downsizing, the withstand voltage of the insulator becomes insufficient. For this reason, there is a possibility that a phenomenon called discharge occurs, in which discharge occurs between the center electrode and the lower end surface of the housing.
On the other hand, since the ignitability is reduced due to the enhancement of the in-cylinder airflow, a stronger spark discharge is desired for the spark plug in order to realize more stable ignition.

In Patent Document 1, a center electrode having a refractory metal tip fixed to the tip, a shaft-like insulator covering the outside thereof, and a main body formed in a cylindrical shape having both ends open and disposed outside the center electrode The metal base and the base metal side are joined to the metal shell and bent back to the bulletin so that the side faces the refractory metal tip at the tip of the center electrode and forms a spark gap with the refractory metal tip. An attachment screw portion is formed on the outer peripheral surface of the metal shell, and the insulator has an outer diameter and a thickness of the insulator at the opening end of the metal shell within a specific range. A spark plug is disclosed in which the withstand voltage is increased to prevent side jumping.
Patent Document 2 discloses an annular housing that is mounted on an internal combustion engine and has a center electrode and a ground electrode that forms a discharge spark between the center electrodes, and is disposed on the outer periphery of the center electrode. In the spark plug for an internal combustion engine provided with an insulator provided between a center electrode and the housing and electrically insulating the center electrode and the housing, the outer diameter surface of the end surface portion of the housing has the Provided with a tapered surface that forms a rectifier that controls the tumble vortex flow of the air-fuel mixture in the combustion chamber of the internal combustion engine toward the center of the interior of the combustion chamber. And a spark plug that can stabilize the flow direction of the discharge spark and realize good ignition without causing ignition failure even when exposed to a strong in-cylinder airflow in the combustion quality. To have.

In the conventional spark plug as disclosed in Patent Document 1, in order to increase the durability of the center electrode that protrudes long into the combustion chamber, the tip of the center electrode is formed in a predetermined outer diameter range using a refractory metal such as Ir. A discharge chip having high heat resistance is formed. As a result, the center electrode can be made thinner, and accordingly, the thickness of the insulator is increased, or the gap between the housing and the insulator tip is widened to suppress the horizontal jump of the spark. In addition, since the center electrode has a small diameter, heat absorption is reduced, and improvement in ignitability is expected. However, the surface temperature of the ground electrode tends to increase.
For this reason, in a high-load operation region, when a high voltage is applied between the center electrode and the ground electrode in accordance with an ignition signal from the engine control device, the temperature rises rather than the spark discharge generated between both electrodes. There is a possibility that a phenomenon called pre-heated surface ignition (also called preignition or preg) is likely to occur.
Further, in the conventional spark plug as disclosed in Patent Document 2, when the spark plug is attached to an actual engine, the spark plug is always attached while maintaining a constant direction with respect to the flow direction of the in-cylinder airflow generated in the combustion chamber. Do not mean.
For this reason, when the ground electrode is located upstream of the in-cylinder airflow and when it is located downstream, there is a large difference in the flow velocity of the air-fuel mixture that contacts the heated ground electrode, and plague occurs. It has been found that the reliability as an ignition device may be reduced.

  The present invention has been made in view of such circumstances, and suppresses preheated surface ignition due to overheating of the ground electrode in a high load operation region, and in lean combustion or a combustion chamber in a low load operation region or a medium load operation region. Provided is a highly reliable spark plug that realizes stable ignitability of an air-fuel mixture even in a state of low ignitability such as when a strong in-cylinder airflow exists.

According to a first aspect of the present invention, there is provided a central electrode mounted on an internal combustion engine and formed in a long axis shape, a substantially cylindrical insulator covering the outer periphery thereof, a substantially cylindrical housing covering the insulator, and extending to the housing. And a grounding electrode facing the center electrode with a predetermined discharge gap, and applying a high voltage between the center electrode and the ground electrode to generate a spark discharge to generate the internal combustion engine. A spark plug for igniting an engine, wherein a front end portion of the housing exposed in a combustion chamber of the internal combustion engine protrudes so as to cover a front end portion of the insulator in a substantially annular shape, and at least one of outer peripheral surfaces thereof. In the spark plug as a rectifying means for rectifying the in-cylinder airflow flowing in the combustion chamber and guiding it in a desired direction, the ground electrode facing the central electrode disposed on the central axis of the spark plug Up the tip of With a predetermined eccentricity angle theta _OFS with respect to the central axis together with allowed to eccentrically on the base end side of the housing, the rectifier means is the outer peripheral surface of the distal end portion of the housing, at least, it connects the ground electrode has been grounded electrode side The slope angle θ ₁ of the slope is larger than the slope angle θ _{2 of the} slope of the anti-ground electrode side slope not connected to the ground electrode. (Claim 1).

