Patent Grant
9318880
This application claims priority to Japanese Patent Application No. 2014-240203 filed on Nov. 27, 2014, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a spark plug for use in an internal combustion engine of an automobile or the like.
2. Description of Related Art
Generally, a spark plug for use in an internal combustion engine of an automobile or the like includes a cylindrical housing, a cylindrical insulator held inside the housing, a center electrode held inside the insulator, and a ground electrode disposed so as to form a spark discharge gap with the center electrode. Inside the insulator, a terminal metal fitting is disposed such that its proximal end portion projects from the insulator. Between the terminal metal fitting and the center electrode within the insulator, a resistor is disposed for suppressing electrical noise. A sealing member made of copper glass, for example, is filled in a space between the resistor and the terminal metal fitting and in a space between the resistor and the center electrode.
To manufacture the above spark plug, the center electrode is put into the insulator at first. Subsequently, a copper glass powder as a material of the sealing member and a powder material of the resistor are put into the insulator from the proximal end side. Further, the copper glass material is put into the insulator form the proximal end side, and then, the terminal metal fitting is inserted into the insulator from the proximal end side. After that, these components and materials are heated to a predetermined temperature, and the terminal metal fitting is pushed toward the axial distal end side. As a result, the copper glass powder and the resistor powder material are melted to flow and adhere to the respective components within the insulator, so that the center electrode, the terminal metal fitting and the resistor are fixed, and gaps are sealed by the copper glass within the insulator.
Accordingly, the terminal metal fitting inserted into the insulator is applied with a large axial force at its small-diameter portion at the time of manufacturing the spark plug.
Recently, it is required to reduce the sizes of spark plugs to enable reducing the sizes of internal combustion engines and increasing design freedom of the internal combustion engines. Therefore, the inner diameter of the insulator, and the diameter of the small-diameter portion of the terminal metal fitting disposed in the insulator are also required to be smaller. Accordingly, the small-diameter portion may be deformed when applied with a large axial force. In this case, there is a concern that the pressing force applied to the sealing member and the resistor by the terminal metal fitting may be insufficient, or varies greatly, causing the adhesion of the sealing member to the center electrode, the terminal metal fitting and the resistor to be insufficient.
Japanese Patent Application Laid-open No. 2013-41753 proposes to specify dimensions of the terminal metal fitting, for example, the outer diameter and length of the leg part of the terminal metal fitting, to overcome the above problem.
However, if the dimensions of the terminal metal fitting are specified and fixed, the design freedom of the terminal metal fitting and accordingly the design freedom of the spark plug are lowered. For example, this may cause a problem that it is difficult to design spark plugs having various shapes, for example the so-called long-reach spark plug having a large axial length.
According to an exemplary embodiment, there is provided a spark plug for an internal combustion engine, including:
a cylindrical housing;
a cylindrical insulator held inside the housing;
a center electrode held inside the insulator such that a distal end portion thereof projects from the insulator;
a terminal metal fitting held inside the insulator such that a proximal end portion thereof projects from the insulator;
a ground electrode disposed so as to form a spark discharge gap with the center electrode;
a resistor disposed inside the insulator so as to be located between the center electrode and the terminal metal fitting;
a first conductive sealing material filled in a space surrounded by the resistor, the terminal metal fitting and the insulator; and
a second conductive insulating material filled in a space surrounded by the resistor, the center electrode and the insulator, wherein
the terminal metal fitting includes an engaging portion engaged into an inner peripheral surface of the proximal end portion of the insulator and a small-diameter portion extending from the engaging portion and having a diameter smaller than a diameter of the engaging portion,
the small-diameter portion is formed with ribs extending in an axial direction of the small-diameter portion and projecting outward from an outer peripheral surface of the small-diameter portion, and
the first conductive sealing member is located at least at part on a distal end side of a gap between an outer peripheral surface of the terminal metal fitting and the inner peripheral surface of the insulator.
According to the exemplary embodiment, there is provided a spark plug a degree of design freedom of which is high, and whose terminal metal fitting can be prevented from being deformed due to an axial force applied thereto during assembly.
Other advantages and features of the invention will become apparent from the following description including the drawings and claims.
In the accompanying drawings:
A spark plug 1 according to a first embodiment of the invention is described with reference to
As shown in
The spark plug 1 includes also a terminal metal fitting 6 held inside the insulator 3 such that its proximal end portion projects from the insulator 3, a ground electrode 5 disposed so as to form a spark discharge gap 11 with the center electrode 4, and a resistor 7 disposed between the center electrode 4 and the terminal metal fitting 6 within the insulator 3. A conductive sealing member 121 is filled in a space between the resistor 7 and the terminal metal fitting 6. A conductive sealing member 122 is filled in a space between the resistor 7 and the center electrode 4.
As shown in
The insulator 3 has a cylindrical shape having an axial hole 31 penetrating therethrough in the axial direction. The center electrode 4, the sealing member 122, the resistor 7, the sealing member 121 and the terminal metal fitting 6 are disposed in the axial hole 31 in this order from the distal end side. The insulator 3 includes a step portion 32 at which the inner diameter of the axial hole 31 is changed. The center electrode 4 includes a brim portion 42 formed at its proximal end portion, the brim portion 41 being retained by the step portion 32, so that the center electrode 4 is positioned in the axial direction within the insulator 3.
