Spark plug

Abstract

To provide a spark plug that can improve ignition performance.SOLUTION: A spark plug includes: a center electrode extending in an axial direction; a main body metal fitting that insulates and holds the center electrode; and a ground electrode that includes one end connected to the main body metal fitting and the other end facing a tip face of the center electrode. A cross section of the other end cut parallel to an end face of the other end is a rectangle with chamfered corners, and in two sets of diagonal corners of the rectangle, the size of the chamfer of two corners constituting one diagonal corner is larger than the size of the chamfer of two corners constituting the other diagonal corner.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a spark plug. [Background technology]

[0002] In a spark plug having a center electrode, a metal shell that insulates and holds the center electrode, and a ground electrode connected to the metal shell, a prior art technique for chamfering the corners of the ground electrode is disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2009 / 066714 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a need in the prior art for further improvements in ignition quality.

[0005] The present invention has been made in response to this demand, and has an object to provide a spark plug that can improve ignition performance. [Means for solving the problem]

[0006] In order to achieve this object, a first aspect of the present invention comprises a center electrode extending in an axial direction, a metal shell that insulates the center electrode, and a ground electrode including one end connected to the metal shell and the other end facing the tip face of the center electrode, wherein a cross section of the other end cut parallel to the end face of the other end is a rectangle with chamfered corners, and two pairs of diagonal corners of the rectangle have a larger chamfering size at two corners constituting one diagonal than at two corners constituting the other diagonal.

[0007] In the second embodiment, the chamfered corners of the first embodiment are rounded.

[0008] In a third aspect, in the first or second aspect, the chamfer dimensions of two corners constituting one diagonal corner satisfy 1≦Y / X≦3, where Y is the dimension in the axial direction and X is the dimension perpendicular to the axial direction, preferably 1.25≦Y / X≦2.67, and more preferably 1.5≦Y / X≦2.67. Effect of the Invention

[0009] According to the present invention, the cross section of the other end of the ground electrode cut parallel to the end face is a rectangle with chamfered corners, and the size of the chamfer of the two corners constituting one diagonal corner of the rectangle is larger than the size of the chamfer of the two corners constituting the other diagonal corner, so that the flow of the air-fuel mixture in the combustion chamber is easily guided between the tip face of the center electrode and the other end of the ground electrode. The flame kernel generated between the center electrode and the ground electrode grows, making it easier to ignite the air-fuel mixture guided between the tip face of the center electrode and the other end of the ground electrode, thereby improving ignition performance. [Brief description of the drawings]

[0010] [Figure 1] 1 is a half-sectional view of a spark plug according to an embodiment; [Diagram 2] FIG. 4 is a cross-sectional view of a ground electrode. [Diagram 3] 3 is a cross-sectional view of the ground electrode taken along line III-III in FIG. 2. [Figure 4] 4 is an enlarged cross-sectional view of a corner portion shown by IV in FIG. 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a half-sectional view of a spark plug 10 according to one embodiment, taken along an axis O. In Fig. 1, the lower side of the paper refers to the leading end side of the spark plug 10, and the upper side of the paper refers to the rear end side of the spark plug 10 (the same applies to Figs. 2 to 4). As shown in Fig. 1, the spark plug 10 includes a center electrode 13 and a ground electrode 18. The center electrode 13 is disposed in an insulator 11, and the ground electrode 18 is connected to a metallic shell 16 disposed in the insulator 11.

[0012] The insulator 11 is a substantially cylindrical member having an axial hole 12 along the axis O. The insulator 11 is made of ceramics such as alumina, which has excellent mechanical properties and insulating properties at high temperatures. The center electrode 13 is disposed in the axial hole 12. The center electrode 13 is a rod-shaped conductive metal member. The center electrode 13 is configured such that a cylindrical base material with a bottom, mainly composed of Ni, covers a core material mainly composed of Cu. It is possible to omit the core material. A tip surface 14 of the center electrode 13 is disposed outside the axial hole 12.

