JP2020045770A - Laser ignition plug - Google Patents

Abstract

To provide a laser ignition plug, in which sealability between protective glass and a holding member holding it is deteriorated.SOLUTION: A laser ignition plug 1 ignites fuel gas in a combustion chamber 100 by radiating laser pulse L in the combustion chamber 100 from a tip positioned in the combustion chamber 100 in an internal combustion engine. A laser pulse generation part 10 generates the laser pulse L, and is housed inside a tubular housing 20. The protective glass 30 passes the laser pulse L generated from the laser pulse generation part 10, protects the laser pulse generation part 10, and is held at a tip of the housing 20 by a holding member 40. The holding member 40 has: a bottom contact part 41 contacting opposite to a bottom face 31 on a side of the protective glass 30 opposite to the combustion chamber 100; and a side peripheral side jointing part 42 jointed to a side peripheral face 32 which is an outside face of the protective glass 30 in a plug radial direction opposite to the side peripheral face 32 via a jointing member 50.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a laser spark plug.

  2. Description of the Related Art Conventionally, as an ignition device for an internal combustion engine or the like, there is an ignition device provided with a laser ignition plug for igniting a fuel gas using a laser pulse. In such a laser spark plug, a protective glass for protecting the inside is provided in an opening for emitting a laser pulse, and the laser pulse passes through the protective glass and is emitted into the combustion chamber. For example, in the configuration disclosed in Patent Literature 1, the holding member is provided on the housing tip region where the mechanical stress does not occur so that the mechanical stress due to tightening when attaching the laser spark plug to the cylinder head does not act on the protective glass. Holding protective glass. And a sealing material is interposed between the holding member and the protective glass.

JP 2013-96392 A

  However, in the configuration disclosed in Patent Document 1, the sealing material is interposed between the bottom surface of the protective glass opposite to the combustion chamber and the opposing surface of the holding member opposing the bottom surface. Therefore, when the protective glass is pressed from the combustion chamber by the combustion pressure generated in the combustion chamber, excessive force is applied to the sealant between the bottom surface of the protective glass and the facing surface of the holding member, and the sealant may be damaged. is there. If the sealing material is broken and the sealing property between the protective glass and the holding member is reduced, fuel gas or exhaust gas may enter the spark plug and cause damage.

  The present invention has been made in view of such a background, and an object of the present invention is to provide a laser spark plug in which a sealing property between a protective glass and a holding member that holds the protective glass is prevented.

One aspect of the present invention is a laser spark plug (1) that irradiates a laser pulse into a combustion chamber from a tip located in a combustion chamber (100) of an internal combustion engine to ignite fuel gas in the combustion chamber,
A laser pulse generator (10) for generating a laser pulse;
A cylindrical housing (20) for housing the laser pulse generator inside;
A protection glass (30) for transmitting the laser pulse generated from the laser pulse generator and emitting the laser pulse into the combustion chamber, and protecting the laser pulse generator;
A holding member (40) for holding the protective glass at a tip of the housing,
With
The holding member includes a bottom surface contact portion (41) that contacts a bottom surface (31) of the protective glass opposite to the combustion chamber, and a side peripheral surface of the protective glass that is a radially outer surface of the plug. A laser spark plug having a side peripheral surface joint (42) opposed to (32) and joined to the side peripheral surface via a joining member (50).

  In the laser spark plug, the bottom surface of the protective glass and the bottom contact portion of the holding member are in contact with each other, and no joining member is interposed between the two. The protective glass is held by the holding member by joining the side peripheral surface of the protective glass and the side peripheral surface joint of the holding member to each other via the joining member. Therefore, even when the protective glass receives the combustion pressure from the combustion chamber side, a force is directly applied to the bottom surface contact portion of the holding member from the bottom surface of the protective glass, and the joining member between the side peripheral surface and the side peripheral surface joining portion. Does not exert excessive force. As a result, breakage of the joining member is prevented, and a decrease in sealing performance between the protective glass and the holding member is prevented.

  As described above, according to the present invention, it is possible to provide a laser spark plug in which a reduction in sealing performance between a protective glass and a holding member that holds the protective glass is prevented.

  Note that reference numerals in parentheses described in the claims and means for solving the problems indicate the correspondence with specific means described in the embodiments described below, and limit the technical scope of the present invention. Not something.

