spark plug

Abstract

Spark plug (100) comprising: a center electrode (20); a ground electrode (30) provided such that a gap for spark discharge is formed between the center electrode (20) and the ground electrode (30); and a spark plug cover (80) covering the center electrode (20) and the ground electrode (30) from a front face of the spark plug (100), the spark plug cover (80) having a through-hole (81), the through-hole (81) of the spark plug cover (80) comprising a diameter-reducing section (Dr) extending in a region of 0.1 mm or less from an outer open end (E1) of the through-hole (81) in a direction along a central axis (CB) of the through-hole (81) and having a diameter that gradually decreases from the outer open end (E1) to an inner open end (E2) of the through-hole (81).and where a diameter at the outer open end (E1) is denoted by x and a diameter at the inner end of the diameter reduction section (Dr) is denoted by y, a ratio of 0 mm < xy < 0.2 mm is satisfied, and wherein a distance (b) from the central axis (CB) to a section (P1) at a leading side of the outer open end (E1) is greater than a distance (a) from the central axis (CB) to a section (P2) at a trailing side of the outer open end (E1).

Description

TECHNICAL AREA

[0001] The present invention relates to a spark plug. BACKGROUND OF THE INVENTION

[0002] A spark plug for an internal combustion engine, e.g. a gasoline engine, is known to have an auxiliary chamber that covers a center electrode and a ground electrode from the front (e.g. Japanese published patent application (kokai) No. H11-224763 A).

[0003] Generally, a spark plug with an auxiliary chamber causes a spark discharge in a discharge gap, which serves to generate a spark and is the gap between a center electrode and a ground electrode. A flame is then generated in the auxiliary chamber. The pressure in the auxiliary chamber is then increased by the flame, and due to the pressure from inside the auxiliary chamber, the flame radiates out through a through-hole to the outside of a spark plug cap. The fuel in a combustion chamber is then ignited using the emitted flame as an ignition source, resulting in explosive combustion.

[0004] The above-mentioned JP-H11 224763 A discloses a spark plug in which a through hole is located at the position of a spark plug in a direction along the axial line of the spark plug, and a through hole is also provided at a position on the front side of the auxiliary chamber.

[0005] The positions of the through-holes were examined as with the spark plug JP-H11 224763 A described above, but the shapes of the through-holes are considered insufficiently studied, and there is room for further improvements from the point of view of improving fuel utilization.

[0006] Furthermore, the inventors have found that the outer open end of the through-hole is exposed to continuous spark ignition from the flame, thereby excessively increasing the temperature of the outer open end, and have found that, as a consequence, the phenomenon of pre-ignition (so-called "pre-ignition") occurs. An object of the present invention is therefore to provide a technology that prevents the occurrence of pre-ignition and also improves fuel utilization. SUMMARY OF THE INVENTION

[0007] The present invention was made to solve the problem described above and can be implemented in the following embodiments. (1) According to one aspect of the present invention, a spark plug is provided. The spark plug comprises: a center electrode; a ground electrode, which is provided such that a gap for spark discharge is formed between the center electrode and the ground electrode; and a spark plug cover, which covers the center electrode and the ground electrode from a front side of the spark plug, the spark plug cover having a through-hole, the through-hole of the spark plug cover comprising a diameter-reducing section formed in a region of 0.1 mm or less from an outer open end of the through-hole in a direction along a central axis of the through-hole, and having a diameter that gradually decreases from the outer open end to an inner open end of the through-hole, and where a diameter at the outer open end is xis designated and a diameter at an inner end of the diameter reduction section with y This spark plug is characterized by a relationship of 0 mm < xy < 0.2 mm. For this type of spark plug, setting xy to a value greater than 0 mm prevents the outer open end from being exposed to the flame. This prevents the temperature of the outer open end from rising excessively, thus preventing pre-ignition. Furthermore, setting xy to less than 0.2 mm prevents a decrease in flame density at the outer open end, thereby preventing a reduction in the exit velocity of the flame. Consequently, the flame spreads sufficiently within the combustion chamber, and fuel efficiency is improved. (2) In the spark plug of the above aspect, the distance from the central axis to a section at the foremost side of the outer open end may be greater than the distance from the central axis to a section at the rearmost side of the outer open end. In the spark plug of this aspect, the flame radiates towards the central side of the combustion chamber, so that the flame spreads sufficiently in the combustion chamber and fuel consumption is improved.

