Patent Application
20200028333
The present disclosure relates to a spark plug for an internal combustion engine.
As disclosed in JP S61-292875 A, for example, there is known a spark plug for an internal combustion engine that is configured to apply high-frequency voltage to a center electrode to generate discharge between a ground electrode and the center electrode. Such a spark plug generates creeping spark discharge along a surface of an insulator between the center electrode and the ground electrode.
A first aspect of the present disclosure is an internal combustion engine spark plug including a tubular ground electrode, a tubular insulator arranged inside the ground electrode and having an insulator protruding portion protruding to a tip end side in a plug axial direction with respect to a tip end of the ground electrode, and a center electrode held inside the insulator and having an exposed portion exposed through a tip end of the insulator protruding portion. The exposed portion of the center electrode has a first part covering the insulator protruding portion from the tip end side in the plug axial direction, and a second part extending from the first part to a base end side in the plug axial direction and covering the entire circumference of an outer peripheral surface of the insulator protruding portion from an outer peripheral side in a plug radial direction. An axial gap is formed between the first part and the insulator protruding portion in the plug axial direction.
In the accompanying drawings:
In the spark plug disclosed in JP S61-292875 A, the insulator is arranged inside the tubular ground electrode, and the center electrode is arranged further inside the insulator. The insulator is arranged such that a tip end thereof protrudes to a tip end side of the ground electrode. Moreover, the center electrode is arranged such that a tip end thereof protrudes to a tip end side of the insulator.
However, in the spark plug described in JP S61-292875 A, a corner portion (i.e., a corner between a tip end surface and an outer peripheral surface of the insulator) of a tip end portion of the insulator is exposed. Thus, creeping spark discharge along a surface of the corner portion of the insulator is formed between the center electrode and the ground electrode. Thus, the discharge generated between the center electrode and the ground electrode is less detached from a surface of the insulator, specifically the surface of the corner portion. Thus, in the spark plug, the discharge generated between the center electrode and the ground electrode is less greatly extended by an air flow in a combustion chamber, and performance of ignition of an air-fuel mixture is less ensured.
The present disclosure has been made in view of such problems, and is intended to provide an internal combustion engine spark plug configured so that performance of ignition of an air-fuel mixture can be improved.
A first aspect of the present disclosure is an internal combustion engine spark plug including a tubular ground electrode, a tubular insulator arranged inside the ground electrode and having an insulator protruding portion protruding to a tip end side in a plug axial direction with respect to a tip end of the ground electrode, and a center electrode held inside the insulator and having an exposed portion exposed through a tip end of the insulator protruding portion. The exposed portion of the center electrode has a first part covering the insulator protruding portion from the tip end side in the plug axial direction, and a second part extending from the first part to a base end side in the plug axial direction and covering the entire circumference of an outer peripheral surface of the insulator protruding portion from an outer peripheral side in a plug radial direction. An axial gap is formed between the first part and the insulator protruding portion in the plug axial direction.
Moreover, a second aspect of the present disclosure is an internal combustion engine spark plug including a tubular ground electrode, a tubular insulator arranged inside the ground electrode and having an insulator protruding portion protruding to a tip end side in a plug axial direction with respect to a tip end of the ground electrode, and a center electrode held inside the insulator and having an exposed portion exposed through a tip end of the insulator protruding portion. The exposed portion of the center electrode has a first part covering the insulator protruding portion from the tip end side in the plug axial direction, and a second part extending from the first part to a base end side in the plug axial direction and covering an entire circumference of an outer peripheral surface of the insulator protruding portion from an outer peripheral side in a plug radial direction. The exposed portion of the center electrode is formed within the ground electrode as viewed in the plug axial direction.
Moreover, a third aspect of the present disclosure is an internal combustion engine spark plug including a tubular ground electrode, a tubular insulator arranged inside the ground electrode and having an insulator protruding portion protruding to a tip end side in a plug axial direction with respect to a tip end of the ground electrode, and a center electrode held inside the insulator and having an exposed portion exposed through a tip end of the insulator protruding portion. The exposed portion of the center electrode has a first part covering the insulator protruding portion from the tip end side in the plug axial direction, and a second part extending from the first part to a base end side in the plug axial direction and covering a part of an outer peripheral surface of the insulator protruding portion in a plug circumferential direction from an outer peripheral side in a plug radial direction. At least a region, in which the second part is formed, of the insulator protruding portion in the plug circumferential direction has a step shape having an outer diameter that decreases in a stepwise manner toward the tip end side in the plug axial direction. As viewed in the plug axial direction, the exposed portion of the center electrode is formed within the ground electrode.
