U.S. patent application number 09/742001 was filed with the patent office on 2001-08-23 for installation structure of engine component with combustion pressure sensor in engine.
Invention is credited to Hattori, Kouichi, Murai, Hiroyuki.
Application Number | 20010015402 09/742001 |
Document ID | / |
Family ID | 18486831 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010015402 |
Kind Code |
A1 |
Murai, Hiroyuki ; et
al. |
August 23, 2001 |
Installation structure of engine component with combustion pressure
sensor in engine
Abstract
In an installation structure of a glow plug with a combustion
pressure sensor, a seat surface is provided in an installation hole
formed in the engine so as to penetrate from outside into a
combustion chamber of the engine. A contact surface is formed in
the glow plug. The glow plug is partly inserted into the
installation hole and is fixed via a ring shaped gasket to the
engine so that the glow plug comes in pressurized contact with the
engine in an axial direction of the installation hole. With the
installation structure mentioned above, the elastic member is
elastically more deformable in an axial direction of the
installation hole than a portion of the glow plug on which the
combustion pressure sensor is mounted.
Inventors: |
Murai, Hiroyuki; (Anjo-city,
JP) ; Hattori, Kouichi; (Ichinomiya-city,
JP) |
Correspondence
Address: |
Pillsbury, Madison & Sutro, LLP
1100 New York Avenue, N.W.
Ninth Floor, East Tower
Washington
DC
20005-3918
US
|
Family ID: |
18486831 |
Appl. No.: |
09/742001 |
Filed: |
December 22, 2000 |
Current U.S.
Class: |
248/554 |
Current CPC
Class: |
F23Q 2007/002 20130101;
F23Q 7/001 20130101; G01L 23/222 20130101 |
Class at
Publication: |
248/554 |
International
Class: |
F16M 013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 1999 |
JP |
11- 366456 |
Claims
What is claimed is
1. An installation structure of an engine component with a
combustion pressure sensor in an engine having a combustion
chamber, the combustion pressure sensor being mounted on the engine
component for generating an output signal based on a force acting
on the engine component responsive to combustion pressure of the
combustion chamber, comprising: an installation hole formed in the
engine so as to penetrate from outside into the combustion chamber;
an elastic member positioned in the installation hole, the elastic
member comprising at least one of a separate body from the engine
component and the engine, an integral part of the engine component
and an integral part of the engine, wherein the engine component is
partly inserted into the installation hole and air tightly fixed
via the elastic element to the engine so that the engine component
comes in pressurized contact with the engine in an axial direction
of the installation hole, and, further, wherein the elastic member
is elastically more deformable in an axial direction of the
installation hole than a portion of the engine component on which
the combustion pressure sensor is mounted.
2. An installation structure according to claim 1, wherein the
installation hole is provided at an inside surface thereof with a
seat surface, the engine component has a contact surface, and the
elastic member is a metal hollow ring whose circumference on one
side thereof contacts the contact surface and whose circumference
on the other side thereof contacts the seat surface.
3. An installation structure according to claim 1, wherein the
installation hole is provided at an inside surface thereof with a
seat surface and the elastic member is a thin thickness portion of
the engine component integrally formed therein and the thin
thickness portion comes in pressurized contact with the seat
surface.
4. An installation structure according to claim 1, wherein the
engine component has a contact surface, the elastic member is a
protruding portion of the engine protruding radially in the
installation hole and the protruding portion is provided with a
seat surface which comes in pressurized contact with the contact
surface.
5. An installation structure according to claim 1, wherein the
engine component is provided at an outer circumferential surface
thereof with a male thread and the installation hole is provided at
an inner circumferential surface thereof with a female thread, and,
further, wherein the engine component is fastened to the engine by
screwing the male thread into the female thread.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] 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
[0002] 1. Field of the Invention
[0003] 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.
[0004] 2. Description of Related Art
[0005] 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 J1 with a combustion
pressure sensor is shown in FIG. 12.
[0006] The conventional glowplug J1 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.
[0007] A part of the plug body 200 on an end side thereof is
inserted into an installation hole 1b (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 201a of a housing 201 is screwed
into a female thread 1c of the installation hole 1b for fixing.
[0008] In the glowplug J1, 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.
[0009] 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.
[0010] Further, the glow plug J1 has a sealing construction with
which a leak of combustion gas through the installation hole 1b is
prevented. As explosive combustion pressure in a combustion chamber
1a 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.
[0011] To ensure the air tightness in the conventional glow plug
J1, 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 1d formed at an inner circumference of the installation
hole 1b 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 1b with a recommended
fastening torque for standardization (for example, 10 to 15
N.multidot.m).
[0012] In more details, a taper angle of the housing taper portion
212 is larger, for example, by 3.degree., than that of the taper
seat surface portion 1d. 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 1d 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 1d. Accordingly, the combustion gas
generated in the combustion chamber 1a is prevented from leaking
outside so that the sealing is ensured.
[0013] 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 1d, a
frictional force of the male thread 201a of the housing 201 and the
female thread 1c of the installation hole 1b, and a mutual elastic
force of the housing 201 and the engine head 1.
[0014] In the glow plug J1 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 31 for the sensor 300 into the male thread 201a of the
housing 201.
[0015] 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.
[0016] 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 1a is transmitted via the
heater body 201 and the housing 201a to the male thread 201a.
Accordingly, the housing 201 including the male thread 201a is
pushed upward in an axial direction of the installation hole 1b 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.
[0017] However, the conventional installation structure of the glow
plug J1 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.
