JP7003709B2 - Spark plug - Google Patents

Description

The present invention relates to a spark plug.

Conventionally, in an internal combustion engine, a spark plug that ignites an air-fuel mixture in a combustion chamber has an insulator that maintains an insulating state of a center electrode having a discharge portion. Since the insulator has a relatively low thermal conductivity, it is easily heated by the heat of the burned air-fuel mixture and becomes high in temperature. When the temperature of the insulating insulator becomes high, the heat of the insulating insulator may cause pre-ignition in which the air-fuel mixture before combustion in the cylinder self-ignites. Therefore, for the purpose of efficiently releasing the heat of the insulator to the outside, for example, in the spark plug described in Patent Document 1, the insulator and the housing are used so that the heat received by the insulator can be efficiently dissipated. A heat radiating member is provided to connect the two to form a heat radiating path.

Japanese Unexamined Patent Publication No. 2010-231935

However, the spark plug described in Patent Document 1 is configured to positively dissipate heat even when the internal combustion engine is operated at a low load, that is, when the insulating insulator is at a relatively low temperature. Then, such a spark plug promotes the generation of "smoldering" in which the carbon adhering to the insulating insulator remains without being burned out during low load operation.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a spark plug that suppresses smoldering during low load operation and prevents the occurrence of pre-ignition during high load operation. be.

The present invention is a spark plug, which is located inside a housing (31), an insulating insulator (35) held inside the housing, a ground electrode (33) provided at one end of the housing, and an insulating insulator. It includes a center electrode (40) that forms a spark capable of igniting fuel with the ground electrode, and a heat dissipation unit (50, 67, 68, 71). The heat radiating portion is provided between the housing and the insulating insulator, and a gap (54) can be formed on the combustion chamber (900) side of the engine (90). In the spark plug of the present invention, the size of the gap changes depending on the temperature of the housing or the insulator.

In the spark plug of the present invention, for example, in a low load operation in which the temperature of the engine is relatively low, the amount of expansion due to the heat of the heat radiating portion is relatively small, so that the gap formed by the heat radiating portion becomes large. When the gap becomes large, it becomes difficult for heat to be transferred between the members via the heat radiating portion. When the heat transfer becomes difficult, the temperature of the insulating insulator tends to be high, so that the carbon adhering to the insulating insulator can be burned off, and "smoldering" in the spark plug can be suppressed.

Further, in the spark plug of the present invention, for example, when the engine is operated under a high load in which the temperature of the engine is relatively high, the amount of expansion due to the heat of the heat radiating portion becomes larger than when the engine is operated at a low load. As a result, the gap formed by the heat radiating portion becomes smaller or disappears. As described above, when the gap formed by the heat radiating portion becomes smaller or smaller, heat transfer through the heat radiating portion becomes easier. When the heat is easily transferred, the insulator is less likely to reach a high temperature, so that the heat of the insulator can suppress the pre-ignition of the fuel.
In the first aspect of the present invention, the length (L1, L2) of the portion of the insulating insulator that comes into contact with the combustion gas generated by the combustion of the fuel becomes long if there is a gap, and shortens if the gap disappears.
In the second aspect of the present invention, the heat radiating portion is provided only on either the housing side or the insulating insulator side.

It is a schematic diagram of the engine to which the spark plug according to 1st Embodiment is applied. It is sectional drawing of the spark plug by 1st Embodiment. FIG. 2 is a cross-sectional view taken along the line III-III of FIG. FIG. 2 is an enlarged view of part IV of FIG. It is a partial cross-sectional view in the state of FIG. 4 of the spark plug by 1st Embodiment. It is a partial cross-sectional view of the state which is different from FIG. 4 of the spark plug by 1st Embodiment. It is a partial cross-sectional view in the state of FIG. 6 of the spark plug by 1st Embodiment. It is a partial cross-sectional view of the spark plug by the 2nd Embodiment. It is a partial cross-sectional view of the spark plug according to the 3rd Embodiment. FIG. 3 is a partial cross-sectional view of the spark plug according to the third embodiment in a state different from that shown in FIG. It is a partial cross-sectional view of the spark plug according to 4th Embodiment. It is a partial cross-sectional view of the spark plug according to the 5th Embodiment. 12 is a cross-sectional view taken along the line XIII-XIII of FIG. 12 is a cross-sectional view taken along the line XIV-XIV of FIG. It is a partial cross-sectional view of the spark plug according to the sixth embodiment. FIG. 15 is a cross-sectional view taken along the line XVI-XVI of FIG. FIG. 15 is a sectional view taken along line XVII-XVII of FIG. It is a partial cross-sectional view of the spark plug according to the 7th Embodiment. It is a partial cross-sectional view of the spark plug according to the 7th Embodiment. It is a partial cross-sectional view of the spark plug according to the eighth embodiment. It is a partial cross-sectional view of the spark plug according to the 9th Embodiment. It is an enlarged view of the XXII part of FIG. 21. It is a partial cross-sectional view of the spark plug according to the tenth embodiment. 11 is a partial cross-sectional view of a spark plug according to the eleventh embodiment.

Hereinafter, a plurality of embodiments will be described with reference to the drawings. In the plurality of embodiments, substantially the same parts as those of the other embodiments are designated by the same reference numerals, and the description thereof will be omitted.

(First Embodiment)
The spark plug according to the first embodiment will be described with reference to FIGS. 1 to 7. The spark plug 1 according to the first embodiment is provided in the engine 90 as the "internal combustion engine" shown in FIG. The engine 90 includes an intake system 91, a cylinder 92, a piston 93, a crankshaft 94, an exhaust system 95, and the like. In FIG. 1, the flow of air flowing into the intake system 91 is indicated by an arrow F1, and the flow of exhaust gas flowing out of the exhaust system 95 is indicated by an arrow F2.

The air flowing through the intake passage 910 of the intake system 91 forms an air-fuel mixture when mixed with the fuel injected by the fuel injection valve 911 provided in the intake system 91. The air-fuel mixture flowing through the intake passage 910 flows into the combustion chamber 900 formed by the cylinder 92 and the piston 93 through the intake port 912. The inflow timing of the air-fuel mixture into the combustion chamber 900 is controlled by opening and closing the intake valve 913 provided in the intake port 912.

The air-fuel mixture introduced into the combustion chamber 900 is ignited and burned by the spark plug 1 provided in the cylinder head 921 of the cylinder 92. The piston 93 is pushed down by the increase in the pressure of the combustion chamber 900 due to the combustion of the air-fuel mixture, and the crankshaft 94 connected to the piston 93 rotates. The rotational torque of the crankshaft 94 is transmitted to the outside of the engine 90, and for example, the tires of the vehicle on which the engine 90 is mounted are rotated.

After the air-fuel mixture in the combustion chamber 900 is burned, the exhaust gas is discharged to the exhaust passage 950 through the exhaust port 951 of the exhaust system 95. The exhaust timing of the exhaust gas from the combustion chamber 900 is controlled by opening and closing the exhaust valve 952 provided in the exhaust port 951. The exhaust gas flowing through the exhaust passage 950 is discharged to the atmosphere.

Next, the configuration of the spark plug 1 will be described with reference to FIGS. 2 to 7. The spark plug 1 includes a housing 31, a ground electrode 33, an insulating insulator 35, a center electrode 40, and a heat radiating unit 50. As shown in FIG. 1, the spark plug 1 is inserted into the mounting hole 922 of the cylinder head 921 and screwed to the cylinder head 921. Note that FIG. 2 shows the direction on the combustion chamber side when the spark plug 1 is attached to the cylinder head 921 as the “combustion chamber direction” and the direction opposite to the combustion chamber 900 as the “terminal direction”.

The housing 31 is a tubular metal member and has a housing first cylinder portion 311 and a housing second cylinder portion 312.

The housing first cylinder portion 311 is a portion located on the combustion chamber side of the housing 31 when the spark plug 1 is attached to the cylinder head 921. The housing first cylinder portion 311 has a thread groove that can be screwed to the cylinder head 921 on the outer wall on the outer side in the radial direction. The housing first cylinder portion 311 has a housing protrusion 313 on the inner wall. The housing protrusion 313 is a portion that protrudes inwardly in a radial direction inside the housing first cylinder portion 311. The first cylinder portion 311 of the housing is provided with a ground electrode 33 at an end portion in the direction of the combustion chamber.

The housing second cylinder portion 312 is a portion provided on the terminal side of the housing first cylinder portion 311. The outer diameter of the housing second cylinder portion 312 is larger than the outer diameter of the housing first cylinder portion 311. The housing second cylinder portion 312 is provided with a gasket 314 on the stepped surface of the housing second cylinder portion 312 on the housing first cylinder portion 311 side. The gasket 314 maintains airtightness between the combustion chamber 900 and the outside when the spark plug 1 is attached to the cylinder head 921. The inner diameter of the housing second cylinder portion 312 is larger than the inner diameter of the housing first cylinder portion 311.

The ground electrode 33 is provided at the end of the housing first cylinder portion 311 in the direction of the combustion chamber. The ground electrode 33 is formed in a substantially L shape. The ground electrode 33 is provided so that a predetermined gap is formed between the end portion on the side opposite to the side connected to the housing first cylinder portion 311 and the discharge portion 41 of the center electrode 40.