In the internal combustion engine of the first aspect, the exposed portion of the center electrode has the first part and the second part. That is, a corner portion of a tip end portion of the insulator protruding portion is covered with the first part and the second part of the center electrode. Thus, discharge is formed between the second part of the center electrode and the ground electrode without generation of discharge on the corner portion of the tip end portion of the insulator protruding portion. Thus, due to an air flow of an air-fuel mixture in a combustion chamber or electrical repulsion, the discharge is easily detached from a surface of the insulator protruding portion, and is easily extended to a downstream side. Accordingly, performance of ignition of the air-fuel mixture can be improved. Moreover, an entirety between the exposed portion of the center electrode covering the entire circumference of the tip end portion of the insulator protruding portion and the ground electrode covering the entire circumference of the insulator protruding portion serves as a discharge formable region. Thus, creeping discharge is repeatedly formed in a particular path of the surface of the insulator protruding portion, and therefore, concentration of so-called channeling, which is erosion of an insulator surface in a groove shape, on the particular path can be prevented from occurring.
In the internal combustion engine spark plug of the third aspect, a part of the corner portion of the tip end portion of the insulator protruding portion is covered with the first part and the second part of the center electrode. Thus, in the present aspect, discharge is also formed between the second part of the center electrode and the ground electrode without generation of discharge on the corner portion of the tip end portion of the insulator protruding portion. Thus, due to the air flow of the air-fuel mixture in the combustion chamber or electrical repulsion, the discharge is easily detached from the surface of the insulator protruding portion, and is easily extended to the downstream side. Accordingly, the performance of ignition of the air-fuel mixture can be improved.
Further, in the internal combustion engine spark plug of the third aspect, at least the region, in which the second part is formed, of the insulator protruding portion in the plug circumferential direction has, along the entirety in the plug axial direction, such a step shape that the outer diameter decreases in the stepwise manner toward the tip end side in the plug axial direction. Thus, a path from the second part to the ground electrode along the surface of the insulator protruding portion can be extended. Accordingly, a distance for creeping discharge can be ensured without extension of the insulator protruding portion in the plug axial direction, and the ignition performance can be enhanced. Further, an area of the section of the tip end portion of the insulator protruding portion perpendicular to the plug axial direction is decreased, and therefore, thermal losses due to loss of heat from the flame generated by the discharge of the spark plug by the insulator protruding portion can be reduced. This also can improve the performance of ignition of the air-fuel mixture.
As described above, according to each of the above-described aspects, the internal combustion engine spark plug being configured so that the performance of ignition of the air-fuel mixture can be improved can be provided.
An embodiment of a spark plug for an internal combustion engine will be described with reference to
As illustrated in
As illustrated in
The spark plug 1 of the present embodiment can be, for example, used as an ignition means in the internal combustion engine for a vehicle such as an automobile. The spark plug 1 for the internal combustion engine is configured to apply high voltage to the center electrode 4 to generate discharge between the ground electrode 2 and the center electrode 4. The spark plug 1 is connected to a not-shown high-voltage power source unit on one end side in the plug axial direction Z, and is arranged in a combustion chamber of the internal combustion engine on the other end side. The high-voltage power source unit includes, for example, a general ignition coil, a power source of an ignition device capable of continuously controlling discharge, and a high-frequency power source capable of applying a high-frequency voltage of 200 kHz to 5 MHz to the center electrode 4.
In the present specification, in the plug axial direction Z, a side on which the spark plug 1 is inserted into the combustion chamber will be referred to as a tip end side, and the opposite side will be referred to as a base end side.
The ground electrode 2 is in a tubular shape. The ground electrode 2 is formed to surround the insulator 3 along the entire circumference thereof. As illustrated in
As illustrated in
As illustrated in
As illustrated in
The center electrode 4 is inserted into and held at a tip end portion of the through-hole 30 of the insulator 3. The center electrode 4 is, as a whole, in a substantially circular columnar shape.
The exposed portion 41 of the center electrode 4 is, as a whole, in a cup shape opening toward the base end side in the plug axial direction Z. The exposed portion 41 has the first part 411 formed in a discoid shape as illustrated in
As illustrated in
As illustrated in
The exposed portion 41 may be formed separately from a part of the center electrode 4 within the insulator protruding portion 31, or may be formed integrally with such a part.
