Patent Application
20160218487
This disclosure relates to a spark plug.
Conventionally, a spark plug has been used for an internal combustion engine. As the spark plug, for example, a spark plug that includes a center electrode, an insulator, a metal shell, and a packing has been used. The center electrode extends in an axial line direction. The insulator has an axial hole extending in the axial line direction. The center electrode is arranged at a front end side of the axial hole. The metal shell is arranged at an outer periphery of the insulator. The packing is arranged between the insulator and the metal shell. As the insulator, for example, an insulator that includes a step part and an insulator nose portion has been used. The step part has an outer diameter reduced to the front end side. The insulator nose portion extends to the front end at the front end side of the step part. The packing is sandwiched between the step part of the insulator and the metal shell. Here, there has been proposed the following technique. To reduce breakage of the insulator, a curved surface portion is disposed between the step part of the insulator and the insulator nose portion. In addition to the step part of the insulator, the packing is also brought into contact with a site at the front end side with respect to an intermediate portion of the curved surface portion.
To improve design freedom of an internal combustion engine, it recently has become desirable to have a spark plug with a small diameter. If the small-diameter spark plug results in the insulator having a small diameter, the insulator is possibly likely to be broken.
This disclosure provides a new technique to reduce a possibility of breaking the insulator.
This disclosure, for example, discloses the following application examples.
In accordance with a first aspect of the present invention, there is provided a spark plug that includes a center electrode, an insulator, a metal shell, and a packing. The center electrode extends in an axial line direction. The insulator includes an axial hole extending in the axial line direction. The center electrode is arranged at a front end side of the axial hole. The insulator includes an outer-diameter-contracted portion and a nose portion. The outer-diameter-contracted portion has an outer diameter decreased toward the front end side in the axial line direction. The nose portion is a part disposed at a front end side of the outer-diameter-contracted portion. The metal shell is arranged at an outer periphery of the insulator. The metal shell includes an inner-diameter-contracted portion. The inner-diameter-contracted portion has an internal diameter decreased toward the front end side in the axial line direction. The packing is arranged between the outer-diameter-contracted portion of the insulator and the inner-diameter-contracted portion of the metal shell. Assuming that in a contact portion of the packing and the insulator, a position at a most front end side is set as a first position, in a surface of the nose portion of the insulator, a position where a length from a front end of the insulator parallel to the axial line direction is 1 mm is set as a second position, a length between the first position and the second position parallel to the axial line direction is set as a first length, in a case where a load perpendicular to the axial line direction is applied to the second position in a state where the insulator is secured at the first position of the insulator and the front end of the insulator is a free end, a ratio of stress at a surface position that is a position on a surface of the insulator to stress at the first position is set as a stress ratio, and in a range of the surface position where the stress ratio is 0.8 or more to 1.15 or less, a length in a continuous range from the first position toward a front end side parallel to the axial line direction is set as a second length, a ratio of the second length to the first length is 0.7 or more.
This configuration reduces a variation in stress at the surface of the insulator compared with the case where the ratio of the second length to the first length is less than 0.7. Accordingly, a possibility of breaking the insulator can be reduced.
In accordance with a second aspect of the present invention, there is provided a spark plug according to the application example 1, wherein the insulator has an outer diameter of 3.5 mm or less at the second position.
This configuration allows reducing a possibility of breaking the insulator due to vibration.
In accordance with a third aspect of the present invention, there is provided the spark plug according to the application example 1 or 2, wherein a nose portion includes a cylinder portion forming a front end side part of the nose portion. The cylinder portion has a constant outer diameter. A length from a rear end of the cylinder portion to the front end of the insulator parallel to the axial line direction is 3.5 mm or less.
This configuration allows reducing a possibility of fracturing the insulator at a part near the cylinder portion.
In accordance with a fourth aspect of the present invention, there is provided a spark plug according to any one of the application examples 1 to 3, wherein a part of the front end side of the nose portion is arranged on a front end side with respect to a front end of the metal shell. A projection area when projecting a part of the nose portion arranged on a front end side with respect to the front end of the metal shell in a direction perpendicular to the axial line direction is 8.7 mm2 or less.
This configuration allows reducing a possibility of fracturing the nose portion.
In accordance with a fifth aspect of the present invention, there is provided a spark plug according to any one of the application examples 1 to 4, wherein the metal shell includes a thread portion for mounting. A nominal diameter of the thread portion is M10 or less.
This configuration allows reducing a possibility of breaking the insulator when using the thin spark plug whose nominal diameter of the thread portion is M10 or less.
In accordance with a sixth aspect of the present invention, there is provided a spark plug according to any one of the application examples 1 to 5, wherein the nose portion includes a cylinder portion forming the front end side part of the nose portion. The cylinder portion has a constant outer diameter. The part of the front end side of the nose portion is arranged on the front end side with respect to the front end of the metal shell. Assuming that a length from the rear end of the cylinder portion to the front end of the insulator parallel to the axial line direction is denoted as Ds1, a section modulus of the insulator at the first position is denoted as Z1, a section modulus of the insulator at the rear end of the cylinder portion is denoted as Z2, a length from the first position to the front end of the insulator parallel to the axial line direction is denoted as L4, and a length of a part of the nose portion positioned on a front end side with respect to the front end of the metal shell parallel to the axial line direction is denoted as De, following relational expressions (1), (2), and (3) are met.
Z1/Z2>3.5 (1)
Ds1>2 mm (2)
Ds1<Ap×(Z1/Z2)Bp (3)
Bp=−0.832−0.014×L4+0.099×De
Units of Ds1, L4, and De are mm.
This configuration can improve the anti-fouling characteristics or performance and the breaking resistance.
The present invention can be achieved by various forms, for example, can be achieved in a form of a spark plug, an internal combustion engine on which the spark plug is mounted, or a similar form.
The spark plug 100 includes an insulator 10 (hereinafter referred to also as a “ceramic insulator 10”), the center electrode 20, the ground electrode 30, the terminal metal fitting 40, a metal shell 50, a conductive first seal portion 60, a resistor 70, a conductive second seal portion 80, a front-end-side packing 8, a talc 9, a first rear end side packing 6, and a second rear end side packing 7.
The insulator 10 is an approximately cylindrically-shaped member with a through hole 12 (hereinafter referred to also as an “axial hole 12”). The through hole 12 extends along the central axis CL so as to pass through the insulator 10. The insulator 10 is formed by sintering alumina (another insulating material can also be used). The insulator 10 includes a nose portion 13, a first outer-diameter-contracted portion 15, a front-end-side trunk portion 17, a collar portion 19, a second outer-diameter-contracted portion 11, and a rear-end-side trunk portion 18, each of which is arranged from the front end side toward the rear end side in this order.
The collar portion 19 is the largest outer diameter part of the insulator 10. The outer diameter of the first outer-diameter-contracted portion 15, which is disposed at the front end side with respect to the collar portion 19, gradually decreases from the rear end side toward the front end side. In the vicinity (the front-end-side trunk portion 17 in the example of
Into the front end side of the through hole 12 of the insulator 10, the center electrode 20 is inserted. The center electrode 20 is a rod-shaped member extending along the central axis CL. The center electrode 20 includes an electrode base material 21 and a core material 22 buried inside of the electrode base material 21. The electrode base material 21 is, for example, formed using Inconel (“INCONEL” is a registered trademark), which is an alloy containing nickel as a main constituent. The core material 22 is formed with a material having higher thermal conductivity (for example, an alloy containing copper) than the electrode base material 21.
