Spark plugs for internal combustion engines

Abstract

To provide a spark plug for internal combustion engines capable of suppressing misfire when starting an internal combustion engine.SOLUTION: A spark plug for internal combustion engines 1 includes: a center electrode 4 and a ground electrode 6 that form a discharge gap G therebetween; and plug cover 5 formed at the tip so as to cover a sub-combustion chamber 50 where the discharge gap G is arranged. In the plug cover 5, a nozzle hole 51 that communicates the sub-combustion chamber 50 with the outside is formed. Defining that the inner diameter of the injection hole 51 as D, the length along the injection hole axis of the injection hole 51 as L, and the contact angle between the inner wall surface of the injection hole 51 and water as θ, at least one injection hole 51 satisfies the following formula (1): (L / 2)×tan(θ / 2)<D (1)SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a spark plug for an internal combustion engine. [Background technology]

[0002] A spark plug equipped with a pre-combustion chamber is disclosed in, for example, Patent Document 1. In such a spark plug, an air-fuel mixture is introduced into the pre-combustion chamber through a nozzle hole. The air-fuel mixture is ignited in the pre-combustion chamber, and a flame jet is injected from the nozzle hole into the main combustion chamber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-184435 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in a spark plug having an auxiliary combustion chamber, there is a problem that if the nozzle hole is blocked by ice, normal ignition becomes difficult. That is, water is produced by the combustion reaction of the internal combustion engine, and depending on the operating conditions, it is conceivable that water may remain in the combustion chamber. This water may then adhere to the nozzle hole of the spark plug. In this situation, for example, if the internal combustion engine is left in an extremely low temperature state and the water that has adhered to the nozzle hole freezes, the nozzle hole may be blocked by the ice. This will prevent the air-fuel mixture from being introduced into the auxiliary combustion chamber through the nozzle hole when the internal combustion engine is started, which may result in misfire.

[0005] The present invention has been made in view of the above problems, and has an object to provide a spark plug for an internal combustion engine that is capable of suppressing misfires when starting the internal combustion engine. [Means for solving the problem]

[0006] One aspect of the present invention is a coil comprising a center electrode (4) and a ground electrode (6) forming a discharge gap (G) between them; a plug cover (5) provided at a tip portion thereof so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, The plug cover is formed with a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, At least one of the nozzle holes is A hydrophilic film (11) is provided on the inner wall surface to improve hydrophilicity. The spark plug for an internal combustion engine satisfies the following formula (1), where D is the inner diameter of the nozzle hole, L is the length of the nozzle hole along its axis, and θ is the contact angle between the inner wall surface of the nozzle hole and water. (L / 2) × tan(θ / 2) <D (1) Effect of the Invention

[0007] In the spark plug for an internal combustion engine, at least one of the nozzle holes satisfies the formula (1). This makes it possible to prevent the nozzle hole from being blocked even if water adheres to the inner wall surface of the nozzle hole and freezes. This makes it possible to prevent a situation in which the introduction of the air-fuel mixture into the auxiliary combustion chamber through the nozzle hole is hindered when the internal combustion engine is started. As a result, misfires can be suppressed when the internal combustion engine is started.

[0008] As described above, according to the above aspect, it is possible to provide a spark plug for an internal combustion engine that is capable of suppressing misfires when starting the internal combustion engine. In addition, the symbols in parentheses described in the claims and the means for solving the problems indicate a correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief description of the drawings]

[0009] [Figure 1] 2. FIG. 4 is a cross-sectional view taken along the line II in FIG. 2, showing a portion of the spark plug in the vicinity of its tip end in accordance with the first embodiment. [Diagram 2]FIG. 2 is a view taken along the arrow II in FIG. [Diagram 3] FIG. 4 is an enlarged cross-sectional view of a nozzle hole in the first reference embodiment. [Figure 4] FIG. 11 is an enlarged cross-sectional view of a nozzle hole with water droplets attached in the first embodiment; [Diagram 5] A cross-sectional view taken along line VV in Figure 4. [Figure 6] FIG. 13 is an enlarged cross-sectional view of a nozzle hole with water droplets attached in a comparative embodiment. [Figure 7] FIG. 13 is an enlarged cross-sectional view of a frozen nozzle hole in a comparative example. [Figure 8] FIG. 11 is an enlarged cross-sectional view of a nozzle hole in the second reference embodiment. [Figure 9] FIG. 11 is an enlarged cross-sectional view of an injection hole in a third embodiment. [Figure 10] FIG. 11 is an enlarged cross-sectional view of a nozzle hole with water droplets attached thereto in embodiment 3. [Figure 11] FIG. 11 is a cross-sectional view taken along the central axis of a spark plug in the vicinity of a tip portion of the spark plug according to a fourth embodiment. [Figure 12] FIG. 13 is an enlarged cross-sectional view of a nozzle hole with water droplets attached in the fourth embodiment. [Figure 13] FIG. 13 is a cross-sectional view taken along the central axis of a plasma ignition plug in the vicinity of its tip portion in a fifth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] ( Reference form 1 ) An embodiment of a spark plug for an internal combustion engine will be described with reference to Figs. 1 and 2, the spark plug 1 of this embodiment has a center electrode 4, a ground electrode 6, and a plug cover 5. The center electrode 4 and the ground electrode 6 form a discharge gap G between them. The plug cover 5 is provided at the tip portion so as to cover the auxiliary combustion chamber 50 in which the discharge gap G is located.