According to the first invention, since the tip of the ground electrode is disposed so as to approach the housing side, the tip of the ground electrode is relatively located on the center axis of the conventional center electrode. The surface temperature of the ground electrode is lowered. In addition, when the ground electrode is on the upstream side with respect to the in-cylinder airflow depending on the state of attachment of the spark plug to the internal combustion engine, the ground electrode has a relatively large inclination angle θ _1. The anti-ground electrode having a relatively small inclination angle θ ₂ when reaching the tip of the ground electrode along the side inclined surface and the ground electrode is downstream of the in-cylinder airflow. Along the side inclined surface, the tip of the ground electrode is reached.
When the ground electrode is upstream, the distance be the inclination angle theta ₁ is relatively large from the rectifying means outer peripheral surface to the ground electrode tip is relatively short flow rate of the in-cylinder air flow greatly without being deceleration in the case where the ground electrode is downstream, since the rectifying means inclined angle theta ₂ even if the distance is relatively long from the outer peripheral surface to the ground electrode tip is relatively small The flow rate of the in-cylinder airflow is not significantly reduced. Therefore, the in-cylinder airflow is rectified so as to go to the tip of the ground electrode regardless of the state of attachment of the spark plug.
For this reason, in a low-load operation region or a medium-load operation region, a lean mixture is always sent between the center electrode where the spark discharge is generated and the ground electrode, so that stable ignition can be realized. Further, in a high load operation region, a strong in-cylinder airflow maintains a relatively high flow velocity and passes over the surface of the ground electrode, so that even when the surface of the ground electrode is at a relatively high temperature, hot surface ignition occurs. Without ignition, ignition is performed only by a spark discharge generated in accordance with an ignition signal transmitted at an appropriate ignition timing from the engine control device.
Therefore, according to the present invention, it is possible to provide a spark plug capable of always suppressing preheated surface ignition and realizing stable ignition regardless of the state of attachment to the internal combustion engine.

  According to a second aspect of the present invention, the outer peripheral surface of the front end portion of the housing is a part of a conical slope whose virtual vertex is one point on a straight line connecting the front end of the center electrode and the front end of the ground electrode. It is characterized (claim 2).

  According to the present invention, the ground electrode of the spark plug may be attached upstream of the in-cylinder airflow even at any attachment position with respect to the in-cylinder airflow flowing through the combustion chamber. Regardless of whether it is attached to the downstream side, the in-cylinder airflow is rectified so as to flow toward the virtual apex, so that the rectification can be performed without significantly reducing the flow velocity. Therefore, it is possible to realize a highly reliable spark plug that exhibits excellent ignitability even in an internal combustion engine in which a strong in-cylinder airflow is generated and that suppresses preheated surface ignition.

  According to a third aspect of the invention, the ground electrode extends from the ground electrode base end connected to the housing into the combustion chamber, and is provided with a substantially L-shaped bent portion so that the tip end side of the ground electrode faces the center electrode. It is characterized by being damped. (Claim 3).

  According to the present invention, the space formed between the center electrode and the ground electrode is widened by the bent portion, and the volumetric and low energy initial flame generated by the spark discharge generated between the two electrodes. Since the nucleus contacts the base end of the ground electrode and is brought into a state of flame growth to some extent without being deprived of heat energy and extinguished by the base end, and then comes into contact with the bent portion, a stable state There is no risk of misfire because it grows in flames. Therefore, a more reliable spark plug can be provided.

(A) is a half sectional view showing an outline of a spark plug of the present invention in a state where it is mounted on an internal combustion engine, and (b) is a perspective view showing a main part of the present invention. (A) is a bottom view of the spark plug of the present invention, (b) is an enlarged cross-sectional view of the main part, and (c) is a characteristic diagram showing a change in the inclination angle of the lower end surface of the housing, which is the main part of the present invention. The principal part enlarged view which shows the effect of the spark plug of this invention in the attachment state from which (a), (b), (c) differs. Explanatory drawing which shows the effect with respect to the ignitability improvement in the spark plug of this invention later on in order of (a) to (C). (A)-(d) is a principal part enlarged view of the spark plug which lacks a part of requirement of this invention shown as a comparative example. (A)-(e) is a principal part schematic diagram which shows the difference of the effect of the Example of this invention, and a comparative example, and the case where the ground electrode is arrange | positioned in the downstream of the in-cylinder airflow on the left side The right side shows a case where the ground electrode is disposed on the upstream side of the in-cylinder airflow. (A) is a characteristic diagram showing the effect on the hot surface ignition occurrence rate of the spark plug of the present invention together with a comparative example, and (b) is a characteristic diagram showing the effect on the combustion limit air-fuel ratio of the spark plug of the present invention together with a comparative example. . (A) is a principal part enlarged view which shows the deformation | transformation tolerance range of the inclined surface of the spark plug of this invention, (b) is a principal part enlarged view which shows the deformation | transformation tolerance range of the ground electrode position of the spark plug of this invention. (A) is a principal part enlarged view which shows the modification of the spark plug of this invention, (b) is a principal part enlarged view which shows the other modification of the spark plug of this invention. The principal part enlarged view which shows another modification of the spark plug of invention. The another example of a spark plug of the present invention is shown, (a) is a bottom view and (b) is the perspective view.

