JP2002246148A - Plug with built-in pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug having an insulation plate as a component which is formed precisely at a low manufacturing cost. SOLUTION: The spark plug with a built-in pressure sensor 1 includes the insulation plate 25 for insulating a piezoelectric element and a main metal fitting divided into two element members 25a, 25a adjacent in a peripheral direction. A gap 25b for drawing out a lead wire 27 to a rear side is formed between end surfaces of one sides of the element members 25a, 25a. The element members 25a, 25a are formed into the same shape and are shared.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a plug with a built-in pressure sensor.

[0002]

2. Description of the Related Art Conventionally, by measuring the pressure (in-cylinder pressure) of a combustion chamber of an internal combustion engine, for example, knocking detection,
It detects the peak position of the combustion pressure, detects misfire, and the like, and is useful for controlling the operation of the internal combustion engine. In some cases, a pressure sensor provided with a piezoelectric element such as an annular piezoelectric ceramic is used for measuring the in-cylinder pressure. Such a pressure sensor is disposed, for example, on a metal shell of a spark plug, which is an embodiment of a plug, and is mounted by screwing a male thread formed on the metal shell and a female thread of a cylinder head.
The spark plug is pushed up by the combustion pressure, and the tightening load on the cylinder head of the spark plug fluctuates. The electrical output generated by the piezoelectric element in response to the fluctuation of the load is taken out to the outside via a lead wire. Is measured.

[0003]

The plug with a built-in pressure sensor as described above has a pressure sensor housed in a sensor case in which an insulating plate, a piezoelectric element, an electrode plate and the like are provided around the metal shell. 2. Description of the Related Art A method is widely used in which a pressure sensor is pressed and held between a sensor holding portion of the mounting portion and a seat surface of a plug hole. In such a pressure sensor, an insulating plate is disposed between the piezoelectric element and the metal shell so as to insulate the piezoelectric element from the metal shell as described above. Further, a configuration is provided in which, for example, a slit-shaped lead wire outlet as shown in FIG. 7 is provided in the insulating plate to take out an electrical output from the piezoelectric element to the outside. However, when the insulating plate is shaped as shown in FIG. 7, the manufacturing cost is increased by the amount corresponding to the formation of the slit as compared with the annular insulating plate having no slit. Due to this, it may not be uniformly shrunk and the whole may have an elliptical shape.

An object of the present invention is to provide a spark plug in which an insulating plate as a component is formed at a low manufacturing cost and with high accuracy.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an axially front end side with a mounting portion for an internal combustion engine, and the mounting portion has an axial direction. A spark plug body having a metal shell having a sensor holding portion projecting in a circumferential direction on a rear side; and a piezoelectric member provided in an annular shape around the metal shell to generate an electric output based on a pressure in a combustion chamber of the internal combustion engine. A pressure sensor-containing plug having an element and an insulating plate disposed between the piezoelectric element and the sensor holding portion in the axial direction and along the circumferential direction around the axis; Is divided into a plurality of circumferentially adjacent element members, and a gap is formed between any one pair of the adjacent element members for taking out a lead wire to a rear side. To provide a force sensor built-in plug.

For example, if the insulating plate is continuous over substantially the entire circumference as shown in FIG. 7, the overall deformation may be remarkable, and the entire insulating plate may not have a desired shape. For example, since the insulating plate is configured to be divided into a plurality of element members, the length of the insulating plate in the circumferential direction can be reduced, and deformation due to shrinkage or the like in a manufacturing stage of each element member can be suppressed. Can be. Further, since it is an arc-shaped member, processing is easy, and there are great advantages in terms of processing accuracy, cost, and the like.

