JP5451490B2 - Spark plug and engine - Google Patents

Description

  In the present invention, a center electrode disposed on a plug center line and a ground electrode provided opposite to the center electrode and having a symmetrical discharge portion with respect to the plug center line are formed in the plug cover. An ignition plug provided in the ignition chamber and provided with a plurality of communication holes in the plug cover for connecting the ignition chamber and the combustion chamber facing the piston of the engine when mounted on the cylinder head, and the ignition plug Relates to an engine equipped with

This type of engine is also called a sub-chamber engine, and Patent Documents 1 and 2 disclose this type of spark plug and sub-chamber engine.
In this sub-chamber engine, in the compression stroke, the mixture of fuel and combustion air flows into the ignition chamber due to the rise of the piston in the combustion chamber, and near the end of the compression stroke or the beginning of the expansion stroke. A combustion flame is generated in the ignition chamber by blowing a spark between the center electrode and the discharge part provided in the ground electrode, and the combustion flame is ejected from the ignition chamber to the combustion chamber through the communication hole in the expansion stroke. The combustion of the mixed gas in the combustion chamber can proceed favorably.
In the ignition system in which the air-fuel mixture that has entered the ignition chamber from the ignition chamber is spark-ignited by an ignition plug, and the generated combustion flame is ejected from the communication hole, the air-fuel mixture in the combustion chamber is rapidly ignited at multiple points and is relatively combustible. Stable operation is possible even with an engine that uses city gas, which is mainly composed of methane or the like, which is low in fuel. Therefore, this type of spark plug has a relatively large bore, fuel is gas, and for a gas engine for power generation with lean combustion, it shortens the combustion period and reduces emissions such as improved thermal efficiency and reduced NOx. It can be said that it is a very useful spark plug that can greatly contribute.

JP 2007-77902 A JP 2007-40174 A JP 2001-284014 A

  As described in Patent Document 3, conventionally, since the ground electrode of the spark plug inhibits the growth of flame nuclei after ignition (flame extinguishing action), those with a wider ground electrode have a greater flame extinguishing action and ignition. It is known that the sex is inferior. However, an ignition chamber as described in the present application is provided in a conventional spark plug, and ignition is performed in the ignition chamber, and rapid combustion of the combustion chamber is caused by a flame injected from a communication hole provided between the combustion chamber and the ignition chamber. In the sub-chamber type spark plug to be realized, it is not clear how the size and configuration of the ground electrode can be improved to improve ignitability and perform stable ignition.

  In particular, in the sub-chamber type spark plug, since the air-fuel mixture enters from the combustion chamber into the ignition chamber through the communication hole in the compression stroke, the flow rate of the air-fuel mixture in the ignition chamber tends to be high, and the high-speed mixed air flow is the center. If the direct flow between the electrode and the ground electrode at a high speed, the formation of the spark may become unstable. On the other hand, if the operation is repeated continuously, the ground electrode tends to become hot, and the ground electrode is cooled (generally referred to as “heat extraction”), which is performed by the air-fuel mixture ejected from the ignition chamber to the combustion chamber through the communication hole. Sub-chamber type ignition plug that the ground electrode itself works as a surface igniter and generates sparks to set the ignition timing if the heat radiation from the ground electrode and the heat transfer to the ground electrode proximal end are not sufficient It also occurs when the role of is lost.

  The present invention has been made paying attention to such a point, and an object thereof is to provide an ignition chamber having a center electrode and a ground electrode in a plug cover, and to generate a spark between the center electrode and the ground electrode. Therefore, the present invention provides a spark plug that can stably and satisfactorily generate spark ignition as a sub-chamber spark plug for setting the ignition timing. Furthermore, to provide an engine having such a sub-chamber type ignition plug and capable of generating spark ignition stably and satisfactorily, and to obtain an engine operation method capable of realizing such operation. is there.