[0013] The center electrode 13 is electrically connected to a terminal fitting 15 in the axial hole 12. The terminal fitting 15 is a rod-shaped member to which a high-voltage cable (not shown) is connected, and is made of a conductive metal material (such as low carbon steel). The terminal fitting 15 is fixed to the rear end of the insulator 11 with its tip side inserted into the axial hole 12.

[0014] The metal shell 16 is a substantially cylindrical member made of a conductive metal material (such as low carbon steel). The metal shell 16 surrounds the tip side of the insulator 11 and holds the insulator 11 inside. A male thread 17 is provided on the outer circumferential surface of the metal shell 16. The male thread 17 is screwed into a female thread of a plug hole provided in an engine (not shown), and the spark plug 10 is attached to the engine.

[0015] The ground electrode 18 is a rod-shaped member made of a conductive metal material. The ground electrode 18 has a base material mainly made of Ni covering a core material mainly made of Cu. The core material can be omitted. The core material is not shown in FIG. 1 (the same applies to FIGS. 2 to 4).

[0016] The ground electrode 18 extends from one end 19 connected to the metallic shell 16 to the other end 20. The ground electrode 18 includes a bent portion 21 between the one end 19 and the other end 20. The ground electrode 18 extends from the one end 19 to the bent portion 21 along the axis O, and extends from the bent portion 21 to the other end 20 approximately perpendicular to the axis O. The other end 20 of the ground electrode 18 intersects with the axis O. The other end 20 is located on the tip side of the center electrode 13 and faces the tip surface 14 of the center electrode 13 in the direction of the axis O with a gap therebetween.

[0017] 2 is a cross-sectional view of the other end 20 of the ground electrode 18. The other end 20 of the ground electrode 18 includes a first surface 22 facing the rear end side, a second surface 23 facing the front end side, a third surface 24 and a fourth surface 25 (see FIG. 3) connecting the first surface 22 and the second surface 23, and an end surface 26 connecting the first surface 22 and the second surface 23. The end surface 26 is also connected to the third surface 24 and the fourth surface 25.

[0018] A discharge member 27 is disposed on the first surface 22 of the other end 20. The discharge member 27 includes a base 28 disposed on the first surface 22 of the other end 20, a tip 29 disposed on the rear end side of the base 28 and mainly composed of a precious metal, and a fusion part 30 connecting the tip 29 and the base 28. The base 28 is connected to the other end 20 via a fusion part 31. The discharge member 27 protrudes from the ground electrode 18 toward the center electrode 13.

[0019] Base 28 is made of a metal material mainly composed of Ni, for example. The precious metal contained in tip 29 is, for example, one or more of Pt, Ir, Rh, and Ru. Melted portion 30 is formed by melting base 28 and tip 29 together, and is made, for example, by laser welding. Melted portion 31 is formed by melting ground electrode 18 and base 28 together, and is made, for example, by resistance welding.

[0020] 3 is a cross-sectional view of the other end 20 (a portion facing the tip surface 14 of the center electrode 13) of the ground electrode 18 taken along line III-III in FIG. 2. FIG. 3 shows a cross section of the other end 20 and the discharge member 27 cut parallel to the end surface 26 (see FIG. 2) of the other end 20. The cross-sectional shape of the other end 20 is a rectangle surrounded by four lines indicating the first surface 22, the second surface 23, the third surface 24, and the fourth surface 25. The rectangle of the cross-sectional shape of the other end 20 has four corners. The four corners are a corner 32 where the first surface 22 and the fourth surface 25 intersect, a corner 33 where the fourth surface 25 and the second surface 23 intersect, a corner 34 where the second surface 23 and the third surface 24 intersect, and a corner 35 where the third surface 24 and the first surface 22 intersect. The corners 32, 33, 34, and 35 are chamfered.