[0018] 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 1d and the female thread 1c in the installation
hole 1b, 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.
[0019] 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.
[0020] 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.
[0021] Another one of the 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
differ 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.times.10.sup.-6 (/.degree. C.) and that of
the engine head 1 (aluminum alloy) is 23 .times.10.sup.-6
(/.degree. C.).
[0022] As clearly understood from a 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 that the load of the plug body 200 is eased
and a fastening is loosed. As an engine speed as one of the engine
operating conditions is higher, the fastening is more loosed since
combustion temperature is more increased.
[0023] As mentioned above, since the loosing amount of the plug
body 200, that is, the load (a fastening force) of the combustion
pressure sensor 300 is changed by temperature variation, there
exists a difference of the output sensitivity based on the high and
low engine speed conditions.
[0024] According to an another experimental test in use of a
pressure gauge with which a change of combustion pressure is
directly detected from the combustion chamber (without an influence
of installation thereto) by changing the engine operating
conditions from a high speed to a low speed, the test result
illustrates that the difference of high and low engine speed
conditions brings a 25% difference with respect to the output
sensitivity (pC/Mpa) of the sensor 300.
[0025] The Two problems mentioned above are applicable not only to
the installation structure of the glow plug with the combustion
pressure sensor but also to that of any other engine component with
the combustion pressure sensor, if a part of the engine component
on one end side thereof is inserted into the installation hole
formed in the engine and the combustion pressure sensor is mounted
on the engine component for outputting a signal representing engine
combustion pressure.
[0026] A spark plug, an injector and soon are typical examples as
the engine component with the combustion pressure sensor. Each of
the components is rigidly retained in the installation hole to
secure the air tightness and there is a difference of the linear
expansion co-efficient between the engine head and the engine
component.
[0027] To study more details of the above problems, FIG. 13 shows a
schematic view of the conventional installation structure of the
glow plug J1 with the combustion pressure sensor in the engine head
1. The combustion pressure sensor 300 has a fixing nut 310, a base
seat 340 and a piezoelectric element 320 put between the fixing nut
310 and the base seat 340. A taper contact portion S indicates a
portion where the taper seat surface portion 1d and the housing
taper portion contact each other. The taper contact portion S hold
the load (axial load) in an axial direction of the installation
hole 1b generated by fastening the plug body 200 to the engine head
1.
[0028] As shown in FIG. 13, it is presumed that transmitting
elements of combustion pressure are basically composed of the
housing 201 of the plug body 200 (presuming that the heater body
206 is integrated with the housing 201), the nut 310 of the
combustion pressure sensor 300, the piezoelectric element 320, the
basic seat 340, the engine head 1 and the taper contact portion
S.
[0029] FIG. 14 shows an equivalent spring system model into which
the transmitting elements mentioned above is converted, while the
engine head 1 is bound. Each spring constant of the transmitting
elements can be shown by K=L/A X E (mm/N) where an axial length of
the element is L (mm), young's modulus thereof is E (N/mm.sup.2),
and a cross section area in a radial direction is A (mm.sup.2).
[0030] Accordingly, a spring constant of the housing 201 kh, a
spring constant of the nut 310 Kn, a spring constant of the
piezoelectric element 320 Kp, a spring constant of the basic seat
340 Kd and a spring constant of the taper contact portion S Kt may
be calculated, respectively. When combustion pressure force F is
applied to the housing 201 (including the heater portion 206), a
force P acting on the piezoelectric element 320, that is, a
transmitting force, is shown by a following formula.
P=F X Kt/(Kh+Kn+Kp+Kd)
[0031] The force P is represented as a function of the spring
constant Kt of the taper contact portion S. And, as a value Kt is
higher, that is, as the taper contact portion S is less resilient
and more flexible and elastic, a transmitting efficiency of the
combustion pressure force to the piezoelectric element 320 is more
increased and the output sensitivity thereof is more increased.
[0032] According to the study mentioned above, it is understood
that, as resiliency of the taper contact portion, that is,
resiliency of a portion where the housing 201 comes in contact with
the engine head 1 in the installation hole 1b, is lower, the
transmitting efficiency of combustion pressure is increased.
SUMMARY OF THE INVENTION
[0033] An object of the present invention is to provide an
installation structure of an engine component with a combustion
pressure sensor to an engine in which a force is transmitted in a
better way from the engine component to the combustion pressure
sensor so that a sensor output sensitivity may be improved and a
change of the output sensitivity according to a change of engine
operating conditions is limited.
[0034] To achieve the object, an installation hole is formed in the
engine so as to penetrate from an outer surface thereof into a
combustion chamber of the engine. The engine component is partly
inserted into the installation hole and is fixed via an elastic
member to the engine so as to come in pressurized contact therewith
in an axial direction of the installation hole. With the
installation structure mentioned above, the elastic member is
elastically more deformable in an axial direction of the
installation hole than a portion of the engine component on which
the combustion pressure sensor is mounted.
[0035] It is preferable that the engine has a seat surface in the
installation hole, the engine component has a contact surface to be
seated via the elastic member on the seat surface, and the elastic
member is a metal hollow ring whose circumference on one side
thereof contacts the contact surface and whose circumference on the
other side thereof contacts the seat surface. Alternatively, the
elastic member may be a thin thickness portion of the engine
component integrally formed therein and the thin thickness portion
comes in pressurized contact with the seat the surface. Further,
the elastic member may be a protruding portion of the engine
protruding radially in the installation hole portion and the
protruding portion comes in pressurized contact with the contact
surface.