As illustrated in
A resistor 13 is arranged on the base end side of the center electrode 4 in the through-hole 30 of the insulator 3 through a glass seal 12 having conductivity. The resistor 13 can be formed in such a manner that a resistor composition containing a resistive material such as carbon or ceramic powder and glass powder is heated and sealed, or can be configured in such a manner that a cartridge resistor is inserted. The glass seal 12 is made of copper glass formed by mixing of glass with copper powder. Moreover, on the base end side of the resistor 13, a stem 15 is arranged through a glass seal 14 made of copper glass. The stem 15 is, for example, made of iron alloy. A base end portion of the stem 15 protrudes from the insulator 3. Moreover, the spark plug 1 is connected to the high-voltage power source unit at a protruding portion of the stem 15.
Next, features and advantageous effects of the present embodiment will be described.
In the spark plug 1 for the internal combustion engine in the present embodiment, the exposed portion 41 of the center electrode 4 has the first part 411 and the second part 412. That is, the corner portion of the tip end portion of the insulator protruding portion 31 is covered with the first part 411 and the second part 412 of the center electrode 4. This can prevent generation, sustention, and fixing of discharge on the corner portion of the tip end portion of the insulator protruding portion 31. Thus, due to an air flow of an air-fuel mixture in the combustion chamber or electrical repulsion, discharge is easily detached from a surface of the insulator protruding portion, and is easily extended to a downstream side. Accordingly, performance of ignition of the air-fuel mixture can be improved. Further, occurrence of channeling at the corner portion of the tip end portion of the insulator protruding portion 31 can be prevented. Moreover, the entirety between the exposed portion of the center electrode covering the entire circumference of the tip end portion of the insulator protruding portion and the ground electrode covering the entire circumference of the insulator protruding portion serves as a discharge formable region. Thus, creeping discharge is repeatedly formed in a particular path of the surface of the insulator protruding portion, and therefore, concentration of so-called channeling, which is erosion of an insulator surface in a groove shape, on the particular path can be prevented from occurring.
Moreover, the end surface 412a of the second part 412 on the base end side in the plug axial direction Z is perpendicular to the plug axial direction Z. Further, the tip end surface 21 of the ground electrode 2 is also perpendicular to the plug axial direction Z. Thus, discharge generated between the center electrode 4 and the ground electrode 2 is easily detached from a surface of the insulator exposed portion 310, and is easily greatly extended to the downstream side of the air flow by the air flow in the combustion chamber of the internal combustion engine attached to the spark plug 1. This will be described later.
As illustrated in
Then, as illustrated in
In association with movement of both points of origin of the discharge spark S in the direction apart from the insulator exposed portion 310 in the plug radial direction, the part between both points of origin of the discharge spark S also moves, as illustrated in
Next, as illustrated in
A spark plug 9 has a circular columnar center electrode protruding portion 941 protruding to the tip end side of an insulator protruding portion 31. The center electrode protruding portion 941 is in a circular columnar shape. As viewed in the plug axial direction Z, the center electrode protruding portion 941 is inside a through-hole 30 of an insulator 3. An outer peripheral surface 941b of the center electrode protruding portion 941 is formed in the plug axial direction Z. Moreover, a corner portion 319 at the tip end of the insulator protruding portion 31 of the insulator 3 is formed in a gentle curved shape.
As illustrated in
Then, as illustrated in
Meanwhile, while the point S2 of origin of the discharge spark S on the ground electrode 2 side is moving as illustrated in
Thus, the part between both points of origin of the discharge spark S less moves apart from the corner portion 319 at the tip end of the insulator protruding portion 31. Accordingly, even when the discharge spark S is extended by the air flow F, the part between both points of origin is less easily greatly extended to the downstream side. Thus, the spark plug 9 described here is worse than the spark plug 1 of the present embodiment in terms of the performance of ignition of the air-fuel mixture in the combustion chamber.
Moreover, the spatial distance between the second part 412 of the center electrode 4 and the ground electrode 2 in the spark plug 1 is constant along the entire circumference. Thus, concentration of discharge generated between the second part 412 of the center electrode 4 and the ground electrode 2 on a position shifted to one side in the plug circumferential direction can be prevented. Thus, at the insulator 3, promotion of wearing of the insulator 3 due to concentration of channeling on the position shifted to one side in the plug circumferential direction can be prevented.
