JP4636703B2 - Built-in pressure sensor plug - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plug with a built-in pressure sensor.
[0002]
[Prior art]
Conventionally, by measuring the pressure (in-cylinder pressure) of a combustion chamber of an internal combustion engine, for example, knocking detection, combustion pressure peak position detection, misfire detection, and the like are performed, which is useful for operation control of the internal combustion engine. For measuring the in-cylinder pressure, a pressure sensor including a piezoelectric element such as an annular piezoelectric ceramic may be used. Such a pressure sensor is disposed, for example, in a metal shell of a spark plug which is an embodiment of the plug, and an electrical output generated by the piezoelectric element in response to a change in a tightening load applied to the cylinder head of the spark plug via a lead wire. There is provided a plug with a built-in pressure sensor that measures the in-cylinder pressure by taking it out.
[0003]
[Problems to be solved by the invention]
By the way, in the plug with a built-in pressure sensor as described above, a pressure sensor in which an insulating plate, a piezoelectric element, an electrode plate, and the like are accommodated in a sensor case is supported by a sensor holding portion of a metal shell, and the sensor holding portion and a seating surface of the plug hole The pressure sensor is pressed and held between the two. In this method, in general, the sensor case is held in place so that the pressure sensor is not displaced with respect to the sensor holding portion of the metal shell, and the airtightness and watertightness in the sensor case are maintained. The pressing force is fixed to the outer peripheral surface of the sensor holding portion of the metal shell.
[0004]
In order to attach such a sensor case to the outside of the pressure sensor, the sensor case is formed in a cylindrical shape, and the pressure sensor is held in the sensor case while being held by a sensor holding part of a metal shell having an outer diameter substantially the same as the sensor case. A method of sealing is used. However, these diameters (specifically, the inner diameter of the opening edge serving as the insertion opening and the outer diameter of the sensor holding portion) are substantially the same in order to ensure good contact between the inner peripheral surface of the sensor case and the outer peripheral surface of the sensor holding portion. Alternatively, if the sensor holding part is formed to have a larger diameter, the sensor holding part is not easily inserted at the opening edge of the sensor case, which makes it difficult to assemble the pressure sensor. Further, when a burr protruding inward at the opening edge occurs, it becomes more difficult to insert the sensor holding portion, and therefore it is essential to provide a burr removing step.
[0005]
The problem to be solved by the present invention is that a pressure sensor built-in plug having a pressure sensor can be assembled with ease and high accuracy in the assembly of the sensor case and the plug main body, and the manufacturing cost can be reduced. The object is to provide a plug with a built-in pressure sensor.
[0006]
[Means for solving the problems and actions / effects]
In order to solve the above-described problems, the present invention has a mounting portion for an internal combustion engine formed on the front end side in the axial direction, and a sensor holding portion projects in the circumferential direction on the rear side in the axial direction of the mounting portion. A spark plug body having a metal shell,
A pressure sensor supported in the form of abutting in the axial direction directly or via another member on a sensor holding portion provided in an annular shape around the metal shell;
It has a side wall portion that surrounds the outer peripheral surface of the pressure sensor and covers at least a part of the outer peripheral surface of the sensor holding portion, and is formed in a cylindrical shape having openings on the front side and the rear side in the axial direction. Including a sensor case attached to the spark plug body in such a manner that the front end side of the spark plug body is inserted from the opening.
The side wall portion of the sensor case is formed with an enlarged diameter portion that increases in diameter as it approaches the rear opening edge, and the inner diameter of the enlarged diameter portion is larger than the outer diameter of the sensor holding portion. The inner peripheral surface of the side wall portion has a temporary fixing portion that is fitted and fixed to the outer peripheral surface of the sensor holding portion, overlaps with a part of the temporary fixing portion, and is sealed along the entire circumference of the side wall portion. There is provided a plug with a built-in pressure sensor, characterized in that a welded portion to be fixed is formed.
[0007]
As the above-described configuration, a larger diameter closer to the opening edge of the pressure sensor insertion side, the inner diameter by forming the sensor case so as to provide an enlarged diameter portion that will be larger than the outer diameter of the sensor holder, the pressure sensor When the sensor holding part or the like is inserted, they enter smoothly. For example, even if a burr may occur near the opening edge of the sensor case at the sensor case manufacturing stage, the influence of the burr on insertion can be greatly reduced. Specifically, if the diameter of the opening edge is increased in advance by the diameter reduction expected due to the occurrence of burrs, the pressure sensor, sensor holding part, etc. can be inserted further inside the burrs protruding. Insertion is not inhibited. Further, the burr is not caught inside the sensor case when the pressure sensor, the sensor holding part, etc. are inserted during assembly.