[0036] According to the conventional installation structure, the
contact surface of the engine component and the seat surface of the
engine are in direct and pressurized contact with and rigidly fixed
to each other so that the output sensibility is low. However,
according to the present invention, force acting on the engine
component in an axial direction of the installation hole responsive
to combustion pressure is appropriately transmitted via the elastic
member to the engine component so that the output sensitivity may
be increased. Further, a gap between the engine component and the
engine and a change of the load generated by a difference of linear
expansion co-efficient therebetween are absorbed by the elastic
member whose elasticity is lager. As a result, a change of the
sensor output sensitivity due to a change of engine operating
conditions may be deduced.
BRIEF DESCRIPTION OF THE DRAWING
[0037] Other features and advantages of the present invention will
be appreciated, as well as methods of operation and the function of
the related parts, from a study of the following detailed
description, the appended claims, and the drawings, all of which
form a part of this application. In the drawings:
[0038] FIG. 1 is a partly cross sectional view showing an outline
of an installation structure of a glow plug with a combustion
pressure sensor in an engine according to an embodiment of the
present invention;
[0039] FIG. 2 A is a partly enlarged view showing a portion of a
gasket in the glow plug with the combustion pressure sensor of FIG.
1;
[0040] FIG. 2 B is a view of the gasket viewed from an arrow IIB of
FIG. 2A;
[0041] FIG. 2 C is a cross sectional view along a line IIC-IIC of
FIG. 2B;
[0042] FIG. 3A is a partly enlarged cross sectional view of a
portion of the combustion pressure sensor in the glow plug with the
combustion pressure sensor of FIG. 1;
[0043] FIG. 3B is a view of the combustion pressure sensor viewed
from an arrow IIIB of FIG. 3A;
[0044] FIG. 4A is a combustion pressure wave form according to a
conventional embodiment;
[0045] FIG. 4B is a combustion pressure wave form according to the
embodiment of the present invention;
[0046] FIG. 4C is another combustion pressure wave form according
to the embodiment of the present invention;
[0047] FIG. 4D is another combustion pressure wave form according
to the conventional embodiment;
[0048] FIG. 4E is still another combustion pressure wave form
according to the embodiment of the present invention;
[0049] FIG. 4F is still another combustion pressure wave form
according to the conventional embodiment;
[0050] FIG. 5 is a partly enlarged cross sectional view showing a
modification of the portion of the gasket in the glow plug with the
combustion pressure sensor;
[0051] FIG. 6A is a view of a first modification of the gasket;
[0052] FIG. 6B is a view taken along a line VIB-VIB of FIG. 6A;
[0053] FIG. 6C is a view of a second modification of the
gasket;
[0054] FIG. 6D is a view taken along a line VID-VID of FIG. 6C;
[0055] FIG. 6E is a view of a third modification of the gasket;
[0056] FIG. 6F is a view taken along a line VIF-VIF of FIG. 6E;
[0057] FIG. 6G is a view of a fourth modification of the
gasket;
[0058] FIG. 6H is a view taken along a line VIH-VIH of FIG. 6G;
[0059] FIG. 7 is an enlarged cross sectional view showing a thin
thickness portion of a housing constituting an elastic member
according to another embodiment of the present invention;
[0060] FIG. 8 is an enlarged cross sectional view showing a
protruding portion of an engine head protruding into an
installation hole for constituting a elastic member according to a
further embodiment of the present invention;
[0061] FIG. 9 is a partly cross sectional view showing an outline
of an installation structure of a spark plug with a combustion
pressure sensor in an engine to which the gasket as a gist of the
present invention is applied;
[0062] FIG. 10 is a partly cross sectional view showing an outline
of an installation structure of an injector with a combustion
pressure sensor in an engine to which the gasket as a gist of the
present invention is applied;
[0063] FIG. 11 is a partly cross sectional view showing an outline
of an installation structure of a volt with a combustion pressure
sensor in an engine to which the gasket as a gist of the present
invention is applied;
[0064] FIG. 12 is a partly cross sectional view showing an outline
of a conventional installation structure of a glow plug with a
combustion pressure sensor in an engine as a prior art;
[0065] FIG. 13 is a schematic view showing elements of transmitting
combustion pressure in the conventional installation structure;
and
[0066] FIG. 14 is a network showing an equivalent spring system
model into which the conventional installation structure is
converted.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0067] An installation structure of an engine component with a
combustion pressure sensor, typically, a glow plug with a
combustion pressure sensor, in an engine according to an embodiment
of the present invention is described with reference to drawings.
FIG. 1 shows a partly cross sectional view of a whole construction
of a glow plug 100 with a combustion pressure sensor installed in
an engine head 1. Portions similar to those of FIG. 12 have same
reference numbers affixed thereto as in FIG. 12.
[0068] The glow plug 100 is composed of a plug body 200 (an engine
component of the present invention) having a heater body, through
which engine combustion pressure is transmitted, a combustion
pressure sensor 300 having a piezo electric member that converts a
force acting on the plug body 200 into an electric signal in
accordance with a piezoelectric characteristic thereof and
generating an output signal representing engine combustion
pressure, and a lead wire 500 for sending the output signal from
the combustion pressure sensor 300 to an outside circuit (ECU for
vehicle in the present embodiment).
[0069] The engine head 1 is made of, for example, aluminum alloy or
iron and is provided with an installation hole 1b (a plug hole, a
threaded hole) penetrating from an outer surface thereof to a
combustion chamber 1a inside thereof. A part of the plug body 200
on one end side thereof (lower end side in FIG. 1) is inserted into
the installation hole 1b and is rigidly fixed to the engine head
1.