Moreover, the radial gap rc is formed between the outer peripheral surface 31b of the insulator protruding portion 31 and the inner peripheral surface 412b of the second part 412 of the center electrode 4 in the plug radial direction. Thus, the air flow in the combustion chamber also flows into the radial gap rc. Then, the air flow having flowed into the radial gap rc flows out toward the outside in the plug radial direction, i.e., a side apart from the insulator exposed portion 310, between the center electrode 4 and the ground electrode 2. Thus, the discharge spark is easily extended away from the insulator exposed portion 310.
As described above, according to the present embodiment, the internal combustion engine spark plug configured so that the performance of ignition of the air-fuel mixture can be improved can be provided.
The present embodiment is an embodiment in which an axial gap ac is formed between a first part 411 and an insulator protruding portion 31 in a plug axial direction Z as illustrated in
Note that in the present embodiment, a diameter A is 4.55 mm, an inner diameter B is 4.85 mm, an outer diameter C is 5.85 mm, and a spatial distance D is 5.0 mm.
Other points are similar to those of the first embodiment.
Note that of reference numerals used in a second embodiment or later, the same reference numerals as those used in the already-described embodiment indicate components etc. similar to those of the already-described embodiment, unless otherwise stated.
In the present embodiment, an air flow in a combustion chamber also flows into the axial gap ac and the radial gap rc. Then, the air flow having flowed into the axial gap ac and the radial gap rc flows out toward the outside in a plug radial direction, i.e., toward a side apart from an insulator exposed portion 310, between the center electrode 4 and a ground electrode 2. Thus, the discharge spark is easily extended away from the insulator exposed portion 310.
Moreover, due to a difference between the linear coefficient of expansion of an insulator 3 and the linear coefficient of expansion of the center electrode 4, thermal stress generated at the insulator 3 and the center electrode 4 can be reduced.
On other points, features and advantageous effects similar to those of the first embodiment are provided.
The present embodiment is an embodiment in which the shape of an end surface 411a of a first part 411 on a base end side in a plug axial direction Z and the shape of an inner peripheral surface 412b of a second part 412 are changed from those of the second embodiment as illustrated in
Other points are similar to those of the second embodiment.
In the present embodiment, an air flow having flowed into an axial gap ac and a radial gap rc can be smoothly sent out to between a center electrode 4 and a ground electrode 2. Thus, less turbulence is caused in the air flow flowing out from the axial gap ac and the radial gap rc, and the discharge spark is much more easily extended.
On other points, features and advantageous effects similar to those of the second embodiment are provided.
The present embodiment is an embodiment in which the shape of an exposed portion 41 is changed from that of the first embodiment as illustrated in
Other points are similar to those of the first embodiment.
In the present embodiment, by an air flow in a combustion chamber of an internal combustion engine attached to a spark plug 1, discharge generated between a center electrode 4 and a ground electrode 2 is easily detached from a surface of an insulator exposed portion 310, and is easily greatly extended to a downstream side of the air flow. This will be described later with reference to
As illustrated in
In association with movement of both points of origin of the discharge spark S in the direction apart from the insulator exposed portion 310 in the plug radial direction, a part between both points of origin of the discharge spark S also moves apart from an outer peripheral surface of the insulator exposed portion 310 toward the outer peripheral side. Then, the part, which has moved apart from the outer peripheral surface of the insulator exposed portion 310 toward the outer peripheral side, between both points of origin of the discharge spark S is greatly extended toward a downstream side of the air flow F by the air flow F in the combustion chamber. Specifically, in the present embodiment, both points of origin of the discharge spark S move such that the distance between both points of origin of the discharge spark S in the plug axial direction Z is increased, and therefore, the part between both points of origin of the discharge spark S is much more easily greatly extended. Thus, the area of contact between the discharge spark S and an air-fuel mixture is much more easily earned, and performance of ignition of the air-fuel mixture is much more easily ensured.
On other points, features and advantageous effects similar to those of the first embodiment are provided.
The present embodiment is an embodiment in which the shape of a ground electrode 2 is changed from that of the first embodiment as illustrated in
Other points are similar to those of the first embodiment.