Focusing on an external appearance configuration of the center electrode 20, the center electrode 20 includes a nose portion 25, a collar portion 24, and a head 23. The nose portion 25 forms an end on the front end direction Df side. The collar portion 24 is disposed on the rear end side of the nose portion 25. The head 23 is disposed on the rear end side of the collar portion 24. The head 23 and the collar portion 24 are arranged in the through hole 12. A surface on the front end direction Df side of the collar portion 24 is supported by the inner-diameter-contracted portion 16 of the insulator 10. A part on the front end side of the nose portion 25 is exposed to the outside of the through hole 12 on the front end side of the insulator 10.
The terminal metal fitting 40 is inserted into the rear end side of the through hole 12 of the insulator 10. The terminal metal fitting 40 is formed using a conductive material (for example, a metal such as a low-carbon steel). On a surface of the terminal metal fitting 40, a metal layer is possibly formed for corrosion proof. For example, a Ni layer is formed by plating. The terminal metal fitting 40 includes a collar portion 42, a plug cap installation portion 41, and a nose portion 43. The plug cap installation portion 41 forms the part on the rear end side with respect to the collar portion 42. The nose portion 43 forms the part on the front end side with respect to the collar portion 42. The plug cap installation portion 41 is exposed to the outside of the through hole 12 on the rear end side of the insulator 10. The nose portion 43 is inserted into the through hole 12 of the insulator 10.
In the through hole 12 of the insulator 10, between the terminal metal fitting 40 and the center electrode 20, the resistor 70 for reducing electrical noise is disposed. The resistor 70 is formed of a composition containing glass particles (for example, B2O3—SiO2-based glass) as a main constituent, ceramic particles other than glass (for example, TiO2), and a conductive material (for example, metal such as Mg and carbon particles).
In the through hole 12, between the resistor 70 and the center electrode 20, the first seal portion 60 is arranged. Between the resistor 70 and the terminal metal fitting 40, the second seal portion 80 is disposed. As a result, the center electrode 20 is electrically connected to the terminal metal fitting 40 via the resistor 70 and the seal portions 60 and 80. The seal portions 60 and 80, for example, contain the glass particles similar to the resistor 70 and metal particles (such as Cu and Fe). The use of the seal portions 60 and 80 stabilizes a contact resistance among laminated members 20, 60, 70, 80, and 40, allowing stabilizing a resistance value between the center electrode 20 and the terminal metal fitting 40.
The metal shell 50 is an approximately cylindrically-shaped member with a through hole 59, which extends along the central axis CL so as to pass through the metal shell 50. The metal shell 50 is formed using a low-carbon steel material (another conductive material (for example, a metallic material) can also be used). On the surface of the metal shell 50, the metal layer for corrosion proof is possibly obtained. For example, the Ni layer is formed by plating. The insulator 10 is inserted into the through hole 59 of the metal shell 50. The metal shell 50 is secured to the outer periphery of the insulator 10. On the front end side of the metal shell 50, the front end (in this embodiment, the part on the front end side of the nose portion 13) of the insulator 10 is exposed to the outside of the through hole 59. On the rear end side of the metal shell 50, the rear end (in this embodiment, the part on the rear end side of the rear-end-side trunk portion 18) of the insulator 10 is exposed to the outside of the through hole 59.
The metal shell 50 includes a trunk portion 55, a seat portion 54, a deformed portion 58, a tool engagement portion 51, and a crimp portion 53 that are arranged from the front end side toward the rear end side in this order. The seat portion 54 is a flanged part. At the front end side of the seat portion 54, the trunk portion 55 is disposed. The outer diameter of the trunk portion 55 is smaller than the outer diameter of the seat portion 54. At the outer peripheral surface of the trunk portion 55, a thread portion 52 is formed. The thread portion 52 is screwed with a mounting hole of the internal combustion engine (for example, a gasoline engine). A nominal diameter of the thread portion 52 is 10 mm (M10). Between the seat portion 54 and the thread portion 52, an annular gasket 5 is fitted. The gasket 5 is formed by folding a metal plate.
The metal shell 50 includes an inner-diameter-contracted portion 56. The inner-diameter-contracted portion 56 is arranged on the front end direction Df side with respect to the deformed portion 58. The internal diameter of the inner-diameter-contracted portion 56 gradually decreases from the rear end side toward the front end side. Between the inner-diameter-contracted portion 56 of the metal shell 50 and the first outer-diameter-contracted portion 15 of the insulator 10, the front-end-side packing 8 is sandwiched. The front-end-side packing 8 is made of steel, and is an O-shaped ring (another material (for example, a metallic material such as copper) can also be adopted).
On the rear end side of the seat portion 54, the deformed portion 58 is disposed. The deformed portion 58 has a wall thickness thinner than that of the seat portion 54. The deformed portion 58 is deformed such that the center portion projects toward the outside in the radial direction (the direction away from the central axis CL). On the rear end side of the deformed portion 58, the tool engagement portion 51 is disposed. The shape of the tool engagement portion 51 is a shape (for example, a hexagonal prism) with which a spark plug wrench is engaged. On the rear end side of the tool engagement portion 51, the crimp portion 53 is disposed. The crimp portion 53 has a wall thickness thinner than that of the tool engagement portion 51. The crimp portion 53 is arranged on the rear end side with respect to the second outer-diameter-contracted portion 11 of the insulator 10 so as to form the rear end (namely, the end on the rear end direction Dfr side) of the metal shell 50. The crimp portion 53 is flexed to radially inside.
On the rear end side of the metal shell 50, between the inner peripheral surface of the metal shell 50 and the outer peripheral surface of the insulator 10, an annular space SP is formed. In this embodiment, this space SP is a space surrounded by the crimp portion 53 and the tool engagement portion 51 of the metal shell 50 and the second outer-diameter-contracted portion 11 and the rear-end-side trunk portion 18 of the insulator 10. On the rear end side within this space SP, the first rear end side packing 6 is arranged. On the front end side within this space SP, the second rear end side packing 7 is arranged. In this embodiment, these rear end side packings 6 and 7 are C-shaped rings made of steel (another material can also be adopted). Between the two rear end side packings 6 and 7 within the space SP, the powders of the talc 9 are filled up.
During manufacture of the spark plug 100, the crimp portion 53 is crimped so as to be folded to the inside. Then, the crimp portion 53 is pressed toward the front end direction Df side. Accordingly, the deformed portion 58 is deformed, and the insulator 10 is pressed toward the front end side via the packings 6 and 7 and the talc 9 within the metal shell 50. The front-end-side packing 8 is pressed between the first outer-diameter-contracted portion 15 and the inner-diameter-contracted portion 56 to seal between the metal shell 50 and the insulator 10. The above-described configuration suppresses gas in the combustion chamber of the internal combustion engine from passing through between the metal shell 50 and the insulator 10 and then leaking to the outside. The metal shell 50 is secured to the insulator 10.
The ground electrode 30 is sealed to the front end (that is, the end on the front end direction Df side) of the metal shell 50. In this embodiment, the ground electrode 30 is a rod-shaped electrode. The ground electrode 30 extends from the metal shell 50 toward the front end direction Df, is bent toward the central axis CL, and reaches a front end portion 31. The front end portion 31 forms a gap g with a front end surface 20s1 (the surface 20s1 on the front end direction Df side) of the center electrode 20. The ground electrode 30 is sealed to the metal shell 50 to be electrically continued (for example, by laser beam welding). The ground electrode 30 includes a base material 35 and a core portion 36. The base material 35 forms the surface of the ground electrode 30. The core portion 36 is buried within the base material 35. The base material 35 is formed, for example, using Inconel. The core portion 36 is formed using a material (for example, pure copper) with higher thermal conductivity than that of the base material 35.
