JP7680882B2 - Spark plug - Google Patents

Description

This disclosure relates to spark plugs.

A spark plug that is attached to the engine head and generates a spark discharge between the tip of the center electrode and the ground electrode is known as an ignition spark plug used in an internal combustion engine (for example, see Patent Document 1). Patent Document 1 discloses a pre-chamber plug in which a cover is provided at the tip of the spark plug to form a sub-chamber, and the cover has a uniform thickness.

Japanese Patent Application Publication No. 11-224763

However, the spark plug described in Patent Document 1 had room for improvement in scavenging performance. For this reason, there was a demand for technology that could improve the scavenging performance of pre-chamber plugs.

This disclosure can be realized in the following forms:

(1) According to one aspect of the present disclosure, there is provided a spark plug.
a ground electrode electrically connected to the metal shell and forming a discharge gap between the center electrode and an end of the metal shell; and a cover covering the center electrode and the ground electrode from a tip side to form an auxiliary chamber, the cover being provided with a first through hole passing through the axis and a second through hole present in an area other than the axis, wherein, in a cross section including the axis, an outer wall of the cover has a straight portion that approaches the axis in a straight line toward the tip side and reaches the first through hole, and an inner wall of the cover has a curved portion that approaches the axis in a curved line toward the tip side and reaches the first through hole. In this type of spark plug, the inner wall of the cover has a curved portion that approaches the axis in a curved manner toward the tip. This allows for smoother gas flow in the pre-chamber compared to a case in which the inner wall of the cover is non-curved, thereby improving the scavenging of residual gas in the pre-chamber.

(2) In the spark plug of the above embodiment, in a cross section including the axis, the rear end of the second through hole on the outer wall side in the direction along the axis may be located on the straight portion. With this spark plug, the rear end of the second through hole on the outer wall side is located on the straight portion, so that the second through hole opens in a direction intersecting the axis but not perpendicular thereto, and as a result, the scavenging of residual gas in the auxiliary chamber is improved by the tumble flow.

(3) In the spark plug of the above embodiment, the cross-sectional area of the sub-chamber in a plane perpendicular to the axis may decrease from the rear end of the inner wall of the second through hole toward the tip end. With this spark plug, it is easy to ensure the thickness of the cover in the portion where the second through hole is formed. And by ensuring the thickness of the cover in the portion where the second through hole is formed, heat dissipation is suppressed, improving combustion stability.

The present invention can be realized in various forms, such as a method for manufacturing a spark plug, an engine head to which a spark plug is attached, etc.

1 is a partial cross-sectional view showing a schematic configuration of a spark plug according to an embodiment of the present disclosure; FIG. 4 is a cross-sectional view showing a part of the cover taken along a cross section including an axis line. FIG.

A. Embodiments:
FIG. 1 is a partial cross-sectional view showing a schematic configuration of a spark plug 100 according to an embodiment of the present disclosure. In FIG. 1, the outer shape of the spark plug 100 is shown on the right side of the drawing, and the cross-sectional shape of the spark plug 100 is shown on the left side of the drawing, with the axis CA being the axis of the spark plug 100 as the boundary. In the following description, the lower side of FIG. 1 along the axis CA (the side where a ground electrode 40 described later is arranged) is called the leading end side, the upper side of FIG. 1 (the side where a terminal metal fitting 50 described later is arranged) is called the rear end side, and the direction along the axis CA is called the axial direction AD. In FIG. 1, for convenience of description, an engine head 90 to which the spark plug 100 is attached is shown by a broken line. The spark plug 100 is attached to the engine head 90 so that its leading end is exposed in a combustion chamber 95. The spark plug 100 of this embodiment is configured as a pre-chamber plug in which a sub-chamber 96 described later is formed. The spark plug 100 of this embodiment can be used, for example, in an ignition device or an internal combustion engine.

The spark plug 100 comprises an insulator 10, a center electrode 20, a metal shell 30, a ground electrode 40, a terminal metal fitting 50, and a cover 70. The axis CA of the spark plug 100 coincides with the axis of each of the insulator 10, the center electrode 20, the metal shell 30, the terminal metal fitting 50, and the cover 70.

The insulator 10 has a generally cylindrical exterior shape with an axial hole 11 extending in the axial direction AD. A part of the center electrode 20 is disposed in the axial hole 11 at the front end, and a part of the terminal metal fitting 50 is disposed at the rear end. The insulator 10 holds the center electrode 20 within the axial hole 11. The front end portion of the insulator 10 is housed in the axial hole 31 of the main metal fitting 30 described below, and the rear end portion is exposed from the axial hole 31. The insulator 10 is made of an insulating porcelain formed by sintering a ceramic material such as alumina.