[0008] The present invention can be implemented in various embodiments, e.g. in forms such as an engine head on which a spark plug is mounted. List of characters

[0009] Embodiments of the invention are described with reference to the drawings, without being limited thereto. Fig. Figure 1 is an explanatory illustration showing a partial cross-section of a spark plug. Fig. Figure 2 is a schematic representation of a candle cover as seen from the front. Fig. Figure 3 is a schematic diagram describing the cross-sectional shape of a through hole. Fig. Figure 4 is a diagram showing experimental results that support the effects achieved by one embodiment. VARIANTS FOR THE EXECUTION OF THE FIRST INVENTIONAL FORM:

[0010] Fig. Figure 1 is an explanatory illustration showing a partial cross-section of a spark plug 100 shows. In Fig. 1 is connected to an axial line CA , which is the axis of the spark plug 100 represents, as a limitation, the external appearance of the spark plug. 100 shown on the right side of the drawing sheet is the cross-sectional shape of the spark plug. 100 shown on the left side of the drawing sheet. In the description of the present embodiment, the lower side of Fig. 1 as the front of the spark plug 100 and the upper side of Fig. 1 as the back of the spark plug 100 designated.

[0011] The spark plug 100 contains: an insulator 10 with an axial hole 12 along the axial line CA ; a central electrode 20 , which are in the axial hole 12 is provided for; a tubular metal housing 50 , which is located on the outer circumference of the insulator 10 is arranged; a ground electrode 30 with one attached to the metal casing 50 attached foot end 32 ; and a candle cover 80 , which is the center electrode 20 and the ground electrode 30 Covered. Here is the axial line. CA the spark plug 100 the same as the axial line of the center electrode 20 .

[0012] The insulator 10It is a ceramic insulator produced by firing a ceramic material such as aluminum oxide. The insulator 10 is a tubular element located on the inner circumference of the metal casing 50 is arranged and the axial hole 12 has a central element formed in the middle of it and in which part of the central electrode 20 housed at the front, and part of a metal connector 40 It is located at the rear. A central section of the fuselage. 19 with a large outer diameter is located in the middle in the axial direction of the insulator. 10 trained. A rear torso section 18 with a smaller outer diameter than the central fuselage section 19 is located on the rear side of the central torso section 19 formed. A front torso section 17 with a smaller outer diameter than the rear fuselage section 18is located at the front of the central fuselage section 19 trained. One leg section 13 with an outer diameter that corresponds to the center electrode 20 The decrease is located further forward on the front of the forward fuselage section. 17 trained.

[0013] The metal casing 50 is a cylindrical metal part that extends from a part of the rear fuselage section 18 up to the leg section 13 extending section of the insulator 10 surrounds and holds. The metal casing 50 It is made, for example, of low-carbon steel and completely coated with nickel, zinc, or similar materials. The metal casing 50 includes a tool intervention section 51 , a sealing section 54 and a mounting thread section 52 in order from the back. A tool for securing the spark plug. 100On a motor head, at the tool engagement section 51 attached. The mounting thread section 52 is a section with an external thread that is attached to the outer circumference of the metal housing 50 over its entire circumference and that into a threaded groove 86 the candle cover 80 It is screwed in. The sealing section 54 is a section that is in a flange shape at the root of the fastening thread section 52 is formed by bending a plate. It is a ring-shaped seal. 65 is placed between the sealing section 54 and a cover sealing section 84 the candle cover 80 inserted and fitted. One end surface 57 on the front of the metal casing 50 has a hollow circular shape, and the front end of the leg section 13 of the insulator 10 and the front end of the center electrode20 protrude from the center of the end surface 57 out of here.