In order to achieve the above object, a characteristic configuration of a spark plug according to the present invention includes a center electrode disposed on a plug center line, a discharge that is provided opposite to the center electrode and is symmetrical with respect to the plug center line. A ground electrode having a portion in an ignition chamber formed in the plug cover,
In the ignition plug in which the plug cover is provided with a plurality of communication holes that connect the ignition chamber and the combustion chamber facing the piston of the engine in a mounted state mounted on the cylinder head,
The intersection of the center lines of the plurality of communication holes is set on the plug center line at a position on the discharge part side and on the opposite side of the center electrode from the ignition chamber side opening of the communication hole, Each of the plurality of communication holes is formed as a communication hole toward the intersection, and is uniformly arranged around the periphery of the plug center line, and the center electrode is provided with a tip small-diameter portion facing the discharge portion, A gas flow that flows into the ignition chamber from the combustion chamber through the communication hole merges at the intersection and flows to the ground electrode side, and bypasses the ground electrode between the discharge portion and the tip small-diameter portion. Configured to flow in,
0.3 <Z / L ′ <, where Z is the distance from the tip small-diameter portion along the plug center line to the intersection, and L ′ is the diameter of the imaginary circle connecting the center of opening of each communication hole on the combustion chamber side. The point is that there is a relationship of 0.7 .

According to this characteristic configuration, each of the plurality of communication holes is evenly arranged on the periphery of the plug center line as a communication hole toward the intersection of the center lines of the plurality of communication holes. The inflowing air-fuel mixture is merged at the intersection of the center lines of the plurality of communication holes. Since the intersection of the center lines of the plurality of communication holes is set on the plug center line at a position on the discharge part side from the ignition chamber side opening of the communication holes and on the opposite side of the center electrode from the discharge part. The air-fuel mixture merged at the intersection is prevented from flowing directly between the center electrode and the discharge portion due to the presence of the ground electrode, and bypasses the ground electrode. Therefore, the air-fuel mixture merged at the intersection is decelerated between the center electrode and the discharge part, and the flow rate of the air-fuel mixture flowing between the center electrode and the discharge part does not become high, A spark can be formed stably. In addition, since the center electrode is provided with the tip small-diameter portion that faces the discharge portion, the tip small-diameter portion is located at a position hidden from the ground electrode from the above-mentioned intersection side. As a result, the ignition point formed between the center electrode and the discharge part is reached in a state where the main flow of the air-fuel mixture merged at the intersection is reliably removed.
From the above, an ignition chamber having a center electrode and a ground electrode is provided in the plug cover, and spark ignition is performed as a sub-chamber type ignition plug that generates sparks between the center electrode and the ground electrode to set the ignition timing. Thus, it is possible to realize a sub-chamber type spark plug that can stably and well generate.

If the distance Z from the tip small-diameter portion along the plug center line to the intersection is reduced, the cooling effect of the ground electrode is reduced, the temperature of the ground electrode is increased, and abnormal combustion occurs. On the other hand, if the distance Z is increased, the flow rate of the ascending airflow of the air-fuel mixture that merged at the intersection becomes too slow, and similarly, the cooling effect of the ground electrode is reduced.
Therefore, according to this feature configuration, the above-described distance Z is set to 0.3 <Z / L ′ <0.7 as a ratio to the diameter L ′ of the virtual circle connecting the centers of the communication holes. Thereby, the cooling effect of a ground electrode can be acquired effectively. Moreover, as shown in FIG. 5 showing the relationship between Z / L ′ and COVi (the rate of change in the indicated mean effective pressure), COVi is set to 1. by setting 0.3 <Z / L ′ <0.7. It can be suppressed to 0% or less, and combustion can be performed stably.

A further characteristic configuration of the ignition plug according to the present invention is such that the ignition chamber side opening of the communication hole is located closer to the ground electrode side than the combustion chamber side opening, and the plug center line and the communication hole are in the clockwise direction. The angle with the center line is 40 degrees or more and 70 degrees or less.
If the angle formed by the plug center line and the center line of the communication hole is made smaller than 40 degrees, when injecting flame from the ignition chamber to the combustion chamber through the communication hole in the expansion process, it is injected to the piston side, and only that region There is a possibility that the mixed gas in the vicinity of the side surface of the combustion chamber cannot be burned well.