The insulating insulator 35 is a tubular member located inside the housing 31. The insulating insulator 35 maintains the insulation between the housing 31 and the center electrode 40. The insulating insulator 35 has a small inner diameter portion 351 and a large inner diameter portion 352, a large outer diameter portion 353, and a terminal support portion 354.

The small inner diameter portion 351 is a portion inside the housing first cylinder portion 311 and provided on the combustion chamber side of the insulating insulator 35 when the spark plug 1 is attached to the cylinder head 921. The small inner diameter portion 351 is formed in a cylindrical shape, and a columnar space having a certain cross-sectional area is formed inside. The small inner diameter portion 351 is formed so that the outer diameter increases as the distance from the combustion chamber 900 increases. The end of the small inner diameter portion 351 on the large inner diameter portion 352 side has a stepped surface 355 on the outer wall.

The large inner diameter portion 352 is a portion provided inside the housing first cylinder portion 311 and on the terminal side of the small inner diameter portion 351. The large inner diameter portion 352 is formed in a cylindrical shape, and a columnar space having a constant cross-sectional area larger than the inner cross-sectional area of the small inner diameter portion 351 is formed inside. The large inner diameter portion 352 is formed so that the outer diameter is the same as the outer diameter of the end portion of the small inner diameter portion 351 on the large inner diameter portion 352 side.

The large outer diameter portion 353 is a portion provided inside the second cylinder portion 312 of the housing and on the terminal side of the large inner diameter portion 352. The large outer diameter portion 353 is formed in a cylindrical shape, and a columnar space having a constant cross-sectional area of the same size as the inner cross-sectional area of the large inner diameter portion 352 is formed inside. Further, the large outer diameter portion 353 is formed so that the outer diameter is larger than the outer diameter of the large inner diameter portion 352.

The terminal support portion 354 is a cylindrical portion provided on the terminal side of the large outer diameter portion 353. The terminal support portion 354 is provided with a terminal 39 inside. The terminal support portion 354 supports the terminal 39 in a predetermined position. The outer wall of the terminal support portion 354 has a plurality of grooves formed in the circumferential direction.

The center electrode 40 is a member made of metal located inside the insulating insulator 35 in the direction of the combustion chamber of the spark plug 1. The center electrode 40 has a discharge portion 41, a shaft portion 42, an engagement portion 43, and a connection terminal portion 44.

The discharge unit 41 is a portion provided on the combustion chamber side of the center electrode 40 when the spark plug 1 is attached to the cylinder head 921. The discharge portion 41 is formed so that the tip thereof is relatively thin. When a high voltage is applied through the terminal 39, the discharge unit 41 can generate a spark capable of igniting the air-fuel mixture in the gap between the discharge unit 41 and the ground electrode 33.

The shaft portion 42 is a portion provided on the terminal side of the discharge portion 41. The shaft portion 42 is located inside the small inner diameter portion 351. The shaft portion 42 is formed so that the outer diameter is larger than that of the discharge portion 41.

The engaging portion 43 is a portion provided on the terminal side of the shaft portion 42. The outer diameter of the engaging portion 43 is larger than the outer diameter of the shaft portion 42. The end surface 431 of the engaging portion 43 in the direction of the combustion chamber is formed so as to be able to come into contact with the end surface 356 on the side of the large inner diameter portion 352 of the small inner diameter portion 351. As a result, when the center electrode 40 is inserted into the inside of the insulating insulator 35 from the opening of the terminal support portion 354, the end face 431 and the end face 356 come into contact with each other, and the movement of the center electrode 40 toward the combustion chamber is restricted.

The connection terminal portion 44 is a portion provided on the terminal side of the engaging portion 43. The connection terminal portion 44 is formed so as to be electrically connected to the seal member 36 provided in the insulating insulator 35.

The seal member 36 is provided in the terminal direction of the center electrode 40. In the first embodiment, the sealing member 36 is a mixture of glass powder and copper powder, and while electrically connecting the resistor 37 and the center electrode 40, it is welded to the insulating insulator 35 and insulated from the center electrode 40. The airtightness of the combustion chamber 900 is maintained through the gap between the insulator 35 and the insulator 35.

The resistor 37 is provided in the terminal direction of the seal member 36. The resistor 37 is made of, for example, iron and reduces noise due to the high voltage current supplied through the terminal 39.

The seal member 38 is provided in the terminal direction of the resistor 37. The sealing member 38 is a mixture of glass powder and copper powder, and is welded to the insulating insulator 35 while electrically connecting the resistor 37 and the center electrode 40.

The terminal 39 is provided in the terminal direction of the seal member 38. The terminal 39 is electrically connected to the seal member 38. The end of the terminal 39 on the side opposite to the side connected to the seal member 38 is exposed to the outside of the terminal support portion 354. The terminal 39 receives a high voltage current supplied from the outside.

The heat radiating portion 50 is provided between the housing 31 and the insulating insulator 35. The heat radiating unit 50 has a first heat radiating member 51 and a second heat radiating member 52. The first heat radiating member 51 and the second heat radiating member 52 are made of a material having a linear thermal expansion rate larger than that of the housing 31. The first heat radiating member 51 and the second heat radiating member 52 are made of, for example, aluminum, an aluminum alloy, magnesium, a magnesium alloy, copper, or the like.

As shown in FIG. 2, the virtual line from the direction of the combustion chamber of the spark plug 1 toward the terminal is defined as the central axis CA1. In the present embodiment, the upper end 511 of the first heat radiating member 51 and the upper end 521 of the second heat radiating member 52 are provided at substantially the same position in the direction along the central axis CA1. Further, the lower end 512 of the first heat radiating member 51 and the lower end 522 of the second heat radiating member 52 are provided at substantially the same position in the direction along the central axis CA1. This "substantially the same position" is because the linear thermal expansion coefficient of the first heat radiating member 51 is larger than that of the second heat radiating member 52. For example, in a state where the temperature of the engine 90 is relatively low, for example, during low load operation where the temperature of the center electrode 40 is 500 degrees or less, the heat received from the combustion gas of the spark plug 1 is relatively small, so that the first heat dissipation member The temperatures of 51 and the second heat radiating member 52 are relatively low. When the temperatures of the first heat radiating member 51 and the second heat radiating member 52 are relatively low, the changes in the positions of the upper ends 511, 521 and the lower ends 512, 522 due to the thermal expansion of the first heat radiating member 51 and the second heat radiating member 52 small. On the other hand, in a state where the temperature of the engine 90 is relatively high, for example, during high load operation in which the temperature of the center electrode 40 is higher than 500 degrees, the heat received from the combustion gas of the spark plug 1 is relatively large, so that the first heat dissipation member The temperature of the 51 and the second heat radiating member 52 becomes relatively high. When the temperature of the first heat radiating member 51 and the second heat radiating member 52 becomes relatively high, the changes in the positions of the upper ends 511, 521 and the lower ends 512, 522 due to the thermal expansion of the first heat radiating member 51 and the second heat radiating member 52 are changed. growing. As described above, since the temperatures of the first heat radiating member 51 and the second heat radiating member 52 change depending on the operating conditions of the engine 90, the positional relationship between the upper end 511 and the upper end 521 in the direction along the central axis CA1 and the lower end 512 The positional relationship with the lower end 522 can be changed.

The first heat radiating member 51 is a substantially cylindrical member provided on the housing 31 side when viewed from the second heat radiating member 52. The first heat radiating member 51 is formed so that the thickness in the radial direction is thinner than that of the housing 31. As shown in FIG. 2, the first heat radiating member 51 is arranged along the inner wall surface of the housing 31 from the inner wall surface of the second cylinder portion 312 of the housing to the inner wall surface of the housing protrusion 313. As shown in FIGS. 2 and 4, the first heat radiating member 51 has a stretched portion 513 and a contact portion 514.

The extending portion 513 is formed so as to extend toward the terminal of the first heat radiating member 51. The stretched portion 513 is a substantially tubular portion having a relatively thin radial thickness, and is an inner wall 315 on the terminal side of the housing first cylinder portion 311 and an inner wall 316 on the combustion chamber side of the housing second cylinder portion 312. It is provided along with.

The contact portion 514 is provided on the combustion chamber side of the stretched portion 513. The contact portion 514 is provided along the inner wall 317 on the terminal side of the housing protrusion 313. As shown in FIG. 4, the contact portion 514 has a substantially rectangular cross-sectional shape on the virtual surface including the central axis CA1 of the spark plug 1. Specifically, the inner diameter gradually decreases from the end on the side connected to the stretched portion 513 toward the combustion chamber, and then the inner diameter gradually decreases from the innermost end 515 where the inner diameter becomes the smallest toward the lower end 512. It is formed to be large. The contact portion 514 has a contactable surface 516 as a "first contactable surface" connecting the innermost end 515 and the lower end 512.