[0008]
The fitting between the inner circumferential surface of the side wall portion of the sensor case and the outer circumferential surface of the sensor holding portion is an interference fit fitting, and the inner circumferential surface of the side wall portion of the sensor case is set as the fit fitting. Can be configured such that a straight linear portion is formed . In this way, the structure that can sufficiently satisfy the adhesiveness by firmly fixing the sensor case and the spark plug body (specifically, the pressure sensor holding portion) after the insertion while achieving the ease of insertion of the pressure sensor. Can be realized.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to examples shown in the drawings. FIG. 1 is a half cross-sectional front view of a spark plug with a built-in pressure sensor according to an embodiment of the present invention, and a cross-sectional view showing an enlarged part thereof. The pressure sensor built-in spark plug 1 (pressure sensor built-in plug) includes a spark plug body 10 (plug body) and a pressure sensor 20 integrally attached to the metal shell 11 of the spark plug body 10. In the following description, the plug hole PH mounting side of the spark plug 1 with a built-in pressure sensor, that is, the side facing the combustion chamber CR is “front side” (or “front end side”), and the side facing the opposite direction is “back side” (Or “rear end side”).
[0010]
In FIG. 1, the front end portion of the pressure sensor built-in spark plug 1 is an insertion hole 111 formed in communication with the combustion chamber CR in the innermost portion (frontmost) of the plug hole PH formed in the cylinder head of the internal combustion engine. Is inserted into the plug hole PH so as to enter the combustion chamber CR of the internal combustion engine. When a high voltage generated in the ignition coil unit is applied to the spark plug body 10 through the high voltage supply unit, a spark discharge is generated in the combustion chamber CR to burn the air-fuel mixture. The pressure (in-cylinder pressure) of the combustion chamber CR at this time is measured by the pressure sensor 20, and for example, knocking detection, combustion pressure peak position detection, misfire detection, and the like are performed, which is used for operation control of the internal combustion engine.
[0011]
In the spark plug main body 10 shown in FIG. 1, an insulator 12 made of a ceramic sintered body such as alumina or aluminum nitride is fitted inside a metal shell 11 formed in a cylindrical shape. The formed long leg portion 12 b protrudes forward from the metal shell 11. On the other hand, the rear portion of the insulator 12 extends from the rear end of the metal shell 11 to form a corrugation portion 12a on the rear end side, and a terminal electrode 13 protrudes rearward from the rear end of the corrugation portion 12a. A center electrode 14 electrically connected to the terminal electrode 13 protrudes forward from the tip of the long leg portion 12b. Further, the other end side of the ground electrode 15 having one end joined to the tip end of the metal shell 11 is bent back to the side, and the side surface thereof faces the tip end surface of the center electrode 14 to form a spark discharge gap g. .
[0012]
The metal shell 11 is formed from the front side at the bottom of the cylinder head of the internal combustion engine, and is formed in the insertion hole 111 communicating with the combustion chamber. A tool such as a plug wrench is engaged to screw the gasket 11b for sealing the leak, the mounting seat 11c for fixing the pressure sensor 20 to the seating surface, and the external thread formed on the mounting portion 11a. And a tool engaging portion 11c ′. As shown in FIG. 2, the mounting seat portion 11c is formed with a sensor holding portion 11d protruding in the circumferential direction, and is connected to the plug hole mounting side (front side) of the sensor holding portion 11d. A penetration support portion 11e that supports the inside of the pressure sensor 20 with an outer diameter smaller than that of the portion 11d is formed in two stages.
[0013]
3 is an enlarged view of the main part of the half cross-sectional front view of FIG. 1, but the side wall 21a and the bottom 21b are half cross-sectional as shown in FIG. In the inner space of the annular sensor case 21 formed in an L shape, a plate packing 22, a piezoelectric element 23, an electrode plate 24, and an insulating plate each formed in an annular shape so as to be sequentially stacked on the bottom 21b from below (front). 25 is accommodated, and the pressure sensor 20 is configured. As shown in FIG. 3, a lead wire 27 is extended to the rear side from a terminal 24a formed on the outer peripheral edge of the annular electrode plate 24, so that the electrical power of the piezoelectric element 23 based on the pressure in the combustion chamber CR (FIG. 1) is obtained. The output is taken out. Further, the insulating tube 29 of the pressure sensor 20 is placed around the penetration support portion 11 e so as to be positioned inside the piezoelectric element 23.
[0014]
And the penetration support part 11e of the attachment seat part 11c is penetrated so that it may follow along an axial direction in the inner peripheral surface side of the pressure sensor 20, and the pressure sensor 20 is the sensor holding | maintenance which opposes this with the seat surface S of the plug hole PH. It is sandwiched between the sensor support end face 11f of the portion 11d and is pressed and held in the axial direction. Further, the inner peripheral surface of the side wall portion 21a in the sensor case 21 is fitted and fixed to the outer peripheral surface of the sensor holding portion 11d in the mounting seat portion 11c by an interference fit, and the temporary fixing portion T ( A first fixing part) is formed.