In the present embodiment, discharge generated between a center electrode 4 and the ground electrode 2 is, by an air flow in a combustion chamber of an internal combustion engine attached to a spark plug 1, easily detached from a surface of an insulator exposed portion 310, and is easily greatly extended to a downstream side of the air flow. This will be described later with reference to
As illustrated in
In association with movement of both points of origin of the discharge spark S in the direction apart from the insulator exposed portion 310 in the plug radial direction, a part between both points of origin of the discharge spark S also moves apart from an outer peripheral surface of the insulator exposed portion toward the outer peripheral side. Then, the part, which has moved apart from the outer peripheral surface of the insulator exposed portion 310 toward the outer peripheral side, between both points of origin of the discharge spark S is greatly extended toward the downstream side of the air flow by the air flow in the combustion engine. Specifically, in the present embodiment, both points of origin of the discharge spark S move such that the distance in the plug axial direction Z between both points of origin of the discharge spark S is increased, and therefore, the part between both points of origin of the discharge spark S is much more easily greatly extended. Thus, the area of contact between the discharge spark S and an air-fuel mixture is much more easily earned, and performance of ignition of the air-fuel mixture is much more easily ensured.
On other points, features and advantageous effects similar to those of the first embodiment are provided.
The present embodiment is an embodiment in which ventilation holes 40 penetrating an exposed portion 41 from the outside to the inside are formed at the exposed portion 41 as illustrated in
As illustrated in
As illustrated in
Other points are similar to those of the first embodiment.
In the present embodiment, an air flow is, between the center electrode 4 and a ground electrode 2, easily generated toward the outside in the plug radial direction, i.e., a side apart from a surface of an insulator exposed portion 310. That is, in the present embodiment, part of the air flow in a combustion chamber first flows into a radial gap rc from the outside of a spark plug 1 through the ventilation holes 40. Then, the air flow having flowed into the radial gap rc flows out toward the outer peripheral side in the plug radial direction, i.e., the side apart from the insulator exposed portion 310, between the center electrode 4 and the ground electrode 2. Thus, the discharge spark is much more easily extended.
On other points, features and advantageous effects similar to those of the first embodiment are provided.
The present embodiment is an embodiment in which ventilation holes 40 are formed at a first part 411 of a center electrode 4 as illustrated in
As illustrated in
As illustrated in
Other points are similar to those of the sixth embodiment.
In the present embodiment, features and advantageous effects similar to those of the sixth embodiment are provided.
The present embodiment is an embodiment in which the shape of an insulator protruding portion 31 is changed from that of the first embodiment as illustrated in
The insulator protruding portion 31 has an insulator large-diameter portion 311 formed on the base end side in the plug axial direction Z, an insulator small-diameter portion 313 formed on the tip end side of the insulator large-diameter portion 311, and the insulator step portion 312 coupling these portions. The outer diameter of the insulator small-diameter portion 313 is smaller than the outer diameter of the insulator large-diameter portion 311. The insulator step portion 312 is formed at the center of the insulator exposed portion 310 of the insulator protruding portion 31 in the plug axial direction Z. The insulator small-diameter portion 313, the insulator step portion 312, and the insulator large-diameter portion 311 at an outer peripheral surface of the insulator exposed portion 310 are connected to each other in a smooth curved shape. That is, a boundary between the insulator small-diameter portion 313 and the insulator step portion 312 and a boundary between the insulator step portion 312 and the insulator large-diameter portion 311 at the outer peripheral surface of the insulator exposed portion 310 do not define sharp corner portions. At the insulator protruding portion 31, the insulator step portion 312 is formed at a single spot in the plug axial direction Z. That is, the insulator protruding portion 31 in the present embodiment is in a single-step shape. The insulator step portion 312 is at a position on the base end side with respect to an end surface 412a of a second part 412 of a center electrode 4 on the base end side in the plug axial direction Z.
As illustrated in
As illustrated in
Other points are similar to those of the first embodiment.
In the present embodiment, the insulator protruding portion 31 has, as a whole, such a step shape that the outer diameter decreases in a stepwise manner toward the tip end side in the plug axial direction Z. Thus, a path from the second part 412 to the ground electrode 2 along a surface of the insulator exposed portion 310 can be increased. Accordingly, a distance for creeping discharge can be ensured without extension of the insulator exposed portion 310 in the plug axial direction Z, and ignition performance can be enhanced. That is, as illustrated in
Moreover, as viewed in the plug axial direction Z, the exposed portion 41 of the center electrode 4 is formed within the ground electrode 2. Thus, productivity of the spark plug 1 is easily improved. That is, a structure configured such that other components than the housing 11 and the ground electrode 2 are assembled with an insulator 3 is formed in advance, and is inserted into the housing 11 and the ground electrode 2 from the base end side of the housing 11 and the ground electrode 2 so that the spark plug 1 can be easily manufactured. Conversely, in a case where the exposed portion 41 of the center electrode 4 is formed with a larger diameter than that of the ground electrode 2, the exposed portion 41 of the center electrode 4 cannot be inserted into the ground electrode 2. Thus, the insulator 3 not assembled with the exposed portion 41 of the center electrode 4 needs to be first inserted into the ground electrode 2, and thereafter, the exposed portion 41 of the center electrode 4 needs to be assembled with the insulator 3 from the tip end side, for example. This leads to an increase in a manufacturing step.