[0014] A crimp section 53 with a small thickness at the rear in relation to the tool engagement section 51 the metal casing 50 A compression deformation section is also included. 58 with a small thickness similar to the crimp section 53 between the sealing section 54 and the tool engagement section 51 provided. Ring-shaped ring elements 66 and 67 are between the inner circumferential surface of the metal housing 50 and the outer circumferential surface of the rear fuselage section 18 of the insulator 10 from the tool engagement section 51 up to the crimp section 53 arranged, and the space between these ring elements 66 and 67 continues with talcum powder 69 filled. During the manufacture of the spark plug100 The compression deformation section 58 by pressing the crimp section 53 compressed and deformed towards the front, so that the crimp section 53 It is crimped inwards. This is due to the compression deformation of the compression deformation section. 58 The insulator will be 10 inside the metal casing 50 about the ring elements 66 and 67 and the talc ring 69 Pressed towards the front. The talc is compressed. 69 in the direction of the axial line CA compressed, thus compromising the airtightness in the metal housing 50 is increased.

[0015] The metal casing 50 has a metal housing inner stage section 56 , which is shaped so that it fits on the inner circumference of the metal casing 50 protrudes. Additionally, the insulator has 10 an insulator stage section 15 , which is located at the rear end of the leg section13 is located and is shaped in such a way that it is on the outer circumference of the insulator. 10 protrudes. On the inner circumference of the metal casing. 50 is the metal housing inner stage section 56 via a ring-shaped seal 68 with the insulator stage section 15 in contact. The seal 68 is an element for maintaining airtightness between the metal housing 50 and the insulator 10 and prevents the escape of combustion gas. In the present embodiment, a plate gasket is used as the seal.

[0016] The center electrode 20 is a rod-shaped element containing a core material 22 with better thermal conductivity than an electrode element 21 inside the electrode element 21 is embedded. The electrode element 21is formed from a nickel alloy containing nickel as the main component, and the core material 22 It is formed from copper or an alloy containing copper as the main component. For example, a precious metal tip can be made of an iridium alloy or the like, with a front end section of the center electrode. 20 be connected.

[0017] A flange section 23 is near an end section, on the back side, of the center electrode 20 shaped so that it is on the outer circumferential side of the central electrode 20 protrudes. The flange section 23 is in contact with an axial hole inner step section 14 , which enters the axial hole from the rear side on the inner circumferential side 12 of the insulator 10 protrudes and the center electrode 20 inside the insulator 10 positioned. The center electrode 20It has a sealing element on its back. 64 and a ceramic resistor 63 electrically with the metal connection 40 tied together.

[0018] The ground electrode 30 is made of an alloy containing nickel as its main component. The foot end 32 the ground electrode 30 is at the end surface 57 the metal casing 50 attached. The ground electrode 30 extends along the axial line CA from the foot end 32 towards the front and is bent at a middle section thereof so that a side surface of a front end section 33 the ground electrode 30 the front end face of the center electrode 20 is facing a precious metal tip 31 is on the surface of the front end section 33 the ground electrode 30 provided for, the side of the center electrode 20is facing the other side. A gap for spark discharge is located between the precious metal tip. 31 the ground electrode 30 and the center electrode 20 formed. This gap will also be referred to as the "discharge gap" in the following. The precious metal tip 31 It is made, for example, from platinum, iridium, ruthenium, rhodium or an alloy thereof.