  If the angle formed by the plug center line and the center line of the communication hole is larger than 70 degrees, there is a possibility that the air-fuel mixture flowing into the ignition chamber from each communication hole does not become an upward air flow between the center electrode and the ground electrode. is there. Therefore, according to this characteristic configuration, the angle formed by the plug center line and the center line of the communication hole is set to 70 degrees or less, and the air-fuel mixture flowing into the ignition chamber from each communication hole is directed between the center electrode and the ground electrode. Ascending current is set. As a result, the air-fuel mixture merged at the intersection becomes a rising airflow between the center electrode and the ground electrode, bypasses the ground electrode, and flows in by being decelerated between the center electrode and the discharge portion. .

  The spark plug according to the present invention is further characterized in that the diameter of the tip small diameter portion is Dc, the width of the discharge portion is L, the diameter of the communication hole is Do, the number of the communication holes is N, and Dc <L <Do × N relationship.

  By satisfying the condition of Dc <L, with respect to the positional relationship between the tip small diameter portion and the discharge portion, the tip small diameter portion is surely hidden from the above-mentioned intersection side by the ground electrode. In addition, by satisfying the condition of L <Do × N, the mixing that flows between the center electrode and the ground electrode without significantly increasing the width of the ground electrode in relation to the total area of the plurality of communication holes. It is possible to prevent the air flow rate from being excessively suppressed. As a result, the air-fuel mixture merged at the intersection appropriately bypasses the ground electrode and flows moderately between the center electrode and the discharge part to flow in, thereby making the spark formation more stable. Can do.

A further characteristic configuration of the ignition plug according to the present invention is a cantilever structure in which the ground electrode extends beyond the center of the plug from a part of the circumference around the center line of the plug when viewed in the direction of the center line of the plug. A single character structure that connects a pair of circumferential portions located opposite to each other around the plug center line beyond the plug center, or two pairs of circumferential portions located every 90 degrees around the plug center line beyond the plug center. Are cross-linked structures.
Thus, the ground electrode can be accurately arranged at a desired position by any one of the cantilever structure, the single character structure, and the cross structure.

A further characteristic configuration of the spark plug according to the present invention is that the number of the communication holes is 3 or more and 5 or less.
In this way, by limiting the number of communication holes to 5 or less, it is possible to eliminate waste of making unnecessary communication holes. On the other hand, if the number of communication holes is 2 or less, it is difficult to obtain an equal flow with the plug center line as the central axis when introducing the air-fuel mixture flow at the intersection to the ground electrode side. By setting the number to 3 or more, an even flow with the plug center line as the central axis can be obtained.

A further characteristic configuration of the spark plug according to the present invention is that the volume of the ignition chamber is 850 to 1600 mm ³ and the Z is 4 mm <Z <8 mm.
In this way, by defining the volume of the ignition chamber and the range of the distance from the tip small diameter portion along the plug center line to the intersection, the volume of the ignition chamber and the center of the plug suitable for stably forming the spark It can be the distance from the tip small diameter part along the line to the intersection.

A further characteristic configuration of the spark plug according to the present invention is that the tip small diameter portion has a groove formed in a direction away from the discharge portion.
Thus, the formation of the spark is made stable and reliable by providing the groove in the direction away from the discharge portion in the tip small diameter portion.

  A further characteristic configuration of the spark plug according to the present invention is that the fuel of the engine is gas fuel. As a result, even in an engine that performs lean combustion with a low concentration of gas fuel in the combustion chamber, it is possible to stably form a spark and stably perform combustion in the ignition chamber. Thus, the flame can be stably ejected to the combustion chamber through the communication hole, and the lean combustion in the combustion chamber can be appropriately performed.