On other points, features and advantageous effects similar to those of the first embodiment are provided.
The present embodiment is an embodiment in which a basic structure is similar to that of the eighth embodiment but the radial gap rc described in the first embodiment is formed between an outer peripheral surface 31b of an insulator protruding portion 31 and an inner peripheral surface 412b of a second part 412 in a plug radial direction as illustrated in
Note that in the present embodiment, the position of an outer peripheral surface 41b of an exposed portion 41 of a center electrode 4 in the plug radial direction is formed equal to the position of an inner peripheral surface of a ground electrode 2.
Other points are similar to those of the eighth embodiment.
In the present embodiment, an air flow in a combustion chamber also flows into the radial gap rc. Then, the air flow having flowed into the radial gap rc flows out toward the outside in the plug radial direction, i.e., toward a side apart from an insulator exposed portion 310, between the center electrode 4 and the ground electrode 2. Thus, the discharge spark is easily extended away from the insulator exposed portion 310.
On other points, features and advantageous effects similar to those of the eighth embodiment are provided.
The present embodiment is an embodiment in which a basic structure is similar to that of the ninth embodiment but through-holes 20 are formed at a second part 412 of a center electrode 4 as illustrated in
Other points are similar to those of the ninth embodiment.
In the present embodiment, features and advantageous effects similar to those of the sixth and ninth embodiments are provided.
The present embodiment is an embodiment in which a basic structure is similar to that of the ninth embodiment but through-holes 20 are formed at a first part 411 of a center electrode 4 as illustrated in
In the present embodiment, features and advantageous effects similar to those of the seventh and ninth embodiments are provided.
The present embodiment is an embodiment in which the shape of a center electrode 4 is changed from that of the eighth embodiment as illustrated in
In the present embodiment, a part of the center electrode 4 within an insulator protruding portion 31 has an electrode large-diameter portion 42 protruding to an outer peripheral side in a plug radial direction. That is, the electrode large-diameter portion 42 is formed at a tip end portion at the part of the center electrode 4 within the insulator protruding portion 31. In a plug axial direction Z, the electrode large-diameter portion 42 is positioned on a tip end side with respect to an insulator step portion 312. That is, the electrode large-diameter portion 42 is formed inside an insulator small-diameter portion 313 of the insulator protruding portion 31. The tip end side of the electrode large-diameter portion 42 is connected to an exposed portion 41.
The electrode large-diameter portion 42 has a shape rotationally symmetrically about a plug center axis. An electrode expanded-diameter portion 421, an electrode identical-diameter portion 422, and an electrode narrowed-diameter portion 423 are formed in this order from a base end side to the tip end side in the plug axial direction Z at the electrode large-diameter portion 42. The electrode expanded-diameter portion 421 expands the diameter thereof toward the tip end side in the plug axial direction Z. The electrode identical-diameter portion 422 is in a circular columnar shape formed straight in the plug axial direction Z to extend from the expanded-diameter portion 421 to the tip end side in the plug axial direction Z. The electrode narrowed-diameter portion 423 narrows the diameter thereof from the electrode identical-diameter portion 422 to the tip end side in the plug axial direction Z. A diameter change in association with a change in the plug axial direction Z is greater at the electrode narrowed-diameter portion 423 than at the expanded-diameter portion 421.
Other points are similar to those of the eighth embodiment.
In the present embodiment, the electrode large-diameter portion 42 is formed at the part within the insulator protruding portion 31, and therefore, occurrence of pre-ignition is easily prevented. This will be described later.
