Electric lamp and discharge devices: systems – Combined load device or load device temperature modifying... – Electric generator or piezoelectric device
Reexamination Certificate
2000-12-22
2002-06-25
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Combined load device or load device temperature modifying...
Electric generator or piezoelectric device
C313S118000, C313S126000, C123S435000
Reexamination Certificate
active
06411038
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority of Japanese Patent Application No. H.11-366456 filed on Dec. 24, 1999, the content of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an installation structure of an engine component (for example, a glow plug, a spark plug, injector and a volt) with a combustion pressure sensor in an engine in which the engine component is inserted into an installation hole of the engine and fixed to the engine and the combustion pressure sensor is mounted on the engine component for generating a signal representing engine combustion pressure.
2. Description of Related Art
Conventionally, as an example of the engine component with a combustion pressure sensor, a glow plug with a combustion pressure sensor to be used as an ignition aided device for starting a diesel engine, as disclosed in JP-7-139736, is known. A general construction of the conventional glow plug J
1
with a combustion pressure sensor is shown in FIG.
12
.
The conventional glow plug J
1
with a combustion pressure sensor is comprised of a plug body
200
having a heater body
206
for generating heat when energized and a combustion pressure sensor
300
for generating a signal based on a force in responsive to combustion pressure acting on the plug body
200
.
A part of the plug body
200
on an end side thereof is inserted into an installation hole
1
b
(plug hole, a threaded bore) formed in an engine head
1
of a diesel engine and firmly fixed to the engine head
1
. A male thread
201
a
of a housing
201
is screwed into a female thread
1
c
of the installation hole
1
b
for fixing.
In the glow plug J
1
, a voltage is applied via a connecting cover
2
to a central axis
204
from an electric source (not shown). The central axis
204
is grounded via a heating coil
203
, a sheath pipe
202
, and the housing
201
to the engine head
1
.
The heater body
206
, which is composed of the heating coil
203
and the sheath pipe
202
, generates heat for helping ignition of the diesel engine at its starting.
Further, the glow plug J
1
has a sealing construction with which a leak of combustion gas through the installation hole
1
b
is prevented. As explosive combustion pressure in a combustion chamber
1
a
of the diesel engine is higher than that of a gasoline engine and, for example, increases up to 150 Mpa, it is very important to hold a close sealing not to leak combustion gas or pressure to outside. If leaked, the engine cannot be adequately operated due to a reduced engine output and a fluctuated engine revolution that may cause an engine vibration and a deteriorated acceleration, which a driver feels unfavorable.
To ensure the air tightness in the conventional glow plug J
1
, a housing taper portion
212
formed in the plug body
200
on a leading end side of the housing
201
and a taper seat surface portion
1
d
formed at an inner circumference of the installation hole
1
b
of the engine head
1
are provided to face to each other and come closely in pressurized contact with each other by screwing the housing
201
into the installation hole
1
b
with a recommended fastening torque for standardization (for example, 10 to 15 N·m).
More specifically, a taper angle of the housing taper portion
212
is larger, for example, by 3°, than that of the taper seat surface portion
1
d
. When the plug body
200
is fastened, the housing taper portion
212
comes firmly in a circumferential line contact with the taper seat surface portion Id and the plug body
200
is fixed to the engine head
1
in a state that a circumferential part of the housing taper portion
212
in the line contact cuts into the taper seat surface portion
1
d
. Accordingly, the combustion gas generated in the combustion chamber
1
a
is prevented from leaking outside so that the sealing is ensured.
The plug body
200
so fastened can maintain the rigid fixing with the engine head
1
due to a frictional force of the housing taper portion
212
and the taper seat surface portion
1
d
, a frictional force of the male thread
201
a
of the housing
201
and the female thread
1
c
of the installation hole
1
b
, and a mutual elastic force of the housing
201
and the engine head
1
.
In the glow plug J
1
, a ring shaped combustion pressure sensor
300
is fitted into the housing
201
at an outer circumference of the housing
201
and fixed to a surface of the engine head
1
by screwing a fixing nut
310
for the sensor
300
into the male thread
201
a
of the housing
201
.
The combustion sensor
300
may incorporate a piezoelectric member (not shown), as shown in JP-A-139736, which converts a force acting on the plug body
200
into an electric signal (electric charge) according to an piezoelectric characteristic and outputs the electric signal representing combustion pressure.
A load is applied in advance via the housing
201
of the plug body
200
to the combustion pressure sensor
300
. Combustion pressure generated in the combustion chamber
1
a
is transmitted via the heater body
201
and the housing
201
a
to the male thread
201
a
. Accordingly, the housing
201
including the male thread
201
a
is pushed upward in an axial direction of the installation hole
1
b
so as to deform slightly so that the load to the combustion pressure sensor
300
may be eased. A change of the load is converted into the electric signal, which is an output from a lead wire
500
, so that a change of combustion pressure is detected.
However, the conventional installation structure of the glow plug J
1
with the combustion pressure sensor has some drawbacks. One of the drawbacks is that a transmitting efficiency of transmitting the force from the plug body
200
to the combustion pressure sensor
300
is low and an output sensitivity of the sensor
300
is not sufficient enough.
As the plug body
200
is rigidly fixed to the engine head
1
to ensure the air tightness with the recommended fastening torque for standardization so that the housing
201
for transmitting combustion pressure is firmly retained by both of the taper seat surface portion
1
d
and the female thread
1
c
in the installation hole
1
b
, an amount of the deformation of the plug body
200
is remarkably limited according to a change of combustion pressure. As a result, the change of the load is limited so that the output sensitivity of the combustion sensor
300
is low.
If a problem exists in that only the sensitivity is low, the sensitivity may be easily improved in use of an electric amplifying circuit. However, in this case, as mechanical vibration noises and electric noises are also amplified at the same time, a S/N ratio is not changed. Therefore, this is not a favorable solution to cope with the problem.
An experimental test result shows that an obtained output sensitivity (a generating charge per unit pressure pC/Mpa) of an engine component with the combustion pressure sensor shown in
FIG. 12
is only 5% of that of the combustion pressure sensor
300
that is not installed in the plug body and the transmitting efficiency is remarkably low.
Another drawback is that the output sensitivity of the combustion pressure sensor
300
varies largely according to engine operating conditions. A linear expansion co-efficient of the housing
201
, which is a part of the plug body
200
, is largely different from that of the engine head
1
because of a material difference thereof. The linear expansion co-efficient of the housing
201
(steel) is 12×10
−6
(/° C.) and that of the engine head
1
(aluminum alloy) is 23×10
−6
(/° C.).
As clearly understood from the fact that there is a difference of the linear expansion co-efficient therebetween, when both of the plug body
200
and the engine head
1
receive a heating effect after the plug body
200
is fixed to the engine head
1
at a normal temperature (room temperature), the engine head
1
expands more than the plug body
200
so
Hattori Kouichi
Murai Hiroyuki
Denso Corporation
Nixon & Vanderhye PC
Tran Thuy Vinh
Wong Don
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