The second heat radiating member 52 is a substantially cylindrical member provided on the insulating insulator 35 when viewed from the first heat radiating member 51. As shown in FIG. 2, the second heat radiating member 52 extends from the outer wall surface of the large outer diameter portion 353 of the insulating insulator 35 to the outer wall surface of the small inner diameter portion 351 connected to the combustion chamber side of the stepped surface 355 of the insulating insulator 35. Up to, they are arranged along the outer wall surface of the insulating insulator 35. The second heat dissipation member 52 is made of a material whose linear thermal expansion coefficient is smaller than that of the first heat dissipation member 51. As shown in FIGS. 2 and 4, the second heat radiating member 52 has a stretched portion 523 and a contact portion 524.

The extending portion 523 is formed so as to extend toward the terminal of the second heat radiating member 52. The stretched portion 523 is a substantially cylindrical portion having a relatively thin radial thickness, and as shown in FIG. 2, the stepped surface 355 of the small inner diameter portion 351, the inner wall 357 of the large inner diameter portion 352, and the large outer side. It is provided along the inner wall 358 on the combustion chamber side of the diameter portion 353.

The contact portion 524 is provided on the combustion chamber side of the stretched portion 523. The contact portion 524 is provided along the inner wall 359 on the terminal side of the small inner diameter portion 351. As shown in FIG. 4, the contact portion 524 has a substantially rectangular cross-sectional shape on the virtual surface including the central axis CA1 of the spark plug 1. Specifically, it is formed so that the outer diameter gradually increases toward the combustion chamber from the end on the side connected to the stretched portion 523. The contact portion 524 can be contacted as a "second contactable surface" formed so as to face the contactable surface 516 between the end portion on the side connected to the stretched portion 523 and the lower end 522. It has a surface 525. The contactable surface 525 is formed so as to be parallel to the contactable surface 516.

The packing 53 is a metal annular member arranged between the first heat radiating member 51 and the second heat radiating member 52. As shown in FIGS. 2 and 4, the packing 53 is provided in the vicinity of the lower end 512 of the first heat radiating member 51 and the lower end 522 of the second heat radiating member 52. The packing 53 has a seating surface 531 that comes into contact with the first heat radiating member 51 on the side of the first heat radiating member 51. The packing 53 has a seating surface 532 on the side of the second heat radiating member 52 that comes into contact with the second heat radiating member 52. The packing 53 burns a gap 500 (see FIG. 3) between the first heat radiating member 51 and the second heat radiating member 52 in the terminal direction from the position where the packing 53 is provided from the position where the packing 53 is provided. The gap between the first heat radiating member 51 and the second heat radiating member 52 in the room direction and the space between the housing first cylinder portion 311 and the small inner diameter portion 351 of the insulating porcelain 35, that is, between the so-called gas pocket 15. Maintain airtightness.

Next, the operation of the heat radiating unit 50 in the present embodiment will be described with reference to FIGS. 4 to 7.
During low load operation of the engine 90, as shown in FIG. 4, a gap 54 is formed between the contactable surface 516 and the contactable surface 525. When the engine 90 is operated, heat tends to be trapped in the insulating insulator 35 having poor thermal conductivity. When the heat dissipation path from the insulator 35 during low load operation is indicated by arrows, it can be indicated by arrows H11, H12, and H13.

The arrow H11 is a heat dissipation path in which the heat of the insulating insulator 35 is transmitted in the order of the second heat dissipation member 52, the packing 53, the first heat dissipation member 51, and the housing 31. The arrow H12 is a heat dissipation path through which the heat of the insulating insulator 35 is transferred in the insulating insulator 35. The arrow H13 is a heat dissipation path in which the heat of the insulating insulator 35 is transferred to the contact portion 524 of the second heat dissipation member 52.

FIG. 5 is a cross-sectional view of substantially the lower half of the spark plug 1 during low load operation of the engine 90. As described above, the gap 54 is formed during low load operation of the engine 90. Since the packing 53 is provided between the first heat radiating member 51 and the second heat radiating member 52, the corner portion 533 which is the end portion of the packing 53 on the combustion chamber side and is in contact with the second heat radiating member 52 The intrusion of gas toward the terminal is hindered. As a result, the insulating insulator 35 that receives heat from the combustion gas has a length L1 as the "length of the portion in contact with the combustion gas" from the lower end 350 to the arrangement position of the packing 53.

By operating the engine 90 at a high load and raising the temperature of the engine 90, the gap 54 is narrowed by thermal expansion. Alternatively, the contactable surface 516 and the contactable surface 525 come into contact with each other due to thermal expansion, and the gap 54 disappears. As shown in FIG. 6, when the gap 54 is narrowed, the heat between the contactable surface 516 and the contactable surface 525 due to the decrease in thermal resistance between the first heat dissipation member 51 and the second heat dissipation member 52. It becomes easier to move. When the gap 54 disappears, heat transfer becomes active due to the contact between the contactable surface 516 and the contactable surface 525.

The heat dissipation path from the insulator 35 during high load operation of the engine 90 shown in FIG. 6 can be indicated by arrows H11, H12, H14, and H15. As described with reference to FIG. 4, the arrow H11 is a heat dissipation path in which the heat of the insulating insulator 35 is transmitted in the order of the second heat dissipation member 52, the packing 53, the first heat dissipation member 51, and the housing 31. As described with reference to FIG. 4, the arrow H12 is a heat dissipation path through which the heat of the insulating insulator 35 is transferred in the insulating insulator 35.

Since the arrow H14 has no gap 54 and the contactable surface 516 and the contactable surface 525 are in contact with each other, the heat of the insulating insulator 35 is generated by the contact portion 524 of the second heat radiating member 52 and the first heat radiating member 51. It is a heat dissipation path that transmits in the order of the contact portion 514 and the housing 31. The arrow H15 is a heat dissipation path in which the heat of the second heat dissipation member 52 is transmitted to the contact portion 514 of the first heat dissipation member 51. From these facts, it can be seen that the heat dissipation efficiency of the spark plug 1 is higher in the state of FIG. 6 during the high load operation of the engine 90 than in the state of FIG. 4 during the low load operation of the engine 90.

FIG. 7 is a cross-sectional view of substantially the lower half of the spark plug 1 during high load operation of the engine 90. During high load operation of the engine 90, for example, as shown in FIG. 6, the gap 54 disappears. As a result, as shown in FIG. 7, the insulating insulator 35 that receives heat from the combustion gas has a length L2 from the lower end 350 to the lower end 512 or the lower end 522 of the heat radiating portion 50 as the “length of the portion in contact with the combustion gas”. Will be. The length L2 is shorter than that of L1.

The degree to which the heat received by the spark plug is dissipated is called the "heat value".

The low heat value plug has a long so-called insulator leg, and the surface area and the volume of the gas pocket that receive heat from the combustion gas are large. In addition, since the heat dissipation path from the insulator leg to the housing is long, heat dissipation is small and the temperature of the center electrode tends to rise. Specifically, when the temperature of the center electrode is, for example, about 500 degrees or less, free carbon generated when the fuel is not completely burned adheres to the surface of the insulating insulator (smoldering). When free carbon adheres to the surface of the insulating insulator, the insulation between the insulating insulator and the housing is lowered and electricity leakage is likely to occur, so that the ignition in the gap becomes incomplete and causes an ignition error. In that respect, since the temperature of the center electrode of the low heat value plug tends to rise, it easily reaches the self-cleaning temperature, which is the temperature at which carbon is naturally burned out by combustion even at a low speed, and carbon does not easily adhere to the insulating insulator. Here, as an example of the temperature at which smoldering occurs, about 500 degrees or less is mentioned, but the temperature at which smoldering occurs differs depending on the type of engine and is not limited to this temperature.

Further, the high heat value plug has a short insulator leg, and has a small surface area and a small volume of gas pockets that receive heat from combustion gas. In addition, since the heat dissipation path is short, there is a lot of heat dissipation, and the temperature of the center electrode does not rise easily. Specifically, when the temperature of the center electrode is, for example, about 950 degrees or higher, pre-ignition (pre-ignition) occurs in which the electrode of the spark plug becomes a heat source and ignites even if sparks do not fly. For this reason, the output may decrease, leading to melting of the electrodes and damage to the insulator. The high heat value plug does not easily raise the temperature of the center electrode and does not easily reach the pre-ignition temperature. Here, as an example of the temperature at which pre-ignition occurs, about 950 degrees or higher is mentioned, but the temperature at which pre-ignition occurs differs depending on the type of engine and is not limited to this temperature.

(A) The spark plug 1 according to the first embodiment has a size of a gap 54 formed by a heat radiating portion 50 provided between the insulating insulator 35 and the housing 31 according to the temperature of the housing 31 or the insulating insulator 35. Changes. The change in the size of the gap 54 includes a state in which the gap 54 is completely closed.

In the spark plug 1 according to the first embodiment, the amount of linear expansion of the first heat radiating member 51 and the second heat radiating member 52 during low load operation becomes small. Then, the gap 54 between the first heat radiating member 51 and the second heat radiating member 52 becomes relatively large. When the gap 54 becomes large, the thermal resistance between the first heat radiating member 51 and the second heat radiating member 52 becomes large, and it becomes difficult for heat transfer to occur. That is, it can be said that the spark plug 1 is a so-called low heat value plug because the degree of heat dissipation is relatively small. This makes it difficult for the heat of the insulating insulator 35 to be released, and it becomes possible to burn off the carbon adhering to the insulating insulator 35 during low load operation and suppress so-called “smoldering”.