[0019] The candle cover 80 is a hollow body that houses the central electrode 20 and the ground electrode 30 from the front. The candle cover 80 The present embodiment is made of stainless steel. It includes a candle cover. 80 The covered space is also called an auxiliary chamber. R designated. The auxiliary chamber R covers the discharge gap. In the present embodiment, the auxiliary chamber R a room separated from the insulator 10 , the center electrode 20 , the metal casing50 , the seal 68 and the candle cover 80 is surrounded by the threaded groove. 86 , which includes the mounting thread section 52 the metal casing 50 The threaded engagement is located on an inner wall of the candle cover. 80 trained, and the candle cover 80 is attached to the metal casing 50 attached by the metal casing 50 into the candle cover 80 is screwed in.

[0020] The candle cover 80 includes a screw section 82 and the cover sealing section 84 The screw section 82 is a section with an external thread that is attached to the outer circumference of the candle cover 80 It is formed over its entire circumference and is screwed into a threaded groove in the engine head. The cover sealing section 84is a section that is in a flange shape at the root of the screw section 82 is formed by bending a plate. It is a ring-shaped seal. 88 is located on the front of the cover sealing section. 84 inserted and fitted. The thickness of the candle cover 80 is not particularly limited, but can be, for example, about 1.5 mm to 3 mm.

[0021] The candle cover 80 is equipped with a large number of through holes 81 provided which create a connection between the inside and outside of the candle cover 80 produce. Through the through holes 81 Fuel located in the combustion chamber of an engine can be transferred to the auxiliary chamber R stream, and those in the auxiliary chamber R The generated flame can reach the outside of the candle cover. 80 be expelled.

[0022] in the spark plug 100In the present embodiment, a spark discharge is caused in the discharge gap, and then a flame is first ignited in the auxiliary chamber. R This process generates pressure. Afterwards, the pressure in the auxiliary chamber increases. R through the flame, and the flame radiates through the through-holes due to this pressure. 81 to the outside of the candle cover 80 The combustion gas is then burned in the combustion chamber using the ejected flame as an ignition source, resulting in an explosive combustion in the combustion chamber.

[0023] Fig. Figure 2 is a schematic representation of the candle cover. 80 Viewed from the front. In the present embodiment, there are four through holes. 81 at equal intervals around the axial line CA The number of through holes is planned. 81is not limited to this and can be 3 or fewer, or 5 or more. From the perspective of improving fuel efficiency, the number of through-holes is 81 preferably equal to or greater than 2 and equal to or less than 8, and even more preferably equal to or greater than 3 and equal to or less than 6.

[0024] Fig. Figure 3 is a schematic representation to describe a cross-sectional shape of the through hole. 81 In the present embodiment, the through-hole contains 81 the candle cover 80 a diameter reduction section Dr with a diameter extending from an outer open end E1 of the through hole 81 to the inner open end E2 of the through hole 81 The diameter reduction section gradually decreases. Dr is located within 0.1 mm or less of the outer open end E1in one direction along a central axis CB of the through hole 81 trained. In other words, the candle cover 80 is with a section D provided to form a through hole, which forms the through hole 81 forms, and the section D The through-hole has an inner section. Dn including the inner open end E2 , that with the inner surface of the candle cover 80 is connected, and the diameter reduction section Dr including the outer open end E1 , that with the outer surface of the candle cover 80 is connected. In the present embodiment, the diameter of the diameter reduction section takes on a certain size. Dr gradually in a range of 0.08 mm from the outer open end E1 in the direction along the central axis CB of the through hole 81 away.

[0025] If the spark plug 100 In the present embodiment, a diameter at the outer open end E1 with x and a diameter at the inner end of the diameter reduction section Dr with y The ratio 0 mm < xy < 0.2 mm is satisfied. Here, the diameter denotes... x at the outer open end E1 the length of the line segment on the outermost side in the diameter reduction section Dr among the line segments orthogonal to the central axis CB The diameter y at the inner end of the diameter reduction section Dr gives the length of the line segment on the innermost side in the diameter reduction section. Dr among the line segments orthogonal to the central axis CB to.