[0007] Further, the plurality of element members may all be formed in the same shape. With this configuration, it is not necessary to manufacture a plurality of types of components on the insulating plate, so that simplicity is high and component management is easy. In addition, each of the plurality of element members may have a three-dimensional shape that is plane-symmetric with respect to a plane of symmetry parallel to its own thickness direction. If formed in plane symmetry in this manner, the element members can be arranged regardless of the front and back, so that it is not necessary to add a mark for clarifying the front and back to the element members. Further, when the insulating plate is provided, the element members can be shared regardless of the installation position and the front and back. In addition,
In the present invention, the thickness direction of the element member is parallel to the axial direction in the assembled state.

[0008]

Embodiments of the present invention will now be described with reference to the embodiments shown in the drawings. FIG. 1 is a half sectional front view of a spark plug with a built-in pressure sensor according to an embodiment of the present invention and a sectional view showing a part of the spark plug in an enlarged manner. Spark plug 1 with built-in pressure sensor (plug with built-in pressure sensor)
It has a spark plug main body 10 (plug main body) and a pressure sensor 20 integrally attached to a metal shell 11 of the spark plug main body 10. In the following description, the side toward the plug hole PH of the spark plug 1 with a built-in pressure sensor, that is, the side toward the combustion chamber CR is referred to as the “front side”.
(Or “front end side”), and the side facing the opposite direction is referred to as “rear side” (or “rear end side”).

In FIG. 1, the front end of a spark plug 1 with a built-in pressure sensor is formed at the innermost part (forwardmost part) of a plug hole PH formed in a cylinder head of an internal combustion engine so as to communicate with a combustion chamber CR. It is inserted into the insertion hole 111, and is disposed in the plug hole PH such that the tip thereof enters 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 via 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 to perform, for example, knocking detection, combustion pressure peak position detection, misfire detection, and the like, which is used for operation control of the internal combustion engine.

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 metallic shell 11 formed in a cylindrical shape. A leg long portion 12b formed on the distal end side projects forward from the metal shell 11. On the other hand, a rear portion of the insulator 12 extends from a rear end of the metal shell 11 to form a corrugation portion 12a on the rear end side, and a terminal electrode 13 projects rearward from the rear end of the corrugation portion 12a. A center electrode 14 electrically connected to the terminal electrode 13 projects forward from the tip of the leg portion 12b. Further, the other end of the ground electrode 15 having one end joined to the tip of the metal shell 11 is bent back to the side, and its side faces the tip of the center electrode 14 to form a spark discharge gap g. .

The metal shell 11 is formed at the bottom of the cylinder head of the internal combustion engine from the front side, and is formed in an insertion hole 111 communicating with the combustion chamber. A gasket 11b for sealing leakage of combustion gas, a mounting seat 11c for fixing the pressure sensor 20 to a seat surface, and a tool such as a plug wrench for screwing a male screw formed on the mounting portion 11a are involved. And a tool engaging portion 11c 'to be combined. Mounting seat 11
As shown in FIG. 2, c is formed with a sensor holding portion 11d projecting in the circumferential direction and connected to the plug hole mounting side (front side) of the sensor holding portion 11d. A penetrating support portion 11e is formed in two stages to penetrate and support the inside of the pressure sensor 20 with a small outer diameter.

FIG. 3 is an enlarged view of a main part in a half sectional front view of FIG. 1. As shown in FIG. 3 or a detailed sectional view of a part A of FIG. 1, a side wall 21a and a bottom 21b are formed. Are annularly formed in the inner space of an annular sensor case 21 formed in a half-section L-shape in such a manner as to be sequentially stacked from below (front) on a bottom portion 21b, a piezoelectric element 23, and an electrode plate 24. And the insulating plate 25 are accommodated, and the pressure sensor 20 is constituted. As shown in FIG. 3, a lead wire 27 extends rearward from a terminal 24a formed on the outer peripheral edge of the annular electrode plate 24, and electrically connects the piezoelectric element 23 based on the pressure of the combustion chamber CR (FIG. 1). Output is taken out. The insulating tube 29 of the pressure sensor 20
Are positioned inside the piezoelectric element 23 so that
e.