  The present invention is a spark plug used for ignition of an internal combustion engine such as an automobile engine, and particularly used for ignition of a supercharged air-fuel mixture internal combustion engine in which a strong in-cylinder airflow such as a tumble vortex is generated in a combustion chamber. This spark plug is excellent in suppressing hot surface ignition (pre-ignition). In the following description, the upper side of the figure is referred to as the base end side, and the lower side of the figure is referred to as the front end side or the combustion chamber side.

An outline of the spark plug 1 according to the first embodiment of the present invention will be described with reference to FIG. 1A is a half sectional view of the spark plug 1 in a state where it is mounted on the internal combustion engine 40, and FIG. 1B is a bottom perspective view of the spark plug 1 showing the main part of the present invention.
The internal combustion engine 40 includes an engine head 41, a substantially cylindrical cylinder (not shown), and a piston 42 movably housed in the cylinder. The internal wall of the engine head 41, the inner peripheral wall of the cylinder, and the top surface of the piston 42. And the combustion chamber 400 is partitioned. The engine head 41 is formed with an intake cylinder 410 that is opened and closed by an intake valve 411 and an exhaust cylinder 420 that is opened and closed by an exhaust valve 421, and fuel injected from the fuel injection device (not shown) into the combustion chamber 400 and the intake cylinder The air introduced from 410 into the combustion chamber 400 is compressed by the piston 42, and the air-fuel mixture is ignited by the spark plug 1 of the present invention at a predetermined ignition timing.

The spark plug 1 is placed in a plug hole 450 formed in the engine head 41 of the internal combustion engine 40, and is fixed in a state where a tip end portion is exposed in the engine combustion chamber 400.
The spark plug 1 accommodates an insulator 20 formed in a substantially cylindrical shape, a substantially long axis center electrode 10 inserted and fixed in a shaft hole provided in the insulator 20, and the insulator 20 therein. The housing 30 is fixed to the cylinder head 41 of the internal combustion engine 40, and the ground electrode 31 is provided to extend from the tip of the housing 30.

The center electrode 10 is formed in a long axis shape using, for example, a metal material excellent in thermal conductivity such as Cu as an inner material and using a metal material excellent in heat resistance and corrosion resistance such as a Ni-based alloy as an outer material. ing. The center electrode 10 is provided so that the front end surface thereof is exposed from the insulator 20 into the combustion chamber 400. Further, a center electrode discharge tip 101 made of an iridium alloy having high heat resistance or a special Ni alloy is provided on the front end surface of the center electrode 10 so as to protrude toward the combustion chamber 400 side.
On the proximal end side of the center electrode 10, a long-axis stem 11 that is electrically connected to the center electrode 11 via a conductive glass seal is provided inside the shaft hole of the insulator 20. Further, on the base end side, a center electrode terminal portion 12 is formed which is exposed from the insulator head 25 and connected to an external ignition device (not shown).

The insulator 20 is formed in a substantially cylindrical shape using a ceramic material excellent in heat resistance and insulation such as high-purity alumina. A central electrode 10 and a stem 11 formed in a substantially long axis shape are inserted and fixed in the shaft hole of the insulator 20. Engagement portions 22, 23, 24 having a large diameter are formed in the middle of the insulator 20, and are engaged with a housing engagement portion 35 provided inside the housing 30. It is fixed by caulking by a caulking portion 36.
The front end portion 21 of the insulator 20 is exposed to the combustion chamber 400, and the outside thereof is surrounded by a rectifying portion 32 formed in a substantially annular shape, which is a main portion of the present invention, provided at the front end of the housing 30.
On the base end side of the insulator 20, an insulator head 25 that is exposed from the caulking portion 36 of the housing 30 is provided. The insulator head 25 is formed in a corrugated shape and increases the surface distance between the center electrode terminal portion 12 and the housing 30 to prevent creeping leakage.