[0070] The plug body 200 has a cylindrical housing 201 made of
metal (such as low carbon steel). The housing 201 is provided at an
outer circumference with a male thread 201a that is screwed into a
female thread of the installation hole 1b for fixing to the engine
head 1. The plug body 200 is also provided inside the housing 201
with a cylindrical sheath pipe 202 held by the housing 201.
[0071] The sheath pipe 202 is made of heat resistant and erosion
resistant alloy (for example, stainless steel SUS 310). One end
(lower end in FIG. 1) of the sheath pipe 202 is closed and the
other end thereof (upper side in FIG. 1) is opened. A heating coil
203, which is formed by resistance wires made of NiCr and CoFe, is
housed in the sheath pipe 202 on the one end side. A part of a pole
shaped central axis 204 made of metal is inserted into the sheath
pipe 202 on the other end side.
[0072] One end of the heating coil 203 is connected to the closed
end of the sheath pipe 202 and the other end of the heating coil
203 is connected to one end of the central axis 204. The sheath
pipe 202 is filled with heat resistant insulating powder 205 such
as oxide magnesium to insulate the central axis 204 and the heating
coil 203 from the sheath pipe 202.
[0073] The sheath pipe 202 is formed through a swaging drawing
process. Insulating powder 205 is staffed into inside of the sheath
pipe 202 without voids and the central axis 204 and the heating
coil 203 are rigidly fixed via the insulating powder 205 to the
sheath pipe 202.
[0074] A portion of the sheath pipe 202 in which the heating coil
203 is housed, the heating coil 203 and the insulating powder 205
constitute a heater body 206. The heater body 206 is jointed with
and held by an inside of the housing 201 in such a way that a part
of the sheath pipe 202 on the one end side is exposed out of the
housing 201. The heater body 206 (an outer circumference of the
sheath pipe 202) is press fitted or bonded by silver-alloy brazing
to the housing 201.
[0075] A washer 207 made of insulating material such as bakelite,
and an o-ring 208 made of silicon or fluorine rubber are inserted
into the central axis 204 inside the housing 201 on an upper side
thereof. The washer 207 is arranged for a purpose of placing the
central axis 204 at an axial center in the housing 201 and the
o-ring 208 is arranged for a purpose of securing water proof and
air tightness inside the housing 201.
[0076] The central axis 204 is provided on and along an outer
circumference thereof with a terminal thread 204a and fixed via an
insulating bush 209 made of insulating material such as phenol
resin to the housing 201 by screwing a fixing nut 210 into the
terminal thread 204a. The insulating bush 209 serves to prevent the
central axis 204 from coming in contact with and making a short
circuit with the housing 201.
[0077] A connecting bar 2 is fixed and connected in circuit by a
terminal nut 211 to the terminal thread 204a provided in the
central axis 204 on the other end side. The connecting bar 2 is
connected to an electric source (not shown) and is grounded via the
central axis 204, the heating coil 203, the sheath pipe 202 and the
housing 201 to the engine head 1. Therefore, the heater body of the
glow plug 100 can generate heat for an ignition aid of the diesel
engine at a starting time.
[0078] Instead of the metal heater body composed of the metal
resistance wire, a so called ceramic heater body in which
conductive ceramic whose main contents are nitride silicon and
silicon molybdenum is enveloped by sintered insulating ceramic
whose main content is nitride silicon is employed as the heater
body 206.
[0079] As a main gist of the present embodiment, an elastic member
250 is disposed between the plug 200 and an inner surface of the
installation hole 1b in such a manner that the elastic member 250
generates an elastic force in an axial direction of the
installation hole 1b (in an axial direction of the plug body 200).
The plug body 200 is pressed via the elastic member 250 against the
inner surface of the installation hole 1b at least in the axial
direction of the installation hole 1b so that the air tightness in
the combustion chamber 1a (inside the engine) may be secured.
[0080] In more details, the elastic member 250, as shown in FIG. 1,
is a ring shaped hollow gasket 250 having a hole into which the
heater body 206 of the plug body 200 is inserted. The gasket 250 is
placed between a housing taper portion 212 and a taper seat surface
portion 1d of the installation hole 1b and the housing taper
portion 212 is pressed via the gasket 250 against the taper seat
surface portion 1d in the axial direction of the installation hole
1b for securing the air tightness.
[0081] As shown in FIGS. 2A, 2B and 2C, the gasket 250 is made of
heat resistant and erosion resistant metal such as SUS 304 or Ni
base alloy and is an elastic body generally called as a metal C
seal having a circular tube which is formed by pressing in a ring
shape whose cross section is a letter C. The metal C seal has no
joints on a circumference thereof and has a large elastic force. As
typical dimensions of the gasket 250, a tube diameter is 1 mm, a
plate thickness is 0.1 mm and an inner diameter is 6 mm.
[0082] Not only the housing taper portion 212 is axially pressed
against the taper seat surface portion 1d by the elastic force of
the gasket in the axial direction of the installation hole 1b, but
also the housing taper portion 212 is radially pressed against an
inner surface of the installation hole 1b since the housing taper
portion is formed in a taper shape, as shown in FIG. 2A, and the
pressing force acts in a radial direction of the installation hole
1b, too.
[0083] The combustion pressure sensor 300 is formed in a ring shape
as a whole and is fixed to an outer circumferential surface of a
portion of the plug body 200 which protrudes axially from a surface
of the engine head 1 in such a manner that the combustion pressure
sensor 300 contacts the surface of the engine head 1.