[0011] The plug cover 5 is formed with a nozzle hole 51 that connects the auxiliary combustion chamber 50 to the outside. At least one nozzle hole 51 satisfies the following formula (1). (L / 2) × tan(θ / 2) <D (1) 3 and 4, the inner diameter of the nozzle hole 51 is D, the length of the nozzle hole 51 along the nozzle hole axis is L, and the contact angle between the inner wall surface of the nozzle hole 51 and water is θ.

[0012] As shown in Figures 1 and 2, the spark plug 1 has a cylindrical insulator 3, a center electrode 4, a cylindrical housing 2, a ground electrode 6, and a plug cover 5. The center electrode 4 is held on the inner periphery of the insulator 3 and protrudes from the insulator 3 toward the tip side. The housing 2 holds the insulator 3 on its inner periphery. The ground electrode 6 forms a discharge gap G between itself and the center electrode 4. The plug cover 5 is provided at the tip of the housing 2 so as to cover the auxiliary combustion chamber 50.

[0013] The spark plug 1 of this embodiment can be used as an ignition means in an internal combustion engine of an automobile, a cogeneration system, or the like. One end of the spark plug 1 in the plug axial direction Z is disposed in a main combustion chamber of the internal combustion engine. In the plug axial direction Z, the side exposed to the main combustion chamber is referred to as the tip side, and the opposite side is referred to as the base side. In addition, the direction along the circumference centered on the central axis of the plug is referred to as the plug circumferential direction.

[0014] In this embodiment, four injection holes 51 are formed. As shown in Fig. 2, the four injection holes 51 are arranged at equal intervals in the circumferential direction of the plug. In addition, as shown in Fig. 1, the injection hole axis of the injection hole 51 is inclined so as to head toward the base end side as it approaches the auxiliary combustion chamber 50.

[0015] The plug cover 5 has a tip wall portion 52 disposed on the tip side of the auxiliary combustion chamber 50, and a side wall portion 53 disposed on the outer periphery of the auxiliary combustion chamber 50. The tip wall portion 52 and the side wall portion 53 are connected by a curved corner portion. In this embodiment, an injection hole 51 is formed in this corner portion.

[0016] The plug cover 5 is fixed by joining a base end of a side wall portion 53 to a front end of the housing 2 by welding or the like. In addition, the ground electrode 6 is also joined to the front end of the housing 2 by welding or the like.

[0017] In this embodiment, the plug cover 5 is made of a nickel alloy. The injection hole 51 is formed in the plug cover 5 by drilling, punching, electric discharge machining, or the like. In this embodiment, the injection hole 51 has a substantially cylindrical shape.

[0018] As described above, at least one nozzle hole 51 satisfies formula (1). That is, at least one of the four nozzle holes 51 has a dimensional relationship that satisfies formula (1). In this embodiment, in particular, all of the four nozzle holes 51 satisfy formula (1).

[0019] Each nozzle hole 51 satisfies D / L≦1.5. If D / L is too large, it becomes difficult to make the flame jet ejected from the nozzle hole 51 toward the main combustion chamber sufficiently strong. Therefore, it is preferable that all nozzle holes 51 satisfy D / L≦1.5. Furthermore, when the average value of D of the multiple nozzle holes 51 is Dave and the average value of L is Lave, it is preferable that Dave / Lave≦1. In this embodiment, D and L of the four nozzle holes 51 are equal to each other and satisfy D / L≦1.

[0020] It should be noted that the length L is the length along the nozzle hole axis of the nozzle hole 51, but L may vary depending on the measurement position within the same nozzle hole 51. In such a case, the length of the inner wall surface at the position of the inner wall surface of the nozzle hole 51 that has the longest length in the direction along the nozzle hole axis is taken as L.