The drawing shows an exemplary configuration of the nose portion 13. The shown nose portion 13 includes a front cylinder portion 13fc, a tapered portion 13t, and a rear cylinder portion 13bc arranged from the front end side toward the rear end side in this order. The front cylinder portion 13fc is a part on the front end direction Df side in the nose portion 13. The front cylinder portion 13fc is a part having an approximately cylindrical shape with constant outer diameter. A corner at the front end of the front cylinder portion 13fc is chamfered. The rear cylinder portion 13bc is a part on the rear end direction Dfr side in the nose portion 13. The rear cylinder portion 13bc is a part having an approximately cylindrical shape with constant outer diameter. The outer diameter of the rear cylinder portion 13bc is larger than the outer diameter of the front cylinder portion 13fc. The tapered portion 13t is a part between the front cylinder portion 13fc and the rear cylinder portion 13bc. The tapered portion 13t is a part whose outer diameter gradually decreases toward the front end direction Df. The front cylinder portion 13fc is possibly omitted. In this case, the front end of the tapered portion 13t forms the front end of the nose portion 13. The rear cylinder portion 13bc is possibly omitted. In this case, the rear end of the tapered portion 13t forms the rear end of the nose portion 13.
The drawing shows a first position Pa, a second position Pb, a first length L1, the end portion diameter Ddb, the base diameter Dda, an end portion length Ds1, and a base length Ds2. The first position Pa is positioned at the most front end side in a contact portion of the insulator 10 and the front-end-side packing 8. That is, the first position Pa is positioned at the most front end direction Df side in the part secured (namely, supported) by another member in the surface of the insulator 10. The first position Pa is positioned on the surface of the nose portion 13. However, the first position Pa may be positioned on the surface of the first outer-diameter-contracted portion 15.
The second position Pb is a position on the surface of the nose portion 13 of the insulator 10 where a length from a front end 10e1 of the insulator 10 parallel to the central axis CL is a predetermined length Dpb. The following uses 1 mm as the predetermined length Dpb. The bending test, which will be described later, applies to this second position Pb a force in the direction toward the central axis CL perpendicular to the central axis CL.
The first length L1 is a length between the first position Pa and the second position Pb and is parallel to the central axis CL. The third length L3 is a length between a rear end P22 of the first outer-diameter-contracted portion 15 of the insulator 10 and the front end 10e1 of the insulator 10 and is parallel to the central axis CL. Hereinafter, the third length L3 is also referred to as an “insulator nose length L3.” The internal diameter d1 is a diameter of the through hole 12. In this embodiment, the internal diameter d1 is the identical across the entire range from the first position Pa to the second position Pb.
The end portion diameter Ddb is the outer diameter of the insulator 10 at the second position Pb. The base diameter Dda is the outer diameter of the insulator 10 at the first position Pa.
The end portion length Ds1 is a length between the front end 10e1 of the nose portion 13 and a rear end P12 of the front cylinder portion 13fc of the nose portion 13 and is parallel to the central axis CL.
The base length Ds2 is a length between the rear end P22 of the first outer-diameter-contracted portion 15 of the insulator 10 and a front end P21 of the rear cylinder portion 13bc of the nose portion 13 and is parallel to the central axis CL. This base length Ds2 is a total value of the length of the first outer-diameter-contracted portion 15 and the length of the rear cylinder portion 13bc.
If applying such force W to the second position Pb, stress is generated at the surface of the nose portion 13. Here, the following describes stress at a position of interest Pi shown in
Stress Sti at the position of interest Pi can be calculated in accordance with the following calculating formulas (1A) to (1C). These calculating formulas (1A) to (1C) are calculating formulas for stress in the case of a cantilever. The calculating formulas (1A) to (1C) are calculating formulas for stress in the case where the fixed end with the cross-sectional shape shown in
Sti=M/Z (1A)
M=Wf×Li (1B)
Z=(π×(d24−d14))/(32×d2) (1C)
Meaning of each parameter is as follows.
Sti: stress Sti, M: moment, Z: section modulus,
Wf: strength of force W, Li: length of interest Li, π: ratio of the circumference of a circle to its diameter,
d1: internal diameter d1, d2: outer diameter d2
In the drawing, reference stress Sta indicates the stress Sti at the first position Pa. Lower limit stress St1 and upper limit stress St2 indicate a lower limit and an upper limit of a range including the reference stress Sta. Hereinafter, a range Rs of the stress Sti equal to or more than the lower limit stress St1 and equal to or less than the upper limit stress St2 is referred to as the allowable range Rs. Here, the lower limit stress St1 is 0.8 times of the reference stress Sta. The upper limit stress St2 is 1.15 times of the reference stress Sta. The stress Sti being within the allowable range Rs suggests that a ratio of the stress Sti to the reference stress Sta, “Sti/Sta”, is 0.8 or more to 1.15 or less.
The drawing shows a consecutive range Rpi of the position of interest Pi where the stress Sti is in the allowable range Rs (hereinafter referred to as the “stable range Rpi”). This stable range Rpi is the widest range expanding from the first position Pa toward the front end direction Df side. In the drawing, a front end position Px indicates a front end position of this stable range Rpi. A second length L2 is a length of this stable range Rpi and is parallel to the central axis CL.
As shown in
The following describes the first evaluation test using samples of the spark plugs 100. As the first evaluation test, the “bending test” and a “vibration test” were conducted on the insulators 10. The following Table 1 shows configurations of the samples and the evaluation results.
Table 1 lists sample Nos., parameters Ddb, Dda, Ds1, Ds2, and L2/L1, which indicate the configurations of the insulators 10, the results of the bending test, and the results of the vibration test. The first evaluation test evaluates 27 types of the samples from No. A-1 to No. A-27 of mutually different configurations of the insulators 10.
Dimensions common to the 27 types of the samples evaluated in the first evaluation test are as follows.
Length of the first outer-diameter-contracted portion 15 (length parallel to the central axis CL): 0.3 mm
Diameter d1 of the through hole 12: 1.76 mm
Insulator nose length L3: 14 mm
In Table 1, the “End Portion Length Ds1=0” indicates the omission of the front cylinder portion 13fc. Similarly, the “Base Length Ds2=0” indicates the omission of the rear cylinder portion 13bc. As described above, the base length Ds2 is the total value of the length of the first outer-diameter-contracted portion 15 and the length of the rear cylinder portion 13bc. The length of first outer-diameter-contracted portion 15 is not zero (0.3 mm). However, for easy understanding of the omission of the rear cylinder portion 13bc, Table 1 indicates the base length Ds2 by zero in the case where the rear cylinder portion 13bc is omitted.
First, the following describes the bending test. The bending test first installs the spark plug 100 to a test stand (not shown). The test stand has a mounting hole fitting to the thread portion 52 of the metal shell 50. In this state, the insulator 10 is secured at the first position Pa. The front end 10e1 of the insulator 10 is a free end. In this state, as shown in
The “Breaking Load” shown in Table 1 means an average value (an average value of the ten samples) of the strength of the force W at the time point when the insulator 10 was broken (the unit is “newton”). The “Broken Portion” shown in Table 1 is a broken portion of the insulator 10. A “Base Ba” indicates the part near the first position Pa. A “Front End Bb” indicates the part near the second position Pb. The broken portions were the identical among the ten samples with the identical configuration. The evaluation in the bending test was conducted by two stages using the sample No. A-5 as a criterion. Specifically, a first evaluation A indicates that “the breaking load is large compared with the sample No. A-5”, and “the broken portion is the base Ba.” A second evaluation B indicates that at least one of “the breaking load is small compared with the sample No. A-5” and “the broken portion is the front end Bb” is met.