[0015]
On the other hand, the inner peripheral surface of the bottom portion 21b of the sensor case 21 is brought into contact with the outer surface of the lower end portion of the penetrating support portion 11e, and laser welding is performed along the peripheral edge of the lower end of the bottom portion 21b. A first welded portion W1 (second fixed portion) is formed which is fixed in a sealed state so as not to be movable. Further, laser welding is performed along the entire circumference of the side wall portion 21a in a form overlapping with a part of the temporary fixing portion T in the intermediate portion in the axial direction of the side wall portion 21a. The second welded portion W2 (third fixed portion) is formed which is immovable and fixed in a sealed state.
[0016]
The internal space of the sensor case 21 is sealed with a filling layer 26 such as resin or silicon rubber. And the lead wire 27 is extended to the back side from the terminal 24a formed in the outer periphery of the cyclic | annular electrode plate 24, and the electrical output based on the pressure of the combustion chamber CR is taken out outside. Since the pressure sensor 20 is integrally formed with the mounting seat 11c of the metal shell 11, the sensor case 21 and the filling layer 26 are sufficiently water-resistant and airtight.
[0017]
Further, circular lead wire insertion holes 11j and 11k penetrating in the axial direction are formed in the sensor holding portion 11d and the tool engaging portion 11c ′ of the metal shell 11 in order to dispose the lead wires 27, respectively. ing. Accordingly, the lead wire 27 drawn rearward from the terminal 24a of the annular electrode plate 24 is inserted into the lead wire insertion hole 11j of the sensor holding portion 11d, and further through the lead wire insertion hole 11k of the tool engagement portion 11c ′. It passes through and extends rearward, and is pulled out from the rear end opening of the plug hole PH as shown in FIG.
[0018]
Next, the sensor case will be described. As shown in FIG. 4, the sensor case 21 has a side wall portion 21 a that covers the outer peripheral surface of the pressure sensor 20 and is formed in a cylindrical shape having openings on the front side and the rear side in the axial direction. Further, the spark plug main body 10 (FIG. 1) is attached in such a manner that the front end side of the spark plug main body 20 is inserted through the rear opening. Furthermore, it has a bottom portion 21b that abuts and covers the front end surface of the pressure sensor 20, and the side wall portion 21a that covers the outer peripheral surface of the pressure sensor 20 has a cylindrical shape that rises rearward in the axial direction from the outer peripheral edge of the bottom portion 21b. Is formed. And in the side wall part 21a, the enlarged diameter part 21c which diameter-expands is formed so that the opening edge of a back side is approached. The diameter-expanded portion 21c is formed in a tapered shape that increases in diameter toward the opening edge, and the tapered portion has a shape in which the cross-sectional outline of the inner peripheral surface is continuously bent in a longitudinal section as shown in FIG. There is no.
[0019]
The sensor case 21 has an inner diameter D ₁ at the opening edge of the enlarged diameter portion 21c is formed so as to be larger than the outer diameter D ₂ of the sensor holding portion 11d. On the other hand, the side wall portion 21a and the sensor holding portion 11d are fixed in a form that fits tightly. The side wall portion 21 has a straight portion 21d formed so as to extend in a cylindrical shape in the axial direction following the front end side of the diameter-expanded portion 21c, and has a vertical cross-section inner surface outer shape parallel to the axis O. In 21d, the sensor holding portion 11d is fit-fit. Further, the maximum diameter of the enlarged diameter portion 21c (the maximum width in the axial radial direction of the enlarged diameter portion 21c) is formed to be smaller than the inner diameter of the plug hole PH. For example, when the outer peripheral surface of the straight portion 21d is used as a reference surface as shown in FIG. 3, the maximum distance L1 at which the enlarged diameter portion 21c protrudes in the axial radial direction from the reference surface can be made less than ₁ mm. In addition, about manufacture of such a sensor case 21, what is necessary is just to adjust a metal mold | die so that the enlarged diameter part 21c of the said shape may be formed in an opening edge part, for example using deep drawing.
[0020]
Furthermore, the pressure sensor built-in spark plug 1 can be assembled as follows. As shown in FIG. 2, in the inner space of the side wall 21a of the sensor case 21, the plate packing 22, the piezoelectric element 23, the electrode plate 24, and the insulating plate 25 each formed in an annular shape are placed on the bottom 21b from below (front). The pressure sensor 20 is assembled by housing in a stacked manner. When the penetration support portion 11e of the mounting seat portion 11c covered with the insulating tube 29 is inserted along the axial direction on the inner peripheral surface side of the pressure sensor 20 assembled in this way, the pressure sensor 20 is connected to the sensor holding portion 11d. The sensor support end face 11f is pressed and held in the axial direction by a predetermined pressing force (FIG. 2A). At this time, the lead wire 27 connected to the terminal 24a of the electrode plate 24 is connected to the lead wire insertion hole 11j of the sensor holding portion 11d and the lead wire insertion hole 11k of the tool engagement portion 11c ′ as shown in FIG. It is inserted sequentially. Further, the inner peripheral surface of the side wall portion 21a is fitted and fixed to the outer peripheral surface of the sensor holding portion 11d by an interference fit, and a temporary fixing portion T is formed on the side wall portion 21a.