As described above, the characteristic configuration of the engine according to the present invention includes the spark plug according to the present invention, generates a spark between the tip small-diameter portion and the discharge portion, and passes the ignition chamber through the ignition chamber. The point is to ignite the gas fuel.
As described in the spark plug according to the present invention described above, the air-fuel mixture merged at the intersection of the ignition chamber is decelerated between the center electrode and the discharge portion, and flows into the center electrode and the discharge portion. The flow rate of the air-fuel mixture flowing in during this period does not become high, and the spark can be formed stably. In addition, the stable formation of the spark enables stable combustion in the ignition chamber, and the combustion of the ignition chamber enables stable ejection of flame into the combustion chamber through the communication hole. The lean combustion in the chamber can be performed appropriately.

Schematic configuration diagram of an engine of the present invention and a spark plug provided therein Longitudinal sectional view of a spark plug according to the present application Bottom view of spark plug according to the present application Diagram showing the flow velocity distribution of the air-fuel mixture through the communication hole at the ignition timing The figure which shows the relationship between Z / L 'and COVi The longitudinal cross-sectional view and principal part cross-sectional view which show the ignition plug provided with the ground electrode of another embodiment The longitudinal cross-sectional view and principal part cross-sectional view which show the ignition plug of another embodiment provided with the ground electrode of another embodiment The figure which shows the spark plug of another embodiment provided with the ground electrode of another embodiment.

[Overall engine configuration]
As shown in FIG. 1, the engine 1 of the present invention includes a piston 2, a cylinder 4 that houses the piston 2 and forms a combustion chamber 3 together with the top surface 2 a of the piston 2, and a spark plug 11 that is attached to the cylinder head 6. And is configured. The piston 2 is reciprocated in the cylinder 4 and the intake valve 5 and the exhaust valve (not shown) are opened and closed to open and close the intake stroke, the compression stroke, the combustion expansion stroke, and the exhaust stroke in the combustion chamber 3. Are performed sequentially. Thus, the reciprocating motion of the piston 2 is output as the rotational motion of the crankshaft C by the connecting rod. Such a configuration is the same as that of a normal four-stroke engine. The crankshaft C is provided with a cell motor M for ensuring the rotation of the crankshaft without causing combustion in the combustion chamber 3 in the initial stage of startup.

  The engine 1 uses, for example, city gas (13A), which is gaseous fuel, as the fuel G. In the intake stroke, the intake valve 5 is opened and air and fuel G are supplied from the intake port 8 to the combustion chamber 3. An air-fuel mixture (for example, a lean air-fuel mixture) is sucked. In the compression stroke and the combustion expansion stroke, the air-fuel mixture sucked into the combustion chamber 3 is compressed and combusted. In the exhaust stroke, the exhaust valve is opened, and the combustion exhaust gas is discharged from the combustion chamber 3 to an exhaust port (not shown).

  A recess 7 is formed on the top surface 2 a of the piston 2 facing the cylinder head 6. As a result, the combustion chamber 3 is constituted by a space formed by the recess 7 in addition to the space between the top surface 2 a of the piston 2 and the inner surface of the cylinder 4. By forming the combustion chamber 3 in this way, when the piston 2 rises in the compression stroke, a vortex flow from the periphery of the recess 7 toward the center of the recess 7, a so-called squish can be generated.

  The intake port 8 provided in the cylinder head 6 is provided with a fuel supply unit 9 that injects the fuel G with respect to the intake air, and generates an air-fuel mixture (for example, a lean air-fuel mixture). Is configured to do. By opening the intake valve 5, a mixture of air and fuel G (for example, a lean mixture) is sucked into the combustion chamber 3. Here, the fuel injection amount from the fuel supply unit 9 can be changed, and the mixing ratio of air and fuel G can be changed according to the operating state of the engine 1.