FIG. 2 is a partial front sectional view of the laser spark plug according to the first embodiment. FIG. 2 is an enlarged cross-sectional view of a tip end of the laser spark plug according to the first embodiment. FIG. 9 is an enlarged cross-sectional view of a tip end of a laser spark plug according to a first modification. FIG. 9 is a front partial cross-sectional view of a laser spark plug according to a second embodiment. FIG. 9 is an enlarged cross-sectional view of a tip end of a laser spark plug according to a second embodiment. FIG. 10 is an enlarged cross-sectional view of a tip end of a laser spark plug according to a second modification.

(Embodiment 1)
An embodiment of the laser spark plug will be described with reference to FIGS.
As shown in FIG. 1, the laser spark plug 1 of the present embodiment irradiates a laser pulse L into the combustion chamber 100 from a tip located inside the combustion chamber 100 of the internal combustion engine, and applies a laser pulse L to the fuel gas in the combustion chamber 100. Ignite.
The laser spark plug 1 includes a laser pulse generator 10, a housing 20, a protective glass 30, and a holding member 40.
The laser pulse generator 10 generates a laser pulse L.
The housing 20 has a tubular shape and houses the laser pulse generator 10 inside.
The protective glass 30 transmits the laser pulse L generated from the laser pulse generator 10 and protects the laser pulse generator 10.
The holding member 40 holds the protective glass 30 at the tip of the housing 20.
As shown in FIG. 2, the holding member 40 includes a bottom surface contact portion 41 that contacts a bottom surface 31 of the protective glass 30 opposite to the combustion chamber 100, and a plug radial outside X of the protective glass 30. It has a side peripheral surface joint portion 42 which is opposed to the side peripheral surface 32 which is a surface and is joined to the side peripheral surface 32 via a joining member 50.

Hereinafter, the laser spark plug 1 of the present embodiment will be described in detail.
As shown in FIG. 1, the housing 20 has a cylindrical shape extending in the plug axis direction Y, and an attachment screw portion 21 for screwing to a cylinder head 101 of the internal combustion engine is formed on an outer peripheral surface of the housing 20. Have been. In the laser spark plug 1, the mounting screw portion 21 is screwed into the cylinder head 101, and the top surface 33 of the protective glass 30 facing the inside of the combustion chamber 100 on the front end side Y <b> 1 in the plug axial direction Y is connected to the internal combustion engine. Is mounted on the cylinder head 101 so as to be exposed inside the combustion chamber 100.

  As shown in FIG. 1, a laser pulse generator 10 is housed inside a housing 20. The laser pulse generator 10 is connected via an optical fiber to an excitation light source (not shown) provided outside the laser spark plug 1. The laser pulse generator 10 resonates and amplifies the excitation light supplied from the excitation light source, and generates a laser pulse L as pulse light having a high energy density. The configuration of the laser pulse generator 10 is not particularly limited, and a known configuration can be employed.

  As shown in FIG. 1, the laser pulse L generated from the laser pulse generator 10 is diffused to a predetermined width by the diffusion lens 11, and then passes through the condenser lens 12. The entrance surface 121 and the exit surface 122 of the condenser lens 12 have different curvatures. An anti-reflection layer for suppressing reflection of the laser pulse L emitted from the laser pulse generator 10 is formed on the incident surface 121 of the condenser lens 12. The condenser lens 12 is provided on the distal end side Y1 in the plug axis direction Y with respect to the diffusion lens 11 so as to keep a predetermined distance from the diffusion lens 11 in the housing 20. Thereby, the laser pulse L is condensed by the condensing lens 12, passes through the protective glass 30, and is irradiated on the converging point FP in the combustion chamber 100.

  As shown in FIG. 2, the protective glass 30 faces the inside of the combustion chamber 100 and protects the inside of the housing 20 from heat, pressure, combustion products, and the like in the combustion chamber 100. As a material for forming the protective glass 30, a known optical element material such as sapphire glass, optical glass, heat-resistant glass, and quartz glass can be used. In the present embodiment, sapphire glass is used. As shown in FIG. 2, the top surface 33, which is the surface of the protective glass 30 on the combustion chamber 100 side, and the bottom surface 31, which is the surface opposite to the combustion chamber 100, are planes parallel to each other. On the bottom surface 31, an anti-reflection layer for suppressing reflection of the laser pulse L emitted from the condenser lens 12 is formed.