Then, the penetrating support portion 11 of the mounting seat portion 11c is provided.
e is inserted along the axial direction on the inner peripheral surface side of the pressure sensor 20, and the pressure sensor 20 is provided with a seat surface S of the plug hole PH and a sensor holding portion 11d opposed thereto.
, And is pressed and held in the axial direction. Further, the inner peripheral surface of the side wall portion 21a of the sensor case 21 is fitted and fixed to the outer peripheral surface of the sensor holding portion 11d of the mounting seat portion 11c by an interference fit, and the temporary fixing portion T ( 1st fixing | fixed part) is formed.

On the other hand, the inner peripheral surface of the bottom 21b of the sensor case 21 is in contact with the outer surface of the lower end of the through support 11e,
A first welded portion W1 (second fixed portion) fixed to the bottom portion 21b in an axially immovable and hermetically sealed state by performing full-circle laser welding along the lower peripheral edge of 1b.
Are formed. Further, laser welding is performed along the entire periphery of the side wall portion 21a in such a manner as to overlap a part of the temporary fixing portion T at an intermediate portion in the axial direction of the side wall portion 21a. A second welded portion W2 (third fixed portion) which is immovable and fixed in a sealed state is formed.

The internal space of the sensor case 21 is sealed by a filling layer 26 made of resin, silicone rubber, or the like. A terminal 24a formed on the outer peripheral edge of the annular electrode plate 24
A lead wire 27 extends rearward from the outlet to take out an electrical output based on the pressure of the combustion chamber CR to the outside. Since the pressure sensor 20 is integrally formed with the mounting seat portion 11c of the metal shell 11, sufficient water resistance and airtightness are maintained by the sensor case 21 and the filling layer 26.

The sensor holder 11d of the metal shell 11
In order to dispose the lead wire 27, the circular lead wire insertion hole 1 penetrating in the axial direction
1j and 11k are respectively formed. Therefore,
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 passes through the lead wire insertion hole 11k of the tool engagement portion 11c '. As shown in FIG. 1, the plug hole PH is drawn out from the rear end opening of the plug hole PH.

Next, the insulating plate will be described. As shown in FIG. 4, the insulating plate 25 is formed of a material such as alumina, is divided into a plurality of circumferentially adjacent element members, and leads are provided between any one of the adjacent element members. A gap 25b for taking out the line 27 (see FIG. 1 and the like) to the rear side is formed. In this embodiment, the structure is divided into two element members 25a, 25a, and a gap 25b is formed between the end faces on one side of the element members 25a, 25a. The other end faces (opposite to the side where the gap 25b is formed) are in contact with each other. In this way, the number of parts does not become too large when the division is made into two, and the desired effect can be achieved with the minimum necessary number of divisions.

Further, as shown in FIGS. 4 (a) and 4 (b), it is possible to facilitate the component management (that is, to reduce the number of components, etc.) by making the plurality of element members all have the same shape. Specifically, as shown in the figure, each of the two element members 25a, 25a is formed in an arcuate shape in which the outer periphery and the inner periphery form a concentric cylindrical surface. When the two members are arranged so as to coincide with each other, the two members can be formed so as to have a shape that can be arranged symmetrically with respect to a plane (plane A) including the central axis O. With this configuration, the components can be effectively arranged around the metal shell while sharing the components.

As shown in FIGS. 4 (b), 5 (a) and 5 (b), each element member has a three-dimensional shape that is plane-symmetric with respect to a plane of symmetry (plane B) parallel to its own thickness direction. It is good to employ the element member which has. In the present embodiment, the thickness direction is parallel to the direction of the central axis O. In particular,
A plane parallel to the thickness direction of the element member 25a and including the center point P1 of the inner periphery and the middle point P2 of the outer periphery is defined as a symmetry plane B,
It is plane-symmetric with respect to the target plane B. By doing so, the element member 25a is placed in the sensor case 21 (FIG. 1).
Can be arranged regardless of front and back, so that quick and easy assembly can be achieved.