Further, in the spark plug 1 according to the first embodiment, the amount of linear expansion of the first heat radiating member 51 and the second heat radiating member 52 during high load operation becomes large. Then, the gap 54 between the first heat radiating member 51 and the second heat radiating member 52 that expands linearly becomes smaller, and in some cases, the gap 54 disappears. As described above, when the gap 54 between the first heat radiating member 51 and the second heat radiating member 52 becomes smaller, the thermal resistance between the first heat radiating member 51 and the second heat radiating member 52 becomes smaller, and heat transfer is performed. Become so. That is, it can be said that the spark plug 1 is a so-called high heat value plug because the degree of heat dissipation is relatively large. As a result, the heat of the insulating insulator 35 is easily released, and it becomes possible to suppress the pre-ignition of the air-fuel mixture due to the heat during high-load operation.

As described above, the spark plug 1 makes it difficult to release the heat of the insulating insulator 35 during low load operation, and makes it easy to release the heat of the insulating insulator 35 during high load operation. As a result, the spark plug 1 can prevent the occurrence of pre-ignition during high-load operation while suppressing "smoldering" during low-load operation.

(B) In the spark plug 1 according to the first embodiment, the size of the gap 54 changes due to the thermal expansion or contraction of the heat radiating portion 50. Since the heat shrinks at a low temperature, the gap 54 is relatively large, and at a high temperature, the gap 54 becomes narrow due to thermal expansion, whereby the thermal resistance from the insulating insulator 35 toward the housing 31 changes. Further, at a low temperature, since the gap 54 is large, the thermal resistance is large and the degree of heat drawing is small. On the other hand, at high temperatures, the gap 54 is small or zero, so that the thermal resistance is small and the degree of heat drawing is large. This makes it easier for the spark plug 1 to maintain the temperature of the engine 90 during low-temperature, low-load operation, while efficiently dissipating the heat of the engine 90 during high-temperature, high-load operation.

(C) In the spark plug 1 according to the first embodiment, the length of the insulating insulator 35 that comes into contact with the combustion gas of the ignited fuel becomes longer as the gap 54 becomes larger, and becomes shorter as the gap 54 becomes smaller. The length of the insulating insulator 35 in contact with the combustion gas changes depending on the presence or absence of the gap 54. If there is a gap 54 as in low load operation, the length of the insulating insulator 35 that comes into contact with the combustion gas becomes long, and the spark plug 1 tends to be a so-called low heat value plug. When the gap 54 disappears as in high load operation, the length of the insulating insulator 35 in contact with the combustion gas becomes short, and the spark plug 1 tends to become a so-called high heat value plug. As a result, the spark plug 1 can change the degree of heat reception for the combustion gas depending on the presence or absence of the gap 54 formed by the heat radiating portion 50.

(D) In the spark plug 1 according to the first embodiment, the heat radiating portion 50 has a first heat radiating member 51 provided on the housing 31 side and a second heat radiating member 52 provided on the insulating insulator 35 side. At this time, the gap 54 is formed between the first heat radiating member 51 and the second heat radiating member 52. As a result, the gap 54 is formed by the first heat radiating member 51 and the second heat radiating member 52 which are easily thermally expanded or contracted, so that not only the size of the gap 54 can be easily designed, but also the size of the gap 54 can be changed. It can be made relatively large.

(E) Further, in the spark plug 1 according to the first embodiment, the linear thermal expansion rate of the first heat radiating member 51 is larger than the linear thermal expansion rate of the second heat radiating member 52. As a result, when the engine 90 is operated at a low temperature, the gap 54 between the first heat radiating member 51 and the second heat radiating member 52 becomes large, and when the engine 90 is operated at a higher temperature than at a low temperature, the first heat radiating member 51 is thermally expanded. (Ii) By abutting the heat radiating member 52, the gap 54 becomes smaller. Therefore, in the spark plug 1, the change in the size of the gap 54 can be further increased.

(Second embodiment)
Next, the spark plug according to the second embodiment will be described with reference to FIG. In the second embodiment, the shape of the first heat dissipation member is different from that in the first embodiment.

The heat radiating portion 50 included in the spark plug 2 according to the second embodiment is provided between the housing 31 and the insulating insulator 35, and has a first heat radiating member 55 and a second heat radiating member 52. The first heat dissipation member 55 is made of a material having a linear thermal expansion coefficient larger than that of the housing 31.

In the housing 31 of the spark plug 2, the housing first cylinder portion 311 has a housing protrusion 323 on the inner wall. The housing protrusion 323 has a guide surface 324 that abuts on the contact surface 557 of the parallel portion 555 of the first heat radiating member 55, which will be described later, and a radial outer end surface 559 of the contact portion 554 of the first heat radiating member 55. It has a contact surface 325 that comes into contact with. The guide surface 324 is formed so as to be parallel to the seat surface 531 of the packing 53.

The first heat radiating member 55 is a substantially cylindrical member provided on the housing 31 side when viewed from the second heat radiating member 52. The first heat radiating member 55 is formed so that the thickness in the radial direction is thinner than that of the housing 31. The first heat radiating member 55 is arranged along the inner wall surface of the housing 31 from the inner wall surface of the second cylinder portion 312 of the housing to the inner wall surface of the housing protrusion 323. The first heat radiating member 55 is provided at a position where the upper end thereof is substantially the same as the upper end 521 of the second heat radiating member 52 in the direction along the central axis of the spark plug 2. Further, as shown in FIG. 8, the first heat radiating member 55 is provided at a position where the lower end 552 is substantially the same as the lower end 522 of the second heat radiating member 52 in the direction along the central axis of the spark plug 2.

The first heat radiating member 55 has a stretched portion 513, a parallel portion 553, and a contact portion 554.
The parallel portion 553 is provided on the combustion chamber side of the stretched portion 513. The parallel portion 553 has a contact surface 557 that abuts on the guide surface 324 of the housing protrusion 323 and a contact surface 558 that abuts on the seat surface 531 of the packing 53. The contact surface 551 and the contact surface 558 are formed so as to be parallel to each other. In the present embodiment, the seat surface 531 and the seat surface 532 of the packing 53 are formed in parallel. The displacement of the parallel portion 553 when the first heat radiating member 55 thermally expands or contracts is guided by the guide surface 324.

The contact portion 554 is provided on the combustion chamber side of the parallel portion 553. The contact portion 554 is provided along the contact surface 325 of the housing protrusion 323. As shown in FIG. 8, the contact portion 554 has a substantially rectangular cross-sectional shape on the virtual surface including the central axis of the spark plug 2. Specifically, it is formed so that the inner diameter gradually increases from the innermost end 555 located at the end on the side connected to the parallel portion 553 toward the lower end 552. The contact portion 554 has a contactable surface 556 as a "first contactable surface" connecting the innermost end 555 and the lower end 552. The contactable surface 556 is formed so as to be parallel to the contactable surface 525 of the second heat radiating member 52. During low load operation of the engine 90, a gap 54 is formed between the contactable surface 556 and the contactable surface 525.

In the spark plug 2 according to the second embodiment, a gap 54 is formed between the contactable surface 556 of the first heat radiating member 55 and the contactable surface 525 of the second heat radiating member 52 during low load operation of the engine 90. .. Further, during high load operation of the engine 90, the gap 54 becomes small, and in some cases, the gap 54 disappears. As a result, the second embodiment has the same effect as the first embodiment.

Further, the spark plug 2 according to the second embodiment is formed so that the guide surface 324 and the seat surface 531 with which the parallel portion 553 of the first heat radiating member 55 abuts are parallel to each other. As a result, it is possible to prevent the packing 53 from being displaced even if the parallel portion 553 is displaced due to thermal expansion or contraction.

(Third embodiment)
Next, the spark plug according to the third embodiment will be described with reference to FIGS. 9 and 10. In the third embodiment, the shapes of the abuttable surface of the first heat radiating member and the abuttable surface of the second heat radiating member are different from those of the first embodiment.

The heat radiating portion 50 included in the spark plug 3 according to the third embodiment is provided between the housing 31 and the insulating insulator 35, and has a first heat radiating member 56 and a second heat radiating member 57. The first heat radiating member 56 and the second heat radiating member 57 are made of a material having a linear thermal expansion rate larger than that of the housing 31. In the present embodiment, the upper end of the first heat radiating member 56 and the upper end of the second heat radiating member 57 are provided at substantially the same position in the direction along the central axis of the spark plug 3. Further, as shown in FIGS. 9 and 10, the lower end 562 of the first heat radiating member 56 and the lower end 572 of the second heat radiating member 57 are provided at substantially the same positions in the direction along the central axis of the spark plug 3.

The first heat radiating member 56 is a substantially cylindrical member provided on the housing 31 side when viewed from the second heat radiating member 57. The first heat radiating member 56 is formed so that the thickness in the radial direction is thinner than that of the housing 31. The first heat radiating member 56 is arranged along the inner wall surface of the housing 31 from the inner wall surface of the second cylinder portion 312 of the housing to the inner wall surface of the housing protrusion 313. The first heat dissipation member 56 has a stretched portion 513 and a contact portion 564.