The housing 30 is formed in a substantially cylindrical shape using a high heat-resistant metal material such as conductive low carbon steel. At the front end side of the housing 30, a side electrode 33 is formed opposite to the side surface of the center electrode 10 with the insulator 20 interposed therebetween. On the outer peripheral surface of the side electrode 33, a screw portion 34 for fixing to a screw hole provided in the engine head 41 is provided. A substantially annular shroud portion 32 that protrudes into the combustion chamber 400 with the inner wall of the engine head 41 as a reference plane is projected from the distal end side of the screw portion 34. The outer peripheral surface 320 of the shroud portion 32 is a main part of the present invention, and serves as an in-cylinder airflow rectifying means, and a point on a straight line connecting the tip of the center electrode discharge tip 101 and the tip of the ground electrode discharge tip 310 is a virtual vertex P. It forms part of the conical slope.
Locking portions 35 and 36 whose diameter decreases toward the distal end side are formed on the inner circumference of the housing 30, and the locking portions 22 and 23 of the insulator 20 are locked on the inner side, and caulking is performed on the proximal end side A portion 36 is formed and fixed by caulking so as to cover the locking portion 24 of the insulator 20 via a sealing member.
A nut portion 37 for tightening the screw portion 34 is formed on the outer periphery of the base end side of the housing 30. The screw portion 34 is screwed into a screw hole provided in the engine head 41 via a gasket 39.

A ground electrode 31 is formed along the shroud portion 32 of the housing 30. The ground electrode 31 is formed in a substantially prismatic cross section using, for example, a Ni-based alloy containing Ni as a main component.
The ground electrode 31 is formed in a substantially L shape while projecting toward the combustion chamber 400, and a straight line connecting the tip of the ground electrode discharge tip 310 and the tip of the center electrode discharge tip 101 is the center axis C / L of the center electrode 10. On the other hand, it is formed so as to form a predetermined eccentric angle θ _OFS . Further, the size of the spark discharge gap G can be set to about 1 mm, for example. The center electrode discharge chip 101 and the ground electrode discharge chip 310 are made of, for example, an Ir (iridium) alloy, a Pt (platinum) alloy, or the like, and are surfaces facing the center electrode 101 at the tips of the center electrode 11 and the ground electrode 31, respectively. It is joined to the top by laser welding or resistance welding.

With reference to FIG. 2, the shroud part 32 and the ground electrode 31 which are the principal parts of this invention are explained in full detail. 2A is a bottom view of the shroud portion 32 and the ground electrode 31 as viewed from the combustion chamber 400 side, FIG. 2B is a sectional view thereof, and FIG. 2C is an inclination angle 320 of the inclined surface of the shroud portion 32. It is a characteristic view which shows the change of ((psi)).
The shroud portion 32 projects into the combustion chamber 400 by a length L up to the leading edge EDG ₃₂ with the inner wall of the engine head 41 indicated by a thick dashed line in FIG.
The inclined surface of the shroud portion 32 is formed so as to form a part of the inclined surface of the cone CON ₃₂ having the virtual vertex P indicated by a thick dotted line in FIG.
The inclined surface on the side to which the ground electrode 31 is connected is the ground electrode side inclined surface 321, the inclined surface on the side facing the position to which the ground electrode 31 is connected is the anti-ground electrode side inclined surface 322, and the ground electrode side inclined surface is The inclination angle of the surface 321 with the tip edge EDG ₃₂ is the ground electrode side inclination angle θ _1, and the inclination angle of the anti-ground electrode side inclination surface 322 with the tip edge EDG ₃₂ is the anti-ground electrode side inclination angle θ _2. Assuming that the inclination angle 320 (ψ) toward the virtual vertex P at an arbitrary angle ψ in the circumferential direction of the tip edge EDG ₃₂ with the side inclined surface 321 as the origin, the inclination angle 320 (ψ) is shown in FIG. As shown, it is formed so as to change linearly from the ground electrode side inclination angle θ ₁ to the anti-ground electrode side inclination angle θ ₂ .
Further, as shown in FIG. 2B, the ground electrode 31 has a base end portion 313 that is fixed to the inclined surface 322 of the shroud portion 32 of the housing 30 by welding or the like, and extends so as to protrude into the combustion chamber 400. Further, the intermediate portion 312 is bent into a curved shape or a substantially L shape so as to go toward the center electrode discharge tip 101 provided on the center electrode 10.
On the surface 311 facing the center electrode discharge chip 101 on the front end side of the ground electrode 31, a ground electrode discharge chip 310 protruding toward the center electrode discharge chip 101 with a predetermined discharge gap G from the center electrode discharge chip 101 is provided. Is provided.
The tip position of the ground electrode 31 is not the tip side surface 311 of the ground electrode 31 facing the center electrode 10 on the center line C / L of the center electrode 10 as in the prior art, but the tip position of the ground electrode discharge chip 310. A straight line connecting the tip of the center electrode discharge chip 101 is formed so as to form a predetermined eccentric angle θ _OFS with respect to the center axis C / L of the center electrode 10.