  As shown in FIG. 2, the side peripheral surface 32 of the protective glass 30 on the outer side in the plug radial direction X orthogonal to the plug axial direction Y is formed of a first side peripheral surface 321 adjacent to the bottom surface 31 and a first side peripheral surface 321. A second side peripheral surface 322 adjacent to the top surface 33 is located on the distal end side Y1 in the plug axial direction Y. The first side peripheral surface 321 is a tapered surface that is inclined so as to increase in diameter toward the distal end side Y1 in the plug axial direction Y. On the other hand, the second side peripheral surface 322 is a tapered surface that is inclined so as to decrease in diameter toward the distal end side Y1 in the plug axial direction Y. Therefore, the outer diameter of the protective glass 30 is the largest at the boundary 323 between the first peripheral surface 321 and the second peripheral surface 322. As shown in FIG. 1, the protective glass 30 has a hexagonal cross section including the plug central axis 1a.

  As shown in FIGS. 1 and 2, the protective glass 30 is fixed to the distal end 22 of the housing 20 by a holding member 40. The holding member 40 is a metal annular member, and has a bottom surface contact portion 41 and a side peripheral surface joint portion 42 as shown in FIG. The bottom contact portion 41 faces the bottom 31 of the protective glass 30. The bottom contact portion 41 is parallel to the bottom 31 and forms an annular plane along the outer edge of the bottom 31. The bottom surface 31 and the bottom contact portion 41 are in contact with each other, and no joining member or the like is interposed between them. And in this embodiment, both are in contact with each other in the entire circumferential direction.

  As shown in FIG. 2, the side peripheral surface joining portion 42 is joined to the side peripheral surface 32 via the joining member 50 so as to face the side peripheral surface 32 of the protective glass 30. The side peripheral surface joint 42 is a partial conical surface inclined along the first side peripheral surface 321 of the protective glass 30. In the present embodiment, as shown in FIG. 2, in the cross section including the plug central axis 1a, the side peripheral surface joining portion 42 is parallel to the side peripheral surface 32 over the entire area. The side peripheral surface joint 42 and the side peripheral surface 32 may not be parallel in a cross section including the plug central axis 1a, and the side peripheral surface joint 42 may be inclined with respect to the side peripheral surface 32. . The joining member 50 for joining the first side peripheral surface 321 and the side peripheral surface joining portion 42 is made of a brazing material. The brazing material forming the joining member 50 preferably has a high melting point. For example, a brazing material made of an Au-Cu alloy having a melting point of 990 ° C or an Ag-Cu alloy having a melting point of 780 ° C is used as the joining member 50. be able to. In this embodiment, a brazing material made of an Au-Cu alloy is used as the joining member 50.

  In the present embodiment, as shown in FIG. 2, the corner 48 of the holding member 40 is surrounded by the joining member 50, the side peripheral surface 32, the side peripheral surface joining portion 42, and the bottom surface contact portion 41. The space 51 is formed, and the joining member 50 does not contact the corner 48 of the holding member 40. This prevents the joining member 50 melted at the time of brazing from flowing between the bottom surface 31 and the bottom contact portion 41.

  As shown in FIG. 1, an end portion 47 of the holding member 40 on the base end side Y2 in the plug axis direction Y is welded to the front end 22 of the housing 20. As a result, the protective glass 30 is fixed to the distal end side Y1 of the housing 20 in the plug axis direction Y via the holding member 40.

  In the present embodiment, as shown in FIG. 2, the holding member 40 extends from the outer edge of the outer circumferential direction X of the side peripheral surface joining portion 42 to the distal end Y1 and moves inward toward the distal end Y1. And a bent portion 45 bent toward the plug center axis 1a. The ring-shaped member 46 is provided between the bent portion 45 and the second peripheral surface 322. The ring-shaped member 46 has an annular shape and the inner peripheral surface 461 is inclined so as to be along the second side peripheral surface 322. The bent portion 45 is in a state where the inner peripheral surface 461 is in contact with the second side peripheral surface 322. The ring-shaped member 46 is held. This prevents the protective glass 30 from dropping from the holding member 40 into the combustion chamber 100. Since the contact between the ring-shaped member 46 and the protective glass 30 is a surface contact, stress concentration is suppressed at the contact portion between the ring-shaped member 46 and the protective glass 30, and damage to the protective glass 30 is prevented. You. In the present embodiment, the distal end 451 of the bent portion 45 is not in contact with the second side peripheral surface 322, but may be in contact with the second side peripheral surface 322.