[0021] Next, the effects of this embodiment will be described. In the above spark plug 1 for an internal combustion engine, at least one nozzle hole 41 satisfies the above formula (1). This makes it possible to prevent the nozzle hole 51 from being blocked even if water adheres to the inner wall surface of the nozzle hole 51 and freezes. This makes it possible to prevent a situation in which the introduction of the air-fuel mixture into the auxiliary combustion chamber 50 through the nozzle hole 51 is hindered when the internal combustion engine is started. As a result, misfires when the internal combustion engine is started can be suppressed.

[0022] As described above, water is produced by the combustion reaction that accompanies the operation of the internal combustion engine. This water may remain in the combustion chamber depending on the operating state. In this state, if the internal combustion engine is stopped and left in an extremely low temperature environment (for example, an environment below freezing), the water will freeze. It is also possible that the water droplets will freeze when they adhere to the nozzle hole. If the water droplets freeze when they adhere to the nozzle hole so as to block it, there is a risk that the air-fuel mixture will not be able to be introduced into the auxiliary combustion chamber from the nozzle hole when the internal combustion engine is started. In particular, when all the nozzle holes are blocked by freezing, the air-fuel mixture will not enter the auxiliary combustion chamber, which may cause misfire.

[0023] A situation in which water droplets adhering to the inner wall surface of the nozzle hole block the nozzle hole 51 is considered to be, for example, a situation in which the apex of the adhering water droplet W reaches the inner wall surface on the opposite side of the nozzle hole 51, as shown in Fig. 6. This situation is considered to be a situation in which the relationship between the contact angle θ between the inner wall surface of the nozzle hole 51 and the water W, the length L of the nozzle hole 51, and the inner diameter D of the nozzle hole 51 satisfies the following formula (3). (L / 2) × tan(θ / 2) ≧ D (3)

[0024] That is, when the apex of the water droplet W adhering to the inner wall surface of the nozzle hole 51 comes into contact with the opposite inner wall surface of the nozzle hole 51 as shown in Fig. 6, the water W remains inside the nozzle hole 51 due to surface tension as shown in Fig. 7. Then, this water W blocks the entire nozzle hole 51. If the water W is left in this state in an extremely low temperature environment, it will freeze and become ice, blocking the nozzle hole 51.

[0025] In the spark plug 1 of this embodiment, in order to avoid such a situation, at least one nozzle hole 51 is formed to satisfy formula (1). As a result, as shown in Figs. 4 and 5, the water droplets W adhering to the inner wall surface of the nozzle hole 51 do not come into contact with the inner wall surface on the opposite side of the nozzle hole 51. Note that the water droplets W assumed here are, for example, about 0.15 nL or less, and the effect of gravity can be substantially ignored. Therefore, even if the water W freezes, it is possible to avoid blocking the entire nozzle hole 51.

[0026] In other words, when the water droplets W adhere to the entire inner wall surface of the nozzle hole 51 in the nozzle hole axial direction, the height h of the water droplets W is (L / 2) × tan(θ / 2). If this height h is smaller than the inner diameter D of the nozzle hole 51, the water droplets W will not come into contact with the inner wall surface on the opposite side of the nozzle hole 51. Equation (1) expresses the condition that "the height h is smaller than the inner diameter D of the nozzle hole 51." Therefore, in a nozzle hole 51 that satisfies equation (1), even if the water adhering to the nozzle hole 51 freezes, the entire hole is prevented from being blocked.

[0027] Therefore, in the spark plug 1 of this embodiment, at least one nozzle hole 51 can pass the air-fuel mixture and misfire can be suppressed. Even if moisture adheres to the nozzle hole 51 and freezes, the nozzle hole 51 can be prevented from being blocked. Therefore, the air-fuel mixture can pass through the nozzle hole 51 and a flame jet can be injected. The ice in the nozzle hole 51 melts and evaporates due to the heat of the flame jet. Therefore, it is possible to immediately return to a normal state.

[0028] In particular, in this embodiment, since all of the nozzle holes 51 satisfy the formula (1), it is possible to prevent any of the nozzle holes 51 from being blocked by freezing, and therefore it is possible to more reliably reduce the risk of misfire during starting.

[0029] As described above, according to the present embodiment, it is possible to provide a spark plug for an internal combustion engine that is capable of suppressing misfires when starting the internal combustion engine.