The sealing members 121 and 122 are made of conductive copper glass which is a mixture of copper and glass. The sealing member 122 disposed on the distal end side of the resistor 7 adheres to the proximal end portion of the center electrode 4, the distal end portion of the resistor 7 and the inner peripheral surface of the insulator 3. The resistor 7 is made of a mixture of carbon and glass, and has a certain electrical resistance. The sealing member 121 disposed on the proximal end side of the resistor 7 adheres to the proximal end portion of the resistor 7, the distal end portion of the terminal metal fitting 6 and the inner peripheral surface of the insulator 3.
As shown in
The small-diameter portion 62 includes an uneven surface portion 621 formed at its distal end portion, and a middle portion 622 formed between the uneven surface portion 621 and the engaging portion 61. The uneven surface portion 621 may have a screw shape or a knurling shape.
The small-diameter portion 62 is formed with three or more ribs 63. In this embodiment, four ribs 63 are formed at even intervals in the circumferential direction of the small-diameter portion 62. The four ribs 63 have the same projection height and the same axial length. Accordingly, the shape of the small-diameter portion 62 including the ribs 63 is rotation symmetric with respect to the center axis thereof. In this embodiment, the small-diameter portion 62 including the ribs 63 has four-fold symmetry.
As shown in
The ribs 63 project outward from the outer periphery of the small-diameter portion 62 to such an extent that they do not project beyond the outer shape of the engaging portion 61. Accordingly, the diameter of the circumscribed circle connecting the projection ends of the ribs 63 in the cross section of the terminal metal fitting 63 perpendicular to the axial direction (see
The diameter of the small-diameter portion 62 is smaller than the inner diameter of the insulator 3 (the diameter of the axial hole). Accordingly, as shown in
At the time of assembling the center electrode 4, the sealing member 122, the resistor 7, the sealing member 121 and the terminal metal fitting 6 inside the insulator 3 to manufacture the spark plug 1, the insulator 3 is held in a holding jig 141 such that the proximal end faces upward as shown in
Next, as shown in
After that, as shown in
The sealing members (copper glass) 121 and 122 are cooled to be solidified adhering to the center electrode 4, the resistor 7 and the terminal metal fitting 6 within the insulator 3. In this way, the center electrode 4, the terminal metal fitting 6 and the resistor 7 are fixed within the insulator 3, and the inner space of the insulator 3 is sealed by the sealing members 121 and 122.
The first embodiment described above provides the following advantages. The small-diameter portion 62 of the terminal metal fitting 6 is formed with the ribs 63 which are arranged in the circumferential direction. This makes it possible to increase the rigidity of the small-diameter portion 62 to prevent deformation of the terminal metal fitting 6. That is, the small-diameter portion 62 can be prevented from being deformed when an axial force is applied to the terminal metal fitting 6 during assembly of the spark plug 1. Further, the provision of the ribs 63 in the small-diameter portion 62 makes it possible to increase the rigidity of the small-diameter portion 62 while ensuring the gap 13 in which the sealing member 121 is disposed between the outer peripheral surface of the small-diameter portion 62 and the inner peripheral surface of the insulator 3.
Since the rigidity of the small-diameter portion 62 is sufficiently increased by the ribs 63, the terminal metal fitting 6 can be designed freely without being restricted to any specific diameter or length of the small-diameter portion 62. Accordingly, the spark plug 1 can be designed to have a long-reach shape, or a small diameter, for example.
The small-diameter portion 62 is formed with three or more ribs 63 along the circumferential direction at even intervals. This makes it possible to effectively increase the rigidity of the small-diameter portion 62. That is, since the small-diameter portion 62 has three (or more)-fold symmetry, it can be prevented from being deformed in a specific direction when applied with a compressive force in the axial direction. Therefore, deformation of the small-diameter portion 62 can be effectively prevented, and variation of the pressing force applied to the resistor 7 and the sealing members 121 and 122 can be reduced. According to this embodiment, since the four ribs 63 are formed along the circumferential direction at even intervals, the rigidity of the small-diameter portion 62 can be more increased.
In addition, since the ribs 63 are connected to the distal end of the engaging portion 61, the rigidity of the terminal metal fitting 63 can be further increased.
According to this embodiment, there is provided a spark plug for an internal combustion engine, which can prevent deformation of its terminal metal fitting, and is high in design freedom.
Next, a second embodiment of the invention is described with reference to
Except for the ribs 63, the second embodiment is the same in structure as the first embodiment.
According to the second embodiment, the rigidity of the small-diameter portion 62 can be further increased. Other than this, the second embodiment provides the same advantages as those provided by the first embodiment.
It is a matter of course that various modifications can be made to the above embodiments as described below. The number of the ribs 63 is not limited to four. It may be three, or more than or equal to five. The ribs 63 may be formed at a plurality of areas of the small-diameter portion 62, the areas being different in their axial positions.
The above explained preferred embodiments are exemplary of the invention of the present application which is described solely by the claims appended below. It should be understood that modifications of the preferred embodiments may be made as would occur to one of skill in the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-240203 | Nov 2014 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20130140975 | Yoshida et al. | Jun 2013 | A1 |
| Number | Date | Country |
|---|---|---|
| 2013-041753 | Feb 2013 | JP |
| WO 2012042774 | Apr 2012 | WO |