As shown in FIG. 4B, when the two element members 25a, 25a are arranged symmetrically with respect to a plane A including the central axis O, the two element members 2a
5a and 25a at both ends in the circumferential direction,
c and 25c can be formed so that they can be arranged so as to face each other so as to be parallel to each other. FIG.
As shown in FIG. 4 (b), a plurality of gaps 25b (two in FIG.
4) may be formed, or one end face may be brought into contact with the shape as shown in FIG. In addition,
In FIG. 4B, each element member has a configuration in which both end faces 25c, 25c are formed in a direction orthogonal to the symmetry plane B.

Further, as shown in FIGS. 4A and 5, at least one of the circumferential end surfaces 25c may be formed in the axial direction in each of the element members 25a. More specifically, the circumferential end surfaces 25c that come into contact with each other
Are formed so that both are formed in the axial radial direction.
If a and 25a are formed, the end surfaces are supported on the entire surface to stably hold the position.

In the example shown in FIGS. 5A and 5B, 2
In each of the two element members 25a, 25a, both end surfaces 25c in the circumferential direction are formed in the axial radial direction, respectively. In this case, the entire end surface is in good contact with any of the opposing sides, so there is no need to determine which side is the abutment side and which is the gap formation side. In FIG. 5A, when the two members 25a, 25a are arranged such that the center of the inner and outer peripheries of the element member 25a coincides with the center axis O, the plane A including the center axis O is bilaterally symmetric. The shape satisfies both a shape that can be arranged and a three-dimensional shape that is plane-symmetric with respect to a symmetry plane (plane B) parallel to its own thickness direction. In this case, the sharing of the element members can be extremely effectively performed, and the configuration is easy to assemble. In addition, in the shape of FIG.
The angle θ formed by the end face on the side forming 5 c is adjusted to such an extent that it can pass through the lead wire 27. FIG.
As shown in (b), the two element members 25a, 25a may be formed so that their shapes are different from each other.

Further, a spark plug 1 with a built-in pressure sensor
Can be assembled as follows. As shown in FIG. 2, in the space inside the side wall portion 21a of the sensor case 21, the plate packing 22 and the piezoelectric element 2 each formed in an annular shape are provided.
3. The pressure sensor 20 is assembled by housing the electrode plate 24 and the insulating plate 25 in the form of being sequentially stacked from below (front) on the bottom 21b. On the inner peripheral surface side of the pressure sensor 20 assembled in this way, when the penetration support portion 11e of the mounting seat portion 11c covered with the insulating tube 29 is inserted along the axial direction, the pressure sensor 20 becomes the sensor holding portion 11d.
Is pressed and held in the axial direction with a predetermined pressing force on the sensor support end face 11f side (FIG. 2A). At this time, the electrode plate 2
The lead wire 27 connected to the terminal 24a of FIG.
As shown in (b), the lead wire insertion hole 1 of the sensor holding portion 11d
1j and the lead wire insertion hole 11k of the tool engagement portion 11c '. 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 interference fit, and a temporary fixing portion T is formed on the side wall portion 21a.

Further, as shown in FIG. 6, when the top and bottom of the spark plug main body 10 and the pressure sensor 20 are inverted and the sensor case 21 is pressed by the pressing tool P from outside the bottom 21b, the sensor case 21 is moved to the bottom 21b. The pressure sensor 20 moves in the axial direction until the inner peripheral surface comes into contact with the outer surface of the lower end portion of the through support portion 11e, and the pressure sensor 20 is pressed and held on the sensor holding end surface 11f side of the sensor holding portion 11d by a predetermined pressing force in the axial direction. You. In this state, by irradiating the laser beam LB from the laser welding machine LW along the lower peripheral edge of the bottom portion 21b and performing the entire circumference laser welding, the bottom portion 21b cannot be moved in the axial direction and is sealed. A fixed first weld W1 is formed. Furthermore, the laser beam LB is irradiated from the laser welding machine LW along the entire periphery of the side wall 21a so as to be superimposed on a part of the temporary fixing portion T, and laser welding is performed. Welded part W2 fixed in a closed state so that it cannot move to
Is formed (FIG. 6A).