  The effects of the present invention will be described with reference to FIGS. FIG. 3 schematically shows the surface temperature distribution of the ground electrode 31 and the state of the in-cylinder airflow flowing in the combustion chamber 400. FIG. 3A shows the downstream side (EX side) of the ground electrode 31 with respect to the in-cylinder airflow TMB. (B) shows a case where the ground electrode 31 is attached at a position where the in-cylinder airflow TMB is received on the side surface, and (c) shows an upstream of the in-cylinder airflow TMB. The case where it is attached to the side (IN side) is shown. FIG. 4 schematically shows how a flame grows from the occurrence of spark discharge in the order of (a) to (c).

As the basic configuration of the present invention, since the tip of the ground electrode 31 is offset to the base end side, the protruding length into the combustion chamber 400 becomes relatively short, so that the temperature of the surface of the ground electrode becomes lower than the conventional one. .
In addition, as shown in FIG. 3A, when the ground electrode 31 is on the downstream side (EX side) of the in-cylinder airflow TMB, the in-cylinder airflow TMB is caused by the anti-grounding electrode inclined surface 322 to generate a virtual vertex P. Since the direction is gradually changed and rectified, the contact is made with the tip side of the ground electrode 31 having the highest surface temperature without almost losing the flow velocity. Therefore, even if the surface temperature of the ground electrode is relatively high in the high-load operation region, the air-fuel mixture has a high flow velocity, so there is no possibility of causing early hot surface ignition.
Further, as shown in (b), even when the in-cylinder airflow TMB hits the ground electrode 31 from the side surface direction, the in-cylinder airflow TMB is gradually changed in direction toward the virtual vertex P by the inclined surface 323 and rectified. Therefore, it contacts the front end side of the ground electrode 31 having the highest surface temperature without losing the flow velocity. Therefore, even if the surface temperature of the ground electrode becomes relatively high in the high load operation region, the flow rate of the air-fuel mixture is high, so there is no possibility of causing preheated surface ignition.
Further, as shown in (c), when the ground electrode 31 is on the upstream side (IN side) of the in-cylinder airflow TMB, the in-cylinder airflow TMB with a high flow velocity collides with the ground electrode 31 and the ground electrode Since the in-cylinder airflow TMB flowing around the base end portion 313 of the 31 is gradually rectified and rectified toward the virtual vertex P by the ground electrode side inclined surface 321, the surface temperature is the highest without almost losing the flow velocity. It contacts the tip side of the high ground electrode 31. Therefore, even if the surface temperature of the ground electrode becomes relatively high in the high load operation region, the flow rate of the air-fuel mixture is high, so there is no possibility of causing preheated surface ignition.
Therefore, according to the present invention, regardless of the direction in which the spark plug 1 is attached, the in-cylinder airflow is always guided to the virtual vertex P while maintaining a high flow velocity, and the highest temperature grounding is maintained while maintaining the high flow velocity. Since it reaches the tip surface of the electrode 31, it is difficult to cause preheated surface ignition.

The effect of the present invention on improving the ignitability will be described with reference to FIG.
When a high voltage is applied between the center electrode 10 and the ground electrode 31, a spark discharge is generated between the center electrode discharge chip 101 and the ground electrode discharge chip 310, as shown in FIG. Along with the in-cylinder airflow TMB rectified toward the virtual vertex P existing in the middle of the discharge path by the inclined surface of the shroud portion 32, the air-fuel mixture is carried to the center of the spark discharge, and an initial flame kernel is generated. At this time, since the bent portion 312 is formed in the ground electrode 31, a relatively wide space is formed between the center electrode 10 and the ground electrode 31. For this reason, there is no risk that the relatively low energy initial flame kernel contacts the ground electrode 31 and loses energy, and the in-cylinder airflow rectified toward the virtual vertex P as shown in FIG. The air-fuel mixture is further supplied to the initial flame kernel together with the TMB, and the flame kernel continues to grow without being extinguished because it contacts the ground electrode 31 when it has grown to a relatively stable flame kernel. Further, as shown in FIG. 4C, the air-fuel mixture is successively supplied to the flame nuclei by the in-cylinder airflow TMB, and the flame nuclei are greatly grown and conveyed to the downstream side (EX side) by the in-cylinder airflow. A combustion explosion occurs.

According to the spark plug of the present invention, in the low-load operation region and the medium-load operation region, the center electrode 10 in which a lean air-fuel mixture always generates a spark discharge by the in-cylinder airflow TMB rectified toward the peak P. Since it is sent between the electrode and the ground electrode 31, stable ignition can be realized.
Further, in the high load operation region, the strong in-cylinder airflow TMB maintains a relatively high flow rate and passes over the surface of the ground electrode 31, so that even if the surface of the ground electrode 31 is at a relatively high temperature, Without ignition, ignition is performed only by a spark discharge generated according to an ignition signal transmitted at an appropriate ignition timing from the engine control device.