[0021] 4 is a cross-sectional view of the corner 33 enlarged from the portion indicated by IV in FIG. 3. The size of the chamfer applied to the corner 33 is represented by the area of ​​a triangle 41 connecting an intersection 38 between a straight line 36 extending from the straight line indicating the fourth surface 25 and a straight line 37 extending from the straight line indicating the second surface 23, an intersection 39 between the corner 33 and the straight line 36, and an intersection 40 between the corner 33 and the straight line 37. In this embodiment, the chamfer of the corner 33 is an R-chamfer connecting the intersection 39 and the intersection 40 with a curve. Since the chamfer of the corner 33 is an R-chamfer, the corner 33 is represented by a curve that is convex toward the intersection 38 with respect to a line segment 42 connecting the intersection 39 and the intersection 40.

[0022] The chamfering of corner 33 is not limited to R-chamfering. It is of course possible for corner 33 to be chamfered as C-chamfering, which connects intersection 39 and intersection 40 with line segment 42. Even when corner 33 is chamfered as C-chamfering, which connects intersection 39 and intersection 40 with line segment 42, the size of the chamfering of corner 33 is represented by the area of ​​triangle 41 connecting intersections 38, 39, and 40.

[0023] The chamfer dimensions of the corner portion 33 are represented by the dimension Y in the direction of the axis O (see FIG. 1) and the dimension X in the direction perpendicular to the axis O. The dimension Y is the distance between the intersection point 39 and the intersection point 38 (the length of the straight line 36), and the dimension X is the distance between the intersection point 40 and the intersection point 38 (the length of the straight line 37). The relationship between the dimension Y and the dimension X is arbitrary, and can be either Y>X, Y<X, or Y = X. The chamfer shape, size, dimension X, and dimension Y applied to the corner portions 32, 34, and 35 are represented in the same manner as the chamfer shape, size, dimension X, and dimension Y applied to the corner portion 33 described with reference to FIG. 4.

[0024] Returning to FIG. 3 for explanation. The quadrilateral indicated by the other end portion 20 has two pairs of opposite corners (diagonals). Among the corner portions 32, 33, 34, and 35, the corner portions 33 and 35 constitute one diagonal, and the corner portions 32 and 34 constitute the other diagonal. The chamfer size of the corner portions 33 and 35 is larger than the chamfer size of the corner portions 32 and 34. In other words, the smaller chamfer size of the corner portions 33 and 35 is larger than the larger chamfer size of the corner portions 32 and 34.

[0025] When the spark plug 10 is attached to an engine (not shown), the tip surface 14 of the center electrode 13 and the other end portion 20 of the ground electrode 18 are exposed in the combustion chamber of the engine. The spark plug 10 is arranged in the engine with the third surface 24 of the other end portion 20 facing the upstream side of the flow of the air-fuel mixture in the combustion chamber and the fourth surface 25 of the other end portion 20 facing the downstream side (exhaust valve side).

[0026] When the secondary voltage of the ignition coil of an ignition device (not shown) rises and the insulation between the center electrode 13 and the ground electrode 18 breaks down, first, a spark (hereinafter referred to as a "capacitance spark") is generated between the center electrode 13 and the ground electrode 18 by the electrical energy stored in the secondary circuit. Next, a spark with a long duration (hereinafter referred to as an "inductive spark") is generated by the electromagnetic energy of the ignition coil. The generation of the inductive spark continues until the energy of the ignition coil is consumed. The discharge path connecting the center electrode 13 and the ground electrode 18 extends along the flow of the air-fuel mixture. When the discharge path extends, the voltage between the center electrode 13 and the ground electrode 18 rises, and a phenomenon called short-circuiting or re-discharge of the discharge path occurs.

[0027] The flame kernel generated in the discharge path by the discharge spark grows between the tip surface 14 of the center electrode 13 and the discharge member 27, or grows downstream between the electrodes due to the extension of the discharge path. Ignition performance can be improved by controlling the flow around the other end 20 of the ground electrode 18, guiding the air-fuel mixture between the tip surface 14 of the center electrode 13 and the other end 20 of the ground electrode 18, or extending the discharge path by riding on the flow.