The spark plug 11 includes a plug main body 12 and a plug cover 13 that forms an ignition chamber 14 at the tip end portion (the lower end portion in FIG. 1) of the plug main body 12, and the plug cover 13 is the plug main body 12. Are integrally formed. The plug cover 13 is formed in a bottomed cylindrical shape, and is apex on the distal end side (lower side in FIG. 1) of the plug body 12 in a cross-sectional view taken along a plane passing through the plug center line (straight line W in FIG. 1) of the combustion chamber 3 It has a dome shape.
The plug body 12 is provided such that its plug center line coincides with the cylinder center line of the combustion chamber 3 (straight line W in FIG. 1). The spark plug 11 is provided so that its plug cover head 13 a protrudes into the combustion chamber 3 in a state of passing through an opening 20 that connects the upper portion of the cylinder head 6 formed in the cylinder head 6 and the combustion chamber 3. It has been.

  In the plug cover 13 (specifically, the plug cover head portion 13a), a plurality of communication holes 15 for communicating the combustion chamber 3 and the ignition chamber 14 are formed. The spark plug 11 sparks and ignites the air-fuel mixture flowing into the ignition chamber 14 from the combustion chamber 3 through the communication hole 15, and jets the combustion flame formed by the combustion into the combustion chamber 3 through the communication hole 15. It is configured. In this way, the inflow of the air-fuel mixture from the combustion chamber 3 to the ignition chamber 14 and the ejection of the combustion flame from the ignition chamber 14 to the combustion chamber 3 are performed by the plurality of communication holes 15, thereby The inhaled air-fuel mixture is burned. Here, the air-fuel mixture flowing into the ignition chamber 14 is all the air-fuel mixture flowing from the combustion chamber 3 through the communication hole 15, and the fuel G and the air-fuel mixture are supplied to the ignition chamber 14 from other than the combustion chamber 3. Never happen.

  The control device 40 is constituted by a microprocessor or the like that can execute a program for controlling the engine 1. The control device 40 is configured to control the timing of spark discharge between the center electrode 16a of the spark plug 11 and the ground electrode 16b.

[Basic engine operation]
In the steady operation such as the rated operation, the engine 1 performs an intake stroke in which the air-fuel mixture is taken into the combustion chamber 3 when the piston 2 descends from the top dead center with the intake valve 5 opened. Next, the piston 2 ascends while the intake valve 5 and the exhaust valve are closed, thereby performing a compression stroke for compressing the air-fuel mixture in the combustion chamber 3. In this compression stroke, the volume of the combustion chamber 3 is reduced by raising the piston 2 from the bottom dead center, so that the air-fuel mixture sucked into the combustion chamber 3 flows into the ignition chamber 14 through the communication hole 15.
The control device 40 that controls the operation of the engine 1 operates the plug main body 12 at the ignition timing (for example, immediately before the top dead center), sparks at the ignition point, and ignites the air-fuel mixture in the ignition chamber 14. Then, the combustion in the ignition chamber 14 proceeds, and the combustion flame is ejected to the combustion chamber 3 through the communication hole 15. Thereby, the air-fuel mixture in the combustion chamber 3 is combusted and a combustion expansion stroke is performed. Next, when the piston 2 rises with the exhaust valve opened, a discharge stroke is performed in which the combustion exhaust gas in the combustion chamber 3 is led to the exhaust port and discharged.
Thus, the engine 1 is configured as a four-stroke engine that repeatedly performs a series of operations for performing each stroke in the order of the intake stroke, the compression stroke, the combustion expansion stroke, and the exhaust stroke.

  The above is the description of the schematic configuration of the spark plug and the engine according to the present invention and the operation method thereof. Hereinafter, the unique configuration of the spark plug of the present invention will be described.