FIG. 5 shows a configuration that does not include some of the requirements of the present invention as a comparative example.
In this figure (a), in the spark plug 1w shown as the comparative example 1, although the shroud part 32w is substantially cyclic | annular, the taper part is not formed and the ground electrode 31w is curved by the substantially L shape, but it is centered. The electrode discharge chip 101w and the ground electrode discharge chip 310w face each other on the central axis C / L and are not offset.
In the spark plug 1x shown as Comparative Example 2 in FIG. 4B, the shroud portion 32x has a tapered portion formed with the same inclination angle over the entire circumference, and the ground electrode 31x is substantially omitted. Although curved in an L shape, the center electrode discharge tip 101x and the ground electrode discharge tip 310x face each other on the center axis C / L and are not offset.
In this figure (c), in the spark plug 1y shown as the comparative example 3, the shroud portion 32y has a substantially annular shape, is not formed with a taper portion, and the ground electrode 31y is curved in a substantially L shape. The electrode discharge tip 101y and the ground electrode discharge tip 310y are opposed to each other with a predetermined inclination angle θ _OFS with respect to the central axis C / L.
In the spark plug 1z shown as Comparative Example 4 in FIG. 4D, the shroud portion 32z is formed with a taper portion formed with the same inclination angle over the entire circumference, and the ground electrode 31z is linear. The center electrode discharge tip 101z and the ground electrode 31z are opposed to each other with a predetermined inclination angle θ _OFS with respect to the center axis C / L.

FIG. 6 collectively shows the difference in effect between the example of the present invention and the comparative example. The left side of the figure shows the case where the ground electrode is downstream of the in-cylinder airflow, the right side of the figure shows the case where the ground electrode is upstream of the in-cylinder airflow, and (a) is an embodiment of the present invention. , (B) to (e) show Comparative Examples 1 to 4, respectively.
As shown in FIG. 6 (a), in Example 1, when the ground electrode 31 on the upstream side of the cylinder air flow TMB (IN side), rectifying means outer circumferential inclination angle theta ₁ is also relatively large Since the distance from the surface 321 to the tip of the ground electrode 31 is relatively short, the flow velocity of the in-cylinder airflow TMB is not significantly reduced, and the rectifying means is used when the ground electrode 31 is on the downstream side (EX side). never the distance from the outer peripheral surface 322 to the tip of the ground electrode 31 is relatively longer inclined angle theta ₂ is relatively small the flow velocity of the in-cylinder airflow TMB is greatly decelerated. Therefore, regardless of whether the ground electrode 31 is on the upstream side (IN side) or the downstream side (EX side), the in-cylinder airflow TMB contacts the surface of the ground electrode 31 while maintaining a high flow rate. There is no risk of surface ignition.
On the other hand, as shown in this figure (b), in the comparative example 1, since the ground electrode 31w is long and protrudes in the combustion chamber 400, surface temperature tends to become high. In addition, since the taper is not formed on the outer peripheral surface of the shroud portion 32w, the in-cylinder airflow TMB that collides with the side surface of the shroud portion 32w can be suddenly changed in direction, so that it passes through the side surface of the shroud portion 32w. Swirl is likely to occur, and when contacting the surface of the ground electrode 31w, the flow rate is slow, and preheated surface ignition PIG is likely to occur.
As shown in FIG. 6C, in Comparative Example 2, since the ground electrode 32x is not offset, the surface temperature becomes high as in Comparative Example 1, and the condition that the preheated surface ignition PIG is relatively likely to occur. It has become. When the ground electrode 32x is on the downstream side, the in-cylinder airflow TMB is carried in the tip direction of the ground electrode 32x by the taper provided on the outer peripheral surface of the shroud portion 32x without decreasing the flow velocity. Is less likely to occur. However, since the taper is formed at the same angle over the entire circumference, when the ground electrode 32x is on the upstream side, the airflow around the ground electrode 32x does not go to the tip of the ground electrode 32x. Premature heating surface ignition PIG is likely to occur.
As shown in FIG. 4D, in Comparative Example 3, since the ground electrode 31y is offset with respect to the central axis C / L, the surface temperature of the ground electrode 31y is relatively low. However, since the tapered portion is not provided on the outer peripheral surface of the shroud portion 32y, the flow velocity is reduced when the in-cylinder airflow TMB collides with the side surface of the shroud portion 32y. For this reason, when the ground electrode 31y is on the downstream side of the in-cylinder airflow TMB, preheated surface ignition is less likely to occur. However, when the ground electrode 31y is on the upstream side of the in-cylinder airflow TMB, the flow velocity is low, so Premature heating surface ignition PIG is likely to occur.
As shown in FIG. 5E, in Comparative Example 4, the outer peripheral surface of the shroud portion 32z is tapered, and the ground electrode 31z is also offset with respect to the central axis C / L. The surface temperature is low, and preheated surface ignition PIG hardly occurs. However, since the ground electrode 31z is formed in a straight line, the space between the center electrode 10z and the ground electrode 31z is narrow, and the ground electrode 31z comes into contact with the ground electrode 31z at an early stage where the flame nucleus FK generated at the time of ignition does not grow. May lose energy and extinguish. In particular, since the air-fuel ratio is high and lean in the low load operation region to the medium load operation region, there is a possibility that the initial flame kernel Fk is skipped by the strong in-cylinder airflow TMB and misfire is caused.