The center electrode 20 is a rod-shaped electrode extending along the axial direction AD. The center electrode 20 is insulated and held on the inner periphery of the metal shell 30. The tip 21 of the center electrode 20 protrudes toward the tip side of the axial hole 11. A precious metal tip made of, for example, an iridium alloy may be joined to the tip 21.

In the axial hole 11 of the insulator 10, a leading end seal material 61, a resistor 62, and a trailing end seal material 63 are arranged between the center electrode 20 and the terminal metal fitting 50 in this order from the leading end side to the trailing end side. Therefore, the center electrode 20 is electrically connected to the terminal metal fitting 50 at the trailing end side via the leading end seal material 61, the resistor 62, and the trailing end seal material 63.

The resistor 62 is made of ceramic powder, conductive material, and glass. The resistor 62 functions as an electrical resistor between the terminal fitting 50 and the center electrode 20, thereby suppressing the generation of noise when spark discharge occurs. The leading end sealing material 61 and the trailing end sealing material 63 are each made of conductive glass powder. In this embodiment, the leading end sealing material 61 and the trailing end sealing material 63 are made of a powder mixture of copper powder and calcium borosilicate glass powder.

The metal shell 30 is a cylindrical member extending along the axis CA. Specifically, the metal shell 30 has a generally cylindrical external shape with an axial hole 31 formed along the axial direction AD, and holds the insulator 10 within the axial hole 31. The metal shell 30 is made of, for example, low carbon steel, and is plated entirely with nickel plating, zinc plating, or the like. A tool engagement portion 32 and a male thread portion 33 are formed on the outer periphery of the metal shell 30. The tool engagement portion 32 engages with a tool (not shown) when the spark plug 100 is attached to the engine head 90. The male thread portion 33 has a thread formed on the outer periphery at the tip of the metal shell 30, and is screwed into the female thread portion 93 of the engine head 90.

A through hole 35 is formed in the metal shell 30 at the tip end in the axial direction AD, penetrating the metal shell 30 in the thickness direction. That is, the through hole 35 connects the outer peripheral surface and the inner peripheral surface of the metal shell 30. In this embodiment, the through hole 35 is formed along a radial direction perpendicular to the axial direction AD. One end 41 of the ground electrode 40 is inserted and positioned in the through hole 35.

The ground electrode 40 is made of a rod-shaped metal member and extends along the radial direction of the spark plug 100. In the following description, the direction in which the ground electrode 40 extends is also referred to as the "extension direction ED". One end 41 of the ground electrode 40 is located on the rear end side in the extension direction ED, and the other end 42 of the ground electrode 40 is located on the front end side in the extension direction ED. The other end 42 faces the front end 21 of the center electrode 20 and forms a discharge gap G for spark discharge between the front end 21 and the front end 21. In other words, the ground electrode 40 forms a discharge gap G between the center electrode 20 and its own end. The ground electrode 40 of this embodiment is formed of a nickel alloy mainly composed of nickel.

In this embodiment, the ground electrode 40 is fixed by being pressed into the through hole 35 from the radial outside of the spark plug 100. In other words, the ground electrode 40 is electrically connected to the metal shell 30. Note that the ground electrode 40 may be fixed into the through hole 35 by any method, such as welding, instead of or in addition to being pressed into. Also, the ground electrode 40 does not have to be pressed into the through hole 35 and fixed thereto; for example, the ground electrode 40 may be attached to the tip of the metal shell 30.

The terminal fitting 50 is provided at the rear end of the spark plug 100. The tip side of the terminal fitting 50 is housed in the axial hole 11 of the insulator 10, and the rear end side of the terminal fitting 50 is exposed from the axial hole 11. A high-voltage cable (not shown) is connected to the terminal fitting 50, and high voltage is applied. This application generates a spark discharge in the discharge gap G. The spark generated in the discharge gap G ignites the air-fuel mixture.