[0084] As shown in FIGS. 3A and 3B, the combustion pressure sensor
300 is provided with a nut 310 (sensor fixing portion) for
installing a sensor unit in the plug body 200, a piezoelectric
member 320 generating an electric signal (electric charge) in
accordance with a force responsive to combustion pressure, a lead
portion 330 for picking up the electric signal generated in the
piezoelectric member 320 and sending the same to the lead wire 500,
a base seat 340 for holding the piezoelectric member 320 together
with the nut 31 and also fixing a part of the lead portion 330, and
a metal case 320 for securing a dust and water proof with respect
to the piezoelectric member 320.
[0085] The nut 310 made of metal is provided with a thread portion
311 for fastening the nut 310 to an outer circumference of the
housing 201 and fixing the sensor unit to the housing 201 by
screwing into the thread 201a of the housing 201, a hexagonal
portion 312, a large diameter portion 313 on a lower side of the
hexagonal portion 312 and a small diameter portion 314 on a further
lower side of the hexagonal portion 312. A heat shrinkable
insulating tube 315 made of silicon is closely fitted to an outer
circumference of the small diameter portion 314.
[0086] The lead portion 330 for connecting the piezoelectric member
320 in circuit to one end of the leadwire 500 is provided with an
electrode 331, an insulator 332 and a fixing metal sheath 333. The
electrode 331 is made of metal and formed in a ring shape. The
insulator 332, which is made of insulating material such as mica or
alumina, is disposed between the electrode 331 and the nut 310 for
insulating the electrode 331 from the nut 310 the nut 31 and the
base seat 340. The electrode 331 and the insulator 315 are fitted
around an outer circumference of the insulating tube 315
surrounding and coating the small diameter portion 314 of the nut
310.
[0087] The lead wire 500 is composed of a conductive signal wire
501, an insulating coating 502, a conductive ground shield wire 503
and an insulating coating 505, which are piled up in order from an
inside toward an outside. The signal wire 501 is insulated in
circuit from the ground shield wire 503. Each of the signal wire
501, the insulating coating 502 and the ground shield wire 503 is
partly exposed on the one end side of the lead wire 500.
[0088] The signal wire 501 on the one end side of the lead wire 500
passes through a hole 316 formed in the nut 310 and a bore 332a
formed in the insulator 332 and is connected by welding to the
electrode 331 at a hole 331a thereof. The other end of the lead
wire 500 is coupled with a connector (not shown) to connect in
circuit to an outside circuit (ECU for the vehicle).
[0089] The fixing metal sheath 333, which is cylindrical in shape,
is disposed around an outer circumference of the lead wire 500 on
the one end side thereof for fixing the lead wire 500 to the nut
310. The hole 316 of the nut 310 is further provided on an upper
side thereof with a holding hole 316a for holding the fixing metal
sheath 333. The fixing metal sheath 333 is partly inserted into and
fixed to the holding hole 316.
[0090] The fixing metal sheath 333 is fixed by caulking to the lead
wire 500 and also connected in circuit with the ground shield wire
503. An outer circumferential part of the fixing metal sheath 333
protruding fromthe holding hole 316 is covered with a heat
shrinkable silicon insulating coating 333a.
[0091] The piezoelectric member 320 is formed in a ring shape so
that an inner hole thereof faces the small diameter portion 314 of
the nut 310 and installed via the insulating tube 315 around an
outer circumference of the small diameter portion 314. The
piezoelectric member 320 is composed of 3 layers piezoelectric
ceramics 321 (piezoelectric elements), a signal-transmitting washer
322 and a ground washer 323, which are piled up in each other.
[0092] The piezoelectric ceramics 321 are identical disks in
dimension each formed in a ring shape and made of titanium oxide
lead or titanium-zirconium oxide lead. The 3 layers of the
piezoelectric ceramics 321 are connected in circuit in parallel to
each other. Respective output sensitivities of the 3 layers of the
piezoelectric ceramics 321 are summed so that a total sensitivity
is remarkably improved.
[0093] The base seat 340, which is metal and formed in near ring
shape, is provided on an inner side surface thereof on a side of
contacting the engine head 1 with a rotation stopper 341. As shown
in FIG. 3B, the rotation stopper 341 is formed in a shape
corresponding to an oval shape of a rotation stopper 317 provided
in a leading end of the small diameter portion 314 of the nut 310
and fitted into the rotation stopper 314. Accordingly, the rotation
of the base seat 340 relative to the nut 310 in an angular
direction of the plug is prevented.
[0094] A cylindrical metal case 350 made of metal such as SUS 304
surrounds an outer periphery of the base seat 340 so as to envelop
all over an outer circumference of the combustion pressure sensor
300. The metal case 350 is formed in a cylindrical shape by drawing
a thin metal sheet whose thickness is less than 0.5 mm and bonded
to the circumference of the base seat 340 by laser welding or
cupper brazing.
[0095] The metal case 350 is integrated with the base seat 340 in a
state that the rotation stopper 341 is accurately fitted to the
rotation stopper 317 of the nut 310. The base seat 340 is closely
fitted to the small diameter portion 314 of the nut 310 via an
o-ring 343 made of silicon or fluorine rubber which is housed in a
groove provided at a near center of the small diameter portion 314.
An inner periphery surface of the metal case 350 is fitted to an
outer surface of the large diameter portion 350 of the nut 310 and
a whole circumference of the internal fitting portion between the
metal case 350 and the large diameter portion 350 is bonded by YAG
laser welding.