[Communication hole]
In the present embodiment, as shown in FIG. 2, four communication holes 15 that connect the combustion chamber 3 and the ignition chamber 14 are equally arranged around the plug center line with a phase difference of 90 degrees. ing. Further, the communication hole 15 is oriented in the direction toward the intersection point O described so far, and the ignition chamber side opening 15b is positioned on the ground electrode 16b side from the combustion chamber side opening 15a in the clockwise direction. Thus, the angle formed by the plug center line W and the center line w of the communication hole 15 is 60 degrees. Therefore, the air-fuel mixture flow from the communication hole 15 to the ground electrode 16b side through the intersection point O can be formed.

[Center electrode]
As shown in FIGS. 2 to 4, the center electrode 16 a is provided so as to protrude from the support portion 19 made of an insulating material such as alumina ceramic to the communication hole 15 side in the ignition chamber 14, and has a base portion 16 n and a tip end side thereof. On the (ground electrode 16b side), a tip small-diameter portion 17 is provided at a position facing the discharge portion 18 of the ground electrode 16b. The tip small-diameter portion 17 is formed in a cylindrical shape with a circular cross section from a metal material having excellent heat conductivity such as Cu as an inner material and a metal material having excellent heat resistance and corrosion resistance such as a Ni-based alloy as an outer material. . The distal end surface of the distal end small diameter portion 17 is a plane parallel to the discharge portion 18, and an air-fuel mixture guide portion 17 a whose diameter decreases as it approaches the ground electrode 16 b side on the proximal end side of the distal end small diameter portion 17. Is provided. Further, an air-fuel mixture space 190 into which the air-fuel mixture can enter is formed around the support portion 19, and the outer peripheral surface 19 a of the support portion 19 is an inclined surface whose diameter decreases as it approaches the ground electrode 16 b side. The inclination direction of the outer peripheral surface 19a is a direction toward the center electrode side end 160 of the ground electrode 16b as shown in FIG. 4 when the ground electrode 16b is viewed from the front end side.
As a result, an axial flow velocity distribution with the plug center line W as the central axis is realized around the support portion 19, the center electrode 16a, and the ground electrode 16b in the short direction of the ground electrode 16b (the front and back direction in FIG. 2). Is done.

  Further, as shown in FIG. 2, the formation of the spark is made stable and reliable by providing the small-diameter portion 17 at the tip with a linear groove 17b formed in a direction away from the discharge portion 18.

[Ground electrode]
As can be seen from FIG. 3, in the present embodiment, the ground electrode 16 b has a cantilever structure that extends beyond the center of the plug from a part of the circumference around the plug center line. A noble metal tip made of Pt or a Pt alloy is fixed to a portion of the ground electrode 16b facing the tip small-diameter portion 17 at a portion previously called the discharge portion 18, and the entire ground electrode 16b is made of, for example, Cr. It is comprised from the Ni alloy containing this.

[Relationship between multiple communication holes and electrodes]
In the spark plug of the present invention, the intersection O of the center lines w of the plurality of communication holes 15 is on the plug center line W with respect to the ground electrode 16b side from the ignition chamber side opening 15b of the communication hole 15 and to the discharge portion 18. It is set at a position on the opposite side of the center electrode 16a. A plurality (4 in the example shown in FIG. 2) of the communication holes 15 are formed so as to be evenly arranged on the periphery of the plug center line W as the communication holes 15 toward the intersection point O.
By adopting this configuration, in the spark plug of the present invention, the gas flow of the air-fuel mixture flowing into the ignition chamber 14 from the combustion chamber 3 through the plurality of communication holes 15 merges at the intersection point O and the ground electrode 16b side. And flows between the discharge portion 18 and the tip small diameter portion 17 by bypassing the ground electrode 16b (see FIGS. 2 and 4).