FIG. 7 shows a more specific effect of the present invention together with a comparative example. This figure (a) is a characteristic figure which shows the preheating surface ignition incidence with respect to a ground electrode temperature, and this figure (b) is a characteristic figure which shows a combustion limit air fuel ratio.
As shown in FIG. 7A, in the case of Comparative Example 3, preheated surface ignition starts when the surface temperature of the ground electrode 31y is 900 ° C. or higher, and overheated with a probability of almost 100% at 1000 ° C. Surface ignition is occurring.
On the other hand, in the embodiment of the present invention, the preheating surface ignition does not occur when the surface temperature of the ground electrode 31 is 1000 ° C. or less, and the preheating surface ignition begins to occur when the surface temperature is 1050 ° C. or more. About the rate of occurrence in Example 3, it was found that when the temperature is 1200 ° C. or higher, preheated surface ignition occurs with a probability of 100%.
This test is the result of investigating the occurrence of preheated surface ignition while heating the ground electrode and changing the surface temperature under the conditions of an engine speed of 3000 rpm and 400 Nm using a test combustion engine.
In this embodiment, the ground electrode side slope angle θ ₁ is set to 40 degrees, the anti-ground electrode side slope angle θ ₂ is set to 30 degrees, and the protruding length L of the shroud portion 32 is set to 2 mm.
As shown in FIG. 7 (b), the examples of the present invention and the comparative example 3 have the same combustion limit, and the comparative example 4 is confirmed to have a low combustion limit and poor ignitability during lean combustion. It was done.

With reference to FIG. 8, the modification of the spark plug 1 in the 1st Embodiment of this invention is demonstrated.
FIG. 8A is an enlarged view of a main part showing a deformation allowable range of the inclined surface 32 of the spark plug 1 of the present invention, and FIG. 8B is a deformation allowable range of the offset position of the ground electrode 32 of the spark plug 1 of the present invention. FIG.
The position of the virtual vertex P of the cone CON ₃₂ forming the outer peripheral surface of the shroud portion 32 in the spark plug 1 of the present invention is on the straight line connecting the tip of the center electrode discharge tip 101 and the tip of the ground electrode discharge tip 310. leading edge EDG ₃₂ parts 32 and the inclination angle θ formed between the virtual apex P, as a reference surface to the inner wall of the engine head 41 shown by a bold dashed line in the figure, the intersection between the outer periphery of the reference plane and the shroud portion 32 and it can be appropriately changed in a range AP from the intersection _{P 1} of a straight line LL ₁ connecting the leading edge _{EDG 32} of shroud portion 32 to the connecting portion the lower end _{P 2} of the ground electrode discharge tip 310. At this time, it can be set in the range of theta _1max from _1min ground electrode side inclined angle theta ₁ theta, anti ground electrode inclination angle theta ₂ is made possible settings from theta _2min in the range of theta _2max. Specifically, θ ₂ is desirably an angle of 20 degrees or more and 60 degrees or less.
Further, the virtual vertex P point can be appropriately changed within a range AP from the intermediate point of the discharge gap G to the connection portion lower end P ₂ of the discharge chip 310. Further, it is on the ground electrode 31 side with respect to the central axis C / L, and is on the central axis C / L side with respect to the tip edge of the ground electrode 31.
It has been found that such a configuration can achieve both suppression of hot surface ignition and ignitability.
The distance L ₃ from the reference plane to the tip of the ground electrode 31, it has been found desirable to or less 8 mm.
Also, when the end edge of the inclined surface 322 of the anti-ground-electrode is exposed from the reference plane, when the projection length and L _2, but L ₂ is as small as possible is desired, 0.2 to L 2 _{/ L} Then, it was found that the effect of the present invention can be obtained. Most of the inclined surfaces of the shroud portion 32 can be used for airflow control.
Further, the tilt angle theta _OFS of the ground electrode 31, can be set in the theta range of _{OFS (min)} from theta _{OFS (max),} it can be changed the position of the virtual vertex P in the range _{A P} denoted by the tolerance hatching . More specifically, it is desirable that θ _{OFS be} an angle greater than 0 degree and 60 degrees or less.