[0096] The base seat 340 is pressed against the surface of the
engine head 1 by an axial force (screw fastening force) of the nut
310. The piezoelectric member 320, the electrode 331 and the
insulator 332 are held between the nut 310 and the base seat 340
and fixed by the axial force of the nut 310 therebetween.
[0097] The combustion pressure sensor 300 is assembled as follows.
The signal wire 501 on the one end side of the lead wire 500 is
welded to the hole 331a of the electrode 331. The fixing metal
sheath 33 is inserted into the holding hole 316a of the nut 310 and
bonded thereto by welding or cupper brazing. The insulator 332 is
installed on the small diameter portion of the nut 310.
[0098] Then, while the other end of the lead wire 500 inserted from
a side of insulator into the hole 316 of the nut 310 in which the
fixing metal sheath 333 and the insulator 332 have been installed,
the electrode 331 to which the one end of the lead wire 500 has
connected is fitted to the small diameter portion 314 of the nut
310.
[0099] After placing the electrode 331 at a predetermined position,
the fixing metal sheath 333 and the ground shield wire 503 are
fixed by caulking. The ground shield wire 503 is connected in
circuit to the fixing metal sheath 333. Then, a part of the lead
wire 500 and the fixing metal sheath 333 are covered by the
insulating coating 333a for the dust proof and the water proof.
[0100] The piezoelectric member 320 having the piezoelectric
ceramics 321 and the washers 322 and 323 is inserted into the small
diameter portion 314 of the nut 310. Then, the base seat 340
integrated with the metal case 350 by brazing is inserted into the
small diameter portion 314 of the nut 310, whilethe rotation
stopper 317 is coupled with the rotation stopper 341. Then, the
metal case 350 is bonded to the large diameter portion 313 of the
nut 310 by laser welding in a state that the nut 310 and the base
seat 340 are closely contacted and pressed to each other.
[0101] After completing the combustion pressure sensor 300 as
mentioned above, the combustion pressure sensor 300 is inserted
from a side of the heater body 206 into the plug body 200 and
assembled tentatively to the plug body 200 by screwing the thread
311 of the nut 310 into the thread 201a of the housing 201 in use
of the hexagonal portion 312. Then, after the gasket 250 is placed
on thetaper seat surface portion 1d in the installation hole 1b,
the plug body 200 tentatively assembled is inserted from the one
end side (from the heater body side) into the installation hole
1b.
[0102] Next, the plug body 200 is screwed into and fastened to the
installation hole 1b by turning in an angular direction a hexagonal
portion 201b (refer to FIG. 1) of the housing 201 with a tool such
as a wrench (not shown). Further, by fastening the nut 310 of the
combustion pressure sensor 300 with the wrench, the sensor 300 is
fixed to the surface of the engine head 1. Thus, the engine
component with the combustion pressure sensor shown in FIG. 1 is
completed.
[0103] An operation of the present embodiment is described
hereinafter. A voltage is applied from an electric source (not
shown) via the connecting bar 2 to the plug body for starting the
diesel engine and is grounded via the central axis 204, the heating
coil 203, the sheath pipe 202 and the housing 201 to the engine
head 1. Accordingly, the heater body 206 generates heat for the
ignition aid of the diesel engine at the starting time.
[0104] After the engine starts, combustion pressure generated in
the engine is transmitted via the heater body 206 and the housing
201 to the thread 201a. Combustion pressure transmitted to the
thread 201a serves to loose a fastening torque of the glow plug 100
to the engine head 1. Therefore, the load (in an axial direction of
the plug body) in the combustion pressure sensor 300, which is
applied via the thread 311 of the nut 310 to the piezoelectric
ceramics 321, is eased. That is, a loading state of the
piezoelectric ceramics 321 is changed.
[0105] Charges to be generated as an output of the electric signal
according to piezoelectric characteristics of the piezoelectric
ceramics 321 are changed. The changed electric signal (charge) is
sent from the electrode 331 and the lead wire 500 to the outside
circuit in which the electric signal is converted into voltage and,
after passing through amplifying and filtering processes, is used
as a combustion pressure wave signal applicable for combustion
control. That is a process of detecting combustion pressure in the
glow plug 100.
[0106] The embodiment mentioned above has a distinctive feature
that the gasket 250 (elastic member) is placed between the housing
taper portion 212 and the taper seat surface portion 1d and presses
the housing taper portion 212 and the taper seat surface portion 1d
in an axial direction so that the air tightness in the combustion
chamber 1a may be assured.
[0107] With the distinctive feature mentioned above, when the plug
body 200 is fastened by the axial load which falls within an
allowable elastic force of the gasket 250, the housing taper
portion 212 and the taper seat surface portion 1d are alternately
pressed by the gasket due to the elastic force of the gasket 250
owned by itself. As a result, the higher air tightness is
maintained.
[0108] Further, the force based on combustion pressure acting in an
axial direction of the installation hole 1b can be beneficially
transmitted to the housing 201 of the plug body 200 due to the
elastic force of the gasket 250 to improve the sensor sensitivity
since a resilient value of the taper contact portion in the
equivalent spring system model shown in FIG. 14 is limited.
[0109] Furthermore, the gasket 250 serves to limit a change of the
output sensitivity caused by a looseness of the plug body 200 due
to heat. This is because that a change of a gap between the housing
taper portion 212 and the taper seat surface portion 1d generated
due to a linear expansion co-efficient difference and a change of
the consequent axial load are mostly absorbed by a compression
recovery force of the gasket 250. That is, the change of the load,
which adversely affect on the output sensitivity of the combustion
pressure sensor 300, can be lowered.