[0021]
Further, when the top of the spark plug body 10 and the pressure sensor 20 is reversed as shown in FIG. 5 and the sensor case 21 is pressed by the pressing tool P from the outside of the bottom portion 21b, the sensor case 21 has an inner peripheral surface of the bottom portion 21b. Moves in the axial direction until it comes into contact with the outer surface of the lower end portion of the penetration support portion 11e, and the pressure sensor 20 is pressed and held in the axial direction by a predetermined pressing force on the sensor support end surface 11f side of the sensor holding portion 11d. In that state, the laser beam LB is irradiated from the laser welding machine LW along the peripheral edge of the lower end of the bottom portion 21b to perform all-around laser welding, so that the bottom portion 21b cannot move in the axial direction and is sealed. A fixed first weld W1 is formed. Further, the side wall 21a is irradiated with a laser beam LB from the laser welding machine LW along the entire circumference of the side wall 21a in a form overlapping with a part of the temporarily fixed portion T, so that the side wall 21a is axially aligned. A second weld W2 is formed which is immovable and fixed in a sealed state (FIG. 5A).
[0022]
Further, as shown in FIG. 5B, the top and bottom of the spark plug main body 10 and the pressure sensor 20 are reversed again, the resin is injected into the internal space of the sensor case 21 by the resin injector RI, and the sensor case 21 is injected by the filling layer 26. To seal. Thus, the assembly of the pressure sensor built-in spark plug 1 is completed.
[0023]
Although the above description has been given only for the embodiment of the spark plug with a built-in pressure sensor, the present invention is also applicable to a glow plug with a built-in pressure sensor. Further, in the embodiment of the present invention, the male screw formed at the distal end portion of the metal shell is formed in the insertion hole of the plug hole so that the spark plug with the pressure sensor is fixed to the cylinder head by screwing into the screw. However, the present invention is also applicable to a mode in which the mounting seat portion of the metal shell is pressed and fixed to the seat surface of the plug hole by other means.
[Brief description of the drawings]
FIG. 1 is a half sectional front view and a partially enlarged sectional view of a spark plug with a built-in pressure sensor according to an embodiment of the present invention.
2 is a perspective view and a partially cutaway front view showing an assembly process of the pressure sensor built-in spark plug of FIG. 1; FIG.
FIG. 3 is an enlarged view showing an essential part of the pressure sensor in FIG. 1;
FIG. 4 is a partial cross-sectional side view showing the sensor case.
5 is a partially broken front view showing the assembly process following FIG. 2. FIG.
[Explanation of symbols]
1 Spark plug with built-in pressure sensor (plug with built-in pressure sensor)
10 Spark plug body (plug body)
11 metal shell 11a mounting part 11d sensor holding part 20 pressure sensor 21 sensor case 21a side wall part 21c enlarged diameter part

Claims (2)

A spark plug main body having a metal shell in which a mounting portion to the internal combustion engine is formed on the front end side in the axial direction and a sensor holding portion protrudes in the circumferential direction on the rear side in the axial direction of the mounting portion;
A pressure sensor supported in a form that abuts in the axial direction directly or via another member on the sensor holding portion provided annularly around the metal shell;
It has a side wall portion that surrounds the outer peripheral surface of the pressure sensor and covers at least a part of the outer peripheral surface of the sensor holding portion, and is formed in a cylindrical shape having openings on the front side and the rear side in the axial direction, Including a sensor case attached to the spark plug body in such a manner that the front end side of the spark plug body is inserted from the rear side opening.
A diameter-enlarged portion is formed on the side wall of the sensor case so as to increase in diameter toward the opening edge on the rear side, and the inner diameter of the enlarged-diameter portion is larger than the outer diameter of the sensor holding portion. The inner peripheral surface of the side wall portion has a temporary fixing portion that is fitted and fixed to the outer peripheral surface of the sensor holding portion, and overlaps with a part of the temporary fixing portion, along the entire circumference of the side wall portion. A plug with a built-in pressure sensor, wherein a welded portion that is fixed in a sealed state is formed.   The fitting between the inner circumferential surface of the side wall portion of the sensor case and the outer circumferential surface of the sensor holding portion is an interference fit fitting, and the inner circumferential surface of the side wall portion of the sensor case that is the fit fitting. The pressure sensor built-in plug according to claim 1, wherein a straight linear portion is formed.

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