The broken portion being the front end Bb means that although the base part of the insulator 10 (namely, the part near the first position Pa) is not broken but endures, the front end portion (namely, the part near the second position Pb) is broken. That is, this means that the strength of the front end part of the insulator 10 is locally low. Accordingly, it was determined that the evaluation result of the broken portion being a base Ba was better than the evaluation result of the broken portion being the front end Bb.
The following describes the vibration test. The vibration test of the first evaluation test installed the samples of the spark plugs 100 to tools for vibration test. Under the following conditions, the samples were vibrated in the direction perpendicular to the central axis CL.
Amplitude: 5 mm, frequency: 50 Hz, vibrating time: 1 min
Such vibration test was conducted on ten samples with the identical configuration for each type from No. A-1 to No. A-27. Such vibration test possibly cracks the insulator 10 at the part near the first position Pa. Based on a count of the cracked samples, the evaluation in the vibration test was conducted. Specifically, the first evaluation A indicates that the count of the cracked samples is zero. The second evaluation B indicates that the count of cracked samples is one or more to five or less. A third evaluation C indicates that the count of cracked samples is six or more to ten or less. The above-described conditions for the vibration test are set severely so that the insulator of the conventional spark plug is possibly cracked by the vibration test to make a difference among the plurality of types of samples in the evaluation result.
As shown in Table 1, the 12 types of samples whose ratio (L2/L1) was 0.70 or more (No. A-2, No. A-7, No. A-8, from No. A-12 to No. A-15, No. A-18, No. A-20, No. A-21, No. A-25, and No. A-26) obtained the first evaluation A in both the bending test and the vibration test. Thus, the use of the ratio of 0.70 or more (L2/L1) can reduce the break of the insulator 10. It can be inferred that the wider stable range Rpi allows reducing the break of the insulator 10. Therefore, it can be inferred that as the ratio (L2/L1), various values smaller than 1.0, which is a theoretical maximum value, can be used. The ratio (L2/L1) of the 12 types of samples that obtained good evaluation is: 0.70, 0.71, 0.72, 0.75, 0.78, 0.79, 0.80, 0.81, 0.83, and 0.86. Among these values, any given value can be used as the lower limit of the preferable range (the range equal to or more than the lower limit and equal to or less than the upper limit) of the ratio (L2/L1). Among these values, any given value equal to or more than the lower limit can be used as the upper limit of the preferable range of the ratio (L2/L1).
Regarding the parameters Ddb, Dda, Ds1, and Ds2, as shown in Table 1, good evaluations were obtained with various values. Each parameter Ddb, Dda, Ds1, and Ds2 of the 12 types of samples where good evaluations were obtained is as follows.
End portion diameter Ddb: 2.9, 3.0, 3.2, 3.4 (mm)
Base diameter Dda: 4.9, 5.2 (mm)
End portion length Ds1: 0, 1, 2, 3 (mm)
Base length Ds2: 0, 1, 2, 3 (mm)
The preferable range (the range equal to or more than the lower limit and equal to or less than the upper limit) of the end portion diameter Ddb is as follows. As the lower limit, among these values of the end portion diameter Ddb, any given value can be used. As the upper limit, among these values of the end portion diameter Ddb, any given value equal to or more than the lower limit can be used. Similarly, regarding the other parameters Dda, Ds1, and Ds2, any given value among the above-described values of the 12 types of samples where good evaluations were obtained can be used as the lower limit. Among the above-described values, any given value equal to or more than the lower limit can be used as the upper limit.
The lower limit of the end portion diameter Ddb is not limited to the above-described values. Various values greater than the outer diameter of the part arranged on the inner peripheral side of the second position Pb of the insulator 10 among the center electrode 20 (in this embodiment, the nose portion 25 of the center electrode 20) can be used. With a typical spark plug, as the above-described outer diameter of the center electrode 20, a value within the range of equal to or more 1 mm and equal to or less than 3 mm is used. Therefore, as the lower limit of the end portion diameter Ddb, a value within the range of 1 mm or more and 3 mm or less can be used.
Between the two types of samples of No. A-21 and No. A-27, the end portion diameter Ddb mutually differs; however, the base diameter Dda, the end portion length Ds1, and the base length Ds2 are common. Comparing the results of the bending test among these samples, the No. A-21 whose end portion diameter Ddb is large has large breaking load compared with the No. A-27 whose end portion diameter Ddb is small, and has the broken portion that is not the front end Bb but the base Ba. This reason can be inferred as follows. That is, the larger end portion diameter Ddb can enhance the strength at a part near the second position Pb of the insulator 10. Therefore, the larger end portion diameter Ddb can reduce that the part near the second position Pb is broken although the part near the first position Pa of the insulator 10 is not broken but endures. The tendency similar to the end portion diameter Ddb, the breaking load, and the broken portion can also be confirmed on other samples (for example, No. A-1 and No. A-3).
Between the two types of samples of No. A-19 and No. A-25, the end portion diameter Ddb mutually differs; however, the base diameter Dda, the end portion length Ds1, and the base length Ds2 are common. Comparing the results of the vibration test among these samples, the No. A-25 whose end portion diameter Ddb is small exhibits good evaluation result of the vibration test compared with the No. A-19 whose end portion diameter Ddb is large. This reason can be inferred as follows. That is, the smaller end portion diameter Ddb reduces a weight of the front end portion (namely, the part near the second position Pb) of the insulator 10. Therefore, in the case where the spark plug 100 vibrates, the force that the part near the first position Pa of the insulator 10 receives becomes small as the end portion diameter Ddb becomes small. Consequently, the smaller end portion diameter Ddb can reduce the break of the insulator 10 due to vibration. The tendency similar to the end portion diameter Ddb and the evaluation result of the vibration test can also be confirmed on other samples (for example, No. A-1 and No. A-5).
Typically, compared with the case of concentrating the stress, the case of dispersing the stress is less likely to cause the break. Furthermore, as shown in Table 1, also in the case where the configuration of the insulator 10 (in particular, the configuration of the nose portion 13) variously changes, the use of the ratio (L2/L1) of 0.70 or more allowed obtaining the good evaluation results. Therefore, even if the internal diameter d1 is not 1.76 mm, the above-described preferable range for the ratio (L2/L1) can be inferred as applicable.
The following Table 2 shows configurations of samples of the spark plugs 100 used for the second evaluation test and the evaluation results. To examine an influence of the insulator nose length L3 to durability of the insulator 10, the second evaluation test conducted the bending test and the vibration test on samples of a plurality of types where the insulator nose lengths L3 (
Similar to Table 1, Table 2 lists the sample Nos., the parameters Ddb, Dda, Ds1, Ds2, and L2/L1, which indicate the configurations of the insulators 10, the results of the bending test, and the results of the vibration test. The second evaluation test evaluates 16 types of the samples from No. B-1 to No. B-16 of mutually different configurations of the insulators 10. The insulator nose length L3 is any of 8, 10, 12, and 16 (mm). The length of the first outer-diameter-contracted portion 15 and the diameter d1 of the through hole 12 are common among the 16 types of samples, and identical to the samples for the first evaluation test.
The 16 types of samples are divided into four groups where the insulator nose length L3 mutually differs. The correspondence relation between the insulator nose length L3, the sample Number, and the criterion for the evaluation of the bending test of each group is as follows.