The contact portion 564 is provided on the combustion chamber side of the stretched portion 513. The contact portion 564 is provided along the inner wall 317 on the terminal side of the housing protrusion 313. As shown in FIGS. 9 and 10, the contact portion 564 has a substantially rectangular cross-sectional shape on the virtual surface including the central axis of the spark plug 3. The contact portion 564 is formed so that the inner diameter gradually increases from the innermost end 565, which has the smallest inner diameter, toward the lower end 562. The contact portion 564 has a contactable surface 566 as a "first contactable surface" connecting the innermost end 565 and the lower end 562. As shown in FIGS. 9 and 10, the contactable surface 566 is formed in an uneven shape.

The second heat radiating member 57 is a substantially cylindrical member provided on the insulating insulator 35 when viewed from the first heat radiating member 56. The second heat radiating member 57 extends from the outer wall surface of the large outer diameter portion 353 of the insulating insulator 35 to the outer wall surface of the small inner diameter portion 351 connected to the combustion chamber side of the stepped surface 355 of the insulating insulator 35. It is arranged along the wall surface. The second heat dissipation member 57 is made of a material whose linear thermal expansion coefficient is smaller than that of the first heat dissipation member 56. The second heat radiating member 57 has a stretched portion 523 and a contact portion 574.

The contact portion 574 is provided on the combustion chamber side of the stretched portion 523. The contact portion 574 is provided along the inner wall 359 on the terminal side of the small inner diameter portion 351. The contact portion 574 has a substantially rectangular cross-sectional shape on a virtual surface including the central axis of the spark plug 3. The contact portion 574 can be contacted as a "second contactable surface" formed so as to face the contactable surface 566 between the end portion on the side connected to the stretched portion 523 and the lower end 572. It has a surface 575. The contactable surface 575 is formed in an uneven shape so as to be able to mesh with the unevenness of the contactable surface 566.

FIG. 10 is a diagram showing a heat dissipation path from the insulating insulator 35 during high load operation of the engine 90. During low load operation of the engine 90, as shown in FIG. 9, a gap 54 is formed between the contactable surface 566 of the first heat radiating member 56 and the contactable surface 575 of the second heat radiating member 57. ..
By operating the engine 90 at a high load and heating the engine 90 to a high temperature, the gap 54 is narrowed by the thermal expansion of each of the first heat radiating member 56 and the second heat radiating member 57. Alternatively, the contactable surface 566 and the contactable surface 575 are in contact with each other due to thermal expansion and are in a state of meshing with each other. When the gap 54 is narrowed, the decrease in thermal resistance facilitates heat transfer between the contactable surface 566 and the contactable surface 575. When the gap 54 disappears, heat transfer becomes more active due to the contact between the contactable surface 566 and the contactable surface 575.

The heat dissipation path is indicated by arrows H31, H32, H33, H34. The arrow H31 is a heat dissipation path in which the heat of the insulating insulator 35 is transmitted in the order of the second heat dissipation member 57, the packing 53, the first heat dissipation member 56, and the housing 31. The arrow H32 is a heat dissipation path through which the heat of the insulating insulator 35 is transferred in the insulating insulator 35. The arrow H33 is a heat dissipation path in which the heat of the insulating insulator 35 is transmitted in the order of the contact portion 574 of the second heat dissipation member 57, the first heat dissipation member 56, and the housing 31. The arrow H34 is a heat dissipation path in which the heat of the insulating insulator 35 is transferred to the contact portion 574 of the second heat dissipation member 57 and the first heat dissipation member 56 in this order.

In the spark plug 3 according to the third embodiment, a gap 54 is formed between the contactable surface 566 of the first heat radiating member 56 and the contactable surface 575 of the second heat radiating member 57 during low load operation of the engine 90. .. Further, during high load operation of the engine 90, the gap 54 becomes small, and in some cases, the gap 54 disappears. As a result, the third embodiment has the same effect as the first embodiment.

Further, in the spark plug 3 according to the third embodiment, the abuttable surface 566 of the first heat radiating member 56 and the abuttable surface 575 of the second heat radiating member 57 are formed in an uneven shape so as to be able to mesh with each other. As a result, when the first heat radiating member 56 and the second heat radiating member 57 come into contact with each other, the heat transfer area between the first heat radiating member 56 and the second heat radiating member 57 becomes large. The heat dissipation of H34 can be promoted. Therefore, in the third embodiment, the heat of the insulator 35 can be further efficiently transferred during the high load operation of the engine 90.

(Fourth Embodiment)
Next, the spark plug according to the fourth embodiment will be described with reference to FIG. In the fourth embodiment, the shape of the first heat dissipation member is different from that of the first embodiment.

The heat radiating portion 50 included in the spark plug 4 according to the fourth embodiment is provided between the housing 31 and the insulating insulator 35, and has a first heat radiating member 59 and a second heat radiating member 52. The first heat dissipation member 59 is made of a material having a linear thermal expansion coefficient larger than that of the housing 31.

The first heat radiating member 59 is a substantially cylindrical member provided on the housing 31 side when viewed from the second heat radiating member 52. The first heat radiating member 59 is formed so that the thickness in the radial direction is thinner than that of the housing 31. The first heat radiating member 59 is arranged along the inner wall surface of the housing 31 from the inner wall surface of the second cylinder portion 312 of the housing to the inner wall surface of the housing protrusion 323. The first heat radiating member 59 is provided at a position where the upper end thereof is substantially the same as the upper end 521 of the second heat radiating member 52 in the direction along the central axis of the spark plug 4. Further, the first heat radiating member 59 is provided at a position where the lower end thereof is substantially the same as the lower end 522 of the second heat radiating member 52 in the direction along the central axis of the spark plug 4.

The first heat radiating member 59 has a stretched portion 513 and a contact portion 594.

The contact portion 594 is provided on the combustion chamber side of the stretched portion 513. The contact portion 594 is provided along the inner wall 317 on the terminal side of the housing protrusion 313. The contact portion 594 has a contactable surface 596 as a "first contactable surface" capable of contacting the contactable surface 525 of the second heat dissipation member 52. As shown in FIG. 11, the abuttable surface 596 has eight notch-shaped recesses 597 at substantially equal intervals in the circumferential direction. During low load operation of the engine 90, as shown in FIG. 11, a gap 54 is formed between the contactable surface 596 and the contactable surface 525.

In the spark plug 4 according to the fourth embodiment, a gap 54 is formed between the contactable surface 596 of the first heat radiating member 59 and the contactable surface 525 of the second heat radiating member 52 during low load operation of the engine 90. .. Further, during high load operation of the engine 90, the gap 54 becomes small, and in some cases, the gap 54 disappears. As a result, the fourth embodiment has the same effect as the first embodiment.

Further, in the spark plug 4 according to the fourth embodiment, the contact area between the first heat radiating member 59 and the second heat radiating member 52 can be adjusted by adjusting the shape of the recess 597. Thereby, the amount of heat transfer between the first heat radiating member 59 and the second heat radiating member 52, that is, the amount of heat radiated from the spark plug 4 can be adjusted. Therefore, in the fourth embodiment, the heat value of the spark plug 4 can be adjusted.

(Fifth Embodiment)
Next, the spark plug according to the fifth embodiment will be described with reference to FIGS. 12 to 14. In the fifth embodiment, the shape of the first heat dissipation member is different from that of the first embodiment.

The heat radiating portion 50 included in the spark plug 5 according to the fifth embodiment is provided between the housing 31 and the insulating insulator 35, and has a first heat radiating member 61 and a second heat radiating member 52. The first heat dissipation member 61 is made of a material having a linear thermal expansion coefficient larger than that of the housing 31.

The first heat radiating member 61 is a substantially cylindrical member provided on the housing 31 side when viewed from the second heat radiating member 52. The first heat radiating member 61 is formed so that the thickness in the radial direction is thinner than that of the housing 31. The first heat radiating member 61 is arranged along the inner wall surface of the housing 31 from the inner wall surface of the second cylinder portion 312 of the housing to the inner wall surface of the housing protrusion 323. The first heat radiating member 61 is provided at a position where the upper end thereof is substantially the same as the upper end 521 of the second heat radiating member 52 in the direction along the central axis of the spark plug 5. Further, the first heat radiating member 61 is provided at a position where the lower end 612 is substantially the same as the lower end 522 of the second heat radiating member 52 in the direction along the central axis of the spark plug 5.

The first heat dissipation member 61 has a stretched portion 513 and a plurality of contact portions 614.

The contact portion 614 is provided on the combustion chamber side of the stretched portion 513. As shown in FIG. 12, the contact portion 614 is provided along the inner wall 317 on the terminal side of the housing protrusion 313. As shown in FIG. 13, the contact portion 614 has a cross-sectional shape on a virtual plane perpendicular to the central axis CA5 of the spark plug 5 formed in a substantially arc shape centered on a point on the central axis CA5. In the present embodiment, four contact portions 614 are provided at equal intervals about a point on the central axis CA5. Each of the plurality of contact portions 614 has a contactable surface 616 as a "first contactable surface" facing the contactable surface 525 of the second heat radiating member 52. During low load operation of the engine 90, as shown in FIG. 13, a gap 54 is formed between the contactable surface 616 and the contactable surface 525.