FIG. 9A is an enlarged view of a main part showing a modification of the spark plug of the present invention, and FIG. 9B is an enlarged view of a main part showing another modification of the spark plug of the present invention.
As shown to Fig.9 (a), in the spark plug 1a in this embodiment, you may form in the curved surface shape in which the inclined surface of the shroud part 32a was dented inside. However, it is desirable that the tangent line at the leading edge EDG 32 a of the shroud portion 32 a of the concave surface portion is directed toward the virtual vertex P. By adopting such a configuration, the in-cylinder airflow is rectified toward the virtual apex P without greatly reducing the speed, regardless of the direction in which the spark plug 1a is attached. The same effect as the above embodiment of the present invention that suppresses ignition is exhibited.
In the spark plug 1b in the embodiment shown in FIG. 9B, in addition to the same configuration as that in the above embodiment, the center electrode discharge chip 101b and the surface of the ground electrode discharge chip 310 are parallel to the surface of the center electrode discharge chip 101b. The point that the discharge chip 101b is inclined is different. By adopting such a configuration, in addition to the same effects as those of the above-described embodiment, an improvement in durability of the center electrode discharge tip 101b can be expected.

FIG. 10 is an enlarged view of a main part showing another modification of the spark plug of the present invention, and FIG. 11 is a bottom view and a perspective view showing another modification of the spark plug of the present invention.
In the spark plug 1c shown in FIG. 10, in addition to the same configuration as that of the above embodiment, the angle formed between the inclined surface of the conical surface having the virtual vertex P as the vertex and the lower edge EDG ₃₂ of the shroud portion 32c is constant. The lower edge EDG32 is inclined. Even in such a configuration, the same effect as in the above embodiment is exhibited. Furthermore, in the present embodiment, it is easy to process the inclined surface of the shroud portion 32c.
In the spark plug 1d shown in FIG. 11, the inclined surface of the shroud portion 32d may be formed by inclined surfaces having a plurality of different inclination angles as shown by S1, S2, S3, and S4 instead of the conical inclined surface. . Even if it is partially inclined as in this embodiment, the same effect can be obtained if the airflow is controlled.

DESCRIPTION OF SYMBOLS 1 Spark plug 10 Center electrode 11 Center electrode center shaft part 110 Center electrode discharge part 12 Center electrode terminal part 20 Insulator 21 Insulator tip part 30 Housing 31 Ground electrode 32 Shroud part (rectifying means)
321 Ground electrode side slope 322 Anti-ground electrode side slope 40 Internal combustion engine 400 Combustion chamber 41 Engine head 450 Plug hole P Virtual vertex θ _OFS eccentric angle θ ₁ Ground electrode side tilt angle θ ₂ Anti-ground electrode side tilt angle L Shroud protrusion length The

JP 2000-243535 A JP 2008-10479 A

Claims (3)

A center electrode mounted on an internal combustion engine and formed in a long axis, a substantially cylindrical insulator covering the outer periphery thereof, a substantially cylindrical housing covering the insulator, and the center electrode extending to the housing A spark having a predetermined discharge gap and opposing ground electrode, and applying a high voltage between the center electrode and the ground electrode to generate a spark discharge to ignite the internal combustion engine A plug,
An in-cylinder airflow that flows through at least a part of the outer peripheral surface of the housing exposed in the combustion chamber of the internal combustion engine so as to cover the tip of the insulator in a substantially annular shape. In the spark plug that is a rectifying means that rectifies and guides in a desired direction
The front end of the ground electrode facing the center electrode disposed on the center axis of the spark plug is decentered toward the base end side of the housing with a predetermined eccentric angle θ _OFS with respect to the center axis;
The rectifier means, the outer peripheral surface of the distal end portion of the housing, at least, the inclination angle theta ₁ of the connected ground electrode-side slope of the ground electrode, the inclination of the anti-ground-electrode-side inclined surface which is not connected to the ground electrode A spark plug characterized by having an angle larger than the angle θ ₂ . 2. The outer peripheral surface of the front end portion of the housing is a part of a conical slope whose virtual vertex is one point on a straight line connecting the front end of the center electrode and the front end of the ground electrode. Spark plug as described in.   The ground electrode extends from the ground electrode base end connected to the housing into the combustion chamber, and is provided with a substantially L-shaped bent portion so that the front end side of the ground electrode faces the center electrode. The spark plug according to claim 1 or 2.

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