The evaluation method for the bending test is the identical to the evaluation method for the first evaluation test. For example, in the first group, the first evaluation A indicates that “the breaking load is large compared with the sample No. B-1”, and “the broken portion is the base Ba.” The second evaluation B indicates that at least one of “the breaking load is small compared with the sample No. B-1” and “the broken portion is the front end Bb” is met. Similarly, the evaluations in the bending test are conducted for the other groups using the criterion for each group.
In any groups, the criterion sample omits the front cylinder portion 13fc and the rear cylinder portion 13bc (the end portion length Ds1=zero and the base length Ds2=zero), the end portion diameter Ddb is 3.5 mm, and the base diameter Dda is 4.7 mm. The other three types of samples have common base diameter Dda (5.2 mm), the end portion length Ds1 (2 mm), and the base length Ds2 (2 mm). The end portion diameter Ddb is 3.2, 3.4, and 3.6.
As shown in Table 2, the eight types of samples whose ratio (L2/L1) was 0.70 or more (No. B-3, No. B-4, No. B-6, No. B-7, No. B-10, No. B-11, No. B-14, and No. B-15) obtained the first evaluation A in both the bending test and the vibration test. Thus, in the case where the insulator nose length L3 is changed as well, the use of the ratio (L2/L1) of 0.70 or more allows reducing the break of the insulator 10.
Generalizing Tables 1 and 2, the ratios (L2/L1) of the 20 types of samples that obtained the first evaluation A in both the bending test and the vibration test were 0.70, 0.71, 0.72, 0.74, 0.75, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, and 0.86. Among these values, any given value can be used as the lower limit of the preferable range (the range equal to or more than the lower limit and equal to or less than the upper limit) of the ratio (L2/L1). Among these values, any given value equal to or more than the lower limit can be used as the upper limit of the preferable range of the ratio (L2/L1).
Generalizing Tables 1 and 2, regarding the parameters Ddb, Dda, Ds1, Ds2, and L3, good evaluations were obtained with various values. Each parameter Ddb, Dda, Ds1, Ds2, and L3 of the 20 types of samples where the first evaluation A was obtained in both the bending test and the vibration test is as follows.
The preferable range (the range equal to or more than the lower limit and equal to or less than the upper limit) of the end portion diameter Ddb is as follows. As the lower limit, among these values of the end portion diameter Ddb, any given value can be used. As the upper limit, among these values of the end portion diameter Ddb, any given value equal to or more than the lower limit can be used. Similarly, regarding the other parameters Dda, Ds1, Ds2, and L3, any given value among the above-described values of the 20 types of samples where good evaluations were obtained can be used as the lower limit. Among the above-described values, any given value equal to or more than the lower limit can be used as the upper limit. For example, the insulator nose length L3 is preferably 8 mm or more. The insulator nose length L3 is preferably 16 mm or less. It can be inferred that the internal diameter d1 can also use various values different from 1.76 mm.
The following Table 3 shows configurations of samples of the spark plugs 100 used for the third evaluation test and the evaluation results. To examine an influence of the end portion diameter Ddb to the durability of the insulator 10, the third evaluation test conducted the bending test and the vibration test on six types of samples from No. C-1 to No. C-6 whose end portion diameter Ddb mutually differs.
Similar to Table 1, Table 3 lists the sample Nos., the parameters Ddb, Dda, Ds1, Ds2, and L2/L1, which indicate the configurations of the insulators 10, the results of the bending test, and the results of the vibration test. The end portion diameter Ddb is, in the order from No. C-1 to No. C-6, 3.2, 3.3, 3.4, 3.5, 3.6, and 3.7 (mm). The ratio (L2/L1) is, in the order from No. C-1 to No. C-6, 0.83, 0.81, 0.79, 0.75, 0.70, and 0.64. The base diameter Dda (5.4 mm), the end portion length Ds1 (2.5 mm), and the base length Ds2 (2.5 mm) are common to the six types of samples. The insulator nose length L3, the length of the first outer-diameter-contracted portion 15, and the diameter d1 of the through hole 12 are common among the six types of samples, and identical to the samples for the first evaluation test.
The content and the evaluation method of the bending test are the identical to the first evaluation test. The criterion for the evaluation of the bending test is the sample No. A-5 in the above-described Table 1. To make a difference among the plurality of types of samples in the evaluation result, the vibration test was conducted under conditions severer than the conditions for the first evaluation test. Specifically, the amplitude is 8 mm, which is greater than the amplitude of the first evaluation test (5 mm). The frequency (50 Hz) and the vibrating time (1 min) are identical to those for the first evaluation test.
As shown in Table 3, the evaluation results of the bending test were the first evaluation A on all the samples. The evaluation results of the vibration test were the first evaluation A on the four types of samples from No. C-1 to No. C-4 whose end portion diameter Ddb was 3.5 mm or less. The evaluation results were the second evaluation B on the two types of samples No. C-5 and No. C-6 whose end portion diameter Ddb was greater than 3.5 mm. Thus, in the case where the ratio (L2/L1) is 0.70 or more, the use of the end portion diameter Ddb of 3.5 mm or less further allows reducing the break of the insulator 10 due to vibration. This reason can be inferred as follows. In the vibration of the spark plug 100, the small end portion diameter Ddb receives a small force at the part near the first position Pa of the insulator 10 compared with the large end portion diameter Ddb.
As described above, the vibration test in the third evaluation test was conducted under severer conditions than the conditions for the first evaluation test. Accordingly, the following can be inferred. Conducting the vibration test under the conditions identical to the first evaluation test possibly obtaining the first evaluation A even in the case where the end portion diameter Ddb is greater than 3.5 mm.
The base diameter Dda of the sample used for the third evaluation test was 5.4 mm. The use of the base diameter Dda greater than 5.4 mm can enhance the strength of the nose portion 13 against vibration. Therefore, the end portion diameter Ddb of 3.5 mm or less is applicable to the various spark plugs 100 whose base diameter Dda is 5.4 mm or more. Additionally, the following can be inferred. In the case where the base diameter Dda is greater than 5.4 mm, the use of the end portion diameter Ddb of greater than 3.5 mm can also reduce the break of the insulator 10.
The following Table 4 shows configurations of samples of the spark plugs 100 used for the fourth evaluation test and the evaluation results. To examine an influence of the end portion length Ds1 to the insulator 10, the fourth evaluation test conducted the bending test on four types of samples from No. D-1 to No. D-4 whose end portion length Ds1 mutually differs.
Table 4 lists sample Nos., the parameters Ddb, Dda, Ds1, Ds2, and L2/L1, which indicate the configurations of the insulators 10, and the results of the bending test. The end portion length Ds1 is, in the order from No. D-1 to No. D-4, 3.4, 3.5, 3.6, and 3.7 (mm). The other parameters Ddb (3.2 mm), Dda (4.9 mm), Ds2 (2.5 mm), and L2/L1 (0.79) are common to the four types of samples. The insulator nose length L3, the length of the first outer-diameter-contracted portion 15 and the diameter d1 of the through hole 12 are common among the four types of samples, and identical to the samples for the first evaluation test.
The content and the evaluation method of the bending test are the identical to the first evaluation test. The criterion for the evaluation of the bending test is the sample No. A-5 in the above-described Table 1. In the fourth evaluation test, the breaking load of all the samples was greater than the criterion breaking load (230 N). Therefore, the first evaluation A indicates that “the broken portion is the base Ba.” The second evaluation B indicates that “the broken portion is the front end Bb.”