  FIG. 4 shows the flow velocity distribution of the air-fuel mixture through the communication hole 15 at the ignition timing. At the ignition timing, the air-fuel mixture flowing from the combustion chamber 3 into the ignition chamber 14 is in the vicinity of the communication hole 15 in the vicinity of the air-fuel mixture. The maximum air velocity (8 to 10 m / s) is reached near the intersection O, which is the junction, and below the ground electrode 16b. However, the mixed airflow rising from the intersection O to the ground electrode 16b is prevented from flowing, By detouring the ground electrode 16b, it is decelerated and flows between the center electrode 16a and the ground electrode 16b. Accordingly, it is possible to ensure stable generation of sparks between the center electrode 16a and the discharge portion 18 provided on the ground electrode 16b.

a Z / L '
As shown in FIGS. 2 and 3, the distance from the tip small-diameter portion 17 along the plug center line W to the intersection point O is Z, and the diameter of a virtual circle C0 connecting the center of the opening of each communication hole on the combustion chamber side is L ′. , 0.3 <Z / L ′ <0.7.
FIG. 5 is a diagram showing the relationship between Z / L ′ and COVi (the rate of change in the indicated mean effective pressure). As can be seen from this figure, when Z / L ′ deviates from the above range, COVi increases. It can be seen that the combustion becomes unstable.
Here, the volume of the ignition chamber is 850 to 1600 mm ³ , the diameter L ′ of the imaginary circle C0 connecting the combustion chamber side opening centers of the communication holes 15 is 10 to 14 mm, and Z is set to 4 mm <Z <8 mm. Has been.

b Dc <L <Do × N
As shown in FIGS. 2 and 3, assuming that the diameter of the tip small diameter portion 17 is Dc, the width of the discharge portion 18 is L, the hole diameter of the communication hole 15 is Do, the number of the communication holes 15 is N, and L is Dc <L The relation of <Do × N is set.
Here, the width L of the discharge part 18 is the width of the discharge part 18 corresponding to the tip small diameter part 17 provided at the tip of the center electrode 16a as shown in FIGS. When the beam 16b has a cantilever structure, the width of the beam in the short direction (the radial direction passing through the center of the tip small-diameter portion 17 in a state where the tip small-diameter portion is viewed from the bottom surface side (see FIGS. 3 and 6B). (Width in the vertical direction)). As shown in FIGS. 7 and 8, in the case of a double-ended structure, it means the width in the short direction of the beam in the case of a single character structure, and the width in the short direction of one beam in the case of a cross structure.

Now, by satisfying the condition of Dc <L, the tip small-diameter portion 17 of the center electrode 16a from the above-described intersection O side is located at a position hidden on the back surface side of the ground electrode 16b.
On the other hand, by satisfying the condition of L <Do × N, the flow of the air-fuel mixture is reduced between the tip small diameter portion 17 of the center electrode 16a and the discharge portion 18 of the ground electrode 16b without significantly increasing the width L of the ground electrode 16b. The ignition by sparks can be satisfactorily generated.

[Another embodiment]
(1) In the above embodiment, the ground electrode has a cantilever structure formed by a rectangular parallelepiped whose length in the beam width direction does not change with respect to the longitudinal direction. However, as shown in FIG. Thus, a trapezoidal structure that is wide at the cantilever base end side and narrow at the cantilever tip end side may be employed. In this case, a change in the distance between the center electrode and the ground electrode can be suppressed. Further, as shown in FIG. 7, a single character structure may be used in which a pair of circumferential portions opposed to each other around the plug center line W are connected beyond the plug center as viewed in the plug center line direction. When this configuration is adopted, the ground electrode 16b can be reliably supported from the plug body.
Furthermore, as shown in FIG. 8, a cross structure may be used in which two pairs of circumferential portions positioned every 90 degrees around the plug center line are connected beyond the plug center as viewed in the plug center line direction. By adopting this configuration, the ground electrode 16b can be more reliably supported from the plug body.

(2) In the above embodiment, the number of communication holes 15 is four, but it is preferably 3 or more and 5 or less. By limiting the number of communication holes to 5 or less, it is possible to eliminate the waste of making unnecessary communication holes. On the other hand, when the number of communication holes is 2 or less, it is difficult to obtain an equal flow with the plug center line as the central axis in the configuration in which the flow of the air-fuel mixture is guided to the ground electrode side by joining at the intersections described so far. .