In the present embodiment, as shown in FIG. 14, the stretched portion 513 has a cross-sectional shape on a virtual plane perpendicular to the central axis CA5 formed in a substantially annular shape centered on a point on the central axis CA5.

In the spark plug 5 according to the fifth embodiment, a gap 54 is formed between the contactable surface 616 of the first heat radiating member 61 and the contactable surface 525 of the second heat radiating member 52 during low load operation of the engine 90. .. Further, during high load operation of the engine 90, the gap 54 becomes small, and in some cases, the gap 54 disappears. As a result, the fifth embodiment has the same effect as the first embodiment.

Further, in the spark plug 5 according to the fifth embodiment, the first heat radiating member 61 has a contact portion 614 divided into four. Each of the four contact portions 614 has a contactable surface 616 capable of forming a gap 54 with the contactable surface 525 of the second heat radiating member 52. Thereby, by adjusting the shape of the contact portion 614, the contact area between the first heat radiating member 61 and the second heat radiating member 52 can be adjusted. In addition, the degree of freedom in designing the heat dissipation state of the spark plug 5 can be increased.

(Sixth Embodiment)
Next, the spark plug according to the sixth embodiment will be described with reference to FIGS. 15 to 17. In the sixth embodiment, the shape of the first heat dissipation member is different from that of the first embodiment.

The heat radiating portion 50 included in the spark plug 6 according to the sixth embodiment is provided between the housing 31 and the insulating insulator 35, and has a plurality of first heat radiating members 66 and a second heat radiating member 52. Each of the plurality of first heat radiating members 66 is made of a material having a linear thermal expansion coefficient larger than that of the housing 31.

The first heat radiating member 66 is provided on the housing 31 side when viewed from the second heat radiating member 52. As shown in FIGS. 16 and 17, each of the first heat radiating members 66 has a cross-sectional shape on a virtual plane perpendicular to the central axis CA6 of the spark plug 6 having a substantially arc shape centered on a point on the central axis CA6. It is formed. In the present embodiment, four first heat radiating members 66 are provided at equal intervals about a point on the central axis CA6. The first heat radiating member 66 is formed so that the thickness in the radial direction is thinner than that of the housing 31. The first heat radiating member 66 is arranged along the inner wall surface of the housing 31 from the inner wall surface of the second cylinder portion 312 of the housing to the inner wall surface of the housing protrusion 323. The first heat radiating member 66 is provided at a position where the upper end thereof is substantially the same as the upper end 521 of the second heat radiating member 52 in the direction along the central axis of the spark plug 5. Further, the first heat radiating member 66 is provided at a position where the lower end 662 is substantially the same as the lower end 522 of the second heat radiating member 52 in the direction along the central axis of the spark plug 5.

Each of the first heat radiating members 66 has a stretched portion 663 and a contact portion 664.

The extending portion 663 is formed so as to extend toward the terminal of the first heat radiating member 66. As shown in FIG. 17, the stretched portion 663 has a smaller radial thickness than the radial thickness of the housing first cylinder portion 311. The extension portion 663 is provided along the inner wall 315 on the terminal side of the housing first cylinder portion 311 and the inner wall 316 on the combustion chamber side of the housing second cylinder portion 312. The stretched portion 663 forms a gap 500 with the second heat radiating member 52 on the terminal side from the portion abutting on the packing 53.

The contact portion 664 is provided on the combustion chamber side of the stretched portion 663. As shown in FIG. 15, the contact portion 664 is provided along the inner wall 317 on the terminal side of the housing protrusion 313. As shown in FIG. 16, the contact portion 664 has a contactable surface 666 as a "first contactable surface" facing the contactable surface 525 of the second heat radiating member 52. During low load operation of the engine 90, as shown in FIG. 16, a gap 54 is formed between the contactable surface 666 and the contactable surface 525.

In the spark plug 6 according to the sixth embodiment, a gap 54 is formed between the contactable surface 666 of the first heat radiating member 66 and the contactable surface 525 of the second heat radiating member 52 during low load operation of the engine 90. .. Further, during high load operation of the engine 90, the gap 54 becomes small, and in some cases, the gap 54 disappears. As a result, the sixth embodiment has the same effect as the first embodiment.

Further, the spark plug 5 according to the sixth embodiment has four first heat radiating members 66. Each of the four first heat radiating members 66 has a contactable surface 666 capable of forming a gap 54 with the contactable surface 525 of the second heat radiating member 52. Thereby, by adjusting the shape of the first heat radiating member 66, the contact area between the first heat radiating member 66 and the second heat radiating member 52 can be adjusted. In addition, the degree of freedom in designing the heat dissipation state of the spark plug 6 can be increased.

(Seventh Embodiment)
Next, the spark plug according to the seventh embodiment will be described with reference to FIGS. 18 and 19. In the seventh embodiment, the configuration of the heat radiating portion is different from that in the first embodiment.

The heat radiating member 67 as a "heat radiating portion" included in the spark plug 7 according to the seventh embodiment is one cylindrical member provided between the housing 31 and the insulating insulator 35. The heat radiating member 67 is made of, for example, a material such as aluminum, an aluminum alloy, magnesium, a magnesium alloy, or copper, which has a larger linear thermal expansion rate than the linear thermal expansion rate of the housing 31.

The heat radiating member 67 is provided on the outer wall surface of the insulating insulator 35 from the outer wall surface of the large outer diameter portion 353 of the insulating insulator 35 to the outer wall surface of the small inner diameter portion 351 connected to the combustion chamber side of the stepped surface 355 of the insulating insulator 35. It is arranged along. In the present embodiment, the upper end of the heat radiating member 67 is located on the outer wall surface of the large outer diameter portion 353. Further, the lower end 672 of the heat radiating member 67 is located on the outer wall surface of the end portion of the small inner diameter portion 351 on the large inner diameter portion 352 side. The heat radiating member 67 has a stretched portion 673 and a contact portion 674.

The extending portion 673 is formed in the heat radiating member 67 so as to extend toward the terminal. The stretched portion 673 is a substantially cylindrical portion having a relatively thin radial thickness, and has a stepped surface 355 of the small inner diameter portion 351, an inner wall 357 of the large inner diameter portion 352, and a combustion chamber side of the large outer diameter portion 353. It is provided along the inner wall 358 of the.

The contact portion 674 is provided on the combustion chamber side of the stretched portion 673. The contact portion 674 is provided along the inner wall 359 on the terminal side of the small inner diameter portion 351. As shown in FIG. 19, the contact portion 674 has a substantially rectangular cross-sectional shape on the virtual surface including the central axis of the spark plug 7. Specifically, it is formed so that the outer diameter becomes constant to some extent from the end on the side connected to the stretched portion 673 toward the combustion chamber. The contact portion 674 has a contactable surface 675 formed so as to face the radially inner end surface 318 of the housing protrusion 313 between the end portion on the side connected to the extension portion 673 and the lower end portion 672. .. The contactable surface 675 is formed so as to be parallel to the end surface 318. During low load operation of the engine 90, as shown in FIG. 19, a gap 54 is formed between the contactable surface 675 and the end surface 318.

The seat surface 531 of the packing 53 is in contact with the inner wall 317 of the housing protrusion 313. The seat surface 532 of the packing 53 is in contact with the extended portion 673 of the heat radiating member 67.

In the spark plug 7 according to the seventh embodiment, a gap 54 is formed between the contactable surface 675 of the heat radiating member 67 and the end surface 318 of the housing protrusion 313 during low load operation of the engine 90. Further, during high load operation of the engine 90, the gap 54 becomes small, and in some cases, the gap 54 disappears. As a result, the seventh embodiment has the same effect as the effects (a) to (c) of the first embodiment.

In the spark plug 7 according to the seventh embodiment, the heat radiating member 67 provided along the insulating insulator 35 thermally expands or contracts due to the temperature change of the insulating insulator 35. At this time, since the temperature of the insulating insulator 35 tends to be relatively high, the contact portion 674 of the heat radiating member 67 tends to thermally expand. Thereby, the change in the size of the gap 54 can be made relatively large.

Further, in the spark plug 7 according to the seventh embodiment, the deformation of the contact portion 674 due to thermal expansion or contraction is radial outward deformation when viewed from the insulating insulator 35. As a result, the insulating insulator 35 is less likely to be pressed, so that damage to the insulating insulator 35 can be prevented.

Further, in the spark plug 7 according to the seventh embodiment, the heat radiating member 67 is composed of one member. As a result, the heat value of the spark plug 7 can be adjusted with a small number of parts.

(Eighth embodiment)
Next, the spark plug according to the eighth embodiment will be described with reference to FIG. In the eighth embodiment, the configuration of the heat radiating portion is different from that of the first embodiment.

The heat radiating member 68 as the "heat radiating portion" included in the spark plug 8 according to the eighth embodiment is one cylindrical member provided between the housing 31 and the insulating insulator 35. The heat radiating member 68 is made of, for example, a material such as aluminum, an aluminum alloy, magnesium, a magnesium alloy, or copper, which has a larger linear thermal expansion rate than the linear thermal expansion rate of the housing 31.