[0030] ( Reference form 2 ) As shown in FIG. 6, in the spark plug 1 of this embodiment, at least one injection hole 51 satisfies the following formula (2). L × tan(θ / 2) <D (2)

[0031] The condition for satisfying the above formula (2) is stricter than the condition for satisfying the formula (1). In order to satisfy the formula (2), for example, Reference form 1 Possible measures include increasing the inner diameter D of the injection hole 51, shortening the length L of the injection hole 51, and decreasing the contact angle θ, as compared to the spark plug 1 of the previous embodiment. By combining these measures, it is also possible to configure the spark plug 1 to satisfy the above formula (2). Others: Reference form 1 It is the same as: Reference form 2 Among the symbols used hereinafter, the same symbols as those used in the above-mentioned embodiments represent the same components, etc. as those in the above-mentioned embodiments, unless otherwise specified.

[0032] In this embodiment, clogging of the nozzle hole 51 due to freezing can be more reliably prevented. For example, as shown in FIG. 8, even if water droplets W adhere to both of the opposing inner wall surfaces of the same nozzle hole 51, clogging of the nozzle hole 51 can be prevented. In other words, satisfying formula (2) means making the inner diameter D of the nozzle hole 51 at least twice the maximum height h of the heights of the adhering water droplets W. Therefore, even if water droplets W adhere to both of the opposing inner wall surfaces of the same nozzle hole 51 and freeze, clogging of the nozzle hole 51 can be prevented. others, Reference form 1 It has the same effect as above.

[0033] (Embodiment 3) In the spark plug 1 of this embodiment, as shown in Figs. 9 and 10, at least one injection hole 51 is provided with a hydrophilic film 11 on the inner wall surface. The hydrophilic film 11 is a film that improves hydrophilicity. In other words, the hydrophilicity of the surface after the hydrophilic film 11 is formed is higher than that of the surface without the hydrophilic film 11. The high hydrophilicity is a state in which the contact angle θ with water is small.

[0034] The contact angle θ of the hydrophilic film 11 with water is equal to or less than 30°. More preferably, the contact angle θ of the hydrophilic film 11 with water is equal to or less than 10°. In other words, it is more preferable that the hydrophilic film 11 has superhydrophilicity.

[0035] The hydrophilic film 11 is formed on the entire inner wall surface of at least one nozzle hole 51. In this embodiment, the hydrophilic film 11 is formed on the inner wall surface of all the nozzle holes 51 .

[0036] The hydrophilic film 11 is, for example, silica ( SiO As an example, the hydrophilic film 11 may be made of a material containing the following base agent and hardener in a 1:1 weight ratio.

[0037] Here, the base material is composed of 4-6 wt% aluminum phosphate (AlPO4), 90-95 wt% silica (SiO2), 1.0-1.5 wt% alumina (Al2O3), and 0.3 to 0.7 wt% zinc oxide (ZnO). The hardener is composed of 2.0 wt% sodium oxide (Na2O), 82.2 wt% potassium oxide (K2O), and 15.8 wt% silicone (nSiO2). Others: Reference form 1 is the same as:

[0038] In this embodiment, the contact angle θ between the inner wall surface of the injection hole 51 and water can be made small. For example, even if the contact angle θ between the inner wall surface of the injection hole 51 and water is about 90° when no hydrophilic film is formed, by forming a hydrophilic film, the contact angle θ between the inner wall surface and water can be made, for example, 30° or less, or 10° or less. Therefore, it is possible to satisfy the formula (1) without adjusting the length L and the inner diameter D of the injection hole 51. The length L and the inner diameter D of the injection hole 51 are parameters that can affect the function of the spark plug 1. By satisfying the formula (1) without changing these parameters, misfires at the time of starting can be easily suppressed without affecting other functions of the spark plug 1. others, Reference form 1 It has the same effect as above.

[0039] ( Reference form 4 ) As shown in FIGS. 11 and 12, the spark plug 1 of this embodiment has a nozzle hole 51 formed in a front end wall portion 52 of a plug cover 5. As shown in FIG. The nozzle hole 51 provided in the tip wall portion 52 will be referred to as a tip nozzle hole 510 hereinafter.

[0040] In this embodiment, at least the tip nozzle hole 510 is configured to satisfy formula (1). As shown in Fig. 12, the tip wall portion 52 in which the tip nozzle hole 510 is formed is substantially flat. Therefore, the length L of the tip nozzle hole 510 is equal to the thickness t of the tip wall portion 52.