Further, as shown in FIG. 6B, the top and bottom of the spark plug main body 10 and the pressure sensor 20 are again inverted,
The resin is injected into the inner space of the sensor case 21 by the resin injection machine RI, and the sensor case 21 is sealed by the filling layer 26. As described above, the spark plug 1 with a built-in pressure sensor
Is completed.

Although the above description has been given only of 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. In the embodiment of the present invention, the spark plug with the built-in pressure sensor is fixed to the cylinder head by screwing a male screw formed at the end of the metal shell into the insertion hole of the plug hole and screwing it 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.

FIGS. 2A and 2B are a perspective view and a partially broken front view showing an assembly process of the spark plug with a built-in pressure sensor of FIG. 1;

FIG. 3 is an enlarged view showing a main part of the pressure sensor of FIG. 1 in an enlarged manner.

FIG. 4 is a plan view showing some examples of an insulating plate.

FIG. 5 is a plan view showing a modification of FIG. 4;

FIG. 6 is a partially cutaway front view showing an assembling step following FIG. 2;

FIG. 7 is a plan view showing an example of a conventional insulating plate.

[Explanation of symbols]

Reference Signs List 1 spark plug with built-in pressure sensor (plug with built-in pressure sensor) 10 spark plug main body (plug main body) 11 metal shell 11a mounting portion 11d sensor holding portion 20 pressure sensor 23 piezoelectric element 25 insulating plate 25a element member 25b gap O axis B symmetry plane

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F055 AA23 BB12 CC11 DD20 EE23 FF43 GG12 3G019 KA28 5G059 AA10 CC02 KK03

Claims (6)

[Claims] 1. A spark plug body having a metal shell having a mounting portion to an internal combustion engine formed at a front end side in an axial direction, and a sensor holding portion projecting in a circumferential direction at a rear side in the axial direction of the mounting portion. A piezoelectric element that is annularly provided on the front side of the sensor holding unit and generates an electrical output based on a pressure of a combustion chamber of the internal combustion engine; and between the piezoelectric element and the sensor holding unit in the axial direction. And a pressure sensor including an insulating plate disposed in the circumferential direction around the axis, and the insulating plate is divided into a plurality of circumferentially adjacent element members. And a gap for taking out the lead wire to the rear side is formed between any one pair of the adjacent element members. 2. The pressure sensor built-in plug according to claim 1, wherein each of the plurality of element members has a three-dimensional shape that is plane-symmetric with respect to a plane of symmetry parallel to its own thickness direction. 3. The pressure sensor built-in plug according to claim 1, wherein each of the plurality of element members has at least one of its circumferential end faces formed in the axial radial direction. 4. The pressure sensor built-in plug according to claim 1, wherein each of the plurality of element members has a circumferential end face formed in an axial radial direction. 5. The insulating plate comprises the two element members, and when the two element members are arranged symmetrically with respect to a plane including the central axis, both ends in the circumferential direction of the two element members. The plug with a built-in pressure sensor according to any one of claims 1 to 3, wherein the plug is formed so as to be capable of facing each other such that end faces thereof are parallel to each other. 6. The insulating plate comprises two element members, the two element members being formed in an arcuate shape having a concentric cylindrical surface with an outer periphery and an inner periphery, and a center of the inner and outer peripheries of the element members. 6. The device according to claim 1, wherein when the two members are arranged so as to coincide with the center axis, the members have shapes that can be arranged symmetrically with respect to a plane including the center axis. 7. Plug with built-in pressure sensor.