The cover 70 has a bottomed cylindrical appearance and is fixed to the fixing surface 34 located at the tip of the metal shell 30. The cover 70 is a member that covers the center electrode 20 and the ground electrode 40 from the tip side to form a sub-chamber. In other words, the cover 70 forms a sub-chamber 96 by covering the discharge gap G formed by the tip 21 of the center electrode 20 and the other end 42 of the ground electrode 40 from the tip side in the axial direction AD. The sub-chamber 96 in this embodiment is a space surrounded by the insulator 10, the tip 21 of the center electrode 20, the metal shell 30, and the cover 70. In this embodiment, the rear end surface 72 of the cover 70 in the axial direction AD is welded and fixed to the fixing surface 34 of the metal shell 30, but is not limited to this, and may be fixed to the metal shell 30 by any method such as press fitting. Also, the cover 70 and the metal shell 30 may be fitted together and fixed by providing a step between the rear end surface 72 of the cover 70 and the fixing surface 34 of the metal shell 30 for fitting. In this embodiment, the cover 70 is fixed to the metal shell 30 in the final step of the manufacturing process of the spark plug 100.

2 is a cross-sectional view showing a part of the cover 70 in a cross section including the axis CA. The cover 70 has through holes as multiple injection holes penetrating the plate thickness. Specifically, the cover 70 has a first through hole 71 passing through the axis CA and a second through hole 73 existing in an area other than the axis CA. That is, the second through hole 73 is located farther from the axis CA than the first through hole 71. Therefore, as shown in FIG. 2, the first through hole 71 and the second through hole 73 communicate the combustion chamber 95 and the auxiliary chamber 96. The mixture in the combustion chamber 95 flows into the auxiliary chamber 96 through the first through hole 71 and the second through hole 73, and is ignited by a spark generated in the discharge gap G in the auxiliary chamber 96. The flame generated at the time of ignition is ejected into the combustion chamber 95 through the first through hole 71 and the second through hole 73.

The positions and number of the second through holes 73 are preset according to the engine specifications. In this embodiment, four second through holes 73 are provided at equal intervals in the circumferential direction, and all are provided at the same position in the axial direction AD. However, this is not limited to this, and for example, the number of second through holes 73 may be three or less or five or more, and may be provided at different positions in the axial direction AD.

As shown in FIG. 2, in a cross section including the axis CA, the outer wall of the cover 70 has a straight section SL. The straight section SL approaches the axis CA in a straight line toward the tip side, and reaches the first through hole 71. In addition, in a cross section including the axis CA, the inner wall of the cover 70 has a curved section CL. The curved section CL approaches the axis CA in a curved line toward the tip side, and reaches the first through hole 71. A cover 70 having such a shape can be produced, for example, by cutting the inner wall portion. In this embodiment, in a cross section including the axis CA, the curved section CL approaches the axis CA to an increasing extent toward the tip side.

In addition, in this embodiment, in a cross section including the axis CA, the rear end E1 on the outer wall side of the second through hole 73 in the axial direction AD is located on the straight section SL. However, this is not limited to this, and in a cross section including the axis CA, the rear end E1 on the outer wall side of the second through hole 73 in the axial direction AD may be located further rearward than the straight section SL.

In addition, as shown in FIG. 1, in this embodiment, the second through hole 73 is located closer to the tip end than the discharge gap G in the axial direction AD. By doing so, the second through hole 73 opens in a direction that intersects with the axis CA without being perpendicular thereto, improving the scavenging of residual gas in the auxiliary chamber by the tumble flow.

In addition, in this embodiment, the cross-sectional area of the auxiliary chamber 96 in a plane perpendicular to the axis CA decreases from the rear end E2 on the inner wall side of the second through hole 73 toward the tip end.

According to the spark plug 100 of this embodiment described above, the inner wall of the cover 70 has a curved portion CL that curves closer to the axis CA toward the tip and reaches the first through-hole 71. Therefore, according to the spark plug 100 of this embodiment, the flow of gas in the auxiliary chamber 96 is smoother than when the inner wall of the cover 70 is non-curved, and as a result, the scavenging of residual gas in the auxiliary chamber 96 is improved. The fact that such an effect is obtained will be explained using the following simulation results.

Figure 3 shows the simulation results. Specifically, the left side of the page shows the simulation results of the flow velocity distribution, and the right side of the page shows the simulation results of the pressure distribution. The simulation results of the flow velocity distribution are further shown in an enlarged view of the flow velocity distribution near the first through hole 71. The simulation results of this embodiment are shown in the upper part of the page, and the simulation results of a comparative example are shown in the lower part of Figure 3. In the comparative example, the inner wall of the cover approaches the axis in a straight line toward the tip side, reaching the first through hole, but otherwise the configuration is the same as this embodiment. Here, the thickness of the cover in the comparative example is constant.