In the housing 31 of the spark plug 8, the housing first cylinder portion 311 has a housing protrusion 328 on the inner wall. As shown in FIG. 20, the housing protrusion 328 is formed so that the cross-sectional shape on the virtual plane including the central axis of the spark plug 8 is substantially triangular. The seat surface 531 of the packing 53 is in contact with the inner wall 327 on the terminal side of the housing protrusion 328. The end surface 329 of the housing protrusion 328 on the combustion chamber side is formed so as to face the contactable surface 685 of the contact portion 684 of the heat dissipation member 68, which will be described later. The end face 329 has a larger area than the end face 318 of the housing protrusion 313 of the seventh embodiment.

The heat radiating member 68 is provided on the outer wall surface of the insulating insulator 35 from the outer wall surface of the large outer diameter portion 353 of the insulating insulator 35 to the outer wall surface of the small inner diameter portion 351 connected to the combustion chamber side of the stepped surface 355 of the insulating insulator 35. It is arranged along. In the present embodiment, the upper end of the heat radiating member 68 is located on the outer wall surface of the large outer diameter portion 353. Further, the lower end 682 of the heat radiating member 68 is located on the outer wall surface of the end portion of the small inner diameter portion 351 on the large inner diameter portion 352 side. The heat radiating member 68 has a stretched portion 683 and a contact portion 684.

The extending portion 683 is formed in the heat radiating member 68 so as to extend toward the terminal. The stretched portion 683 is a substantially cylindrical portion having a relatively thin radial thickness, and has a stepped surface 355 of the small inner diameter portion 351, an inner wall 357 of the large inner diameter portion 352, and a combustion chamber side of the large outer diameter portion 353. It is provided along the inner wall 358 of the.

The contact portion 684 is provided on the combustion chamber side of the stretched portion 683. The contact portion 684 is provided along the inner wall 359 on the terminal side of the small inner diameter portion 351. As shown in FIG. 20, the contact portion 684 has a substantially rectangular cross-sectional shape on the virtual surface including the central axis of the spark plug 8. Specifically, it is formed so that the outer diameter increases toward the combustion chamber from the end on the side connected to the stretched portion 683. The abutting portion 684 has an abuttable surface 685 formed so as to face the end surface 329 of the housing protrusion 328 between the end portion on the side connected to the extending portion 683 and the lower end portion 682. The contactable surface 685 is formed so that the area is larger than the area of the contactable surface 675 of the heat radiation member 67 of the seventh embodiment and is parallel to the end surface 329. During low load operation of the engine 90, as shown in FIG. 20, a gap 54 is formed between the contactable surface 685 and the end surface 329.

In the spark plug 8 according to the eighth embodiment, a gap 54 is formed between the contactable surface 685 of the heat radiating member 68 and the end surface 329 of the housing protrusion 328 during low load operation of the engine 90. Further, during high load operation of the engine 90, the gap 54 becomes small, and in some cases, the gap 54 disappears. As a result, the eighth embodiment has the same effect as the seventh embodiment.

Further, in the spark plug 7 according to the eighth embodiment, the end surface 329 has a larger area than the end surface 318 of the housing protrusion 313 of the seventh embodiment, and the contactable surface 685 has an area of the heat dissipation member of the seventh embodiment. It is larger than the area of the contactable surface 675 of 67. As a result, when the contactable surface 685 and the end surface 329 come into contact with each other, the contact area between the heat radiating member 68 and the housing 31 becomes larger than that in the seventh embodiment. Therefore, the heat dissipation of the insulating insulator 35 can be efficiently performed.

(Ninth Embodiment)
Next, the spark plug according to the ninth embodiment will be described with reference to FIGS. 21 and 22. In the ninth embodiment, the configuration of the heat radiating portion is different from that in the first embodiment.

The heat radiating member 71 as a "heat radiating portion" included in the spark plug 9 according to the ninth embodiment is one cylindrical member provided between the housing 31 and the insulating insulator 35. The heat radiating member 71 is made of, for example, a material such as aluminum, an aluminum alloy, magnesium, a magnesium alloy, or copper, which has a larger linear thermal expansion rate than that of the housing 31.

As shown in FIG. 21, the heat radiating member 71 is arranged along the inner wall surface of the housing 31 from the inner wall surface of the second cylinder portion 312 of the housing to the inner wall surface of the housing protrusion 323. In the present embodiment, the upper end of the heat radiating member 71 is located on the inner wall surface of the second cylinder portion 312 of the housing. Further, as shown in FIG. 21, the heat radiating member 71 has a lower end 712 located at the innermost tip 320 in the radial direction of the housing protrusion 328 provided in the housing first cylinder portion 311.

The heat radiating member 71 has a stretched portion 713 and a contact portion 714.
The extending portion 713 is formed so as to extend toward the terminal of the heat radiating member 71. The stretched portion 713 is a substantially tubular portion having a relatively thin radial thickness, and is an inner wall 315 on the terminal side of the housing first cylinder portion 311 and an inner wall 316 on the combustion chamber side of the housing second cylinder portion 312. It is provided along with.

The contact portion 714 is provided on the combustion chamber side of the stretched portion 713. The contact portion 714 has a contact surface 717 that abuts on the inner wall 327 of the housing protrusion 328 and a contact surface 718 that abuts on the seat surface 531 of the packing 53. The contact surface 717 and the contact surface 718 are formed so as to be parallel to each other. In the present embodiment, the seat surface 531 and the seat surface 532 of the packing 53 are formed in parallel. The displacement of the contact portion 714 when the heat radiating member 71 is thermally expanded or contracted is guided by the inner wall 327 of the housing protrusion 328.

The contact portion 714 has a contactable surface 716 inside in the radial direction. The contactable surface 716 is formed so as to face and be parallel to the inner wall 359 on the terminal side of the small inner diameter portion 351. During low load operation of the engine 90, a gap 54 is formed between the contactable surface 716 and the inner wall 359, as shown in FIG. 22.

In the spark plug 9 according to the ninth embodiment, a gap 54 is formed between the contactable surface 716 of the heat radiating member 67 and the inner wall 359 of the insulating insulator 35 during low load operation of the engine 90. Further, during high load operation of the engine 90, the gap 54 becomes small, and in some cases, the gap 54 disappears. As a result, the ninth embodiment has the same effect as the effects (a) to (c) of the first embodiment.

In the spark plug 9 according to the ninth embodiment, the inner wall 327 of the housing protrusion 328 to which the contact portion 714 of the heat radiating member 71 abuts and the seat surface 531 of the packing 53 are formed to be parallel to each other. As a result, it is possible to prevent the packing 53 from being displaced even if the contact portion 714 is displaced due to thermal expansion or thermal contraction.

Further, in the spark plug 9 according to the ninth embodiment, the heat radiating member 71 is composed of one member. As a result, the heat value of the spark plug 9 can be adjusted with a small number of parts.

(10th Embodiment)
Next, the spark plug according to the tenth embodiment will be described with reference to FIG. 23. The tenth embodiment is different from the first embodiment in the position where the first heat radiating member is provided.

The heat radiating portion 50 included in the spark plug 10 according to the tenth embodiment is provided between the housing 31 and the insulating insulator 35, and has a first heat radiating member 76 and a second heat radiating member 77. The first heat radiating member 76 and the second heat radiating member 77 are made of a material having a linear thermal expansion rate larger than that of the housing 31.

The first heat dissipation member 76 is arranged along the inner wall surface of the housing 31 from the inner wall surface of the second cylinder portion 312 of the housing to the end surface 329 of the housing protrusion 328 of the housing first cylinder portion 311 on the combustion chamber side. There is. In the present embodiment, the upper end 761 of the first heat radiating member 76 is located on the end surface 329 of the housing protrusion 328 on the combustion chamber side. Further, the lower end 762 of the first heat radiating member 76 is located on the outer wall surface of the end portion of the small inner diameter portion 351 on the large inner diameter portion 352 side. The first heat radiating member 76 has a stretched portion 763 and a contact portion 764.

The stretched portion 763 is formed in the first heat radiating member 76 so as to extend toward the combustion chamber. The stretched portion 763 is a substantially tubular portion having a relatively thin radial thickness, and is provided along the inner wall surface of the housing first tubular portion 311 and along the inner wall surface on the combustion chamber side of the housing protrusion 328. There is.

The contact portion 764 is provided on the terminal side of the extension portion 763. The contact portion 764 is provided along the end surface 329 of the housing protrusion 328. As shown in FIG. 23, the contact portion 764 has a substantially rectangular cross-sectional shape on the virtual surface including the central axis of the spark plug 10. The abutting portion 764 has a abuttable surface 766 as a "first abutable surface" on the inner side in the radial direction.

The second heat radiating member 77 extends from the outer wall surface of the large outer diameter portion 353 of the insulating insulator 35 to the outer wall surface of the small inner diameter portion 351 connected to the combustion chamber side of the stepped surface 355 of the insulating insulator 35. It is arranged along the wall surface. In the present embodiment, the upper end of the second heat radiating member 77 is located on the outer wall surface of the large outer diameter portion 353. Further, the lower end 772 of the second heat radiating member 77 is located on the outer wall surface of the end portion of the small inner diameter portion 351 on the large inner diameter portion 352 side. The second heat radiating member 77 has a stretched portion 773 and a contact portion 774.