Next, the operation and effect of the laser spark plug 1 of the present embodiment will be described in detail.
According to the laser spark plug 1 of the present embodiment, the bottom surface 31 of the protective glass 30 and the bottom contact portion 41 of the holding member 40 are in contact with each other, and the bottom surface 31 and the bottom contact portion 41 are joined together. No member is interposed. The side peripheral surface 32 of the protective glass 30 and the side peripheral surface joining portion 42 of the holding member 40 are joined to each other via the joining member 50, and the protective glass 30 is held by the holding member 40. Therefore, even if the protective glass 30 receives the combustion pressure from the combustion chamber 100 side, a force is directly applied from the bottom surface 31 of the protective glass 30 to the bottom contact portion 41 of the holding member 40, and an excessive force is applied to the joining member 50. Absent. As a result, breakage of the joining member 50 is prevented, and a decrease in sealing performance between the protective glass 30 and the holding member 40 is prevented.

  In this embodiment, as shown in FIG. 2, the corner 48 between the bottom surface contact portion 41 and the side peripheral surface joint portion 42 of the holding member 40 is formed between the bottom surface 31 of the protective glass 30 and the side peripheral surface. 32 and the protruding corner 38 are parallel to each other and have shapes similar to each other. Instead, as in Modification 1 shown in FIG. 3, a corner 48 between the bottom surface contact portion 41 and the side peripheral surface joint portion 42 of the holding member 40 is provided at the corner 48 between the bottom surface 31 and the side of the protective glass 30. A relief portion 480 formed in a concave shape so as to be separated from the protruding corner portion 38 between the peripheral surface 32 and the peripheral surface 32 may be provided. In the first modification, the relief portion 480 is formed in a concave shape toward the base end side Y2 in the plug axis direction Y and the outer side X in the plug radial direction with respect to the corner 48 of the first embodiment shown in FIG. .

  As shown in FIG. 3, the provision of the escape portion 480 prevents the protruding corner portion 38 of the protective glass 30 from interfering with the holding member 40, and the bottom surface 31 and the bottom surface contact portion 41 abut against each other. It will be easier to touch. As a result, when the protective glass 30 receives the combustion pressure, the concentration of the stress generated between the bottom surface 31 and the bottom contact portion 41 is reduced, and the damage to the protective glass 30 can be suppressed. Further, when the joining member 50 which is a brazing material is brazed, when the joining member 50 which has melted arrives at the corner 48, the joining member 50 which has melted is kept at the escape portion 480, so that the bottom surface 31 and the bottom surface 31 are formed. It is possible to prevent sneaking around between the contact portion 41. Thereby, it is possible to ensure a wide contact area between the side peripheral surface 32 and the side peripheral surface joint 42 and the joint member 50 while preventing the joint member 50 from intervening between the bottom surface 31 and the bottom contact portion 41. it can. As a result, the sealing performance between the protective glass 30 and the holding member 40 can be further improved, and the holding force of the protective glass 30 by the holding member 40 can be improved.

  As described above, according to the present embodiment and the modified embodiment, it is possible to provide the laser spark plug 1 in which the sealing property between the protective glass 30 and the holding member 40 is prevented from being reduced.

(Embodiment 2)
In the first embodiment, the protective glass 30 having a hexagonal cross section including the plug central axis 1a as shown in FIGS. 1 and 2 is provided. Instead, as shown in FIGS. 4 and 5, a protective glass 300 having a rectangular cross section including the plug central axis 1a is provided. Further, as shown in FIG. 5, the holding member 40 does not have the bent portion 45 in the first embodiment shown in FIG. Other components are the same as those in the first embodiment, and the same reference numerals as in the first embodiment denote the same components in the present embodiment, and a description thereof will be omitted.

  As shown in FIG. 5, in this embodiment, the protective glass 30 has a columnar shape and a rectangular cross section including the plug central axis 1a. It is a right angle in the cross section including the plug center axis 1a. The length h1 of the joining member 50 in the plug axis direction Y may be a length that can maintain the joined state between the protective glass 30 and the holding member 40 and secure the sealing property between the two. In the embodiment, as shown in FIG. 5, the length h1 of the joining member 50 in the plug axial direction Y is equal to or less than half the length of the protective glass 30 in the plug axial direction Y, that is, the thickness h2 of the protective glass 30. The length is such that the sealing property between the protective glass 30 and the holding member 40 can be ensured.