[0026] in the spark plug 100 The present embodiment can be modified by adjusting x-y The flame exposure of the outer open end is greater than 0 mm. E1 compared to the case where x-y This prevents the temperature of the outer open end from reaching 0 mm. E1 is excessively increased. Consequently, the occurrence of pre-ignition, which is the phenomenon of auto-ignition before spark ignition, can be prevented. From the point of view of preventing pre-ignition, x-y preferably larger than 0.01 mm, x-y is even more preferred if it is larger than 0.05 mm.

[0027] Furthermore, the spark plug 100 the present embodiment by adjusting of x-y a decrease in flame density at the outer open end of less than 0.2 mm E1 compared to the case in which x-y This prevents a deviation of 0.2 mm or greater. In this way, a decrease in the exit velocity of the fluid from the through-hole can be avoided. 81 The escaping flame is inhibited. As a result, the flame spreads sufficiently within the combustion chamber, and the combustion rate of the fuel gas is increased, thus improving fuel utilization. From the perspective of increasing the combustion rate, x-y preferably equal to or smaller than 0.15 mm.

[0028] Also, in the spark plug 100 in the present embodiment a distance b from the central axis CB of the through hole 81 to a section P1 , on the front side, of the outer open end E1 greater than a distance a from the central axis CB to a section P2 , on the rearmost side, of the outer open end E1In such a configuration, the air spreads out of the through-hole. 81 The exiting flame is directed towards the front. This means the flame radiates towards the central side of the combustion chamber, allowing it to spread sufficiently within the chamber and improving fuel efficiency. In the present embodiment, the spark plug cover has... 80 the large number of through holes 81 , and the distance b is greater than the distance a in all the through holes 81 In such a configuration, the [something] spreads out of all the through-holes. 81 The escaping flame is directed towards the front, further improving fuel efficiency.

[0029] Fig. Figure 4 is a diagram showing experimental results that support the effects achieved with the present embodiment. In this experiment, as in Fig. 4 shown, samples of spark plugs produced in which (i) the diameter x at the outer open end E1 , (ii) the diameter y at the inner end of the diameter reduction section Dr , (iii) the distance a and (iv) the distance b were done differently for each sample.

[0030] The measurement of each of the values ​​of x , y , a and b was carried out by drilling the through hole 81 was filled with resin, then the candle cover 80 was cut along a plane defined by the axial line CA and the central axis CB of the through hole 81 runs, and each of the values ​​of x , y , a and bThe measurements were taken on the cross-sectional plane using a microscope. In this experiment, an assessment was made for pre-ignition and an assessment for combustion rate.

[0031] For the ignition advance analysis, a sample was fitted to a 1.3-liter, 4-cylinder, in-line naturally aspirated engine, and the engine was run at 6000 rpm with the throttle wide open (WOT). The frequency of ignition advance was then measured for each ignition point defined by a crankshaft angle. Generally, where the ignition timing is advanced, ignition advance is more likely to occur.

[0032] A point where no advance occurs when the ignition timing is 2° ahead of a standard spark plug was 1 point, and a point where advance occurs when the ignition timing is 2° ahead of a standard spark plug was 0 points.

[0033] To evaluate the combustion rate, a sample was attached to a 4-cylinder in-line turbocharged direct-injection engine with a displacement of 1.6 liters, and the combustion rate was measured under conditions of a mean net effective pressure (NMEP) of 1000 kPa and an engine speed of 2000 rpm. The combustion rate was calculated from the time required for mass fraction combustion (MFB) to reach 90 mass fraction.

[0034] The combustion rate was assessed using a score based on the ratio by which the combustion rate was increased compared to a commercial spark plug. Specifically, the combustion rate was evaluated as follows. A higher score indicates a higher combustion rate and also indicates better fuel efficiency. 20% or more: 3 points 5% or more and less than 20%: 1 point Less than 5%: 0 points

[0035] In addition, the overall score was calculated as the sum of the score for pre-ignition and the score for combustion rate.