[0028] 3 indicate the flow of fluid around the other end 20. The chamfering size of corners 32, 34 of the other end 20 is smaller than the chamfering size of corners 33, 35. As a result, the airflow passing through corners 33, 35 tends to flow along corners 33, 35 compared to the airflow passing through corners 32, 34.

[0029] For example, the flow F1 flowing from corner 35 to corner 32 is unlikely to flow along fourth surface 25 when passing corner 32, and the flow is unlikely to disperse at corner 32, so the flow speed is unlikely to decrease. The flow F3 flowing from corner 34 to corner 35 is unlikely to flow along second surface 23 when passing corner 34, and the flow speed is unlikely to decrease because the flow is unlikely to disperse at corner 34.

[0030] On the other hand, the flow F2 from the corner 32 to the corner 33 tends to flow along the second surface 23 when passing through the corner 33, and tends to flow from the corner 33 to the corner 34. The flow F4 from the corner 34 to the corner 35 tends to flow along the first surface 22 when passing through the corner 35, and the fluid is easily guided between the tip surface 14 (see FIG. 1) of the center electrode 13 and the first surface 22.

[0031] The corners 32, 33, 34, and 35 provided at the other end 20 facilitate the introduction of the flow F4 between the tip surface 14 of the center electrode 13 and the first surface 22 of the other end 20, making it easier to ignite even a lean mixture. Furthermore, the discharge path is easily extended by the flow F1. This improves ignition performance.

[0032] It is preferable that the chamfering of the corners 32, 33, 34, and 35 is all R-chamfering, which provides a rounded surface at the corners. This is because, compared to C-chamfering, which provides a flat surface at the corners, R-chamfered corners 32, 33, 34, and 35 are less likely to cause separation when fluid passes through them, thereby reducing resistance due to separation.

[0033] Regarding ignition performance, the chamfer dimensions X and Y of the corners 33 and 35, which are larger than the chamfer dimensions of the corners 32 and 34, are different from each other and preferably satisfy 1≦Y / X≦3, more preferably 1.25≦Y / X≦2.67, and particularly preferably 1.5≦Y / X≦2.67, because this increases the effect of guiding the flow of the fluid. EXAMPLES

[0034] The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0035] Example 1 The tester prepared various samples No. 1-7 with different shapes and sizes of chamfering of the corners 32, 33, 34, 35 of the other end 20 of the ground electrode 18. The distance between the first surface 22 and the second surface 23 of the other end 20 and the distance between the third surface 24 and the fourth surface 25 of the other end 20 of the sample No. 1-7 were the same. The corners 32, 33, 34, 35 of the sample No. 1-6 were chamfered with a C-shape to provide a 45° angle. The size of the chamfering of the sample No. 7 was the same as that of the sample No. 2, but instead of the C-shape, the corners 32, 33, 34, 35 were chamfered with an R-shape to make the corners round. The size of the chamfering (the area of ​​the corners removed) of the corners 32, 33, 34, 35 of the sample No. 1-7 is shown in Table 1.

[0036] [Table 1]

[0037] In sample No. 1-7, corners 33, 35 constitute one diagonal, and corners 32, 34 constitute the other diagonal. Sample No. 1 was a sample in which the size of the chamfering of all four corners was the same. Samples No. 2 and 7 were samples in which the size of the chamfering of corners 33, 35 constituting one diagonal was larger than the size of the chamfering of corners 32, 34 constituting the other diagonal. Samples No. 3-6 were samples in which the size of the chamfering of corners 33, 35 constituting one diagonal was not larger than the size of the chamfering of corners 32, 34 constituting the other diagonal.

