Electric lamp and discharge devices – Spark plugs
Reexamination Certificate
2001-10-19
2003-05-06
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
Spark plugs
C313S141000
Reexamination Certificate
active
06559577
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pressure sensor-incorporating spark plug which, is attached to an internal combustion engine in order to generate spark discharge within a cylinder and includes a piezoelectric element for detecting the internal pressure of the cylinder.
2. Description of the Related Art
A spark plug is attached to an internal combustion engine in order to generate spark discharge within a cylinder and thereby burn an air-fuel mixture. In relation to such a spark plug, a pressure sensor-incorporating spark plug is known which includes a built-in pressure sensor for detecting the internal pressure of the cylinder and for outputting an electric signal corresponding to the detected pressure.
FIG. 6
shows an exemplary conventional pressure sensor-incorporating spark plug. The pressure sensor-incorporating spark plug
101
shown in FIG.
6
(
a
) includes a substantially cylindrical metallic shell
17
to be attached to an internal combustion engine; a substantially cylindrical insulator
15
, which is held by the metallic shell
17
such that its center axis coincides with the center axis of the metallic shell
17
; an electricity reception terminal
13
, which is disposed at one axial end of the insulator
15
and which receives high voltage for ignition; a center electrode
19
, which is disposed at the other axial end of the insulator
15
and is electrically connected to the electricity reception terminal
13
via the interior of the insulator
15
; and a ground electrode
21
, which is provided at an axial end of the metallic shell
17
corresponding to the axial end of the insulator
15
at which the center electrode
19
is provided.
A radially bulged flange portion
17
b
is formed at a longitudinal center portion of the metallic shell
17
. The flange portion
17
b
includes a hexagonal portion
17
a
, which is formed at a portion closer to the electricity reception terminal
13
and onto which a tightening tool is fit; and a sensor case
29
, which accommodates a piezoelectric element (not shown) for outputting an electric signal corresponding to the internal pressure of a cylinder. A bottom portion of the sensor case
29
serves as a mounting seat
17
g
, which abuts a cylinder head upon attachment of the spark plug to the internal combustion engine.
The pressure sensor-incorporating spark plug
101
further includes an output cable
27
for leading to external equipment the electric signal output from the piezoelectric element provided on the metallic shell
17
. The output cable
27
is passed through a metal pipe
35
, which is fixed to a side surface of the hexagonal portion
17
a
, and is fixed to the metal pipe
35
to thereby fix the output cable
27
to the hexagonal portion
17
a
. Thus, the output cable
27
extends from the pressure sensor-incorporating spark plug
101
.
The pressure sensor-incorporating spark plug
101
is attached to the cylinder head of the internal combustion engine by means of a screw-engagement groove
17
c
, which is formed on the metallic shell
17
located between the flange portion
17
b
and the ground electrode
21
. However, as shown in FIG.
6
(
b
), which is a view from above the pressure sensor-incorporating spark plug
101
(as viewed in the direction of arrow B in FIG.
6
(
a
)), the metal pipe
35
is fixed to the side surface of the hexagonal portion
17
a
, making it impossible to fit an ordinary plug wrench onto the hexagonal portion
17
a
. Therefore, when the pressure sensor-incorporating spark plug
101
is attached to the cylinder head of the internal combustion engine, a dedicated plug wrench having a slit at a portion corresponding to the metal pipe
35
must be used.
In addition, if such a plug wrench having a slit is used to tighten or remove the pressure sensor-incorporating spark plug
101
in a state in which the plug wrench has not been completely fit onto the hexagonal portion
17
a
and thus the output cable
27
engages a slit wall, the output cable
27
may be damaged, and in some cases may be pulled out.
In view of this problem, a pressure sensor-incorporating spark plug disclosed in Japanese Utility-Model Application Laid-Open (kokai) No. 60-138292 has been proposed. This pressure sensor-incorporating spark plug is configured such that an output cable is passed through a through hole formed in the hexagonal portion. That is, since the output cable is led outward from an upper end surface (end surface on the electricity reception terminal side), the hexagonal portion can maintain a hexagonal cross section to which an ordinary plug wrench can be fit. Thus, the pressure-sensor-incorporating spark plug can be tightened or removed using an ordinary plug wrench.
The above-described structure eliminates an accident in which the output cable engages a slit wall of a plug wrench, to thereby prevent damage to or pulling out of the output cable.
3. Problems to be Solved by the Invention
However, the pressure sensor-incorporating spark plug described in the above patent publication (Japanese Utility-Model Application Laid-Open No. 60-138292) has a drawback, in that the output cable is susceptible to being pulled out. This is because the output cable is fixed to the wall of the through hole of the hexagonal portion by means of a heat-resistant resin, which is charged into the space between the output cable and the wall of the through hole.
In view of this drawback, the above patent publication discloses an embodiment in which the wall of the through hole is roughened in order to improve the output cable's resistance to being pulled out. However, this raises a problem of an increase in the number of work steps for fixing the output cable.
SUMMARY OF THE INVENTION
In view of the forgoing problems of the prior art, an object of the present invention is to provide a pressure sensor-incorporating spark plug which has a tightening portion onto which an ordinary plug wrench having no slit can be fit, which has an output cable having increased resistance to being pulling out, and which facilitates work for fixing the output cable.
In order to achieve the above object, a first aspect of the invention provides a pressure sensor-incorporating spark plug comprising: a spark plug main body including a substantially cylindrical metallic shell having a radially bulged flange portion at a center portion of the metallic shell, the flange portion having a mounting seat which abuts a cylinder head upon attachment of the spark plug to an internal combustion engine, and a tightening portion which is provided at a location apart from the mounting seat and onto which a tightening tool is fit, the tightening portion having a cross-sectional shape having a vertex portion; a piezoelectric element attached to the metallic shell and outputting an electric signal corresponding to cylinder internal pressure of the internal combustion engine; and an output cable for leading the electric signal generated by the piezoelectric element to the outside. The pressure sensor-incorporating spark plug is further characterized in that a cable accommodation portion for accommodating the output cable is provided at the vertex portion of the tightening portion, and the output cable is placed in the cable accommodation portion and is fixed to the tightening portion by crimping a portion of the tightening portion around the cable accommodation portion.
That is, in the pressure-sensor-incorporating spark plug of the first aspect of the invention, the output cable is placed in the cable accommodation portion and is fixed to the tightening portion by crimping a portion of the tightening portion around the cable accommodation portion, so that the tightening portion nips the output cable to thereby fix the output cable. The cable accommodation portion may be a through hole, where the output cable is passed through the through hole.
Since a structure for fixing the output cable by crimping is employed, the number of work steps can be decreased as compared with the case in which the output ca
Matsui Masayoshi
Okazaki Koji
Suzuki Takahiro
Day Michael H.
NGK Spark Plug Co. Ltd.
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