[0041] By satisfying formula (1), the tip nozzle hole 510 can also prevent clogging due to freezing in the same manner as described above. Moreover, by further satisfying formula (2), the tip nozzle hole 510 can more reliably prevent clogging due to freezing. It is also preferable that the nozzle holes 51 other than the tip nozzle hole 510 also satisfy the formula (1). Furthermore, it is more preferable that the nozzle holes 51 other than the tip nozzle hole 510 also satisfy the formula (2). others, Reference form 1 It has the same configuration and effect as that of the above.

[0042] As a means for satisfying the above formula (1) or formula (2), there are various means other than the means using the hydrophilic film 11 as shown in the above-mentioned embodiment 3. That is, means such as increasing the inner diameter D of the injection hole 51 and shortening the length L of the injection hole 51 are conceivable. However, as described above, the inner diameter D and the length L of the injection hole 51 may affect the various functions of the spark plug. Therefore, it may be difficult to greatly change these parameters just to prevent the injection hole 51 from being blocked by freezing. From this point of view, it is effective to use the hydrophilic film 11 as in embodiment 3. On the other hand, there is a concern that the material cost is likely to be high when the hydrophilic film 11 is formed. Therefore, as a means for reducing the contact angle θ without providing the hydrophilic film 11, for example, it is conceivable to improve the hydrophilicity by roughening or mirror-finishing the inner wall surface of the injection hole 51. Alternatively, it is conceivable to improve the hydrophilicity by plating the inner wall surface of the injection hole 51.

[0043] ( Reference form 5 ) As shown in FIG. 13, this embodiment is a plasma ignition plug 9 having a protrusion 95 with a permeation flow passage 951 formed therein. In the permeation flow passage 951 of the plasma ignition plug 9, Reference form 1 A configuration similar to that of the nozzle hole 51 in the spark plug 1 can be applied.

[0044] As shown in Fig. 13, the plasma ignition plug 9 has a center electrode 94 held inside a housing 12 via an insulator 93. A discharge space 940 is formed inside the insulator 93 on the tip side of the center electrode 94, allowing discharge to occur between the center electrode 94 and a ground electrode 96. The discharge space 940 opens to the tip side. A plate-shaped protrusion 95 that protrudes to the tip side is formed on the housing 12. A permeation flow path 951 that penetrates the protrusion 95 in the plate thickness direction is formed.

[0045] When the plasma ignition plug 9 having such a configuration is installed in an internal combustion engine and operated, plasma state gas is injected from the discharge space 940 to the tip side of the plasma ignition plug 9. The gas in the plasma state ignites the air-fuel mixture in the combustion chamber, forming a plasma flame kernel.

[0046] In order to prevent this plasma flame kernel from being blown away by the air current in the combustion chamber, protrusions 95 are provided. On the other hand, permeation channels 951 are formed in protrusions 95 so that the air-fuel mixture can be supplied to the plasma flame kernel. Therefore, if permeation channels 951 are blocked, there is a concern that the supply of the air-fuel mixture to the plasma flame kernel may be insufficient.

[0047] Therefore, it is possible to satisfy the following formula (1a) for the permeate channel 951 as well. In the following formula (1a), Da represents the inner diameter of the permeate channel 951, La represents the length of the permeate channel 951, and θa represents the contact angle between the inner wall surface of the permeate channel 951 and water. (La / 2) × tan(θa / 2) <Da (1a) More preferably, the following formula (2a) is satisfied. La × tan(θa / 2) <Da (2a)

[0048] The basic configuration of the plasma ignition plug 9 of this embodiment can be the same as that disclosed in Japanese Patent Application Laid-Open No. 2010-3605.

[0049] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the gist of the present invention. [Explanation of symbols]

[0050] 1 Spark plug 4 Center electrode 5 Plug cover 50 Auxiliary combustion chamber 51 Spray hole 6 Ground electrode G Discharge gap

Claims

1. a center electrode (4) and a ground electrode (6) forming a discharge gap (G) between them; a plug cover (5) provided at a tip portion thereof so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, The plug cover is formed with a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, At least one of the nozzle holes is provided with a hydrophilic film (11) for improving hydrophilicity on an inner wall surface thereof, and further, when an inner diameter of the nozzle hole is D, a length of the nozzle hole along an axis of the nozzle hole is L, and a contact angle between the inner wall surface of the nozzle hole and water is θ, the following formula (1) is satisfied: (L / 2)×tan(θ / 2)<D (1)

2. 2. The spark plug for an internal combustion engine according to claim 1, wherein at least one of the nozzle holes satisfies the following formula (2): L×tan(θ / 2)<D (2)

Images