[0110] As mentioned above, the glowplug 100 with the combustion
pressure sensor in which the elastic member 250 is inserted between
the taper portions according to the present embodiment has an
advantage that the output sensitivity of the sensor is improved and
a change of the output sensitivity of the sensor to be caused by a
change of engine operating conditions is limited without adversely
affecting on main functions of the glow plug 100.
[0111] When the gasket 250 placed between the housing taper portion
212 and the taper seat surface portion 1d receives combustion
pressure (at a time of increasing combustion pressure), the
combustion pressure F is applied nearly uniformly to an inner
surface 261 of the gasket 250, as shown in FIG. 2A. The combustion
pressure F acts to expand radially the inner surface of the gasket
250.
[0112] Accordingly, in addition to face pressure based on the axial
load generated when the plug body is fastened, internal pressure
due to the combustion pressure F is further applied to a housing
contact portion 213 and a seat surface contact portion 1e, both of
which are surfaces in contact with the gasket 250. As a result,
both contact surfaces 213 and 1e are more strongly pressed to
secure a higher degree of the air tightness during the engine
operation.
[0113] According to a test result of an experimental test, it is
concluded that the elastic member has to endure more than 2 KN
force or load causing a plastic deformation in view of maintaining
the air tightness, while the gasket 250 is more effective as the
elastic force of the gasket 250 is larger (more flexible). A spring
constant of the gasket (elastic member) showing favorable result in
the above experimental test is 2.5 to 20 (.times.10.sup.-5
mm/N).
[0114] The fastening torque of the plug body 200 itself (glow plug
without the sensor) is primarily standardized and is 10 to 15
N.multidot.m in case that a thread size at a screw portion of a
housing commonly used is M 10.times.1.25. A value converted into
the axial load is presumably 4 to 6 kN. It is thought that this
value is necessary not only for securing the air tightness but also
for preventing the looseness of the plug body 200 due to vibration.
The minimum value 2 kN or more as the endurance force of the
elastic member based on the experimental test mentioned above seems
to be a little small for preventing the looseness, judging from the
above standard value of the glow plug itself.
[0115] In the case of the glow plug without the sensor, the glow
plug is fixed to the engine head 1 based on 3 elements consisting
of a frictional force between the housing taper portion 212 and the
taper seat surface portion 1d, a frictional force between the
thread 201a of the housing 201 and the thread 1c of the
installation hole 1b, and mutual elastic forces of the housing 201
and the engine head 1. However, in the case of the glow plug 100
with the combustion pressure sensor, the plug body 200 is fixed to
the engine head 1 based on 6 elements consisting of a frictional
force between and elastic forces of the housing taper portion 212
and the gasket 250, a frictional force between the thread 201a of
the housing 201 and the thread 1c of the installation hole 1b, a
frictional force between and elastic forces of the thread 311 of
the nut 310 of the combustion pressure sensor 300 and the thread
201a of the housing 201, and a frictional force between the base
seat 340 of the combustion pressure sensor 300 and the engine head
1.
[0116] Accordingly, in the glow plug with the combustion pressure
sensor according to the embodiment, there exist practically no
problems of the looseness due to vibration. According to a
vibration endurance test conducted on the plug body 200 with the
combustion pressure sensor 300 in a state shown in FIG. 1 in use of
a vibration exciter under conditions of 50 to 2000 Hz and 25 to 10
G acceleration speed, it is proved that both of the plug body 200
and the combustion pressure sensor 300 are not loosed.
[0117] FIGS. 4A to 4F show a comparison of combustion pressure
waveforms between the present embodiment and the conventional one.
FIGS. 4B, 4C and 4E show the combustion pressure waveforms of the
glow plug 100 with the combustion pressure sensor. FIGS. 4A, 4D and
4F show the combustion pressure waveforms of the conventional
embodiment having the glow plug J1 with the combustion pressure
sensor (refer to FIG. 12). FIGS. 4A to 4D show test results under
engine operating conditions of 2000 rpm and 50 N.multidot.m load
and FIGS. 4E and 4F show test results under engine operating
conditions of 4000 rpm and a full load.
[0118] As shown in FIGS. 4A and 4B, the output sensitivity (height
of waveform) of the combustion pressure sensor of the present
embodiment having the gasket 300 as the elastic member is twice,
compared with that of the conventional embodiment.
[0119] FIGS. 4D and 4F show the waveforms obtained by amplifying
about twice the output signals of the combustion pressure sensor of
the conventional embodiment in use of an amplifying circuit in
order to make the output sensitivity or the height of the waveforms
thereof nearly even to that of the waveforms according to the
present embodiment. It can be concluded from these test results
that S/N ratio of the output signal of the present embodiment shown
in FIGS. 4C and 4E, whose output sensitivity of the combustion
pressure sensor is larger, is superior to that of the conventional
embodiment shown in FIG. 4D and 4F.
[0120] Further, with respect to the change of the load of the
combustion pressure sensor 300 due to heat change, that is, due to
a change of the engine operating conditions, another experimental
test results show that, under engine operating conditions covering
from an idling to 4000 rpm full load, a sensitivity change of the
present embodiment having the gasket 250 is 10% and that of the
conventional embodiment is 25% ,compared with the value measured by
the pressure gauge.