As shown in Table 4, the shorter the end portion length Ds1 was, the larger the breaking load was. Furthermore, the evaluation results of No. D-1 and No. D-2 whose end portion length Ds1 was 3.5 mm or less was the first evaluation A. The evaluation results of the No. D-3 and No. D-4 whose end portion length Ds1 was more than 3.5 mm was the second evaluation B. Thus, the use of the end portion length Ds1 of 3.5 mm or less can reduce the break of the insulator 10 due to force attempting to bend the insulator 10 compared with the case of using the end portion length Ds1 more than 3.5 mm. This reason can be inferred as follows. That is, the outer diameter of the front cylinder portion 13fc is smaller than the outer diameters of the other parts 13t and 13bc of the nose portion 13. Accordingly, the strength of the front cylinder portion 13fc is lower than the strength of the other parts 13t and 13bc. Therefore, it can be inferred that the shorter the length of the front cylinder portion 13fc, namely, the shorter the end portion length Ds1 is, the strength of the nose portion 13 can be enhanced.
The end portion diameter Ddb of the sample used for the fourth evaluation test is 3.2 mm. The use of the end portion diameter Ddb greater than 3.2 mm can enhance the strength of the front cylinder portion 13fc of the nose portion 13. Therefore, the end portion length Ds1 of 3.5 mm or less is applicable to the various spark plugs 100 whose end portion diameter Ddb is 3.2 mm or more. Additionally, the following can be inferred. In the case where the end portion diameter Ddb is greater than 3.2 mm, the use of the end portion length Ds1 greater than 3.5 mm can also reduce the break of the insulator 10.
The following Table 5 shows configurations of samples of the spark plugs 100 used for the fifth evaluation test and the evaluation results. The fifth evaluation test conducted a test for evaluating durability of the insulator 10 against knocking on the internal combustion engine (hereinafter referred to as a “knocking test”).
Table 5 lists sample Nos., the end portion diameters Ddb, the external lengths De, the projection areas Sp, and the evaluation results of the knocking test.
As shown in the drawing, a part 13p on the front end direction Df side of the nose portion 13 of the insulator 10 is arranged on the front end direction Df side with respect to the end (hereinafter referred to as a “front end 50e1”) on the front end direction Df side of the metal shell 50. This part 13p is a part (hereinafter referred to as the “external part 13p”) arranged outside of the metal shell 50. In the drawing, the external part 13p is hatched. The external length De is a length parallel to the central axis CL of the external part 13p. In other words, the external length De is a distance between the front end 50e1 of the metal shell 50 and the front end 10e1 of the insulator 10, and is parallel to the central axis CL.
The projection area Sp is a projection area in the case where the external part 13p is projected on a plane (hereinafter referred to as a “projection plane”) parallel to the central axis CL along a direction perpendicular to the projection plane (namely, the direction perpendicular to the central axis CL). The area of the hatched region in
As shown in Table 5, the knocking test was conducted on 15 types of samples where at least one of the external length De and the projection area Sp mutually differs. The knocking test forcibly generated a knocking on the internal combustion engine to which the sample of the spark plug 100 was installed. Then, whether the insulator 10 was cracked or not was confirmed. Such test was conducted on ten samples with the identical configuration for each type from No. E-1 to No. E-15. The first evaluation A indicates that all the ten samples were not cracked while the second evaluation B indicates that at least one piece of sample was cracked. If the knocking occurs, by a shock wave generated inside the combustion chamber of the internal combustion engine, a force in the direction intersecting with the central axis CL (for example, the direction perpendicular to the central axis CL), like the force W in
As shown in Table 5, the nine types of samples from No. E-1 to No. E-9 are formed using the insulator 10 with the end portion diameter Ddb of 3.3 mm. The configuration of the insulator 10 is the identical among these nine types of samples. The external length De, furthermore, the projection area Sp is adjusted by changing a position in the direction parallel to the central axis CL of the inner-diameter-contracted portion 56 of the metal shell 50 (
The six types of samples from No. E-10 to No. E-15 are formed using the insulator 10 with the end portion diameter Ddb of 3.5 mm. The configuration of the insulator 10 is the identical among these six types of samples. The method for adjusting the external length De, furthermore, the projection area Sp is the identical to the method for the samples from No. E-1 to No. E-9. The external length De increases in the order from No. E-10 to No. E-15 and in increments of 0.5 mm from 2.0 mm to 4.5 mm.
The 15 types of samples each omit the front cylinder portion 13fc and the rear cylinder portion 13bc (namely, the end portion length Ds1=zero and the base length Ds2=zero). In each of 15 types of samples, the insulator nose length L3 is 14 mm, the base diameter Dda is 5.2 mm, and the ratio L2/L1 is 0.7 or more.
As shown in Table 5, regardless of the end portion diameter Ddb, the six types of samples whose projection area Sp is 8.7 mm2 or less (No. E-1, No. E-2, No. E-3, No. E-4, No. E-10, and No. E-11) obtained the first evaluation A in the evaluation result of the knocking test. Thus, the use of the projection area Sp of 8.7 mm2 or less can reduce the crack of the insulator 10. This reason is inferred as follows. Compared with the large projection area Sp, the small projection area Sp has the small external part 13p of the nose portion 13, that is, a small part to which the force in the direction perpendicular to the central axis CL is possibly applied.
As shown in Table 5, the projection areas Sp of the six types of samples (from No. E-1 to No. E-4, No. E-10, and No. E-11) that obtained the first evaluation A were 3.2, 4.9, 6.5, 6.9, 8.2, and 8.7 (mm2). Among these values, any given value can be used as the lower limit of the preferable range (the range equal to or more than the lower limit and equal to or less than the upper limit) of the projection areas Sp. Among these values, any given value equal to or more than the lower limit can be used as the upper limit of the preferable range of the projection areas Sp.
As the lower limit of the projection area Sp, 0 mm2 can be used. The projection area Sp being 0 mm2 means that when viewing the spark plug 100 facing the direction perpendicular to the central axis CL, the entire nose portion 13 is hidden in the through hole 59 of the metal shell 50. In case of knocking, the use of such configuration can reduce the application of the force in the direction perpendicular to the central axis CL to the nose portion 13. This allows reducing the crack of the nose portion 13.
The base diameter Dda of the sample used for the fifth evaluation test is 5.2 mm. The use of the base diameter Dda greater than 5.2 mm can enhance the durability of the nose portion 13. Therefore, the projection area Sp of 8.7 mm2 or less is applicable to the various spark plugs 100 whose base diameter Dda is 5.2 mm or more. Additionally, the following can be inferred. In the case where the base diameter Dda is greater than 5.2 mm, the use of the projection area Sp greater than 8.7 mm2 can also reduce the breaking of the insulator 10.
The following describes the sixth evaluation test using samples of the spark plugs 100. The sixth evaluation test evaluated the “breaking resistance” and the “anti-fouling characteristics or performance” of the insulator 10. The following Table 6 shows the configurations of the samples and the evaluation results.
Table 6 lists sample Nos., the parameters Dda, Ddc, d1, Z1/Z2, Ds1, and De, which indicate the configurations of the insulator 10, the evaluation results of the breaking resistance, and the evaluation results of the anti-fouling characteristics or performance. The sixth evaluation test evaluates 28 types of the samples from No. F-1 to No. F-28 of mutually different configurations of the insulators 10. The base diameter Dda was common to the all samples, 5.2 mm. The second end portion diameter Ddc was set to any of 3.3, 3.5, 3.7, and 4 (mm). The internal diameter d1 was set to any of 1.76, 1.96, and 2.16 (mm). The ratio Z1/Z2 was any of 2.33, 3.05, 3.56, and 4.20. The end portion length Ds1 was set to any of 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, and 7.5 (mm). The exposed length De was set to any of 0.5 and 1.5 (mm). The 28 types of samples evaluated in the sixth evaluation test had the second insulator nose length L4 of 14 mm and the base length Ds2 of 2.5 mm. Regarding the ratio L2/L1, the samples having the ratio L2/L1 of 0.7 or more were six types, No. F-4, No. F-7, No. F-8, No. F-10, No. F-11, and No. F-14. The adjustment of the exposed length De with the second insulator nose length L4 fixed was performed by adjusting a position in the direction parallel to the axial line CL of the inner-diameter-contracted portion 56 of the metal shell 50.