The stretched portion 773 is formed in the second heat radiating member 77 so as to extend toward the terminal. The stretched portion 773 is a substantially cylindrical portion having a relatively thin radial thickness, and has a stepped surface 355 of the small inner diameter portion 351, an inner wall 357 of the large inner diameter portion 352, and a combustion chamber side of the large outer diameter portion 353. It is provided along the inner wall 358 of the.

The contact portion 774 is provided on the combustion chamber side of the stretched portion 773. The contact portion 774 is provided along the inner wall 359 on the terminal side of the small inner diameter portion 351. As shown in FIG. 23, the contact portion 774 has a substantially rectangular cross-sectional shape on the virtual surface including the central axis of the spark plug 10. The contact portion 774 has a contactable surface 775 as a "second contactable surface" formed so as to face the contactable surface 766 of the first heat dissipation member 76. During low load operation of the engine 90, a gap 54 is formed between the contactable surface 775 and the contactable surface 766.

The seat surface 531 of the packing 53 is in contact with the inner wall 327 of the housing protrusion 328. The seat surface 532 of the packing 53 is in contact with the extended portion 673 of the heat radiating member 67.

In the spark plug 10 according to the tenth embodiment, a gap 54 is formed between the contactable surface 766 of the first heat radiating member 76 and the contactable surface 775 of the second heat radiating member 77 during low load operation of the engine 90. .. Further, during high load operation of the engine 90, the gap 54 becomes small, and in some cases, the gap 54 disappears. As a result, the tenth embodiment has the same effect as that of the first embodiment. In particular, the heat of the housing 31 can be efficiently transferred to the cylinder head 921.

Further, in the spark plug 10 according to the tenth embodiment, the first heat radiating member 76 is provided on the side closer to the combustion chamber than the first heat radiating member of the first embodiment. As a result, the first heat radiating member 76 tends to heat the heat of the combustion gas, so that it easily expands. Therefore, the change in the size of the gap 54 can be made relatively large.

Further, in the spark plug 10 according to the tenth embodiment, since the first heat radiating member 76 that easily expands thermally is not provided on the seat surface 531, 532 of the packing 53, it is possible to prevent the packing 53 from being displaced.

Further, in the spark plug 10 according to the tenth embodiment, the generation of creeping discharge can be suppressed.

(Eleventh Embodiment)
Next, the spark plug according to the eleventh embodiment will be described with reference to FIG. 24. In the eleventh embodiment, the length of the heat radiating portion is different from that of the first embodiment.

The heat radiating portion 50 included in the spark plug 11 according to the eleventh embodiment is provided between the housing 31 and the insulating insulator 35, and has a first heat radiating member 81 and a second heat radiating member 82. The first heat radiating member 81 and the second heat radiating member 82 are made of a material having a linear thermal expansion coefficient larger than that of the housing 31.

As shown in FIG. 24, the virtual line from the direction of the combustion chamber of the spark plug 11 toward the terminal is defined as the central axis CA11. In the present embodiment, the upper end 811 of the first heat radiating member 81 and the upper end 821 of the second heat radiating member 82 are located near the end of the housing first cylinder portion 311 on the side connected to the housing second cylinder portion 312. It is provided at substantially the same position in the direction along the central axis CA11. Further, the lower end 812 of the first heat radiating member 81 and the lower end 822 of the second heat radiating member 82 are located near the inner wall 317 on the terminal side of the housing protrusion 313, and are provided at substantially the same position in the direction along the central axis CA11. Has been done. In the present embodiment, an insulating insulator is formed between the contactable surface formed in the vicinity of the lower end 812 of the first heat radiating member 81 and the contactable surface formed in the vicinity of the lower end 822 of the second heat radiating member 82. A gap whose size changes depending on the temperature of 35 is formed.

In the spark plug 11 according to the eleventh embodiment, a gap is formed between the first heat radiating member 81 and the second heat radiating member 82 during low load operation of the engine 90. Further, during high load operation of the engine 90, the gap becomes small, and in some cases, the gap disappears. As a result, the eleventh embodiment has the same effect as the first embodiment.

(Other embodiments)
(A) In the above-described embodiment, the first heat radiating member is a member having a larger linear thermal expansion rate than the second heat radiating member. However, the second heat radiating member may be a member having a larger linear thermal expansion rate than the first heat radiating member. Further, the first heat dissipation member and the second heat dissipation member have a higher linear thermal expansion rate than the housing. However, the first heat dissipation member and the second heat dissipation member may have a linear thermal expansion coefficient smaller than that of the housing.

The "parallel" in the relationship between the two planes described above is not exactly parallel, but may be a relationship that is seemingly parallel. As a result, the positional relationship may be such that heat transfer is promoted when the two planes are attached to each other.

In the fourth embodiment, the contactable surface of the first heat radiating member has eight notch-shaped recesses at substantially equal intervals in the circumferential direction. However, characteristics such as the shape or number of recesses can be appropriately determined.

In the sixth embodiment, in the first heat radiating member, four plate-shaped members having substantially the same shape are arranged at substantially equal intervals in the circumferential direction, and the above-mentioned four-divided shape is realized. However, the number of first heat dissipation members and the like can be appropriately determined.

The second to sixth embodiments may be applied to the eleventh embodiment. Further, in the eleventh embodiment, the second heat dissipation member may not be provided.

In the above-described embodiment, as an example, the state where the temperature of the center electrode is 500 ° C. or lower is defined as the low load operation of the engine 90. Further, as an example, a state in which the temperature of the center electrode is higher than 500 ° C. is defined as high load operation of the engine 90. However, these numerical values are merely examples, and the definitions of low load operation and high load operation change depending on the characteristics required for the spark plug or engine.

As described above, the present invention is not limited to such an embodiment, and can be implemented in various embodiments without departing from the gist thereof.

1,2,3,4,5,6,7,8,9,10,11 ... Spark plug 31 ... Housing 33 ... Ground electrode 35 ... Insulator 40 ... Center electrode 50 , 67, 68, 71 ... Heat dissipation part 54 ... Gap

Claims (13)

Housing (31) and
The insulating insulator (35) held inside the housing and
A ground electrode (33) provided at one end of the housing and
A center electrode (40) located inside the insulator and forming a spark capable of igniting fuel between the ground electrode and the center electrode (40).
A heat radiating portion (50, 67, 68, 71) provided between the housing and the insulating insulator and capable of forming a gap (54) on the combustion chamber (900) side of the engine (90).
Equipped with
The size of the gap changes according to the temperature of the housing or the insulator .
The insulating insulator is a spark plug in which the lengths (L1, L2) of the portions in contact with the combustion gas generated by the combustion of fuel become longer if there is a gap, and shorten if the gap disappears . The spark plug according to claim 1, wherein the size of the gap changes due to thermal expansion or contraction of the heat radiating portion. The heat radiating portion includes a first heat radiating member (51, 55, 56, 59, 61, 66, 76, 81) provided on the housing side and a second heat radiating member (52, 57) provided on the insulating insulator side. , 77, 82)
The spark plug according to claim 1 or 2 , wherein the gap is formed between the first heat radiating member and the second heat radiating member. The linear thermal expansion rate of the first heat radiating member is larger than the linear thermal expansion rate of the second heat radiating member.
The spark plug according to claim 3 , wherein the size of the gap when the engine is operated with a low load is larger than the size of the gap when the engine is operated with a high load. The first contactable surface (516,556,556,569,616,666,766) of the first heat dissipation member capable of contacting the second heat dissipation member and the first heat dissipation member can be contacted. The spark plug according to claim 3 or 4 , which is formed so as to be parallel to the second contactable surface (525, 575, 775) of the second heat radiating member. The spark plug according to claim 5 , wherein the first contactable surface and the second contactable surface have irregularities so as to mesh with each other. The spark plug according to any one of claims 3 to 6 , wherein the housing has a guide surface (324) for guiding displacement of the first heat dissipation member due to thermal expansion or contraction. A packing provided between the first heat radiating member and the second heat radiating member located on the side opposite to the center electrode when viewed from the gap, and in contact with the first heat radiating member and the second heat radiating member. 53) further prepared,
The spark plug according to claim 7 , wherein the seat surface (531) of the packing that abuts on the first heat dissipation member and the guide surface are formed so as to be parallel to each other. The spark plug according to claim 1 or 2 , wherein the heat radiating portion is provided only on either the housing side or the insulating insulator side. Housing (31) and
The insulating insulator (35) held inside the housing and
A ground electrode (33) provided at one end of the housing and
A center electrode (40) located inside the insulator and forming a spark capable of igniting fuel between the ground electrode and the center electrode (40).
A heat radiating portion (50, 67, 68, 71) provided between the housing and the insulating insulator and capable of forming a gap (54) on the combustion chamber (900) side of the engine (90).
Equipped with
The size of the gap changes according to the temperature of the housing or the insulator .
The heat radiating portion is a spark plug provided only on either the housing side or the insulating insulator side . The spark plug according to claim 10 , wherein the size of the gap changes due to thermal expansion or contraction of the heat radiating portion. The spark plug according to claim 3 , wherein the first heat radiating member is provided in the gas pocket (15). The spark plug according to any one of claims 1 to 12 , wherein the heat radiating portion has a linear thermal expansion rate larger than that of the housing.

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