  In the conventional configuration, the joining member between the holding member and the bottom surface and the side peripheral surface of the protective glass are provided, and the length of the joining member on the side peripheral surface of the protective glass in the plug axis direction Y is increased to increase the joining strength. The joint pressure between the bottom surface of the protective glass and the holding member is prevented from being damaged by the combustion pressure by increasing the pressure so that the joining member on the side peripheral surface of the protective glass also receives the combustion pressure. On the other hand, according to the laser spark plug 1 of the present embodiment, similarly to the first embodiment, the joining member 50 is interposed between the bottom surface 31 of the protective glass 30 and the bottom contact portion 41 of the holding member 40. However, since both are in contact with each other, the bottom surface contact portion 41 of the holding member 40 directly receives the combustion pressure applied to the protective glass 30. This eliminates the need for the joining member 50 on the side peripheral surface 32 to receive the combustion pressure, so that the joining member 50 on the side peripheral surface 32 does not need to increase the joining strength and can maintain the sealing property. Can be made shorter than before. As a result, the amount of the joining member 50 can be reduced, and the cost can be reduced.

  Further, according to the laser spark plug 1 of the present embodiment, similarly to the first embodiment, the joint member 50 is prevented from being damaged, so that the joining member 50 allows the side peripheral surface 32 of the protective glass 30 and the side of the holding member 40 to be closed. Since the bonding state with the peripheral surface bonding portion 42 is sufficiently maintained, there is no possibility that the protective glass 30 will fall from the holding member 40 into the combustion chamber 100. Therefore, the bent portion 45 and the ring-shaped member 46 in the first embodiment become unnecessary, and the configuration of the holding member 40 can be simplified and the number of components can be reduced. Further, since the bent portion 45 becomes unnecessary, the side peripheral surface 32 does not need to have a tapered shape so that the shape of the protective glass 30 can be restricted by the bent portion 45. Therefore, as in the present embodiment, since the cross-sectional shape of the protective glass 30 including the plug central axis 1a can be made rectangular, the shape of the protective glass 30 can be simplified, and the manufacturing cost can be reduced. It also contributes to miniaturization. In this embodiment, the same operation and effect as those of the first embodiment can be obtained.

  Note that, as in Modification 2 shown in FIG. 6, a relief portion 481 may be provided at the corner 48 of the holding member 40. As shown in FIG. 6, in Modification 2, the relief portion 481 is formed in a concave shape toward the base end side Y2 in the plug axial direction Y with respect to the corner 48 of Embodiment 2 shown in FIG. , Are not formed on the outer side X in the plug radial direction. Thereby, since the size of the gap between the side peripheral surface 32 of the protective glass 30 and the side peripheral surface joining portion 42 of the holding member 40 does not change due to the relief portion 481, the side peripheral surface 32 via the joining member 50 in the manufacturing process. It becomes easy to manage the joining state of the and the side peripheral surface joining part 42, and it becomes easy to maintain the joining state of both well. It should be noted that the second modification has the same operation and effect as those of the first and second embodiments and the first modification.

  The present invention is not limited to the above embodiments, and can be applied to various embodiments without departing from the gist thereof. For example, the configuration of the relief portion 481 in the second modification may be applied to the corner 48 in the first embodiment, or the configuration of the relief 480 in the first modification may be applied to the corner 48 in the second embodiment. Is also good.

DESCRIPTION OF SYMBOLS 1 Laser spark plug 10 Laser pulse generation part 20 Housing 30, 300 Protective glass 31 Bottom surface 32 Side peripheral surface 38 Outer corner part 40 Holding member 41 Bottom contact part 42 Side peripheral surface joint part 48 Inner corner part 480, 481 Escape part 50 Joining member 100 Combustion chamber

Claims (3)

A laser spark plug (1) for irradiating a laser pulse into a combustion chamber from a tip located in a combustion chamber (100) of an internal combustion engine to ignite fuel gas in the combustion chamber,
A laser pulse generator (10) for generating a laser pulse;
A cylindrical housing (20) for housing the laser pulse generator inside;
A protection glass (30) for transmitting the laser pulse generated from the laser pulse generator and emitting the laser pulse into the combustion chamber, and protecting the laser pulse generator;
A holding member (40) for holding the protective glass at a tip of the housing,
With
The holding member includes a bottom surface contact portion (41) that contacts a bottom surface (31) of the protective glass opposite to the combustion chamber, and a side peripheral surface of the protective glass that is a radially outer surface of the plug. A laser spark plug having a side peripheral surface joint (42) opposed to (32) and joined to the side peripheral surface via a joining member (50).   A protruding corner (38) between the bottom surface and the side peripheral surface of the protective glass is provided at a corner (48) between the bottom contact portion and the side peripheral surface joint of the holding member. 2. The laser spark plug according to claim 1, further comprising a relief portion (480, 481) formed in a concave shape so as to be separated from the laser ignition plug.   The laser ignition plug according to claim 1, wherein a shape of a cross section of the protective glass including a plug central axis (1 a) is rectangular.

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