The breaking resistance was evaluated by conducting the above-described vibration test in the first evaluation test under severer conditions. Specifically, the amplitude was increased from 5 mm to 10 mm. Other conditions on the vibration test are the identical to the conditions on the vibration test in the first evaluation test. Such vibration test was conducted on five samples for each type from No. F-1 to No. F-28. The vibration test under such severe conditions broke off the insulator 10. The breaking position was any of a part near the first position Pa (
The anti-fouling characteristics or performance was evaluated by a test run, which will be described later. First, on a chassis dynamometer in a low-temperature test room set to Celsius −15 degrees, a vehicle with four-cylinder engine at a displacement of 0.66 L was prepared. To this engine of the vehicle, the sample of the spark plug 100 was assembled. Then, a driving cycle was repeated. The driving cycle performs a first running pattern, which will be described later, natural cooling by engine stop, and a second running pattern, which will be described later, in this order as one cycle. Here, each time that the one-time driving cycle was ended, a resistance meter of the spark plug 100 was measured. An insulation resistance is an electrical resistance between the terminal metal fitting 40 and the metal shell 50. Then, the test was ended by a condition of declining the resistance meter to 100 MΩ or less. If the count of cycles at the end of the test was five cycles or less, the evaluation result was determined as the second evaluation B. When the count of cycles at the end of the test exceeded five cycles, the evaluation result was determined as the first evaluation A.
The above-described first running pattern is as follows. After racing the engine three times, the gear is set to the third speed and the vehicle runs at a speed of 35 km/h for 40 seconds. After a 90-second idling, the vehicle runs again with the gear at the third speed at 35 km/h for 40 seconds.
The above-described second running pattern races three times and then repeats the running and the engine stop. This running was repeated three times. The one-time running was performed with the gear at the first speed and at 15 km/h for 20 seconds. The engine stop was performed for 30 seconds. After the second running pattern, the engine was stopped. Then, the first running pattern in the next cycle was performed.
Repeating the above-described driving cycle drops the resistance meter. This reason is as follows. Due to fouling (for example, accumulation of carbon to the surface of the insulator 10) in the insulator 10 in association with burning inside the combustion chamber, an electrical resistance using a route passing through from the center electrode 20 to the surface of the insulator 10 and reaching the metal shell 50 drops. Such fouling induces a lateral spark. The lateral spark is a discharge passing through from the center electrode 20 to the surface of the insulator 10 and reaching the metal shell 50. Such lateral spark is likely to occur in the part near the front end 50e1 of the metal shell 50. Improving the anti-fouling characteristics or performance can reduce a decline of the electrical resistance at the surface of the insulator 10. Therefore, improving the anti-fouling characteristics or performance can reduce the lateral spark.
As shown in Table 6, all the 28 types of samples obtained the first evaluation A in at least one of the breaking resistance and the anti-fouling characteristics or performance. No sample obtained the second evaluation B on both the breaking resistance and the anti-fouling characteristics or performance.
As shown in the drawing, in the case where the end portion length Ds1 is constant, increasing the ratio Z1/Z2 improved the anti-fouling characteristics or performance (refer to the first type measurement point DP1 and the second type measurement point DP2). This reason is inferred as follows. As shown in the above-described calculating formula (1C), the section modulus becomes large as the outer diameter increases. Therefore, if the ratio Z1/Z2 is large, the ratio of the second section modulus Z2 to the first section modulus Z1 is small. That is, the ratio of the outer diameter Ddc at the front base P12 to an outer diameter Dda at the first position Pa is small. If the ratio of the outer diameter Ddc at the front base P12 is small, a volume of the front end portion of the insulator 10 is small. Accordingly, in association with burning inside the combustion chamber, a temperature at the front end portion of the insulator 10 is likely to increase. Therefore, even if a carbon accumulates at the surface of the front end portion of the insulator 10, the carbon can be easily burnt through. As a result, it is inferred that the larger ratio Z1/Z2 improves the anti-fouling characteristics or performance.
As shown in Table 6 and
As shown by, for example, No. F-2, a maximum value R1 among the ratio Z1/Z2 of the samples having the anti-fouling characteristics or performance with the second evaluation B (
In the case where the ratio Z1/Z2 is constant, lengthening the end portion length Ds1 improved the anti-fouling characteristics or performance (refer to the first type measurement point DP1 and the second type measurement point DP2). This reason is inferred as follows. In the case where the end portion length Ds1 is long, since the front cylinder portion 13fc is long, the volume of the front end portion of the insulator 10 is small. Accordingly, in association with burning inside the combustion chamber, a temperature at the front end portion of the insulator 10 is likely to increase. Therefore, even if a carbon accumulates at the surface of the front end portion of the insulator 10, the carbon can be easily burnt through. It is inferred that this results in improving the anti-fouling characteristics or performance.
In the case where the ratio Z1/Z2 is the first ratio R1 (3.05), as shown by No. F-2, the anti-fouling characteristics or performance of the end portion length Ds1 at 1.5 mm was the second evaluation B. As shown by No. F-6, the anti-fouling characteristics or performance of the end portion length Ds1 at 2.5 mm was the first evaluation A. In the case where the ratio Z1/Z2 is the second ratio R2 (3.56), as shown by No. F-3 and No. F-7, both the end portion length Ds1 at 1.5 mm and the end portion length Ds1 at 2.5 mm achieved the first evaluation A in the anti-fouling characteristics or performance. Therefore, assume the case where the ratio Z1/Z2 is greater than a value (for example, 3.5) between the first ratio R1 (3.05) and the second ratio R2 (3.56). It is inferred that the use of a value greater than a value (for example, 2 mm) between 1.5 mm and 2.5 mm as the end portion length Ds1 can achieve the anti-fouling characteristics or performance with the first evaluation A.
As shown in Table 6 and
In the case where the end portion length Ds1 is constant, decreasing the ratio Z1/Z2 improved the breaking resistance (refer to the first type measurement point DP1 and the third type measurement point DP3 in
In the case where the ratio Z1/Z2 is constant, shortening the end portion length Ds1 improved the breaking resistance (refer to the first type measurement point DP1 and the third type measurement point DP3). This reason is inferred as follows. The short end portion length Ds1 has a small part (the external part 13p) on the front end direction Df side with respect to the front base P12 compared with the long end portion length Ds1. Accordingly, the stress at the front base P12 is small during the vibration. Thus, to reduce the breakage near the front base P12, shortening the end portion length Ds1 is preferable.
The outer diameter of the insulator 10 gradually increases from the front base P12 toward a rear end direction Dfr2. That is, the shortest distance between the position on the surface of the insulator 10 and the metal shell 50 gradually shortens from the front base P12 toward the rear end direction Dfr2. Therefore, in the case where the front base P12 is close to the front end 50e1 of the metal shell 50, since a distance between the front end 50e1 of the metal shell 50 and the insulator 10 (in particular, a part on the rear end direction Dfr2 side from the front base P12) becomes short, the lateral spark is likely to occur. Here, in the case where the second insulator nose length L4 is constant, lengthening the end portion length Ds1 can keep the front base P12 away of the front end 50e1 of the metal shell 50 to the rear end direction Dfr2 side. It is inferred that this consequently reduces the lateral spark.