[0038] The tester attached each sample to a 1.6-liter, four-cylinder, direct-injection engine with a turbocharger and operated the engine. The engine operating conditions were a rotation speed of 1,800 rpm, a load of 500 kPa indicated mean effective pressure (NMEP), and an excess air ratio λ = 1. The series of actions from taking in the mixture into the engine's combustion chamber to burning and discharging the combustion gas is considered to be one cycle, and the test was conducted to measure the number of cycles in which the mixture failed to ignite by detecting the pressure in the combustion chamber during 1,000 cycles. This test was conducted five times for each sample, and the percentage of cycles in which ignition failed was calculated.

[0039] The ignition ability of each sample was judged as A to D depending on the percentage of ignition failures. The ignition failure rate was A if it was less than 8%, B if it was between 8% and 10%, C if it was between 10% and 12%, and D if it was between 12% and 14%. The judgements are shown in Table 1.

[0040] As shown in Table 1, sample No. 2, in which the size of the chamfer at corners 33 and 35 constituting one diagonal is larger than the size of the chamfer at corners 32 and 34 constituting the other diagonal, was judged as B, whereas samples Nos. 1 and 3-6, which did not have such a relationship, were judged as C or D.

[0041] According to the embodiment, it was revealed that ignition performance can be improved by making the chamfer size of the corners 33, 35 constituting one diagonal corner larger than the chamfer size of the corners 32, 34 constituting the other diagonal corner. It is presumed that this is because if the chamfer size of the corners 33, 35 is larger than the chamfer size of the corners 32, 34, the air-fuel mixture is easily guided between the tip surface 14 of the center electrode 13 and the other end 20 of the ground electrode 18.

[0042] Comparing samples No. 2 and No. 7, which have the same chamfer size, No. 7, which has R-chamfered corners, was judged to be an A, while No. 2, which has C-chamfered corners, was judged to be a B. It became clear that R-chamfering the corners improves ignition ability compared to C-chamfered corners. It is presumed that this is because R-chamfered corners make it less likely for fluid to separate than C-chamfered corners.

[0043] Example 2 The tester prepared various samples No. 8-18 in which the chamfer size of the corners 33, 35 of the other end 20 of the ground electrode 18 was larger than the chamfer size of the corners 32, 34, and the chamfer dimensions Y, X of the corners 33, 35 were different. The chamfers of the corners 32, 33, 34, 35 of the sample No. 8-18 were all C-chamfered, and the chamfer dimensions Y, X of the corners 32, 34 were each 0.2 mm. In the sample No. 8-18, the chamfer dimensions Y, X of the corner 33 and the chamfer dimensions Y, X of the corner 35 were the same, and the distance between the first surface 22 and the second surface 23 of the other end 20 and the distance between the third surface 24 and the fourth surface 25 were the same. Table 2 shows the chamfer dimensions Y, X of the corners 33, 35 of the sample No. 8-18, and the value obtained by dividing the dimension Y by the dimension X.

[0044] [Table 2]

[0045] The tester attached each sample to a 4-cylinder direct injection engine with a supercharger and a displacement of 1.6 liters and operated the engine. The operating conditions of the engine were set as a rotational speed of 1200 rpm, a load NMEP = 350 kPa, and an air-fuel ratio λ = 1. A series of operations from taking in the air-fuel mixture into the combustion chamber of the engine to burning and discharging the combustion gas was defined as one cycle. A test was conducted to measure the number of cycles in which ignition of the air-fuel mixture failed by detecting the pressure in the combustion chamber during 1000 cycles. This test was performed 5 times for each sample, and the ratio of ignition failures was determined.

[0046] According to the ratio of ignition failures, the ignitability of each sample was determined as one of A to D. The determination was as follows: when the ratio of ignition failures was less than 4%, it was A; when it was 4% or more and less than 5%, it was B; when it was 5% or more and less than 6%, it was C; and when it was 6% or more, it was D. The determination is shown in Table 2.

[0047] As shown in Table 2, for Samples No. 10 - 18 with 1.00 ≦ Y / X ≦ 3.00, the determination was A - C, while for Samples No. 8 and 9 with Y / X < 1.00, the determination was D. It is presumed that for Samples No. 8 and 9 with Y / X < 1.00, the improvement effect of the fluid motion by the corners 33 and 35 was poor.