First, in the present embodiment, the insulator protruding portion 31 has, as a whole, such a step shape that an outer diameter decreases in a stepwise manner toward the tip end side in the plug axial direction Z, and therefore, the thermal capacity of a tip end portion of the insulator protruding portion 31 is decreased and a temperature is easily increased. Accordingly, the temperature of a tip end portion of the center electrode 4 positioned at the periphery of the tip end portion of the insulator protruding portion 31 is also easily increased. Thus, as in the present embodiment, the electrode large-diameter portion 42 is formed at the part within the insulator protruding portion 31 to ensure the thermal capacity of the tip end portion of the center electrode 4, and therefore, a rapid increase in the temperature of the tip end portion of the center electrode 4 can be prevented.
On other points, features and advantageous effects similar to those of the eighth embodiment are provided.
The present embodiment is an embodiment in which the shape of an exposed portion 41 of a center electrode 4 is changed from that of the eighth embodiment as illustrated in
As illustrated in
As illustrated in
As illustrated in
Moreover, the second part 412 extends from one end portion of the first part 411 in the lateral direction X to the base end side. The second part 412 is formed in a plate shape having a thickness in the lateral direction X. Moreover, as illustrated in
The first part 411 and the second part 412 cover part of a corner portion of a tip end portion of the insulator protruding portion 31 in the plug circumferential direction. The second part 412 is formed along an outer peripheral surface of an insulator small-diameter portion 313. Moreover, in the present embodiment, a base-end-side end surface 412a of the second part 412 is formed at a position separated from an insulator step portion 312 toward the tip end side.
As illustrated in
Other points are similar to those of the eighth embodiment.
In the present embodiment, part of the corner portion of the tip end portion of the insulator protruding portion 31 is covered with the first part 411 and the second part 412 of the center electrode 4. Thus, discharge is not generated on the corner portion of the tip end portion of the insulator protruding portion 31, but is formed between the second part 412 of the center electrode 4 and a ground electrode 2. Accordingly, due to the air flow of the air-fuel mixture in the combustion chamber or electrical repulsion, discharge is easily detached from a surface of the insulator protruding portion 31, and is easily extended to a downstream side. Thus, performance of ignition of the air-fuel mixture can be improved.
Further, at least a region, in which the second part 412 is formed, of the insulator protruding portion 31 in the plug circumferential direction has, along the entirety in the plug axial direction Z, such a step shape that an outer diameter decreases in a stepwise manner toward the tip end side in the plug axial direction Z. Thus, a path from the second part 412 to the ground electrode 2 along a surface of an insulator exposed portion 310 can be extended. Thus, a distance for creeping discharge can be ensured without extension of the insulator exposed portion 310 in the plug axial direction Z, and the ignition performance can be enhanced. Further, the area of the section of a tip end portion of the insulator protruding portion 31 perpendicular to the plug axial direction Z is decreased, and therefore, thermal losses due to loss of heat from the flame generated by discharge of the spark plug 1 by the insulator protruding portion 31 can be reduced. This also can improve the performance of ignition of the air-fuel mixture.
Moreover, it is configured such that the air flow of the air-fuel mixture passing through the tip end portion of the spark plug 1 flows, as viewed in the plug axial direction Z, in the direction perpendicular to the arrangement direction (i.e., the lateral direction X) of the second part 412 and the plug center axis. Thus, the air flow in the combustion chamber directly passes between the second part 412 and the ground electrode 2. Accordingly, turbulence of the air flow passing between the second part 412 and the ground electrode 2 can be reduced, and the discharge spark generated between the second part 412 and the ground electrode 2 is much more easily extended.
On other points, features and advantageous effects similar to those of the eighth embodiment are provided.
The present embodiment is an embodiment in which the shape of an insulator protruding portion 31 is changed from that of the thirteenth embodiment as illustrated in
In the present embodiment, the insulator protruding portion 31 has multiple insulator step portions 312. Specifically, the insulator protruding portion 31 has two insulator step portions 312. Two insulator step portions 312 are each arranged at such positions that the insulator exposed portion 310 is trisected in a plug axial direction Z. That is, a base-end-side end surface 412a of a second part 412, two insulator step portions 312, and a tip end surface 21 of a ground electrode 2 are arranged at equal intervals in the plug axial direction Z.
Other points are similar to those of the thirteenth embodiment.
In the present embodiment, the insulator protruding portion 31 has multiple insulator step portions 312. Thus, even when the length of the insulator exposed portion 310 in the plug axial direction Z is shortened, a creepage surface distance from the second part 412 to the ground electrode 2 along a surface of the insulator exposed portion 310 can be ensured. Thus, the size of a spark plug 1 can be reduced without influencing ignition performance.