This simulation uses fluid simulation as its analytical method, and only considers the air in the auxiliary chamber, with a flow velocity of 25 m/s and an ambient temperature of 27°C.

In particular, the simulation results of the flow velocity distribution show that, compared to the comparative example, the present embodiment provides smoother gas flow within the auxiliary chamber and a larger pressure difference between the inside and outside of the auxiliary chamber 96 at the first through-hole 71. As a result, it is found that the scavenging performance of residual gas within the auxiliary chamber 96 is improved.

In addition, according to the spark plug 100 of this embodiment, as shown in FIG. 2, in a cross section including the axis CA, the rear end E1 of the outer wall side of the second through hole 73 in the axial direction AD is located in the straight section SL, so that the flow of gas discharged from the second through hole 73 is not perpendicular to the axis CA but intersects it, and as a result, the tumble flow improves the scavenging of residual gas in the auxiliary chamber.

In addition, with the spark plug 100 of this embodiment, the cross-sectional area of the auxiliary chamber 96 in a plane perpendicular to the axis CA decreases from the rear end E2 on the inner wall side of the second through hole 73 toward the tip end. This makes it easier to ensure the thickness of the cover in the portion where the second through hole is formed. By ensuring the thickness of the cover in the portion where the second through hole is formed, heat dissipation is suppressed, improving combustion stability.

B. Other embodiments:
The configuration of the spark plug 100 in the above embodiment is merely an example and can be modified in various ways.

In the above embodiment, the second through hole 73 is located closer to the tip than the discharge gap G in the axial direction AD, but this is not limited to the above. The discharge gap G and the second through hole 73 may be located in the same position in the axial direction AD, or the discharge gap G may be located closer to the tip than the second through hole 73.

In the above embodiment, the cross-sectional area of the auxiliary chamber 96 in a plane perpendicular to the axis CA decreases from the rear end E2 on the inner wall side of the second through hole 73 toward the tip side, but this is not limited to this. For example, the cross-sectional area of the auxiliary chamber 96 in a plane perpendicular to the axis CA may be constant within a predetermined range from the rear end E2 on the inner wall side of the second through hole 73.

In addition, in the above embodiment, the metal shell 30 and the cover 70 are separate bodies, but the metal shell 30 and the cover 70 may be configured as one body. Furthermore, the effects obtained from the above embodiment can be obtained in the same way regardless of the screw diameter.

The present invention is not limited to the above-described embodiments, and can be realized in various configurations without departing from the spirit of the present invention. For example, the technical features in the embodiments corresponding to the technical features in each form described in the Summary of the Invention column can be replaced or combined as appropriate to solve some or all of the above problems or to achieve some or all of the above effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate.

10...insulator, 11...shaft hole, 20...center electrode, 21...tip portion, 30...metal shell, 31...shaft hole, 32...tool engagement portion, 33...male thread portion, 34...fixing surface, 35...through hole, 40...ground electrode, 41...one end portion, 42...other end portion, 50...terminal metal, 61...tip seal material, 62...resistor, 63...rear end seal material, 70...cover, 71...first through hole, 72...rear end surface, 73...second through hole, 90...engine head, 93...female thread portion, 95...combustion chamber, 96...auxiliary chamber, 100...spark plug, AD...axial direction, CA...axis, CL...curved portion, E1...rear end, E2...rear end, ED...extension direction, G...discharge gap, SL...straight portion

Claims (3)

a cylindrical metal shell extending along an axis;
a center electrode that is insulated and supported on an inner circumferential side of the metallic shell;
a ground electrode electrically connected to the metallic shell and forming a discharge gap between the center electrode and an end of the ground electrode;
a cover that covers the center electrode and the ground electrode from a tip side to form an auxiliary chamber;
Equipped with
a first through hole passing through the axis and a second through hole present in a region other than the axis,
In a cross section including the axis,
the outer wall of the cover has a straight portion that approaches the axis in a straight line toward the tip side and reaches the first through hole,
a curved portion of an inner wall of the cover that curves toward the axis in a curved manner toward the tip side and reaches the first through hole. 2. The spark plug of claim 1,
In a cross section including the axis,
a rear end of the second through hole on an outer wall side in a direction along the axis is located on the straight portion. 3. A spark plug according to claim 1 or 2,
a cross-sectional area of the sub-chamber in a plane perpendicular to the axis decreases from a rear end of an inner wall of the second through hole toward the tip end.

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