[0036] From the in Fig. The following results were obtained from the four experiments shown. Specifically, by comparing the experimental results of the samples... 1 and 9Compared to the other samples, it was found that the occurrence of pre-ignition is inhibited when xy is greater than 0. Meanwhile, by comparing the experimental results of the samples 7 , 8 , 15 and 16 Compared to the other samples, it was found that the combustion rate is increased when xy is less than 0.2 mm.

[0037] Furthermore, by comparing the experimental results of the sample 17 and sample 18 with each other and by comparing the experimental results of the sample 19 and sample 20 They jointly determined that the combustion rate is higher when the distance b greater than the distance a is. OTHER VERSIONS:

[0038] The present invention is not limited to the embodiment described above and can be implemented in various configurations without departing from the core of the present invention. For example, the technical features in the embodiment that correspond to the technical features described in each aspect of the abstract of the invention can be suitably replaced or combined to solve some or all of the aforementioned problems or to achieve some or all of the aforementioned effects. Furthermore, such technical features can be suitably deleted if they are not described as essential in this description.

[0039] In the embodiment described above, the metal housing 50 and the candle cover 80separate elements, but are not limited to this and can be integrated together. Furthermore, the ground electrode 30 with the metal casing 50 connected, but not limited to that and can be used, for example, with the candle cover 80 be connected.

[0040] In the embodiment described above, as in Fig. As shown in 3, the distance b from the central axis CB of the through hole 81 to the section P1 , on the front side, of the outer open end E1 greater than the distance a from the central axis CB to the section P2 , on the rearmost side, of the outer open end E1 The distance b However, it is not limited to that. The distance b can equal to the distance a or smaller than the distance a be. Reference symbol list 10: Insulator 12: Axial hole 13: Leg section 14: Axial hole inner step section 15: Insulator stage section 17: forward fuselage section 18: rear fuselage section 19: central fuselage section 20: Center electrode 21: Electrode element 22: Core material 23: Flange section 30: Ground electrode 31: Precious metal peak 32: Foot end 33: front end section 40: Metal connection 50: Metal casing 51: Tool engagement section 52: Mounting thread section 53: Crimp section 54: Sealing section 56: Metal housing inner stage section 57: End surface 58: Compression deformation section 63: Ceramic resistor 64: Sealing body 65: Seal 66, 67: Ring element 68: Seal 69: Talc 80: Candle cover 81: Through hole 82: Screw section 84: Cover sealing section 86: Threaded groove 88: Seal 100: Spark plug CA: Axial line CB: central axis D: Section for forming a through hole Dn: inner section Dr: Diameter reduction section E1: outer open end E2: inner open end P1: Section P2: Section R: Auxiliary chamber a: distance b: distance x: Diameter y: diameter QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP H11224763 A [0004, 0005]

Claims

[1] Spark plug (100), comprising: a central electrode (20); a ground electrode (30) which is provided such that a gap for spark discharge is formed between the center electrode (20) and the ground electrode (30); and a spark plug cover (80) which covers the center electrode (20) and the ground electrode (30) from a front side of the spark plug (100), wherein the spark plug cover (80) has a through hole (81), wherein the through-hole (81) of the candle cover (80) comprises a diameter reduction section (Dr) which is formed in a region of 0.1 mm or less from an outer open end (E1) of the through-hole (81) in a direction along a central axis (CB) of the through-hole (81) and which has a diameter that gradually decreases from the outer open end (E1) to an inner open end (E2) of the through-hole (81), and where a diameter at the outer open end (E1) is denoted by x and a diameter at the inner end of the diameter reduction section (Dr) is denoted by y, a ratio of 0 mm < xy < 0.2 mm is fulfilled. [2] Spark plug (100) according to claim 1, wherein a distance (b) from the central axis (CB) to a section (P1) at a front side of the outer open end (E1) is greater than a distance (a) from the central axis (CB) to a section (P2) at a rear side of the outer open end (E1).

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