[0121] Other Embodiments
[0122] Instead of the housing taper portion 212 and the taper seat
surface portion 1d between which the gasket 250 is put, portions of
the housing 201 and the installation hole 1b between which the
gasket is put are not tapered surfaces but may be right-angled flat
surfaces confronting to each other, as shown in FIG. 5.
[0123] The elastic ring shaped gasket 250 having no joints on the
circumference thereof may be modified to any one of the shapes as
shown in FIGS. 6A to 6H.
[0124] A gasket 250 shown in FIGS. 6A and 6B as a first
modification has a groove on an outer circumferential surface
thereof. A gasket 250 shown in FIGS. 6C and 6D as a second
modification is formed in a hollow o-ring shape and has a pressure
introduction hole 250a on an inner circumference thereof, which has
a same effect as the gasket 250 shown in FIGS. 2A to 2C. The
pressure introduction hole 250 is not always essential. A gasket
250 shown in FIGS. 6E and 6F as a third modification is a ring
whose cross section is filled and shaped circular. A gasket 250
shown in FIGS. 6G and 6H as a fourth modification is a ring whose
cross section is shaped a rectangular so that the gasket 250 comes
in surface contact with the housing taper portion 212 and the taper
seat surface portion 1d. The cross sectional shape of the gasket
250 is not limited to the rectangular but may be a polygon if the
gasket 250 comes in surface contact with the tapered portions or
may be a triangle so that the gasket 250 comes in surface contact
with one of the tapered portions and in line contact with the other
of the tapered portions.
[0125] As mentioned above, material, a dimension and the cross
sectional shape of the ring gasket 250 may be modified to have a
spring constant adequate to a given condition. The values (mm/N) of
respective spring constants of the first to fourth modification of
the gasket 250 are smaller in order. Further, instead of the gasket
250 mentioned above, an elastic member, as shown in FIG. 7 or 8,
may be employed.
[0126] The elastic member shown in FIG. 7 is a partly thin
thickness portion 251 of the housing 201 that is formed by
machining a leading end of the housing 201 so as to have
elasticity. The thin thickness portion 251 is pressed against the
taper seat surface portion 1d. That is, the plug body 200 is
pressed in an axial direction of the installation hole 1b via the
thin thickness portion 251 functioning as the elastic member
against the inner surface of the installation hole 1b.
[0127] The elastic member shown in FIG. 8 is a part of the engine
head 1 which is formed by machining to have elasticity, that is, a
protruding portion 252 of the engine head 1 protruding radially in
the installation hole 1b. The protruding portion 252 constitutes a
surface which receives the axial load of the plug body 200. The
housing taper portion 212 is pressed in an axial direction of the
installation hole 1b against the taper seat surface portion 1d
provided on the protruding portion 252.
[0128] As shown in FIG. 7 or 8, the elastic member 251 or 252 may
be integrally formed with the plug body 200 or the engine head 1b.
The elastic member 251 or 252 is superior to the gasket 250
separately provided as far as the assembling easiness is
concerned.
[0129] The gist of the present invention mentioned above is not
limited to the application to the glow plug with the combustion
pressure sensor but applicable to any other engine component (for
example, an injector, a volt and a spark plug) with the combustion
pressure sensor, if a part of the engine component on one end side
thereof is inserted into the installation hole formed in the engine
and the combustion pressure sensor is installed in the engine
component for outputting a signal representing engine combustion
pressure.
[0130] An application example to a spark plug is shown in FIG. 9,
to an injector 800 in FIG.10 and to a volt 900 in FIG. 11,
respectively.
[0131] As shown in FIG. 9, the spark plug 700 (one of engine
components) is fixed to the installation hole 1b of the engine head
1 for gasoline engines by a thread 701a formed in a housing 701
into. Further, as shown in FIG. 10, the injector 800 (one of engine
components) for injecting fuel from a fuel pump to the combustion
chamber 1a is fixed to the installation hole 1b of the engine head
1 for gasoline or diesel engines by a fixing volt 801 and a thread
801a. Furthermore, as shown in FIG. 11, the volt 900 (one of engine
components), which is partly exposed to the combustion chamber 1a
in the engine, is fixed to the installation hole 1b of the engine
head 1 by a thread 901a.
[0132] The combustion pressure sensor 300 is mounted on each of the
thread 701a, 801a and 901a of the respective engine components. The
combustion pressure sensor detects engine combustion pressure in
such a manner that a force acting on the engine component
responsive to combustion pressure is converted into an electric
signal according to piezoelectric characteristics of the
piezoelectric element 321.
[0133] As shown in FIGS. 9, 10 or 11, the gasket 250 (elastic
member) elastically deformable in an axial direction of the
installation hole 1b is placed between the engine component 700,
800 or 900 and the installation hole 1b and the engine component
700, 800 or 900 is pressed at least in an axial direction of the
installation hole 1b via the gasket 250 against the inner surface
of the installation hole 1b. The gasket 250 may be modified
similarly to any other type of the elastic members mentioned in the
other embodiments.
[0134] Instead of the installation structure that the engine
component 200, 700, 800 or 900 is fastened to the installation hole
1b by the thread 201a, 701a, 801a or 901a formed around the outer
circumference of the engine component 200, 700, 800 or 900, it is
possible to have an installation structure that the engine
component 200, 700, 800 or 900 is rigidly fixed to the installation
hole 1b by pushing the engine component from an outside thereof in
an axial direction of the installation hole 1b in use of a
retaining member such as a flange provided separately from or
integrally with the engine component.
* * * * *