On other points, features and advantageous effects similar to those of the thirteenth embodiment are provided.
Note that in the present embodiment, an example where the insulator protruding portion 31 has two insulator step portions 312 has been described, but the present disclosure is not limited to such an example. For example, as illustrated in
The present embodiment is an embodiment in which the shape of an insulator protruding portion 31 is changed from that of the thirteenth embodiment as illustrated in
In the present embodiment, an outer peripheral surface of an insulator small-diameter portion 313 is in a corrugated shape (a recessed-raised shape) in a section parallel to a plug axial direction Z. The outer diameter of the insulator small-diameter portion 313 of the present embodiment fluctuates in the plug axial direction Z at a micro level, but the insulator small-diameter portion 313 has a constant outer diameter in the plug axial direction Z at a macro level.
At the macro level, the insulator protruding portion 31 has, along the entirety thereof in the plug axial direction Z, such a step shape that an outer diameter decreases in a stepwise manner toward a tip end side in the plug axial direction Z.
Other points are similar to those of the thirteenth embodiment.
In the present embodiment, the outer peripheral surface of the insulator small-diameter portion 313 is in the corrugated shape. Thus, even when the length of an insulator exposed portion 310 in the plug axial direction Z is shortened, a creepage surface distance from a second part 412 to a ground electrode 2 along a surface of the insulator exposed portion 310 can be ensured. Thus, the size of a spark plug 1 can be reduced without influencing ignition performance.
On other points, features and advantageous effects similar to those of the thirteenth embodiment are provided.
Note that in the present embodiment, only the outer peripheral surface of the insulator small-diameter portion 313 is in the corrugated shape, but the present disclosure is not limited to above. Only an outer peripheral surface of an insulator large-diameter portion 311 may be in a corrugated shape, or both of the outer peripheral surface of the insulator small-diameter portion 313 and the outer peripheral surface of the insulator large-diameter portion 311 may be in the corrugated shape.
The present embodiment is an embodiment in which the shape of an insulator protruding portion 31 is changed from that of the thirteenth embodiment as illustrated in
Moreover, as illustrated in
Other points are similar to those of the thirteenth embodiment.
In the present embodiment, the step shape of the insulator protruding portion 31 is, in the plug circumferential direction, formed only in the region in which the second part 412 is arranged. As described above, the step shape is formed only at a spot necessary for ensuring a creepage surface distance. Thus, excessive decrease in the volume of an insulator 3 and excessive decrease in a thermal capacity can be prevented. Thus, occurrence of pre-ignition is easily prevented.
On other points, features and advantageous effects similar to those of the thirteenth embodiment are provided.
The present embodiment is an embodiment in which the shape of a center electrode 4 is changed from that of the thirteenth embodiment.
As illustrated in
Other points are similar to those of the thirteenth embodiment.
In the present embodiment, the electrode large-diameter portion 42 is formed at the part within the insulator protruding portion 31, and therefore, occurrence of pre-ignition is easily prevented as in the twelfth embodiment.
On other points, features and advantageous effects similar to those of the thirteenth embodiment are provided.
The present disclosure is not limited to each of the above-described embodiments, and can be applied to various embodiments without departing from the gist of the present disclosure.
For example, the fourth embodiment and the fifth embodiment may be combined such that the shape of the center electrode is the shape described in the fourth embodiment and the shape of the ground electrode is the shape described in the fifth embodiment.
Moreover, the exposed portion is formed integrally with the part of the center electrode within the insulator protruding portion, but the present disclosure is not limited to above. The exposed portion and the part of the center electrode within the insulator protruding portion may be separated from each other.
Further, the form in which the ground electrode is joined to the tip end portion of the housing has been described, but the housing and the ground electrode may be integrally formed. That is, part of the housing may be the ground electrode.
In addition, in the sixth embodiment and the seventh embodiment, the form in which four ventilation holes are formed at the exposed portion of the center electrode has been described, but the number of ventilation holes at the exposed portion may be one or more.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-069872 | Mar 2017 | JP | national |
| 2018-052539 | Mar 2018 | JP | national |
The present application is a continuation application of International Application No. PCT/JP2018/013102, filed Mar. 29, 2018, which claims the benefit of priority from earlier Japanese Patent Applications No. 2017-69872, filed Mar. 31, 2017, and No. 2018-52539, filed Mar. 20, 2018, the descriptions of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2018/013102 | Mar 2018 | US |
| Child | 16584998 | US |