  In the above embodiment, the angle formed by the plug center line W and the center line w of the communication hole 15 is set to 60 degrees. However, it is only necessary to be able to form a flow toward the ground electrode 16b, and it may be 60 degrees or less.

  The spark plug of the present invention is a sub-chamber type spark plug that sets an ignition timing by providing a spark chamber between the center electrode and the ground electrode by providing an ignition chamber having a center electrode and a ground electrode in the plug cover. It was possible to provide a sub-chamber type spark plug that can stably and satisfactorily generate spark ignition. Furthermore, it is possible to provide an engine that includes such a sub-chamber ignition plug and can stably and satisfactorily generate spark ignition, and an engine operating method that can realize such operation.

1: Engine 2: Piston 3: Combustion chamber 11: Spark plug 13: Plug cover 14: Ignition chamber 15: Communication hole 15a: Combustion chamber side opening 15b: Ignition chamber side opening 16: Electrode 16a: Center electrode 16b: Ground electrode 16n : Base 17: Tip small diameter part 17a: Air-fuel mixture guide part 18: Discharge part 19: Support part W: Plug center line w: Center line of communication hole

Claims (9)

A center electrode disposed on the plug center line and a ground electrode provided opposite to the center electrode and having a discharge portion symmetrical to the plug center line are provided in an ignition chamber formed in the plug cover. ,
A spark plug in which the plug cover is provided with a plurality of communication holes that connect the ignition chamber and the combustion chamber facing the piston of the engine when mounted on the cylinder head,
The intersection of the center lines of the plurality of communication holes is set on the plug center line at a position on the discharge part side and on the opposite side of the center electrode from the ignition chamber side opening of the communication hole,
Each of the plurality of communication holes is formed so as to be evenly arranged on the periphery of the plug center line as a communication hole toward the intersection.
Provide a tip small diameter portion facing the discharge portion in the center electrode,
The gas flow that flows into the ignition chamber from the combustion chamber through the plurality of communication holes merges at the intersection and flows to the ground electrode side, and between the discharge portion and the tip small-diameter portion, Configured to flow around the electrodes ,
0.3 <Z / L ′ <, where Z is the distance from the tip small-diameter portion along the plug center line to the intersection, and L ′ is the diameter of the imaginary circle connecting the center of opening of each communication hole on the combustion chamber side. Spark plug with a relationship of 0.7 . The ignition chamber side opening of the communication hole is located closer to the ground electrode than the combustion chamber side opening,
The spark plug according to claim 1 , wherein an angle formed by the center line of the plug and the center line of the communication hole in the clockwise direction is 40 degrees or more and 70 degrees or less . The diameter of the tip small diameter part is Dc, the width of the discharge part is L, the hole diameter of the communication hole is Do, and the number of the communication holes is N,
The spark plug according to claim 1 or 2, wherein Dc <L <Do x N. A cantilever structure in which the ground electrode extends beyond the center of the plug from a part of the circumference around the plug center line, as viewed from the plug center line direction, a pair of circumferences facing each other around the plug center line Any one of the character structure which connects a part beyond a plug center, or the cross structure which connects two pairs of circumferential parts located every 90 degree | times around the said plug center line beyond a plug center. A spark plug according to claim 1. The spark plug according to any one of claims 1 to 4, wherein the number of the communication holes is 3 or more and 5 or less . The volume of the ignition chamber is 850 to 1600 mm ³ ;
The spark plug according to claim 1, wherein the Z is 4 mm <Z <8 mm . The spark plug according to any one of claims 1 to 6, further comprising a groove formed in the tip small diameter portion in a direction away from the discharge portion . The spark plug according to any one of claims 1 to 7, wherein the fuel of the engine is gas fuel . An engine comprising the spark plug according to any one of claims 1 to 8, wherein a spark is generated between the tip small diameter portion and the discharge portion, and gas fuel in the combustion chamber is ignited through the ignition chamber. .