[0048] According to Samples No. 10 - 18, in the range of 1.00 < Y / X ≦ 2.67, it was revealed that as the value of Y / X increased beyond 1.00, the ignitability improved, but when the value of Y / X exceeded 2.67, the ignitability decreased. When the value of Y / X exceeded 2.67, while the ratio of the air-fuel mixture flowing toward the tip of the insulator 11 increased, the ratio of the air-fuel mixture guided between the tip surface 14 of the center electrode 13 and the other end 20 of the ground electrode 18 decreased, and it is presumed that the ignitability decreased.

[0049] For Samples No. 12 - 16 with 1.25 ≦ Y / X ≦ 2.67, the determination was A or B. For Samples No. 14 - 16 with 1.50 ≦ Y / X ≦ 2.67, the determination was A. According to the examples, it was revealed that the ignitability can be improved when the range of the value of Y / X is 1.25 ≦ Y / X ≦ 2.67, particularly 1.50 ≦ Y / X ≦ 2.67.

[0050] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention without departing from the spirit of the present invention.

[0051] For example, it is of course possible to omit the base 28 of the discharge member 27 disposed at the other end 20 of the ground electrode 18 and join the tip 29 to the other end 20, or to omit the discharge member 27. This is because, regardless of the presence or absence of the discharge member 27, the flow of fluid can be controlled by the chamfered corners 32, 33, 34, and 35 of the other end 20.

[0052] In the embodiment, the second surface 23 is flat except for the corners 33, 34 of the other end 20, but this is not necessarily limited to this. It is of course possible to raise a part of the first surface 22 by plastically deforming a part of the second surface 23 of the other end 20 excluding the discharge member 27 and recessing it toward the first surface 22.

[0053] It is of course possible to provide a film containing a precious metal such as Pt, Ir, Ru, or Rh on the raised portion of the first surface 22, or to bond a chip 29 to the raised portion of the first surface 22. Even if a part of the second surface 23 of the other end 20 is recessed or a part of the first surface 22 is raised, the cross section of the other end 20 cut parallel to the end face 26 of the other end 20 has a rectangular shape. This is because the flow of the fluid can be controlled by the chamfered corners 32, 33, 34, and 35 of the other end 20, regardless of the presence or absence of a recess in the second surface 23 or a rise in the first surface 22. [Explanation of symbols]

[0054] 10 Spark plug 13 Center electrode 14 Tip surface 16 Metal fitting 18 Ground electrode 19 One end 20 Other end 26 End face 32, 33, 34, 35 Corners Axis O

Claims

1. A center electrode extending in an axial direction; a metal shell that insulates and holds the center electrode; a ground electrode including one end connected to the metallic shell and another end facing a tip end surface of the center electrode, A cross section of the other end taken parallel to an end face of the other end is a rectangle with chamfered corners, The spark plug has two pairs of diagonal corners of the rectangle, and the size of the chamfer of two corners constituting one pair of diagonal corners is larger than the size of the chamfer of two corners constituting the other pair of diagonal corners.

2. 2. The spark plug according to claim 1, wherein said corners are rounded.

3. 3. The spark plug according to claim 1, wherein a dimension of the chamfer of two corners constituting one of the diagonal corners satisfies 1≦Y / X≦3, where Y is a dimension in the direction of the axis and X is a dimension in a direction perpendicular to the axis.

4. 3. The spark plug according to claim 1, wherein a dimension of the chamfer of two corners constituting one of the diagonal corners satisfies 1.25≦Y / X≦2.67, where Y is a dimension in the direction of the axis and X is a dimension in a direction perpendicular to the axis.

5. 3. The spark plug according to claim 1, wherein a dimension of the chamfer of two corners constituting one of the diagonal corners satisfies 1.5≦Y / X≦2.67, where Y is a dimension in the direction of the axis and X is a dimension in a direction perpendicular to the axis.

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