In the case where the ratio Z1/Z2 is constant, the maximum value of the end portion length Ds1 at which the breaking resistance with the first evaluation A is achievable becomes large as the ratio Z1/Z2 decreases (refer to the first type measurement point DP1 and the third type measurement point DP3 in
Second insulator nose length L4: fixed at 14 mm.
Base diameter Dda: any of 4.6, 4.8, 5.0, and 5.2 (mm)
Second end portion diameter Ddc: any of 3.3, 3.5, 3.7, and 4.0 (mm)
Internal diameter d1: any of 1.76, 1.96, and 2.16 (mm)
The plurality of first type calculation points CP1 in the graph of
Here, the following describes the relation between the end portion length Ds1 and the calculation points CP1, CP2, and CP3 in the case where the ratio Z1/Z2 is constant. When the end portion length Ds1 is identical to the calculation points CP1, CP2, and CP3 with the identical exposed length De, as described above, the stress at the front base P12 is identical to the stress at the first position Pa.
Assume the case where the end portion length Ds1 was set smaller than the calculation points CP1, CP2, and CP3 of the identical exposed length De (the other parameters are not changed). Then, the distance between the front base P12 and the load position Pc becomes short, decreasing the stress at the front base P12. On the other hand, the distance between the first position Pa and the load position Pc does not change; therefore, the stress at the first position Pa does not change. Due to the above-described circumstances, the stress at the front base P12 becomes smaller than the stress at the first position Pa. Therefore, it is inferred that a possibility of a breakage near the first position Pa is greater than a possibility of a breakage near the front base P12. Here, the graph of
Inversely, assume that the end portion length Ds1 is set larger than the calculation points CP1, CP2, and CP3 with the identical exposed length De (the other parameters are not changed). Then, since the distance between the front base P12 and the load position Pc is long, the stress at the front base P12 increases. On the other hand, since the distance between the first position Pa and the load position Pc does not change, the stress at the first position Pa does not change. As described above, the stress at the front base P12 is larger than the stress at the first position Pa. Accordingly, it is inferred that the possibility of breakage near the front base P12 is greater than the possibility of breakage near the first position Pa. Here, in the graph of
As described above, the end portion length Ds1 calculated under the condition that the stress at the front base P12 is the identical to the stress at the first position Pa can be used as an upper limit value of the end portion length Ds1 to achieve good breaking resistance. Here, approximating the plurality of calculation points CP1, CP2, and CP3 by the function of the ratio Z1/Z2 derives an approximation formula calculating an upper limit value Ds1L of the end portion length Ds1 from the ratio Z1/Z2. As shown in the following, the upper limit value Ds1L will be expressed with the power of the ratio Z1/Z2.
Ds1L=Ap×(Z1/Z2)Bp
Two parameters Ap and Bp in the approximation formula will be expressed with the linear function using the second insulator nose length L4 and the exposed length De as described below.
Ap=a1+a2×L4+a3×De
Bp=b1+b2×L4+b3×De
These six parameters a1, a2, a3, b1, b2, and b3 in the two linear functions are determined such that the upper limit value Ds1L calculated by the approximation formula approximates the plurality of calculation points. Here, as the plurality of calculation points, in addition to the plurality of calculation points CP1, CP2, and CP3 shown in
Ap=0.07+0.986×L4−0.268×De
Bp=−0.832−0.014×L4+0.099×De
Each approximated curve LM1, LM2, and LM3 shown in the graph of
The above-described approximation formula for calculating the upper limit value Ds1L is determined based on the logic “In the case where the stress at the front base P12 is smaller than the stress at the first position Pa, since the breakage near the front base P12 can be reduced, the breaking resistance can be improved.” This logic is thought to be met regardless of the configurations of the insulator 10 (for example, the second insulator nose length L4, the base diameter Dda, the first end portion diameter Ddb, the second end portion diameter Ddc, the internal diameter d1, the exposed length De, the first section modulus Z1, the second section modulus Z2, the ratio Z1/Z2, the first length L1, the ratio L2/L1, and the projection area Sp). Therefore, it is inferred that the above-described approximation formula for calculating the upper limit value Ds1L is not limited to the samples shown in Table 6. The approximation formula is applicable to the insulator 10 (furthermore, the spark plug 100) with other various configurations. For example, it is inferred that in the case where the second insulator nose length L4 is 12 mm or 8 mm, furthermore, in the case where the second insulator nose length L4 is in the practical range (for example, within the range of 5 mm or more to 20 mm or less), insofar as the end portion length Ds1 is less than the above-described upper limit value Ds1L, the breaking resistance can be improved. Similarly, it is inferred that also in the case where the other parameters (for example, any of the parameters L4, Dda, Ddc, d1, De, Z1, Z2, Z1/Z2, L1, and L2/L1) is outside the range of the values evaluated in the evaluation test of Table 6, insofar as the end portion length Ds1 is less than the above-described upper limit value Ds1L, the breaking resistance can be improved.
Even if the end portion length Ds1 is equal to or more than the upper limit value Ds1L, as long as the strength of the insulator 10 is stronger than the actual stress possibly applied to the insulator 10 in assumed usage environment of the spark plug 100, the breakage of the insulator 10 can be reduced. Therefore, the end portion length Ds1 may be equal to or more than the upper limit value Ds1L.
In any cases, the use of the ratio L2/L1 (for example, the ratio L2/L1 of 0.7 or more) within the preferable range described in Tables 1 and 2 can reduce the break of the insulator 10. The use of the first end portion diameter Ddb (for example, the first end portion diameter Ddb of 3.5 mm or less) within the preferable range described in Table 3 can reduce the break of the insulator 10 due to vibration. Here, the second end portion diameter Ddc is almost identical to the first end portion diameter Ddb. Accordingly, the use of the second end portion diameter Ddc of 3.5 mm or less allows reducing the break of the insulator 10 due to vibration. The use of the end portion length Ds1 (for example, the end portion length Ds1 of 3.5 mm or less) within the preferable range described in Table 4 can reduce the break of the insulator 10. The use of the projection area Sp (for example, the projection area Sp within 8.7 mm2 or less) within the preferable range described in Table 5 allows reducing the crack of the insulator 10. However, at least one of these parameters L2/L1, Ddb, Ddc, Ds1, and Sp may be outside of the corresponding preferable range.
(1) The configuration of the insulator 10 can employ various configurations different from the above-described configurations. Especially, the configuration on the rear end direction Dfr side from the first position Pa in contact with the front-end-side packing 8 can use any given configuration. In any cases, the use of the above-described configurations as the configuration on the front end direction Df side from the first position Pa can reduce the break of the insulator 10.
(2) The configuration of the spark plug 100 can employ various configurations different from the configuration described in
The resistor 70 may be omitted. The head 23 of the center electrode 20 may be omitted. A gap may be formed between a side surface (that is, the outer peripheral surface) of the center electrode and the ground electrode. A noble metal tip may be disposed at a part where the gap is formed, in the center electrode. The noble metal tip may be disposed at the part where the gap is formed, in the ground electrode. As a material of the noble metal tip, an alloy containing a noble metal, such as iridium and platinum, can be used.
The present invention has been described above based on the embodiments and the modifications. The above-described embodiments of the invention are for ease of understanding of the present invention and do not limit the present invention. The present invention may be modified or improved without departing from the gist and the claims of the present invention, and includes the equivalents.
This disclosure is preferably applicable to a spark plug used for an internal combustion engine or a similar engine.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-213840 | Oct 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/077248 | 10/10/2014 | WO | 00 |
